United States Department of Agriculture

Natural Resources Conservation Service

Soil Survey Laboratory

Methods Manual

Soil Survey

Investigations Report

No. 42

Version 4.0

November 2004
SOIL SURVEY LABORATORY 

METHODS MANUAL 

Rebecca Burt, Editor 

Soil Survey Investigations Report No. 42 

Version 4.0 

November 2004 
Cover Photo:The cover illustrates the continuum of data collected or produced for the soil 

survey of a geographic area. The soil survey map, landscape, and pedon are from northern 

Iredell County, North Carolina and are representative of the Banister pedon. This series is 

classified as a fine, mixed, active, mesic Aquic Hapludalf. This soil is a very deep, moderately 

to somewhat poorly drained soil on stream terrace positions in the Piedmont physiographic 

province of Virginia and North Carolina. Laboratory data sheet illustrates particle-size data 

produced by the Soil Survey Laboratory. The photomicrograph of soil fabric features a slightly 

altered, exfoliated biotite grain under cross-polarized light. Bar scale in photo is 0.25 mm. 

(Photo credit of Banister landscape and pedon: John Kelly and Michael A. Wilson, NRCS, 

Raleigh, NC and NRCS, Lincoln, NE.) 
FOREWORD 

Laboratory data are critical to the understanding of the properties and genesis of a 

single pedon, as well as to the understanding of fundamental soil relationships based on many 

observations of a large number of soils. Development of both an analytical database and the 

soil relationships based on those data are the cumulative effort of generations of soil scientists 

at the Soil Survey Laboratory (SSL). 

The purpose of the Soil Survey Investigations Report (SSIR) No., Soil Survey 

Laboratory Methods Manual is to document methodology and to serve as a reference for the 

laboratory analyst. It is expected that this document will continue to evolve and change over 

time as new methods are developed and old methods are modified or retired based on new 

knowledge or technologies. This manual is an historical document in that it describes both 

current and obsolete methods at the SSL. This manual also provides historical perspective, 

documenting the contributions of many soil scientists who have gone before us. Many of these 

scientists are noted in the section on contributors. 

Dr. Rebecca Burt, author of the Soil Survey Information Manual (SSIR No. 45, 1995), 

served as technical editor for all versions of the SSIR No. 42 (1989, 1992, 1996, 2004). Her 

contribution is significant in scope; she wrote some of the methods; is responsible for the 

review process encompassing additions, corrections, and consistency of other methods; and 

provided leadership in the assemblage of this document. 
PREFACE

The standard methods described in the Soil Survey Investigations Report (SSIR) No. 

42, Soil Survey Laboratory Methods Manual are those used by the Soil Survey Laboratory 

(SSL), National Soil Survey Center (NSSC). Included in the SSIR No. 42 are descriptions of 

current as well as obsolete methods, both of which are documented by method codes and linked 

with analytical results that are stored in the SSL database. This linkage between laboratory 

method codes and the respective analytical results is reported on the SSL data sheets. 

The methods in current use at this laboratory are described in enough detail that they 

can be performed in many laboratories without reference to other sources. An introduction to 

each group of related methods describes common characteristics. However, some repetition is 

included in order to make the method descriptions complete in themselves and to minimize 

reference to other parts of the manual. 

Some analytical results in the SSL national database were obtained using procedures 

that are no longer used at the SSL. Descriptions for these procedures are located in a section 

following the current methods. Information is not available to describe these procedures in the 

same detail as used to describe the current methods in the laboratory. 

Since the publication of the SSIR No. 42 (1996), there has been a significant increase in 

the number and kinds of methods performed at the SSL, resulting in a re-structuring of the 

method codes. As in past versions of the SSIR No. 42, the current method codes are 

hierarchical and alphanumerical. However, the obsolete method code structure had only a 

maximum of four characters, e.g., 6A2b, whereas the new structure has more characters, 

carrying more information about the method, e.g., particle-size and sample weight bases for 

reporting data. This version of the SSIR No. 42 carries not only the new method codes but also 

the older ones as well. The table for cross-referencing these older codes precede the method 

descriptions of the obsolete SSL methods. This linkage between the method code systems is 

important to maintain, as many older SSL data sheets and scientific publications report these 

older codes. The table of contents presents the ensemblage of this manual, beginning with the 

current methods and codes followed by obsolete methods with respective obsolete codes. 

The SSL data have been provided in reports, e.g., Primary and Supplementary 

Characterization Data Sheets, and in electronic forms, including tapes, disks, and CD-ROMs. 

More recently, other reports have been developed, e.g., Soil Taxonomy Characterization Data 

Sheets, and data are available via the NRCS Soils web site http://soils.usda.gov/. Historically, the 

SSIR No. 42 has described and assigned method codes only to those data reported on the 

Primary Characterization Data Sheets. This tradition is followed in this version of the SSIR 

No. 42. With the exception of some SSL primary analytical data included for user 

convenience, the data on the Supplementary and Taxonomy Characterization Data Sheets are 

derived data, using analytical data as a basis for calculation and do not carry method codes. 

Data on the Supplementary and Taxonomy Characterization Data Sheets are not described in 

this manual. For more detailed information about the calculation and application of these 

derived values, refer to the other important source documents provided by the United States 

Department of Agriculture, Natural Resources Conservation Service (USDA-NRCS) 

referenced in this maual. 

The methods described herein identify the specific type of analytical or calculated data. 

Most of these methods are analytical in nature, i.e., quantitative or semi-quantitative 

measurements, and include physical, chemical, mineralogical, and biological analyses. Sample 

collection and preparation in the field and the laboratory are also described. Historically, the 

SSIR No. 42 has described some derived values, e.g., coefficient of linear extensibility (COLE) 

and water retention difference (WRD) and reported these values along with the analytical data 

on the SSL Primary Characterization Data Sheets. This version of the SSIR No. 42 follows this 

tradition. Since the publication of the SSIR No. 42 (1996), several more derived values have 

been added to the Primary Characterization Data Sheets. While these data have been assigned 

method codes, detailed descriptions are not included in this version of the SSIR No. 42. For 
more detailed information about the calculation and application of these derived values, refer to 

other important source documents provided by USDA-NRCS referenced in this manual. 

The purpose of this manual is to document methodology and to serve as a reference for 

the laboratory analyst. The standard methods described in this SSIR No. 42, Soil Survey 

Laboratory Methods Manual, Version 4.0 replaces as a methods reference all earlier versions of 

the SSIR No. 42 (1989, 1992, and 1996, respectively) and SSIR No. 1, Procedures for 

Collecting Soil Samples and Methods of Analysis for Soil Survey (1972, 1982, and 1984). All 

SSL methods are performed with methodologies appropriate for the specific purpose. The SSL 

SOP’s are standard methods, peer-recognized methods, SSL-developed methods, and/or 

specified methods in soil taxonomy (Soil Survey Staff, 1999). An earlier version of this manual 

(1996) also served as the primary document from which a companion manual, Soil Survey 

Laboratory Information Manual (SSIR No. 45, 1995), was developed. The SSIR No. 45 

describes in greater detail the application of SSL data. 

Trade names are used in the manual solely for the purpose of providing specific 

information. Mention of a trade name does not constitute a guarantee of the product by USDA 

nor does it imply an endorsement by USDA. 

Rebecca Burt, Editor 

Reseach Soil Scientist 

Soil Survey Investigations 

USDA-NRCS 

Lincoln, Nebraska 

USDA Nondiscrimination Statement 

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and 

activities on the basis of race, color, national origin, sex, religion, age, disability, political 

beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all 

programs.) Persons with disabilities who require alternative means for communication of 

program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET 

Center at 202-720-2600 (voice and TDD). 

To file a complaint of discrimination write USDA, Director, Office of Civil Rights, Room 326-

W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call 

202-720-5964 (voice or TDD). USDA is an equal opportunity provider and employer. 
CONTRIBUTORS 

Laboratory data are critical to the understanding of the properties and genesis of a 

single pedon, as well as to the understanding of fundamental soil relationships based on many 

observations of a large number of soils. The development of laboratory methods, the analytical 

database, and the soil relationships based on those data are the cumulative effort of several 

generations of scientists. These efforts may be defined as methods development, database 

design and development, and investigations of data relationships. Methods development in the 

Soil Survey Laboratory results from a broad knowledge of soils, encompassing topical areas of 

pedology, geomorphology, micromorphology, physics, chemistry, mineralogy, biology, and 

field and laboratory sample collection and preparation. The following lists many of these 

contributing scientists, some of whom have since retired from USDA-NRCS and/or are 

deceased. Some of these contributions are cited throughout this manual as scientific 

publications. The following list is not comprehensive for developmental work preceding the 

formation of the Soil Survey Laboratory in Lincoln, Nebraska. In addition to the scientists, the 

current Soil Survey Laboratory technicians are also listed. These analysts play a key role not 

only in performing the analyses but also in developing new or modifying old methods, and 

ensuring data quality. Scientists (past and current) and physical science technicians (current) 

are listed alphabetically as follows: 

Scientists: 

Lyle T. Alexander, Steven L. Baird, Otto W. Baumer, Ellis C. Benham, C. Reese Berdanier Jr., 

Wade A. Blankenship, Benny R. Brasher, Laurence E. Brown, Rebecca Burt, John G. Cady, 

Frank J. Carlisle, James H. DeMent, Joe D. Dixon, Moustafa A. Elrashidi, Richard R. 

Ferguson, Klaus W. Flach, Carol D. Franks, Donald P. Franzmeier, Erling E. Gamble, Don W. 

Goss, Robert B. Grossman, George C. Holmgren, C. Steven Holzhey, Robert H. Jordan, R. Leo 

Juve, Fredrick M. Kaisaki, John M. Kimble, Leo C. Klameth, Ellis G. Knox, Susan E. SamsonLiebig, Warren C. Lynn, Maurice J. Mausbach, M. Dewayne Mays, Dean C. McMurty, Milton 

M. Meyer, John L. Millet, Reuben E. Nelson, W. Dennis Nettleton, Carolyn G. Olson, Ronald 

F. Paetzold, Roger B. Parsons, Richard L. Pullman, Ivan W. Ratcliff Jr., Thomas G. Reinsch, 

Earnest D. Rivers, Sam J. Ross, Philip J. Schoeneberger, Leo G. Shields, Christopher W. 

Smith, Terrence M. Sobecki, John A. Thompson, Geroge W. Threlkeld, Michael A. Wilson, 

Douglas A. Wysocki, Ronald D. Yeck, and Keith K. Young. 

Physical Science Technicians: 

Larry V. Arnold, Michelle A. Etmund, Kristina Goings, Diane G. Hooper, Patricia E. Jones, 

Janis L. Lang, Christopher W. Lee, Valerie M. Murray, James F. Neal, Kathyrn L. Newman, 

Michael J. Pearson, Susan J. Reidel, Crystal A. Schaecher, Emily K. Rose Seifferlein, James E. 

Thomas, Pamela A. VanNeste, Lester E. Williams, and Thomas J. Zimmer. 
ACKNOWLEDGEMENTS 

We gratefully acknowledge those individuals who provided technical review of the Soil 

Survey Laboratory methods by topical area. Their thoughtful comments and suggestions are 

deeply appreciated. These reviewers of the Soil Survey Laboratory Methods Manual, Soil 

Survey Investigations Report No. 42, Version 4.0 are listed alphabetically as follows: 

Reviewers 

Jacob H. Dane, Department of Agronomy and Soils, 202 Funchess Hall, Auburn University, 

Auburn, Alabama 36849-5412 

Richard P. Dick, Department of Crop and Soil Science, Agricultural and Life Sciences Building 

3067, Oregon State University, Corvallis, Oregon 97331 

Glendon W. Gee, 1637 Birch Avenue, Richland, Washington, 99352 

Mark Flock, Vice-President, Soil and Plant Analysis Council, Brookside Laboratory, Inc., 308 

S. Main Street, New Knoxsville, Ohio 45871 

Willie G. Harris, Soil and Water Science Department University of Florida, 2169 McCarty 

Hall, Gainesville, Florida 32611-0000 

Yash Kalra, Canadian Forest Service, 5320 – 122 Street, Edmonton, Alberta, Canada T6H 3S5 

Robert Miller, Coordinator, North American Proficiency Testing Program, Soil and Crop 

Science Department, Colorado State University, Fort Collins, Colorado 80523 
METHODS OF ANALYSIS FOR SOILS, WATER, 

AND BIOLOGICAL MATERIALS

CONTENTS 

METHOD TITLE METHOD PAGE 

CODE

SAMPLE COLLECTION AND PREPARATION 1 1 

Field Sample Collection and Preparation 1A 1 

Site Selection 1A1 1 

Geomorphic 1A1a 1 

Pedon 1A1b 1 

Water 1A1c 1 

Biological 1A1d 1 

Laboratory Sample Collection and Preparation 1B 16 

 Soils 1B1 16 

Samples 1B1a 16 

Bulk 1B1a1 16 

Natural Fabrics 1B1a2 17 

Clods 1B1a3 17 

Cores 1B1a4 17 

Preparation 1B1b 17 

Field-Moist Preparation 1B1b1 19 

Whole Soil 1B1b1a 20 

Histosol Analysis 1B1b1a1 20 

Biological Analysis 1B1b1a2 20 

<2-mm Fraction 1B1b1b 20 

Chemical and Selected Physical Analysis 1B1b1b1 20 

1500-kPa Water Content 1B1b1b2 20 

Field-Field-Moist/Air-dry Ratio 1B1b1b3 21 

<2-mm Fraction Sieved to < 0.425 mm 1B1b1c 21 

Atterberg Limits 1B1b1c1 21 

Air-Dry Preparation 1B1b2 21 

Whole Soil 1B1b2a 21 

Aggregate Stability 1B1b2a1 21 

Repository Samples 1B1b2a2 22 

<2-mm Fraction 1B1b2b 22 

Standard Chemical, Physical, Mineralogical Analysis 1B1b2b1 22 

Salt Analysis 1B1b2b2 22 

1500-kPa Water Content 1B1b2b3 23 

Air-Dry/Oven-Dry Ratio 1B1b2b4 23 

Presence of Carbonates 1B1b2b5 23 

<2-mm Fraction Sieved to <0.425 mm 1B1b2c 23 

Atterberg Limits 1B1b2c1 23 

<2-mm Fraction Processed to ≈ 180 μm 1B1b2d 24 

i
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Total Carbon, Nitrogen, and Sulfur 1B1b2d1 24 

Carbonates and/or Gypsum 1B1b2d2 24 

Chemical Analysis of Organic Materials 1B1b2d3 24 

<2-mm Fraction Sieved to 75 μm 1B1b2e 24 

Major and/or Trace Elements 1B1b2e1 24 

Particles >2 mm 1B1b2f 24 

Particle-Size Analysis 1B1b2f1 25 

Particle-Size Analysis, Recorded 1B1b2f1a 25 

2- to 20-mm Fraction Processed to <2-mm 1B1b2f1a1 25 

Chemical, Physical, and Mineralogical Analysis 1B1b2f1a1a 25 

2- to 20-mm Fraction Processed to <2-mm and Recombined 1B1b2f1a2 26 

 with <2-mm Fraction 

Chemical, Physical, and Mineralogical Analysis 1B1b2f1a2a 26 

Proportion and Particle-Size of Air-Dry Rock Fragments that 1B1b2f1a3 27 

Resist Abrupt Immersion in Tap Water 

Particle-Size Analysis, Not Recorded 1B1b2f1b 25 

Whole-Soil Processed to <2-mm 1B1b2f1b1 26 

Chemical, Physical, and Mineralogical Analysis 1B1b2f1b1a 26 

Water 1B2 29 

Samples 1B2a 29 

Preparation 1B2b 29 

Biological Materials 1B3 30 

Samples 1B3a 30 

Biology Bulk Sample 1B3a1 30 

Microbial Biomass Sample 1B3a2 30 

Preparation 1B3b 30 

Field-Moist Preparation 1B3b1 30 

<2-mm Fraction 1B3b1a 30 

Microbial Biomass 1B3b1a1 30 

Air-Dry Preparation 1B3b2 30 

<2-mm Fraction Sieved <53 μm, with <53 μm (C-Mineral) and 1B3b2a 30 

 > 53 μm (Particulate Organic Matter) Processed to ≈ 180 μm 

Total Carbon, Nitrogen, and Sulfur Analysis 1B3b2a1 30 

<2-mm Fraction 1B3b2b 30 

Other Biological Analyses 1B3b2b1 30 

Dry (50 C) Preparation 1B3b3 31 

Roots 1B3b3a 31 

Root Biomass 1B3B3a1 31 

Roots Processed to ≈ 180 μm 1B3b3a1a 31 

Total Carbon, Nitrogen, and Sulfur Analysis 1B3b3a1a1 31 

Plants 1B3b3b 31 

Plant Biomass 1B3b3b1 31 

Plants Processed to ≈ 180 μm 1B3b3b1a 31 

Total Carbon, Nitrogen, and Sulfur Analysis 1B3b3b1a1 31 

ii
CONTENTS

METHOD TITLE METHOD PAGE 

CODE 

CONVENTIONS 2 31 

Methods and Codes 2A 31 

Data Types 2B 32 

Particle-Size Fraction Base for Reporting Data 2C 32 

Particles <2 mm 2C1 32 

Particles >2mm 2C2 32 

Sample Weight Base for Reporting Data 2D 33 

Air-Dry/Oven-Dry 2D1 33 

Field-Field-Moist/Oven-Dry 2D2 33 

Correction for Crystal Water 2D3 33 

Significant Figures and Rounding 2E 33 

Data Sheet Symbols 2F 33 

SOIL PHYSICAL AND FABRIC-RELATED 3 34 

ANALYSES 

Particle-Size Distribution Analysis 3A 34 

Particles <2 mm 3A1 34 

Pipet Analysis for routinely reported size fractions 3A1a 34 

(1, 0.5, 0.25, 0.1, 0.047 mm, <20 μm, and <2 μm), with or 

 without <0.2-μm fraction, with or without <2-μm carbonate clay 

Pipet Analysis with Standard Pretreatments and Dispersion 3A1a1 41 

Air-Dry 3A1a1a 41 

Field-Moist 3A1a1b 50 

Pipet Analysis with Carbonate Removal 3A1a2 46 

Air-Dry 3A1a2a 46 

Field-Moist 3A1a2b 51 

Pipet Analysis with Iron Removal 3A1a3 46 

Air-Dry 3A1a3a 46 

Field-Moist 3A1a3b 52 

Pipet Analysis with Silica Removal 3A1a4 47 

Air-Dry 3A1a4a 47 

Field-Moist 3A1a4b 53 

Pipet Analysis with Ultrasonic Dispersion 3A1a5 47 

Air-Dry 3A1a5a 47 

Field-Moist 3A1a5b 53 

Pipet Analysis with Water Dispersion 3A1a6 48 

Air-Dry 3A1a6a 48 

Field-Moist 3A1a6b 55 

iii
CONTENTS

METHOD TITLE METHOD PAGE 

CODE Particles >2 mm 3A2 66 

Weight Estimates 3A2a 67 

By Field and Laboratory Weighing 3A2a1 67 

From Volume and Weight Estimates 3A2a2 70 

Volume Estimates 3A2b 70 

 Bulk Density 3B 73 

Saran-Coated Natural Clods 3B1 75 

Field State 3B1a 75 

33 kPa 3B1b 80 

Oven-dry 3B1c 86 

Rewet 3B1d 89 

Reconstituted 3B2 99 

33 kPa 3B2a 99 

Oven-Dry 3B2b 99 

Compliant Cavity 3B3 98 

Field State 3B3a 98 

Ring Excavation 3B4 100 

Field State 3B4a 100 

Frame Excavation 3B5 102 

Field State 3B5a 102 

Soil Cores 3B6 104

Field State 3B6a 104 

Water Retention 3C 105 

Pressure-Plate Extraction 3C1 106 

6 10, 33, 100, or 200 kPa Water Retention 3C1a-e 106 

<2 mm Sieved, Air-Dry 3C1a-e1a 106 

Natural Clods 3C1a-d2 108 

Soil Cores 3C1a-d3 114 

Rewet 3C1c4 117 

Reconstituted 3C1c5 121 

Pressure-Membrane Extraction 3C2 125 

1500 kPa Water Retention 3C2a 125 

<2 mm Sieved, Air-Dry 3C2a1a 125 

<2 mm Sieved, Field-Moist 3C2a1b 129 

 

Water Retention at Field State 3C3 131 

 

iv
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Ratios and Estimates Related to Particle Size 3D 132 

Analysis, Bulk Density, and Water Retention

Air-Dry/Oven-Dry Ratio 3D1 132 

Field-Moist/Oven-Dry Ratio 3D2 132 

Correction for Crystal Water 3D3 132 

Coefficient of Linear Extensibility 3D4 135 

Air-Dry or Oven-Dry to 33-kPa Tension 3D4a 135 

Water Retention Difference, Whole Soil 3D5 137 

Between 33-kPa and 1500-kPa Tension 3D5a 137 

Between 10-kPa and 1500-kPa Tension 3D5b 137 

Between 33-kPa and 1500-kPa (Air-Dry) Tension 3D5c 137 

1500 kPa Water/Clay Ratio 3D6 138 

Total Silt Fraction 3D7 138 

Total Sand Fraction 3D8 138 

2- to 5-mm Fraction 3D9 138 

5- to 20-mm Fraction 3D10 139 

20- to 75-mm Fraction 3D11 139 

0.1- to 75-mm Fraction 3D12 139 

>2-mm Fraction 3D13 139 

 

Micromorphology 3E 140 

Thin sections 3E1 140 

Preparation 3E1a 140 

Interpretation 3E1b 143 

Wet Aggregate Stability 3F 163 

Wet Sieving 3F1 163 

Air-dry 3F1a 163 

2 to 1 mm 3F1a1 163 

2- to 0.5-mm Aggregates Retained 3F1a1a 163

Particle Density 3G 165 

Pycnometer Gas Displacement 3G1 165 

Oven-dry 3G1a 165 

<2 mm 3G1a1 165 

>2 mm 3G1a2 165 

 

Atterberg Limits 3H 167 

Liquid Limit 3H1 167 

Air-Dry, <0.4 mm 3H1a1 167 

Field-Moist, <0.4 mm 3H1b1 167 

Plasticity Index 3H2 167 

Air-Dry, <0.4 mm 3H2a1 167 

Field-Moist, <0.4 mm 3H2b1 167 

v
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

SOIL AND WATER CHEMICAL EXTRACTIONS 4 167 

AND ANALYSES 

Acid Standardization 4A 167 Ion Exchange and Extractable Cations 4B 173 

Displacement after Washing 4B1 173 

 

NH4OAc, pH 7 4B1a 173 

Automatic Extractor 4B1a1 173 

2 M KCl Rinse 4B1a1a 173 

Steam Distillation 4B1a1a1 173 

HCl Titration 4B1a1a1a 173 

Cation Exchange Capacity (CEC-7) 4B1a1a1a1 173 

Air-Dry, <2 mm 4B1a1a1a1a1 173 

Field-Moist, <2 mm 4B1a1a1a1b1 173 

Atomic Absorption Spectrophotometer 4B1a1b 184 

Calcium, Magnesium, Potassium, and Sodium 4B1a1b1-4 184 

Air-Dry, <2 mm 4B1a1b1-4a1 184 

Field-Moist, <2 mm 4B1a1b1-4b1 184 

 

NH4Cl, Neutral Unbuffered 4B1b 181 

Automatic Extractor 4B1b1 181 

2M KCl Rinse 4B1b1a 181 

Steam Distillation 4B1b1a1 181 

HCl Titration 4B1b1a1a 181 

Cation Exchange Capacity 4B1b1a1a1 181 

Air-Dry, <2 mm 4B1b1a1a1a1 181 

Field-Moist, <2 mm 4B1b1a1a1b1 181 

Atomic Absorption Spectrophotometer 4B1a1b 188 

Calcium, Magnesium, Potassium, and Sodium 4B1b1b1-4 188 

Air-Dry, <2 mm 4B1b1b1-4a1 188 

Field-Moist, <2 mm 4B1b1b1-4b1 188 

 

BaCl2-Triethanolamine, pH 8.2 Extraction 4B2 191 

Automatic Extractor 4B2a 191 

Automatic Titrator 4B2a1 191 

Back Titration with HCl 4B2a1a 191 

Extractable Acidity 4B2a1a1 191 

Air-Dry, <2 mm 4B2a1a1a1 191 

Field-Moist, <2 mm 4B2a1a1b1 191 

Centrifuge 4B2b 194 

Automatic Titrator 4B2b1 194 

Back Titration with HCl 4B2b1a 194 

Extractable Acidity 4B2b1a1 194 

Air-Dry, <2 mm 4B2b1a1a1 194 

Field-Moist, <2 mm 4B2b1a1b1 194 

vi
CONTENTS

METHOD TITLE METHOD PAGE 

CODE 

1 N KCl Extraction 4B3 197 

Automatic Extractor 4B3a 197 

Inductively Coupled Plasma Spectrophotometer 4B3a1 197 

Radial Mode 4B3a1a 197 

Al, Mn 4B3a1a1-2 197 

Air-Dry, <2 mm 4B3a1a1-2a1 197 

Field-Moist, <2 mm 4B3a1a1-2b1 197 

Ratios and Estimates Related to Ion Exchange and 4B4 201 

Extractable Cations 

Sum of Extractable Bases 4B4a 201 

Sum of Extractable Bases by NH4OAc, pH 7 4B4a1 201 

Sum of Extractable Bases by NH4OAc, pH 7, Calculated 4B4a1a 201 

Sum of Extractable Bases by NH4Cl 4B4a2 201 

Sum of Extractable Bases by NH4Cl, Calculated 4B4a2a 201 

Cation Exchange Capacity (CEC) 4B4b 202 

CEC-8.2 (Sum of Cations) 4B4b1 202 

CEC-8.2, Calculated 4B4b1a 202 

CEC-8.2, Not Calculated 4B4b1b 202 

Effective Cation Exchange Capacity (ECEC) 4B4b2 202 

Sum of NH4OAc Extractable Bases + 1 N KCl Extractable 4B4b2a 202 

Aluminum , Calculated 

Sum of NH4OAc Extractable Bases + 1 N KCl Extractable 4B4b2b 202 

Aluminum , Not Calculated 

Base Saturation 4B4c 202 

Base Saturation by NH4OAc, pH 7 (CEC-7) 4B4c1 202 

Base Saturation by CEC-7, Calculated 4B4c1a 202 

Base Saturation by CEC-7, Set to 100% 4B4c1b 202

Base Saturation by NH4Cl 4B4c2 203 

Base Saturation by NH4Cl, Calculated 4B4c2a 203 

Base Saturation by NH4Cl, Set to 100% 4B4c2b 203 

Base Saturation by CEC-8.2 4B4c3 203 

Base Saturation by CEC-8.2, Calculated 4B4c3a 203 

Base Saturation by CEC-8.2, Not Calculated 4B4c3b 203 

Base Saturation by ECEC 4B4c4 203 

Base Saturation by Sum of NH4OAc Extractable Bases 4B4c4a 203 

+ 1 N KCl Extractable Aluminum, Calculated 

 Base Saturation by Sum of NH4OAc Extractable Bases 4B4c4b 203 

+ 1 N KCl Extractable Aluminum, Not Calculated 

Aluminum Saturation 4B4d 204 

Aluminum Saturation by ECEC 4B4d1 204 

Aluminum Saturation by Sum of NH4OAc Extractable Bases 4B4d1a 204 

+ 1 N KCl Extractable Aluminum, Calculated 

Aluminum Saturation by Sum of NH4OAc Extractable Bases 4B4d1b 204 

+ 1 N KCl Extractable Aluminum, Not Calculated 204 

vii
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Activity 4B4e 204 

CEC-7FOD\ 4B4e1 204

Reaction 4C 204 

Soil Suspensions 4C1 204 

Electrode 4C1a 204 

Standard Glass Body Combination 4C1a1 204 

Digital pH/Ion Meter 4C1a1a 204 

1 N NaF, pH 7.5 – 7.8 4C1a1a1 205 

Air-Dry, <2 mm 4C1a1a1a1 205 

Field-Moist, <2 mm 4C1a1a1b1 205 

Saturated Paste pH 4C1a1a2 207 

Air-Dry, <2 mm 4C1a1a2a1 207 

Oxidized pH 4C1a1a3 209 

Organic Materials pH, Final Solution ≈ 0.01 M CaCl2 pH 4C1a1a4 211 

Combination pH-reference electrode 4C1a2 213 

Automatic Titrator 4C1a2a 213 

1:1 water pH 4C1a2a1 213 

Air-Dry, <2 mm 4C1a2a1a1 213 

Field-Moist, <2 mm 4C1a2a1b1 213 

1:2 0.01 M CaCl2 pH 4C1a2a2 213 

Air-Dry, <2 mm 4C1a2a2a1 213 

Field-Moist, <2 mm 4C1a2a2b1 213 

1 M KCl pH 4C1a2a3 215 

Air-Dry, <2 mm 4C1a2a3a1 215 

Field-Moist, <2 mm 4C1a2a3b1 215 

Soil Test Analyses 4D 217 

Anion Resin Extraction 4D1 219 

Two-Point Extraction 4D1a 219 

1 h, 24h, 1 M 1DClD1a1a119 

UV-Visible Spectrophotometer, Dual-Beam 4D1a1a1a 219 

Phosphorus (2 points) 4D1a1a1a1-2 219 

Air-Dry, <2 mm 4D1a1a1a1-2a-b1 219 

Field-Moist, <2 mm 4D1a1a1a1-2b1 219 

Aqueous Extraction 4D2 223 

Single-Point Extraction 4D2a 223 

1:10, 30 min 4D2a1 223 

UV-Visible Spectrophotometer, Dual Beam 4D2a1a 223 

viii
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Phosphorus 4D2a1a1 223 

Air-Dry, <2 mm 4D2a1a1a1 223 

Field-Moist, <2 mm 4D2a1a1b1 223 

Flow Injection, Automated Ion Analyzer 4D2a1b 226 

Phosphorus 4D2a1b1 226 

Air-Dry, <2 mm 4D2a1b1a1 226 

Field-Moist, <2 mm 4D2a1b1b1 226 

Bray P-1 Extraction 4D3 231 

UV-Visible Spectrophotometer, Dual Beam 4D3a 231 

Phosphorus 4D3a1 231 

Air-Dry, <2 mm 4D3a1a1 231 

Field-Moist, <2 mm 4D3a1b1 231 

Flow Injection, Automated Ion Analyzer 4D3b 234 

Phosphorus 4D3b1 234 

Air-Dry, <2 mm 4D3b1a1 234 

Field-Moist, <2 mm 4D3b1b1 234 

Bray P-2 Extraction 4D4 239 

UV-Visible Spectrophotometer, Dual-Beam 4D4a 239 

Phosphorus 4D4a1 239 

Air-Dry, <2 mm 4D4a1a1 239 

Field-Moist, <2 mm 4D4a1b1 239 

Olsen Sodium-Bicarbonate Extraction 4D5 242 

UV-Visible Spectrophotometer, Dual Beam 4D5a 242 

Phosphorus 4D5a1 242 

Air-Dry, <2 mm 4D5a1a1 242 

Field-Moist, <2 mm 4D5a1b1 242 

Mehlich No. 3 Extraction 4D6 246 

UV-Visible Spectrophotometer, Dual Beam 4D6a 246 

Phosphorus 4D6a1 246 

Inductively Coupled Plasma Atomic Emission 4D6b 249 

Spectrophotometer 

Axial Mode 4D6b1 249 

Ultrasonic Nebulizer 4D6b1a 249 

Aluminum, Arsenic, Barium, Calcium, Cadmium, Cobalt, 4D6b1a1-18 249 

Chromium, Copper, Iron, Potassium, Magnesium, Manganese, 

Sodium, Nickel, Phosphorus, Lead, Selenium, and Zinc 

Air-Dry, <2 mm 4D6b1a1-18a1 249 

Field-Moist, <2 mm 4D6b1a1-18b1 249 

Citric Acid Soluble 4D7 253 

UV-Visible Spectrophotometer, Dual Beam 4D7a 253 

Phosphorus 4D7a1 253 

Air-Dry, <2 mm 4D7a1a1 253 

Field-Moist, < 2 mm 4D7a1b1 253 

ix
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

New Zealand P Retention 4D8 257 

UV-Visible Spectrophotometer, Dual Beam 4D8a 257 

Phosphorus 4D8a1 257 

Air-Dry, <2 mm 4D8a1a1 257 

Field-Moist, <2 mm 4D8a1b1 257 

1 M KCl Extraction 4D9 260 

Cadmium-Copper Reduction 4D9a 260 

Sulfanilamide N-1-Naphthylethylenediamine Dihydrochloride 4D9a1 260 

Flow-Injection, Automated Ion Analyzer 4D9a1a 260 

Nitrate-Nitrite 4D9a1a1-2 260 

Air-Dry, <2 mm 4D9a1a1-2a1 260 

Field-Moist, <2 mm 4D9a1a1-2b1 260 

Field-Moist, <2 mm, Fumigated and Non-fumigated 4D9a1a1-2b2-3 260 

Anaerobic Incubation 4D10 265 

2 M KCl Extraction 4D10a 265 

Ammonia – Salicylate 4D10a1 265 

Flow Injection, Automated Ion Analyzer 4D10a1a 265 

N as NH3 – Mineralizable N 4D10a1a1 265 

Air-Dry, <2 mm 4D10a1a1a1 265 

Field-Moist, <2 mm 4D10a1a1b1 265 

Carbonate and Gypsum 4E 269 

3 N HCl Treatment 4E1 269 

CO2 Analysis 4E1a 269 

Manometer, Electronic 4E1a1 269 

Carbonates 4E1a1a 269 

Calcium Carbonate 4E1a1a1 269 

Air-Dry, <2 mm 4E1a1a1a1 269 

Air-Dry, 2 to 20 mm 4E1a1a1a2 269 

Aqueous Extraction 4E2 273 

Precipitation in Acetone 4E2a 273 

Conductivity Bridge 4E2a1 273 

Electrical Conductivity 4E2a1a 273 

Gypsum, qualitative and quantitative 4E2a1a 273 

Air-Dry, <2 mm 4E2a1a1a1 273 

Air-Dry, 2 to 20 mm 4E2a1a1a2 273 

Electrical Conductivity and Soluble Salts 4F 277 

Aqueous Extraction 4F1 277 

1:2 Aqueous Extraction 4F1a 277 

Conductivity Bridge 4F1a1 277 

Electrical Conductivity 4F1a1a 277 

x
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Salt Prediction 4F1a1a1 277 

Air-Dry, <2 mm 4F1a1a1a1 277 

Saturated Paste 4F2 278 

Gravimetric 4F2a 282 

Water Percentage 4F2a1 282 

Air-Dry, <2 mm 4F2a1a1 282 

Conductivity Bridge 4F2b 284 

Electrical Conductivity 4F2b1 284 

Air-Dry, <2 mm 4F2b1a1 284 

Resistivity 4F2b2 286 

Air-Dry, <2 mm 4F2b2a1 286 

Saturated Paste Extraction 4F2c 289 

Automatic Extractor 4F2c1 289 

Atomic Absorption Spectrophotometer 4F2c1a 290 

Calcium, Magnesium, Potassium, and Sodium 4F2c1a1-4 290 

Air-Dry, <2 mm 4F2c1a1-4a1 290 

Ion Chromatograph 4F2c1b 294 

Conductivity Detector 4F2c1b1 294 

Self-Regeneration Suppressor, 4F2c1b1a 294 

Bromide, Acetate, Chloride, Fluoride, Nitrate, Nitrite, 4F2c1b1a1-8 294 

Phosphate, and Sulfate 

Air-Dry, <2 mm 4F2c1b1a1-8a1 294 

Automatic Titrator 4F2c1c 299 

Combination pH-Reference Electrode 4F2c1c1 299 

Acid Titration, H2SO4 4F2c1c1a 299 

Carbonate and Bicarbonate 4F2c1c1a1-2 299 

Air-Dry, <2 mm 4F2c1c1a1-2a1 299 

Ratios and Estimates Related to Soluble Salts 4F3 301 

Exchangeable Sodium Percentage (ESP) 4F3a 301 

ESP, Calculated without Saturated Paste Extraction 4F3a1 301 

ESP, Calculated with Saturated Paste Extraction 4F3a2 302 

Sodium Adsorption Ratio (SAR) 4F3b 303 

Estimated Total Salt 4F3c 303 

Selective Dissolutions 4G 303

Dithionite-Citrate Extraction 4G1 307 

Atomic Absorption Spectrophotometer 4G1a 307 

Aluminum, Iron, and Manganese 4G1a1-3 307 

Air-Dry, <2 mm 4G1a1-3a1 307 

Field-Moist, <2 mm 4G1a1-3b1 307 

xi
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Ammonium Oxalate Extraction 4G2 312 

Automatic Extractor 4G2a 312 

Inductively Coupled Plasma Atomic Emission 4G2a1 312 

Spectrophotometer 

Radial Mode 4G2a1a 312 

Aluminum, Iron, Manganese, Phosphorus, and Silicon 4G2a1a1-5 312 

Air-Dry, <2 mm 4G2a1a1-5a1 312 

Field-Moist, <2 mm 4G2a1a1-5b1 312 

UV-Visible Spectrophotometer, Dual Beam 4G2a2 312 

Transmittance 4G2a2a 312 

Optical Density 4G2a2a1 312 

Air-Dry, <2 mm 4G2a2a1a1 312 

Field-Moist, <2 mm 4G2a2a1b1 312 

Ratios and Estimates Related to Ammonium Oxalate Extraction 4G2b 317 

Al + 1⁄2 Fe 4G2b1 317 

Sodium Pyrophosphate Extraction 4G3 317 

Atomic Absorption Spectrophotometer 4G3a 317 

Aluminum, Iron, and Manganese 4G3a1-3 317 

Air-Dry, <2 mm 4G3a1-3a1 317 

Field-Moist, <2 mm 4G3a1-3b1 317 

Acid Digestion 4G3b 317 

K2Cr2O7 + (H2SO4 + H3PO4 Digestion) 4G3b1 317 

Nesbitt Bulb 4G3b1 317 

CO2 Evolution, Gravimetric 4G3b1a 317 

Organic Carbon 4G3b1a1 317 

Air-Dry, <2 mm 4G3b1a1a1 317 

Field-Moist, <2 mm 4G3b1a1b1 317 

Total Analysis 4H 324 

Acid Digestion 4H1 324 

HNO3 + HCl Digestion 4H1a 324 

Microwave 4H1a1 324 

Inductively Coupled Plasma Atomic Emission 4H1a1a 324 

Spectrophotometer 

Axial Mode 4H1a1a1 324 

Ultrasonic Nebulizer 4H1a1a1a 324 

Silver, Arsenic, Barium, Beryllium, Cadmium, Cobalt, 4H1a1a1a1-20 324 

Chromium, Copper, Manganese, Molybdenum, Nickel, 

Phosphorus, Lead, Antimony, Tin, Strontium, Thallium, 

Vanadium, Tungsten, Zinc 

Air-Dry, <2 mm 4H1a1a1-20a1 324 

 

xii
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

HCl Digestion 4H1a1b 331 

Water Bath 4H1a1b1 331 

Flow through Hydride-Generation and Atomic 4H1a1b1 331 

Absorption Spectrophotometer 

Arsenic and Selenium 4H1a1b1a1-2 331 

Air-Dry, <2 mm 4H1a1b1a1-2a1 331 

Cold Vapor Atomic Absorption Spectrophotometer 4H1a1c 336 

Mercury 4H1a1c1 336 

Air-Dry, <2 mm 4H1a1c1a1 336 

HF + HNO3 + HCl Digestion 4H1b 341 

Microwave 4H1b1 341 

Boric Acid 4H1b1a 341 

Inductively Coupled Plasma Atomic Emission 4H1b1a1 341 

Spectrophotometer 

Radial Mode 4H1b1a1a 341 

Aluminum, Calcium, Iron, Potassium, Magnesium, Manganese, 4H1b1a1a1-11 341 

Sodium, Phosphorus, Silicon, Zirconium, Titanium 

Air-Dry, <2 mm 4H1b1a1a1-11a1 341 

Oven-Dry, <2 μm 4H1b1a1a1-11b2 341 

Dry Combustion 4H2 347 

Thermal Conductivity Detector 4H2a 347 

Carbon, Nitrogen, and Sulfur 4H2a1-3 347 

Air-Dry, <2 mm 4H2a1-3a1 347 

 

Ground and Surface Water Analyses 4I 352 

Reaction 4I1 352 

Electrode 4I1a 352 

Standard Glass Body Combination 4I1a1 352 

Digital pH/Ion Meter 4I1a1a 352 

pH 4I1a1a1 352 

Electrical Conductivity and Salts 4I2 353 

Conductivity Bridge and Cup 4I2a 353 

Electrical Conductivity 4I2a1 353 

Atomic Absorption Spectrophotometer 4I2b 355 

Calcium, Magnesium, Potassium, and Sodium 4I2b1-4 355 

Ion Chromatograph 4I2c 358 

Conductivity Detector 4I2c1 358 

Self-Regeneration Suppressor 4I2c1a 358 

Bromide, Acetate, Chloride, Fluoride, Nitrate, Nitrite, 4I2c1a1-8 358 

Phosphate, and Sulfate 

Automatic Titrator 4I2d 363 

Combination pH-reference Electrode 4I2d1 363 

Acid Titration, H2SO4 4I2d1a 363 

Carbonate and Bicarbonate 4I2d1a1-2 363 

xiii
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Total Analysis 4I3 365 

Inductively Coupled Plasma Atomic Emission 4I3a 365 

Spectrophotometer 

$[ial ModeI3a1 365 

Ultrasonic Nebulizer 4I3a1a 365 

Aluminum, Iron, Manganese, Phosphorus, and Silicon 4I3a1a1-5 365 

ANALYSIS OF ORGANIC SOILS OR MATERIALS 5 368 

Mineral Content 5A 368 

Pyrophosphate Color 5B 369 

Fiber Volume 5C 371 

Melanic Index 5D 374 

Ratios and Estimates Related to Organic Matter 5E 375 

SOIL BIOLOGICAL AND PLANT ANALYSES 6 375 

Soil Analyses 6A 375 

0.5 M K2SO4 Extraction + Heating with Disodium 6A1 376 

Bicinchoninic Reagent 

UV-Visible Spectrophotometer, Dual Beam 6A1a 376 

Hot Water Extractable Organic Carbon 6A1a1 376 

Air-Dry, <2 mm 6A1a1a1 376 

0.02 M KMnO4 Extraction 6A2 379 

UV-Visible Spectrophotometer, Dual Beam 6A2a 379 

Active Carbon 6A2a1 379 

Air-Dry, <2 mm 6A2a1a1 379

Acid Dissolution 6A3 381 

1 N HCl Dissolution + FeCl2 6A3a 381 

Gas Chromatography 6A3a1 381 

CO2 Analysis 6A3a1a 381 

Carbonates 6A3a1a1 381 

Air-Dry, <2 mm 6A3a1a1a1 381

Particulate Organic Matter and Carbon-Mineral 6A4 385 

Total Analysis 6A4a 385 

Dry Combustion 6A4a1 385 

Thermal Conductivity Detector 6A4a1a 385 

Carbon, Nitrogen, and Sulfur 6A4a1a1-3 385 

Air-Dry, >53 μm (POM) 6A4a1a1-3a1 385 

Air-Dry, <53 μm (C-Min) 6A4a1a1-3a2 385 

xiv
xv

CONTENTS

METHOD TITLE METHOD PAGE

CODE

Fumigation Incubation 6B 388 

Gas Chromatography 6B1 388

CO2 Analysis 6B1a 388

Soil Microbial Biomass 6B1a1 388

Field-Moist, Whole-Soil 6B1a1a1 388

2 M KCl Extraction 6B2 388

Automatic Extractor 6B2a 388

Ammonia – Salicylate 6B2a1 388

Flow Injection, Automated Ion Analyzer 6B2a1a 388

N as NH3 – Mineralizable N 6B2a1a1 388

Field-Moist, Whole-Soil Fumigated, Whole-Soil 6B2a1a1a1-2 388

Non-Fumigated

 

Plant Analyses 6C 394 

Root Biomass 6C1 394

Plant (above-ground) Biomass 6C2 394

Plant Nutrition 6C3 394

Total Analysis 6C3a 394

Dry Combustion 6C3a1 394

Thermal Conductivity Detector 6C3a1a 394

Carbon, Nitrogen, and Sulfur 6C3a1a1-3 394

Dry (50°C), Roots 6C3a1a1-3a1 394

Dry (50°C), Plants (above-ground) 6C3a1a1-3a2 394

Ratios and Estimates Related to Biological Analyses 6E 398 MINERALOGY 7 398 

Instrumental Analyses 7A 398 

X-Ray Diffraction 7A1 399

Thin Film on Glass, Resin Pretreatment II 7A1a 399

Mg Room Temperature, Mg Glycerol Solvated, K 300°C, 7A1a1 399

K 500°C 

 

Thermogravimetric Analysis 7A2 410

Thermal Analyzer 7A2a 410

Differential Scanning Calorimetry 7A3 410

Thermal Analyzer 7A3a 410

Differential Thermal Analysis 7A4 415

Thermal Analyzer 7A4a 415
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Surface Area 7A5 418 

N2 Adsorption 7A5a 418 

Brunauer, Emmett and Teller Theory 7A5a1 418 

Vacuum Degassing 7A5a1a 418 

Multi-Point 7A5a1a1 418 

Air-Dry, <2 mm 7A5a1a1a1 418 

Single Point 7A5a1a2 418 

Air-Dry, <2 mm 7A5a1a2a1 418 

Optical Analyses 7B 422 

Grain Studies 7B1 422 

Analysis and Interpretation 7B1a 422 

Separation by Heavy Liquids 7B1a1 428 

Grain Mounts, Epoxy 7B1a2 428 

Platy Grains 7B2 434 

Magnetic Separation 7B2a 434 

Static Tube Separation 7B2b 437 

Froth Flotation 7B2c 439 

Ratios and Estimates Related to Optical Analysis 7C 442 

Total Resistant Minerals 7C1 442 

Mineralogy Codes 443 

xvi
SOIL SURVEY LABORATORY METHODS 

(Obsolete Methods with Old Method Codes) 

METHOD TITLE METHOD PAGE 

CODE

SAMPLE COLLECTION AND PREPARATION 1 609 

Laboratory Preparation of Soil Samples 1B 609 

 Carbonate-Containing Material 1B3 609 

 Carbonate-Indurated Material 1B4 609 

 

PARTICLE-SIZE ANALYSIS 3 610 Particles <2 mm (pipet method) 3A 610 

 Air-Dry Samples 3A1 610 

 Carbonate and Noncarbonate I 3A1a 612 

 Moist Samples 3A2 613 

 Carbonate and Noncarbonate I 3A2a 613 

 

FABRIC-RELATED ANALYSES 4 613 Bulk Density 4A 613 

 Saran-Coated Clods 4A1 613 

 Air-Dry 4A1b 616 

 30-cm Absorption 4A1c 616 

 1/3-Bar Desorption II 4A1e 616 

 1/3-Bar Desorption III 4A1f 616 

 1/10-Bar Desorption 4A1g 616 

 Paraffin Coated Clods 4A2 616 

 Oven-Dry 4A2a 616 

 Nonpolar-Liquid-Saturated Clods 4A4 617 

 

Water Retention 4B 617 

 Pressure-Plate Extraction 4B1 617 

 Soil Pieces 4B1b 617 

 Sand-Table Absorption 4B3 617 

 

Micromorphology 4E 618 

 Thin Sections 4E1 618 

 Moved-Clay Percentage 4E1c 618 

 Scanning Electron Microscope 4E2 618 

ION EXCHANGE ANALYSES 5 

 

Cation Exchange Capacity (CEC) 5A 

 NH4OAc, pH 7.0, Buchner Funnel (CEC-7) 5A1 619 

 Direct Distillation 5A1a 619 

 Displacement Distillation 5A1b 620 

xvii
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

 NaOAc, pH 8.2 5A2 621 

 Centrifuge Method 5A2a 621 

 KOAc, pH 7.0 5A4 621 

 BaCl2, pH 8.2 5A5 622 

 Barium by Flame Photometry 5A5a 622 

 NH4OAc, pH 7.0 (CEC-7.0), Leaching Tube 5A6 622

 Direct Distillation 5A6a 623 

 NH4Cl, pH 7.0, Mechanical Extraction 5A7 623 

 Direct Distillation 5A7a 623 

 NH4OAc, pH 7.0 (CEC-7.0), Automatic Extractor 5A8 

 Direct Distillation 5A8a 623 

 Steam Distillation I 5A8b 561 

 Steam Distillation II 5A8c 463 

 NH4Cl, pH 7.0, Automatic Extractor 5A9 

 Direct Distillation 5A9a 624 

 Steam Distillation I 5A9b 564 

 Steam Distillation II 5A9c 466 

 

 Extractable Bases 5B 624 

 NH4OAc. pH 7.0, Buchner Funnel 5B1 624 

 Uncorrected (extractable) 5B1a 624 

 Corrected (exchangeable) 5B1b 624 

 KCl-TEA Extraction, pH 8.2 5B2 624 

 KCl-TEA Extraction, pH 8.2 (revised) 5B3 624 

 Uncorrected (extractable) 5B3a 625 

 Corrected (exchangeable) 5B3b 625 

 NH4OAc, pH 7.0, Leaching Tube 5B4 625 

 Uncorrected (extractable) 5B4a 625 

 Corrected (exchangeable) 5B4b 625 

 NH4OAc, pH 7.0, Automatic Extractor 5B5 625 

 Corrected (exchangeable) 5B5b 625 

 

Base Saturation 5C 625 

 NH4OAc, pH 8.2 5C2 625 

 

Exchangeable Sodium Percentage (ESP) 5D 625 

 NH4OAc, pH 8.2 5D1 625 

 

Calcium-Saturation 5F 626 

 NH4OAc, pH 7.0 5F1 626 

 

CHEMICAL ANALYSES 6 

 

 Organic Carbon 6A 

 Acid-Dichromate Digestion 6A1 

 FeSO4 Titration 6A1a 626 

 CO2 Evolution, Gravimetric 6A1b 627 

 FeSO4 Titration, Automatic Titrator 6A1c 469 

xviii
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

 Dry Combustion 6A2 

 CO2 Evolution I 6A2a 628 

 CO2 Evolution II 6A2b 629 

 CO2 Evolution III 6A2c 630 

 CO2 Evolution IV 6A2d 567 

 CO2 Evolution V 6A2e 473 

 Peroxide Digestion 6A3 631 

 Weight Loss 6A3a 631 

 Sodium Pyrophosphate Extraction II 6A4 631 

 Atomic Absorption 6A4a 631 

 

Nitrogen 6B 

 Kjeldahl Digestion I 6B1 631 

 Ammonia Distillation 6B1a 631 

 Ammonia Distillation, Automatic Titrator 6B1b 632 

 Semimicro Kjeldahl 6B2 633 

 Ammonia Distillation 6B2a 633 

 Kjeldahl Digestion II 6B3 569 

 Ammonia Steam Distillation, Automatic Titrator 6B3a 569 

 Dry Combustion 6B4 475 

 N2 Evolution 6B4a 475 

 Kjeldahl Digestion III 6B5 477 

 Ammonia Steam Distillation 6B5a 477 

 

Iron 6C 

 Dithionite Extraction 6C1 634 

 Dichromate Titration 6C1a 634 

 EDTA Titration 6C1b 635 

 Dithionite-Citrate Extraction 6C2 

 Orthophenanthroline Colorimetry 6C2a 636 

 Atomic Absorption I 6C2b 479 

 Atomic Absorption II 6C2c 483 

 Dithionite-Citrate-Bicarbonate Extraction 6C3 637 

 Potassium Thiocyanate Colorimetry 6C3a 637 

 Pyrophosphate-Dithionite Extraction 6C4 638 

 Sodium Pyrophosphate Extraction I 6C5 638 

 Atomic Absorption 6C5a 639 

 Ammonium Oxalate Extraction 6C6 639 

 Atomic Absorption 6C6a 639 

 

 HF Dissolution 6C7 

 Atomic Absorption 6C7a 572 

 HF + HNO3 + HCl Dissolution 

 Inductively Coupled Plasma Spectrometry 6C7b 487 

 Sodium Pyrophosphate Extraction II 6C8 490 

 Atomic Absorption 6C8a 490 

 Ammonium Oxalate Extraction 6C9 

 Inductively Coupled Plasma Spectrometry I 6C9a 575 

 Inductively Coupled Plasma Spectrometry II 6C9b 495

xix
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Manganese 6D 

 Dithionite Extraction 6D1 640 

 Permanganate Extraction 6D1a 640 

 Dithionite-Citrate Extraction 6D2 479 

 Atomic Absorption I 6D2a 479 

 Atomic Absorption II 6D2b 483 

 1 N KCl Extractable, Automatic Extractor 6D3 

 Inductively Coupled Plasma Spectrometry I 6D3 580 

 Inductively Coupled Plasma Spectrometry II 6D3b 500 

 Atomic Absorption II 6D3c 504 

 Sodium Pyrophosphate Extraction II 6D4 490 

 Atomic Absorption 6D4a 490 

 Ammonium Oxalate Extraction 6D5 495 

 Inductively Coupled Plasma Spectrometry 6D5b 495 

 HF + HNO3 + HCl Dissolution 6D6 487 

 Inductively Coupled Plasma Spectrometry 6D6a 487 

 

Calcium Carbonate 6E 641 

 HCl Treatment 6E1 641 

 Gas Volumetric 6E1a 641 

 Manometric 6E1b 641 

 Weight Loss 6E1c 641 

 Weight Gain 6E1d 643 

 Titrimetric 6E1e 643 

 Warburg Method 6E1f 643 

 Sensitive Qualitative Method 6E2 644 

 Visual, Gas Bubbles 6E2a 644 

 H2SO4 Treatment 6E3 644 

 Gravimetric Weight Gain 6E3a 644 

 

Gypsum 6F 645 

 Water Extract 6F1 645 

 Indirect Estimate 6F1b 645 

 Ion Chromatograph 6F1c 645 

 Weight Loss 6F2 646 

 Gypsum Requirement 6F5 647 

 

Aluminum 6G 

 KCl Extraction I, 30 min. 6G1 647 

 Aluminon I 6G1a 648 

 Aluminon II 6G1b 649 

 Aluminon III 6G1c 649 

 Fluoride Titration 6G1d 649 

 Atomic Absorption 6G1e 650 

 KCl Extraction II, Overnight 6G2 650 

 Aluminon I 6G2a 650 

 NH4OAc Extraction 6G3 650 

 Aluminon III 6G3a 650 

xx
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

 NaOAc Extraction 6G4 650 

 Aluminon III 6G4a 650 

 Sodium Pyrophosphate Extraction I 6G5 650 

 Atomic Absorption 6G5a 651 

 Ammonium Oxalate Extraction 6G6 651 

 Atomic Absorption 6G6a 651 

 Dithionite-Citrate Extraction 6G7 479 

 Atomic Absorption I 6G7a 479 

 Atomic Absorption II 6G7b 483 

 NH4Cl, Automatic Extractor 6G8 651 

 Atomic Absorption 6G8a 651 

 1 N KCl Extractable, Automatic Extractor 6G9 

 Atomic Absorption I 6G9a 584 

 Inductively Coupled Plasma Spectrometry I 6G9b 580 

 Inductively Coupled Plasma Spectrometery II 6G9c 500 

 Atomic Absorption II 6G9d 504 

 Sodium Pyrophosphate Extraction II 6G10 490 

 Atomic Absorption 6G10a 490 

 HF Dissolution 6G11 

 Atomic Absorption 6G11a 572 

 HF + HNO3 + HCl Dissolution 

 Inductively Coupled Plasma Spectrometry 6G11b 487 

 Ammonium Oxalate Extraction 6G12 

 Inductively Coupled Plasma Spectrometry I 6G12a 575 

 Inductively Coupled Plasma Spectrometry II 6G12b 495 

 

Extractable Acidity 6H 652 

 BaCl2-Triethanolamine I 6H1 652 

 Back-Titration with HCl 6H1a 652 

 BaCl2-Triethanolamine II 6H2 653 

 Back-Titration with HCl 6H2a 653 

 KCl-Triethanolamine II 6H3 653 

 Back-Titration with NaOH 6H3a 653 

 BaCl2-Triethanolamine III 6H4 654 

 Back-Titration with HCl Automatic Extractor 6H4a 654 

 

Carbonate 6I 655 

 Saturation Extraction 6I1 655 

 Acid Titration 6I1a 655 

 

Bicarbonate 6J 655 

 Saturation Extraction 6J1 655 

 Acid Titration 6J1a 655 

 

xxi
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Chloride 6K 

 Saturation Extraction 6K1 

 Mohr Titration 6K1a 656 

 Potentiometric Titration 6K1b 657 

 Anion Chromatograph 6K1c 588 

 Anion Chromatograph, Ionic Suppressor 6K1d 508 

 

Sulfate 6L 

 Saturation Extraction 6L1 

 Gravimetric, BaSO4 6L1a 657 

 EDTA Titration 6L1b 658 

 Anion Chromatograph 6L1c 588 

 Anion Chromatograph, Ionic Suppressor 6L1d 508 

 NH4OAc Extraction 6L2 659 

 Gravimetric, BaSO4 Precipitation 6L2a 659 

 

Nitrate 6M 

 Saturation Extraction 6M1 

 Phenyldisulfonic (PDS) Acid Colorimetry 6M1a 659 

 Diphenylamine 6M1b 660 

 Anion Chromatograph 6M1c 588 

 Anion Chromatograph, Ionic Suppressor 6M1d 508 

 

Calcium 6N 

 Saturation Extraction 6N1 

 EDTA Titration 6N1a 660 

 Atomic Absorption I 6N1b 514 

 Atomic Absorption II 6N1c 517 

 NH4OAc Extraction 6N2 

 EDTA-Alcohol Separation 6N2a 661 

 Oxalate-Permanganate I 6N2b 662 

 Oxalate-Permanganate II 6N2c 663 

 Oxalate-Cerate 6N2d 663 

 Atomic Absorption I 6N2e 521 

 Atomic Absorption II 6N2f 524 

 NH4Cl-EtOH Extraction 6N3 664 

 EDTA Titration 6N3a 666 

 

 KCl-TEA Titration 6N4 666 

 Oxalate-Permanganate 6N4a 666 

 EDTA Titration 6N4b 666 

 Atomic Absorption 6N4c 667 

 HF Dissolution 6N5 667 

 Atomic Absorption 6N5a 667 

 HF + HNO3 + HCl Dissolution 

 Inductively Coupled Plasma Spectrometry 6N5b 487 

xxii
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Magnesium 6O 

 Saturation Extraction 6O1 

 EDTA Titration 6O1a 667 

 Atomic Absorption I 6O1b 514 

 Atomic Absorption II 6O1c 517 

 NH4OAc Extraction 6O2 

 EDTA-Alcohol Separation 6O2a 668 

 Phosphate Titration 6O2b 669 

 Gravimetric 6O2c 670 

 Atomic Absorption I 6O2d 521 

 Atomic Absorption II 6O2e 524 

 NH4Cl-EtOH Extraction 6O3 671 

 EDTA Titration 6O3a 671 

 KCl-TEA Extraction 6O4 671 

 Phosphate Titration 6O4a 671 

 EDTA Titration 6O4b 671 

 Atomic Absorption 6O4c 672 

 HF Dissolution 6O5 

 Atomic Absorption 6O5a 672 

 HF + HNO3 + HCl Dissolution 

 Inductively Coupled Plasma Spectrometry 6O5b 487 

 

Sodium 6P 

 Saturation Extraction 6P1 

 Flame Photometry 6P1a 672 

 Atomic Absorption I 6P1b 514 

 Atomic Absorption II 6P1c 517 

 NH4OAc Extraction 6P2 

 Flame Photometry 6P2a 673 

 Atomic Absorption I 6P2b 521 

 Atomic Absorption II 6P2c 524 

 HF Dissolution 6P3 

 Atomic Absorption 6P3a 673 

 HF + HNO3 + HCl Dissolution 

 Inductively Coupled Plasma Spectrometry 6P3b 487 

 

Potassium 6Q 

 Saturation Extraction 6Q1 

 Flame Photometry 6Q1a 674 

 Atomic Absorption I 6Q1b 514 

 Atomic Absorption II 6Q1c 517 

 NH4OAc Extraction 6Q2 

 Flame Photometry 6Q2a 674 

 Atomic Absorption I 6Q2b 521 

 Atomic Absorption II 6Q2c 524 

 HF Dissolution 6Q3 

 Atomic Absorption 6Q3a 572 

 HF + HNO3 + HCl Dissolution 

 Inductively Coupled Plasma Spectrometry 6Q3b 487

xxiii
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Sulfur 6R 

 NaHCO3 Extract, pH 8.5 6R1 675 

 Methylene Blue Colorimetry 6R1a 675 

 HCl Release (sulfide) 6R2 675 

 Iodine Titration 6R2a 675 

 SO2 Evolution 6R3 

 KIO3 6R3a 676 

 Infrared I 6R3b 594 

 Infrared II 6R3c 528 

 

Phosphorus 6S 

 Perchloric Acid Digestion 6S1 677 

 Molybdovanadophosphoric Acid Colorimetry 6S1a 677 

 Adsorption Coefficient 6S2 678 

 Bray P-1 Absorbed Phosphorus 6S3 530 

 Spectrophotometer 6S3 530 

 New Zealand P Retention 6S4 

 Spectrophotometer I 6S4 596 

 Spectrophotometer II 6S4b 534 

 Citric Acid Extractable 6S5 536 

 Spectrophotometer 6S5 536 

 HF + HNO3 + HCl Dissolution 6S6 487 

 Inductively Coupled Plasma Spectrometry 6S6a 487 

 

Boron 6T 681 

 Saturation Extract 6T1 681 

 Carmine Colorimetry 6T1a 681 

 

Fluoride 6U Saturation Extraction 6U1 

 Anion Chromatograph 6U1a 588 

 Anion Chromatograph, Ionic Suppressor 6U1b 508 

 

Silicon 6V 

 HF Dissolution 6V1 

 Atomic Absorption 6V1a 681 

 HF + HNO3 + HCl Dissolution 

 Inductively Coupled Plasma Spectrometry 6V1b 487 

 Ammonium Oxalate Extraction 6V2 

 Inductively Coupled Plasma Spectrometry I 6V2a 575 

 Inductively Coupled Plasma Spectrometry II 6V2b 495 

 

Nitrite 6W 

 Saturation Extraction 6W1 

 Anion Chromatograph 6W1a 588 

 Anion Chromatograph, Ionic Suppressor 6W1b 508

xxiv
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

MINERALOGY 7 

 

Instrumental Analyses 7A 

 Preparation 7A1 682 

 Carbonate Removal 7A1a 682 

 Organic-Matter Removal 7A1b 682 

 Iron Removal 7A1c 682 

 Disaggregation and Particle-Size Fractionation 7A1d 683 

 Particle-Size Distribution Analysis Pretreatment 7A1e 683 

 X-Ray Diffraction 7A2 

 Thin Film on Glass 

 Solution Pretreatment 7A2a 684 

 Resin Pretreatment I 7A2b 685 

 NaPO3 Pretreatment I 7A2c 685 

 Thin Film on Tile 

 Solution Pretreatent 7A2d 685 

 Resin Pretreatment 7A2e 685 

 Sodium Metaphosphate Pretreatment 7A2f 685 

 Powder Mount 

 Diffractometer Recording 7A2g 686 

 Camera Recording 7A2h 686 

 Thin Film on Glass 

 Resin Pretreatment II 7A2i 540 

 NaPO3 Pretreatment 7A2j 686 

 Powder Mounts 7A2k 686 

 Differential Thermal Analysis 7A3 687 

 DTA I 7A3 687 

 Thermal Gravimetric Analysis 7A4 

 TGA I 7A4a 688 

 TGA II 7A4b 598 

 Infrared Analyses 7A5 688 

 Differential Scanning Calorimetry 7A6 602 

 DSC I 7A6 602 

 

Optical Analysis 7B 689 

 Grain Studies 

 Grain Mounts, Canada Balsam 7B1b 689 

 Electron Microscopy 7B2 689 

 

Total Analysis 7C 

 Na2CO3 Fusion 7C1 689 

 X-Ray Emission Spectrography 7C2 689 

 HF Dissolution 7C3 606 

 HF + HNO3 + HCl Dissolution 7C4a 550 

 

Surface Area 7D 

 Glycerol Retention 7D1 690 

 EGME Retention 7D2 555

xxv
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

MISCELLANEOUS 8 

 

Saturated Paste, Mixed 8A 690 

 Saturation Extract 8A1 690 

 Conductivity 8A1a 690 

 Conductivity, Quick Test 8A1b 691 

 Saturated Paste, Mixed 

 Bureau of Soils Cup, Conductivity 8A2 692 

Saturated Paste, Capillary Rise 8B 692 

 Saturation Extract 8B1 692 

 Conductivity 8B1a 693

 

Reaction (pH) 8C 693 

 Soil Suspensions 8C1 693 

 Water Dilution 8C1a 693 

 KCl 8C1c 693 

 CaCl2 8C1e 693 

 

Ratios and Estimates 8D 557 

 To Noncarbonate Clay 8D2 557 

 Ca to Mg (Extractable) 8D3 557 

 Estimated Clay Percentage 8D4 557 

Estimated Total Salt 8D5 557 

 Iron Plus Aluminum, Pyrophosphate 

 Extractable to Dithionite Citrate Extractable 8D6 558 

 Index of Accumulation 8D7 558 

 

Optical Density (Ammonium Oxalate Extract) 8J 575

 

Zircon 8K 487 

 HF + HNO3 + HCl Dissolution 8K1 487 

 Inductively Coupled Plasma Spectrometry 8K1a 487 

Copper 8L 487 

 HF + HNO3 + HCl Dissolution 8L1 487 

 Inductively Coupled Plasma Spectrometry 8L1a 487 

 

Zinc 8M 487 

 HF + HNO3 + HCl Dissolution 8Ml 487 

 Inductively Coupled Plasma Spectrometry 8M1a 487 

 

Arsenic 8N 487 

 HF + HNO3 + HCl Dissolution 8Nl 487 

 Inductively Coupled Plasma Spectrometry 8N1a 487 

 

Titanium 8O 487 

 HF + HNO3 + HCl Dissolution 8O1 487 

 Inductively Coupled Plasma Spectrometry 8O1a 487 

xxvi
CONTENTS

METHOD TITLE METHOD PAGE 

CODE

Selenium 8P 487 

 HF + HNO3 + HCl Dissolution 8Pl 487 

 Inductively Coupled Plasma Spectrometry 8P1a 487 

 

Cadmium 8Q 487 

 HF + HNO3 + HCl Dissolution 8Q1 487 

 Inductively Coupled Plasma Spectrometry 8Q1a 487 

 

Lead 8R 487 

 HF + HNO3 + HCl Dissolution 8Rl 487 

 Inductively Coupled Plasma Spectrometry 8R1a 487 

xxvii
SAMPLE COLLECTION AND PREPARATION (1) 

Field Sample Collection and Preparation (1A) 

Site Selection (1A1) 

Geomorphology (1A1a) 

Pedon (1A1b) 

Water (1A1c) 

Biological (1A1d) 

1. Application General: The United States National Cooperative Soil Survey (NCSS) Program has 

prepared soil maps for much of the country. Both field and laboratory data are used to design 

map units and provide supporting information for scientific documentation and predictions of 

soil behavior. A soil map delineates areas occupied by different kinds of soil, each of which 

has a unique set of interrelated properties characteristic of the material from which it is formed, 

its environment, and its history (Soil Survey Division Staff, 1993). The soils mapped by the 

NCSS are identified by names that serve as references to a national system of soil taxonomy 

(Soil Survey Staff, 1999). Coordination of mapping, sampling site selection, and sample 

collection in this program contributes to the quality assurance process for laboratory 

characterization (Burt, 1996). Requisites to successful laboratory analysis of soils occur long 

before the sample is analyzed (Soil Conservation Service, 1984; Soil Survey Staff, 1996). In 

the field, these requisites include site selection, descriptions of site and soil pedon, and careful 

sample collection. A complete description of the sampling site not only provides a context for 

the various soil properties determined but it is also a useful tool in the evaluation and 

interpretation of the soil analytical results (Patterson, 1993). Landscape, landform, and pedon 

documentation of the sampling site serves as a link in a continuum of analytical data, sampled 

horizon, pedon, landscape, and overall soil survey area. This continuum is illustrated on the 

cover of this manual. 

The objectives of a project or study form the basis for designing the sampling strategy. 

A carefully designed sampling plan is required to provide reliable samples for the purpose of 

sampling. The plan needs to address the site selection, depth of sampling, type and number of 

samples, details of collection, and sampling and sub-sampling procedures to be followed. The 

Soil Survey Laboratory (SSL) primarily serves the NCSS, which is conducted jointly by USDA 

Natural Resources Conservation Service (NRCS), the Bureau of Land Management (BLM), 

Forest Service, and representatives of U.S. Universities and Agricultural Experiment Stations. 

In this context, the primary objective of SSL sampling programs has been to select sites and 

pedons that are representative of a soil series and to collect samples that are representative of 

horizons within the pedon. 

There are various kinds of sampling plans, e.g., intuitive and statistical, and many types 

of samples, e.g., representative, systematic, random, and composite. In the field, the SSL has 

more routinely used intuitive sampling plans to obtain representative samples. The intuitive 

sampling plan is one based on the judgment of the sampler, wherein general knowledge of 

similar materials, past experience, and present information about the universe of concern, 

ranging from knowledge to guesses, are used (Taylor, 1988). A representative sample is one 

that is considered to be typical of the universe of concern and whose composition can be used 

to characterize the universe with respect to the parameter measured (Taylor, 1988). 

In the laboratory, the primary objectives of sample collection and preparation are to 

homogenize and obtain a representative soil sample to be used in chemical, physical, and 

mineralogical analyses (method 1B). The analyst and the reviewer of data assume that the 

sample is representative of the soil horizon being characterized. Concerted effort is made to 

keep analytical variability small. Precise laboratory work means that the principal variability in 

characterization data resides in sample variability, i.e., sampling is the precision-limiting 

1
variable. As a result, site-selection and sample collection and preparation are critical to 

successful soil analysis. 

Geomorphic Considerations1: Soils form a vital, complex continuum across the 

Earth’s landscape. The prime goal of the Soil Survey is to segregate the soil continuum into 

individual areas that have similar properties, and therefore, similar use and management. Soils 

can not be fully understood or studied using a single observation scale. Instead, soil scientists 

use multiple scales to study and segregate soils and to transfer knowledge to soil users. To 

accomplish the task of Soil Survey at reasonable cost and time, soil scientists extend 

knowledge from point observations and descriptions to larger land areas. 

Soil map-unit delineations are the individual landscape areas defined during and 

depicted in a soil survey. Soil observation, description, and classification occur at the pedon 

scale (1 to ≈ 7 m), and represent a small portion of any map unit (10’s to 1000’s hectares). 

Further, pedons selected, described, and sampled for laboratory analysis represent only a small 

subset of the observation points. Pedon descriptions and classifications along with measured 

lab data, however, accurately apply to a named soil map unit or landscape areas (soil 

component) within the map unit. Soil scientists can reliably project (“scale up”) pedon 

information to soil map units based on experience and the strong linkages among soils, 

landforms, sediment bodies, and geomorphic processes. 

Thus, soil geomorphology serves several key functions in Soil Survey, which can be 

summarized as:

1. Provides a scientific basis for quantitatively understanding soil landscape relationships, 

stratigraphy, parent materials, and site history. 

2. Provides a geologic and geographic context or framework that explains regional soil 

patterns. 

3. Provides a conceptual basis for understanding and reliably predicting soil occurrence at the 

landscape scale. 

4. Communicates effectively and succinctly soil location within a landscape. 

During a Soil Survey soil scientists achieve these functions both tacitly and by 

deliberate effort. Geomorphic functions are best explained by citing examples. The first 

function listed above involves planned, detailed soil landscape studies (e.g., Ruhe et al, 1967; 

Daniels et al, 1970; Gamble et al, 1970; Parsons et al., 1970; Gile et al., 1981; Lee et al., 2001; 

2003a; 2003b), which are an important component of the Soil Survey. Such studies quantify 

and explain the links between soil patterns and stratigraphy, parent materials, landforms, 

surface age, landscape position, and hydrology. Studies of this nature provide the most 

rigorous, quantitative, and complete information about soil patterns and landscapes. The 

required time and effort are significant, but justified by the quantitative information and 

scientific understanding acquired. Soil survey updates by MLRA can and should involve 

similar studies. 

The three remaining geomorphic functions are tacit and to a degree inherent in a soil 

survey. A number of earth science sources (Fenneman 1931, 1938, 1946; Hunt, 197; 

WahUKHftig, 1965;) identify and name geomorphic regions, which are grouped by geologic and 

landform similarity. The value of relating soil patterns to these regions is self-evident. Terms 

such as Basin and Range, Piedmont, Columbia Plateau, and Atlantic Coastal Plain provide both 

a geologic and geographic context for communicating regional soil and landform knowledge. 

Soils occurrence can be accurately predicted and mapped using observable landscape 

features (e.g., landforms, vegetation, slope inflections, parent material, bedrock outcrops, 

1

 Douglas A. Wyosocki and Philip J. Schoeneberger, Research Soil Scientists, NSSC, NRCS, 

Lincoln, NE, wrote the geomorphic component of this procedure. 

2
stratigraphy, drainage, photo tonal patterns). During a soil survey soil scientists develop a tacit

knowledge of soil occurrence generally based on landscape relationships. Soil occurrence is 

consistently linked to a number of geomorphic attributes. Among these are landform type, 

landscape position, parent material distribution, slope shape and gradient, and drainage pattern. 

This tacit soil landscape knowledge model is partially encapsulated in block diagrams and map 

unit and pedon descriptions. In turn a clear, concise geomorphic description effectively 

conveys soil location within a landscape to other soil scientists and soil users. Recent 

publications (Soil Survey Staff, 1998; Schoeneberger et al., 2002; Wysocki et al., 2000) 

provide a comprehensive and consistent system for describing geomorphic and landscape 

attributes for soil survey. The Geomorphic Description Systems (GDS) is not discussed here. 

Refer to Soil Survey Staff, 1998; Wysocki et al., 2000; and Schoeneberger et al, 2002 for more 

detailed information. 

Geomorphology is an integral part of all soil survey processes and stages. Preliminary 

or initial soil pattern knowledge is commonly based on landscape or geomorphic relationships. 

Observations during a soil survey refine existing landscape models, or sometimes compel and 

create new models. Map unit design includes landform recognition and naming, and 

observations on landscape position, parent materials, and landscape and soil hydrology. Soil 

scientists capture this observational and expert knowledge through soil map unit and pedon 

descriptions, which should convey soil property, soil horizon, landscape and geomorphic 

relationships, and parent material properties. 

Any study plan, site selection, or pedon sampling must also consider and address the 

geomorphology. Study or sampling objectives can vary. Every sample pedon should include 

both a complete soil and geomorphic description. In a characterization project, the sample 

pedons should be representative of the landscape unit (e.g., stream terrace, backslope etc.) it 

occurs upon. Note that the landscape unit that is sampled can be multi-scale. The unit could be 

a landform (e.g., stream terrace, dune, or drumlin), a geomorphic component (e.g., nose slope), 

a hillslope position (e.g., footslope), or all of these. 

Keep in mind that the sampled pedon represents both a taxonomic unit and landscape 

unit. Both the landscape and taxonomic unit should be considered in site selection. Note that a 

single landscape unit (e.g., backslope) may contain one or more taxonomic units. A landscape 

unit is a more easily field recognizable and mappable feature than a soil taxonomic unit. For 

characterization project select the dominant taxonomic unit within a given landscape unit. The 

existence of other soils or taxa can and should be included in the soil description and also the 

map unit description. 

Soil patterns on landscapes follow catenary relationships. It is important to characterize 

both individual pedon properties and the soil relationships both above and below on the 

landscape. This goal requires that soils be sampled as a catenary sequence (i.e., multiple 

samples across the same hillslope). This appears intensive, but serves multiple purposes. A 

sample pedon or set of pedons provides vital characterization data and also can quantify the 

catenary pattern and processes. This is an efficient use of both sampling time and effort, as well 

as, laboratory resources. Moreover, it provides an understanding of the entire soil landscape. 

Lastly, and perhaps most importantly, soil geomorphic relationships deserve and 

sometimes demand specific study during a soil survey. Crucial problems can be addressed by 

appropriately designed geomorphic, stratigraphic, or parent material study. For example, a silty 

or sandy mantle over adjacent soils and/or landforms may be of eolian origin. A well-designed 

geomorphic study can test this hypothesis. In another geomorphic setting soil distribution and 

hydrology may be controlled by stratigraphic relationships rather than by elevation or 

landscape patterns. A drill core or backhoe pit sequence can address this hypothesis. These 

studies need not be elaborate, but they require fore thought and planning. Such studies are 

applicable and necessary to the Major Land Resource Area (MLRA) soil survey approach. 

Pedon, Water, and Soil Biology Sampling: The pedon is presented in soil taxonomy 

(Soil Survey Staff, 1999) as a unit of sampling within a soil, i.e., the smallest body of one kind 

of soil large enough to represent the nature and arrangement of horizons and variability in the 

other properties that are preserved in samples (Soil Survey Division Staff, 1993). In the U.S. 

3
soil Survey Program, laboratory pedon data combined with field data (e.g., transects and pedon 

descriptions) are used to define map unit components, establish ranges of component 

properties, establish or modify property ranges for soil series, and answer taxonomic and 

interpretive questions (Wilson et al., 1994). 

Biological samples are also collected for analysis at the SSL, either in conjunction with 

pedon sampling or independently. Measurable biological indices have been considered as a 

component to assess soil quality (Gregorich et al., 1997; Pankhurst et al., 1997). A large 

number of soil biological properties have been evaluated for their potential use as indicators of 

soil quality/health (Doran and Parkin, 1994; Pankhurst et al., 1995). The USDA NRCS has 

utilized soil biology and carbon data in macro-nutrient cycling, soil quality determinations, 

resource assessments, global climate change predictions, long-term soil fertility assessments, 

impact analysis for erosion effects, conservation management practices, and carbon 

sequestration (Franks et al., 2001). 

Water samples are analyzed by the SSL on a limited basis in the support of specific 

research projects. These projects are typically in conjunction with soil investigations and have 

involved monitoring seasonal nutrient flux to evaluate movement of N and P via subsurface 

and overland flow from agricultural lands into waterways and wetlands. 

2. Summary of Method 

A site is selected that meets the objectives of the laboratory sampling. The site and soil 

pedon are described and georeferenced. These descriptions include observations of specific 

soil properties such as texture, color, slope, and depth. Descriptions may also include 

inferences of soil quality (soil erodibility and productivity) as well as soil-forming factors 

(climate, topography, vegetation, and geologic material). 

A soil pit is often excavated with a back-hoe (Fig. 1). Depth and breadth of pit depend 

on the soil material and objectives of sampling. Soil horizons or zones of uniform 

morphological characteristics are identified for sampling (Fig. 2). Photographs are typically 

taken of soil profile after the layers have been identified (Fig. 3) but before the vertical section 

by the sampling process (Fig. 4). 

The variable nature or special problems of the soil itself, e.g., Vertisols, Histosols, or 

permafrost-affected soils, may require the use of specific excavation and sampling techniques. 

For example, the shear failure that forms slickensides in Vertisols also disrupts the soil to the 

point that conventional soil horizons do not adequately describe the morphology. 

Representative samples are collected and mixed for chemical, physical, and 

mineralogical analyses. A representative sample is collected using the boundaries of the 

horizon to define the vertical limits and the observed short-range variability to define the lateral 

limits. The tag on the sample bag is labeled to identify the site, pedon, and soil horizon for the 

sample. 

In the field, the 20- to 75-mm fraction is generally sieved, weighed, and discarded. In 

the laboratory, the <20-mm fraction is sieved and weighed. The SSL estimates weight 

percentages of the >2-mm fractions from volume estimates of the >20-mm fractions and weight 

determinations of the <20-mm fractions by method 3A2. 

Undisturbed clods are collected for bulk density and micromorphological analysis. 

Clods are obtained in the same part of the pit as the mixed, representative sample. Bulk density 

clods are used for water retention data; to convert from a weight to volume basis; to determine 

the coefficient of linear extensibility (COLE); to estimate saturated hydraulic conductivity; and 

to identify compacted horizons. Microscope slides of soil prepared for micromorphology are 

used to identify fabric types, skeleton grains, weathering intensity, illuviation of argillans, and 

to investigate genesis of soil or pedological features. 

Biological samples are also be collected for analysis at the laboratory, either in 

conjunction with pedon sampling or independently. As with pedon sampling, sampling for root 

biomass includes selecting a representative site, sampling by horizon, and designating and 

sampling a sub-horizon if root mass and morphology change. The same bulk sample collected 

for soil mineralogical, physical, and chemical analyses during pedon sampling can also be used 

4
Fig. 1. Excavated pit for pedon sampling. 

Fig. 2. Soil horizons or zones of uniform morphological characteristics are identified for 

sampling. 

5
Fig. 3. Photographs are typically taken of soil profile after 

the layers have been identified but before the vertical 

section by the sampling process. 

Fig. 4. Pedon sampling activities. 

6
for some soil biological analyses. Alternatively, a separate bio-bulk sample can be collected in 

the field. Surface litter and O horizons are sampled separately, as with pedon sampling. If 

certain biological analyses, e.g., microbial biomass, are requested, these samples require 

expedited transport under ice or gel packs and are refrigerated (4°C) immediately upon arrival 

at the laboratory to avoid changes in the microbial communities. 

Water samples can also be collected for laboratory analyses at the same time as pedon 

sampling. Choice of water sampling site depends not only on the purpose of the investigation 

but also on local conditions, depth, and the frequency of sampling (Velthorst, 1996). Specific 

recommendations are not applicable, as the details of collection can vary with local conditions. 

Nevertheless, the primary objective of water sampling is the same as with soil and biological 

sampling, i.e., to obtain a representative sample in laboratory analyses. Water samples require 

expedited transport under ice or gel packs and are refrigerated (4°C) immediately upon arrival 

at the laboratory. 

3. Interferences 

In the process of sampling, a number of obstacles may arise from external sources, e.g., 

weather, accessibility, steep terrain, wet terrain, insects, and large rock fragments. Sometimes 

pits have to be hand-excavated. Common sense and the guidelines for obtaining representative 

samples are applied to the extent possible. 

Preservation of sample integrity, avoiding changes or contamination during sampling 

and transport is important. Sampling for trace element analysis requires the use of clean, nonmetallic equipment. Extreme care and precision are required for samples with low natural 

elemental concentrations. 

Do not allow soils to dry, as some soils irreversibly harden upon drying, affecting some 

laboratory analyses such as particle size (Kubota, 1972; Espinoza et al., 1975; and Nanzyo, 

1993). High temperatures can also alter microbial populations and activity (Wollum, 1994). 

Avoid contamination of water samples by not touching the inner part of the sample 

container, screw cap, or sample water. Gloves (powderless) may be used. Water samples are 

affected by microbial activity, resulting in a change in the concentration of some elements (e.g., 

nitrate, phosphate, and ammonium); the reduction of sulfate to sulfide and chlorine to chloride; 

and the loss of iron through precipitation or oxidation (Velthorst, 1996). The addition of 

microbial inhibitors may be necessary. 

In general, plastic bags will suffice for most biological samples, as they are generally 

permeable to CO2 and O2, preventing sample drying, i.e., aerobic samples will remain aerobic 

during transport to the laboratory (Wollum, 1994). The SSL recommends double-bagging zip 

locked plastic bags to prevent loss of sample water content. 

The kind of water sample container (adsorption, desorption) as well as the bottle 

volume can affect the analytical results, e.g., polyethylene bottles increase the chlorine content 

with time or adsorb organic material; errors increase with the permeability of bottle wall; glass 

bottles release sodium and silicon with time; small sample volume has more contact with larger 

bottles compared to small bottles (Velthorst, 1996). Water sample containers should be acid 

washed and capped in the laboratory prior to collection in the field. The drying of these 

containers should also be considered with regards to interferences or contaminants. Ceramic 

cups for collection of soil water may require an acid pretreatment prior to installation in the 

field, as these cups have a small cation exchange capacity, sorbing dissolved organic carbon, 

and releasing aluminum and silica (Velhorst, 1996). Refer to the respective manufacturer’s 

manual, e.g., Soil Moisture Corporation, for the appropriate treatment of these cups before use. 

Avoid long periods between collection and laboratory analysis of water and some types 

of biological (e.g., microbial biomass) and soil samples (e.g., sulfidic materials). To prevent 

significant changes (e.g., degradation, volatilization, alteration in microbial community), these 

samples require expedited transport under ice or gel packs and are refrigerated (4°C) 

immediately upon arrival at the laboratory. Avoid freezing water samples, which can influence 

pH and the separation of dissolved organic matter from the water phase. 

7
4. Safety 

Sampling pits deeper than 125 cm (5 feet) need to be shored to meet U.S. Department of 

Labor Occupational Safety and Health Administration (OSHA) standards, or one side has to be 

opened and sloped upward to prevent entrapment. Acetone used in the saran mix is flammable 

and should be used down wind from a site to keep fumes from collecting in the bottom of the 

pit. Take precautions when operating or in the proximity of machinery, e.g., backhoe, drill rig, 

or hydraulic probe, and when lifting sample bags. 

5. Equipment

5.1 Plastic bags, for mixed soil samples 

5.2 Zip locked plastic freezer bags, for biological samples 

5.3 Tags, for bagged samples 

5.4 Plastic bags, for bulk density and thin section clods 

5.5 Aluminum case, for shipping clod boxes 

5.6 Shipping bags (canvas, leather, or burlap) for mixed samples 

5.7 Clod boxes, cardboard with dividers 

5.8 Core boxes, to transport cores from drill rig or hydraulic probe 

5.9 Stapler, with staples 

5.10 Hair nets 

5.11 Rope 

5.12 Clothes pins 

5.13 Felt markers, permanent 

5.14 Sampling pans 

5.15 Sampling knives 

5.16 Chisel 

5.17 Rock hammer 

5.18 Nails 

5.19 Measuring tape 

5.20 Photo tape 

5.21 Sieves (3-inch and 20-mm) 

5.22 Plastic sheets 

5.23 Canvas tarp 

5.24 Camera 

5.25 Frame, 50 cm x 50 cm 

5.26 Garden clippers 

5.27 Pruning shears 

5.28 Bucket 

5.29 Scale, 100-lb capacity, for rock fragments 

5.30 Analytical balance, ± 0.01 g sensitivity, for weighing roots and plant residue 

5.31 Cooler, with ice or gel packs, for biological samples 

5.32 Containers, with screw caps, acid-washed, for water samples 

5.33 Gloves, plastic, powderless 

5.34 Bulk density equipment, if natural clods are not appropriate technique, e.g., bulk density 

frame or ring excavations, compliant cavity (procedure 3B5, 3B4, 3B3, respectively) 

6. Reagents 

6.1 Acetone 

6.2 Water, in spray bottle 

6.3 Dow Saran F-310 Resin. Available from Dow Chemical Company. 

8
7. Procedures 

Project and Sampling Objectives

The number and types of samples collected from a site are governed in part by the 

objectives of the information needed. Example sampling schemes presented as general project 

categories based on project needs are as follows: 

Reference Projects: These projects are designed to answer specific questions on 

mapping or soil classification, provide data for transect of a mapping unit, or for collection of 

calibration standards. Samples are typically collected from specific horizons in 3 to 5 locations 

that relate to the question or are representative of the map unit. A limited number of analyses, 

specific to the questions asked, are performed on these samples. 

If a transect is used to test map unit composition, an appropriate sample from each 

transect point may be collected for analyses that are critical to distinguishing between map unit 

components. Also, samples may be collected as standards for the survey project for texture, 

organic carbon, or for calibration of field office analyses such as base saturation. 

Characterization Projects: These projects are designed to obtain comprehensive soil 

characterization data for a representative pedon of a map unit or a pedon which is included in a 

research study. Samples collected from each horizon include bulk samples of approximately 3 

kg, as well as clods of natural fabric for bulk density and micromorphology. A standard suite 

of laboratory analyses are performed on each horizon. In addition, specific analyses, such as 

mineralogy or andic properties, may be requested to provide more complete information on the 

specific pedon sampled. 

Geomorphology and Stratigraphy Projects: These projects are designed to study 

relationships between soils, landforms, and/or the stratigraphy of their parent materials. For 

example, a specific project may be designed to study the relationships between a catena of 

soils, their morphological properties, e.g., redoximorphic features, and the hydrology of the 

area. Another study may be designed to determine the lateral extent of stratigraphic breaks. 

Site or pedon selection is governed by the objectives of the study but often is selected to 

represent typical segments of the landform. Sampling and analytical requests may be similar to 

the scheme used in a characterization or reference project. Often, core samples may be 

collected to several meters in depth through the use of a hydraulic probe. 

Pedon Sampling Techniques 

Excavated Pits: A pit may be excavated by hand or with a backhoe. Hand-digging 

may be necessary depending on site location, type of soil material, or availability of a backhoe. 

Pedons are generally excavated through the solum and into the parent material, or to a 

maximum depth of 2 meters. When using a backhoe, dig the pit in the form of an arc with a 

minimum working face deeper than about 150 cm (5 ft). Slope the pit upward toward the 

backhoe for an escape route. The pit can also be modified from the back side to form a T with 

the back of the trench opened and widened for an escape route. If this is not practical, shoring 

is required to meet OSHA standards if the pit is deeper than 125 cm (5 ft). 

The sampling procedure is the same for hand-dug and backhoe pits. Mark horizons or 

zones to be sampled. Take a representative sample from boundary to boundary of a horizon 

and for a lateral extent to include the observed short-range variability. Unless the soil exhibits 

little short range variability, the best procedure is to place 4 to 5 kg soil on the plastic sheet or 

canvas tarp, mix thoroughly by rolling action, and place a representative sub-sample, minimum 

of 3 kg (3 qt), in a plastic sample bag. Label a tag with soil name, soil survey number, horizon 

(zone), and depth (as a minimum). Double fold the top of the plastic bag (forward and reverse) 

and staple the top of the tag under the folds. The sampling may be extended deeper by bucket 

auger or hydraulic probe as appropriate to meet the objectives of the project. If the soil has 

rock fragments in one or more horizons, the soil and coarse fragments need to be sieved and 

weighed as described below. 

Collect 3 bulk density clods from each horizon. Two clods are used in the primary 

analysis. The third clod is reserved for a rerun, if needed. Clods should be roughly fist-sized 

9
and should fit into the cell (8 x 6 x 6 cm) of a clod box fairly snugly. Take the clods in the 

same vicinity of the pit as the mixed sample. Carve out a working section in the pit wall to 

remove an undisturbed block. Break the block into fist-sized pieces and pare into a ovoid (eggshaped) clod. Place the clod in a hair net. If the clod is dry, mist the clod with water just until 

the surface glistens to inhibit saran penetration of the clod. Dip once, briefly, in saran mix to 

coat the clod, and hang from a rope with a clothes pin to dry. Clods can be dipped and then 

hung, or can be hung and then dipped by raising the container up to immerse the clod, briefly. 

Keep the saran container covered except when dipping clods to prevent acetone evaporation. 

Coat only once in the field. Additional coats are applied in the laboratory. When the clod is 

dry (bottom is not sticky to the touch), place the clod in a plastic bag, and put into a cell of a 

clod box. Label the appropriate cell on the inside of the lid of the box to identify the soil 

survey number and horizon (zone) for the clod. Clod boxes are designed to identify sequences 

of 3 clods per horizon. 

Collect 2 clods from each horizon for preparation of thin sections and 

micromorphological examination. Place a staple in the top of each clod for orientation. Clods 

should be roughly fist size, but kept unmodified otherwise. If the soil fabric is fragile, the clod 

can be placed in a hairnet and dipped briefly in saran as described above. Place the clod in a 

plastic bag and put into a cell of a clod box. The sampler should make special note of any 

features to be studied by thin section. Label the appropriate cell on the inside of the lid of the 

box to identify the soil survey number and horizon (zone) for the clod. 

If the material is too sandy and/or too dry to hold together in a clod, bulk density 

samples can be collected with an aluminum can or other small can of known volume. 

Sampling is easier if the can has a small hole in the bottom to allow air to escape as the can is 

inserted. Smooth a planar area in the pit face, or, if sampling from the top down, smooth a 

planar horizontal area. In either case, choose an area that appears representative of the horizon. 

With the palm of the hand, gently push the can into the smoothed area until the bottom of the 

can is flush with the wall or until resistance stops you. In this case, lay a board across the 

bottom of the can and tap lightly with a hammer or geology pick until the bottom of the can is 

flush with the pit wall. Then dig out the sampling can plus extra sample and, with a knife 

blade, smooth off the sample flush with the top of the can. Empty the contents of the can into a 

plastic bag, tie the top of the bag in a single knot and put into a cell in a clod box. Label the 

appropriate cell on the inside of the lid of the box to identify the soil survey number and 

horizon (zone) for the sample. Collect two samples per horizon. Indicate the volume of the 

sampling can in the sampling notes. It is assumed that there is no volume change with water 

content in sandy soils. Therefore, one density is representative for all water contents of coarsetextured soils. 

Avoid leaving empty cells in a clod box. Fill empty cells with a wadded paper. This 

prevents clods from shifting in transit. Tape down the top of a filled clod box with nylon 

filament tape (one short piece on each end and two short pieces in front). Label the top of the 

box to identify type of sample (bulk density or thin section) and appropriate soil survey 

numbers and horizons (zones) for the samples. Place six clod boxes in an aluminum case for 

shipment. Single clod boxes also ship well.

Hand Probe: Remove surface if it is not suitable for coring. Remove core sections and 

lay in order on plastic sheet. Measure core length against depth in hole to determine if the core 

has been compressed. Mark horizon breaks on the plastic. Mix the horizon or zone to be 

sampled. Place sample in a plastic bag and label with soil survey number, horizon (zone), and 

depth for the core. Samples need to be a minimum of 500 g (1 pt), and are generally suitable 

for a limited number of analyses only. 

Hydraulic probe: Remove surface if it is not suitable for coring. Remove core sections 

and lay in order on plastic sheet. With a sharp knife trim the exterior to remove any oil and 

contaminating soil material. Split one core open to mark horizons, describe and then sample. 

Measure core length against depth in hole to determine if the core has been compressed. Mark 

horizon breaks on the plastic. Mix the horizon or zone to be sampled. Place in a plastic bag 

10
and label with soil survey number, horizon (zone), and depth for the core. Obtain a minimum 

of 500 g (1 pt) for a reference sample or 3 kg (3 qt) for a characterization sample. 

If the core has not been compressed, and the core diameter is 3 inches or more, samples 

for bulk density can be taken from a second core. Mark a segment 8-cm long on an 

undisturbed section and slice a cylindrical segment. Measurements of core diameter and length 

can be used to calculate volume and density at the field-state water content. Core segments can 

be placed in a hair net, dipped once briefly in saran mix to coat the clod, hung from a rope with 

a clothes pin to dry, placed in a plastic bag and then put into a cell of a clod box. 

Rotary drill (hollow stem): Remove drill core sections and lay in order on plastic 

sheet. Measure core length against depth in hole to determine if the core has been compressed. 

Mark horizon breaks on the plastic. Mix the horizon or zone to be sampled. Place in a plastic 

bag and label with soil survey number, horizon (zone), and depth for the core. Obtain a 

minimum of 500 g (1 pt) for a reference sample or 3 kg (3 qt) for a characterization sample. 

If the core has not been compressed, and the core diameter is 3 inches or more, samples 

for bulk density can be taken from the core. Mark a segment 8 cm long on an undisturbed 

section and slice a cylindrical segment. Note the core diameter and length in the soil 

description. Place the core segment in a plastic bag and place bag into a bulk density (clod) 

box for shipment. Measurements of core diameter and length can be used to calculate volume 

and density at the field-state water content. Core segments can be placed in a hair net, dipped 

once, briefly in saran mix to coat the clod, hung from a rope with a clothes pin to dry, placed in 

a plastic bag and then put into a cell of a clod box. Label the appropriate cell number on the 

inside of the box lid to identify the site, pedon, and horizon. 

A core segment can be taken for thin section. Place a staple in the top of the core, place 

the core in a plastic bag and put the bag into a cell in a clod box. Label the appropriate cell 

number on the inside of the box lid to identify the site, pedon, and horizon. 

Bucket Auger: Remove surface if it is not suitable for auguring. Remove auger loads 

and lay in order on plastic sheet. When horizon breaks are detected, measure depth in hole and 

mark it on the plastic. Mix the horizon or zone to be sampled. Place in a plastic bag and label 

with soil survey number, horizon (zone), and depth for the sample. Obtain a minimum of 500 g 

(1 pt) for a reference sample or 3 kg (3 qt) for a characterization sample. Sampling depth in a 

pit can be extended by the use of an auger in the pit bottom. 

Specific Pedon Sampling Techniques

Soils with Rock Fragments: If coarse fragments up to 75 mm (3 in) in diameter are to 

be weighed in the field, place excavated sample in a bucket of known weight (tare) and weigh. 

Sieve the sample through both a 75-mm and 20-mm sieve (3/4 in) onto a canvas tarp which can 

be suspended from a scale. Estimate the coarse fragment volume percent of both the 75 to 250 

mm (10 in) fraction and > 250-mm fraction, and record these values in the description or 

sampling notes. Weigh the 20 to 75 mm and the <20 mm fractions in pounds or kilograms, and 

record these weights. Weights are calculated to an oven-dry base in the laboratory. Place a 

minimum of 4 kg (1 gal) in a plastic bag, double fold the bag, and staple. The water content is 

determined on the sample in the laboratory. If the 20 to 75-mm fraction is not weighed in the 

field, estimate the volume percent and record in the sampling notes or description. 

Organic Soils: If the soils are drained or the natural water table is below the surface, 

obtain samples of upper layers from a pit. If the hydraulic conductivity is slow enough, dig and 

remove samples below the water table as far as practical with due haste and place on a plastic 

sheet in an orderly fashion for describing and processing. If undisturbed blocks can be 

removed for bulk density, carve out cubes of known dimension (e.g., 5 cm on a side), place the 

block in a plastic bag and tie the top in a knot. Place in a second plastic bag if soil is saturated, 

tie the top in a knot. Put the double bagged sample in a clod box and label the appropriate cell 

on the inside of the lid to identify the soil survey number and horizon (zone) for the sample. 

Note the sample dimensions in the sampling notes. 

Collect samples from below the water table with a Macaulay peat sampler. If the 

samples appear undisturbed, mark 10-cm segments, slice with a knife, and place a single 

11
segment in a plastic bag. Tie the top in a knot and place in a second plastic bag and tie the top 

of that bag in a knot. Put the double bagged sample in a clod box and label the appropriate cell 

on the inside of the lid to identify the soil survey number and horizon (zone) for the sample. 

Note the sampler diameter and length of core in sampling notes. The sample shape is a halfcylinder. As an alternative, carve a block to fit snugly in a tared water can. Place lid on can, 

put can in a plastic bag, tie the top, and put in a clod box. Identify can number, depth in 

sampling notes along with the tare weight. Take replicate samples for the mixed sample, as 

necessary. 

Larger samples can be taken below the water table by removing the surface mat with a 

spade and sampling lower layers with a post-hole digger. Place samples of each layer on 

plastic for examination. Transfer samples to small plastic bags, knead to remove air. Put two 

small bags of sample into one large plastic bag, fold top, staple, and tag. 

Sulfidic Soil Materials: These materials as defined by soil taxonomy (Soil Survey 

Staff, 1999) commonly occur in intra-tidal zones adjacent to oceans, and are saturated most or 

all of the time. Use containers with an airtight cover. Mason jars and plastic containers with a 

positive sealing mechanism work well. Glass containers must be adequately packed for 

shipment to prevent breakage. Fill the container nearly full of sample and add ambient soil 

water so that all air is eliminated when the lid is secured. Keep containers in the dark and cool. 

Sulfidic soil samples require expedited transport in a cooler and are refrigerated (4 °C) 

immediately upon arrival at the laboratory. Once in the lab, if it appears air remained in the 

container, nitrogen gas can be bubbled through the sample for a few minutes to displace air, 

then replace the lid. The intent is to keep the material at the field pH prior to running the 

oxidized pH test. 

Permafrost Affected Soils: Soils with permafrost present two special sampling 

problems. The permafrost is very resistant to excavation and the cryoturbation disrupts horizon 

morphology. In many cases the surface layers are organic materials. The following sampling 

approach is suggested. 

Test the depth to the frost table with a small (1 to 2 mm) diameter steel rod. Excavate a 

small pit (about 0.7 by 1.3 m) to leave about 10 cm of unfrozen material over the permafrost. If 

a cyclic pattern (up to a few meters) is evident in the surface topography, extend the pit through 

at least one cycle. The organic layers can be carved out with a sharp knife or shovel in many 

cases and removed. Save the large chunks, if possible. 

The objective is to record the morphology of the unfrozen soil before the permafrost is 

disturbed. Examine the surface and designate horizons. If the soil is disrupted to the extent 

that lateral horizons do not represent the morphology, impose a grid over the pit face and 

sketch the morphology on graph paper. Describe the soil down to the frost table. When the 

description of the unfrozen material is complete, remove all unfrozen material to examine the 

conformation of the frost table. Note on graph paper if necessary and photograph. 

Frozen earth can be removed in successive steps with a gasoline-powered jackhammer. 

Place pieces from each step on a separate plastic sheet. Examine pieces and describe the 

morphology as they are removed. Note thickness of segregated ice lenses and make a visual 

estimate of relative volume of segregated ice. Place representative pieces into a water-tight 

container so that the sample can be weighed, dried, and weighed again to calculate the amount 

of water and volume of ice. Excavate to a depth of 30 to 50 cm below the frost table, if 

practical. Clean off the pit face and be ready to photograph immediately. Sample each horizon 

or zone for mixed sample, bulk density, and thin section as is practical. 

Vertisols: The shear failure that forms slickensides in Vertisols also disrupts the soil to 

the point that conventional horizons do not adequately describe the morphology. A gilgai 

surface topography is reflected in the subsurface by bowl-shaped lows and highs. One 

convention is to sample pedons out of the low and the high areas which represent extremes in 

the cyclic morphology. 

In order to examine morphology and associated soil properties in more spatial detail, 

the following procedure is suggested: Dig a trench long enough to cover two or three cycles of 

morphological expression. From the bottom of the pit remove soil from the non-work face so it 

12
slopes up and away. Use nails and string to outline boundaries of morphological cells. Assign 

a number and a horizon designation to each cell. 

Construct a level line about one meter below the highest point on the surface. Hammer 

a spike into the wall at one end of the pit. Tie a loop in string, place the loop over the spike, 

and run the string to the far end of the pit. Place a line level on the string, tie another loop in 

the string, place a second spike through the loop, pull the string taut, raise or lower the spike 

until the string is level, and hammer the spike into the pit face. 

Place a marker at each meter along the string from one end to the other. Transfer the 

morphology outlined by the string to graph paper by measuring the x-coordinate along the 

string and the y-coordinate above or below the string, both in centimeters. Use a level or a 

plumb bob to make the y measurement vertical. 

Sample each cell for characterization analysis as described above. The sampling 

scheme can include traditional pedon sequences by sampling vertical sequences of cells at low, 

high, and intermediate positions along the cycle. 

Soil Biology Sampling 

Biological samples are also be collected for laboratory analysis, either in conjunction 

with pedon sampling or independently. At the time of sampling for above-ground biomass, the 

plants should be identified either in the field or later using a plant identification key so as to 

determine which plants are associated with the soil microbial communities. Typically a 50 x 

50-cm area is sampled. All vegetation is clipped to the soil surface, separated by genus or 

species and by live and dead fractions. Each plant fraction is weighed, dried, and re-weighed 

to determine above-ground biomass. As with pedon sampling, sampling for root biomass 

includes selecting a representative site, sampling by horizon, and designating and sampling a 

sub-horizon if root mass and morphology change. The sampling area is approximately 1 m2

. These samples are weighed, dried, and re-weighed to determine root biomass. Typically the 

roots are separated by hand sieving at the laboratory. The same bulk sample collected for soil 

mineralogical, physical, and chemical analyses during pedon sampling can also be used for 

some soil biological analyses, e.g., particulate organic matter (POM), total N, C, and S. 

Alternatively, a separate bio-bulk sample can be collected in the field. As with pedon 

sampling, surface litter and O horizons are sampled separately by cutting out a 50 x 50-cm area 

in a square to a measured depth for bulk density determinations. Include replicate samples in 

the sampling plan, the primary purpose of which is to identify and/or quantify the variability in 

all or part of the sampling and analysis system. Properly label samples to show important 

information, e.g., soil, depth, horizon, etc. If certain biological analyses, e.g., microbial 

biomass, are requested, these samples require expedited transport under ice or gel packs and are 

refrigerated (4°C) immediately upon arrival at the laboratory to avoid changes in the microbial 

communities. Other USDA-NRCS field procedures and sampling protocols for samples that do 

not require analysis at the SSL are not covered in this manual. Refer to http://soils.usda.gov for 

more detailed discussion of these topics. 

Water Sampling 

Water samples can also be collected for laboratory analyses, either in conjunction with 

pedon sampling or independently. The amount and composition of water samples vary strongly 

with small changes in location. Choice of water sampling site depends not only on the purpose 

of the investigation but also on local conditions, depth, and the frequency of sampling 

(Velthorst, 1996). Specific recommendations are not applicable, as the details of collection can 

vary with local conditions. Nevertheless, the primary objective of water sampling is the same 

as with soil sampling, i.e., to obtain a representative sample for use in laboratory analyses. The 

USDA-NRCS projects requiring collection of water samples have typically been in conjunction 

with special soil investigations. For more detailed discussion of sampling protocols and 

investigations of water quality, refer to the U.S. Geological Survey field manual, available 

online at http://pubs.water.usgs.gov/. Detailed information about the elements of a water quality 

13
monitoring and assessment program may be found at the U.S. Environmental Protection 

Agency’s website http://www.epa.gov/. 

Preserve samples in the field-state until analysis at the laboratory, without the 

introduction of change or contamination. Before water sampling in the field, rinse the 

containers several times with the sample water and completely fill the container and screw cap 

with the sample water. Avoid touching the sample water, inner part of the container or screw 

cap. Gloves (powderless) may be used. Include blank samples in the sampling plan, the 

primary purpose of which is to identify potential sources of sample contamination and assess 

the magnitude of contamination with respect to concentration of target analytes. There are 

many possible types of blanks (e.g., source-solution, equipment, trip, ambient, and field 

blanks). Include replicate samples in the sampling plan, the primary purpose of which is to 

identify and/or quantify the variability in all or part of the sampling and analysis system. 

Common types of replicate samples include concurrent, sequential, and split. Refer to Wilde et 

al. (1999) for more detailed descriptions of the purpose and processing procedures for blanks 

and replicate samples. Properly label sample containers to show important information, e.g., 

location, depth, time, etc. Water samples require expedited transport under ice or gel packs and 

are refrigerated (4 °C) immediately upon arrival at the laboratory. 

Some water analyses, e.g., electrical conductivity, total and inorganic C, need to be 

performed promptly, as optimal preservation is not possible (Velthorst, 1996). Upon 

completion of these analyses, sample filtration (0.45-μm membrane) is used to separate 

dissolved from suspended material. The sample is then split into two sub-samples, with one 

acidified to pH 2 for cation analyses (e.g., Al, Fe, Mn) and the other for anion analyses. These 

other water analyses also need to be performed as promptly as possible. 

8. References 

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Espinoza, W., R.H. Rust, and R.S. Adams, Jr. 1975. Characterization of mineral forms in 

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Laboratory Sample Collection and Preparation (1B) 

Soil (1B1) 

Samples (1B1a) 

 The purpose of any soil sample is to obtain information about a particular soil and its 

characteristics. Sampling provides a means to estimate the parameters of these soil 

characteristics with an acceptable accuracy at the lowest possible cost (Petersen and Calvin, 

1986). Sub-sampling also may be used, as it permits the estimation of some characteristics of 

the larger sampling unit without the necessity of measurement of the entire unit. Sub-sampling 

reduces the cost of the investigation, but usually decreases the precision with which the soil 

characteristics are estimated. Efficient use of sub-sampling depends on a balance between cost 

and precision (Petersen and Calvin, 1986). 

Soil variability and sample size are interferences to sample collection and preparation. 

The objective of laboratory preparation is to homogenize the soil samples used in chemical, 

physical, and mineralogical analyses. At each stage of sampling, an additional component of 

variability, the variability within the larger units, is added to the sampling error (Petersen and 

Calvin, 1986). Soil material needs to be adequate in amount and thoroughly mixed in order to 

obtain a representative sample. 

The SSL receives bulk soil samples from across the U.S. and internationally for a wide 

variety of chemical, physical, and mineralogical analyses. The SSL also typically receives 

natural fabrics, clods, and cores. Undisturbed clods are used to investigate micromorphology 

and determine some physical properties, e.g., bulk density. 

Bulk Samples (1B1a1)

Laboratory identification numbers and preparation codes are assigned to bulk soil 

samples. These identification numbers are unique client- and laboratory-assigned numbers that 

carry important information about the soil sample (e.g., pedon, soil horizon, location, and year 

sampled). Laboratory preparation codes depend on the properties of the sample and on the 

requested analyses. These codes carry generalized information about the characteristics of the 

analyzed fraction, i.e., the water content (e.g., air-dry, field-moist) and the original and final 

particle-size fraction (e.g., sieved <2-mm fraction processed to 75 μm) and by inference, the 

type of analyses performed. Identification numbers and preparation codes are reported on the 

SSL Primary Characterization Data Sheets. Refer to the Soil Survey Investigations Report 

(SSIR) No. 45 (1995) for a detailed explanation of sample identification numbers. Since the 

publication of the SSIR No. 42 (1996), there has been a significant revision of these 

preparation codes. This version of the SSIR No. 42 (2004) does not describe in detail the 

revised preparation codes. Detailed information on the current preparation codes as they appear 

on the Primary Characterization Data Sheets may be obtained from the SSL upon request. 

All soils from quarantined areas are strictly controlled under APHIS quarantine 

regulations 7 CFR 330. For preparation procedures for soil bulk samples, proceed to 1B1b. 

16
Natural Fabrics, Clods, and Cores (1B1a2-4) 

Laboratory identification number and preparation codes are assigned to natural fabrics 

(NF), clods, and cores. These identification numbers typically relate to a corresponding bulk 

sample. Refer to 1B1a1 for information on these identification numbers, preparation codes, 

and soil quarantine regulations. 

Soil Sample Preparation (1B1b) 

1. Application 

In the SSIR No. 42 (1996), laboratory preparation procedures were described as standalone methods based on various procedures summarized by specific preparation codes that are 

reported on the SSL Primary Characterization Data Sheets. In this version of the SSIR No. 42 

(2004), these procedures are described more as a procedural process. A process approach is 

appropriate in that any one sample received from the field may result in a number of laboratory 

sub-samples being collected and prepared based on analytical requests and type of materials. 

This approach is the logic base whereby laboratory procedures are described in this version of 

the SSIR No. 42. The intent herein is not to detail all possibilities of the universe but to 

describe some of the master preparation procedures that are typically requested for laboratory 

analyses. 

Laboratory analyses of soil samples are generally determined on the air-dry, fine-earth 

(<2-mm) fraction (method 1B1b2b1). Air-dry is generally the optimum water content to handle 

and to process soil. In addition, the weight of air-dry soil remains relatively constant, and 

biological activity is low during storage. For routine soil analyses, most U.S. and Canadian 

laboratories homogenize and process samples to pass a 2-mm sieve (Bates, 1993). For some 

standard air-dry analyses, the <2-mm fraction is further processed so as to be in accordance 

with a standard method, e.g., Atterberg Limits (1B1b2c1); to meet the sample preparation 

requirements of the analytical instrument, e.g., total C, N, and S (1B1b2d1); or to achieve 

greater homogeneity of sample material, e.g., total elemental analysis (1B1b2e1) and 

carbonates and/or gypsum (1B1b2d2). Additionally, some standard air-dry analyses by 

definition may require non-sieved material, e.g., whole-soil samples for aggregate stability 

(1B1b2a1) 

A field-moist, <2-mm sample is prepared when the physical properties of a soil are 

irreversibly altered by air-drying, e.g., water retention (1B1b1b2), particle-size analysis, and 

plasticity index for Andisols and Spodosols (1B1b1c1), and/or when moist chemical analyses 

(1B1b1b1) are appropriate. Some biological analyses require field-moist samples (1B1b1a2), as 

air-drying may cause significant changes in the microbial community. The decomposition state 

of organic materials is used in soil taxonomy (Soil Survey Staff, 1999) to define sapric, hemic, 

and fibric organic materials, and as such the evaluation of these materials (Histosol analysis) 

require a field-moist, whole-soil sample (1B1b1a1). 

Knowing the amount of rock fragments is necessary for several applications, e.g., 

available water capacity and linear extensibility. Generally, the >2-mm fractions are sieved, 

weighed, and discarded (1B1b2f1a) and are excluded from most chemical, physical, and 

mineralogical analysis. Some exceptions include but are not limited to samples containing 

coarse fragments with carbonate- or gypsum-indurated material or material from Cr and R soil 

horizons. In these cases, the coarse fragments may be crushed to <2 mm and analytical results 

reported on that fraction, e.g., 2 to 20 mm (1B1b2f1a2a), or the coarse fragments and fine-earth 

material are homogenized and crushed to < 2 mm with laboratory analyses made on the wholesoil (1B1b2f1b1a). Additionally, depending on the type of soil material, samples can be tested 

for the proportion and particle-size of air-dry rock fragments that resist abrupt immersion in tap 

water (1B1b2f1a3). 

17
2. Summary of Method 

Any one soil sample received from the field may result in a number of laboratory subsamples being collected and prepared based on the properties of the sample and on the 

requested analyses. For most standard chemical, physical, and mineralogical analysis, the field 

sample is air-dried, crushed, and sieved to <2 mm. Field-moist, fine-earth fraction samples are 

processed by forcing the material through a 2-mm screen by hand or with a large, rubber 

stopper and placed in a refrigerator for future analysis. Depending on the nature of the soil 

material and requested analyses, air-dry and/or field-moist samples may also be prepared as 

whole-soil samples or processed further to finer fractions than <2 mm, e.g., <0.425 mm for 

Atterberg Limits and ≈ 180 μm for chemical analysis of organic materials. Air-dry, <75 μm 

sub-samples for major and trace elements are processed metal-free. 

Generally, weight measurements are made and recorded on the 20- to 75-mm, 5- to 20-

mm, and 2- to 5-mm fractions, with these fractions then discarded. In some cases, these weight 

measurements may not be recorded. Additionally, some or all of these >2-mm fractions may 

be processed to a finer fraction and saved for chemical, physical, and mineralogical analysis. 

For example, after the respective weights of the 5- to 20-mm and 2- to 5-mm fractions are 

recorded, these fractions may be recombined and crushed to <2 mm in a laboratory jaw crusher, 

with the recombined material saved for laboratory analysis. In other cases, the fine-earth 

fraction and the >2-mm fractions are homogenized and passed through a laboratory jaw crusher 

to reduce all material to pass a 2-mm sieve, with the processed material saved for laboratory 

analysis. 

3. Interferences 

Soil variability and sample size are interferences to sample collection and preparation. 

At each stage of sampling, an additional component of variability, the variability among 

smaller elements within the larger units, is added to the sampling error (Petersen and Calvin, 

1986). Soil material needs to be in adequate amount and thoroughly mixed to obtain a 

representative sample. 

Soil is mixed by moving it from the corners to the middle of processing area and then 

by redistributing the material. This process is repeated four times. Enough soil material needs 

to be sieved and weighed to obtain statistically accurate rock fragment content. In order to 

accurately measure rock fragments with a maximum particle diameter of 20 mm, the minimum 

specimen size ("dry" weight) that needs to be sieved and weighed is 1.0 kg. Refer to ASTM 

Standard Practice D 2488 (American Society for Testing and Materials, 2004). A homogenized 

soil sample is more readily obtained from air-dry material than from field-moist material. 

Whenever possible, "moist" samples or materials should have weights two to four times larger 

than for "dry" specimens (American Society for Testing and Materials, 2004). Refer to ASTM 

Standard Practice D 2488 (American Society for Testing and Materials, 2004). 

4. Safety 

Dust from sample processing is a nuisance. A mask should be worn in order to avoid 

breathing dust. Keep clothing and hands away from the crusher and pulverizer when these 

machines are in use. Use a face-shield and goggles when operating the jaw crusher. Use 

goggles when operating the air compressor. The HCl used to check carbonates can destroy 

clothing and irritate skin. Immediately rinse acid with water from clothing or skin and seek 

professional medical help, if needed. 

5. Equipment 

5.1 Electronic Balance, ±1-g sensitivity and 15-kg capacity 

5.2 Cardboard trays for sample storage 

5.3 Trays, plastic, tared 

5.4 Sieves, square-hole, stainless steel 

5.4.1 80 mesh, 180 μm 

18
5.4.2 10 mesh, 2 mm 

5.4.3 4 mesh, 4.75 mm 

5.4.4 19 mm, 3/4 in 

5.4.5 76 mm, 3 in 

5.4.6 200-mesh, 75 μm, nylon cloth sieve 

5.4.7 40-mesh, 0.425 mm 

5.5 Pulverizer 

5.6 Wooden rolling pin 

5.7 Rubber roller 

5.8 Laboratory jaw crusher, Retsch, Model BB2/A, Brinkmann Instruments Inc., Des Plaines, 

IL. 

5.9 Metal plate, 76 x 76 x 0.5 cm 

5.10 Containers, paper, 12-oz, with lids 

5.11 Containers, plastic, 1-pint, 1, 4, and/or 8 oz with tops 

5.12 Scintillation glass vials, 20-mL 

5.13 Metal weighing cans, 2-oz 

5.14 Brown Kraft paper 

5.15 Air compressor, Cast-iron Series, SpeedAire, Campbell Hausfeld Mfg. Co., Harrison, 

OH. 

5.16 Planetary ball mill, Fritsch, Model P-5, Gilson, Lewis Center, OH 

5.17 Syalon balls, 12- to 15-mm, and bowls, 80-mL 

5.18 Metal weighing cans, 2-oz 

5.19 Cross beater mill, Retsch, Brinkmann Instruments Inc., Des Plaines, IL.

6. Reagents 

6.1 Reverse osmosis (RO) water 

6.2 1 N HCl 

6.3 Sodium hexametaphosphate solution. Dissolve 35.7 g of sodium hexametaphosphate 

(NaPO3)6 and 7.94 g of sodium carbonate (Na2CO3) in 1 L of RO water. 

7. Procedures 

Soil Bulk Sample Preparation (1B1b) 

7.1 Weigh soil sample in sample bag to nearest g when logged-in and record weight. 

7.2 Weigh sample in sample bag to nearest g before air-drying and record weight. 

7.3 Remove soil sample from sample bag and distribute on a plastic tray. Thoroughly mix soil 

material. 

7.4 If field-moist sub-samples are requested, proceed to procedure 1B1b1. 

7.5 If only air-dry sub-samples are requested, proceed to procedure 1B1b2. 

Soil Bulk Sample Preparation (1B1b) 

Field-Moist Preparation (1B1b1) 

7.6 If field-moist, whole-soil sub-samples are requested, proceed to procedure 1B1b1a. 

7.7 If only field-moist, <2-mm sub-samples are requested, proceed to procedure 1B1b1b. 

19
Soil Bulk Sample Preparation (1B1b) 

Field-Moist Preparation (1B1b1) 

Whole-soil (1B1b1a) 

7.8 Procedures for field-moist, whole-soil sub-samples include but are not limited to 1B1b1a1 

and 1B1b1a2 as follows: 

Soil Bulk Sample Preparation (1B1b) 

Field-Moist Preparation (1B1b1) 

Whole-soil (1B1b1a) 

Histosol Analysis (1B1b1a1) 

7.9 For Histosol analysis, select material for representative sub-samples from at least five 

different areas on the plastic tray. Prepare a sub-sample of the field-moist, whole-soil prepared 

in an 8-oz container. Store in the refrigerator for future analysis. 

Soil Bulk Sample Preparation (1B1b) 

Field-Moist Preparation (1B1b1) 

Whole-soil (1B1b1a) 

Biological Analysis (1B1b1a2) 

7.10 For biological analyses, select material for representative sub-samples from at least five 

different areas on the plastic tray. Prepare a sub-sample of field-moist, whole-soil prepared in a 

plastic container. This sub-sample is termed a biology bulk sample, which may be obtained 

from the bulk soil sample upon arrival at the laboratory. Store the biology bulk sample in the 

refrigerator for future analysis. For additional information on biology collection and 

preparation procedures, proceed to 1B3. 

Soil Bulk Sample Preparation (1B1b) 

Field-Moist Preparation (1B1b1) 

 <2-mm Fraction (1B1b1b)

7.11 Procedures for field-moist, <2-mm sub-samples include but are not limited to 1B1b1b1, 

1B1b1b2, 1B1b1b3, and 1B1b1c1 as follows: 

Soil Bulk Sample Preparation (1B1b) 

Field-Moist Preparation (1B1b1) 

 <2-mm Fraction (1B1b1b) 

Chemical and Selected Physical Analysis (1B1b1b1) 

7.12 For moist chemical analysis, select material for representative sub-samples from at least 

five different areas on the plastic tray. Process a sub-sample of field-moist material by forcing 

the material through a 2-mm screen by hand or with a large, rubber stopper and place in a 1-

pint plastic container. Store in the refrigerator for future analysis. 

Soil Bulk Sample Preparation (1B1b) 

Field-Moist Preparation (1B1b1) 

 <2-mm Fraction (1B1b1b)

1500-kPa Water Content (1B1b1b2) 

7.13 For moist 1500-kPa water content of mineral and organic material, select material for 

representative sub-samples from at least five different areas on the plastic tray. Process a subsample of field-moist material by forcing the material through a 2-mm screen by hand or with a 

20
large, rubber stopper and place in a 4-oz plastic container. Store in the refrigerator for future 

analysis. 

Soil Bulk Sample Preparation (1B1b) 

Field-Moist Preparation (1B1b1) 

 <2-mm Fraction (1B1b1b)

Field-Moist/Oven-Dry Ratio (1B1b1b3) 

7.14 For field-moist/oven-dry (FMOD) ratio (required if any moist analyses are determined), 

select material for representative sub-samples from at least five different areas on the plastic 

tray. Process a sub-sample of field-moist material by forcing the material through a 2-mm 

screen by hand or with a large, rubber stopper and place in a 2-oz metal weighing can. 

Soil Bulk Sample Preparation (1B1b) 

Field-Moist Preparation (1B1b1) 

<2-mm Fraction Sieved to <0.425 mm (1B1b1c) 

Atterberg Limits (1B1b1c1) 

7.15 For moist Atterberg Limits, select material for representative sub-samples from at least 

five different areas on the plastic tray. Process a sub-sample of field-moist material by forcing 

the material through a 2-mm screen by hand or with a large, rubber stopper and then sieved to 

40-mesh (0.425 mm). Place sub-sample in a 12-oz plastic container and store in the refrigerator 

for future analysis. 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

7.16 Before air-drying, weigh sample on a tared tray (tray weight) to nearest g and record 

weight. 

7.17 Air-dry the sample in an oven at 30 to 35° C for 3 to 7 days. 

7.18 Weigh sample to nearest g after air-drying and record weight. 

7.19 If air-dry, whole-soil sub-samples are requested, proceed to procedure 1B1b2a. 

7.20 If only air-dry, <2-mm sub-samples are requested, proceed to procedure 1B1b2b. 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

Whole-Soil (1B1b2a) 

7.21 Procedures for air-dry, whole-soil sub-samples include but are not limited to 1B1b2a1 and 

1B1b2a2 as follows: 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

Whole-Soil (1B1b2a) 

Aggregate Stability Analysis (1B1b2a1) 

7.22 For aggregate stability analysis, select material for representative sub-samples from at 

least five different areas on the plastic tray. Prepare an air-dry, whole-soil sample in a 12-oz 

paper container. 

21
Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

Whole-Soil (1B1b2a) 

Repository Samples (1B1b2a2) 

7.23 For comprehensive sampling projects, prepare a 12-oz paper container of fine-earth 

material. Also prepare a 12-oz container for natural fabric (NF) sample. Store soil samples in 

repository. If a NF sample was not selected in the field, select one from air-dried bulk sample. 

Generally, do not select NF samples for reference projects. 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

<2-mm Fraction (1B1b2b) 

7.24 Weigh sample to nearest g and record weight. This weight includes the >2-mm fractions. 

7.25 Roll soil material on a flat, metal plate that is covered with brown Kraft paper with 

wooden rolling pin and/or rubber roller to crush clods to pass a 2-mm sieve. For samples with 

easily crushed coarse fragments, substitute a rubber roller for a wooden rolling pin. Roll and 

sieve until only the coarse fragments that do not slake in sodium hexametaphosphate solution 

remain on sieve. Crush clayey soils that contain no coarse fragments in a laboratory jaw 

crusher. 

7.26 Process air-dry soil by sieving to <2-mm. Thoroughly mix material by moving the soil 

from the corners to the middle of the processing area and then by redistributing the material. 

Repeat process four times. For preparation of the >2-mm fractions, proceed to procedure 

1B1b2f . 

7.27 Procedures for air-dry, <2-mm fractions include but are not limited to 1B1b2b1, 1B2b2b2, 

1B2b2b3, 1B2b2b4, 1B2b2b5, 1b2b2c1, 1B2b2d1, 1b2b2d2, 1B2b2d3, and 1B2b2e1 as 

follows: 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

<2-mm Fraction (1B1b2b) 

Standard Chemical, Physical and Mineralogical Analysis (1B1b2b1) 

7.28 For standard chemical, physical, and mineralogical analysis, select material for 

representative sub-samples from at least five different areas on the plastic tray. Prepare one 

sub-sample of the air-dry, sieved <2-mm fraction in a 12-oz paper container. 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

<2-mm Fraction (1B1b2b) 

Salt Analysis (1B1b2b2) 

7.29 For a saturation paste when salt analyses are requested, select material for representative 

sub-samples from at least five different areas on the plastic tray. Prepare one sub-sample of the 

air-dry, sieved <2-mm fraction in a 1-pint plastic container. 

22
Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

<2-mm Fraction (1B1b2b) 

1500-kPa Water Content (1B1b2b3) 

7.30 For air-dry 1500-kPa water content of mineral and organic materials, select material for 

representative sub-samples from at least five different areas on the plastic tray. Prepare a subsample of air-dry, sieved <2-mm fraction in a 1-oz plastic cup.

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

<2-mm Fraction (1B1b2b) 

Air-Dry/Oven-Dry Ratio (1B1b2b4) 

7.31 For air-dry/oven-dry (ADOD) ratio (required if any air-dry analysis are determined), 

select material for representative sub-samples from at least five different areas on the plastic 

tray. Prepare a sub-sample of the air-dry, sieved <2-mm fraction in a 2-oz metal weighing can. 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

<2-mm Fraction (1B1b2b) 

Presence of Carbonates (1B1b2b5) 

7.32 Use a sub-sample of the ADOD sample (procedure 1B1b2b4) and check for the presence 

of carbonates. Reference samples (knowns) are available for comparisons. Place 1 g of the airdry fine-earth fraction in porcelain spot plate, add reverse osmosis water, and stir to remove 

entrapped air. Add 1 N HCl to soil, observe amount of effervescence, and record as follows: 

None – No visual efferevescence. 

Very Slight - Bubbles rise at a few points in the sample and consistently appear at the same 

point in either a steady stream of tiny bubbles or in a slower stream of larger bubbles. Do not 

mistake trapped air bubbles for a positive test. Generally, these air bubbles appear immediately 

after the addition of 1 N HCl. 

Slight - More small bubbles, and possibly a few larger bubbles, appear throughout the sample 

than with a very slight reaction. 

Strong - More large bubbles are evident than with a slight reaction. Often the reaction is 

violent at first and then quickly decreases to a reaction that produces many small bubbles. 

Violent - The sample effervesces violently. Many large bubbles appear to burst from the spot 

plate. 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

<2-mm Fraction Sieved to 0.425 mm (1B1b2c) 

Atterberg Limits (1B1b2c1) 

7.33 For Atterberg Limits, select material for representative sub-samples from at least five 

different areas on the plastic tray. Prepare one sub-sample of the air-dry, sieved <2-mm 

material sieved to 40-mesh (0.425 mm) in a 12-oz paper container. 

23
Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

<2-mm Fraction Processed to ≈ 180 μm (1B1b2d) Total Carbon, Nitrogen, and Sulfur Analysis (1B1b2d1) 

7.34 For total C, N, and S analyses, select material for representative sub-samples from at least 

five different areas on the plastic tray. Prepare one sub-sample of the air-dry, sieved <2-mm 

fraction processed in a cross beater mill to (≈ 80 mesh, 180 μm) in a 20-mL scintillation glass 

vial. 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

<2-mm Fraction Processed to ≈ 180 μm (1B1b2b) Calcium Carbonate and Gypsum (1B1b2d2) 

7.35 Use the prepared sub-sample (procedure 1B1b2d1) for the determination of the amount of 

carbonates and/or gypsum. 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

<2-mm Fraction Processed to ≈ 180 μm (1B1b2b) Chemical Analysis of Organic Materials (1B1b2d3) 

7.36 For chemical analysis of organic materials, select material for representative sub-samples 

from at least five different areas on the plastic tray. Prepare a sub-sample of the air-dry, sieved 

<2-mm fraction processed in a cross beater to a fine grind (≈ 80 mesh, 180 μm) in a 12-oz 

paper container.

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

<2-mm Fraction Sieved to 75 μm (1B1b2e) Total Major and/or Trace Elements (1B1b2e1) 

7.37 For total major and/or trace element analyses, select material for representative subsamples from at least five different areas on the plastic tray. Prepare one sub-sample of the airdry, metal free, sieved <2-mm fraction processed in a planetary ball mill for 2 min and sieved 

to <75 μm (200 mesh) in a 20-mL scintillation glass vial. 

 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

>2-mm Fractions (1B1b2f) 

7.38 The following procedures are used for samples with >2 mm fractions. These fractions 

include mineral coarse fragments as well wood fragments that are >20 mm in cross section and 

cannot be crushed and shredded with the fingers. If the >2-mm fractions are to be weighed, 

recorded, and discarded, with no further laboratory analysis, proceed to procedure 1B1b2f1a. 

When the data for >2-mm fractions are not recorded, proceed to procedure 1B1b2f1b. If the >2-

mm fractions contain carbonate- or gypsum-indurated material, and laboratory analysis is 

requested, proceed to procedure 1B1b2f1a1a. If the >2-mm fractions are Cr or R material (Soil 

Survey Staff, 1999), and laboratory analysis is requested, proceed to procedure 1B1b2f1b1a. If 

testing is requested for the proportion and particle-size of the air-dry, >2-mm fraction that resist 

abrupt immersion in tap water, proceed to procedure 1B1b2f1a3. 

24
Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

>2-mm Fractions (1B1b2f) 

Particle-Size Analysis (1B1b2f1) 

Particle-Size Analysis, Recorded (1B1b2f1a) 

7.39 Process the air-dry soil by sieving to <2 mm as described in procedure 1B1b2b. In this 

procedure (1B1b2f1a), weight measurements are made on the 20- to 75-mm, 5- to 20-mm, and 

2- to 5-mm fractions. Weigh soil material with diameters of 2 to 5 mm. If difficult to separate 

the <2-mm fraction from fragments, soak (100 g of 2- to 5-mm fraction) in sodium 

hexametaphosphate solution for 12 h. Air-dry, weigh the material that does not slake, record 

weight, and discard. Weigh, record weight, and discard particles with diameters of 20 to 75 mm 

and 5 to 20 mm. The <2-mm fraction is saved for chemical, physical, and mineralogical 

analysis (1B1b2b) 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

>2-mm Fractions (1B1b2f) 

Particle-Size Analysis (1B1b2f1) 

Particle-Size Analysis, Not Recorded (1B1b2f1b) 

7.40 This procedure (1B1b2f1b) is the same as described in procedure 1B1b2f1a except the 

weight of the >2-mm fractions are not recorded and all analytical results are reported on a <2-

mm basis. 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

>2-mm Fractions (1B1b2f) 

Particle-Size Analysis (1B1b2f1) 

Particle-Size Analysis, Recorded (1B1b2f1a) 

2- to 20-mm Fraction Processed to <2-mm (1B1b2f1a1) 

Chemical, Physical, and Mineralogical Analysis (1B1b2f1a1a) 

7.41 This procedure (1B1b2f1a1a) is commonly used for samples with carbonate- or gypsumindurated material. Process the air-dry soil by sieving to <2 mm as described in procedure 

1B1b2b. Weigh soil material with diameters of 20- to 75-mm, 5 to 20-mm, and 2 to 5-mm and 

record weights as described in procedure 1B1b2f1a. The 5- to 20-mm and 2- to 5-mm fractions 

are then recombined after their respective weights are recorded. The recombined, 2- to 20-mm, 

material is crushed to <2 mm in a laboratory jaw crusher. This material is saved for laboratory 

analysis and analytical results reported on the 2- to 20-mm basis. The <2-mm material is also 

saved for chemical, physical, and mineralogical analysis as described in procedure 1B1b2b. If 

carbonate or gypsum accumulations are soft and easily pass a 2-mm sieve, the standard 

procedure (1B1b2b) is usually requested. 

25
Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

>2-mm Fractions (1B1b2f) 

Particle-Size Analysis (1B1b2f1) 

Particle-Size Analysis, Recorded (1B1b2f1a) 

2- to 20-mm Fraction Processed to <2-mm and Recombined with <2-mm 

Fraction (1B1b2f1a2) 

Chemical, Physical, Mineralogical Analysis (1B1b2f1a2a) 

7.42 This procedure (1B1b2f1a2a) is rarely requested. Process the air-dry soil by sieving to <2 

mm as described in procedure 1B1b2b.Weigh soil material with diameters of 20- to 75-mm, 5 

to 20-mm, and 2 to 5-mm and record weights as described in procedure 1B1b2f1a. The 5- to 

20-mm and 2- to 5-mm fractions are then recombined after their respective weights are 

recorded. The recombined, 2- to 20-mm, material is crushed to <2 mm in a laboratory jaw 

crusher. This material is then recombined with the <2-mm fraction. These analytical results are 

reported on the <20-mm basis or are calculated to the <2-mm basis. 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

>2-mm Fractions (1B1b2f) 

Particle-Size Analysis (1B1b2f1) 

Particle-Size Analysis, Not Recorded (1B1b2f1b) 

Whole-Soil Processed to <2-mm (1B1b2f1b1) 

Chemical, Physical, and Mineralogical Analysis (1B1b2f1b1a) 

7.43 This procedure (1B1b2f1b1a) is mainly used to prepare samples from Cr or R soil 

horizons (Soil Survey Staff, 1999). Homogenize particles with diameters >2 mm and the fineearth material (<2-mm) and crushed to <2-mm in a laboratory jaw crusher. This material is 

saved for laboratory analysis and analytical results reported on the whole-soil basis. 

8. Calculations 

Calculations for coarse fragments are reported in 3A2. 

9. Report 

Reported data include but are not limited to the following: 

 9.1 Weight (g) of field-moist soil sample 

9.2 Weight (g) of air-dry soil sample 

9.3 Weights (g) of processed air-dry soil 

9.4 Weight (g) of 20- to 75-mm fraction 

9.5 Weight (g) of 5- to 20-mm fraction 

9.6 Weight (g) of 2- to 5-mm fraction 

9.7 Weight (g) of sub-sample of 2- to 5-mm fraction before slaking 

9.8 Weight (g) of sub-sample of 2- to 5-mm fraction after slaking 

9.9 Effervescence with HCl (None, Very Slight, Slight, Strong, Violent) 

10. Precision and Accuracy

Precision and accuracy data are available from the SSL upon request. 

11. References 

American Society for Testing and Materials. 2004. Standard practice for description and 

identification of soils (visual-manual procedure). D 2488.. Annual book of ASTM 

standards. Construction. Section 4. Soil and rock; dimension stone; geosynthesis. Vol. 

04.08. ASTM, Philadelphia, PA. 

26
Bates, T.E. 1993. Soil handling and preparation. p. 19-24. In M.R. Carter (ed.) Soil 

sampling and methods of analysis. Can. Soc. Soil Sci. Lewis Publ., CRC Press, Boca 

Raton, FL. 

Petersen, R.G., and L.D. Calvin. 1986. Sampling. p. 33-51. In A. Klute (ed.) Methods of 

soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. Monogr 9. 

ASA and SSSA, Madison, WI. 

Soil Survey Staff. 1995. Soil survey laboratory information manual. Version No. 1.0. 

USDA-NRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, 

Washington, DC. 

Soil Survey Staff. 1996. Soil survey laboratory methods manual. Version No. 3.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, 

DC. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. 2nd ed. Agric. Handb. No. 436. USDA-NRCS. U.S. Govt. 

Print. Office, Washington, DC. 

Soil Bulk Sample Preparation (1B1b) 

Air-Dry Preparation (1B1b2) 

>2-mm Fractions (1B1b2f) 

Particle-Size Analysis (1B1b2f1) 

Particle-Size Analysis, Recorded (1B1b2f1a) 

Proportion and Particle-Size of Air-Dry Rock Fragments that Resist Abrupt 

Immersion in Tap Water (1B1b2f1a3) 

1. Application 

It is widely accepted that the mechanical preparation of soil for laboratory analysis is 

difficult to standardize for samples that contain >2-mm particles with rupture resistance 

intermediate between earthy bodies and fragments of highly resistant rock (Grossman, 2004). 

There is a need for a procedure that is both reproducible and subjects the >2-mm fraction to an 

intermediate stress less than standard mechanical preparation. Abrupt immersion in tap water 

of the initially air-dry >2-mm fraction has been chosen as the manner in which stress is applied. 

For some situations, comparison of the results to use a dispersing agent may be valuable; for 

this another procedure would need establishment. 

This method (1B1b2f1a3) provides a comparison to mechanical preparation methods 

and should aid in the development of more precise mechanical preparation dependent on 

sample properties (Grossman, 2004). Certain analyses can be run on the >2-mm fraction after 

separation by the water-immersion method. The resulting values can be subtracted from 

analyses on the whole ground sample to obtain estimates for the <2-mm fraction as removed by 

the water immersion treatment. 

2. Summary of Method 

A representative sub-sample of the air-dry field sample is weighed and passed through a 

No.10 sieve. The >2-mm fraction is placed abruptly in tap water, left overnight, gently 

agitated, passed through a No. 10 sieve, and the wet >2-mm passed through a nest of No. 10, 

No. 4, 9.5-mm (nominally 10 mm), and 20-mm sieves. 

3. Interferences 

There are no known interferences. 

4. Safety 

Dust from sample processing is a nuisance. A mask should be worn in order to avoid 

breathing dust. 

27
5. Equipment 

5.1 Buckets, plastic, 10-L with 1-L marks 

5.2 Bucket, plastic, in which 20-cm diameter sieve fits snugly 

5.3 Bucket, 19-L (5-gal), straight-sided, with 30-cm diameter 

5.4 Drying trays, fiberglass, 35 x 48 cm 

5.5 Cake pans, aluminum foil, 20 x 20 x 4cm 

5.6 Sieves: 30-cm diameter No. 10, 20-mm diameter No. 4, 9.5- and 20-mm plus bottom pan 

5.7 Top loading balance, 1-g sensitivity and >10,000-g capacity, with pan large enough to 

mount the trays listed under Section 5.4 

5.8 Pan, plastic, 60 x 40 x 15 cm 

5.9 Plastic sheet, 8-mm, large enough to line plastic container 

5.10 Plastic beads, 9 x 6 mm, segregated by different colors 

5.11 Teaspoon, tablespoon 

6. Reagents 

6.1 CaCl2·2H2O

6.2 Tap water of acceptable dispersability (taken as Zone A in Flanagan and Holmgren, 1977). 

7. Procedure 

7.1 Remove roughly a one-fourth representative sub-sample inclusive of the >20-mm fraction 

from the field sample and weigh. 

7.2 Pass through a No. 10 sieve. Weigh the >2-mm particles and discard the<2-mm fraction. 

Immerse the >2-mm fraction abruptly in tap water in a 10-L bucket in which there is 

approximately 1-L of water for roughly every 500 g of >2-mm particles. Leave the sample 

overnight. 

7.3 Insert the hand to the bottom of the bucket and rotate the mass at one rotation per second 20 

times. In the sink, place the 30-cm diameter No. 10 sieve over the top of a 19-L diameter 

bucket. Quantitatively transfer the >2-mm particles into the No.10 sieve and wash with a water 

stream to remove the material not resistant to the immersion treatment. Use a minimum 

amount of water. 

 

7.4 After the 19-L bucket is full, add about 30 g of CaCl2. Allow to stand until settled out. 

Pour off into the sink as much of the water as possible without transfer of solids to the sink. 

Dry the sediment in the bucket by evaporation, followed by disposal as a solid. 

7.5 Follows 7.3 directly if no strength measurements. Quantitatively transfer from the 30-cm 

diameter sieve to a tray. Air-dry the sample on the tray at 30 to 35°C. Pass through a nest of 

20-mm, No. 4 and No. 10 sieves. 

7.6 Weigh each separate to the nearest g and report. Subtract the >20-mm weight from the 

initial >2-mm weight. Obtain the 2 to 5, 5 to 20, and 2- to 20-mm particles as a percent of the 

<20-mm fraction. 

8. Calculations 

8.1 A = [B/(C – D)] x 100 

8.2 E = [F/(C – D)] x 100 

8.3 G = A + E 

28
where: 

A = Weight percentage 2- to 5-mm fraction on <20-mm basis (%) 

B = Air-dry weight of 2- to 5-mm fraction after water immersion (g) 

C = Air-dry total weight of whole soil sub-sample (g) 

D = Air-dry weight of >20-mm fraction after water immersion (g) 

E = Weight percentage of 5- to 20-mm fraction on <20-mm basis (%) 

F = Air-dry weight of 5- to 20-mm fraction after water immersion (g) 

G = Weight percentage 2- to 20-mm fraction on <20-mm basis (%) 

9. Report 

Report the 2 to 5, 5 to 20, and 2- to 20-mm fractions as weight percentages of the <20-

mm fraction. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Flanagan, C.P., and G.G.S. Holmgren. 1977. p. 121-134. Field methods for determination 

of soluble salts and percent sodium from extract for identifying dispersive clay soils. In 

J.L. Sherard and R.S. Decker (eds.) Dispersive clays, related piping, and erosion in 

geotechnical projects, ASTM STP 623. American Society of Testing Materials, West 

Conshohocken, PA. 

Grossman, R.B. 2004. Proportion and particle-size of air-dry rock fragments that resist 

abrupt immersion in tap water. USDA-NRCS, Lincoln, NE. 

Laboratory Sample Collection and Preparation (1B) 

Water (1B2) 

Samples (1B2a) 

As with soil samples, laboratory identification numbers and preparation codes are 

assigned to water samples. Refer to 1B1a1 for information on these identification numbers and 

preparation codes. 

Water (1B2) 

Water Sample Preparation (1B2b) 

Avoid long periods between collection and laboratory analysis of water. To prevent 

significant changes (e.g., degradation, volatilization), water samples require expedited transport 

under ice or gel packs and are refrigerated (4°C) immediately upon arrival at the laboratory. 

Avoid freezing water samples, which can influence pH and the separation of dissolved organic 

matter from the water phase. 

Some water analyses, e.g., electrical conductivity, total and inorganic C, need to be 

performed promptly, as optimal preservation is not possible (Velthorst, 1996). Upon 

completion of these analyses, sample filtration (0.45-μm membrane) is used to separate 

dissolved from suspended material. The sample is then split into two sub-samples, with one 

acidified to pH 2 for cation analyses (e.g., Al, Fe, Mn) and the other for anion analyses. These 

other water analyses also need to be performed as promptly as possible. 

29
Biological Materials (1B3) 

Samples (1B3a) 

Biology Bulk Sample (1B3a1) 

Microbial Biomass Sample (1B3a2) 

As with soil and water samples, laboratory identification numbers and preparation 

codes are assigned to biology samples. Refer to 1B1a1 for information on these identification 

numbers and preparation codes. Some biology samples arrive at the laboratory as part of the 

soil bulk sample. If this is the case, biological sub-samples are collected and prepared as 

described in 1B1b1a2. In other cases, biology bulk samples may be split in the field (1B3a1) 

and are separate sampling units from the soil bulk sample (1B1a1). Additionally, some 

biological samples, e.g., microbial biomass (1B3a2), are separate units from the soil bulk or 

other biology samples, requiring expedited transport under ice or gel packs and are refrigerated 

(4°C) immediately upon arrival at the laboratory. 

Biological Materials (1B3) 

Biological Material Preparation (1B3b) 

Avoid long periods between collection and laboratory analysis of biological samples to 

prevent significant changes (e.g., microbial community). Store biology samples in the 

refrigerator (4°C) for future analysis. Biological preparation includes but is not limited to the 

following: 

Biological Materials (1B3) 

Biological Material Preparation (1B3b) 

Field-Moist Preparation (1B3b1) 

<2 mm (1B3b1a) 

Microbial Biomass (1B3b1a1) 

Refer to the section on soil biological and plant analyses (6) for additional information 

on the further processing and preparation of these biological samples for laboratory analysis. 

Biological Materials (1B3) 

Biological Material Preparation (1B3b) 

Air-Dry Preparation (1B3b2) 

<2-mm Fraction Sieved to <53 μm, with > 53 μm (Particulate Organic Matter) and <53 μm Processed to ≈ 180 μm (1B3b2a) Total Carbon, Nitrogen, and Sulfur (1B3b2a1) 

Refer to the section on soil biological and plant analyses (6) for additional information 

on the further processing and preparation of these biological samples for laboratory analysis. 

Biological Materials (1B3) 

Biological Material Preparation (1B3b) 

Air-Dry Preparation (1B3b2) 

<2-mm Fraction (1B3b2b) 

Other Biological Analyses (1B3b2b1) 

Refer to the section on soil biological and plant analyses (6) for additional information 

on the further processing and preparation of biological samples for laboratory analysis. 

30
Biological Materials (1B3) 

Biological Material Preparation (1B3b) 

Dry (50°C) Preparation (1B3b3) Roots (1B3b3a) 

Root Biomass (1B3b3a1) 

Roots Processed to ≈ 180 μm (1B3b3a1a) Total Carbon, Nitrogen, and Sulfur (1B3b3a1a1) 

Plants (1B3b3b) 

Plant Biomass (1B3b3b1) 

Plants Processed to ≈ 180 μm (1B3b3b1a) Total Carbon, Nitrogen, and Sulfur (1B3b3b1a1) 

 Refer to the section on soil biological and plant analyses (6) for additional information 

on the further processing and preparation of these biological samples for laboratory analysis. 

References 

Velthorst, E.J. 1996. Water analysis. p. 121-242. In P. Buurman, B. van Lagen, and E.J. 

Velthorst (eds.) Manual for soil and water analysis. Backhuys Publ. Leiden. 

CONVENTIONS (2) 

Methods and Codes (2A) 

The SSL ensures continuity in its analytical measurement process with the use of 

standard operating procedures (SOP’s). A standard method is defined herein as a method or 

procedure developed by an organization, based on consensus opinion or other criteria and often 

evaluated for its reliability by a collaborative testing procedure (Taylor, 1988). A SOP is a 

procedure written in a standard format and adopted for repetitive use when performing a 

specific measurement or sampling operation, i.e., a SOP may be a standard or one developed by 

a user (Taylor, 1988). 

The use of SOP’s provides consistency and reproducibility in soil preparations and 

analyses and helps to ensure that these preparations and analyses provide results of known 

quality. The standard methods described in the SSIR No. 42, Soil Survey Laboratory Methods 

Manual, Version 4.0 replaces as a methods reference all earlier versions of the SSIR No. 42 

(1989, 1992, and 1996, respectively) and SSIR No. 1, Procedures for Collecting Soil Samples 

and Methods of Analysis for Soil Survey (1972, 1982, and 1984). All SSL methods are 

performed with methodologies appropriate for the specific purpose. The SSL SOP’s are 

standard methods, peer-recognized methods, SSL-developed methods, and/or specified 

methods in soil taxonomy (Soil Survey Staff, 1999). This manual also serves as the primary 

document from which a companion manual, Soil Survey Laboratory Information Manual (SSIR 

No. 45, 1995), has been developed. The SSIR No. 45 describes in greater detail the application 

of SSL data. 

Included in the SSIR No. 42 are descriptions of current as well as obsolete methods, 

both of which are documented by method codes and linked with analytical results that are 

stored in the SSL database. This linkage between laboratory method codes and the respective 

analytical results is reported on the SSL data sheets. Reporting the method by which the 

analytical result is determined helps to ensure user understanding of SSL data. In addition, this 

linkage provides a means of technical criticism and traceability if data are questioned in the 

future. 

The methods in current use at the SSL are described in the SSIR No. 42 in enough 

detail that they can be performed in many laboratories without reference to other sources. 

Descriptions of the obsolete methods are located at the back of this methods manual. 

31
Information is not available to describe some of these obsolete procedures in the same detail as 

used to describe the current methods in the laboratory. 

Since the publication of the SSIR No. 42 (1996), there has been a significant increase in 

the number and kind of methods performed at the SSL, resulting in a re-structuring of the 

method codes. As in past versions of the SSIR No. 42, the current method codes are 

hierarchical and alphanumerical. However, the older method code structure had only a 

maximum of four characters, e.g., 6A1b, whereas the new structure has more characters, 

carrying more information about the method, e.g., particle-size and sample weight bases for 

reporting data. This version of the SSIR No. 42 carries not only the new method codes but also 

the older ones as well. These older codes are cross-referenced in a table preceding the method 

descriptions of the obsolete SSL methods This linkage between the two method code systems 

is important to maintain, as many older SSL data sheets and scientific publications report these 

older codes. 

The SSL data have been provided in reports, e.g., Primary and Supplementary 

Characterization Data Sheets, and in electronic forms, including tapes, disks, and CD-ROMs. 

More recently, other reports have been developed, e.g., Soil Taxonomy Characterization Data 

Sheets, and data are available via the NRCS Soils web site http://soils.usda.gov/. Historically, the 

SSIR No. 42 has described and assigned method codes to only those data reported on the 

Primary Characterization Data Sheets. This tradition is followed in this version of the SSIR 

No. 42. With the exception of some SSL primary analytical data included for user 

convenience, the data on the Supplementary and Taxonomy Characterization Data Sheets are 

derived data, using analytical data as a basis for calculation and do not carry method codes. 

Data on the Supplementary and Taxonomy Characterization Data Sheets are not described in 

this manual. Additionally, there are other calculated data on the Primary Characterization Data 

Sheets that appear as “Pedon Calculations”, e.g., Weighted Average Clay. These calculated 

data are not assigned method codes nor described in this manual. For more detailed 

information about the calculation and application of these derived values, refer to the SSIR No. 

45, Soil Survey Information Manual (1995) and Soil Taxonomy (Soil Survey Staff, 1999). 

Additional information may also be obtained from the SSL upon request. 

Data Types (2B) 

The methods described herein identify the specific type of analytical or calculated data. 

Most of these methods are analytical in nature, i.e., quantitative or semi-quantitative 

measurements, and include physical, chemical, mineralogical, and biological analyses. Sample 

collection and preparation in the field and the laboratory are also described. Historically, the 

SSIR No. 42 has described some derived values, e.g., coefficient of linear extensibility (COLE) 

and water retention difference (WRD) and reported these values along with the analytical data 

on the SSL Primary Characterization Data Sheets. This version of the SSIR No. 42 follows this 

tradition. Since the publication of the SSIR No. 42 (1996), there have been a few more 

derived 

values added to the Primary Characterization Data Sheets. While these data have been 

assigned method codes, detailed descriptions are not included in this version of the SSIR No. 

42. For more detailed information about the calculation and application of these derived values, 

refer to the SSIR No. 45 (1995) and Soil Taxonomy (Soil Survey Staff, 1999). 

Size-Fraction Base for Reporting Data (2C) 

Particles <2 mm (2C1) 

Particles <Specified Size>2mm (2C2) 

The reporting conventions for particle-size fractions for the < 2 mm and > 2mm 

fractions are herein designated as 2C1 and 2C2, respectively. Unless otherwise specified, all 

data are reported on the basis of the <2-mm material. Other size fractions reported on the 

Primary Characterization Data Sheets include but are not limited to the <0.4, <20, <75 mm, and 

32
the whole-soil base. The maximum coarse-fragment size for the >2-mm base varies. The base 

usually includes those fragments as large as 75 mm (3 in), if present in the soil. The maximum 

size for fragments >75 mm, commonly termed whole soil, includes boulders with maximum 

horizontal dimensions less than those of the pedon. The maximum particle-size set is recorded 

in the parentheses in the column heading. The base with which to calculate the reported >2-

mm percentages includes all material in the sample smaller than the particle size recorded in 

the column heading. 

Sample Weight Base for Reporting Data (2D) 

Air-Dry/Oven-Dry (2D1) 

Field-Moist/Oven-Dry (2D2) 

Correction for Crystal Water (2D3) 

Unless otherwise specified, all data are reported on an oven-dry weight or volume basis 

for the designated particle-size faction. The calculation of the air-dry/oven-dry (AD/OD) ratio 

is used to adjust AD results to an OD weight basis and, if required in a procedure, to calculate 

the sample weight that is equivalent to the required OD soil weight. The AD/OD ratio is 

calculated by procedure 3D1. The AD/OD ratio is converted to a crystal water basis by 

procedure 3D3 for gypsiferous soils (Nelson et al., 1978). The calculation of the fieldmoist/oven-dry (FM/OD) ratio is used to adjust FM results to an OD weight basis, and if 

required in a procedure, to calculate the sample weight that is equivalent to the required OD 

soil weight. The FM/OD ratio is calculated by procedure 3D2. 

AD and OD weights are defined herein as constant sample weights obtained after 

drying at 30±5°C (≈ 3 to 7 days) and at 110±5°C (≈ 12 to 16 h), respectively. As a rule of 

thumb, air-dry soils contain about 1 to 2 percent water and are drier than soils at 1500-kPa 

water content. FM weight is defined herein as the sample weight obtained without drying prior 

to laboratory analysis. In general, these weights are reflective of the water content at the time of 

sample collection. 

Significant Figures and Rounding (2E) 

Unless otherwise specified, the SSL uses the procedure of significant figures to report 

analytical data. Historically, significant figures are said to be all digits that are certain plus 

one, which contains some uncertainty. If a value is reported as 19.4 units, the 0.4 is not certain, 

i.e., repeated analyses of the same sample would vary more than one-tenth but generally less 

than a whole unit. 

Data Sheet Symbols (2F) 

The analytical result of “zero” is not reported by the SSL. The following symbols are 

used or have been used for trace or zero quantities and for samples not tested. 

tr, Tr, TR Trace, either is not measurable by quantitative procedure used or is less than 

reported amount. 

tr(s) Trace, detected only by qualitative procedure more sensitive than quantitative procedure 

used. 

- Analysis run but none detected. 

-- Analysis run but none detected. 

-(s) None detected by sensitive qualitative test. 

33
blank Analysis not run. 

nd Not determined, analysis not run. 

< Either none is present or amount is less than reported amount, e.g., <0.1 is in fact <0.05 

since 0.05 to 0.1 is reported as 0.1. 

References 

Soil Conservation Service. 1972. Soil survey laboratory methods and procedures for collecting 

soil samples. USDA-SCS. Soil Survey Investigations Report No. 1. U.S. Govt. Print. Office, 

Washington, DC. 

Soil Conservation Service. 1982. Soil survey laboratory methods and procedures for collecting 

soil samples. USDA-SCS. Soil Survey Investigations Report No. 1. U.S. Govt. Print. Office, 

Washington, DC. 

Soil Conservation Service. 1984. Soil survey laboratory methods and procedures for collecting 

soil samples. USDA-SCS. Soil Survey Investigations Report No. 1. U.S. Govt. Print. Office, 

Washington, DC. 

Soil Survey Staff, 1989. Soil survey laboratory methods manual. Version No. 1.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, DC. 

Soil Survey Staff, 1992. Soil survey laboratory methods manual. Version No. 2.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, DC. 

Soil Survey Staff. 1995. Soil survey laboratory information manual. Version No. 1.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, DC. 

Soil Survey Staff. 1996. Soil survey laboratory methods manual. Version No. 3.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, DC. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys. 2nd ed. Agric. Handb. No. 436. USDA-NRCS. U.S. Govt. Print. 

Office, Washington, DC. 

SOIL PHYSICAL AND FABRIC-RELATED ANALYSES (3) 

Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

1. Application 

General: One of the most requested SSL characterization analysis is particle-size 

distribution analysis (PSDA). The behavior of most soil physical and many chemical properties 

are sharply influenced by the particle-size distribution classes present and their relative 

abundance. Precise meaning is given to the term soil texture only through the concept of 

particle-size distribution (Skopp, 1992). 

Particle-size distribution analysis is a measurement of the size distribution of individual 

particles in a soil sample. These data may be presented on a cumulative PSDA curve. These 

distribution curves are used in many kinds of investigations and evaluations, e.g., geologic, 

hydrologic, geomorphic, engineering, and soil science (Gee and Bauder, 1986). In soil science, 

particle-size is used as a tool to explain soil genesis, quantify soil classification, and define soil 

texture. 

In the USDA classification system (Soil Survey Staff, 1953, 1993), soil texture refers to 

the relative proportions of clay, silt, and sand on a <2-mm basis. It also recognizes proportions 

of five subclasses of sand. In addition to the USDA soil classification scheme, there are other 

classification systems, e.g., the particle-size classes for differentiation of families in soil 

taxonomy (Soil Survey Staff, 1999); International Union of Soil Science (IUSS); the Canadian 

Soil Survey Committee (CSSC); and American Society for Testing and Materials (ASTM). In 

34
reporting and interpreting data, it is important to recognize that these other classification 

systems are frequently cited in the literature, especially engineering systems, e.g., American 

Association of State Highway and Transportation Officials (AASHTO) and the ASTM Unified 

Soil Classification System (USCS) (Gee and Bauder, 1986). 

Standard SSL PSDA (3A1a1): The procedure described herein covers the destruction 

or dispersion of <2-mm diameter soil aggregates into discrete units by chemical, mechanical, or 

ultrasonic means, followed by the separation or fractionation of these particles according to 

size limits through sieving and sedimentation (Gee and Bauder, 1986). Upon isolation of these 

particle-sizes or size increments, the amount of each size-fraction is then gravimetrically 

measured as a percent of the total sample weight on an oven-dry basis. The Kilmer and 

Alexander (1949) pipet method was chosen by the USDA Soil Conservation Service because it 

is reproducible in a wide range of soils. 

The SSL routinely determines the soil separates of total sand (0.05 to 2.0 mm), silt 

(0.002 to 0.05 mm), and clay (< 2 μm), with five subclasses of sand (very coarse, coarse, 

medium, fine, and very fine) and two subclasses of silt (coarse and fine). The coarse silt is a 

soil separate with 0.02 to 0.05-mm particle diameter. The 0.02-mm (20 μm) is the break 

between sand and silt in the International Classification system. The particle-size separation at 

20 μm also has significance in optical microscopy, as this class limit represents the optical 

limits of the polarizing light microscope. Particle-size classes are a compromise between 

engineering and pedologic classes (Soil Survey Staff, 1999). In engineering classifications, the 

limit between sand and silt is a 0.074-mm diameter. The break between sand and silt is 0.05 

and 0.02 mm in the USDA and International classification systems, respectively. In engineering 

classes, the very fine sand (VFS) separate is split. In particle-size classes of soil taxonomy (Soil 

Survey Staff, 1999), the VFS is allowed to float, i.e., the VFS is treated as sand if the texture is 

fine sand, loamy fine sand, or a coarser class and is treated as silt if the texture is very fine 

sand, loamy very fine sand, sandy loam, silt loam, or a finer class (Soil Survey Staff, 1999). 

Refer to the Soil Survey Staff (1999) for additional discussion on particle-size classes. 

Fine-Clay and Carbonate Clay: In addition to the routine soil separates of sand, silt, 

and clay, the SSL determines the fine-clay and/or carbonate clay fractions, depending on 

analytical requests and properties of the sample. The fine-clay fraction consists of mineral soil 

particles with an effective diameter of <0.2 μm. The percentage fine clay is determined for 

soils that are suspected of having illuviated clay. Fine-clay data can be used to determine the 

presence of argillic horizons or as a tool to help explain soil genesis. The carbonate-clay 

fraction is considered important in PSDA because clay-size carbonate particles have properties 

that are different from non-carbonate clay. The cation exchange capacity of carbonate clay is 

very low compared to non-carbonate clay. Water holding capacity of carbonate clay is ≈ two 

thirds that of non-carbonate clay. Since carbonate clay is a diluent, it is often subtracted from 

the total clay in order to make inferences about soil genesis and clay activities. 

Pretreatment and Dispersion Techniques: The phenomena of flocculation and 

dispersion (deflocculation) are very important in determining the physical behavior of the 

colloidal fraction of soils and thus indirectly, have a major bearing on the physical properties 

which soils exhibit (Sumner, 1992). In the standard SSL procedure (3A1a1), soils are 

pretreated to remove organic matter and soluble salts. Samples are chemically treated with 

hydrogen peroxide and sodium hexametaphosphate to effect dispersion. The primary 

objectives of dispersion are the removal of cementing agents; re-hydration of clays; and the 

physical separation of individual soil particles (Skopp, 1992). The hydrogen peroxide oxidizes 

the organic matter. The sodium hexametaphosphate complexes any calcium in solution and 

replaces it with sodium on the exchange complex. Upon completion of the chemical treatments, 

mechanical agitation through shaking is used to enhance separation of particles and facilitates 

fractionation. 

Complete dispersion by procedure 3A1a1 may be prevented in the presence of 

cementing agents such calcium carbonate, Fe, and Si. In these instances, special pretreatment 

and dispersion procedures (3A1a2-5) may be performed upon request by the project 

coordinator on the sample as follows: 

35
Carbonate Removal (3A1a2): Soils high in carbonate content do not readily disperse. 

Pretreatment of these soils with acid removes the carbonates (Grossman and Millet, 1961; 

Jackson, 1969; Gee and Bauder, 1986; Gee and Or, 2002). The determination of particle-size 

distribution after the removal of carbonates is used primarily for studies of soil genesis and 

parent material. 

Iron Removal (3A1a3): Iron and other oxides coat and bind particles of sand, silt, and 

clay form aggregates. Soils with iron cementation do not readily disperse. The iron oxides are 

removed using bicarbonate-buffered, sodium dithionite-citrate solution (Mehra and Jackson, 

1960; Gee and Bauder, 1986; Gee and Or, 2002). 

Silica Removal (3A1a4): Soils that are cemented by Si do not completely disperse with 

hydrogen peroxide pretreatment and sodium hexametaphosphate. A pretreatment with a weak 

base dissolves the Si bridges and coats and increases the soil dispersion. The determination is 

used for soil parent material and genesis studies. 

Ultrasonic Dispersion (3A1a5): Soils that do not completely disperse with standard 

PSDA can be dispersed using ultrasonic dispersion (Gee and Bauder, 1986; Gee and Or, 2002). 

Pretreatments coupled with ultrasonic dispersion yield maximum clay concentrations (Mikhail 

and Briner, 1978). This is a developmental procedure as no standard method has been adopted 

using ultrasonic dispersion. 

Water Dispersible PSDA (3A1a6): This method provides a means of evaluating the 

susceptibility of a soil to water erosion. The degree to which a soil disperses without the 

oxidation of organic matter or the removal of soluble salts, or the addition of a chemical 

dispersant may be compared with results from chemical dispersion (Bouyoucos, 1929). 

Field-Moist PSDA (3A1a1b): The standard SSL procedure for particles with <2-mm 

diameter is the air-dry method (3A1a1a). While a homogenized sample is more easily obtained 

from air-dry material than from moist material, some soils irreversibly harden when dried and 

as such moist PSDA (3A1a1b) may be used. The phenomenon of aggregation through oven or 

air-drying is an important example of irreversibility of colloidal behavior in the soil-water 

system (Kubota, 1972; Espinoza et al. 1975). Drying such soils decreases the measured clay 

content. This can be attributed to the cementation upon drying (Maeda et al., 1977). The 

magnitude of the effect varies with the particular soil (Maeda et al., 1977). 

SSL PSDA Process: In the SSIR No. 42 (1996), stand-alone methods were described 

for the non-routine pretreatment and dispersion techniques as well as for the analysis of 

particles not routinely reported, e.g., fine and/or carbonate-clay fractions. In this version of the 

SSIR No. 42 (2004), these procedures are described more as a procedural process. This 

approach is appropriate in that certain procedural steps may be modified, omitted, or enhanced 

by the investigator, depending on the properties of the sample and on the requested analyses. 

The process by which specific procedural steps are selected for sample analysis is based upon 

knowledge or intuition of certain soil properties or related to specific questions, e.g., special 

studies of soil genesis and parent material. 

2. Summary of Method 

Standard SSL PSDA: The standard SSL procedure for analysis of particles with <2-

mm diameters is the air-dry method (procedure 3A1a1a), whereby a 10-g sample is pretreated 

to remove organic matter and soluble salts. The sample is dried in the oven to obtain the initial 

weight, dispersed with a sodium hexametaphosphate solution, and mechanically shaken. The 

sand fraction is removed from the suspension by wet sieving and then fractionated by dry 

sieving. The clay and fine silt fractions are determined using the suspension remaining from 

the wet sieving process. This suspension is diluted to 1 L in a sedimentation cylinder, stirred, 

and 25-mL aliquots removed with a pipet at calculated, predetermined intervals based on 

Stokes' law (Kilmer and Alexander, 1949). The aliquots are dried at 110°C and weighed. 

Coarse silt is the difference between 100% and the sum of the sand, clay, and fine silt 

percentages. 

Fine-Clay Determination: The soil suspension from procedure 3A1a1a is used to 

determine the fine-clay fraction. This suspension is stirred, poured into a centrifuge bottle, and 

36
centrifuged at 1500 rpm. A 25-mL aliquot is withdrawn with a pipet. The aliquot is dried in the 

oven, weighed, and the percentage of fine clay is calculated based on the total sample weight. 

The time of centrifugation is determined from the following equation modified from Stokes' 

law (Jackson, 1969). 

tm = (63.0x108η log (rs-1)) (Nm

2

 Dμ

2 ∆ρ)-1

where: 

tm = Time in minutes 

η = Viscosity in poises 

r = Radius in cm from center of rotation to sampling depth (3 cm + s) 

s = Radius in cm from center of rotation to surface of suspension 

Nm = rpm (1500) 

Dμ = Particle diameter in microns (0.2 μm) 

∆ρ = Difference in specific gravity between solvated particles and suspension liquid 

63.0x108 = Combination of conversion factors for convenient units of time in minutes, tmin, Nm

as rpm, and particle diameter in microns, Dμ. 

Carbonate-Clay Determination: The residue from procedure 3A1a1a is used to 

determine the carbonate-clay fraction. This residue is treated with acid in a closed system. The 

pressure of the evolved gas is measured. The pressure is related linearly to the CO2 content in 

the carbonates. A manometer is used to measure the pressure. 

Pretreatment and Dispersion Techniques: In the standard PSDA, an air-dry soil 

sample is pretreated to remove organic matter and soluble salts (3A1a1a). There are additional 

non-routine chemical pretreatments for the removal of cementing agents that often prevent 

complete dispersion. These pretreatments may be requested by the project coordinator as 

follows: 

Carbonate Removal (3A1a2a): Carbonates are destroyed with a 1 N NaOAc solution 

buffered to pH 5. The NaOAc solution is added to sample until carbonate bubbles no longer 

evolve. The NaOAc solution is then washed from the sample. After destruction of carbonates, 

the remainder of procedure 3A1a1 is followed. 

Iron Removal (3A1a3a): Soil samples are pretreated with H2O2 to remove organic 

matter. Iron oxides are removed with bicarbonate-buffered, sodium dithionite-citrate solution 

and heated until the sample color changes to a grayish color. The suspension is flocculated 

with saturated NaCl solution and filtered to remove soluble salts. After removal of iron oxides, 

the remainder of procedure 3A1a1 is followed. 

Silica Removal (3A1a4a): Soils are pretreated with H2O2 to remove organic matter. 

Soils with Si cementation or coatings are pretreated with a weak NaOH solution overnight. 

After removal of siliceous cementing agents, the remainder of procedure 3A1a1 is followed. 

Ultrasonic Dispersion (3A1a5a): A soil sample is pretreated to remove organic matter 

and soluble salts. The sample is dried in the oven and weighed to obtain the initial weight. 

Sodium hexametaphosphate solution is added to the sample and then made to 100-mL volume 

with RO water. The sample is subjected to ultrasonic vibration for 5 min. After dispersion with 

the ultrasonic probe, procedure 3A1a1 is followed. 

Water Dispersible PSDA (3A1a6a): Water dispersible particle-size distribution 

analysis may also be determined from a soil suspension without the removal of organic matter 

or soluble salts, or without the use of a chemical dispersant. Upon omitting these procedural 

steps, the remainder of procedure 3A1a1 is followed. 

SSL Field-moist PSDA: For soils that irreversibly harden when dried, moist particlesize analysis (procedure 3A1a1b) may be requested by project coordinator. This procedure 

requires two 10-g samples of <2-mm, moist soil to be pretreated to remove organic matter and 

soluble salts. One sample is dried in the oven to obtain the oven-dry weight, and the other 

sample is further processed as outlined in procedure 3A1a1a. Similar to an air-dry sample, a 

field-moist soil may also be subjected to special pretreatment and dispersion techniques 

37
(3A1a2-6b). Both the air-dry and moist PSDA data are determined as percent of the <2-mm 

fraction on an oven-dry basis.

 

3. Interferences 

Standard SSL PSDA: The sedimentation equation that is used to measure the settling 

rates of particles of different sizes is as follows: 

ν = 2r2g(ρs-ρl)/(9η) 

where: 

ν = Velocity of fall 

r = Particle radius 

g = Acceleration due to gravity 

ρs = Particle density 

ρl = Liquid density 

η = Fluid viscosity 

This formula results from an application of Stokes' law and is referred to as Stokes' law. 

Assumptions used in applying Stokes' law to soil sedimentation measurements are as follows: 

1. Terminal velocity is attained as soon as settling begins. 

2. Settling and resistance are entirely due to the viscosity of the fluid. 

3. Particles are smooth and spherical. 

4. There is no interaction between individual particles in the solution (Gee and Bauder, 1986; 

Gee and Or, 2002). 

Since soil particles are not smooth and spherical, the radius of the particle is considered 

an equivalent rather than an actual radius. In this method, particle density is assumed to be 

2.65 g cc-1. Gypsum interferes with PSDA by causing flocculation of particles. Gypsum is removed 

by stirring and washing the soil with reverse osmosis water. This procedure is effective if the 

soil contains <25% gypsum. 

Partial flocculation may occur in some soils if excess H2O2 is not removed from the soil 

after its use in organic matter oxidation. 

Treatment of micaceous soils with H2O2 causes exfoliation of the mica plates and a 

matting of particles when dried in the oven. Since exfoliation occurs in these soils, a true 

measurement of fractions is uncertain (Drosdoff and Miles, 1938). 

Fine-Clay Determination: In the fine-clay determination, the distance from the center 

of rotation to the surface of the suspension must be constant for each centrifuge bottle. The 

particle density (ρp) of the fine clay is assumed to be 2.5 g cc-1 (Jackson, 1969). The 

suspension temperature must be used to enter the correct liquid viscosity in the equation. 

Position the bottle under pipet without sudden movement of the centrifuge rotor, which causes 

disturbance of solution. The withdrawal rate with pipet should be constant. 

Carbonate-Clay Determination: The carbonate-clay analysis is semi-quantitative. It 

is assumed that all of the carbonates are converted to CO2. This method measures all forms of 

carbonates. In addition to Ca, the carbonates of Mg, Na, and K also react with the acid. 

Analytical interferences may be caused by temperature changes within the reaction vessel. The 

analyst should not touch the glass of the vessel when reading the pressure. When sealing the 

vessel, the analyst should not hold onto the vessel any longer than necessary to tighten the cap. 

The internal pressure must be equalized with the atmosphere. Approximately 3 to 5 s are 

38
required to equalize the internal pressure of the bottle when piercing the septa with a needle. 

The analyst should replace septa and O rings at regular intervals, as they develop leaks after 

extensive use. 

Pretreatment and Dispersion Techniques: The PSDA results are dependent on the 

pretreatments used to disperse the soil. The presence of cementing agents such as carbonates, 

Fe, and Si often prevent complete dispersion. In these cases, special pretreatment and 

dispersion procedures may be performed upon request on either an air-dry or field-moist 

sample. However, these special techniques in themselves may interfere with PSDA as follows: 

Carbonate Removal (3A1a2): The removal of carbonates with 1 N NaOAc (pH 5) 

results in sample acidification. This pretreatment can destroy the primary mineral structure of 

clay (Gee and Bauder, 1986). 

Iron Removal (3A1a3): If the temperature of the water bath exceeds 80° C during Fe 

removal, elemental S can precipitate (Mehra and Jackson, 1960). This pretreatment can destroy 

primary mineral grains in the clay fraction (El-Swaify, 1980). 

Silica Removal (3A1a4): The effects of Si removal with 0.1 N NaOH on the clay 

fraction and particle-size distribution are unknown. 

Ultrasonic Dispersion (3A1a5): Ultrasonic dispersion has been reported to destroy 

primary soil particles. Watson (1971) summarized studies that reported the destruction of 

biotite and breakdown of microaggregates by ultrasonic dispersion. However, Saly (1967) 

reported that ultrasonic vibration did not cause the destruction of the clay crystalline lattice or 

the breakdown of primary grains. The samples ranged from sandy to clayey soils. The 

cementing agents represented humus, carbonates, and hydroxides of Fe and Al. No standard 

procedures have been adopted using ultrasonic dispersion. 

Field-Moist PSDA: Soils that irreversibly harden when dried are difficult to disperse. 

The PSDA for these soils can be determined on moist samples (procedure 3A1a1b) upon the 

request of the project coordinator. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when handling acid and H2O2. Mix acids in ventilated 

fume hoods. Use sodium bicarbonate and water to neutralize and dilute spilled acids. Heat 

samples in ventilated fume hoods for removal of organic matter or cementing agents in 

ventilation hoods. Handle heated samples with leather gloves. Perform the transfer of acid to 

gelatin capsules near a sink in case of leakage or spills. 

Users should be familiar with centrifuge operation. Opposite centrifuge bottles need to 

be balanced. Centrifuge should not be opened until centrifuge rotor has completely stopped 

5. Equipment 

5.1 Fleakers, 300 mL, tared to 1 mg 

5.2 Ceramic filter candles, .3 μm absolute retention (source currently unavailable) 

5.3 Rack to hold ceramic filter candle and sample container. 

5.4 Mechanical shaker, horizontal, 120 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.5 Cylinders, 1 L, white line fused onto glass at 1-L mark 

5.6 Oven, 110°C 

5.7 Hot plate, 100°C 

5.8 Vacuum, 0.8 bars (80kPa) 

5.9 Thermometer, 0 to 150°C 

5.10 Desiccator 

5.11 Motor driven stirrer, (Kilmer and Mullins, 1954) 

5.12 Hand stirrer, perforated disk fastened to a rod 

5.13 Adjustable pipet rack (Shaw, 1932; Fig.1-3) 

5.14 Lowy pipets, 25 mL, with overflow bulb 

5.15 Polyurethane foam, pipe insulation that fits snugly around cylinder. 

39
5.16 Sieve shaker with 12.7-mm (1/2 in) vertical and lateral movement at 500 oscillations min1

. Accommodates a nest of 76-mm (3 in) sieves. 

5.17 Weighing bottles, 90 mL, with screw caps, tared to 1 mg 

5.18 Weighing bottles, 90 mL, tared to 1 mg 

5.19 Weighing bottles, 90 mL, tared to 0.1 mg 

5.20 Drying dishes, aluminum

5.21 Timer or clock with second hand 

5.22 Electronic balance, ±0.10-mg sensitivity 

5.23 Electronic balance, ±1.0-mg sensitivity 

5.24 Watch glass, 50- and 65-mm diameters 

5.25 Evaporating dish, porcelain, 160-mm diameter, 31-mm height, with lip 

5.26 Set of 76-mm (3 in) sieves, square weave phosphor bronze wire cloth except 300 mesh 

which is twilled weave. U.S. series and Tyler Screen Scale equivalent designations are 

as follows: 

Sand Size Opening 

(mm) 

U.S. No. Tyler Mesh 

Size 

VCS 1.0 18 16 

CS 0.5 35 32 

MS 0.25 60 60 

FS 0.105 140 150 

VFS 0.047 300 300 

5.27 Centrifuge, International No. 11, with No. 949 rotor head, International Equip. Co., 

Boston, MA 

5.28 Centrifuge bottle, 500 mL 

5.29 Torsion balance 

5.30 Manometer, hand-held gauge and differential pressure, PCL-200A/C Series, Omega 

Engineering, Stamford, CT. 

5.31 Gelatin capsules, 5 mL 

5.32 Threaded weighing bottles, 90 mL 

5.33 Machined PVC caps for threaded 90-mL weighing bottles, 3.2-cm (1 1/4 in) diameter 

with 1.1-cm (7/16 in) diameter hole drilled in center, O-ring seal 

5.34 O-rings, 3.2 x 38.1 mm (1/8 x 1 1/2 in) 

5.35 Septa, rubber, 7.9-mm (5/16 in) diameter. Place in machined cap. 

5.36 Hypodermic needle, 25.4 mm (1 in), 23 gauge 

5.37 Ultrasonic probe, 19-mm (3/4 in) horn, 20 kHz, 300 watts 

6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

6.2 Hydrogen peroxide (H2O2), 30 to 35% 

6.3 Sodium hexametaphosphate ((NaPO3)6), reagent grade 

6.4 Sodium carbonate (Na2CO3), reagent grade 

6.5 Sodium hexametaphosphate solution. Dissolve 35.7 g of (NaPO3)6 and 7.94 g of Na2CO3

in 1 L of RO water. See Section 7.12 for standardization of sodium hexametaphosphate 

solution. 

6.6 Ethyl alcohol 

6.7 Calcium sulfate (anhydrous) or equivalent desiccant 

6.8 Hydrochloric acid (HCl), 6 N, technical grade. Dilute 1 L of concentrated HCl with 1 L 

of RO water 

6.9 Sodium carbonate (Na2CO3) reagent. Dissolve 10.6 g Na2CO3 in RO water and make to 1 

L (10 mg CaCO3 

40
6.10 1 N sodium acetate (NaOAc) solution, buffered to pH 5. Dissolve 680 g of NaOAc in 4 L 

of RO water. Add ≈ 250 mL of acetic acid. Make to 5-L volume with RO water. 

6.11 Sodium citrate solution, 0.3 M Na3C6H5O7·2H2O (88.4 g L-1) 

6.12 Sodium bicarbonate buffer solution, 1 M NaHCO3 (84 g L-1) 

6.13 Sodium dithionite (Na2S2O4 - hydrosulphite) 

6.14 Saturated NaCl solution (solubility at 20°C; 360 g L-1) 

6.15 Sodium hydroxide solution (NaOH), 0.1 N. Dissolve 4 g NaOH pellets in 1 L of RO 

water. 

7. Procedures 

Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

7.1 If the standard air-dry PSDA procedure for the <2-mm fraction is requested, proceed to 

procedure 3A1a1a. 

7.2 If PSDA is requested on a field-moist sample, proceed to procedure 3A1a1b. 

7.3 If special pretreatment and dispersion techniques (removal of carbonate, Fe, or Si; 

ultrasonic dispersion; or water dispersible) are requested on air-dry soil samples, proceed to 

procedures 3A1a2-6a, respectively. 

7.4 If special pretreatment and dispersion techniques (removal of carbonate, Fe, or Si; 

ultrasonic dispersion; or water dispersible) are requested on field-moist soil samples, proceed 

to procedures 3A1a2-6b, respectively. 

Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Standard Pretreatments and Dispersion (3A1a1) 

Air-Dry (3A1a1a) 

7.5 Weigh 10 g of <2-mm, air-dry soil to nearest mg on an electronic balance and place into a 

numbered, tared 300-mL, fleaker. Wash and tare these fleakers once every two months. A 

quality control sample is included in each batch (<24 samples). 

7.6 Add ≈ 50 mL of RO water and 5 to 7.5 mL of H2O2 to the soil sample at ambient 

temperature. Cover the soil sample with a 50-mm watch glass. Allow initial oxidation of 

organic matter to complete and then place sample on hot plate. If the froth from the reaction 

exceeds the capacity of the fleaker, transfer the sample to a larger beaker. 

7.7 Place the sample on a hot plate and heat to 90°C. Add four 5 to 7.5-mL increments of H2O2

at 30-min intervals. If oxidation is incomplete, add additional H2O2 until organic matter 

oxidation is complete. Heat the sample for an additional 45 min to decompose excess H2O2. If 

the reaction is violent, do one or any combination of the following: (a) add small increments of 

ethyl alcohol to the sample; (b) remove the sample from the hot plate to slow the reaction; (c) 

transfer sample to a 1000-mL beaker; or (d) reduce the amount of H2O2 to sample. Record any 

unusual sample reactions. 

7.8 Place the sample on the filter rack. Add 150 mL of RO water. Insert a filter candle, 

connect to the vacuum trap assembly with tubing, and turn on the vacuum. Aspirate until 

liquid is removed and only slightly dampened sample remains. Wash the sample four 

41
additional times with ≈ 150 mL of RO water. Stir the sample with filter candle to ensure all 

soil particles will be rinsed. During aspiration, it may be necessary to occasionally apply backpressure to filter candle and remove build-up of soil which inhibits aspiration. If the sample 

contains gypsum and flocculates, then the following additional washings may be used. If the 

sample contains 1 to 5% gypsum, stir the sample with a magnetic stirrer for 5 min and wash 5 

times with ≈ 250 mL of RO water each time. If the sample contains >5% gypsum, place the 

sample in a 1000-mL beaker and stir the sample with a magnetic stirrer for 5 min then wash 5 

times with ≈ 750 mL of RO water each time to remove soluble gypsum. 

7.9 Place sample in oven. Dry the sample overnight at 110°C. Remove the sample from the 

oven, place in a desiccator, and cool to ambient temperature. 

7.10 Record the total weight (TW) of the sample to the nearest mg. 

7.11 Add the exact volume of sodium hexametaphosphate solution (≈ 10 mL), equivalent to 

0.4408 g of sodium hexametaphosphate, to each sample. Subtract the weight of the sodium 

hexametaphosphate (DW) that is contained in the extracted aliquot from the silt and clay 

weights to calculate silt and clay percentages. To determine the exact volume of sodium 

hexametaphosphate to add to each sample, refer to Section 7.12. Let stand until sample is 

completely moistened by sodium hexametaphosphate. Add ≈ 175 mL of RO water. 

7.12 A sodium hexametaphosphate standardization is performed with each new batch of 

solution. Use only designated weighing bottles for standardization. Wash and tare these 

bottles after each standardization. Add duplicate aliquots (8.5, 9.0, 9.3, 9.6, 10.0, 10.3, 10.6, 

11.0 mL) of sodium hexametaphosphate solution to numbered tared, 90-mL weighing bottles. 

Oven-dry aliquots overnight and record dry residue weight of sodium hexametaphosphate. 

Determine the exact volume of sodium hexametaphosphate to add to each sample by regressing 

the volume of sodium hexametaphosphate against the dry residue weight of sodium 

hexametaphosphate and then by predicting the volume needed to dispense 0.4408 g of sodium 

hexametaphosphate into each sample. 

7.13 Place the sample in a horizontal shaker set at 120 oscillations min-1 and shake for 15 h 

(overnight). 

7.14 Remove the sample from the shaker and pour through a 300-mesh (0.047-mm) sieve 

mounted on a ring stand. Finger-rubbing of sample may be required during transfer to speed 

washing of sample. Place a funnel below the sieve and a 1-L cylinder below the funnel. Collect 

the silt and clay in the 1-L cylinder. Avoid using jets of water in washing the sample. Wash 

and rub all particles from the fleaker into the sieve. Continue to wash until the suspension 

volume in the cylinder is ≈ 800 mL. Sand and some of the coarse silt remain on the sieve. 

Rinse all <20-μm particles into the cylinder. Fill the cylinder to 1 L and cover with a 65-mm 

watch glass. Place pipe insulation around sample and blank cylinders to prevent rapid changes 

in temperatures. Prepare a RO water blank to measure temperature fluctuations. Allow the 

cylinder to stand overnight to equilibrate the suspension with the room temperature. Wash the 

sand into an evaporation dish and dry the sand at 110°C overnight. 

7.15 Transfer the dried sand to a nest of sieves that has a top-to-bottom order of 1.0, 0.5, 0.25, 

0.1, and 0.047 mm. Shake the sand for 3 min on a shaker that has 1.3-cm vertical and lateral 

movements and oscillates at 500 strokes min-1. Record the weight of each separate sand 

fraction (SWi) to the nearest mg. If optical analysis is requested, place the very fine sand and 

fine sand fractions in gelatin capsules and the remaining sand fractions in a labeled vial. Store 

capsules in the labeled vial. Wash sand dishes after every use. 

42
7.16 Determine the percentage of fine silt and clay gravimetrically by removing an aliquot from 

the suspension in the 1-L cylinder with a Lowy, 25-mL pipet. Periodically, gravimetrically 

calibrate the delivery volume of the pipet by weighing the amount of RO water dispensed from 

the pipet. Record the delivery volume (DV) and use the value to calculate the results. 

Regulate the vacuum such that the pipet fills in ≈12 s. Record temperature (T1) of blank. 

Mount the pipet on an adjustable pipet rack (Shaw, 1932). Stir the silt and clay suspension 

with mechanical stirrer for at least 5 min. Place the cylinder on a stable, vibrationless table and 

stir with a hand stirrer in an up-and-down motion for 30 s. Timing is started upon completion 

of the stirring. Record the time that stirring is stopped. For the <20-μm fraction, slowly lower 

the closed pipet to a 10-cm depth in the suspension, turn on the vacuum, and withdraw an 

aliquot at the calculated time (Table 1). Dispense the aliquot into a tared and numbered, 90-mL 

weighing bottle. Rinse the pipet twice with RO water and dispense into the tared, weighing 

bottle with the aliquot. For the <2-μm fraction, pipet after a time of 4.5, 5, 5.5, or 6.5 h. 

Record temperature (T2) of blank. Use the average of T1 and T2 and adjust the pipet depth in 

the suspension as indicated in Table 2. Repeat the procedure described for the <20-μm 

fraction. If determination of carbonate is required, use weighing bottle with screw threads. 

Dry the aliquots at 110°C overnight and cool in a desiccator that contains calcium sulfate or an 

equivalent desiccant. Record the weight of the residue (RW) to the nearest 0.1mg. 

 

7.17 Use the 90-mL, round-bottomed, weighing bottles for the <20-μm aliquots. 

Wash and tare after every fourth use. Use the 90-mL, square-bottomed, weighing bottles for 

the <2-μm aliquots. Wash and tare after every use. 

7.18 If optical mineralogy, fine-clay and/or carbonate clay determinations are not requested, 

the procedural aspects of the standard air-dry PSDA for the <2-mm fraction are complete. If 

optical mineralogy is requested, save the sediment and proceed on with the section on optical 

mineralogy. If fine-clay and/or carbonate clay are requested, proceed on with the sections on 

these analyses. . 

Optical Mineralogy 

7.19 If optical mineralogy is requested, decant the suspension and transfer the sediment to a 

400-mL beaker. Fill the beaker to a 5.5-cm height. Stir the sediment and allow to settle for 

5 min. Discard the supernatant. Refill the beaker to 5.5-cm height. Stir again, allow to settle 

for 3 min, and then decant. Repeat the filling and the stirring; allow to settle for 2 min; and 

then decant until top half of suspension is clear. Transfer the sediment, which is dominantly 20 

to 50μm, to a labeled drying dish. Wash with ethanol, air-dry, and save in the drying dish for 

optical mineralogy. 

Fine Clay Determination (<0.2 μm) 

7.20 Stir the silt and clay suspension with mechanical stirrer for 5 min. Remove sample from 

mechanical stirrer and place on table. Stir with the hand stirrer in an up-and-down motion for 

30 s and allow the suspension to settle for 15 min. 

7.21 Pour the suspension into a centrifuge bottle and fill to the line marked on the bottle. The 

marked line on each bottle is 13 cm which is the distance from the center of rotation to the 

surface of the suspension. Stopper and shake well to mix the suspension. 

7.22 Balance opposite centrifuge loads, which consist of centrifuge bottle, trunnion carrier and 

bucket. Place loads on a torsion balance and add water to the lighter bucket until both loads 

weigh the same. 

7.23 Read the temperature of the suspension. 

7.24 Centrifuge at 1500 rpm. 

43
7.24.1 For procedures3A1a1-5a and 3A1a1-5b, vary the centrifuge time according to the 

temperature as follows: 

Temp 

(°C) 

Viscosity 

η

Delta-Density 

∆ρ

Time 

Min 

18 0.01055 1.501 39.0 

19 0.01029 1.501 38.0 

20 0.01004 1.502 37.1 

21 0.00980 1.502 36.2 

22 0.00957 1.502 35.3 

23 0.00934 1.502 34.5 

24 0.00913 1.502 33.7 

25 0.00892 1.503 32.9 

26 0.00872 1.503 32.2 

27 0.00853 1.503 31.4 

28 0.00834 1.503 30.8 

29 0.00816 1.504 30.1 

30 0.00799 1.504 29.4 

7.24.2 For procedures, 3A1a6a and 3A1a6b, vary the centrifuge time according to the 

temperature as follows: 

Temp 

(°C) 

Viscosity 

η

Delta-Density 

∆ρ

Time 

Min 

18 0.01053 1.501 38.9 

19 0.01028 1.502 37.9 

20 0.01002 1.502 37.0 

21 0.00978 1.502 36.1 

22 0.00955 1.502 35.2 

23 0.00933 1.502 34.4 

24 0.00911 1.503 33.6 

25 0.00890 1.503 32.8 

26 0.00871 1.503 32.1 

27 0.00851 1.503 31.4 

28 0.00833 1.504 30.7 

29 0.00815 1.504 30.0 

30 0.00798 1.504 29.4 

where: 

s = 15 cm 

r = 18 cm 

Nm = 1500 rpm 

ρp = 2.5 g cc-1

7.25 After centrifuging, lower the pipet to a 3-cm depth in the suspension. Withdraw a 25-mL 

aliquot at a rate of ≈ 12 s. Avoid turbulence. Transfer the aliquot to a weighing bottle 

44
7.26 Place weighing bottle with aliquot in oven. Dry overnight at 110°C. Remove sample 

from oven, place in desiccator with calcium sulfate or equivalent desiccant, and cool to ambient 

temperature. 

7.27 Weigh residue weight (RW) to nearest 0.1 mg. 

7.28 Use the 90-mL, round-bottomed, weighing bottles for the <0.2μm aliquots. Wash and tare 

after every fourth use. 

Carbonate Clay (<2 μm): Manometer Calibration 

7.29 Calibrate the manometer quarterly or whenever equipment changes. Calibrate by placing 

replicated aliquots of 0.0 to 20.0 mL of the Na2CO3 reagent into numbered, tared, 90-mL 

weighing bottles. Dry the standard samples in the oven overnight at 110°C. Remove samples 

from oven, place in desiccator and cool to ambient temperature. Record the weight of the 

standard samples to nearest 0.1mg. 

7.30 Lubricate the lip of the 90-mL, weighing bottle that contains the Na2CO3 with a thin film 

of glycerine. Dispense 3 mL of 6 N HCl into a gelatin capsule and place the top on the capsule. 

If HCl leaks from the capsule, discard the capsule. Place the capsule into the glass bottle and 

immediately cap the bottle. Release pressure in the bottle by piercing the septa with a 

hypodermic needle which is not connected to the manometer. Allow 3 to 5 s for internal 

pressure in bottle to equalize. 

7.31 After the gelatin capsule has dissolved (several minutes), slowly tip the bottle and rotate it 

to saturate the standard sample adhering to the sides of the bottle. Avoid changing the 

temperature of the container by only handling the cap. Allow sample to stand for at least 30 

min. 

7.32 Adjust the manometer to zero before taking measurements. Insert the hypodermic needle 

in the septa stopper which is connected to the transducer. Measure the pressure inside the 

weighing bottle. Record the manometer readings (mm Hg) to the nearest whole number. 

7.33 Calculate the linear regression equation, i.e., the dependent variable is the Na2CO3 weights 

(regressed or predicted values) and the independent variable is the corresponding manometer 

readings. 

Carbonate Clay: Analysis

7.34 Determine the presence of carbonates in <2-mm soil by placing soil on a spot plate and 

adding two or three drops of 1 N HCl. The rate of CO2 evolution indicates the relative amount 

of carbonates (1B1b2b5). 

7.35 If the soil contains more than a “slight” amount of carbonates, determine the amount of 

carbonate clay in the <2-μm dry residue. Use the 90-mL, square-bottomed, weighing bottles for 

the <2-μm aliquots and carbonate determination. Wash and tare after every use. 

7.36 With a thin film of glycerine, lubricate the lip of the 90-mL, weighing bottle that contains 

the <2-μm residue. In each analysis batch, include an empty weighing bottle as a blank. 

Dispense 3 mL of 6 N HCl into a gelatin capsule and place the top on the capsule. If HCl leaks 

from the capsule, discard the capsule. Place the capsule into the glass bottle and immediately 

cap the bottle. Release any pressure in the bottle by piercing the septa with a hypodermic 

needle that is not connected to the manometer. Approximately 3 to 5 s are required to equalize 

the internal pressure of the bottle. 

45
7.37 After the gelatin capsule has dissolved (several minutes), slowly tip the bottle and rotate it 

to saturate the clay adhering to the sides of the bottle. Handle only the cap to avoid changing 

the temperature of the container. Allow sample to stand for at least 30 min. 

7.38 Adjust the manometer to zero before taking measurements. Insert the hypodermic needle 

in septa stopper which is connected to the transducer. Measure the pressure inside the 

weighing bottle and record the manometer readings (MR) to the nearest whole number (mm 

Hg). Begin readings with the blank (BR). 

7.39 Compare the sample readings with those of a standard curve prepared by measuring CO2

evolved from a series of Na2CO3 aliquots with a range 0 to 200 mg. 

Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Carbonate Removal (3A1a2) 

Air-Dry (3A1a2a) 

7.40 Weigh sufficient sample to yield 10 g of <2-mm, air-dry carbonate-free soil sample, e.g. if 

the sample contains 50% carbonates, weigh 20 g of soil. Place the <2-mm, air-dry sample into 

a 300-mL, tared, fleaker. 

7.41 Add ≈ 200 mL of the 1 N NaOAc solution to the sample, mix with a stirring rod, and 

cover with a watch glass. Allow the sample to stand overnight. 

7.42 Place the sample on the hot plate and heat to ≈ 90°C until bubbles are no longer evident. 

Do not boil. Heating accelerates reaction. Decant the solution and add more 1 N NaOAc 

solution. If a reaction occurs, repeat the heating procedure. Continue to decant, add NaOAc 

solution, and heat until all the carbonates are removed. The speed of dissolution can be 

increased by lowering the pH of the 1 N NaOAc solution (Rabenhorst and Wilding, 1984). 

7.43 When no more carbonate bubbles are observed, insert the ceramic filter candle into the 

solution. Apply vacuum and candle the sample to dryness. Rinse once with 200 mL of RO 

water. Proceed to procedure 3A1a1a for remaining PSDA procedural steps. 

Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Iron Removal (3A1a3) 

Air-Dry (3A1a3a) 

7.44 A maximum of ≈ 0.5 g of Fe2O3 can be dissolved in 40 mL of the citrate solution. Adjust 

the weight of the <2-mm, air-dry soil sample so that any one fleaker does not contain more than 

0.5 g of Fe2O3. Split the sample into different fleakers if necessary. Total sample weight after 

dissolution should be ≈ 10 g. Place the sample into a tared, labeled, 300-mL fleaker. 

7.45 Add ≈ 50 mL of RO water and 5 mL of H2O2 to the soil sample at ambient temperature. 

Cover the soil sample with a 50-mm watch glass. Allow initial oxidation of organic matter to 

complete, and then place sample on hot plate. If the froth from the reaction exceeds the 

capacity of the fleaker, transfer the sample to a larger beaker. 

7.46 Place the sample on a hot plate and heat to 90°C. Add 5-mL increments of H2O2 at 45-

min intervals until oxidation has completed or until 30 mL of H2O2 have been added. Heat the 

sample for an additional 45 min to decompose excess H2O2. If the reaction is violent, add 

46
small increments of ethyl alcohol to the sample or remove the sample from the hot plate to slow 

the reaction. 

7.47 Add 40 mL of the citrate solution and 5 mL of the sodium bicarbonate. Heat to 80°C in a 

water bath, but do not exceed 80°C. Add 1 g of sodium dithionite powder with a calibrated 

scoop. Stir constantly with a glass rod for 1 min and then occasionally for 15 min. Add 10 mL 

of saturated NaCl solution and mix. 

7.48 Centrifuge or candle the sample to remove the dissolved Fe2O3. Combine the split 

samples into fewer fleakers. 

7.49 If the sample contains less than 0.5 g of Fe2O3, repeat the dissolution treatment. For 

samples with more than 0.5 g of Fe2O3, repeat the dissolution treatment two more times. Upon 

completion of Fe removal, proceed to procedure 3A1a1a for remaining PSDA procedural steps. 

Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Silica Removal (3A1a4) 

Air-Dry (3A1a4a) 

7.50 Weigh 10 g of <2-mm, air-dry soil to nearest mg on an electronic balance and place in a 

300-mL, tared fleaker. 

7.51 Add ≈ 50 mL of RO water and 5 mL of H2O2 to soil sample at ambient temperature. 

Cover the soil sample with 50-mm watch glass. Allow initial oxidation of organic matter to 

complete, and then place sample on hot plate. If the froth from the reaction exceeds the 

capacity of the fleaker, transfer the sample to a larger beaker. 

7.52 Place the sample on a hot plate and heat to 90°C. Add 5-mL increments of H2O2 at 45-

min intervals until oxidation has completed or until 30 mL of H2O2 have been added. Heat the 

sample for an additional 45 min to decompose excess H2O2. If the reaction is violent, add 

small increments of ethyl alcohol to the sample or remove the sample from the hot plate to slow 

the reaction. 

7.53 Soak the sample overnight in 100 mL of 0.1 N NaOH. Upon removal of siliceous 

cementing agents, proceed to procedure 3A1a1a for remaining PSDA procedural steps. 

Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Ultrasonic Dispersion (3A1a5) 

Air-Dry (3A1a5a) 

7.54 Weigh 10 g of <2-mm, air-dry soil to nearest mg on an electronic balance and place into a 

numbered, tared, 300-mL, fleaker. Wash and tare these fleakers once every two months. A 

quality control sample is included in each batch (<24 samples). 

7.55 Add ≈ 50 mL of RO water and 7.5 mL of H2O2 to the soil sample at ambient temperature. 

Cover the soil sample with a 50-mm watch glass. Allow initial oxidation of organic matter to 

complete and then place sample on hot plate. If the froth from the reaction exceeds the 

capacity of the fleaker, transfer the sample to a larger beaker. 

47
7.56 Place the sample on a hot plate and heat to 90°C. Add four 5 to 7.5-mL increments of 

H2O2 at 30-min intervals. If oxidation is incomplete, add additional H2O2 until organic matter 

oxidation is complete. Heat the sample for an additional 45 min to decompose excess H2O2. If 

the reaction is violent, do one or any combination of the following: (a) add small increments of 

ethyl alcohol to the sample; (b) remove the sample from the hot plate to slow the reaction; (c) 

transfer sample to a 1000-mL beaker; or (d) reduce the amount of H2O2 to sample. Record any 

unusual sample reactions. Record any unusual sample reactions. 

7.57 Place the sample on the filter rack. Add 150 mL of RO water. Insert a filter candle, 

connect to the vacuum trap assembly with tubing, and turn on the vacuum. Aspirate until 

liquid is removed and only slightly dampened sample remains. Wash the sample four 

additional times with ≈ 150 mL of RO water. Stir the sample with filter candle to ensure all 

soil particles will be rinsed. During aspiration, it may be necessary to occasionally apply backpressure to filter candle and remove build-up of soil which inhibits aspiration. If the sample 

contains gypsum and flocculates, then the following additional washings may be used. If the 

sample contains 1 to 5% gypsum, stir the sample with a magnetic stirrer for 5 min and wash 5 

times with ≈ 250 mL of RO water each time. If the sample contains >5% gypsum, place the 

sample in a 1000-mL beaker and stir the sample with a magnetic stirrer for 5 min then wash 5 

times with ≈ 750 mL of RO water each time to remove soluble gypsum. 

7.58 Place sample in oven. Dry the sample overnight at 110°C. Remove the sample from the 

oven, place in a desiccator, and cool to ambient temperature. 

7.59 Record the total weight (TW) of the sample to the nearest mg. 

7.60 Add ≈ 100 mL of RO water and the exact volume of sodium hexametaphosphate solution 

(≈ 10 mL), equivalent to 0.4408 g of sodium hexametaphosphate, to sample. Subtract the 

weight of the sodium hexametaphosphate (DW) that is contained in the extracted aliquot from 

the silt and clay weights to calculate silt and clay percentages. To determine the exact volume 

of sodium hexametaphosphate to add to each sample, refer to Section 7.61. 

7.61 A sodium hexametaphosphate standardization is performed with each new batch of 

solution. Use only designated weighing bottles for standardization. Wash and tare these bottles 

after each standardization. Add duplicate aliquots (8.5, 9.0, 9.3, 9.6, 10.0, 10.3, 10.6, 11.0 mL) 

of sodium hexametaphosphate solution to numbered tared, 90-mL weighing bottles. Oven-dry 

aliquots overnight and record dry residue weight of sodium hexametaphosphate. Determine the 

exact volume of sodium hexametaphosphate to add to each sample by regressing the volume of 

sodium hexametaphosphate against the dry residue weight of sodium hexametaphosphate and 

then by predicting the volume needed to dispense 0.4408 g of sodium hexametaphosphate into 

each sample. 

7.62 Disperse the suspension with ultrasonic vibrations. Ensure the power supply is properly 

tuned. Consult the instruction manual. Immerse the probe in the suspension to a 3-cm depth. 

Set timer to 5 min. Press start button. Adjust output control as required. Between samples, 

clean the probe by placing it in water or alcohol and energizing it for a few seconds. 

7.63 After ultrasonic dispersion, add ≈ 75 mL RO water and pour the suspension through a 

300-mesh (0.047-mm) sieve mounted on a ring stand. Finger-rubbing of sample may be 

required during transfer to speed washing of sample. Place a funnel below the sieve and a 1-L 

cylinder below the funnel. Collect the silt and clay in the 1-L cylinder. Avoid using jets of 

water in washing the sample. Wash and rub all particles from the fleaker into the sieve. 

Continue to wash until the suspension volume in the cylinder is ≈ 800 mL. Sand and some of 

the coarse silt remain on the sieve. Rinse all <20-μm particles into the cylinder. Fill the 

cylinder to 1 L and cover with a 65-mm watch glass. Place pipe insulation around sample and 

48
blank cylinders to prevent rapid changes in temperatures. Prepare a RO water blank to measure 

temperature fluctuations. Allow the cylinder to stand overnight to equilibrate the suspension 

with the room temperature. Wash the sand into an evaporation dish and dry the sand at 110°C 

overnight. Proceed to procedure 3A1a1a for remaining PSDA procedural steps. 

Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Water Dispersion (3A1a6) 

Air-Dry (3A1a6a) 

7.64 Weigh 10 g of <2-mm, air-dry soil to nearest mg on an electronic balance and place into a 

numbered, tared 300-mL, fleaker. Wash and tare these fleakers once every two months. A 

quality control sample is included in each batch (<24 samples). 

7.65 Dry the sample in an oven at 110°C overnight. Remove the sample from the oven, place 

in a desiccator, and cool to ambient temperature. 

7.66 Record the total weight (TW) of the sample to the nearest mg. 

7.67 Add ≈ 175 mL of RO water to sample. Place the sample in a horizontal shaker set at 120 

oscillations min-1 and shake for 15 h (overnight). 

7.68 Remove the sample from the shaker and pour through a 300-mesh (0.047-mm) sieve 

mounted on a ring stand. Finger-rubbing of sample may be required during transfer to speed 

washing of sample. Place a funnel below the sieve and a 1-L cylinder below the funnel. Collect 

the silt and clay in the 1-L cylinder. Avoid using jets of water in washing the sample. Wash 

and rub all particles from the fleaker into the sieve. Continue to wash until the suspension 

volume in the cylinder is ≈ 800 mL. Sand and some of the coarse silt remain on the sieve. 

Rinse all <20-μm particles into the cylinder. Fill the cylinder to 1 L and cover with a 65-mm 

watch glass. Place pipe insulation around sample and blank cylinders to prevent rapid changes 

in temperatures. Prepare a RO water blank to measure temperature fluctuations. Allow the 

cylinder to stand overnight to equilibrate the suspension with the room temperature. Wash the 

sand into an evaporation dish and dry the sand at 110°C overnight. 

7.69 Transfer the dried sand to a nest of sieves that has a top-to-bottom order of 1.0, 0.5, 0.25, 

0.1, and 0.047 mm. Shake the sand for 3 min on a shaker that has 1.3-cm vertical and lateral 

movements and oscillates at 500 strokes min-1. Record the weight of each separate sand 

fraction (SWi) to the nearest mg. If optical analysis is requested, place the very fine sand and 

fine sand fractions in gelatin capsules and the remaining sand fractions in a labeled vial. Store 

capsules in the labeled vial. Wash sand dishes after every use. 

7.70 Determine the percentage of fine silt and clay gravimetrically by removing an aliquot from 

the suspension in the 1-L cylinder with a Lowy, 25-mL pipet. Periodically, gravimetrically 

calibrate the delivery volume of the pipet by weighing the amount of RO water dispensed from 

the pipet. Record the delivery volume (DV) and use the value to calculate the results. 

Regulate the vacuum such that the pipet fills in ≈ 12 s. Record temperature (T1) of blank. 

Mount the pipet on an adjustable pipet rack (Shaw, 1932). Stir the silt and clay suspension 

with mechanical stirrer for at least 5 min. Place the cylinder on a stable, vibrationless table 

and stir with a hand stirrer in an up-and-down motion for 30 s. Timing is started upon 

completion of the stirring. Record the time that stirring is stopped. For the <20-μm fraction, 

slowly lower the closed pipet to a 10-cm depth in the suspension, open the pipet, turn on the 

vacuum, and withdraw an aliquot at the calculated time (Table 3). Dispense the aliquot into a 

tared and numbered, 90-mL weighing bottle. Rinse the pipet twice with RO water and dispense 

49
into the tared, weighing bottle with aliquot. For the <2-μm fraction, pipet after a time of 4.5, 5, 

5.5, or 6.5 h. Record temperature (T2) of blank. Use the average of T1 and T2 and adjust the 

pipet depth in the suspension as indicated in Table 4. Repeat the procedure described for the 

<20-μm fraction. Dry the aliquots at 110°C overnight and cool in a desiccator that contains 

calcium sulfate or an equivalent desiccant. Record the residue weight (RW) to the nearest 0.1 

mg. Proceed to procedure 3A1a1a for remaining PSDA procedural steps. 

Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Standard Pretreatments and Dispersion (3A1a1) 

Field-Moist (3A1a1b) 

7.71 Weigh enough <2mm, moist soil to achieve two ≈ 10-g samples of air-dry soil. Weigh to 

nearest mg on an electronic balance and place into numbered, tared, 300-mL, tared fleakers. 

Wash and tare these fleakers once every two months. A quality control sample is included in 

each batch (<24 samples). 

7.72 Add ≈ 50 mL of RO water and 7.5 mL of H2O2 to both soil sub-samples at ambient 

temperature. Cover the soil samples with a 50-mm watch glass. Allow initial oxidation of 

organic matter to complete and then place sample on hot plate. If the froth from the reaction 

exceeds the capacity of the fleaker, transfer the sample to a larger beaker. 

7.73 Place the samples on a hot plate and heat to 90°C. Add four 5 to 7.5-mL increments of 

H2O2 at 30-min intervals. If oxidation is incomplete, add additional H2O2 until organic matter 

oxidation is complete. Heat the sample for an additional 45 min to decompose excess H2O2. If 

the reaction is violent, do one or any combination of the following: (a) add small increments of 

ethyl alcohol to the sample; (b) remove the sample from the hot plate to slow the reaction; (c) 

transfer sample to a 1000-mL beaker; or (d) reduce the amount of H2O2 to sample. Record any 

unusual sample reactions. 

7.74 Place the sample on the filter rack. Add 150 mL of RO water. Insert a filter candle, 

connect to the vacuum trap assembly with tubing, and turn on the vacuum. Aspirate until 

liquid is removed and only slightly dampened sample remains. Wash the sample four 

additional times with ≈ 150 mL of RO water. Stir the sample with filter candle to ensure all 

soil particles will be rinsed. During aspiration, it may be necessary to occasionally apply backpressure to filter candle and remove build-up of soil which inhibits aspiration. If the sample 

contains gypsum and flocculates, then the following additional washings may be used. If the 

sample contains 1 to 5% gypsum, stir the sample with a magnetic stirrer for 5 min and wash 5 

times with ≈ 250 mL of RO water each time. If the sample contains >5% gypsum, place the 

sample in a 1000-mL beaker and stir the sample with a magnetic stirrer for 5 min then wash 5 

times with ≈ 750 mL of RO water each time to remove soluble gypsum. 

7.75 Place one of the samples in the oven and dry overnight at 110°C. Remove the sample 

from the oven, place in a desiccator, and cool to ambient temperature. 

7.76 Record the total weight (TW) of the H2O2-treated, oven-dry sample to the nearest mg. 

The H202-treated, oven-dry sample is not used in the remaining PSDA procedural steps. 

Proceed to procedure 3A1a1a and use the H2O2-treated sample that was not dried in oven for 

remaining PSDA procedural steps. 

50
Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Carbonate Removal (3A1a2) 

Field-Moist (3A1a2b) 

7.77 Weigh two 10-g samples of <2-mm, moist soil to nearest mg on an electronic balance and 

place into 300-mL, tared fleakers. Weigh sufficient samples to yield 10 g of <2-mm, moist, 

carbonate-free soil sample, e.g., if the sample contains 50% carbonates, weigh 20 g of soil. 

7.78 Add ≈ 200 mL of the 1 N NaOAc solution to both samples, mix with a stirring rod, and 

cover with a watch glass. Allow the samples to stand overnight. 

7.79 Place the samples on the hot plate and heat to ≈ 90°C until bubbles are no longer evident. 

Do not boil. Heating accelerates reaction. Decant the solution and add more 1 N NaOAc 

solution. If a reaction occurs, repeat the heating procedure. Continue to decant, add NaOAc 

solution, and heat until all the carbonates are removed. The speed of dissolution can be 

increased by lowering the pH of the 1 N NaOAc solution (Rabenhorst and Wilding, 1984). 

7.80 When no more carbonate bubbles are observed, insert the ceramic filter candle into the 

solution. Apply vacuum and candle the samples to dryness. Rinse once with 200 mL of RO 

water. 

7.81 Add ≈ 50 mL of RO water and 5 mL of H2O2 to both soil samples at ambient temperature. 

Cover the soil samples with 50-mm watch glass. Allow initial oxidation of organic matter to 

complete and then place samples on hot plate. If the froth from the reaction exceeds the 

capacity of the fleakers, transfer the samples to larger beakers. 

7.82 Place the samples on the hot plate and heat to ≈ 90°C. Add 5-mL increments of H2O2 at 

45-min intervals until oxidation has completed or until 30 mL of H2O2 have been added. Heat 

the sampled for an additional 45 min to decompose excess H2O2. If the reaction is violent, add 

small increments of ethyl alcohol to the samples or remove the samples from the hot plate to 

slow the reaction. 

7.83 Place the samples on the filter rack. Add 150 mL of RO water. Insert filter candle, 

connect to the vacuum trap assembly with tubing, and turn on vacuum. Wash the samples four 

additional times with ≈ 150 mL of RO water. If the samples contain gypsum and flocculates, 

then the following additional washings may be used. If the samples contain 1 to 5% gypsum, 

stir the samples with a magnetic stirrer for 5 min and wash 5 times with ≈ 250 mL of RO water 

each time. If the samples contain >5% gypsum, stir the samples with a magnetic stirrer for 5 

min then wash 5 times with ≈ 750 mL of RO water each time to remove soluble gypsum. 

7.84 Place one of the samples in the oven and dry overnight at 110°C. Remove the sample 

from the oven, place in a desiccator, and cool to ambient temperature. 

7.85 Record the total weight (TW) of the H2O2-treated, oven-dry sample to the nearest mg. 

The H2O2-treated, oven-dry sample is not used in the remaining PSDA procedural steps. 

Proceed to procedure 3A1a1a and use the H2O2-treated sample that was not dried in oven for 

remaining PSDA procedural steps. 

51
Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Iron Removal (3A1a3) 

Field-Moist (3A1a3b) 

7.86 Weigh two 10-g samples of <2-mm, moist soil to nearest mg on an electronic balance and 

place into 300-mL, tared fleakers. As a maximum of ≈ 0.5 g of Fe2O3 can be dissolved in 40 

mL of the citrate solution, adjust the weight of the <2-mm, moist soil sample so that any one 

fleaker does not contain more than 0.5 g of Fe2O3. Split the sample into different fleakers if 

necessary. Total sample weight after dissolution should be ≈ 10 g. 

7.87 Add ≈ 50 mL of RO water and 5 mL of H2O2 to both soil samples at ambient temperature. 

Cover the soil samples with 50-mm watch glass. Allow initial oxidation of organic matter to 

complete, and then place samples on hot plate. If the froth from the reaction exceeds the 

capacity of the fleaker, transfer the samples to larger beakers. 

7.88 Place the samples on a hot plate and heat to 90°C. Add 5-mL increments of H2O2 at 45-

min intervals until oxidation has complete or until 30 mL of H2O2 have been added. Heat the 

samples for an additional 45 min to decompose excess H2O2. If the reaction is violent, add 

small increments of ethyl alcohol to the samples or remove the samples from the hot plate to 

slow the reaction. 

7.89 Add 40 mL of the citrate solution and 5 mL of the sodium bicarbonate. Heat to 80°C in a 

water bath, but do not exceed 80°C. Add 1 g of sodium dithionite powder with a calibrated 

scoop. Stir constantly with a glass rod for 1 min and then occasionally for 15 min. Add 10 mL 

of saturated NaCl solution and mix. 

7.90 Centrifuge or candle the samples to remove the dissolved Fe2O3. Combine the split 

samples into fewer fleakers. 

7.91 If the samples contain less than 0.5 g of Fe2O3, repeat the dissolution treatment. For 

samples with more than 0.5 g of Fe2O3, repeat the dissolution treatment two more times. 

7.92 Place the samples on the filter rack. Add 150 mL of RO water. Insert a filter candle, 

connect to the vacuum trap assembly with tubing, and turn on the vacuum. Wash the samples 

four additional times with ≈ 150 mL of RO water. If the samples contain gypsum and 

flocculates, then the following additional washings may be used. If the sample contains 1 to 

5% gypsum, stir the sample with a magnetic stirrer for 5 min and wash 5 times with ≈ 250 mL 

of RO water each time. If the sample contains >5% gypsum, stir the sample with a magnetic 

stirrer for 5 min then wash 5 times with ≈ 750 mL of RO water each time to remove soluble 

gypsum. 

7.93 Place one sample in the oven and dry overnight at 110°C. Remove the sample from the 

oven, place in a desiccator, and cool to ambient temperature. 

7.94 Record the total weight (TW) of the sample to the nearest mg. The H2O2 oven-dry sample 

is not used in the remaining PSA procedural steps. Proceed to procedure 3A1a1a and use the 

H2O2-treated sample that was not dried in oven for remaining PSDA procedural steps. 

52
Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Silica Removal (3A1a4) 

Field-Moist (3A1a4b) 

7.95 Weigh two 10-g of <2-mm, moist soil to nearest mg on an electronic balance and place in 

300-mL, tared fleakers. 

7.96 Add ≈ 50 mL of RO water and 5 mL of H2O2 to both soil samples at ambient temperature. 

Cover the soil samples with 50-mm watch glass. Allow initial oxidation of organic matter to 

complete, and then place samples on hot plate. If the froth from the reaction exceeds the 

capacity of the fleaker, transfer the sample to larger beakers. 

7.97 Place the samples on a hot plate and heat to 90°C. Add 5-mL increments of H2O2 at 45-

min intervals until oxidation has completed or until 30 mL of H2O2 have been added. Heat the 

samples for an additional 45 min to decompose excess H2O2. If the reaction is violent, add 

small increments of ethyl alcohol to the samples or remove the samples from the hot plate to 

slow the reaction. 

7.98 Soak the samples overnight in 100 mL of 0.1 N NaOH. 

7.99 Place the samples on the filter rack. Add 150 mL of RO water. Insert filter candle, 

connect to the vacuum trap assembly with tubing, and turn on the vacuum. Wash the samples 

four additional times with ≈ 150 mL of RO water. If the sample contains gypsum and 

flocculates, then the following additional washings may be used. If the samples contain 1 to 

5% gypsum, stir the samples with a magnetic stirrer for 5 min and wash 5 times with ≈ 250 mL 

of RO water each time. If the samples contain >5% gypsum, stir the sample with a magnetic 

stirrer for 5 min then wash 5 times with ≈ 750 mL of RO water each time to remove soluble 

gypsum. 

7.100 Place one sample in the oven and dry overnight at 110°C. Remove the sample from the 

oven, place in a desiccator, and cool to ambient temperature. 

7.101 Record the total weight (TW) of the sample to the nearest mg. The H2O2-treated, ovendry sample is only used for calculation of results and is not used in the remaining PSDA 

procedural steps. Proceed to procedure 3A1a1a and use the H2O2-treated sample that was not 

dried in oven for all of the remaining PSDA procedural steps. 

Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Ultrasonic Dispersion (3A1a5) 

Field-Moist (3A1a5b) 

7.102 Weigh enough <2mm, moist soil to achieve two ≈ 10-g samples of air-dry soil. Weigh to 

nearest mg on an electronic balance and place into numbered, tared, 300-mL, tared fleakers. 

Wash and tare these fleakers once every two months. A quality control sample is included in 

each batch (<24 samples). 

 

7.103 Add ≈ 50 mL of RO water and 7.5 mL of H2O2 to the soil samples at ambient 

temperature. Cover the soil samples with 50-mm watch glass. Allow initial oxidation of 

organic matter to complete and then place samples on hot plate. If the froth from the reaction 

exceeds the capacity of the fleaker, transfer the samples to a larger beaker. 

53
7.104 Place the samples on a hot plate and heat to 90°C. Add four 5 to 7.5-mL increments of 

H2O2 at 30-min intervals. If oxidation is incomplete, add additional H2O2 until organic matter 

oxidation is complete. Heat the sample for an additional 45 min to decompose excess H2O2. If 

the reaction is violent, do one or any combination of the following: (a) add small increments of 

ethyl alcohol to the sample; (b) remove the sample from the hot plate to slow the reaction; (c) 

transfer sample to a 1000-mL beaker; or (d) reduce the amount of H2O2 to sample. Record any 

unusual sample reactions. 

7.105 Place the sample on the filter rack. Add 150 mL of RO water. Insert a filter candle, 

connect to the vacuum trap assembly with tubing, and turn on the vacuum. Aspirate until 

liquid is removed and only slightly dampened sample remains. Wash the sample four 

additional times with ≈ 150 mL of RO water. Stir the sample with filter candle to ensure all 

soil particles will be rinsed. During aspiration, it may be necessary to occasionally apply backpressure to filter candle and remove build-up of soil which inhibits aspiration. If the sample 

contains gypsum and flocculates, then the following additional washings may be used. If the 

sample contains 1 to 5% gypsum, stir the sample with a magnetic stirrer for 5 min and wash 5 

times with ≈ 250 mL of RO water each time. If the sample contains >5% gypsum, place the 

sample in a 1000-mL beaker and stir the sample with a magnetic stirrer for 5 min then wash 5 

times with ≈ 750 mL of RO water each time to remove soluble gypsum. 

7.106 Place one sample in oven and dry overnight at 110°C. Remove sample from oven, place 

in a desiccator, and cool to ambient temperature. 

7.107 Record the total weight (TW) of the H202-treated, oven-dry sample to the nearest mg. 

The H2O2-treated, oven-dry sample is only used for the calculations of results and is not used in 

the remaining PSDA procedural steps. Use the H2O2-treated sample that was not dried in oven 

for the following PSDA procedural steps. 

7.108 Add ≈ 100 mL of RO water and the exact volume of sodium hexametaphosphate solution 

(≈ 10 mL), equivalent to 0.4408 g of sodium hexametaphosphate, to sample. Subtract the 

weight of the sodium hexametaphosphate (DW) that is contained in the extracted aliquot from 

the silt and clay weights to calculate silt and clay percentages. To determine the exact volume 

of sodium hexametaphosphate to add to each sample refer to Section 7.109. 

7.109 A sodium hexametaphosphate standardization is performed with each new batch of 

solution. Use only designated weighing bottles for standardization. Wash and tare these bottles 

after each standardization. Add duplicate aliquots (8.5, 9.0, 9.3, 9.6, 10.0, 10.3, 10.6, 11.0 mL) 

of sodium hexametaphosphate solution to numbered tared, 90-mL weighing bottles. Oven-dry 

aliquots overnight and record dry residue weight of sodium hexametaphosphate. Determine the 

exact volume of sodium hexametaphosphate to add to each sample by regressing the volume of 

sodium hexametaphosphate against the dry residue weight of sodium hexametaphosphate and 

then by predicting the volume needed to dispense 0.4408 g of sodium hexametaphosphate into 

each sample. 

7.110 Disperse the suspension with ultrasonic vibrations. Ensure the power supply is properly 

tuned. Consult the instruction manual. Immerse the probe in the suspension to a 3-cm depth. 

Set timer to 5 min. Press start button. Adjust output control as required. Between samples, 

clean the probe by placing it in water or alcohol and energizing it for a few seconds. 

7.111 After ultrasonic dispersion, add ≈ 75 mL RO water and pour the suspension through a 

300-mesh (0.047-mm) sieve mounted on a ring stand. Finger-rubbing of sample may be 

required during transfer to speed washing of sample. Place a funnel below the sieve and a 1-L 

cylinder below the funnel. Collect the silt and clay in the 1-L cylinder. Avoid using jets of 

54
water in washing the sample. Wash and rub all particles from the fleaker into the sieve. 

Continue to wash until the suspension volume in the cylinder is ≈ 800 mL. Sand and some of 

the coarse silt remain on the sieve. Rinse all <20-μm particles into the cylinder. Fill the 

cylinder to 1 L and cover with a 65-mm watch glass. Place pipe insulation around sample and 

blank cylinders to prevent rapid changes in temperatures. Prepare a RO water blank to measure 

temperature fluctuations. Allow the cylinder to stand overnight to equilibrate the suspension 

with the room temperature. Wash the sand into an evaporation dish and dry the sand at 110°C 

overnight. Proceed to procedure 3A1a1a for remaining PSDA procedural steps. 

Particle-Size Distribution Analysis (3A) 

Particles <2 mm (3A1) 

Pipet Analysis (3A1a) 

Water Dispersion (3A1a6) 

Field-Moist (3A1a6b) 

7.112 Weigh enough <2mm, moist soil to achieve two ≈ 10-g samples of air-dry soil. Weigh to 

nearest mg on an electronic balance and place into numbered, tared, 300-mL, tared fleakers. 

Wash and tare these fleakers once every two months. A quality control sample is included in 

each batch (<24 samples). 

7.113 Dry one sample in an oven at 110°C overnight. Remove the sample from the oven, place 

in a desiccator, and cool to ambient temperature. 

7.114 Record the total weight (TW) of the sample to the nearest mg. The oven-dry sample is 

not used in the remaining PSA procedural steps. 

7.115 Add ≈ 175 mL of RO water to sample that was not dried in the oven. Place sample in a 

horizontal shaker set at 120 oscillations min-1 and shake for 15 h (overnight). 

7.116 Remove the sample from the shaker and pour through a 300-mesh (0.047-mm) sieve 

mounted on a ring stand. Finger-rubbing of sample may be required during transfer to speed 

washing of sample. Place a funnel below the sieve and a 1-L cylinder below the funnel. Collect 

the silt and clay in the 1-L cylinder. Avoid using jets of water in washing the sample. Wash 

and rub all particles from the fleaker into the sieve. Continue to wash until the suspension 

volume in the cylinder is ≈ 800 mL. Sand and some of the coarse silt remain on the sieve. 

Rinse all <20-μm particles into the cylinder. Fill the cylinder to 1 L and cover with a 65-mm 

watch glass. Place pipe insulation around sample and blank cylinders to prevent rapid changes 

in temperatures. Prepare a RO water blank to measure temperature fluctuations. Allow the 

cylinder to stand overnight to equilibrate the suspension with the room temperature. Wash the 

sand into an evaporation dish and dry the sand at 110°C overnight. 

7.117 Transfer the dried sand to a nest of sieves that has a top-to-bottom order of 1.0, 0.5, 0.25, 

0.1, and 0.047 mm. Shake the sand for 3 min on a shaker that has 1.3-cm vertical and lateral 

movements and oscillates at 500 strokes min-1. Record the weight of each separate sand 

fraction (SWi) to the nearest mg. If optical analysis is requested, place the very fine sand and 

fine sand fractions in gelatin capsules and the remaining sand fractions in a labeled vial. Store 

capsules in the labeled vial. Wash sand dishes after every use. 

7.118 Determine the percentage of fine silt and clay gravimetrically by removing an aliquot 

from the suspension in the 1-L cylinder with a Lowy, 25-mL pipet. Periodically, 

gravimetrically calibrate the delivery volume of the pipet by weighing the amount of RO water 

dispensed from the pipet. Record the delivery volume (DV) and use the value to calculate the 

results. Regulate the vacuum such that the pipet fills in ≈ 12 s. Record temperature (T1) of 

blank. Mount the pipet on an adjustable pipet rack (Shaw, 1932). Stir the silt and clay 

55
suspension with mechanical stirrer for at least 5 min. Place the cylinder on a stable, 

vibrationless table and stir with a hand stirrer in an up-and-down motion for 30 s. Timing is 

started upon completion of the stirring. Record the time that stirring is stopped. For the <20-

μm fraction, slowly lower the closed pipet to a 10-cm depth in the suspension, turn on the 

vacuum, open the pipet, and withdraw an aliquot at the calculated time (Table 1). Place the 

aliquot into a tared and numbered, 90-mL weighing bottle. Rinse the pipet with RO water into 

the tared, weighing bottle. For the <2-μm fraction, pipet after a time of 4.5, 5, 5.5, or 6.5 h. 

Record the temperature (T2) of blank. Use the average of T1 and T2 and adjust the pipet depth 

in the suspension as indicated in Table 2. Repeat the procedure described for the <20-μm 

fraction. Dry the aliquots at 110°C overnight and cool in a desiccator that contains calcium 

sulfate or an equivalent desiccant. Record the residue weight (RW) to the nearest 0.1 mg. 

Proceed to procedure 3A1a1a for remaining PSDA procedural steps. Also proceed to procedure 

3A1a1a for determination of fine-clay and/or carbonate clay. 

 

8. Calculations 

Use calculations in sections 8.1 – 8.6 for all PSDA procedures (3A1a1-5a and 3A1a1-5b) 

except water dispersible PSDA. Use calculations in sections 8.7 – 8.10 for water dispersible 

PSDA (3A1a6a and 3A1a6b). 

Calculations 8.2 – 8.6 for procedures 3A1a1-5a and 3A1a1-5b as follows: 

8.1 Clay % = 100 x ((RW 2 - DW) x (CF/TW)) 

where: 

RW2 = Residue weight (g), <2-μm fraction 

DW = Dispersing agent weight (g) = (0.4408/CF) 

CF = 1000 mL/DV 

DV = Dispensed pipet volume 

TW = Total weight (g), H2O2-treated, oven-dry sample 

8.2 Fine Silt % = 100 x ((RW20-DW) x (CF/TW)) - Clay % 

where: 

RW20 = Residue weight (g) of <20-μm fraction 

8.3 Sand % = ∑ (SWi /TW) x 100 

where: 

SWi = Weight of sand fractions (1.0, 0.5, 0.25, 0.1, and 0.047 mm) 

8.4 Coarse silt % = 100 - (Clay % + Fine Silt % + Sand %) 

8.5 Fine Clay (%) = 100 x ((RW-DW) x (CF/TW)) 

where: 

RW = Residue weight (g) of <0.2-μm fraction 

DW = Dispersing agent weight (g) = (0.4364/CF) 

CF = 1000 mL/DV 

DV = Dispensed pipet volume 

TW = Total weight of H2O2-treated, oven-dry sample 

56
8.6 Calculate carbonate clay percentage as follows: 

8.6.1 Correct the manometer reading as follows: 

CR = (MR - BR) 

where: 

CR = Corrected reading 

MR = Manometer reading 

BR = Blank reading 

Three blanks are run with each batch (<24 samples). The average of three blanks is used as 

BR. 

8.6.2 Calculate two regression equations, i.e., one for corrected manometer readings <100 and 

another for corrected readings >100. Use the Na2CO3 weights as the dependent variable 

(regressed or predicted values) and the corresponding manometer readings as the independent 

variable. 

8.6.3 Use the corrected (CR) linear regression equations to estimate the g of CaCO3 in the 

sample. 

8.6.4 Carbonate Clay Equivalent (<2 μm) (%) = ((g CaCO3 ) x 100 x CF)/TW 

where: 

CF = 1000 mL/dispensed pipet volume (mL) 

TW = Total weight of H2O2-treated oven-dry sample 

8.6.5 Noncarbonate Clay (<2 μm) (%) = Total Clay (%) - Carbonate Clay Equivalent (%) 

Calculations 8.7 – 8.10 for procedures 3A1a6a and 3A1a6b as follows: 

8.7 Clay % = 100 x ((RW 2 x CF)/TW) 

where: 

RW2 = Residue weight (g), <2-μm fraction 

CF = 1000 mL/DV 

DV = Dispensed pipet volume 

TW = Total weight (g), oven-dry sample 

8.8 Fine Silt % = (100 x (RW20 x CF)/TW)) - Clay % 

where: 

RW20 = Residue weight (g) of <20-μm fraction 

8.9 Sand % = ∑ (SWi /TW) x 100 

where: 

SWi = Weight of sand fractions (1.0, 0.5, 0.25, 0.1, and 0.047 mm) 

8.10 Coarse silt % = 100 - (Clay % + Fine Silt % + Sand %) 

9. Report 

Report each particle-size fraction to the nearest 0.1 percent. 

57
10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Bouyoucos, G.B. 1929. The ultimate natural structure of soil. Soil Sci. 28:27-37. 

Drosdoff, M., and E.F. Miles. 1938. Action of hydrogen peroxide on weathered mica. Soil 

Sci. 46:391-395. 

El Swaify, S.A. 1980. Physical and mechanical properties of Oxisols. p. 303-324. In 

B.K.G. Theng (ed.) Soils with variable charge. N.Z. Soc. Soil Sci., Lower Hutt, N.Z. 

Espinoza, W., R.H. Rust, and R.S. Adams Jr. Characterization of mineral forms in Andepts 

from Chile. Soil Sci. Soc. Am. Proc. 39:556-561. 

Gee, G.W., and J.W. Bauder. 1986. Particle-size analysis. p. 383-411. In A. Klute (ed.) 

Method of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. 

Monogr. 9. ASA and SSSA, Madison, WI. 

Gee, G.W., and D. Or. 2002. Particle-size analysis. p. 255-293. In J.H. Dane and G.C. 

Topp (eds.) Methods of soil analysis. Part 4. Physical methods. Soil Sci. Am. Book 

Series No. 5. ASA and SSSA, Madison, WI. 

Grossman, R.B., and J.L. Millet. 1961. Carbonate removal from soils by a modification of 

the acetate buffer method. Soil Sci. Soc. Am. Proc. 25:325-326. 

Jackson, M.L. 1969. Soil chemical analysis—advanced course. 2nd ed. Univ. Wisconsin, 

Madison. 

Kilmer, V.J., and L.T. Alexander. 1949. Methods of making mechanical analyses of soils. 

Soil Sci. 68:15-24. 

Kilmer, V.J., and J.K. Mullins. 1954. Improved stirring and pipeting apparatus for 

mechanical analysis of soils. Soil Sci. 77:437-441. 

Kubota, T. 1972. Aggregate formation of allophonic soils; Effects of drying on the 

dispersion of soils. Soil Sci. and Plant Nutr. 18:79-87. 

Maeda, T., H. Takenaka, and B.P. Warkentin. 1977. p. 229-263. Physical properties of 

allophone soils. In N.C. Brady (ed.) Adv. Agron. Acad. Press, Inc., New York, NY. 

Mehra, O.P., and M.L. Jackson. 1960. Iron oxide removal from soils and clays by a 

dithionite-citrate system buffered with sodium bicarbonate. p. 237-317. In Clays and 

clay minerals. Proc. 7th Conf. Natl. Acad. Sci. Natl. Res. Counc. Pub., Washington, 

DC. 

Mikhail, E.H., and G.P. Briner. 1978. Routine particle size analysis of soils using sodium 

hypochlorite and ultrasonic dispersion. Aust. J. Soil Res. 16:241-244. 

Rabenhorst, M.C., and L.P. Wilding. 1984. Rapid method to obtain carbonate-free residues 

from limestone and petrocalcic materials. Soil Sci. Soc. Am. J. 48:216-219. 

Saly, R. 1967. Use of ultrasonic vibration for dispersing of soil samples. Sov. Soil Sci. 

11:1547-1559. 

Shaw, T.M. 1932. New aliquot and filter devices for analytical laboratories. Ind. Eng. 

Chem. Anal. Ed. 4:409. 

Shields, L.G., and M.W. Meyer. 1964. Carbonate clay: Measurement and relationship to 

clay distribution and cation exchange capacity. Soil Sci. Soc. Am. Proc. 28:416-419. 

Skopp, J. 1992. Concepts of soil physics. University of Nebraska, Lincoln, NE. 

Soil Survey Division Staff. 1993. Soil survey manual. USDA. Handb. No. 18. U.S. Govt. 

Print. Office, Washington, DC. 

Soil Survey Staff. 1996. Soil survey laboratory methods manual. Version No. 3.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, 

DC. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. 2nd ed. Agric. Handb. No. 436. USDA-NRCS. U.S. Govt. 

Print. Office, Washington, DC. 

58
Sumner, M.E., 1992. The electrical double layer and clay dispersion. p. 1-32. In M.E. 

Sumner and B.A. Stewart (eds.) Soil crusting, chemical, and physical processes. CRC 

Press Inc., Boca Raton, FL. 

Watson, J.R. 1971. Ultrasonic vibration as a method of soil dispersion. Soil Fertil. 34:127-

134. 

Williams, D.E. 1948. A rapid manometric method for the determination of carbonate in 

soils. Soil Sci. Soc. Am. Proc. 13:127-129. 

59
Fig 1. Shaw Pipet (Shaw, 1932). 

60
Fig. 2. Close-up of the Shaw Pipet apparatus. 

Fig. 3. Shaw Pipet used for particle-size analysis of 

the <2-mm fraction at the USDA-NRCS Soil Survey 

Laboratory. 

61
Table 1. Sampling times at 10-cm depth, 0.4408 g L-1 NaHMP solution, and 2.65 g cc-1 particle density.1

 Temp (°C) 20 μ m 5 μm 

min s min s 

15.00 5 17 84 36 

16.00 5 9 82 22 

17.00 5 1 80 16 

18.00 4 53 78 12 

18.50 4 50 77 13 

19.00 4 46 76 17 

19.50 4 42 75 18 

20.00 4 39 74 23 

20.25 4 37 73 56 

20.50 4 36 73 29 

20.75 4 34 73 2 

21.00 4 32 72 35 

21.25 4 31 72 9 

21.50 4 29 71 43 

21.75 4 27 71 18 

22.00 4 26 70 52 

22.25 4 24 70 27 

22.50 4 23 70 2 

22.75 4 21 69 37 

23.00 4 20 69 13 

23.25 4 18 68 48 

23.50 4 17 68 24 

23.75 4 15 68 0 

24.00 4 14 67 37 

24.25 4 12 67 13 

24.50 4 11 66 50 

24.75 4 9 66 27 

25.00 4 8 66 4 

25.25 4 6 65 42 

25.50 4 5 65 19 

25.75 4 4 64 57 

26.00 4 2 64 35 

26.25 4 1 64 13 

26.50 3 59 63 52 

26.75 3 58 63 30 

27.00 3 57 63 9 

27.25 3 56 62 48 

27.50 3 54 62 27 

27.75 3 53 62 7 

28.00 3 52 61 46 

28.25 3 50 61 26 

28.50 3 49 61 6 

28.75 3 48 60 46 

29.00 3 47 60 26 

29.25 3 45 60 6 

29.50 3 44 59 47 

29.75 3 43 59 28 

30.00 3 42 59 9 ____________________________________________________________________________________________________________________________________ 

1

Use this table with procedures 3A1a1-5a and 3A1a1-5b. 

62
Table 2. Sampling depths (cm) for 2μm clay, 0.4408 g L-1 NaHMP solution, and 2.65 g cc-1 particle density.1

Temp (°C) Time (h) 

4.5 5.0 5.5 6.0 6.5 

15.00 5.11 5.67 6.24 6.81 7.38 

16.00 5.25 5.83 6.41 6.99 7.58 

17.00 5.38 5.98 6.58 7.18 7.77 

18.00 5.52 6.14 6.75 7.37 7.98 

18.50 5.59 6.22 6.84 7.46 8.08 

19.00 5.66 6.29 6.92 7.55 8.18 

19.50 5.74 6.37 7.01 7.65 8.29 

20.00 5.81 6.45 7.10 7.74 8.39 

20.25 5.84 6.49 7.14 7.79 8.44 

20.50 5.88 6.53 7.19 7.84 8.49 

20.75 5.92 6.57 7.23 7.89 8.54 

21.00 5.95 6.61 7.27 7.93 8.60 

21.25 5.99 6.65 7.32 7.98 8.65 

21.50 6.02 6.69 7.36 8.03 8.70 

21.75 6.06 6.73 7.41 8.08 8.75 

22.00 6.10 6.77 7.45 8.13 8.81 

22.25 6.13 6.81 7.49 8.18 8.86 

22.50 6.17 6.85 7.54 8.22 8.91 

22.75 6.21 6.89 7.58 8.27 8.96 

23.00 6.24 6.94 7.63 8.32 9.02 

23.25 6.28 6.98 7.67 8.37 9.07 

23.50 6.32 7.02 7.72 8.42 9.12 

23.75 6.35 7.06 7.76 8.47 9.18 

24.00 6.39 7.10 7.81 8.52 9.23 

24.25 6.43 7.14 7.85 8.57 9.28 

24.50 6.46 7.18 7.90 8.62 9.34 

24.75 6.50 7.22 7.95 8.67 9.39 

25.00 6.54 7.26 7.99 8.72 9.44 

25.25 6.58 7.31 8.04 8.77 9.50 

25.50 6.61 7.35 8.08 8.82 9.55 

25.75 6.65 7.39 8.13 8.87 9.61 

26.00 6.69 7.43 8.18 8.92 9.66 

26.25 6.73 7.47 8.22 8.97 9.72 

26.50 6.76 7.52 8.27 9.02 9.77 

26.75 6.80 7.56 8.31 9.07 9.83 

27.00 6.84 7.60 8.36 9.12 9.88 

27.25 6.88 7.64 8.41 9.17 9.94 

27.50 6.92 7.69 8.45 9.22 9.99 

27.75 6.96 7.73 8.50 9.27 10.05 

28.00 6.99 7.77 8.55 9.32 10.10 

28.25 7.03 7.81 8.59 9.38 10.16 

28.50 7.07 7.86 8.64 9.43 10.21 

28.75 7.11 7.90 8.69 9.48 10.27 

29.00 7.15 7.94 8.74 9.53 10.33 

29.25 7.19 7.99 8.78 9.58 10.38 

29.50 7.23 8.03 8.83 9.63 10.44 

29.75 7.27 8.07 8.88 9.69 10.49 

30.00 7.30 8.12 8.93 9.74 10.55 ____________________________________________________________________________________________________________________________________ 

1

Use this table with procedures 3A1a1-5a and 3A1a1-5b. 

63
Table 3. Sampling times at 10-cm depth and 2.65 g cc-1 particle density.1

 Temp (°C) 20 μ m 5 μm 

min s min s 

15.00 5 17 84 26 

16.00 5 8 82 12 

17.00 5 0 80 7 

18.00 4 53 78 3 

18.50 4 49 77 4 

19.00 4 45 76 8 

19.50 4 42 75 9 

20.00 4 38 74 14 

20.25 4 37 73 47 

20.50 4 35 73 20 

20.75 4 33 72 53 

21.00 4 32 72 27 

21.25 4 30 72 0 

21.50 4 28 71 35 

21.75 4 27 71 9 

22.00 4 25 70 43 

22.25 4 24 70 18 

22.50 4 22 69 53 

22.75 4 21 69 29 

23.00 4 19 69 4 

23.25 4 17 68 40 

23.50 4 16 68 16 

23.75 4 15 67 52 

24.00 4 13 67 28 

24.25 4 12 67 5 

24.50 4 10 66 42 

24.75 4 9 66 19 

25.00 4 7 65 56 

25.25 4 6 65 34 

25.50 4 4 65 11 

25.75 4 3 64 49 

26.00 4 2 64 27 

26.25 4 0 64 6 

26.50 3 59 63 44 

26.75 3 58 63 23 

27.00 3 56 63 1 

27.25 3 55 62 40 

27.50 3 54 62 20 

27.75 3 52 61 59 

28.00 3 51 61 39 

28.25 3 50 61 18 

28.50 3 39 60 58 

28.75 3 47 60 38 

29.00 3 46 60 19 

29.25 3 45 59 59 

29.50 3 44 59 40 

29.75 3 43 59 21 

30.00 3 41 59 1 ____________________________________________________________________________________________________________________________________

1

Use this table with procedures 3A1a6a and 3A1a6b. 

64
Table 4. Sampling depths (cm) for 2-μm clay and 2.65 g cc-1 particle density.1

Temp (°C) Time (h) 

4.5 5.0 5.5 6.0 6.5 

15.00 5.12 5.69 6.25 6.82 7.39 

16.00 5.26 5.84 6.42 7.01 7.59 

17.00 5.39 5.99 6.59 7.19 7.79 

18.00 5.54 6.15 6.77 7.38 8.00 

18.50 5.61 6.23 6.85 7.47 8.10 

19.00 5.67 6.31 6.94 7.57 8.20 

19.50 5.75 6.39 7.03 7.66 8.30 

20.00 5.82 6.47 7.11 7.76 8.41 

20.25 5.86 6.51 7.16 7.81 8.46 

20.50 5.89 6.55 7.20 7.86 8.51 

20.75 5.93 6.59 7.24 7.90 8.56 

21.00 5.96 6.63 7.29 7.95 8.61 

21.25 6.00 6.67 7.33 8.00 8.67 

21.50 6.04 6.71 7.38 8.05 8.72 

21.75 6.07 6.75 7.42 8.10 8.77 

22.00 6.11 6.79 7.47 8.14 8.82 

22.25 6.14 6.83 7.51 8.19 8.88 

22.50 6.18 6.87 7.55 8.24 8.93 

22.75 6.22 6.91 7.60 8.29 8.98 

23.00 6.25 6.95 7.64 8.34 9.03 

23.25 6.29 6.99 7.69 8.39 9.09 

23.50 6.33 7.03 7.73 8.44 9.14 

23.75 6.37 7.07 7.78 8.49 9.19 

24.00 6.40 7.11 7.83 8.54 9.25 

24.25 6.44 7.16 7.87 8.59 9.30 

24.50 6.48 7.20 7.92 8.64 9.36 

24.75 6.51 7.24 7.96 8.69 9.41 

25.00 6.55 7.28 8.01 8.74 9.46 

25.25 6.59 7.32 8.05 8.79 9.52 

25.50 6.63 7.36 8.10 8.84 9.57 

25.75 6.66 7.41 8.15 8.89 9.63 

26.00 6.70 7.45 8.19 8.94 9.68 

26.25 6.74 7.49 8.24 8.99 9.74 

26.50 6.78 7.53 8.28 9.04 9.79 

26.75 6.82 7.57 8.33 9.09 9.85 

27.00 6.85 7.62 8.38 9.14 9.90 

27.25 6.89 7.66 8.42 9.19 9.96 

27.50 6.93 7.70 8.47 9.24 10.01 

27.75 6.97 7.74 8.52 9.29 10.07 

28.00 7.01 7.79 8.57 9.34 10.12 

28.25 7.05 7.83 8.61 9.40 10.18 

28.50 7.09 7.87 8.66 9.45 10.23 

28.75 7.12 7.92 8.71 9.50 10.29 

29.00 7.16 7.96 8.75 9.55 10.35 

29.25 7.20 8.00 8.80 9.60 10.40 

29.50 7.24 8.05 8.85 9.65 10.46 

29.75 7.28 8.09 8.90 9.71 10.52 

30.00 7.32 8.13 8.95 9.76 10.57 ____________________________________________________________________________________________________________________________________

1

Use this table with procedures 3A1a6a and 3A1a6b. 

65
Particle-Size Distribution Analysis (3A)

Particles >2 mm (3A2)

Rock and pararock fragments are defined as particles >2mm in diameter and include all 

particles with horizontal dimensions less than the size of a pedon (Soil Survey Division Staff, 

1993). Rock fragments are further defined as strongly cemented or more resistant to rupture, 

whereas pararock fragments are less cemented than the strongly cemented class, with most of 

these fragments broken into particles 2 mm or less in diameter during the preparation of 

samples for particle-size analysis in the laboratory. Rock fragments are generally sieved and 

excluded from most chemical, physical, and mineralogical analyses. Exceptions are described 

in method 1B1b2f. It is necessary to know the amount of rock fragments for several 

applications, e.g., available water capacity and linear extensibility (Grossman, 2002). 

The SSL determines weight percentages of the >2-mm fractions by field and laboratory 

weighings by procedure 3A2a1. In the field or in the laboratory, the sieving and weighing of 

the >2-mm fraction are limited to the <75-mm fractions. In the field, fraction weights are 

usually recorded in pounds, whereas in the laboratory, fraction weights are recorded in grams. 

The 20- to 75-mm fraction is generally sieved, weighed, and discarded in the field. This is the 

preferred and usually the most accurate method. Less accurately, the 20- to 75-mm fraction is 

estimated in the field as a volume percentage of the whole soil. If it is sieved and weighed in 

the laboratory, the results are usually not reliable because of small sample size. 

The SSL estimates weight percentages of the >2-mm fractions from volume estimates 

of the >20-mm fractions and weight determinations of the <20-mm fractions by procedure 

3A2a2. The volume estimates are visual field estimates. Weight percentages of the >20-mm 

fractions are calculated from field volume estimates of the 20- to 75-mm, 75- to 250-mm, and 

>250-mm fractions. The >250-mm fraction includes stones and boulders that have horizontal 

dimensions that are smaller than the size of the pedon. Weight measurements for the 2- to 20-

mm fraction are laboratory measurements. Weight measurements of the 20- to 75-mm 

fractions in the field are more accurate than visual volume estimates. Weight measurements of 

this fraction in the laboratory are not reliable. The volume estimates that are determined in the 

field are converted to dry weight percentages. For any >2-mm fractions estimated by volume 

in the field, the SSL calculates weight percentages by procedure 3A2b. The visual volume 

estimates of the >20-mm fraction are subjective. The conversion of a volume estimate to a 

weight estimate assumes a particle density of 2.65 g cc-1 and a bulk density for the fine-earth 

fraction of 1.45 g cc-1. Measured values can be substituted in this volume to weight 

conversion, if required. 

Soil variability and sample size are interferences to weight determinations of the >2-

mm particles. Enough soil material needs to be sieved and weighed to obtain statistically 

accurate rock fragment content. In order to accurately measure rock fragments with maximum 

particle diameters of 20 and 75 mm, the minimum dry specimen sizes that need to be sieved 

and weighed are 1.0 and 60.0 kg, respectively. Refer to ASTM method D 2488 (American 

Society for Testing and Materials, 2004). Whenever possible, the field samples or "moist" 

material should have weights two to four times larger (American Society for Testing and 

Materials, 2004). Therefore, sieving and weighing the 20- to 75-mm fraction should be done in 

the field. The <20-mm fractions are sieved and weighed in the laboratory. 

Procedures for reporting data for a size fraction base are outlined in Section 2C. Unless 

otherwise specified, the particle-size fractions 2 to 5, 5 to 20, 20 to 75, and 0.1 to 75 mm are 

reported on a <75-mm oven-dry weight percentage basis. The total >2-mm fraction is reported 

on a whole soil oven-dry weight percentage base. 

66
Particle-Size Distribution Analysis (3A) 

Particles >2 mm (3A2) 

Weight Estimates (3A2a) 

By Field and Laboratory Weighing (3A2a1) 

1. Application 

Procedure 3A2a1 is used to determine weight percentages of the >2 mm fractions by 

field and laboratory weighings. The 20- to 75-mm fraction is generally sieved, weighed, and 

discarded in the field or is obtained from a field volume percentage estimate. However, the 20- 

to 75-mm fraction can be sieved and weighed in the laboratory. The <20-mm fractions are 

sieved and weighed in the laboratory. 

2. Summary of Method 

Field weights are determined for the 20- to 75-mm fraction. This is the preferred 

method. When field determinations are not possible, weight measurements for the 20- to 75-

mm fraction can be determined in the laboratory. The <20-mm fractions are sieved and 

weighed in the laboratory. The percentage of any 2- to 75-mm fraction on a <75-mm oven-dry 

weight basis is calculated. 

3. Interferences

Soil variability and sample size are interferences to weight determinations of the >2-

mm particles. Enough soil material needs to be sieved and weighed to obtain statistically 

accurate rock fragment content. In order to measure accurately rock fragments with maximum 

particle diameters of 20 and 75 mm, the minimum specimen sizes ("dry" weights) that need to 

be sieved and weighed are 1.0 and 60.0 kg, respectively. Refer to ASTM method D 2488 

(American Society for Testing and Materials, 2004). Samples received in the laboratory 

generally have a maximum weight of 4 kg. Therefore, sieving and weighing the 20- to 75-mm 

fraction should be done in the field. The <20-mm fractions are sieved and weighed in the 

laboratory. 

4. Safety 

The main hazards are in the field during sample collection. Some hazards are sharpedged excavation tools, snake bites, and falls. 

5. Equipment 

5.1 Electronic balance, ±1-g sensitivity and 15-kg capacity 

5.2 Trays, plastic, tared 

5.3 Sieves, square-hole 

5.3.1 9 mesh, 2 mm 

5.3.2 4 mesh, 4.76 mm 

5.3.3 20 mm, 3/4 in 

5.3.4 76 mm, 3 in 

5.4 Mechanical shaker with 9-mesh and 4-mesh sieves 

5.5 Rubber roller 

5.6 Metal plate, 76 x 76 x 0.5 cm 

5.7 Scale, 100-lb (45-kg) capacity 

5.8 Brown Kraft paper 

6. Reagents

6.1 Reverse osmosis (RO) water 

6.2 1 N HCl. Refer to procedure 1B. 

6.3 Sodium hexametaphosphate solution. Dissolve 35.7 g of sodium hexametaphosphate 

(NaPO3)6 and 7.94 g of sodium carbonate (Na2C03) in L of distilled water. 

67
7. Procedure

Field

7.1 Sieve a representative horizon sample with a 76-mm sieve. Sieve about 60 kg of material 

to accurately measure rock fragments that have a maximum particle diameter of 75 mm. As a 

60-kg sample may not be feasible because of limitations of time and/or soil material, actual 

sample size may be 30 or 40 kg. Discard the >75-mm material. Weigh and record weight (lbs) 

of <75-mm fraction. Sieve this material with a 20-mm sieve. Discard the 20- to 75-mm 

fraction. Weigh and record weight (lbs) of <20-mm fraction. Place a sub-sample of the <20-

mm material in a plastic bag. Label and send to laboratory for analyses. 

Laboratory

7.2 Distribute the field sample on a plastic tray, weigh, and record moist weight. Air-dry, 

weigh, and record weight. 

7.3 Process air-dry material on a flat, metal plate that is covered with brown Kraft paper. 

Thoroughly mix material by moving the soil from the corners to the middle of the processing 

area and then by redistributing the material. Repeat process four times. Roll material with 

wooden rolling pin to crush clods to pass a 2-mm sieve. For samples with easily crushed 

coarse fragments, substitute rubber roller for wooden rolling pin. Sieve clayey soils that 

contain many coarse fragments in the mechanical shaker. Roll and sieve until only the coarse 

fragments that do not slake in sodium hexametaphosphate solution on the sieve. 

7.4 If more sample is received than is needed for processing, select a sub-sample for 

preparation. Weigh sub-sample and record weight. 

7.5 Weigh soil material with diameters of 2 to 5 mm. Soak in sodium hexametaphosphate 

solution for 12 h. Air-dry, weigh the material that does not slake, and discard. Weigh, record 

weight, and discard coarse fragments with diameters of 20 to 75 mm and 5 to 20 mm. Most 

laboratory samples do not contain 20- to 75-mm fragments, as this fraction is generally sieved, 

weighed, and discarded in the field. 

8. Calculations

8.1 If field weight measurements are determined for the <75-mm and the 20- to 75-mm 

fraction, convert these weights in pounds to grams. If laboratory measurements are determined 

for the <75 mm and the 20- to 75-mm fractions, these weights are already in grams. 

8.2 Determine field-moist weight of the sub-sample as received in the laboratory. Determine 

air-dry weight of sub-sample. Air-dry weight is defined as a constant sample weights obtained 

after drying at 30±5°C (≈ 3 to 7 days). 

8.3 Determine ratio of slaked, air-dried weight (g) to unslaked, air-dried weight (g) for the 2- to 

5-mm fraction. Using this ratio, adjust weight of coarse fragments with <5-mm diameters. 

8.4 Base coarse fragment calculation on oven-dry weight-basis. Use the AD/OD (air-dry/ovendry ratio) (procedure 3D1) to calculate the oven-dry weight of <2-mm fraction. Use the 

following equation to determine the percentage of any 2- to 75-mm fraction on a <75-mm 

oven-dry weight-basis. 

Percentage >2 mm fraction(<75-mm basis) = (A/B) x 100 

where: 

68
A = Weight of 2- to 75- mm fraction (g) 

B = Weight of <75-mm fraction (g) 

 

8.5 Determine oven-dry weight by weighing the sample after oven-drying at 110°c for 24 h or 

by calculating as follows: 

Oven-dry weight (g) = [Air-dry weight (g)]/ADOD 

where: 

ADOD = Air-dry/oven-dry weight 

8.6 Similarly, determine oven-dry weight from the field-moist weight of a sample by 

calculating as follows: 

Oven-dry weight (g) = [Field-moist weight (g)]/[Field-moist weight (g)/Oven-dry weight (g)] 

8.7 In calculations of the oven-dry weight percentages of the >2-mm fraction, make corrections 

for the field-water content of the <75-mm sample at sampling and for the water content of the 

air-dry bulk laboratory sample. Base the corrections for the field-water content on the 

difference between the field-moist weight and air-dry weight of the bulk sample. 

9. Report

Field

9.1 Weight (lbs) of field-moist, <75-mm fraction 

9.2 Weight (lbs) of field-moist, 20- to 75-mm fraction 

Laboratory

9.3 Weight (g) of field-moist soil sample 

9.4 Weight (g) of air-dry soil sample 

9.5 Weight (g) of air-dry processed soil sample 

9.6 Weight (g) 20-to 75-mm fraction 

9.7 Weight (g) 5- to 20-mm fraction 

9.8 Weight (g) 2- to 5-mm fraction 

9.9 Weight (g) of sub-sample 2- to 5-mm fraction before slaking 

9.10 Weight (g) of sub-sample 2- to 5-mm fraction after slaking 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References

American Society for Testing and Materials. 2004. Standard Practice for Description and 

Identification of Soils (Visual-Manual Procedure). D 2488. Annual book of ASTM 

standards. Construction. Section 4. Soil and rock; dimension stone; geosynthesis. Vol. 

04.08. ASTM, Philadelphia, PA. 

Grossman, R.B., and T.G. Reinsch. 2002. Bulk density and linear extensibility. p. 201-228. 

In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis. Part 4. Physical methods. 

Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Soil Survey Division Staff. 1993. Soil survey manual. USDA. Handb. No. 18. U.S. Govt. 

Print. Office, Washington, DC. 

69
Particle-Size Distribution Analysis (3A)

Particles >2 mm (3A2) Weight Estimates (3A2a) 

From Volume and Weight Estimates (3A2a2) 

Volume Estimates (3A2b)

1. Application

Procedure 3A2a2 is used to determine weight percentages of the >2 mm fractions from 

volume estimates and weight determinations. The volume estimates are visual field estimates 

for any fractions that are >20 mm. The weight estimates are laboratory measurements for the 

2-to 20-mm or 2- to 75-mm fractions. The volume estimates for any fractions that are >20 mm 

are converted to weight percentages. The total >2-mm fraction is reported on an oven-dry 

weight basis for whole soil. Method 3A2b is the calculations used to derive weight percentages 

from volume percentages of all the >2-mm material. 2. Summary of Method 

Visual field volume estimates are determined for any fractions that are >20 mm. These 

volume estimates include, if applicable, the 20- to 75-mm, 75- to 250-mm, and the >250-mm 

fractions. The >250-mm fraction includes stones and boulders that have horizontal dimensions 

that are less than those of the pedon. Instead of visual field volume estimates, field weights for 

the 20- to 75-mm fraction may be determined. This is the preferred method. If these 

measurements are unavailable, visual field volume estimates of the 20- to 75-mm fraction are 

used rather than laboratory weights of this fraction. The <20-mm fractions are sieved and 

weighed in the laboratory. 

3. Interferences

Soil variability and sample size are interferences to weight determinations of the >2-

mm particles. Enough soil material needs to be sieved and weighed to obtain statistically 

accurate rock fragment content. In order to accurately measure rock fragments with maximum 

particle diameters of 20 and 75 mm, the minimum specimen sizes ("dry" weights) that need to 

be sieved and weighed are 1.0 and 60.0 kg, respectively. Refer to ASTM Standard Practice D 

2488 (American Society for Testing and Materials, 2004). Samples received in the laboratory 

generally have a maximum weight of 4 kg. Therefore, sieving and weighing the 20- to 75-mm 

fraction should be done in the field. 

The visual volume estimates of the >75-mm fractions are subjective. The conversion of 

a volume estimate to a weight estimate assumes a particle density of 2.65 g cc-1 and a bulk 

density for the fine-earth fraction of 1.45 g cc-1. If particle density and bulk density 

measurements are available, they are used in the calculations. 

4. Safety

The main hazards are in the field during sample collection. Some hazards are sharpedged excavation tools, snake bites, and falls. 

5. Equipment 

5.1 Electronic balance, ±1-g sensitivity and 15-kg capacity 

5.2 Trays, plastic, tared 

5.3 Sieves, square-hole 

5.3.1 9 mesh, 2 mm 

5.3.2 4 mesh, 4.76 mm 

5.3.3 20 mm, 3/4 in 

5.3.4 76 mm, 3 in 

5.4 Mechanical shaker with 9-mesh and 4-mesh sieves 

5.5 Rubber roller 

70
5.6 Metal plate, 76 x 76 x 0.5 cm 

5.7 Scale, 45-kg (100-lb) capacity 

5.8 Brown Kraft paper 

6. Reagents

6.1 Reverse osmosis (RO) water 

6.2 1 N HCl. Refer to procedure 1B. 

6.3 Sodium hexametaphosphate solution. Dissolve 35.7 g of sodium hexametaphosphate 

(NaPO3)6 and 7.94 g of sodium carbonate (Na2C03) in L of distilled water. 

7. Procedure 

Field

7.1 Determine volume estimates as percentages of soil mass for the 75- to 250-mm and for the 

>250-mm fractions. The >250-mm fraction includes stones and boulders with horizontal 

dimensions less than those of the pedon. 

7.2 Determine either weight measurements in pounds or visual field volume estimates in 

percentages for the 20- to 75-mm fragments. Weight measurements for the 20- to 75-mm 

fraction are the preferred method. However, volume estimates are more accurate than 

laboratory weights using small samples. 

7.3 If field weight measurements are determined for the 20- to 75-mm fraction, sieve an entire 

horizon sample with a 76-mm sieve. Sieve ≈ 60 kg of material to accurately measure rock 

fragments that have a maximum particle diameter of 75 mm. A 60-kg sample may not be 

possible because of limitations of time and/or soil material. Actual sample size may be 30 or 

40 kg. Discard the >75-mm material. Weigh and record weight of <75-mm fraction. Sieve 

this material with a 20-mm sieve. Discard the 20- to 75-mm fraction. Weigh and record 

weight of <20-mm fraction. Place a sub-sample of the <20-mm material in an 8-mL, plastic 

bag. Label and send to laboratory for analyses. 

Laboratory

7.4 Distribute the field sample on a plastic tray, weigh, and record moist weight. Air-dry, 

weigh, and record weight. 

7.5 Process air-dry material on a flat, metal plate that is covered with brown Kraft paper. 

Thoroughly mix material by moving the soil from the corners to the middle of the processing 

area and then by redistributing the material. Repeat process four times. Roll material with 

wooden rolling pin to crush clods to pass a 2-mm sieve. For samples with easily crushed 

coarse fragments, substitute rubber roller for wooden rolling pin. Sieve clayey soils that 

contain many coarse fragments in the mechanical shaker. Roll and sieve until only the coarse 

fragments that do not slake in sodium hexametaphosphate solution remain on the sieve. 

7.6 If more sample is received than is needed for processing, select sub-sample for preparation. 

Weigh sub-sample and record weight. 

7.7 Weigh soil material with diameters of 2 to 5 mm. Soak in sodium hexametaphosphate 

solution for 12 h. Air-dry, weigh the material that does not slake, and discard. Weigh, record 

weight, and discard coarse fragments with diameters of 20 to 75 mm and 5 to 20 mm. Most 

laboratory samples do not contain 20- to 75-mm fragments as this fraction is generally 

weighed, sieved, and discarded in the field. 

71
8. Calculations 

From Volume and Weight Estimates (3A2a2)

8.1 Calculate weight percentages from volume percentages using measured bulk density (Dbm) 

and particle density (Dp). If measurements are unavailable, assume a Dbm of 1.45 g cc-1 and a 

Dp of 2.65 g cc-1. 

8.2 Use the following equation to convert all volume estimates to weight percentages for 

specified fractions. 

Percentage >2 mm (wt basis) = [100 Dp (x)]/[Dp (x) + Dbm (1-x)]

where: 

Dp = Particle density (2.65 g cc-1, unless measured) 

Dbm = Bulk density (1.45 g cc-1 for <2-mm fraction, unless measured) 

x = [volume fragments > i mm]/[volume whole soil]

where: 

i = size fraction above which volume estimates are made and below which weight percentages 

are determined, usually 20 or 75 mm in diameter 

8.3 Use the preceding equation to calculate any individual fraction >j mm (j = any size 

fraction) by substituting an appropriate value of Dbm representing the fabric <j mm. 

Volume Estimates (3A2b)

8.4 Use the following equation to determine the volume of the <2-mm fraction per unit volume 

of whole soil. 

 

Cm = [Volume moist <2-mm fabric]/[Volume moist whole-soil] = [Dp (1-y) (1-x)]/[Dp (1-y) + Dbm (y)]

where: 

Cm = Rock fragment conversion factor 

Volume moist whole soil = Volume of fine earth + rock fragments on moist whole-soil basis 

y = [weight material between 2 mm and i mm]/[weight material < i mm]

8.5 Use the following formula to convert laboratory data on a <2-mm weight basis to moist 

whole soil volume basis. 

Cm x Dbm x lab datum 

8.6 Use the following formula to determine the volume percentage of <2-mm fabric in whole 

soil. 

Cm x 100 

8.7 Use the following formula to determine the volume percentage of >2-mm fabric in whole 

soil. 

100 (1-Cm) 

72
8.8 Use the following formula to report weight of <2-mm fabric per unit volume of whole soil 

for some soils. 

(Cm x Dbm) 

9. Report 

Field

9.1 Volume (%) >250-mm fraction (includes stones and boulders with horizontal dimensions 

smaller than size of a pedon) 

9.2 Volume (%) 75- to 250-mm fraction 

9.3 Volume (%) 20- to 75-mm fraction (not needed if weighed in field) 

9.4 Weight (lbs) <75-mm fraction 

9.5 Weight (lbs) 20-to 75-mm fraction 

Laboratory

9.6 Weight (g) of field moist soil sample 

9.7 Weight (g) of air-dry soil sample 

9.8 Weight (g) of air-dry processed soil sample 

9.9 Weight (g) 20-to 75-mm fraction 

9.10 Weight (g) 5- to 20-mm fraction 

9.11 Weight (g) 2- to 5-mm fraction 

9.12 Weight (g) of sub-sample 2- to 5-mm fraction before slaking 

9.13 Weight (g) of sub-sample 2- to 5-mm fraction after slaking 

10. Precision and Accuracy

Precision and accuracy data are available from the SSL upon request. 

11. References 

American Society for Testing and Materials. 2004. Standard Practice for Description and 

Identification of Soils (Visual-Manual Procedure). D 2488. Annual book of ASTM 

standards. Construction. Section 4. Soil and rock; dimension stone; geosynthesis. Vol. 

04.08. ASTM, Philadelphia, PA. 

SOIL PHYSICAL AND FABRIC RELATED ANALYSES (3) 

Bulk Density (3B) 

Density is defined as mass per unit volume. Soil bulk density of a sample is the ratio of 

the mass of solids to the total or bulk volume. This total volume includes the volume of both 

solids and pore space. Bulk density is distinguished from particle density which is mass per 

unit volume of only the solid phase. Particle density excludes pore spaces between particles. 

As bulk density (Db) is usually reported for the <2-mm soil fabric, the mass and volume of 

rock fragments are subtracted from the total mass and volume. 

Bulk density maybe highly dependent on soil conditions at the time of sampling. 

Changes in soil volume due to changes in water content will alter bulk density. Soil mass 

remains fixed, but the volume of soil may change as water content changes (Blake and Hartge, 

1986). Bulk density, as a soil characteristic, is actually a function rather than a single value. 

Therefore, subscripts are added to the bulk density notation, Db, to designate the water state of 

the sample when the volume was measured. The SSL uses the bulk density notations of Dbf, 

Db33, Dbod, and Dbr for field-state, 33-kPa equilibration, oven-dry, and rewet, respectively. 

Field-state (Dbf) is the bulk density of a soil sample at field-soil water content at time of 

sampling. The 33-kPa equilibration (Db33) is the bulk density of a soil sample that has been 

73
desorbed to 33kPa (1/3 bar). The oven-dry (Dbd) is the bulk density of a soil sample that has 

been dried in an oven at 110°C. The rewet (Dbr) is the bulk density of soil sample that has 

been equilibrated, air-dried, and re-equilibrated. The Dbr is used to determine the irreversible 

shrinkage of soils and subsidence of organic soils. The determinations of these bulk density 

values, Dbf, Db33, Dbod, and Dbr, are described in procedures 3B1a, 3B1b, 3B1c, and 3B1d, 

respectively. Bulk density also may be determined for field-moist soil cores of known volume 

(procedure 3B6a). The bulk density of a weak or loose soil material for which the clod or core 

method is unsuitable may be determined by the compliant cavity method (procedure 3B3a). 

In general, there are two broad groupings of bulk density methods as follows: (1) one 

for soil materials coherent enough that a field-sample can be removed; and (2) the other for 

soils too fragile to remove a sample and an excavation operation must be performed. Under the 

former, there are clod methods in which the sample has an undefined volume, is coated, and the 

volume is determined by submergence. Also under the former there are various methods in 

which a cylinder of known volume is obtained of soil sufficiently coherent that it remains in the 

cylinder. The complete cylinder may be inserted (3B6a) or only part of the cylinder is inserted 

and the empty volume is subtracted from the total volume of the core (e.g., variable height 

method, Grossman and Reinsch, 2002). Three excavation procedures have been used to 

determine Dbf as follows: (1) compliant cavity (3B3a); (2) ring excavation (3B4a); and (3) 

frame excavation (3B5a) (Grossman and Reinsch, 2002). The frame-excavation provides for a 

larger sample area and is advantageous where there is large, very local variability as found in 

the O horizons (Soil Survey Staff, 1999) of woodlands. 

The complication concerning the difference between bulk density of the soil and that of 

the sample is particularly important for the clod method as presented here which permits 

determination of the volume at different water contents and hence volumes. If the water 

content is at or near field capacity, desiccation cracks are closed and the bulk density (Db33 or 

Dbf if field-water is near field capacity) of the soil and of the sample are considered the same. 

However, if the sample is at a water content below field-capacity through drying after sampling 

or because the sample was taken below field-capacity, then desiccation cracks that occur in 

place are excluded from the soil and the sample bulk density exceeds that of the soil. If the 

sample is large and inclusive of the desiccation cracks, as in some excavation procedures, then 

again the sample and soil bulk density are the same. The difference between sample and soil 

bulk density is particularly large for oven-dry clods (Dod) of soils with high extensibility. And 

may also be hard for soils subject to a large increase if taken through a rewet cycle. Grossman 

and Reinsch (2002) discuss the manipulation of clod bulk densities (the sample) at water 

contents below field capacity to obtain an estimate of the soil bulk density at such water 

contents. Similarly, estimates of soil bulk density at intermediate field-water contents between 

field capacity and oven-dryness inclusive of desiccation crack space are discussed by 

Grossman et al. (1990). 

References 

Blake, G.R., and K.H. Hartge. 1986. Bulk density. p. 363-382. In A. Klute (ed.) Methods of 

soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. Monogr. 9. ASA 

and SSSA, Madison, WI. 

Grossman, R.B., F.B. Pringle, R.J. Bigler, W.D. Broderson, and T.M. Sobecki. 1990. 

Systematics and field morphology for a use-dependent, temporal soil data base for 

edaphological and environmental applications. p. 452-460. In Int. Symp. On Advanced 

Technology in Natural Resource Management, 2nd. ed. Georgetown Univ., Washington, 

DC. 

Grossman, R.B., and T.G. Reinsch. 2002. Bulk density and linear extensibility. p. 201-228. In

J.H. Dane and G.C. Topp (eds.) Methods of soil analysis. Part 4. Physical methods. Soil 

Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys. 2nd ed. Agric. Handb. No. 436. USDA-NRCS. U.S. Govt. Print. 

Office, Washington, DC. 

74
Bulk Density (3B) 

Saran-Coated Clods (3B1) 

Field-State (Dbf) (3B1a)

1. Application 

Bulk density is used to convert data from a weight to a volume basis; to estimate 

saturated hydraulic conductivity; and to identify compacted horizons. The procedure 3B1a 

determines the bulk density value Dbf of a soil sample at field-soil water content at time of 

sampling. Field-bulk density (Dbf ) offers the opportunity to obtain relatively cheaply bulk 

density information without the expense incurred to obtain water retention. Dbf is particularly 

useful if the soil layers are at or above field capacity and/or the soils have low extensibility and 

do not exhibit desiccation cracks even if below field capacity. 

2. Summary of Method 

Field-occurring fabric (clods) is collected from the face of an excavation. One coat of 

plastic lacquer is applied in the field. Additional coats of plastic lacquer are applied in the 

laboratory. In its field-water state or after equilibration, the clod is weighed in air to measure 

its mass and in water to measure its volume. After the clod is dried in oven at 110°C, its mass 

and volume are determined again. A correction is made for the mass and volume of rock 

fragments and plastic coatings (Brasher et al., 1966; Blake and Hartge, 1986; Grossman and 

Reinsch, 2002). 

3. Interferences 

Errors are caused by non-representative samples. Only field-occurring fabric (clods) 

should be sampled. The whole soil bulk density may be overestimated because sampled clods 

frequently exclude the crack space between clods (Grossman and Reinsch, 2002). 

The penetration of plastic lacquer into the voids of sandy or organic soils interferes with 

the corrections for mass and volume of the plastic coat and with the accuracy of water content 

determinations. Penetration can be reduced by spraying water on the clod followed by 

immediately dipping the clod in the plastic lacquer. 

Loss of soil during the procedure will void the analyses because all calculations are 

based on the oven-dry soil mass. Holes in the plastic coating, which are detected by escaping 

air bubbles from submerged clod, introduce errors in volume measurement. An inadequate 

evaporation of the plastic solvent results in overestimation of the soil mass. A drying time of 1 

h is usually sufficient time for evaporation of solvent. However, clods with high organic matter 

content may need to dry longer. 

Bulk density is reported for <2-mm soil fabric. Correction for rock fragments >2-mm 

requires either knowledge or assumption of the rock fragment density. Estimate or 

measurement errors of rock fragment density will affect the accuracy of the value for soil bulk 

density. Rock fragments may contain water which complicates the application to actual waterholding capacity. 

4. Safety 

Methyl ethyl ketone (MEK) is extremely flammable. A type B fire extinguisher should 

be in close proximity in the laboratory. No open flames or nearby operation of electrical 

equipment are permitted while using MEK. The MEK vapor is classified as a sensory irritant. 

The 8-h time-weighted average (TWA) exposure limit is 200 ppm, and the short-term exposure 

limit (STEL) is 300 ppm (Occupational Safety and Health Administration, 1989). Avoid 

physical contact. Use with adequate ventilation. In closed buildings, use a fume hood. Keep 

in tightly closed containers. Use safety glasses, proper gloves, and a lab coat. Wash hands 

immediately after handling MEK. Additional information on the safe handling of MEK is 

available in Chemical Safety Data Sheet SD-83, Manufacturing Chemists’ Association, Inc., 

1825 Connecticut Ave. NW, Washington, DC. 

75
Saran F-310 resin will decompose rapidly at temperatures >200°C releasing hydrogen 

chloride gas. Avoid contact with Fe, Zn, Cu, and Al in solution. Avoid all contact with strong 

bases. 

5. Equipment 

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Rigid shipping containers. The SSL uses a corrugated box with compartments. 

5.3 Plastic bags, 1 mL, 127 x 89 x 330 mm 

5.4 Wire. The SSL uses a 28-awg coated copper wire. 

5.5 Hairnets 

5.6 Stock tags, 25.4-mm (1-in) diameter paper tag, with metal rim 

5.7 Hook assembly for weighing below balance 

5.8 Plexiglass water tank mounted on a fulcrum and lever to elevate tank 

5.9 Oven, 110°C 

5.10 Sieve, No. 10 (2-mm openings) 

5.11 Rope, 3 m 

5.12 Clothespins 

5.13 Silt loam soil 

5.14 Hot plate 

5.15 Spray bottle 

5.16 Liquid vapor trap. The SSL constructs a tin enclosure over hot plate with a chimney and 

duct to transfer vapor to water stream. 

6. Reagents 

6.1 Methyl ethyl ketone (MEK), practical (2-butanone) 

6.2 Water 

6.3 Alcohol 

6.4 Liquid detergent. The SSL uses Liqui-Nox. 

6.5 Dow Saran F-310 Resin, available from Dow Chemical Company. 

6.6 Plastic lacquer. Prepare plastic lacquer with resin to solvent ratios of 1:4 and 1:7 on a 

weight basis. Fill a 3.8-L (1-gal) metal paint can with 2700 ± 200 mL of solvent. Fill to 

the bottom of handle rivet. Add 540 or 305 g of resin to make 1:4 or 1:7 plastic lacquer, 

respectively. For the initial field and laboratory coatings, use the 1:4 plastic lacquer. Use 

1:7 plastic lacquer for the last two laboratory coats. The 1:7 plastic lacquer is used to 

conserve the resin and to reduce cost. In the field, mix solvent with a wooden stick. In 

the laboratory, stir solvent with a non-sparking, high speed stirrer while slowly adding 

resin. Stir plastic lacquer for 15 min at 25°C. Store plastic lacquer in covered plastic or 

steel containers. Acetone may be substituted for MEK. 

7. Procedure 

Field 

7.1 Collect field-occurring clods, ≈ 100 to 200 cm3

 in volume (fist-sized), from the face of the 

excavation. Three clods per horizon are recommended. It is important that these clods be as 

representative of the bulk sample volume as possible. Remove a piece of soil larger than clod 

from the face of sampling pit. From this piece, prepare a clod by gently cutting or breaking 

protruded peaks and compacted material from clod. If roots are present, trim roots with shears. 

No procedure for sampling clods is applicable to all soils. Adjust field-sampling techniques to 

meet field-conditions at time of sampling. 

7.2 Make a clothesline by stretching a rope between two fixed points. Tie clod with fine 

copper wire or place clod in a hairnet. If clod is dry, moisten surface with a fine mist of water. 

Quickly dip entire clod into plastic lacquer (Fig. 1). Suspend clod from clothesline to dry (Fig. 

2). Dry clod for 30 min or until odor of solvent dissipates. If the value of Dbf is required, store 

76
clods in waterproof plastic bags as soon as coating dries because coating is permeable to water 

vapor. 

7.3 Pack clods in rigid containers to protect them during transport. 

Laboratory

7.4 Prepare a round stock tag with sample identification number. Cut the copper wire and loop 

around the clod. Record weight (TAG) of tag and wire. Loop fine copper wire around clod, 

leaving a tail to which round stock tag is attached. Record weight of clod (CC1). 

7.5 Dip clod in 1:4 plastic lacquer. Wait 7 min and then dip clod in 1:7 plastic lacquer. Wait 

12 min and then dip clod in 1:7 plastic lacquer. Wait 55 min and then reweigh clod. If clod 

has adsorbed >3% plastic by clod weight or smells excessively of solvent, allow longer drying 

time, then reweigh clod and record weight (CC2). 

7.6 The clod should be waterproof and ready for volume measurement by water displacement. 

Suspend the clod below the balance, submerge in water, and record weight (WMCW). 

7.7 Dry clod in an oven at 110°C until weight is constant. Weigh oven-dry clod in air (WODC) 

and in water (WODCW) and record weights. 

7.8 If clod contains >5% rock fragments by weight, remove them from clod. Place clod in a 

beaker and place on hot plate. Cover hot plate with a liquid vapor trap. Use a fume hood. 

Heat clod on hot plate in excess of 200°C for 3 to 4 h. The plastic coating disintegrates at 

temperatures above 200°C. After heating, clod should appear black and charred. Remove clod 

from hot plate, lightly coat with liquid detergent, and add hot water. 

7.9 Wet sieve the cool soil through a 2-mm, square-hole sieve. Dry and record weight (RF) of 

rock fragments that are retained on the sieve. Determine rock fragment density by weighing 

them in air to obtain their mass and in water to obtain their volume. If rock fragments are 

porous and have a density similar to soil sample, do not correct clod mass and volume 

measurement for rock fragments. Correct for rock fragments if these fragments can withstand 

breakdown when dry soil is placed abruptly in water or calgon. 

7.10 Correct bulk density for weight and volume of plastic coating. The coating has an air-dry 

density of ≈ 1.3 g cm-3. The coating loses 10 to 20% of its air-dry weight when dried in oven at 

110°C. 

8. Calculations 

8.1 Dbf = [WODC - RF - ODPC – TAG]/{[(CC2 - WMCW)/WD] - (RF/PD) - (MPC/1.3)} 

where: 

Dbf = Bulk density in g cc-1 of <2-mm fabric at field-sampled water state 

WODC = Weight of oven-dry coated clod 

RF = Weight of rock fragments 

ODPC = MPC x 0.85, weight of oven-dry plastic coat 

TAG = Weight of tag and wire 

CC2 = Weight of tag and wire 

WMCW = Weight of coated clod in water before oven drying 

WD = Water density 

PD = Density of rock fragments 

8.2 MPC = [(CC2 - CC1) + FCE] x RV 

77
where: 

MPC = Weight of plastic coat before oven-drying 

CC1 = Weight of clod before three laboratory plastic coats 

RV = Percent estimate of remaining clod volume after cutting to obtain flat surface (≈ 80%) 

8.3 FCE = 1.5 x [(CC2 -CC1)/3] 

where: 

FCE = Estimate of field-applied plastic coat 

8.4 Dbod = [WODC – RF – ODPC - TAG]/{[(WODC – WODCW)/WD] - (RF/PD) - 

(MPC/1.3)} 

where: 

Dbod = Bulk density in g cm-3 <2-mm fabric at oven dryness 

WODCW = Weight of oven-dry coated clod in water 

8.5 Wf = {[(CC2 – MPC) – (WODC – ODPC)]/[WODC - RF - ODPC – TAG]}x 100 

where: 

Wf = Percent water weight in sampled clod 

9. Report

Bulk density is reported to the nearest 0.01g cm-3. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Blake, G.R. and K.H. Hartge. 1986. Bulk density. p. 363-382. In A. Klute (ed.) Methods of 

soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. Monogr. 9. 

ASA and SSSA, Madison, WI. 

Brasher, B.R., D.P. Franzmeier, V.T. Volassis, and S.E. Davidson. 1966. Use of saran 

resin to coat natural soil clods for bulk density and water retention measurements. Soil 

Sci. 101:108. 

Grossman, R.B., and T.G. Reinsch. 2002. Bulk density and linear extensibility. p. 202-228. 

In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis, Part 4. Physical methods. 

Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Occupational Safety and Health Administration. 1989. Air contaminants; final rule. 

Federal Register. 29 CFR Part 1910. Vol. 54. No. 12. p. 2452-2453. U.S. Govt. Print. 

Office, Washington, DC. 

78
Fig. 1. Dipping clods with hairnet in plastic-lacquer. 

Fig. 2. After dipping, clods are tied to clothesline to dry. 

79
Bulk Density (3B) 

Saran-Coated Clods (3B1) 

33-kPA Desorption (Db33) (3B1b)

1. Application 

Bulk density is used to convert data from a weight to a volume basis; to determine the 

coefficient of linear extensibility; to estimate saturated hydraulic conductivity; and to identify 

compacted horizons. The procedure 3B1b determines the bulk density value (Db1/3) of a soil 

sample equilibrated at 33 kPa. 

2. Summary of Method 

Field-occurring fabric (clods) are collected from the face of an excavation. One coat of 

plastic lacquer is applied in the field. Additional coats of plastic lacquer are applied in the 

laboratory. The clod is desorbed to 33 kPa. After equilibration, the clod is weighed in air to 

measure its mass and in water to measure its volume. After the clod is dried in the oven at 

110°C, its mass and volume are determined again. A correction is made for the mass and 

volume of rock fragments and for plastic coatings (Brasher et al., 1966; Blake and Hartge, 

1986). 

3. Interferences 

Errors are caused by non-representative samples. Only field-occurring fabric (clods) 

should be sampled. The whole soil bulk density may be overestimated because sampled clods 

frequently exclude the crack space between clods (Grossman and Reinsch, 2002). 

The penetration of plastic lacquer into the voids of sandy and organic soils interferes 

with the corrections for mass and volume of the plastic coat and with the accuracy of water 

content determinations. Penetration can be reduced by spraying water on the clod followed by 

immediately dipping the clod in the plastic lacquer. Dipping should be done as quickly as 

possible to reduce penetration of plastic. 

Loss of soil during the procedure will void the analyses because all calculations are 

based on the oven-dry soil mass. Holes in the plastic coating, which are detected by escaping 

air bubbles from submerged clod, introduce errors in volume measurement. An inadequate 

evaporation of plastic solvent results in overestimation of the soil mass. A drying time of 1 h is 

usually sufficient time for evaporation of solvent. However, clods with high organic matter 

content may need to dry longer. 

Clods placed in an unsealed plastic bag can lose moisture during storage prior to 

analysis. If clods irreversibly dry below 33-kPa-water content, then Db1/3 values for 33 kPa 

will be erroneous. Completely seal the plastic storage bag to prevent drying. 

Bulk density is reported for <2-mm soil fabric. Correction for rock fragments >2-mm 

requires either knowledge or assumption of the rock fragment density. Estimate or 

measurement errors of rock fragment density will affect the accuracy of the value for soil bulk 

density. Rock fragments may contain water, which complicates the application to actual waterholding capacity. 

4. Safety

Methyl ethyl ketone (MEK) is extremely flammable. A type B fire extinguisher should 

be in close proximity in the laboratory. No open flames or nearby operation of electrical 

equipment are permitted while using MEK. The MEK vapor is classified as a sensory irritant. 

The 8-h time weighted average (TWA) exposure limit is 200 ppm, and the short-term exposure 

limit (STEL) is 300 ppm (Occupational Safety and Health Administration, 1989). Avoid 

physical contact. Use with adequate ventilation. In closed buildings, use a fume hood. Keep 

in tightly closed containers. Use safety glasses, proper gloves, and a lab coat. Wash hands 

immediately after handling MEK. Additional information on the safe handling of MEK is 

80
available in Chemical Safety Data Sheet SD-83, Manufacturing Chemists’ Association, Inc., 

1825 Connecticut Ave. NW, Washington, DC. 

Saran F-310 resin will decompose rapidly at temperatures >200°C releasing hydrogen 

chloride gas. Avoid contact with Fe, Zn, Cu, and Al in solution. Avoid all contact with strong 

bases. 

5. Equipment 

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Pressure plate extractor with porous ceramic plate. 

5.3 Air pressure, 33-kPa 

5.4 Rigid shipping containers. The SSL uses a corrugated box with compartments. 

5.5 Plastic bags, 1 mil, 127 x 89 x 330 mm 

5.6 Wire. The SSL uses a 28-awg coated copper wire. 

5.7 Hairnets 

5.8 Stock tags, 25.4-mm (1-in) diameter paper tag, with metal rim 

5.9 Hook assembly for weighing below balance 

5.10 Plexiglass water tank mounted on a fulcrum and lever to elevate tank 

5.11 Oven, 110°C 

5.12 Sieve, No. 10 (2-mm openings) 

5.13 Rope, 3 m 

5.14 Clothespins 

5.15 Knife 

5.16 Tile cut-off saw with diamond blade 

5.17 Silt loam soil 

5.18 Hot plate 

5.19 Desiccator with ceramic plate 

5.20 Vacuum, 80 kPa (0.8 bar) 

5.21 Metal probe 

5.22 Spray bottle 

5.23 Liquid vapor trap. The SSL constructs a tin enclosure over hot plate with a chimney and 

duct to transfer vapor to water stream. 

5.24 Reinforced paper towels or cheesecloth 

5.25 Tension table. The SSL constructs a tension table by placing porous firebricks, covered 

with reinforced paper towels, in a tub of water. 

6. Reagents

6.1 Methyl ethyl ketone (MEK), practical (2-butanone) 

6.2 Water 

6.3 Alcohol 

6.4 Liquid detergent. The SSL uses Liqui-Nox. 

6.5 Dow Saran F-310 Resin, available from Dow Chemical Company. 

6.6 Plastic lacquer. Prepare plastic lacquer with resin to solvent ratios of 1:4 and 1:7 on a 

weight basis. Fill a 3.8-L (1-gal) metal paint can with 2700 ±200 mL of solvent. Fill to 

the bottom of handle rivet. Add 540 or 305 g of resin to make 1:4 or 1:7 plastic lacquer, 

respectively. For the initial field and laboratory coatings, use the 1:4 plastic lacquer. 

Use 1:7 plastic lacquer for the last two laboratory coats. The 1:7 plastic lacquer is used 

to conserve the resin and to reduce cost. In the field, mix solvent with a wooden stick. In 

the laboratory, stir solvent with a non-sparking, high-speed stirrer while slowly adding 

resin. Stir plastic lacquer for 15 min at 25°C. Store plastic lacquer in covered plastic or 

steel containers. Acetone may be substituted for MEK. 

81
7. Procedure

Field 

7.1 Collect field-occurring clods, ≈ 100 to 200 cm3 in volume (fist-sized), from the face of the 

excavation. Three clods per horizon are recommended. It is important that these clods be as 

representative of the bulk sample volume as possible. Remove a piece of soil larger than clod 

from the face of sampling pit. From this piece, prepare a clod by gently cutting or breaking 

protruded peaks and compacted material from clod. If roots are present, trim roots with shears. 

No procedure for sampling clods is applicable to all soils. Adjust field-sampling techniques to 

meet field-conditions at time of sampling. 

7.2 Make a clothesline by stretching a rope between two fixed points. Tie clod with fine 

copper wire or place clod in a hairnet. If the clod is dry, moisten surface with a fine mist of 

water. Quickly dip entire clod into plastic lacquer (See Fig. 1, procedure 3B1a). Suspend clod 

from clothesline to dry (See Fig. 2, procedure 3B1a). Dry clod for 30 min or until odor of 

solvent dissipates. If the value of Dbf is required, store clods in waterproof plastic bags as soon 

as coating dries because coating is permeable to water vapor. 

7.3 Pack clods in rigid containers to protect them during transport. 

Laboratory

7.4 Prepare a round stock tag with sample identification number. Cut the copper wire and loop 

around the clod (Fig. 1). Record weight (TAG) of tag and wire. Loop fine copper wire around 

clod, leaving a tail to which round stock tag is attached. Record weight of clod (CC1). 

7.5 Dip clod in 1:4 plastic lacquer. Wait 7 min and then dip clod in 1:7 plastic lacquer. Wait 

12 min and then dip clod in 1:7 plastic lacquer. Wait 55 min and then reweigh clod. If clod 

has adsorbed >3% plastic by clod weight or smells excessively of solvent, allow longer drying 

time, then reweigh clod and record weight (CC2). 

7.6 With a diamond saw, cut a flat surface on the clod. Place cut clod surface on a tension 

table, maintained at 5-cm tension (Fig.2). Periodically check clod to determine if it has reached 

equilibrium by inserting metal probe, touching, or by weight comparison. When clod has 

reached equilibrium, remove clod and record weight (WSC). 

7.7 If cut clod does not adsorb water, place clod in a desiccator on a water-covered plate with a 

0-cm tension. Submerge only the surface of clod in the water. Add a few mL of alcohol. Use 

in-house vacuum and apply suction until clod has equilibrated at saturation. Remove clod and 

record weight (WSC). 

7.8 Place clod in a pressure plate extractor. To provide good contact between clod and ceramic 

plate, cover ceramic plate with a 5-mm layer of silt loam soil and saturate with water. Place a 

sheet of reinforced paper towel or cheesecloth over the silt loam soil. Place surface of cut clod 

on paper towel. Close container and secure lid. Apply gauged air pressure of 33 kPa. When 

water ceases to discharge from outflow tube, clod is at equilibrium. Extraction usually takes 3 

to 4 wk. Remove clod and record weight (WMC). Compare WMC to WSC. If WMC > WSC, 

equilibrate clod on tension table and repeat desorption process. 

7.9 Dip clod in the 1:4 plastic lacquer. Wait 7 min and then dip clod in 1:7 plastic lacquer. 

Wait 12 min and then dip clod in 1:7 plastic lacquer. Wait 12 min and dip clod in 1:7 plastic 

lacquer. After 55 min, reweigh clod and record weight (CC3). If clod has adsorbed >3% 

plastic by weight or smells excessively of solvent, allow longer drying time, then reweigh clod. 

82
7.10 The clod should be waterproof and ready for volume measurement by water displacement. 

Suspend clod below the balance, submerge in water, and record weight (WMCW). 

7.11 Dry clod in an oven at 110°C until weight is constant. Weigh oven-dry clod in air 

(WODC) and in water (WODCW) and record weights. 

7.12 If clod contains >5% rock fragments by weight, remove them from clod. Place clod in a 

beaker and place on hot plate. Cover hot plate with a liquid vapor trap. Use a fume hood. 

Heat clod on hot plate in excess of 200°C for 3 to 4 h. The plastic coating disintegrates at 

temperatures above 200°C. After heating, clod should appear black and charred. Remove clod 

from hot plate, lightly coat with liquid detergent, and add hot water. 

7.13 Wet sieve the cool soil through a 2-mm, square-hole sieve. Dry and record weight (RF) of 

rock fragments that are retained on the sieve. Determine rock fragment density by weighing 

them in air to obtain their mass and in water to obtain their volume. If rock fragments are 

porous and have a density similar to soil sample, do not correct clod mass and volume 

measurement for rock fragments. Correct for rock fragments if these fragments can withstand 

breakdown when dry soil is placed abruptly in water or calgon. 

7.14 Correct bulk density for weight and volume of plastic coating. The coating has an air-dry 

density of ≈ 1.3g cm-3. The coating loses 10 to 20% of its air-dry weight when dried in oven at 

110°C. 

8. Calculations

 

8.1 Db33 = [WODC - RF - ODPC – TAG]/{[(CC3 - WMCW)/WD] - (RF/PD) - (MPC1/1.3)} 

where: 

Db33 = Bulk density in g cc-1 of <2-mm fabric at 33-kPa tension 

WODC = Weight of oven-dry coated clod 

RF = Weight of rock fragments 

TAG = Weight of tag and wire 

ODPC = MPC1 x 0.85, weight of oven-dry plastic coat 

CC3 = Weight of equilibrated clod after four additional plastic coats 

WD = Water density 

PD = Density of rock fragments 

MPC1 = Weight of plastic coat before oven-drying 

WMCW = Weight in water of coated clod equilibrated at 33-kPa tension 

8.2 MPC1 = {[(CC2 - CC1) + FCE] x RV} + (CC3-WMC) 

where: 

MPC1 = Weight of plastic coat before oven-drying 

CC2 = Weight of clod after three laboratory plastic coats 

CC1 = Weight of clod before three laboratory plastic coats 

WMC = Weight of coated clod equilibrated at 33-kPa tension 

RV = Percent estimate of remaining clod volume after cutting to obtain flat surface (≈ 80%) 

8.3 FCE = 1.5 x [(CC2 -CC1)/3] 

where: 

FCE = Estimate of field-applied plastic coat 

83
8.4 Dbod = [WODC– RF– ODPC - TAG]/ {[(WODC - WODCW)/WD] - (RF/PD) - 

(MPC1/1.3)} 

where: 

Dbod = Bulk density in g cc-1 <2-mm fabric, oven-dry fabric 

WODCW = Weight of oven-dry clod coated in water 

8.5 W33 ={[(CC3 – MPC1) – (WODC - ODPC)]/[(WODC - RF - ODPC – TAG)]} x 100 

where: 

W33 = Percent water weight retained at 33-kPa tension 

9. Report

Bulk density is reported to the nearest 0.01g cm-3. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References

Blake, G.R., and K.H. Hartge. 1986. Bulk density. p. 363-382. In A. Klute (ed.) Methods 

of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. Monogr. 9. 

ASA and SSSA, Madison, WI. 

Brasher, B.R., D.P. Franzmeier, V.T. Volassis, and S.E. Davidson. 1966. Use of saran 

resin to coat natural soil clods for bulk density and water retention measurements. Soil 

Sci. 101:108. 

Grossman, R.B. and T.G. Reinsch. 2002. Bulk density and linear extensibility. p. 201-228. 

In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis, Part 4. Physical methods. 

Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Occupational Safety and Health Administration. 1989. Air contaminants; final rule. 

Federal Register. 29 CFR Part 1910. Vol. 54. No. 12. p. 2452-2453. U.S. Govt. Print. 

Office, Washington, DC. 

84
Fig. 1. A round stock tag with sample identification number is prepared. 

The cut copper wire is looped around the clod. 

Fig. 2. After a flat surface on the clod is cut with a diamond saw, the clod 

is placed on a tension table, maintained at 5-cm tension. 

85
Bulk Density (3B) 

Saran-Coated Clods (3B1) 

Oven-Dry (Dbod) (3B1c)

1. Application 

Bulk density is used to convert data from a weight to a volume basis; to determine the 

coefficient of linear extensibility; to estimate saturated hydraulic conductivity; and to identify 

compacted horizons. The procedure 3B1c determines the bulk density value (Dbod) of an ovendry soil sample. 

2. Summary of Method 

Field-occurring fabric (clods) is collected from the face of an excavation. One coat of 

plastic lacquer is applied in the field. Additional coats of plastic lacquer are applied in the 

laboratory. The clod is dried in an oven at 110°C and then weighed in air to measure its mass 

and in water to measure its volume. A correction is made for the mass and volume of rock 

fragments and for plastic coatings (Brasher et al., 1966; Blake and Hartge, 1986). 

3. Interferences

Errors are caused by non-representative samples. Only field-occurring fabric (clods) 

should be sampled. The whole soil bulk density may be overestimated because sampled clods 

frequently exclude the crack space between clods (Grossman and Reinsch, 2002). 

The penetration of plastic lacquer into the voids of sandy or organic soils interferes with 

the corrections for mass and volume of the plastic coat and with the accuracy of water content 

determinations. Penetration can be reduced by spraying water on the clod followed by 

immediately dipping the clod in the plastic lacquer. Dipping should be done as quickly as 

possible to reduce penetration of plastic. 

Loss of soil during the procedure will void the analyses because all calculations are 

based on the oven-dry soil mass. Holes in the plastic coating, which are detected by escaping 

air bubbles from submerged clod, introduce errors in volume measurement. An inadequate 

evaporation of plastic solvent results in overestimation of the soil mass. A drying time of 1 h is 

usually sufficient time for evaporation of solvent. However, clods with high organic matter 

content may need to dry longer. 

Bulk density is reported for <2-mm soil fabric. Correction for rock fragments >2-mm 

requires either knowledge or assumption of the rock fragment density. Estimate or 

measurement errors of rock fragment density will affect the accuracy of the value for soil bulk 

density. Rock fragments may contain water, which complicates the application to actual waterholding capacity. 

4. Safety

Methyl ethyl ketone (MEK) is extremely flammable. A type B fire extinguisher should 

be in close proximity in the laboratory. No open flames or nearby operation of electrical 

equipment are permitted while using MEK. The MEK vapor is classified as a sensory irritant. 

The 8-h time weighted average (TWA) exposure limit is 200 ppm, and the short-term exposure 

limit (STEL) is 300 ppm (Occupational Safety and Health Administration, 1989). Avoid 

physical contact. Use with adequate ventilation. In closed buildings, use a fume hood. Keep 

in tightly closed containers. Avoid physical contact. Use safety glasses, proper gloves, and a 

lab coat. Wash hands immediately after handling MEK. Additional information on the safe 

handling of MEK is available in Chemical Safety Data Sheet SD-83, Manufacturing Chemists’ 

Association, Inc., 1825 Connecticut Ave. NW, Washington, DC. 

Saran F-310 resin will decompose rapidly at temperatures >200°C releasing hydrogen 

chloride gas. Avoid contact with Fe, Zn, Cu, and Al in solution. Avoid all contact with strong 

bases. 

86
5. Equipment

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Rigid shipping containers. The SSL uses a corrugated box with compartments. 

5.3 Plastic bags, 1 mil, 127 x 89 x 330 mm 

5.4 Wire. The SSL uses a 28-awg coated copper wire. 

5.5 Hairnets 

5.6 Stock tags, 25.4-mm (1-in) diameter paper tag with metal rim 

5.7 Hook assembly for weighing below balance 

5.8 Plexiglass water tank mounted on a fulcrum and lever 

5.9 Oven, 110°C 

5.10 Sieve, no. 10 (2-mm openings) 

5.11 Rope, 3 m 

5.12 Clothespins 

5.13 Hot plate 

5.14 Spray bottle 

5.15 Liquid vapor trap. The SSL constructs a tin enclosure over hot plate with a chimney and 

duct to transfer vapor to water stream. 

5.16 Tension table. The SSL constructs a tension table by placing porous firebricks, covered 

with reinforced paper towels, in a tub of water. 

6. Reagents

6.1 Methyl ethyl ketone (MEK), practical (2-butanone). 

6.2 Water. 

6.3 Liquid detergent. The SSL uses Liqui-Nox. 

6.4 Dow Saran F-310 Resin, available from Dow Chemical Company. 

6.5 Plastic lacquer. Prepare plastic lacquer with resin to solvent ratios of 1:4 and 1:7 on a 

weight basis. Fill a 3.8-L (1-gal) metal paint can with 2700 ±200 mL of solvent. Fill to 

the bottom of handle rivet. Add 540 or 305 g of resin to make 1:4 or 1:7 plastic lacquer, 

respectively. For the initial field and laboratory coatings, use the 1:4 plastic lacquer. 

Use 1:7 plastic lacquer for the last two laboratory coats. The 1:7 plastic lacquer is used 

to conserve the resin and to reduce cost. In the field, mix solvent with a wooden stick. In 

the laboratory, stir solvent with a non-sparking, high-speed stirrer while slowly adding 

resin. Stir plastic lacquer for 15 min at 25°C. Store plastic lacquer in covered plastic or 

steel containers. Acetone may be substituted for MEK. 

7. Procedure

Field 

7.1 Collect field-occurring clods, ≈ 100 to 200 cm3

 in volume (fist-sized), from the face of the 

excavation. Three clods per horizon are recommended. It is important that these clods be as 

representative of the bulk sample volume as possible. Remove a piece of soil larger than clod 

from the face of sampling pit. From this piece, prepare a clod by gently cutting or breaking 

protruded peaks and compacted material from clod. If roots are present, trim roots with shears. 

No procedure for sampling clods is applicable to all soils. Adjust field-sampling techniques to 

meet field conditions at time of sampling. 

7.2 Make a clothesline by stretching a rope between two fixed points. Tie clod with fine 

copper wire or place clod in a hairnet. If the clod is dry, moisten surface with a fine mist of 

water. Quickly dip entire clod into plastic lacquer (See Fig. 1, procedure 3B1a). Suspend clod 

from clothesline to dry (See Fig. 2, procedure 3B1a). Dry clod for 30 min or until odor of 

solvent dissipates. If the value of Dbf is required, store clods in waterproof plastic bags as soon 

as coating dries because coating is permeable to water vapor. 

7.3 Pack clods in rigid containers to protect them during transport. 

87
Laboratory

7.4 Prepare a round stock tag with sample identification number. Cut the copper wire and loop 

around the clod. Record weight (TAG) of tag and wire. Loop fine copper wire around clod, 

leaving a tail to which round stock tag is attached. Record weight of clod (CC1). 

7.5 Dip clod in 1:4 plastic lacquer. Wait 7 min and then dip clod in 1:7 plastic lacquer. Wait 

12 min and then dip clod in 1:7 plastic lacquer. Wait 55 min and then reweigh clod. If clod 

has adsorbed >3% plastic by clod weight or smells excessively of solvent, allow longer drying 

time, then reweigh clod and record weight (CC2). 

7.6 Dry clod in an oven at 110°C until weight is constant. Weigh oven-dry clod in air (WODC) 

and in water (WODCW) and record weights. 

7.7 If clod contains >5% rock fragments by weight, remove them from clod. Place clod in a 

beaker and place on hot plate. Cover hot plate with a liquid vapor trap. Use a fume hood. 

Heat clod on hot plate in excess of 200°C for 3 to 4 h. The plastic coating disintegrates at 

temperatures above 200°C. After heating, clod should appear black and charred. Remove clod 

from hot plate, lightly coat with liquid detergent, and add hot water. 

7.8 Wet sieve the cool soil through a 2-mm, square- hole sieve. Dry and record weight (RF) of 

rock fragments that are retained on the sieve. Determine rock fragment density by weighing 

them in air to obtain their mass and in water to obtain their volume. If rock fragments are 

porous and have a density similar to soil sample, do not correct clod mass and volume 

measurement for rock fragments. If rock fragments are porous and have a density similar to soil 

sample, do not correct clod mass and volume measurement for rock fragments. Correct for 

rock fragments if these fragments can withstand breakdown when dry soil is placed abruptly in 

water or calgon. 

7.9 Correct bulk density for weight and volume of plastic coating. The coating has an air-dry 

density of ≈ 1.3 g cm-3. The coating loses 10 to 20% of its air-dry weight when dried in oven at 

110°C. 

8. Calculations

8.1 Dbod = [WODC- RF-ODPC – TAG]/{[(WODC – WODCW)/WD] - (RF/PD) - (MPC/1.3)} 

where: 

Dbod = Bulk density in g cm-3 of <2-mm, oven-dry fabric 

WODC = Weight of oven-dry coated clod 

RF = Weight of rock fragments 

TAG = Weight of tag and wire 

ODPC = MPC1 x 0.85, weight of oven-dry plastic coat 

WD = Water density 

PD = Density of rock fragments 

WODCW = Weight of oven-dry coated clod in water 

8.2 MPC = [(CC2 - CC1) + FCE] x RV 

where: 

MPC = Weight of plastic coat before oven-drying 

CC2 = Weight of clod after three laboratory plastic coats 

CC1 = Weight of clod before three laboratory plastic coats 

RV = Percent estimate of remaining clod volume after cutting to obtain flat surface (≈ 80%) 

88
8.3 FCE = 1.5 x [(CC2 -CC1)/3] 

where: 

FCE = Estimate of field-applied plastic coat 

9. Report

Bulk density is reported to the nearest 0.01g cm-3. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References

Blake, G.R., and K.H. Hartge. 1986. Bulk density. p. 363-382. In A. Klute (ed.) Methods 

of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. Monogr. 9. 

ASA and SSSA, Madison, WI. 

Brasher, B.R., D.P. Franzmeier, V.T. Volassis, and S.E. Davidson. 1966. Use of saran 

resin to coat natural soil clods for bulk density and water retention measurements. Soil 

Sci. 101:108. 

Grossman, R.B., and T.G. Reinsch. 2002. Bulk density and linear extensibility. p. 201-228. 

In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis, Part 4. Physical methods. 

Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Occupational Safety and Health Administration. 1989. Air contaminants; final rule. 

Federal Register. 29 CFR Part 1910. Vol. 54. No. 12. p. 2452-2453. U.S. Govt. Print. 

Office, Washington, DC. 

Bulk Density (3B) 

Saran-Coated Clods (3B1) 

Rewet (Dbr) (3B1d)

1. Application

Bulk density is used to convert data from a weight to a volume basis; to determine the 

coefficient of linear extensibility; to estimate saturated hydraulic conductivity; and to identify 

compacted horizons. The rewet bulk density (Dbr) is used to determine irreversible shrinkage 

of soils and subsidence of organic soils. The procedure 3B1d determines the bulk density value 

(Dbr) of a re-wetted soil sample. 

2. Summary of Method 

Field-occurring fabric (clods) is collected from the face of an excavation. One coat of 

plastic lacquer is applied in the field. Additional coats of plastic lacquer are applied at the 

laboratory. After equilibration, the clod is weighed in air to measure its mass and in water to 

measure its volume. The clod is air-dried, re-equilibrated, and its mass and volume remeasured. After the clod is dried in the oven at 110°C, its mass and volume are determined 

again. A correction is made for the mass and volume of rock fragments and for plastic coatings 

(Brasher et al., 1966; Blake and Hartge, 1986; Grossman and Reinsch, 2002). 

3. Interferences

Errors are caused by non-representative samples. Only field-occurring fabric (clods) 

should be sampled. The whole soil bulk density may be overestimated because sampled clods 

frequently exclude the crack space between clods (Grossman and Reinsch, 2002). 

The penetration of plastic lacquer into the voids of sandy or organic soils interferes with 

the corrections for mass and volume of the plastic coat and with the accuracy of water content 

determinations. Penetration can be reduced by spraying water on the clod followed by 

89
immediately dipping the clod in the plastic lacquer. Dipping should be done as quickly as 

possible to reduce penetration of plastic. 

Loss of soil during the procedure will void the analyses because all calculations are 

based on the oven-dry soil mass. Holes in the plastic coating, which are detected by escaping 

air bubbles from submerged clod, introduce errors in volume measurement. Inadequate drying 

results in overestimation of the soil mass. An inadequate evaporation of plastic solvent results 

in overestimation of the soil mass. A drying time of 1 h is usually sufficient time for 

evaporation of solvent. However, clods with high organic matter content may need to dry 

longer. 

Bulk density is reported for <2-mm soil fabric. Correction for rock fragments >2-mm 

requires either knowledge or assumption of the rock fragment density. Estimate or 

measurement errors of rock fragment density will affect the accuracy of the value for soil bulk 

density. Rock fragments may contain water, which complicates the application to actual waterholding capacity. 

4. Safety

Methyl ethyl ketone (MEK) is extremely flammable. A type B fire extinguisher should 

be in close proximity in the laboratory. No open flames or nearly operation of electrical 

equipment are permitted while using MEK. The MEK vapor is classified as a sensory irritant. 

The 8 h time weighted average (TWA) exposure limit is 200 ppm, and the short term exposure 

limit (STEL) is 300 ppm (Occupational Safety and Health Administration, 1989). Avoid 

physical contact. Use with adequate ventilation. In closed buildings, use a fume hood. Keep 

in tightly closed containers. Avoid physical contact. Use safety glasses, proper gloves, and a 

lab coat. Wash hands immediately after handling MEK. Additional information on the safe 

handling of MEK is available in Chemical Safety Data Sheet SD-83, Manufacturing Chemists’ 

Association, Inc., 1825 Connecticut Ave. NW, Washington, DC. 

Saran F-310 resin will decompose rapidly at temperatures >200°C releasing hydrogen 

chloride gas. Avoid contact with Fe, Zn, Cu, and Al in solution. Avoid all contact with strong 

bases. 

5. Equipment

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Pressure plate extractor with porous ceramic plate. 

5.3 Air pressure, 33-kPa 

5.4 Rigid shipping containers. The SSL uses a corrugated box with compartments. 

5.5 Plastic bags, 1 mil, 127 x 89 x 330 mm 

5.6 Wire. The SSL uses a 28-awg coated copper wire. 

5.7 Hairnets 

5.8 Stock tags, 25.4-mm (1-in) diameter paper tag, with metal rim 

5.9 Hook assembly for weighing below balance 

5.10 Plexiglass water tank mounted on a fulcrum and lever to elevate tank 

5.11 Oven, 110°C 

5.12 Sieve, No. 10 sieve (2-mm openings) 

5.13 Rope, 3 m 

5.14 Clothespins 

5.15 Knife 

5.16 Tile cut-off saw with diamond blade 

5.17 Silt loam soil 

5.18 Hot plate 

5.19 Desiccator with ceramic plate 

5.20 Vacuum, 80 kPa, (0.8 bar) 

5.21 Metal probe 

5.22 Spray bottle 

90
5.23 Liquid vapor trap. The SSL constructs a tin enclosure over hot plate with a chimney and 

duct to transfer vapor to water stream. 

5.24 Reinforced paper towels or cheesecloth 

5.25 Tension table. The SSL constructs a tension table by placing porous firebricks, covered 

with reinforced paper towels, in a tub of water. 

6. Reagents 

6.1 Methyl ethyl ketone (MEK), practical (2-butanone). 

6.2 Water. 

6.3 Alcohol. 

6.4 Liquid detergent. The SSL uses Liqui-Nox. 

6.5 Dow Saran F-310 Resin, available from Dow Chemical Company. 

6.6 Plastic lacquer. Prepare plastic lacquer with resin to solvent ratios of 1:4 and 1:7 on a 

weight basis. Fill a 3.8-L (1-gal) metal paint can with 2700 ±200 mL of solvent. Fill to 

the bottom of handle rivet. Add 540 or 305 g of resin to make 1:4 or 1:7 plastic lacquer, 

respectively. For the initial field and laboratory coatings, use the 1:4 plastic lacquer. Use 

1:7 plastic lacquer for the last two laboratory coats. The 1:7 plastic lacquer is used to 

conserve the resin and to reduce cost. In the field, mix solvent with a wooden stick. In the 

laboratory, stir solvent with a non-sparking, high-speed stirrer while slowly adding resin. 

Stir plastic lacquer for 15 min at 25°C. Store plastic lacquer in covered plastic or steel 

containers. Acetone may be substituted for MEK. 

7. Procedure

Field 

7.1 Collect field-occurring clods, ≈ 100 to 200 cm3

 in volume (fist-sized), from the face of the 

excavation. Three clods per horizon are recommended. It is important that these clods be as 

representative of the bulk sample volume as possible. Remove a piece of soil larger than clod 

from the face of sampling pit. From this piece, prepare a clod by gently cutting or breaking 

protruded peaks and compacted material from clod. If roots are present, trim roots with shears. 

No procedure for sampling clods is applicable to all soils. Adjust field sampling techniques to 

meet field conditions at time of sampling. 

7.2 Make a clothesline by stretching a rope between two fixed points. Tie clod with fine 

copper wire or place clod in a hairnet. If the clod is dry, moisten surface with a fine mist of 

water. Quickly dip entire clod into plastic lacquer (See Fig. 1, procedure 3B1a). Suspend clod 

from clothesline to dry (See Fig. 2, procedure 3B1a). Dry clod for 30 min or until odor of 

solvent dissipates. If the value of Dbf is required, store clods in waterproof plastic bags as soon 

as coating dries because coating is permeable to water vapor. 

7.3 Pack clods in rigid containers to protect them during transport. 

Laboratory

7.4 Prepare a round stock tag with sample identification number. Cut the copper wire and loop 

around the clod. Record weight (TAG) of tag and wire. Loop fine copper wire around clod, 

leaving a tail to which round stock tag is attached. Record weight of clod (CC1). 

7.5 Dip clod in 1:4 plastic lacquer. Wait 7 min and then dip clod in 1:7 plastic lacquer. Wait 

12 min and then dip clod in 1:7 plastic lacquer. Wait 55 min and then reweigh clod. If clod 

has adsorbed >3% plastic by clod weight or smells excessively of solvent, allow longer drying 

time, then reweigh clod and record weight (CC2). 

7.6 With a diamond saw, cut a flat surface on the clod. 

91
7.7 Place cut clod surface on a tension table, maintained at 5-cm tension. Periodically check 

clod to determine if it has reached equilibrium by inserting metal probe, touching, or by weight 

comparison. When clod has reached equilibrium, remove clod and record weight (WSC). 

7.8 If cut clod does not adsorb water, place clod in a desiccator on a water-covered plate with a 

0-cm tension. Submerge only the surface of clod in the water. Add a few mL of alcohol. Use 

in-house vacuum and apply suction until clod has equilibrated at saturation. Remove clod and 

record weight (WSC). 

7.9 Place clod in a pressure plate extractor. To provide good contact between clod and ceramic 

plate, cover ceramic plate with a 5-mm layer of silt loam soil and saturate with water. Place a 

sheet of reinforced paper towel or cheesecloth over the silt loam soil. Place surface of cut clod 

on paper towel. Close container and secure lid. Apply gauged air pressure of 33-kPa. When 

water ceases to discharge from outflow tube, clod is at equilibrium. Extraction usually takes 3 

to 4 wk. Remove clod and record weight (WMC). Compare WMC to WSC. If WMC > WSC, 

equilibrate clod on tension table and repeat desorption process. 

7.10 Dip clod in the 1:4 plastic lacquer. Wait 7 min and then dip clod in 1:7 plastic lacquer. 

Wait 12 min and then dip clod in 1:7 plastic lacquer. Wait 12 min and dip clod in 1:7 plastic 

lacquer. After 55 min, reweigh clod and record weight (CC3). If clod has adsorbed >3% 

plastic by weight or smells excessively of solvent, allow longer drying time, then reweigh clod. 

7.11 The clod should be waterproof and ready for volume measurement by water displacement. 

Suspend clod below the balance, submerge in water, and record weight (WMCW). 

7.12 Remove layer of plastic from flat surface of clod. Air-dry clod at room temperature (~ 20 

to 25°C) for 4 to 6 days. Dry clod at 40 to 50°C for 2 to 3 days or until weight is constant. 

7.13 Repeat steps 7.7, 7.8, and 7.9. After equilibrium is obtained, remove clod and record 

weight (WAR). 

7.14 Dip clod in the 1:4 plastic lacquer. Wait 7 min and then dip clod in 1:7 plastic lacquer. 

Wait 12 min and then dip clod in 1:7 plastic lacquer. Wait 12 min and dip clod in 1:7 plastic 

lacquer. After 55 min, reweigh clod and record weight (CC4). If clod has adsorbed >3% 

plastic by weight or smells excessively of solvent, allow longer drying time, then reweigh clod. 

7.15 After coating, record weight of clod suspended in air (CC4) and in water (WARW). 

7.16 Dry clod in an oven at 110°C until weight is constant. Weigh oven-dry clod in air 

(WODC) and in water (WODCW) and record weights. 

7.17 If clod contains >5% rock fragments by weight, remove them from clod. Place clod in a 

beaker and place on hot plate. Cover hot plate with a liquid vapor trap. Use a fume hood. 

Heat clod on hot plate in excess of 200°C for 3 to 4 h. The plastic coating disintegrates at 

temperatures above 200°C. After heating, clod should appear black and charred. Remove clod 

from hot plate, lightly coat with liquid detergent, and add hot water. 

7.18 Wet sieve the cool soil through a 2-mm, square- hole sieve. Dry and record weight (RF) 

of rock fragments that are retained on the sieve. Determine rock fragment density by weighing 

them in air to obtain their mass and in water to obtain their volume. If rock fragments are 

porous and have a density similar to soil sample, do not correct clod mass and volume 

measurement for rock fragments. If rock fragments are porous and have a density similar to soil 

sample, do not correct clod mass and volume measurement for rock fragments. Correct for 

92
rock fragments if these fragments can withstand breakdown when dry soil is placed abruptly in 

water or calgon. 

7.19 Correct bulk density for weight and volume of plastic coating. The coating has an air-dry 

density of ≈ 1.3 g cm-3. The coating loses 10 to 20% of its air-dry weight when dried in oven at 

110°C. 

8. Calculations

8.1 Db33 = [WODC - RF - ODPC – TAG]/{[(CC3 - WMCW)/WD] - (RF/PD) - (MPC1/1.3)} 

where: 

Db33 = Bulk density in g cm-3 of <2-mm fabric at 33-kPa tension 

WODC = Weight of oven-dry coated clod 

RF = Weight of rock fragments 

ODPC = MPC1 x 0.85, weight of oven-dry plastic coat 

TAG = Weight of tag and wire 

CC3 = Weight of equilibrated clod after four additional plastic coats 

WD = Water density 

PD = Density of rock fragments 

WMCW = Weight in water of coated clod equilibrated at 33-kPa tension 

8.2 MPC1 = {[(CC2 - CC1) + FCE] x RV} + (CC3-WMC) 

where: 

MPC1 = Weight of plastic coat before air-drying and rewet 

CC2 = Weight of clod after three laboratory plastic coats 

CC1 = Weight of clod before three laboratory plastic coats 

RV = Percent estimate of remaining clod volume after cutting to obtain flat surface (≈ 80%) 

WMC = Weight of coated clod equilibrated at 33-kPa tension 

8.3 FCE = 1.5 x [(CC2 -CC1)/3] 

where: 

FCE = Estimate of field-applied plastic coat. 

 

8.4 Dbr= [WODC – RF – ODPC - TAG]/ {[(CC4 - WARW)/WD] - (RF/PD) - (MPC2/1.3)} 

where: 

Dbr = Bulk density in g cm-3 <2-mm fabric at 33-kPa tension after rewetting 

CC4 = Weight of clod after twelve plastic coats 

WARW = Weight in water of coated clod equilibrated at 33-kPa tension after rewet 

8.5 MPC2 = {[(CC2 - CC1) + FCE] x RV2} + (CC3-WMC) + (CC4-WAR) 

where: 

MPC2 = Weight of plastic coat after rewet and before oven drying 

WAR = Weight of clod after rewet equilibration 

RV2 = Percent estimate of remaining clod volume after remaining layer of plastic (≈ 0.95) 

8.6 Dbod = [WODC– RF– ODPC-TAG]/{[(WODC-WODCW) /WD] - (RF/PD) - (MPC2/1.3)} 

where: 

Dbod = Bulk density in g cm-3 of <2-mm fabric at oven dryness 

93
WODCW = Weight in water of oven-dry coated clod 

8.7 W1/3 = {[(CC3 - MPC1) – (WODC - ODPC)]/(WODC - RF - ODPC – TAG)} x 100 

where: 

W33 = Percent water weight retained at 33-kPa tension 

8.8 Wr ={[(CC4 - MPC2) – (WODC - ODPC)]/ [WODC - RF - ODPC – TAG]} x 100 

where: 

Wr = Percent water weight retained at 33-kPa tension after rewet 

9. Report

Bulk density is reported to the nearest 0.01g cm-3. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References

Blake, G.R., and K.H. Hartge. 1986. Bulk density. p. 383-382. In A. Klute (ed.) Methods 

of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. Monogr. 9. 

ASA and SSSA, Madison, WI. 

Brasher, B.R., D.P. Franzmeier, V.T. Volassis, and S.E. Davidson. 1966. Use of saran 

resin to coat natural soil clods for bulk density and water retention measurements. Soil 

Sci. 101:108. 

Grossman, R.B., and T.G. Reinsch. 2002. Bulk density and linear extensibility. p. 201-228. 

In J.H. Dane and G.C. Topp (eds.). Methods of soil analysis, Part 4. Physical methods. 

Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Occupational Safety and Health Administration. 1989. Air contaminants; final rule. 

Federal Register. 29 CFR Part 1910. Vol. 54. No. 12. p. 2452-2453. U.S. Govt. Print. 

Office, Washington, DC. 

Bulk Density (3B) 

Reconstituted (3B2) 

33 kPa Desorption (Db33) (3B2a) Oven-Dry (Dbod) (3B2b) 

1. Application 

Bulk density is used to convert data from weight to volume basis, to determine the 

coefficient of linear extensibility, to estimate saturated hydraulic conductivity, and to identify 

compacted horizons. Some models and programs require one bulk density to represent a given 

horizon. The reconstituted bulk density provides a single, reproducible value for horizons that 

are subject to tillage or other mechanical disturbances followed by an extreme water-state cycle 

(Reinsch and Grossman, 1995). 

2. Summary of Method 

7KH<2-mm sample is formed into a clod by wetting and GHVVLFFDWLRQF\FOHVWKDW

simulate reconsolidating by water in a field setting. Plastic lacquer is DSSOLHGLQWKH

laboratory to form an impermeable coat on the clod. The clod is desorbed to 33-N3D

After equilibration, the clod is weighed in air to measure the mass and in water to 

measure the volume. After the clod is oven dried at 110°C, its mass and volume are 

determined again (Brasher et al., 1966; Blake and Hartge, 1986; Grossman and Reinsch, 2002). 

94
3. Interferences 

Some samples disintegrate when they are removed from the cells. 

4. Safety 

Methyl ethyl ketone (MEK) is extremely flammable. A type B fire extinguisher should 

be in close proximity in the laboratory. No open flames or nearby operation of electrical 

equipment are permitted while using MEK. The MEK vapor is classified as a sensory irritant. 

The 8-h time-weighted average (TWA) exposure limit is 200 ppm, and the short-term exposure 

limit (STEL) is 300 ppm (Occupational Safety and Health Administration, 1989). Avoid 

physical contact. Use with adequate ventilation. In closed buildings, use a fume hood. Keep 

in tightly closed containers. Use safety glasses, proper gloves, and a lab coat. Wash hands 

immediately after handling MEK. Additional information on the safe handling of MEK is 

available in Chemical Safety Data Sheet SD-83, Manufacturing Chemists’ Association, Inc., 

1825 Connecticut Ave. NW, Washington, DC. 

5. Equipment 

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Pressure plate extractor with porous ceramic plate 

5.3 Air pressure, 33-kPa 

5.4 Clod forming cylinder. We construct the cell by attaching a brass ring or schedule 20 or 

40 PVC pipe, 5.4-cm diameter and 6 to 7 cm high, to a 100-kPa ceramic plate with 

waterproof glue and caulk 

5.5 Anti-sorting device. We construct a wire screen with 0.5-cm openings and 5.2 cm 

diameter with a perpendicular wire attached to the center to reduce natural sorting caused 

by placing the sample in the cell 

5.6 Wire. SSL uses 28-awg-coated copper wire 

5.7 Hairnets 

5.8 Stock tags, 1-inch diameter paper tag with metal rim 

5.9 Hook assembly for weighing below balance 

5.10 Plexiglas water tank mounted on a fulcrum and lever to elevate tank 

5.11 Oven, 110°C 

5.12 Plastic tub at least 10 cm deep 

5.13 Paper discs cut from water insoluble, permeable paper 

5.14 Tile cut-off saw with diamond blade 

5.15 Silt soil 

5.16 Desiccator with ceramic plate 

5.17 Vacuum, 80 kPa (0.8 bar) 

5.18 Metal probe 

5.19 Spray bottle 

5.20 Reinforced paper towels or cheesecloth 

5.21 Tension table. We construct a tension table by placing porous firebricks, covered with 

reinforced paper towels, in a tub of water

6. Reagents 

6.1 Methyl Ethyl Ketone, practical (2-butanone). 

6.2 Water. 

6.3 Alcohol. 

6.4 Dow Saran F-310 Resin, available from Dow Chemical Company. 

6.5 Plastic lacquer. Prepared the plastic lacquer with resin to solvent ratios of 1:4 and 1:7 on a 

weight basis. We fill a metal gallon paint can with 2700 ± 200 ml of solvent (fill to the 

bottom of the handle rivet) and add 540 g or 305 g of resin to make 1:4 or 1:7 plastic 

lacquer, respectively. Use the 1:4 plastic lacquer for the first field and lab coats and the 

1:7 plastic lacquer for the last two coats. The 1:7 plastic lacquer is used to conserve the 

resin and reduce cost. Stir the solvent with a non-sparking, high-speed stirrer while slowly 

95
adding the resin. Stir the plastic lacquer for 15 min at 25°C. In the field, mix with a 

wooden stick. Store the plastic lacquer in covered plastic or steel containers. Acetone 

may be substituted for MEK. 

7. Procedure 

Reconstituted Clod Construction 

7.1 Drape a hairnet in the cell. Place a paper disc in the bottom of the cell. Place the antisorting screen into the cell. Add <2-mm, prepared sample to within a few mm of the top of the 

cell. Lift the anti-sorting screen from the cell. 

7.2 Place the cell on a tension table with the height 5-cm below the top of the table. After 

equilibration, place the cell into a tub and add water to a level higher than the surface of the soil 

in the cell but below the top lip of the cell. This allows the soil to become inundated from 

beneath. Allow the sample to equilibrate. 

7.3 Remove the cell from the tub and allow to dry at room temperature. After drying remove 

the clod by lifting on the hairnet or inverting the cell and lightly tamping the base of the cell. 

The reconstituted clod is used to measure bulk density and water retention. 

Bulk Density Measurement 

7.4 Prepare a round stock tag with sample identification number. Cut the copper wire to loop 

around the clod. Record the weight of the tag and wire (TAG). Loop fine copper wire around 

the clod leaving a tail to which the round stock tag is attached. Record the weight of the clod 

(CC1). 

7.5 Mist the clod with water to create a film of water on the surface of the clod. Dip the clod in 

the 1:4 plastic lacquer. After 7 min, dip the clod in the 1:4 plastic lacquer. After 7 min, dip the 

clod in the 1:7 plastic lacquer. After 12 min, dip the clod in the 1:7 plastic lacquer. After 

55 min, reweigh the clod. If the clod has adsorbed more than 3 percent plastic by clod weight 

or smells excessively of solvent, allow longer drying time, then reweigh the clod and record the 

weight (CC2). 

7.6 Cut a flat surface on the clod with a diamond saw. Place the cut clod surface on a tension 

table maintained at 5-cm tension. Check the clod periodically by inserting a metal probe, 

touching, or weight comparison to determine if it has reached equilibrium. When the clod has 

reached equilibrium, remove the clod and record the weight (WSC). 

7.7 If the clod does not adsorb water, place the clod in a desiccator that has water covering the 

desiccator plate. Add a few ml of alcohol. Apply suction using in-house vacuum for 24 hours. 

Remove the clod and record the weight (WSC). 

7.8 Place the clod in a pressure plate extractor. To provide good contact between the clod and 

ceramic plate, cover the ceramic plate with a 5-mm layer of silt and saturate with water. Place 

a sheet of reinforced paper towel or cheesecloth over the silt . Place the cut surface of the clod 

on the paper towel. Close the container and secure the lid. Apply gauged air pressure of 33-

kPa. When water stops discharging from the outflow tube (usually after 3 or 4 wk in the 

extractor), the clod is at equilibrium. Remove the clod and record the weight (WMC). 

Compare WMC to WSC. If WMC is greater than or equal to WSC, equilibrate the clod on the 

tension table and repeat the desorption process. 

7.9 Dip the clod in the 1:4 plastic lacquer. After 7 min, dip the clod in the 1:7 plastic lacquer. 

After 12 min, dip the clod in the 1:7 plastic lacquer. After 12 min, dip the clod in the 1:7 

plastic lacquer. After 55 min, reweigh the clod and record the weight (CC3). If the clod has 

96
adsorbed more than 3 percent plastic by clod weight or smells excessively of solvent, allow 

longer drying time, then reweigh the clod. 

7.10 The clod should now be waterproof and ready for the volume measurement by water 

displacement. Suspend the clod below the balance, submerge in water, and record the weight 

(WMCW). 

7.11 Dry the clod in an oven at 110°C overnight. Weigh the oven dry clod in air (WODC) and 

in water (WODCW) and record the weights. 

7.12 It is necessary to correct bulk density for weight and volume of the plastic coating. The 

coating has an air-dry density of about 1.3 g/cm3. The coating loses 10 to 20 percent of its airdry weight on oven drying at 110°C. 

8. Calculations 

8.1 Db33 = [WODC - RF - ODPC – TAG]/{[(CC2 - WMCW)/WD] - (RF/PD) - (MPC1/1.3)} 

where: 

Db33 = Bulk density in grams per cubic centimeter of < 2-mm fabric at 33-kPa tension 

WODC = Weight of oven dry coated clod 

ODPC = MPC x 0.85, weight of oven dry plastic coat 

TAG = Weight of tag and wire 

CC3 = Weight of equilibrated clod after four additional plastic coats 

WMCW = Weight of coated clod equilibrated at 33-kPa tension in water 

MPC1 = Weight of plastic coat before oven-drying 

WD = Water density 

8.2 MPC1 = {[(CC2-CC1)] x RV} + (CC3-WMC) 

where: 

MPC1 = Weight of plastic coat before oven-drying 

CC2 = Weight of clod after four laboratory plastic coats 

CC1 = Weight of clod before four laboratory plastic coats 

RV = Percent estimate of remaining clod volume after cutting to obtain flat surface 

(≈95%) 

WMC = Weight of coated clod equilibrated at 33-kPa tension 

8.3 Dbod = [WODC – ODPC - TAG]/{[(WODC – WODCW)/WD] - (MPC/1.3)} 

where: 

Dbod = Bulk density in grams per cubic centimeter of < 2-mm fabric at oven-dryness 

WODCW = Weight of oven dry coated clod in water 

 

8.4 W33 = {[(CC3 – MPC1) - (WODC - ODPC)]/[WODC - ODPC – TAG)]} x 100 

where: 

W33 = Weight percentage of water retained at 33-kPa tension 

9. Report 

Bulk density is reported to the nearest 0.01 g cm-3. 

9. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

97
11. References 

Blake, G.R. and K.H. Hartge. 1986. Bulk density. p. 363-382. In A. Klute (ed.) Methods of 

soil analysis, Part 1. Physical and mineralogical methods. 2nd ed. Agron. Monogr. 9. 

ASA and SSSA, Madison, WI. 

Brasher, B.R., D.P. Franzmeier, V.T. Volassis, and S.E. Davidson. 1966. Use of saran 

resin to coat natural soil clods for bulk density and water retention measurements. Soil 

Sci. 101:108. 

Grossman, R.B., and T.G. Reinsch. 2002. Bulk density and linear extensibility. p. 201-228. 

In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis, Part 4. Physical methods. 

Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Occupational Safety and Health Administration. 1989. Federal Register. Air contaminants; 

final rule. Federal Register. 29 CFR Part 1910. Vol. 54. No. 12. p. 2452-2453. U.S. 

Govt. Print. Office, Washington, DC. 

Reinsch, T.G., and R.B. Grossman. 1995. A method to predict bulk density of tilled Ap 

horizons. Soil and Tillage Res. 34: 95-104. 

Bulk Density (3B) 

Compliant Cavity (3B3) 

Field-State (3B3a) 

1. Application 

Bulk density is used to convert data from a weight to a volume basis; to estimate 

saturated hydraulic conductivity; and to identify compacted horizons. Excavation procedures 

(e.g., compliant cavity, ring, and frame) have applicability to layers that can be described as 

cohesionless, high in rock fragments > 5mm, or thin (<5 cm thick), and for which the clod 

method is unsuitable (Grossman and Reinsch, 2002). The compliant cavity method was 

designed for fragile cultivated near-surface layers and O horizons of forestland soils. This 

method has the important advantage that it is not necessary to flatten the ground surface on 

steep slopes or remove irregularities, i.e., the surficial zone is usually not altered (Grossman 

and Reinsch, 2002). 

2. Summary of Method 

By this procedure (3B3a), the cavity volume on the zone surface is lined with thin 

plastic and water is added to a datum level. Soil is quantitatively excavated in a cylindrical 

form to the required depth. The difference between the initial volume and that after excavation 

is the sample volume. The excavated soil is dried in an oven and then weighed. A correction is 

made for the weight and volume of rock fragments. 

3. Interferences 

Bulk density by compliant cavity can be made on soils with rock fragments but is more 

complex (Grossman and Reinsch, 2002). 

4. Safety 

Follow standard field and laboratory safety precautions. 

5. Equipment 

5.1 Fabricated Plexiglass rings, 9-mm thick, 130-mm inside diameter, and >200-mm outside 

diameter. Make three 16-mm diameter holes that are 10 mm from the outer edge of ring. 

Position holes equidistant apart. Use three, 25 x 50 mm, Plexiglass pieces as guides. 

Attach two pieces on one side to form an "L". Allow a 15-mm gap to permit removal of 

soil material. On the other side, position the single piece in line with the longer leg of the 

"L" so that an adjacent, parallel line forms a diameter. 

98
5.2 Make 50-mm thick foam rings from flexible polyurethane with an "Initial Load 

Displacement" of 15 to 18 kg. The foam rings have the same inside diameter as the 

Plexiglass rings. 

5.3 Fabricate a 240-mm crossbar from 5 x 18 mm metal stock to which legs (25-mm high and 

180 x 180 mm in cross section) are welded. Drill a hole 100 mm from one end of the 

crossbar and 7 mm from the edge and through which a No. 6 machine bolt is placed. 

5.4 Mount hook gauge on crossbar. Make hook gauge from No. 6, round-headed, 100-mm 

long machine bolts and from hexagonal nuts. Obtain the machine bolts from toggle bolt 

assemblies. Sharpen the machine bolt to a sharp point. Drill a hole in the center of the 

crossbar. Insert the machine bolt in the hole. Place nuts above and below the crossbar. 

The two nuts adjust the hook length below the crossbar and provide rigidity. Hold the 

machine bolt by the tightened nuts and heat the bolt. After softening, sharply bend the 

bolt upward to form a U-shape. 

5.5 Use wing nuts and three, 250- to 400-mm long, 10- to 13-mm diameter, threaded rods to 

mount and position the compliant cavity. Sharpen the rods. Place two regular nuts at the 

end of threaded rod to increase the area of surface struck. 

5.6 Syringe, 60 mL 

5.7 Plastic film, 1/2 mil, 380-mm wide or wider; 460-mm wide for larger ring. 

5.8 Plastic bags, 110°C-capability, with ties 

5.9 Sharpie pen 

5.10 Graduate cylinders, plastic, 250 to 2000 mL 

5.11 Level, small 

5.12 Kitchen knife, small 

5.13 Scissors, small, to cut fine roots 

5.14 Hack saw blade to cut large roots 

5.15 Weights for plastic film 

5.16 Clothespins. If wind, use clothespins for corners of plastic film. 

5.17 Hard rubber or plastic mallet 

5.18 Sieve, square-hole, 10 mesh, 2 mm 

6. Reagents 

6.1 Water 

7. Procedure 

7.1 Place a ring of plastic foam on ground and cover with rigid ring (130-mm inside diameter). 

Mount the assembly on the soil surface by securely driving threaded rods into the ground 

through holes in ring and by tightening ring with wing nuts. 

7.2 Line cavity with 1/2-mL plastic. Fill cavity to tip of hook gauge with a known quantity of 

water from graduate cylinder. 

7.3 Remove plastic film and water. Measure the volume of water to tip of hook gauge. This 

volume (Vd) is the measurement of cavity volume prior to excavation (dead space). 

7.4 Excavate soil quantitatively and in a cylindrical form to the required depth. Fill the 

excavation cavity to tip of hook gauge with water from graduated cylinder. Measure the 

volume of water. This volume (Vf) is the measurement of excavated soil and dead space. The 

difference between the two water volumes (Vf - Vd) is the volume of excavated soil (Ve). 

7.5 The excavated soil is dried in oven and weighed. If necessary, make a correction for 

weight and volume of >2-mm material (Vg) in sample and compute bulk density. The weight 

of macroscopic vegetal material (g cm-3) also may be reported. 

99
8. Calculations 

8.1 Ve = Vf - Vd - Vg 

where: 

Ve = Excavation volume of <2-mm fraction (cc) 

Vf = Water volume measurement of excavated soil and dead space (cc) 

Vd = Water volume measurement of dead space (cc) 

Vg = Gravel volume (>2mm- fraction) (cc). Calculate Vg by dividing the weight of >2-mm 

fraction by particle density of the >2-mm fraction. Default value of 2.65 g cc-1. 

8.2 Wf = Wo - Wc 

where: 

Wf = Oven-dry weight of <2-mm soil (g) 

Wo = Oven-dry weight of excavated soil (g) 

Wc = Oven-dry weight of rock fragments (g) 

8.3 Db = Wf/Ve 

where: 

Db = Bulk density (g cc-1) 

Wf = Oven-dry weight of <2-mm soil (g) 

Ve = Excavation volume of <2-mm material (cc) 

9. Report

Bulk density is reported to the nearest 0.01 g cm-3. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Grossman, R.B., and T.G. Reinsch. 2002. Bulk density and linear extensibility. p. 201-228. 

In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis, Part 4. Physical methods. 

Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Bulk Density (3B) 

Ring Excavation (3B4) 

Field-State (3B4a) 

1. Application 

Bulk density is used to convert data from a weight to a volume basis; to estimate 

saturated hydraulic conductivity; and to identify compacted horizons. Excavation procedures 

(e.g., compliant cavity, ring, and frame) have applicability to layers that can be described as 

coheshionless, high in rock fragments > 5mm, or thin (<5 cm thick), and for which the clod 

method is unsuitable (Grossman and Reinsch, 2002). The ring excavation is a robust, simple, 

and rapid method. This method is good for O horizons in the woods where local variability is 

large. The diameter can range down to 15 cm and upwards to 30 cm or more. It is not 

necessary to excavate from the whole area within the ring. A limit of 2 cm on the minimum 

thickness of the sample should be considered. 

2. Summary of Method 

 A 20-cm ring is inserted into the ground. A piece of shelf standard is placed across the 

ring near to a diameter. The distance to the ground surface is measured at eight points equally 

100
spaced along the diameter using the depth-measurement tool to measure the distance. The piece 

of shelf is rotated 90° and eight more measurements are made. The 16 measurements are then 

averaged. The soil is excavated to the desired depth, and the distance measurements repeated. 

The change in distance is calculated on the removal of the soil. This change in distance is then 

multiplied by the inside cross-sectional area of the ring to obtain the volume of soil. The 

excavated soil is oven-dried and weighed. If rock fragments are present, the weight and volume 

of >2-mm material in sample are corrected and bulk density computed. Bulk density of soil is 

reported in g cm-3 by procedure 3B4a. 

3. Interferences 

Rock fragments may make insertion of ring into the ground impossible. 

4. Safety 

Follow standard field and laboratory safety precautions. 

5. Equipment 

5.1 Metallic cylinder, 20-cm diameter, 10- to 20-cm high, and about 1-mm depth 5.2 Shelf standard (slotted rod), 1.5-cm wide, 1-cm high, and 25-cm long 

5.3 Piece of retractable ruler, 30-cm long with 0.1-mm divisions 

5.4 Piece of wood, 10 x 10 x 30 cm 

5.5 Hand digging equipment 

5.6 Depth-measurement tool (Grossman and Reinsch, 2002) 

6. Reagents 

None. 

7. Procedure 7.1 Insert a 20-cm diameter ring below the depth of excavation. 

7.2 Place a piece of shelf standard across the ring near to or along a diameter. Measure the 

distance to the ground surface at eight points equally spaced along the diameter using the 

depth-measurement tool to measure the distance. 

7.3 Rotate the piece of shelf standard 90° and make eight more measurements. Average the 16 

measurements. 

7.4 Excavate the soil to the desired depth. Repeat the distance measurements. 

7.5 Calculate the change in distance on removal of the soil. Multiply the change in distance by 

the inside cross-sectional area of the ring to obtain the volume of the soil (Ve). 

7.6 The excavated soil is dried in oven and weighed. If necessary, make a correction for 

weight and volume of >2-mm material in sample and compute bulk density. The weight of 

macroscopic vegetal material (g cm-3) also may be reported. 

8. Calculations 

8.1 Wf = Wo – We 

where: 

Wf = Oven-dry weight of <2-mm soil (g) 

Wo = Oven-dry weight of excavated soil (g) 

Wc = Oven-dry weight of rock fragments (g) 

101
8.2 Db = Wf/Ve 

Db = Bulk density (g cm-3) 

Wf = Oven-dry weight of <2-mm soil (g) 

Ve = Excavation volume of <2-mm material (cm-3) 

9. Report

Bulk density is reported to the nearest 0.01 g cm-3. 

9. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 11. References 

Grossman, R.B., and T.G. Reinsch. 2002. Bulk density and linear extensibility. p. 201-228. 

In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis, Part 4. Physical methods. 

Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Bulk Density (3B) 

Frame Excavation (3B5) 

Field-State (3B5a) 

1. Application 

Bulk density is used to convert data from a weight to a volume basis; to estimate 

saturated hydraulic conductivity; and to identify compacted horizons. Excavation procedures 

(e.g., compliant cavity, ring, and frame) have applicability to layers that can be described as 

coheshionless, high in rock fragments > 5mm, or thin (<5 cm thick), and for which the clod 

method is unsuitable (Grossman and Reinsch, 2002). This method is good for O horizons in the 

woods where local variability is large and commonly rock fragments are present. The size of 

the 0.1 m2

 is sufficient to encompass considerable local variability. 

2. Summary of Method The assembled frame is placed on the ground surface. The four threaded rods are 

pushed through the holes in the corners of the frame deep enough to hold. The frame is then 

secured onto the soil surface by screwing down wing nuts and plastic placed over the frame and 

secured. The depth-measurement tool is placed on top of a slot to measure the distance to the 

soil surface. The slots are traversed, and measurements of the distance to the ground surface 

are made at about 40 regularly spaced intervals. The plate is then removed and soil is 

excavated and retained. Measurements of the distance to the ground surface are repeated. The 

volume of soil is determined by taking the difference in height and multiplying by 1000 cm2. 

The rock fragments up to 20 mm are included in the sample. Excavated soil is oven-dried and 

weighed. Bulk density of soil is reported in g cm-3 by procedure 3B5a. 

 

3. Interferences 

None. 

4. Safety 

Follow standard field and laboratory safety precautions.. 

5. Equipment 

5.1 Lumber for square wooden frame with 0.1 m2 inside area. Frame is made from 8 pieces of 

wood: 2 pieces, 2 x 4 x 46 cm; 2 pieces, 2 x 4 x 53 cm; and 4 blocks, 4 x 5 x 9 cm 

5.2 Square Plexiglass, 35 cm on edge x 0.6 cm thick, with 5 parallel equally spaced slots, 1.5 

cm across x 28 cm long 

5.3 Four threaded rods, 50 cm long x 0.6-cm diameter with wing nuts 

102
5.4 Depth-measurement tool (Grossman and Reinsch, 2002, p. 209) 

5.5 Hand digging equipment 

6. Reagents 

None. 

7. Procedure 7.1 Assemble the square wooden frame by attaching the 4 x 5 x 9 x cm blocks to the 9 cm of 

each end of both 53-cm long pieces. Two-centimeter-wide cuts are made half-way across each 

of the 46- and 53-cm-long pieces to provide half-lap joints. The cuts are 5 cm in for the 46-cmlong pieces. Holes 1.0 to 1.5 cm in diameter are drilled in the center of the attached blocks. 

The four pieces are joined by the vertical half-lap joints to form a square frame. 

7.2 Place the frame on the ground surface. Push the four threaded rods through the holes in the 

corners of the frame sufficiently deeply to hold. Secure onto the soil surface by screwing down 

wing nuts. 

7.3 Place the plastic plate over the frame and secure. 

7.4 Place the depth-measurement tool on top of a slot and measure the distance to the soil 

surface. 

7.5 Traverse the slots, making measurements of the distance to the ground surface at about 40 

regularly spaced intervals. Remove the plate. 

7.6 Excavate and retain the soil. The walls of the cavity should be vertical and coincident with 

the edge of the frame. 

7.7 Repeat the measurements of the distance to the ground surface. Determine the difference in 

height and multiply by 1000 cm2

 to obtain the volume of soil excavated. Usually rock 

fragments up to 20 mm are included in the sample. 

7.8 The excavated soil is dried in oven and weighed. If necessary, make a correction for 

weight and volume of >2-mm material in sample and bulk density computed. The weight of 

macroscopic vegetal material (g cm-3) also may be reported. 

8. Calculations 

8.1 Wf = Wo – We 

where: 

Wf = Oven-dry weight of <2-mm soil (g) 

Wo = Oven-dry weight of excavated soil (g) 

We = Oven-dry weight of rock fragments (g) 

8.2 Db = Wf/Ve 

Db = Bulk density (g cm-3) 

Wf = Oven-dry weight of <2-mm soil (g) 

Ve = Excavation volume of <2-mm material (cm-3) 

 

9. Report

Bulk density is reported to the nearest 0.01 g cm-3. 

103
10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

 11. References 

Grossman, R.B., and T.G. Reinsch. 2002. Bulk density and linear extensibility. p. 201-228. 

In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis, Part 4. Physical methods. 

Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Bulk Density (3B) 

Soil Cores (3B6) 

Field-State (3B6a) 

1. Application 

Bulk density is used to convert data from a weight to a volume basis; to determine the 

coefficient of linear extensibility; to estimate saturated hydraulic conductivity; and to identify 

compacted horizons. Procedure 3B6a determines the bulk density value of a moist soil core of 

known volume. Field bulk density (Dbf ) offers the opportunity to obtain relatively cheaply 

bulk density information without the expense incurred to obtain water retention. Dbf is 

particularly useful if the soil layers are at or above field capacity and/or the soils have low 

extensibility and do not exhibit desiccation cracks even if below field capacity. 

2. Summary of Method 

A metal cylinder is pressed or driven into the soil. The cylinder is removed extracting a 

sample of known volume. The moist sample weight is recorded. The sample is then dried in a 

oven and weighed. 

3. Interferences 

During coring process, compaction of the sample is a common problem. Compression 

can be observed by comparing the soil elevation inside the cylinder with the original soil 

surface outside the cylinder. If compression is excessive, soil core may not be a valid sample 

for analysis. Rock fragments in the soil interfere with core collection. Dry or hard soils often 

shatter when hammering the cylinder into the soil. Pressing the cylinder into the soil reduces 

the risk of shattering the sample. 

If soil cracks are present, select the sampling area so that crack space is representative 

of sample, if possible. If this is not possible, make measurements between the cracks and 

determine the aerial percentage of total cracks or of cracks in specimen. 

4. Safety 

No known hazard exists with this procedure. 

5. Equipment 

5.1 Containers, air-tight, tared, with lids 

5.2 Electronic balance, ±0.01-g sensitivity 

5.3 Oven 110°C 

5.4 Sieve, No. 10 (2 mm-openings) 

5.5 Coring equipment. Sources described in Grossman and Reinsch (2002). 

6. Reagents 

None 

7. Procedure 

7.1 Record the empty core weights (CW). 

104
7.2 Prepare a flat surface, either horizontal or vertical, at the required depth in sampling pit. 

7.3 Press or drive core sampler into soil. Use caution to prevent compaction. Remove core 

from the inner liner, trim protruding soil flush with ends of cylinder, and place in air-tight 

container for transport to laboratory. If soil is too loose to remain in the liner, use core sampler 

without the inner liner and deposit only the soil sample in air-tight container. Moisture cans 

can also be pushed directly into a prepared face. For fibrous organic materials, trim sample to 

fit snugly into a moisture can. 

7.4 Dry core in an oven at 110°C until weight is constant. Record oven-dry weight (ODW). 

7.5 Measure and record cylinder volume (CV). 

7.6 If sample contains rock fragments, wet sieve sample through a 2-mm sieve. Dry and weigh 

the rock fragments that are retained on sieve. Record weight of rock fragments (RF). 

Determine density of rock fragments (PD). 

8. Calculations 

Db = (ODW - RF – CW)/[CV - (RF/PD)] 

where: 

Db = Bulk density of < 2-mm fabric at sampled, field water state (g cm-3) 

ODW = Oven-dry weight 

RF = Weight of rock fragments 

CW = Empty core weight 

CV = Core volume 

PD = Density of rock fragments 

9. Report

Bulk density is reported as g cc-1 to the nearest 0.01 g cm-3. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Grossman, R.B. and T.G. Reinsch. 2002. Bulk density and linear extensibility. p. 201-228. 

In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis, Part 4. Physical methods. 

Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

PHYSICAL AND FABRIC-RELATED ANALYSES (3) 

Water Retention (3C) 

Water retention is defined as the soil water content at a given soil water suction. By 

varying the soil suction and recording the changes in soil water content, a water retention 

function or curve is determined. This relationship is dependent on particle-size distribution, 

clay mineralogy, organic matter, and structure or physical arrangement of the particles as well 

as hysteresis, i.e., whether the water is absorbing into or desorbing from the soil. The data 

collected in these procedures are from water desorption. Water retention or desorption curves 

are useful directly and indirectly as indicators of other soil behavior traits such as drainage, 

aeration, infiltration, plant available water, and rooting patterns (Topp et al., 1993). 

105
Two desorption procedures are commonly used to measure water retention, a suction 

method and a pressure method. The SSL uses the pressure method (U.S. Salinity Laboratory, 

1954) with either a pressure-plate or pressure-membrane extractor. Procedures 3C1a-e1 

(pressure-plate extraction) are used to determine water retention at 6, 10, 33, 100, or 200 kPa, 

respectively (0.06, 0.1, 1/3, 1, or 2 bar, respectively) for sieved, <2-mm, air-dry soil samples of 

non-swelling soils, loamy sand or coarser soil and for some sandy loams. Procedures 3C1a-d2 

and 3C1a-d3 (pressure-plate extractions) are used to measure water retention of natural clods or 

cores that have been equilibrated at 6, 10, 33, or 100 kPa. Procedures 3C1a-d2 and 3C1a-d3 

are usually used in conjunction with the bulk density procedure 3B1b. 

Procedure 3C1c4 (pressure-plate extraction) is used to determine the water retention of 

a clod equilibrated at 33-kPa, air-dried, and re-equilibrated. The resulting data are called rewet 

water-retention data and are usually used in conjunction with the rewet bulk density data in 

procedure 3B1d to estimate changes in physical properties of a soil as it undergoes wetting and 

drying cycles. Procedure 3C2a1a (pressure-membrane extraction) is used to determine water 

retention at 1500 kPa (15 bar) for <2-mm (sieved), air-dry soil samples. Procedure 3C2a1b is 

used to measure water retention at 1500 kPa for <2-mm (sieved), field moist soil samples. 

Procedure 3C3 is used to determine field water content at the time of sampling for cores, clods, 

or bulk samples. 

References 

Topp, G.C., Y.T. Galganov, B.C. Ball, and M.R. Carter. 1993. Soil water desorption curves. p. 

569-579. In M.R. Carter (ed.) Soil sampling and methods of analysis. Can. Soc. Soil Sci., 

CRC Press, Boca Raton, FL. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of saline 

and alkali soils. USDA Handb. 60. U.S. Govt. Print. Office, Washington, DC. 

Water Retention (3C) 

Pressure-Plate Extraction (3C1) 

6, 10, 33, 100, or 200 kPa (3C1a-e) 

<2-mm (sieved), Air-Dry Samples (3C1a-e1a) 

1. Application 

The data collected are used for the water retention function, water-holding capacity, 

pore-size distribution, porosity, and saturated conductivity of a soil sample at specific water 

contents. The data are also used to calculate unsaturated hydraulic conductivity. Procedures 

3C1a-e1a (pressure-plate extraction) are used to determine water retention at 6, 10, 33, 100, or 

200 kPa, respectively, for <2-mm (sieved), air-dry soil samples of non-swelling soils, loamy 

sand or coarser soil and for some sandy loams. 

2. Summary of Method 

The pressure desorption method (U.S. Salinity Laboratory Staff, 1954) is used. A 

sample of <2-mm (sieved), air-dry soil is placed in a retainer ring sitting on a porous ceramic 

plate in a pressure-plate extractor. The plate is covered with water to wet the samples by 

capillarity. The sample is equilibrated at the specified pressures. The pressure is kept constant 

until equilibrium is obtained (Klute, 1986). The gravimetric water content is determined. 

3. Interferences 

A leaking pressure extractor prevents equilibration of samples. Check for outflow air to 

verify that the pressure-plate extractor is functioning properly and does not leak. The pressure 

should be monitored for stability. Equilibration must be done at constant temperature and 

humidity. 

With extended use, the porous ceramic plate becomes clogged and water outflow is 

restricted. The plate is cleaned by flushing sequentially with 500 mL of 10% H2O2, 1000 mL 

106
of 1 N HCl, and 500 mL of reverse osmosis (RO) water. The solutions are pulled through the 

plate with a vacuum, and the waste is captured in a trap. 

The rubber membrane on the bottom of the plate is checked for leaks. The membrane is 

inflated and then submerged in water. If air bubbles escape from the membrane, the plate is 

removed from service. 

Laboratory-determined, water retention data are usually higher than field-determined 

water retention data, because the confining soil pressure is not present in the laboratory (Bruce 

and Luxmoore, 1986). Water retention data for soils with expansive clay is overestimated 

when sieved samples are used in place of natural soil fabric for tensions of 6, 10, and 33 kPa, 

respectively, (Young and Dixon, 1966). 

Aerated 0.005 M CaSO4 has also been recommended (Dane and Hopmans, 2002), 

especially for fine-textured soils that contain significant amounts of swelling clays. Distilled or 

deionized water can possibly promote dispersion of clays in samples and freshly drawn tap 

water is often supersaturated with air, affecting the water content at a given pressure head 

(Dane and Hopmans, 2002). 

4. Safety 

High pressure plumbing must be maintained in good working order. Ensure that the 

pressure is zero before removing bolts from the pressure extractor lid. Ensure that the bolts are 

tightened before applying pressure. Do not drop the heavy lid. 

5. Equipment 

5.1 Pressure plate extractor 

5.2 Electronic balance, ±0.01-g sensitivity 

5.3 Oven, 110°C 

5.4 Pressure source, regulator, and gauge. 

5.5 Retainer rings. Use 10-mm high and 50-mm diameter rings for organic soils and 10-mm 

high and 40-mm diameter rings for all other soils. 

5.6 Metal weighing cans with lids 

6. Reagents 

6.1 Reverse osmosis (RO) water 

6.2 Hydrogen peroxide (H2O2), 10% solution. Dilute 333 mL of 30% H2O2, technical grade, in 

l L of RO water. 

6.3 Hydrochloric acid (HCl), 1 N. Dilute 83.3 mL of concentrated HCl in 1 L of RO water. 

6.4 Ethyl alcohol, 95%, technical grade 

7. Procedure

7.1 Saturate the ceramic plate by applying RO water through the adapter and apply enough 

pressure so that the rubber membrane is bulging a few centimeters. Care should be taken to 

remove all air. 

7.2 Place the saturated ceramic plate in a pressure plate extractor. Place retainer rings on the 

ceramic plate. Use 50-mm diameter rings for soils that have >12% in organic matter. Use 40-

mm diameter rings for all other soils. 

7.3 Fill retaining ring with 10 to 15 g of <2-mm or fine-grind, air-dry soil. Include a quality 

control (QC) sample in each pressure-plate extractor. 

7.4 Add water to cover the ceramic plate but not to cover the rings. Continue to add water until 

all samples have moistened by capillarity. If samples do not moisten, apply ethyl alcohol to the 

surface of the samples. Close the apparatus and let stand overnight. 

107
7.5 Apply the specified pressure. Monitor the outflow tube for water discharge. Periodically 

submerge the outflow tube in water to monitor for air bubbles that indicate ceramic plate 

failure. Samples are equilibrated when water ceases to emit from the outflow tube. The 

outflow tube can be submerged under water in a burette to measure when water ceases to emit 

from the outflow tube. 

7.6 When samples have equilibrated, quickly transfer the samples to tared water cans (Mc), 

cover with lids, and record the weights (Ms+w). 

7.7 Remove lids, place samples in oven, and dry at 110°C overnight. Record weights (Ms). 

8. Calculations 

H2O % = 100 x [(Ms+w - Ms)/(Ms - Mc)]

where: 

H2O % = Percent gravimetric water content 

Ms+w = Weight of solids + H2O + container 

Ms = Weight of solids + container 

Mc = Weight of container 

9. Report

Report water content to the nearest 0.1 percent. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Bruce, R.R., and R.J. Luxmoore. 1986. Water retention: field methods. p. 663-686. In A. 

Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd 

ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Dane, J.H., and J. W. Hopmans. 2002. Water retention and storage: Laboratory. p. 675-

720. In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis. Part 4. Physical 

methods. Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Klute, A. 1986. Water retention: Laboratory methods. p. 635-662. In Klute, A. (ed.) 

Methods of soil analysis. Part 1. Physical and mineralogical methods. Agron. Monogr. 

9. ASA and SSSA, Madison, WI. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. USDA Handb. 60. U.S. Govt. Print. Office, Washington, DC. 

Young, K.K., and J.D. Dixon. 1966. Overestimation of water content at field capacity 

from sieved-sample data. Soil Sci. 101:104-107. 

Water Retention (3C) 

Pressure-Plate Extraction (3C1) 

6, 10, 33, or 100 kPa (3C1a-d) 

Natural Clods (3C1a-d2) 

1. Application

The data collected are used for the water retention function, water-holding capacity, 

pore-size distribution, porosity, and saturated conductivity of a soil sample at specific water 

contents. The data are also used to calculate unsaturated hydraulic conductivity. Procedures 

3C1a-d2 are used to determine the water retention of natural clods at 6, 10, 33, or 100 kPa, 

respectively. 

108
2. Summary of Method 

The pressure desorption method (U.S. Salinity Laboratory Staff, 1954) is used. Natural 

clods are placed on a tension table and equilibrated at a 5-cm tension at the base of the sample. 

The clods are then transferred to a porous ceramic plate which is placed in a pressure-plate 

extractor. The sample is equilibrated at the specified pressures. The pressure is kept constant 

until equilibrium is obtained (Klute, 1986). The gravimetric water content is determined. 

3. Interferences 

A leaking pressure extractor prevents equilibration of samples. Check outflow air to 

verify that each pressure-plate extractor is functioning properly and does not leak. The 

pressure should be monitored for stability. Equilibration must be done at constant temperature 

and humidity. 

With extended use, the porous ceramic plate becomes clogged and water outflow is 

restricted. The plate is cleaned by flushing sequentially with 500 mL of 10% H2O2, 1000 mL 

of 1 N HCl, and 500 mL of RO water. The solutions are pulled through the plate with a 

vacuum, and the waste is captured in a trap. 

The rubber membrane on the bottom of the plate is checked for leaks in the gasket. The 

membrane is inflated and then submerged in water. If air bubbles escape from the membrane, 

the plate is removed from service. 

Laboratory-determined, water retention data are usually higher than field-determined, 

water retention data because the confining soil pressure is not present in the laboratory (Bruce 

and Luxmoore, 1986). 

Aerated 0.005 M CaSO4 has also been recommended (Dane and Hopmans, 2002), 

especially for fine-textured soils that contain significant amounts of swelling clays. Distilled or 

deionized water can possibly promote dispersion of clays in samples and freshly drawn tap 

water is often supersaturated with air, affecting the water content at a given pressure head 

(Dane and Hopmans, 2002). 

4. Safety 

High pressure plumbing must be maintained in good working order. Ensure that the 

pressure is zero before removing bolts from the pressure-apparatus lid. Ensure that the bolts 

are tightened before applying pressure. Do not drop the heavy lid. 

5. Equipment 

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Pressure plate extractor with porous ceramic plate (Fig.1 and 2) 

5.3 Pressure source, regulator, and gauge. 

5.4 Oven, 110°C 

5.5 Retainer rings, 10-mm height and 40-mm diameter 

5.6 Metal weighing cans with lids 

5.7 Clothespins 

5.8 Knife 

5.9 Tile cut-off saw with diamond blade 

5.10 Silt loam soil 

5.11 Desiccator with ceramic plate 

5.12 Vacuum, 80 kPa (0.8 bar) 

5.13 Needle probe 

5.14 Sieve, No. 10 (2-mm openings) 

5.15 Hot plate 

5.16 Fume hood 

5.17 Reinforced paper towels with nylon fibers, GSA 

5.18 Liquid vapor trap. The SSL constructs a tin enclosure over hot plate with a chimney and 

duct to transfer vapor to water stream. 

109
5.19 Tension table. The SSL constructs a tension table by placing porous firebricks, covered 

with reinforced paper towels, in a tub of water. 

5.20 Stock tags, 25.4-mm (1-in) diameter paper tag, with metal rim 

5.21 Wire. The SSL uses a 28-awg coated copper wire. 

5.22 Retainer rings. Use 10-mm high and 50-mm diameter rings for organic soils and 10-mm 

high and 40-mm diameter rings for all other soils. 

6. Reagents 

6.1 Reverse osmosis (RO) water 

6.2 Hydrogen peroxide (H2O2), 10% solution. Dilute 333 mL of 30% H2O2, technical grade, 

in l L of RO water 

6.3 Hydrochloric acid (HCl), 1 N. Dilute 83.3 mL of concentrated HCl in 1 L of RO water. 

6.4 Ethyl alcohol, 95%, technical grade 

6.5 Liquid detergent. The SSL uses Liqui-Nox 

6.6 Methyl ethyl ketone (MEK), practical (2-butanone) 

6.7 Dow Saran F-310 Resin, available from Dow Chemical Company 

6.8 Plastic lacquer. Prepare plastic lacquer with resin to solvent ratios of 1:4 and 1:7 on a 

weight basis. Fill a 3.8-L (1-gal) metal paint can with 2700 ± 200 mL of solvent. Fill to 

the bottom of handle rivet. Add 540 g or 305 g of resin to make 1:4 or 1:7 plastic 

lacquer, respectively. For the initial field and laboratory coatings, use the 1:4 plastic 

lacquer. Use 1:7 plastic lacquer for the last two laboratory coats. The 1:7 plastic lacquer 

is used to conserve the resin and to reduce cost. In the field, mix solvent with a wooden 

stick. In the laboratory, stir solvent with a non-sparking, high speed stirrer while slowly 

adding resin. Stir plastic lacquer for 30 min at 25°C. Store plastic lacquer in covered 

plastic or steel containers. Acetone may be substituted for MEK. 

6.9 Microbiocide, for tension table, Fisher Scientific 

7. Procedure 

7.1 This procedure is usually combined with the bulk density procedure (3B1b). 

7.2 Prepare a round stock tag with sample identification number. Cut the copper wire and loop 

around the clod. Record the weight of the tag and wire (TAG). Loop fine copper wire around 

the clod, leaving a tail to which the round stock tag is attached. Record the weight of the clod 

(CC1). 

7.3 Dip the clod in the 1:4 plastic lacquer. Wait 7 min and then dip the clod in the 1:7 plastic 

lacquer. Wait 12 min and then dip the clod in the 1:7 plastic lacquer. Wait 55 min and then 

reweigh the clod. If the clod has absorbed >3% in plastic by clod weight or smells excessively 

of solvent, allow longer drying time, then reweigh the clod and record the weight (CC2). 

7.4 Cut a flat surface on the clod with a tile saw. It is necessary to wet the clod above the 

initial desorption point. This is accomplished by placing the cut clod surface on a tension table 

that is maintained at 5-cm tension. Periodically check the clod by inserting a needle probe, 

touching, or by weight comparison to determine if it has reached equilibrium (clod has wetted 

up). When the clod has reached equilibrium, remove the clod and record the weight (WSC). 

7.5 If cut clod does not absorb water, place clod in a desiccator on a water-covered plate with a 

0-cm tension. Submerge only the surface of clod in the water. Add a few mL of alcohol. Use 

in-house vacuum and apply suction until clod has equilibrated at saturation. Remove the clod 

and record the weight (WSC). 

110
7.6 Saturate the ceramic plate by applying RO water through the adapter and apply enough 

pressure so that the rubber membrane is bulging a few centimeters. Care should be taken to 

remove all air. 

7.7 Place the saturated ceramic plate in a pressure plate extractor. To provide good contact 

between the clod and ceramic plate, cover the ceramic plate with a 5-mm layer of silt loam soil 

and saturate with water. Place a sheet of reinforced paper towel over the silt loam soil. Place 

cut clod surface on the paper towel. Prepare a saturated, sieved soil as a quality control (QC) 

sample. Place several retaining rings in the extractor. Fill the retaining rings with the soil 

standard. Close the container and secure lid. 

7.8 Apply gauged air pressure of 6, 10, 33, or 100 kPa. If more than one water retention point is 

requested, begin with the lowest pressure. Periodically submerge the outflow tube in water to 

monitor for air bubbles that indicate ceramic plate failure. Samples are equilibrated when 

water ceases to emit from the outflow tube. The outflow tube can be submerged under water in 

a burette to measure when water ceases to emit from the outflow tube. When water stops 

discharging from the outflow tube, the clod is at equilibrium. Determine the gravimetric water 

content of the QC. If the water content of the QC is higher than twice the standard deviation, 

apply pressure for additional time. Recheck the QC. If the water content of the QC is lower 

than twice the standard deviation, rewet the clods and desorb again. If the water content of the 

QC is within acceptable limits, then the apparatus has functioned properly. 

7.9 Remove the clod and record the weight (WMC). Compare WMC to WSC. If WMC >

WSC, re-equilibrate the clod on the tension table and repeat the desorption process. If 

additional water retention points are requested, then repeat the desorption process at the next 

higher pressure. When the clod is equilibrated at 33 kPa and bulk density is to be measured, 

continue with procedure 3B1b. 

7.10 Dry the clod in an oven at 110°C overnight and record oven-dry weight (WODC). 

7.11 If the clods contains >5% in rock fragments by weight, remove the rock fragments from 

the clod. This determination of the percent rock fragments is based on particle-size data of >2-

mm fraction.. Submerge the remaining soil material in a beaker of water and place on a hot 

plate. Use a fume hood. Boil ≈ 1 h. The plastic coating loosens from soil material upon 

heating. Remove beaker from the hot plate. Allow to cool. Discard plastic coating. 

7.12 Wet sieve the cool soil through a 2-mm sieve. Dry and record the weight (RF) of the rock 

fragments that are retained on the sieve. If the rock fragments have similar properties to the 

soil sample, do not correct the clod mass for the rock fragments. 

8. Calculations 

8.1 H2O % =[(WMC - MPC) - (WODC - ODPC) x 100]/(WODC - RF - ODPC – TAG) 

where: 

H2O % = Percent gravimetric water content 

WMC = Weight of equilibrated, coated clod 

WODC= Weight of oven-dry coated clod 

RF = Weight of rock fragments 

ODPC = MPC x 0.85, weight of oven-dry plastic coat 

TAG = Weight of tag and wire 

8.2 MPC = {[(CC2 - CC1) + FCE] x RV} 

111
where: 

MPC = Weight of plastic coat before oven-drying 

CC2 = Weight of clod after three laboratory plastic coats 

CC1 = Weight of clod before three laboratory plastic coats 

RV = Percent estimate of remaining clod volume after cutting to obtain flat surface (≈ 80%) 

8.3 FCE = 1.5 x [(CC2 - CC1)/3] 

where: 

FCE = Estimate of field-applied plastic coat, if applied 

9. Report

Report water content to the nearest 0.1 percent. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Bruce, R.R., and R.J. Luxmoore. 1986. Water retention: field methods. p. 663-686. In A. 

Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd 

ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Dane, J.H., and J. W. Hopmans. 2002. Water retention and storage: Laboratory. p. 675-

720. In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis. Part 4. Physical 

methods. Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Klute, A. 1986. Water retention: Laboratory methods. p. 635-662. In A. Klute (ed.) 

Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. 

Monogr. 9. ASA and SSSA, Madison, WI. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. USDA Handb. 60. U.S. Govt. Print. Office, Washington, DC. 

112
Fig 1. Clods placed in pressure-plate extractor following saturation. 

Fig. 2. Pressure-plate extraction at 33-kPa for clods. 

113
Water Retention (3C) 

Pressure-Plate Extraction (3C1) 

6, 10, 33, or 100 kPa (3C1a-d) 

Soil Cores (3C1a-d3) 

1. Application 

The data collected are used for the water retention function, water-holding capacity, 

pore-size distribution, porosity, and saturated conductivity of a soil sample at specific water 

contents. The data are also used to calculate unsaturated hydraulic conductivity. Procedures 

3C1a-d3 are used to determine the water retention of soil cores at 6, 10, 33, or 100 kPa, 

respectively. 

2. Summary of Method 

The pressure desorption procedure (U.S. Salinity Laboratory Staff, 1954) is used. A 

metal cylinder is pressed or driven into the soil. Upon removal from the soil, the cylinder 

extracts a sample of known volume. The sample weight is recorded. The sample is dried in the 

oven and then weighed. Soil core is placed on a tension table and equilibrated at a 5-cm 

tension at the base of the sample. The cores are then transferred to a porous ceramic plate 

which is placed in a pressure-plate extractor. The sample is equilibrated at the specified 

pressures. The pressure is kept constant until equilibrium is obtained (Klute, 1986). The 

gravimetric water content is determined. 

3. Interferences 

A leaking pressure extractor prevents equilibration of samples. Check for outflow air to 

verify that the extractor is functioning properly and does not leak. The pressure should be 

monitored for stability. Equilibration must be done at constant temperature and humidity. 

With extended use, the porous ceramic plate becomes clogged and water outflow is 

restricted. The plate is cleaned by flushing sequentially with 500 mL of 10% H2O2, 1000 mL 

of 1 N HCl, and 500 mL of RO water. The solutions are pulled through the plate with a 

vacuum, and the waste is captured in a trap. 

The rubber membrane on the bottom of the plate is checked for leaks in the gasket. The 

membrane is inflated and then submerged in water. If air bubbles escape from the membrane, 

the plate is removed from service. 

Laboratory-determined, water retention data are usually higher than field-determined, 

water retention data because the confining soil pressure is not present in the laboratory (Bruce 

and Luxmoore, 1986). 

Compaction of the sample during the sampling process is a common problem. 

Compression can be observed by comparing the soil elevation inside the cylinder with the 

original soil surface outside the cylinder. If compression is excessive, soil core may not be a 

valid sample for analysis. Rock fragments in the soil interfere with core collection. Dry or hard 

soils often shatter when hammering the cylinder into the soil. Pressing the cylinder into the 

soil reduces the risk of shattering the sample. 

Aerated 0.005 M CaSO4, has also been recommended (Dane and Hopmans, 2002), 

especially for fine-textured soils that contain significant amounts of swelling clays. Distilled or 

deionized water can possibly promote dispersion of clays in samples and freshly drawn tap 

water is often supersaturated with air, affecting the water content at a given pressure head 

(Dane and Hopmans, 2002). 

4. Safety 

High pressure plumbing must be maintained in good working order. Ensure that the 

pressure is zero before removing bolts from the pressure-apparatus lid. Ensure that the bolts 

are tightened before applying pressure. Do not drop the heavy lid. 

114
5. Equipment 

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Pressure plate extractor with porous ceramic plate 

5.3 Pressure source, regulator, and gauge 

5.4 Oven, 110°C 

5.5 Retainer rings, 10-mm height and 40-mm diameter 

5.6 Metal weighing cans with lids 

5.7 Silt loam soil 

5.8 Desiccator with ceramic plate 

5.9 Vacuum, 80 kPa (0.8 bar) 

5.10 Needle probe 

5.11 Sieve, No. 10 (2-mm openings) 

5.12 Fume hood 

5.13 Coring equipment. Sources described in Blake and Hartge (1986). 

5.14 Tension table. The SSL constructs a tension table by placing porous firebricks, covered 

with reinforced paper towels, in a tub of water. 

5.15 Reinforced paper towels with nylon fibers, GSA 

5.16 Retainer rings. Use 10-mm high and 50-mm diameter rings for organic soils and 10-mm 

high and 40-mm diameter rings for all other soils. 

6. Reagents 

6.1 Reverse osmosis (RO) water 

6.2 Hydrogen peroxide (H2O2), 10% solution. Dilute 333 mL of 30% H2O2, technical grade, 

in l L of RO water. 

6.3 Hydrochloric acid (HCl), 1 N. Dilute 83.3 mL of concentrated HCl in 1 L of RO water. 

6.4 Alcohol 

6.5 Liquid detergent. The SSL uses Liqui-Nox. 

6.6 Microbiocide, for tension table, Fisher Scientific 

7. Procedure 

7.1 This procedure can be combined with the bulk density procedure (3B1b). 

7.2 Record the weight (CW) of the sampling cylinders. 

7.3 Prepare a flat surface in the sampling pit, either horizontal or vertical, at the required depth. 

Press or drive the core sampler into the soil. Use caution to prevent compaction. Remove the 

core from the sample holder, trim the protruding soil flush with the cylinder ends, and place 

core in an air-tight container for transport to the laboratory. 

7.4 It is necessary to wet the core above the initial desorption point. This is accomplished by 

placing the flat core surface on a tension table maintained at 5-cm tension. Periodically, check 

the core by inserting a needle probe, touching, or by weight comparison to determine if core 

has reached equilibrium (core has wetted up). When the core has reached equilibrium, remove 

the core and record the weight (WSC). 

7.5 If core does not absorb water, place core in a desiccator on a water-covered plate with a 0-

cm tension. Submerge only the surface of core in the water. Add a few mL of alcohol. Use inhouse vacuum and apply suction until core has equilibrated at saturation. Remove the core and 

record the weight (WSC). 

7.6 Saturate the ceramic plate by applying RO water through the adapter and apply enough 

pressure so that the rubber membrane is bulging a few centimeters. Care should be taken to 

remove all air. 

115
7.7 Place the saturated ceramic plate in a pressure plate extractor. To provide good contact 

between the core and ceramic plate, cover the ceramic plate with a 5-mm layer of silt loam soil 

and saturate with water. Place a sheet of reinforced paper towel over the silt loam soil. Place 

the flat core surface on the paper towel. Prepare a saturated, sieved soil as a quality control 

(QC) sample. Place several retaining rings in the extractor. Fill the retaining rings with the 

soil standard. Close the container and secure lid. 

7.8 Apply gauged air pressure of 6, 10, 33, or 100 kPa. If more than one water retention point 

is requested, begin with the lowest pressure. When water stops discharging from the outflow 

tube, the core is at equilibrium. Determine the gravimetric water content of the standard. If the 

water content of the QC is higher than twice the standard deviation, apply pressure for 

additional time. Recheck the QC. If the water content of the QC is lower than twice the 

standard deviation, rewet the cores and desorb again. If the water content of the QC is within 

acceptable limits, then the apparatus has functioned properly. 

7.9 Remove core and record the weight (WMC). Compare WMC to WSC. If WMC > WSC, 

re-equilibrate core on the tension table and repeat the desorption process. If additional water 

retention points are requested, then repeat the desorption process at the next higher pressure. 

When the core is equilibrated at 33 kPa and bulk density is to be measured, continue with 

method 3B1b. 

7.10 Dry core in an oven at 110°C overnight and record oven-dry weight (WODC). 

7.11 If sample contains rock fragments, wet sieve the sample through a 2-mm sieve. Dry and 

weigh the rock fragments that are retained on the sieve. If the rock fragments have similar 

properties to the soil sample, do not correct the clod mass for the rock fragments. Record the 

weight of the rock fragments (RF). 

8. Calculations 

H2O % = 100 x [(WMC - WODC)/(WODC - CW - RF)]

where: 

H2O % = Percent gravimetric water content 

WMC = Weight of solids + H2O + container 

CW = Weight of solids + container 

WODC = Weight of container 

RF = Weight of rock fragments 

9. Report

Report water content to the nearest 0.1 percent. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Bruce, R.R., and R.J. Luxmoore. 1986. Water retention: field methods. p. 663-686. In A. 

Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd 

ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. . 

Dane, J.H., and J. W. Hopmans. 2002. Water retention and storage: Laboratory. p. 675-

720. In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis. Part 4. Physical 

methods. Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

116
Klute, A. 1986. Water retention: Laboratory methods. p. 635-662. In A. Klute (ed.) 

Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. 

Monogr. 9. ASA and SSSA, Madison. WI. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. USDA Handb. 60. U.S. Govt. Print. Office, Washington, DC. 

Water Retention (3C) 

Pressure-Plate Extraction (3C1) 

33 kPa (3C1c) 

Rewet (3C1c4) 

1. Application 

The data collected are used for the water retention function, water-holding capacity, 

pore-size distribution, porosity, and saturated conductivity of a soil sample at specific water 

contents. The data are also used to calculate unsaturated hydraulic conductivity. The rewet 

water retention data (3C1c4) are used in conjunction with the rewet bulk density (3B1d) to 

estimate the change in physical properties of a soil as it undergoes wetting and drying cycles. 

2. Summary of Method 

The pressure desorption method (U.S. Salinity Laboratory Staff, 1954) is used. Natural 

clods are placed on a tension table and equilibrated at a 5-cm tension at the base of the sample. 

The clods are then transferred to a porous ceramic plate which is placed in a pressure-plate 

extractor. The sample is equilibrated at 33kPa. The pressure is kept constant until equilibrium 

is obtained (Klute, 1986). The equilibrated clod weight is recorded. The clod is air dried and 

then placed on a tension table and desorbed again. After the second equilibration, the 

gravimetric water content is determined. 

3. Interferences 

A leaking pressure extractor prevents equilibration of samples. Check outflow air to 

verify each pressure-plate extractor is functioning properly and does not leak. The pressure 

should be monitored for stability. Equilibration must be done at constant temperature and 

humidity. 

With extended use, the porous ceramic plate becomes clogged and water outflow is 

restricted. The plate is cleaned by flushing sequentially with 500 mL of 10% H2O2, 1000 mL 

of 1 N HCl, and 500 mL of RO water. The solutions are pulled through the plate with a 

vacuum, and the waste is captured in a trap. 

The rubber membrane on the bottom of the plate is checked for leaks in the gasket. The 

membrane is inflated and then submerged in water. If air bubbles escape from the membrane, 

the plate is removed from service. 

Laboratory-determined, water retention data are usually higher than field-determined, 

water retention data because the confining soil pressure is not present in the laboratory (Bruce 

and Luxmoore, 1986). 

Aerated 0.005 M CaSO4, has also been recommended (Dane and Hopmans, 2002), 

especially for fine-textured soils that contain significant amounts of swelling clays. Distilled or 

deionized water can possibly promote dispersion of clays in samples and freshly drawn tap 

water is often supersaturated with air, affecting the water content at a given pressure head 

(Dane and Hopmans, 2002). 

4. Safety 

High pressure plumbing must be maintained in good working order. Ensure that the 

pressure is zero before removing bolts from the pressure-plate lid. Ensure that the bolts are 

tightened before applying pressure. Do not drop the heavy lid. 

117
5. Equipment 

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Pressure plate extractor with porous ceramic plate 

5.3 Pressure source, regulator, and gauge 

5.4 Oven, 110°C-capability 

5.5 Retainer rings, 10-mm height and 40-mm diameter 

5.6 Metal weighing cans with lids 

5.7 Clothespins 

5.8 Knife 

5.9 Tile cut-off saw with diamond blade 

5.10 Silt loam soil 

5.11 Desiccator with ceramic plate 

5.12 Vacuum, 80 kPa (0.8 bar) 

5.13 Needle probe 

5.14 Sieve, No. 10 (2-mm openings) 

5.15 Hot plate 

5.16 Fume hood 

5.17 Reinforced paper towels with nylon fibers, GSA 

5.18 Liquid vapor trap. The SSL constructs a tin enclosure over hot plate with a chimney and 

duct to transfer vapor to water stream. 

5.19 Tension table. The SSL constructs a tension table by placing porous firebricks, covered 

with reinforced paper towels, in a tub of water. 

5.20 Stock tags, 25.4-mm (1-in) diameter paper tag, with metal rim 

5.21 Wire. The SSL uses a 28-awg coated copper wire. 

5.22 Retainer rings. Use 10-mm high and 50-mm diameter rings for organic soils and 10-mm 

high and 40-mm diameter rings for all other soils. 

6. Reagents 

6.1 Reverse osmosis (RO) water 

6.2 Hydrogen peroxide (H2O2), 10% solution. Dilute 333 mL of 30% H2O2, technical grade, 

in l L of RO water. 

6.3 Hydrochloric acid (HCl), 0.05 N. Dilute 8 mL of concentrated HCl in 1 L of RO water. 

6.4 Ethyl alcohol, 95%, technical grade 

6.5 Liquid detergent. The SSL uses Liqui-Nox. 

6.6 Methyl ethyl ketone (MEK), practical (2-butanone) 

6.7 Dow Saran F-310 Resin. Available from Dow Chemical Company. 

6.8 Plastic lacquer. Prepare plastic lacquer with resin to solvent ratios of 1:4 and 1:7 on a 

weight basis. Fill a 3.8-L (1-gal) metal paint can with 2700 ±200 mL of solvent. Fill to 

the bottom of handle rivet. Add 540 g or 305 g of resin to make 1:4 or 1:7 plastic 

lacquer, respectively. For the initial field and laboratory coatings, use the 1:4 plastic 

lacquer. Use 1:7 plastic lacquer for the last two laboratory coats. The 1:7 plastic lacquer 

is used to conserve the resin and to reduce cost. In the field, mix solvent with a wooden 

stick. In the laboratory, stir solvent with a non-sparking, high speed stirrer while slowly 

adding resin. Stir plastic lacquer for 15 min at 25°C. Store plastic lacquer in covered 

plastic or steel containers. Acetone may be substituted for MEK. 

6.9 Microbiocide, for tension table, Fisher Scientific 

7. Procedure 

7.1 This procedure is usually used in conjunction with the bulk density procedure 4A1i. 

7.2 Prepare a round stock tag with sample identification number. Cut the copper wire. Record 

the weight of the tag and wire (TAG). Loop fine copper wire around the clod, leaving a tail to 

which the round stock tag is attached. Record the weight of the clod (CC1). 

118
7.3 Dip the clod in the 1:4 plastic lacquer. Wait 7 min and then dip the clod in the 1:7 plastic 

lacquer. Wait 12 min and then dip the clod in the 1:7 plastic lacquer. Wait 55 min and then 

reweigh the clod. If the clod has absorbed >3% in plastic by clod weight or smells excessively 

of solvent, allow longer drying time, then reweigh the clod and record the weight (CC2). 

7.4 Cut a flat surface on the clod with a tile saw. 

7.5 It is necessary to wet the clod above the initial desorption point. This is accomplished by 

placing the cut clod surface on a tension table that is maintained at 5-cm tension. Periodically 

check the clod by inserting a needle probe, touching, or by weight comparison to determine if it 

has reached equilibrium (clod has wetted up). When the clod has reached equilibrium, remove 

the clod and record the weight (WSC). 

7.6 If cut clod does not absorb water, place clod in a desiccator on a water-covered plate with a 

0-cm tension. Submerge only the surface of clod in the water. Add a few mL of alcohol. Use 

in-house vacuum and apply suction until clod has equilibrated at saturation. Remove the clod 

and record the weight (WSC). 

7.7 Saturate the ceramic plate by applying RO water through the adapter and apply enough 

pressure so that the rubber membrane is bulging a few centimeters. Care should be taken to 

remove all air. 

7.8 To provide good contact between the clod and ceramic plate, cover the ceramic plate with a 

5-mm layer of silt loam soil and saturate with water. Place a sheet of reinforced paper towel 

over the silt loam soil. Place cut clod surface on the paper towel. Prepare a saturated, sieved 

soil as a quality control (QC) sample. Place several retaining rings in the extractor. Fill the 

retaining rings with the soil standard. Close the container and secure lid. 

7.9 Apply gauged air pressure of 6, 10, 33, or 100 kPa. If more than one water retention point 

is requested, begin with the lowest pressure. When water stops discharging from the outflow 

tube, the clod is at equilibrium. Determine the gravimetric water content of the QC. If the 

water content of the QC is higher than twice the standard deviation, apply pressure for 

additional time. Recheck the QC. If the water content of the QC is lower than twice the 

standard deviation, rewet the clods and desorb again. If the water content of the QC is within 

acceptable limits, then the apparatus has functioned properly. 

7.10 Remove the clod and record the weight (WMC). Compare WMC to WSC. If WMC >

WSC, re-equilibrate the clod on the tension table and repeat the desorption process. If 

additional water retention points are requested, then repeat the desorption process at the next 

higher pressure. When the clod is equilibrated at 33 kPa and bulk density is to be measured, 

continue with procedure 3B1d 

7.11 Air-dry the clod at room temperature (≈ 20 to 25°C) for 4 to 6 days. Dry the clods at 40 to 

50°C for 2 to 3 days or until weights are constant. 

7.12 Repeat steps 7.5, 7.6, 7.7, and 7.8. Record clod weight after equilibration (WMC2). 

Determine bulk density as described in method 3B1d. 

7.13 Dry the clod in oven at 110°C overnight and record oven-dry weight (WODC). 

7.14 If the clod contains >5% in rock fragments by weight, remove the rock fragments from the 

clod. This determination of the percent rock fragments is based on particle-size data of >2-mm 

fraction. Submerge the remaining soil material in a beaker of water and place on a hot plate. 

119
Use a fume hood. Boil ≈ 1 h. The plastic coating loosens from soil material upon heating. 

Remove beaker from the hot plate. Allow to cool. Discard plastic coating. 

 

7.15 Wet sieve the cool soil through a 2-mm sieve. Dry and record the weight (RF) of the rock 

fragments that are retained on the sieve. If the rock fragments have similar properties to the soil 

sample, do not correct the clod mass for the rock fragments. 

8. Calculations 

8.1 H2O % =[(WMC - MPC) - (WODC - ODPC) x 100]/(WODC - RF – ODPC – TAG) 

where: 

H2O % = Percent gravimetric water content 

WMC = Weight of equilibrated, coated clod 

WODC= Weight of oven-dry coated clod 

RF = Weight of rock fragments 

ODPC = MPC x 0.85, weight of oven-dry plastic coat 

TAG = Weight of tag and wire 

8.2 MPC = {[(CC2 – CC1) + FCE] x RV} 

where: 

MPC = Weight of plastic coat before oven-drying 

CC2 = Weight of clod after three laboratory plastic coats 

CC1 = Weight of clod before three laboratory plastic coats 

RV = Percent estimate of remaining clod volume after cutting to obtain flat surface (≈ 80%) 

8.3 FCE = 1.5 x [(CC2 – CC1)/3] 

where: 

FCE = Estimate of field applied plastic coat, if applied 

8.4 H2Or % = {[(WMC2 - MPC2) - (WODC - ODPC2)] x 100}/(WODC - RF – ODPC – TAG) 

where: 

H2Or % = Percent water weight retained at 33-kPa tension after rewetting 

WMC2 = Weight of equilibrated, coated clod after rewetting 

MPC2 = Weight of moist plastic coat after rewetting. Same as MPC unless additional plastic 

coats were added. 

OPC2 = MPC2 x 0.85, weight of oven-dry plastic coat. 

9. Report

Report water content to the nearest 0.1 percent. 

10. Precision and Accuracy

Precision and accuracy data are available from the SSL upon request. 

11. References 

Bruce, R.R., and R.J. Luxmoore. 1986. Water retention: Field methods. p. 663-686. In A. 

Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd 

ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Dane, J.H., and J. W. Hopmans. 2002. Water retention and storage: laboratory. p. 675-720. 

In J.H. Dane and G.C. Topp (ed.) Methods of soil analysis. Part 4. Physical methods. 

Soil Sci. Am. Book Series No. 5. ASAS and SSSA, Madison, WI. 

120
Klute, A. 1986. Water retention: Laboratory methods. p. 635-662. In A. Klute (ed.), 

Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. 

Monogr. 9. ASA and SSSA, Madison, WI. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. U.S. Dept. of Agric. Handb. 60. U.S. Govt. Print. Office, 

Washington, DC. 

Water Retention (3C) 

Pressure-Plate Extraction (3C1) 

33 kPa (3C1c) 

Reconstituted (3C1c5) 

1. Application

The data collected are used for the water retention function, water-holding capacity, 

pore-size distribution, porosity, and saturated conductivity of a soil sample at specific water 

contents. The data are also used to calculate unsaturated hydraulic conductivity. Procedure 

3C1c5 is used to determine the water retention of a reconstituted clod at 33 kPa. 

2. Summary of Method 

The pressure desorption method (U.S. Salinity Laboratory Staff, 1954) is used. Natural 

clods are placed on a tension table and equilibrated at a 5-cm tension at the base of the sample. 

The clods are then transferred to a porous ceramic plate which is placed in a pressure-plate 

extractor. The sample is equilibrated at the specified pressures. The pressure is kept constant 

until equilibrium is obtained (Klute, 1986). The gravimetric water content is determined. 

3. Interferences 

A leaking pressure extractor prevents equilibration of samples. Check outflow air to 

verify that each pressure-plate extractor is functioning properly and does not leak. The 

pressure should be monitored for stability. Equilibration must be done at constant temperature 

and humidity. 

With extended use, the porous ceramic plate becomes clogged and water outflow is 

restricted. The plate is cleaned by flushing sequentially with 500 mL of 10% H2O2, 1000 mL 

of 1 N HCl, and 500 mL of RO water. The solutions are pulled through the plate with a 

vacuum, and the waste is captured in a trap. 

The rubber membrane on the bottom of the plate is checked for leaks in the gasket. The 

membrane is inflated and then submerged in water. If air bubbles escape from the membrane, 

the plate is removed from service. 

Laboratory-determined, water retention data are usually higher than field-determined, 

water retention data because the confining soil pressure is not present in the laboratory (Bruce 

and Luxmoore, 1986). 

Aerated 0.005 M CaSO4 has also been recommended (Dane and Hopmans, 2002), 

especially for fine-textured soils that contain significant amounts of swelling clays. Distilled or 

deionized water can possibly promote dispersion of clays in samples and freshly drawn tap 

water is often supersaturated with air, affecting the water content at a given pressure head 

(Dane and Hopmans, 2002). 

4. Safety 

High pressure plumbing must be maintained in good working order. Ensure that the 

pressure is zero before removing bolts from the pressure-apparatus lid. Ensure that the bolts 

are tightened before applying pressure. Do not drop the heavy lid. 

5. Equipment 

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Pressure plate extractor with porous ceramic plate 

121
5.3 Pressure source, regulator, and gauge 

5.4 Oven, 110°C 

5.5 Retainer rings, 10-mm height and 40-mm diameter 

5.6 Metal weighing cans with lids 

5.7 Clothespins 

5.8 Knife 

5.9 Tile cut-off saw with diamond blade 

5.10 Silt loam soil 

5.11 Desiccator with ceramic plate 

5.12 Vacuum, 80 kPa (0.8 bar) 

5.13 Needle probe 

5.14 Sieve, No. 10 (2-mm openings) 

5.15 Hot plate 

5.16 Fume hood 

5.17 Reinforced paper towels with nylon fibers, GSA 

5.18 Liquid vapor trap. The SSL constructs a tin enclosure over hot plate with a chimney and 

duct to transfer vapor to water stream. 

5.19 Tension table. The SSL constructs a tension table by placing porous firebricks, covered 

with reinforced paper towels, in a tub of water. 

5.20 Stock tags, 25.4-mm (1-in) diameter paper tag, with metal rim 

5.21 Wire. The SSL uses a 28-awg coated copper wire. 

5.22 Retainer rings. Use 10-mm high and 50-mm diameter rings for organic soils and 10-mm 

high and 40-mm diameter rings for all other soils. 

6. Reagents 

6.1 Reverse osmosis (RO) water 

6.2 Hydrogen peroxide (H2O2), 10% solution. Dilute 333 mL of 30% H2O2, technical grade, 

in l L of RO water. 

6.3 Hydrochloric acid (HCl), 1 N. Dilute 83.3 mL of concentrated HCl in 1 L of RO water. 

6.4 Ethyl alcohol, 95%, technical grade 

6.5 Liquid detergent. The SSL uses Liqui-Nox. 

6.6 Methyl ethyl ketone (MEK), practical (2-butanone) 

6.7 Dow Saran F-310 Resin. Available from Dow Chemical Company. 

6.8 Plastic lacquer. Prepare plastic lacquer with resin to solvent ratios of 1:4 and 1:7 on a 

weight basis. Fill a 3.8-L (1-gal) metal paint can with 2700 ± 200 mL of solvent. Fill to 

the bottom of handle rivet. Add 540 g or 305 g of resin to make 1:4 or 1:7 plastic 

lacquer, respectively. For the initial field and laboratory coatings, use the 1:4 plastic 

lacquer. Use 1:7 plastic lacquer for the last two laboratory coats. The 1:7 plastic lacquer 

is used to conserve the resin and to reduce cost. In the field, mix solvent with a wooden 

stick. In the laboratory, stir solvent with a non-sparking, high speed stirrer while slowly 

adding resin. Stir plastic lacquer for 30 min at 25°C. Store plastic lacquer in covered 

plastic or steel containers. Acetone may be substituted for MEK. 

6.9 Microbiocide, for tension table, Fisher Scientific. 

7. Procedure 

7.1 This procedure is usually combined with the bulk density procedure (3B2b). 

7.2 Prepare a round stock tag with sample identification number. Cut the copper wire and loop 

around the clod. Record the weight of the tag and wire (TAG). Loop fine copper wire around 

the clod, leaving a tail to which the round stock tag is attached. Record the weight of the clod 

(CC1). 

122
7.3 Dip the clod in the 1:4 plastic lacquer. Wait 7 min and then dip the clod in the 1:7 plastic 

lacquer. Wait 12 min and then dip the clod in the 1:7 plastic lacquer. Wait 55 min and then 

reweigh the clod. If the clod has absorbed >3% in plastic by clod weight or smells excessively 

of solvent, allow longer drying time, then reweigh the clod and record the weight (CC2). 

7.4 Cut a flat surface on the clod with a tile saw. It is necessary to wet the clod above the 

initial desorption point. This is accomplished by placing the cut clod surface on a tension table 

that is maintained at 5-cm tension. Periodically check the clod by inserting a needle probe, 

touching, or by weight comparison to determine if it has reached equilibrium (clod has wetted 

up). When the clod has reached equilibrium, remove the clod and record the weight (WSC). 

7.5 If cut clod does not absorb water, place clod in a desiccator on a water-covered plate with a 

0-cm tension. Submerge only the surface of clod in the water. Add a few mL of alcohol. Use 

in-house vacuum and apply suction until clod has equilibrated at saturation. Remove the clod 

and record the weight (WSC). 

7.6 Saturate the ceramic plate by applying RO water through the adapter and apply enough 

pressure so that the rubber membrane is bulging a few centimeters. Care should be taken to 

remove all air. 

7.7 Place the saturated ceramic plate in a pressure plate extractor. To provide good contact 

between the clod and ceramic plate, cover the ceramic plate with a 5-mm layer of silt loam soil 

and saturate with water. Place a sheet of reinforced paper towel over the silt loam soil. Place 

cut clod surface on the paper towel. Prepare a saturated, sieved soil as a quality control (QC) 

sample. Place several retaining rings in the extractor. Fill the retaining rings with the soil 

standard. Close the container and secure lid. 

7.8 Apply gauged air pressure of 33 kPa. If more than one water retention point is requested, 

begin with the lowest pressure. Periodically submerge the outflow tube in water to monitor for 

air bubbles that indicate ceramic plate failure. Samples are equilibrated when water ceases to 

emit from the outflow tube. The outflow tube can be submerged under water in a burette to 

measure when water ceases to emit from the outflow tube. When water stops discharging from 

the outflow tube, the clod is at equilibrium. Determine the gravimetric water content of the 

QC. If the water content of the QC is higher than twice the standard deviation, apply pressure 

for additional time. Recheck the QC. If the water content of the QC is lower than twice the 

standard deviation, rewet the clods and desorb again. If the water content of the QC is within 

acceptable limits, then the apparatus has functioned properly. 

7.9 Remove the clod and record the weight (WMC). Compare WMC to WSC. If WMC >

WSC, re-equilibrate the clod on the tension table and repeat the desorption process. If 

additional water retention points are requested, then repeat the desorption process at the next 

higher pressure. When the clod is equilibrated at 33 kPa and bulk density is to be measured, 

continue with procedure 3B1b. 

7.10 Dry the clod in an oven at 110°C overnight and record oven-dry weight (WODC). 

7.11 If the clods contains >5% in rock fragments by weight, remove the rock fragments from 

the clod. This determination of the percent rock fragments is based on particle-size data of >2-

mm fraction.. Submerge the remaining soil material in a beaker of water and place on a hot 

plate. Use a fume hood. Boil ≈ 1 h. The plastic coating loosens from soil material upon 

heating. Remove beaker from the hot plate. Allow to cool. Discard plastic coating. 

123
7.12 Wet sieve the cool soil through a 2-mm sieve. Dry and record the weight (RF) of the rock 

fragments that are retained on the sieve. If the rock fragments have similar properties to the 

soil sample, do not correct the clod mass for the rock fragments. 

8. Calculations 

8.1 H2O % =[(WMC - MPC) - (WODC - ODPC) x 100]/(WODC - RF - ODPC – TAG) 

where: 

H2O % = Percent gravimetric water content 

WMC = Weight of equilibrated, coated clod 

WODC= Weight of oven-dry coated clod 

RF = Weight of rock fragments 

ODPC = MPC x 0.85, weight of oven-dry plastic coat 

TAG = Weight of tag and wire 

8.2 MPC = {[(CC2 - CC1) + FCE] x RV} 

where: 

MPC = Weight of plastic coat before oven-drying 

CC2 = Weight of clod after three laboratory plastic coats 

CC1 = Weight of clod before three laboratory plastic coats 

RV = Percent estimate of remaining clod volume after cutting to obtain flat surface (≈ 80%) 

8.3 FCE = 1.5 x [(CC2 - CC1)/3] 

where: 

FCE = Estimate of field-applied plastic coat, if applied 

9. Report

Report water content to the nearest 0.1 percent. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

12. References 

Bruce, R.R., and R.J. Luxmoore. 1986. Water retention: field methods. p. 663-686. In A. 

Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd 

ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Dane, J.H., and J. W. Hopmans. 2002. Water retention and storage: Laboratory. p. 675-

720. In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis. Part 4. Physical 

methods. Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Klute, A. 1986. Water retention: Laboratory methods. p. 635-662. In A. Klute (ed.) 

Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. 

Monogr. 9. ASA and SSSA, Madison, WI. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. USDA Handb. 60. U.S. Govt. Print. Office, Washington, DC. 

124
Water Retention (3C) 

Pressure-Membrane Extraction (3C2) 

1500-kPa (3C2a) 

<2-mm (sieved), Air-Dry Samples (3C2a1a) 

1. Application 

The data collected are used for the water retention function, water-holding capacity, 

pore-size distribution, porosity, and saturated conductivity of a soil sample at specific water 

contents. The data are also used to calculate unsaturated hydraulic conductivity. Procedure 

3C2a1a is used to determine the water retention at 1500 kPa for <2-mm (sieved), air-dry soil 

samples. 

2. Summary of Method 

The pressure desorption procedure (U.S. Salinity Laboratory Staff, 1954) is used. A 

sample of <2-mm (sieved), air-dry soil is placed in a retainer ring sitting on a cellulose 

membrane in a pressure-membrane extractor. The membrane is covered with water to wet the 

samples by capillarity. The sample is equilibrated at 1500 kPa. The pressure is kept constant 

until equilibrium is obtained (Klute, 1986). The gravimetric water content is determined. 

3. Interferences 

A leaking pressure extractor prevents equilibration of samples. Check outflow air to 

verify that the pressure membrane extractor is functioning properly and does not leak. The 

pressure should be monitored for stability. Equilibration must be done at constant temperature 

and humidity. Samples that do not wet by capillarity are moistened with ethyl alcohol. 

Laboratory-determined, water retention data are usually higher than field-determined, 

water retention data because the confining soil pressure is not present in the laboratory (Bruce 

and Luxmoore, 1986). 

Aerated 0.005 M CaSO4 has also been recommended (Dane and Hopmans, 2002), 

especially for fine-textured soils that contain significant amounts of swelling clays. Distilled or 

deionized water can possibly promote dispersion of clays in samples and freshly drawn tap 

water is often supersaturated with air, affecting the water content at a given pressure head 

(Dane and Hopmans, 2002). 

4. Safety 

High-pressure plumbing must be maintained in good working order. Ensure that the 

pressure is zero before removing bolts from the pressure-apparatus lid. Ensure that the bolts 

are tightened before applying pressure. Do not drop the heavy lid. 

5. Equipment 

5.1 Pressure membrane extractor (Fig.1 and 2) 

5.2 Cellulose membrane 

5.3 Retainer rings. Use 10-mm height and 50-mm diameter rings for organic soils and 10-mm 

height and 40-mm diameter rings for all other soils. 

5.4 Electronic balance, ±0.01-g sensitivity 

5.5 Oven, 110°C 

5.6 Pressure source, regulator, and gauge 

5.7 Metal weighing cans, tared, with lids 

5.8 Vacuum trap assembly 

5.9 Vacuum, 80 kPa (0.8 bar) 

6. Reagents 

6.1 Ethyl alcohol, 95%, technical grade 

6.2 Reverse osmosis (RO) water 

125
7. Procedure 

7.1 Submerge a cellulose membrane in RO water for 12 h or more before use. Install the wet 

cellulose membrane in the pressure extractor. 

7.2 Add water and retaining rings. Add enough water to keep membrane moist. Water level 

should be less than height of retaining rings. Use 5-cm diameter rings for soils that are >12% 

in organic matter. Use 4-cm diameter rings for all other soils. 

7.3 Fill retaining rings with 10 to 15 g of <2-mm or fine-grind, air-dry soil sample. Include a 

quality control (QC) sample with each plate. Continue to add water until all samples have 

moistened by capillarity. If samples do not moisten, apply ethyl alcohol to the surface of the 

sample. Allow ethyl alcohol to evaporate. Cover samples with a sheet of plastic to reduce 

evaporation, close the extractor, and let stand overnight. 

7.4 Remove excess water on the plate with a vacuum and trap assembly. 

7.5 Assemble the extractor and uniformly tighten the bolts. Torque the bolts on both sides of 

the hinge to 138.0 kPa (200 psi). Torque the remaining bolts to 103.5 kPa (150 psi). 

7.6 Increase air pressure ≈ 150 kPa every 15 min until 1500 kPa is reached. After 4 h, apply 

the pressure differential by closing the valve that joins the mercury circuit and by opening the 

pressure release valve until air is forced through the mercury. Quickly close the pressure 

release valve. This forces the rubber diaphragm against the top of the samples. The samples 

are equilibrated when water ceases to emit from the outflow tube. 

7.7 At equilibrium, open the extractor and quickly transfer the samples to water cans, cover 

with lids, and record the weights (Ms+w). 

7.8 Remove the lids, place samples in the oven, and dry at 110°C overnight. Remove samples 

from the oven, replace the lids, allow cans to cool to ambient temperature, and record the 

weights (Ms). 

7.9 Record the weights of the empty cans (Mc). 

8. Calculations 

H2O % = 100 x [(Ms+w - Ms)/ (Ms - Mc)]

where: 

H2O % = Percent gravimetric water content 

Ms+w = Weight of solids + H2O + container 

Ms = Weight of solids + can 

Mc = Weight of container 

Gypsiferous soils are a special case because gypsum (CaSO4·2H2O) loses most of its 

two water molecules at 105°C. Properties of gypsiferous soils such as 1500-kPa water content 

that are reported on an oven-dry weight basis are converted to include the weight of crystal 

water in gypsum. Refer to procedure 3D3 for these conversion calculations. The 1500-kPa 

water content is corrected when the gypsum content of the soil is >1%. Gypsum content of the 

soil is determined in procedure 4E2a1a1. 

9. Report

Report water content to the nearest 0.1 percent. 

126
10. Precision and Accuracy

Precision and accuracy data are available from the SSL upon request. 

11. References

Bruce, R.R., and R.J. Luxmoore. 1986. Water retention: Field methods. p. 663-686. In A. 

Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd 

ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Dane, J.H., and J. W. Hopmans. 2002. Water retention and storage: Laboratory. p. 675-

720. In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis. Part 4. Physical 

methods. Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Klute, A. 1986. Water retention: Laboratory methods. p. 635-662. In A. Klute (ed.) 

Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. 

Monogr. 9. ASA and SSSA, Madison, WI. 

Nelson, R.E., L.C. Klameth, and W.D. Nettleton. 1978. Determining soil content and 

expressing properties of gypsiferous soils. Soil Sci. Soc. Am. J. 42:659-661. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. USDA Agric. Handb. 60. U.S. Govt. Print. Office, Washington, 

DC. 

127
Figure 1. Sieved (<2-mm) soil placed in pressure-membrane extractor. 

Figure 2. Pressure-membrane extraction at 1500-kPa for <2-mm samples. 

128
Water Retention (3C) 

Pressure-Membrane Extraction (3C2) 

1500-kPa (3C2a) 

<2-mm (sieved), Field-Moist Samples (3C2a1b) 

1. Application 

The data collected are used for the water retention function, water-holding capacity, 

pore-size distribution, porosity, and saturated conductivity of a soil sample at specific water 

contents. The data are also used to calculate unsaturated hydraulic conductivity. Procedure 

3C2a1b is used to determine the water retention at 1500 kPa for <2-mm (sieved), field-moist 

soil samples. 

2. Summary of Method 

The pressure desorption method (U.S. Salinity Laboratory Staff, 1954) is used. A 

sample of <2-mm (sieved) moist soil is placed in a retainer ring sitting on a cellulose 

membrane in a pressure-membrane extractor. The membrane is covered with water to wet the 

samples by capillarity. The sample is equilibrated at 1500 kPa. The pressure is kept constant 

until equilibrium is obtained (Klute, 1986). The gravimetric water content is determined. 

3. Interferences 

A leaking pressure extractor prevents equilibration of samples. Check outflow air to 

verify that the pressure membrane extractor is functioning properly and does not leak. The 

pressure should be monitored for stability. Equilibration must be done at constant temperature 

and humidity. Samples that do not wet by capillarity are moistened with ethyl alcohol. 

Laboratory-determined, water retention data are usually higher than field-determined, 

water retention data because the confining soil pressure is not present in the laboratory (Bruce 

and Luxmoore, 1986). 

Aerated 0.005 M CaSO4 has also been recommended (Dane and Hopmans, 2002), 

especially for fine-textured soils that contain significant amounts of swelling clays. Distilled or 

deionized water can possibly promote dispersion of clays in samples and freshly drawn tap 

water is often supersaturated with air, affecting the water content at a given pressure head 

(Dane and Hopmans, 2002). 

4. Safety 

High-pressure plumbing must be maintained in good working order. Ensure that the 

pressure is zero before removing bolts from the pressure-plate apparatus lid. Ensure that the 

bolts are tightened before applying pressure. Do not drop the heavy lid. 

5. Equipment 

5.1 Pressure membrane extractor 

5.2 Cellulose membrane 

5.3 Retainer rings. Use 10-mm height and 50-mm diameter rings for organic soils and 10-mm 

height and 40-mm diameter rings for all other soils. 

5.4 Electronic balance, ±0.01-g sensitivity 

5.5 Oven, 110°C 

5.6 Pressure source, regulator, and gauge. 

5.7 Metal weighing cans, tared, with lids 

5.8 Vacuum trap assembly 

5.9 Vacuum, 80 kPa (0.8 bar) 

6. Reagents 

6.1 Ethyl alcohol, 95%, technical grade 

6.2 Reverse osmosis (RO) water 

129
7. Procedure 

7.1 Submerge a cellulose membrane in RO water for 12 h or more before use. Install the wet 

cellulose membrane in the pressure apparatus. 

7.2 Add water and retaining rings. Add enough water to keep membrane moist. Water level 

should be less than height of retaining rings. Use 5-cm diameter rings for soils that are >12% 

in organic matter. Use 4-cm diameter rings for all other soils. 

7.3 Fill retaining rings with 10 to 15 g of <2-mm or fine-grind, field moist soil sample. Include 

a quality control (QC) sample with each plate. Continue to add water until all samples have 

moistened by capillarity. If samples do not moisten, apply ethyl alcohol to the surface of the 

sample. Cover samples with a sheet of plastic to reduce evaporation, close the extractor, and 

let stand overnight. 

7.4 Remove excess water on the plate with a vacuum and trap assembly. 

7.5 Assemble the extractor and uniformly tighten the bolts. Torque the bolts on both sides of 

the hinge to 138.0 kPa (200 psi). Torque the remaining bolts to 103.5 kPa (150 psi). 

7.6 Increase air pressure ≈ 150 kPa every 15 min until 1500 kPa is reached. After 4 h, apply 

the pressure differential by closing the valve that joins the mercury circuit and by opening the 

pressure release valve until air is forced through the mercury. Quickly close the pressure 

release valve. This forces the rubber diaphragm against the top of the samples. The samples 

are equilibrated when water ceases to emit from the outflow tube. 

7.7 At equilibrium, open the apparatus and quickly transfer the samples to water cans, cover 

with lids, and record the weights (Ms+w). 

7.8 Remove the lids, place samples in the oven, and dry at 110°C until weights are constant. 

Remove samples from the oven, replace the lids, allow cans to cool to ambient temperature, 

and record the weights (Ms). 

7.9 Record the weights of the empty cans (Mc). 

8. Calculations

H2O % = 100 x [(Ms+w - Ms)/(Ms - Mc)]

where: 

H2O % = Percent gravimetric water content 

Ms+w = Weight of solids + H2O + container 

Ms = Weight of solids + container 

Mc = Weight of container 

9. Report

Report water content to the nearest 0.1 percent. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

130
11. References 

Bruce, R.R., and R.J. Luxmoore. 1986. Water retention: Field methods. p. 663-686. In A. 

Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd 

ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Dane, J.H., and J. W. Hopmans. 2002. Water retention and storage: Laboratory. p. 675-

720. In J.H. Dane and G.C. Topp (eds.) Methods of soil analysis. Part 4. Physical 

methods. Soil Sci. Am. Book Series No. 5. ASA and SSSA, Madison, WI. 

Klute, A. 1986. Water retention: Laboratory methods. p. 635-662. In A. Klute (ed.) 

Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. 

Monogr. 9. ASA and SSA, Madison, WI. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. USDA Agric. Handb. 60. U.S. Govt. Print. Office, Washington, 

DC. 

Water Retention (3C) 

Field-State (3C3) 

1. Application 

Field-water content can be determined by weighing, drying, and re-weighing a soil 

sample (3C3). The resulting data are used to estimate the water content at the time of sampling. 

2. Summary of Method 

Soil samples are collected in the field. The samples are stored in plastic or metal 

containers to prevent drying and then transported to the laboratory. Gravimetric water content 

is determined (Gardner, 1986). 

3. Interferences 

Leaks in the plastic or metal storage containers cause the samples to dry, resulting in an 

underestimation of the field water content. 

4. Safety

Use insulated gloves to remove samples from the oven. 

5. Equipment 

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Oven, 110°C 

5.3 Moisture cans, tared 

6. Reagents 

None 

7. Procedure 

7.1 Collect soil samples in the field. Place samples in airtight, metal or plastic containers. 

7.2 Record sample weight (Ms+w). 

7.3 Dry sample in an oven at 110°C overnight. Record oven-dry weight (Ms). 

7.4 Record weight of container (Mc). 

8. Calculations

H2O % = 100 x [(Ms+w - Ms)/(Ms - Mc)]

131
where: 

H2O % = Percent gravimetric water content 

Ms+w = Weight of solids + H2O + container 

Ms = Weight of solids + container 

Mc = Weight of container 

9. Report

Report water content to the nearest 0.1 percent. 

10. Precision and Accuracy

Precision and accuracy data are available from the SSL upon request. 

11. References 

Gardner, W.H. 1986. Water content. p. 493-544. In A. Klute (ed.) Methods of soil 

analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. Monogr. 9. 

ASA and SSA, Madison, WI. 

PHYSICAL AND FABRIC-RELATED ANALYSES (3) 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

Air-Dry/Oven-Dry Ratio (AD/OD) (3D1) 

Field-Moist/Oven-Dry Ratio (FM/OD)(3D2) 

Correction for Crystal Water (3D3) 

1. Application 

Soil properties generally are expressed on an oven-dry weight basis. The calculation of 

the air-dry/oven-dry (AD/OD) ratio (procedure 3D1) or field-moist/oven-dry (FM/OD) ratio 

(procedure 3D2) is used to adjust all results to an oven-dry basis and, if required in a 

procedure, to calculate the sample weight that is equivalent to the required oven-dry soil 

weight. 

Gypsiferous soils are a special case because gypsum (CaSO4·2H2O) loses most of its 

two water molecules at 105°C. Properties of gypsiferous soils that are reported on an oven-dry 

weight basis should be converted to include the weight of crystal water in gypsum. In 

procedure 3D1, the AD/OD ratio is calculated. This ratio is used to convert soil properties to 

an oven-dry basis. In procedure 3D3, the AD/OD ratio is converted to a crystal water basis 

(Nelson et al., 1978). The inclusion of weight of crystal water in gypsum allows the properties 

of gypsiferous soils to be compared with those properties of nongypsiferous soils. This 

conversion also avoids the possible calculation error of obtaining >100% gypsum when the 

data are expressed on an oven-dry basis (Nelson, 1982). 

2. Summary of Method 

A sample is weighed, dried to a constant weight in an oven, and reweighed. The 

moisture content is expressed as a ratio of the air-dry to the oven-dry weight (AD/OD) or as a 

ratio of field-moist to the oven-dry weight (FM/OD). Soil properties of gypsiferous soils that 

are reported on an oven-dry weight basis are converted to include the weight of the crystal 

water. When reporting the water content of gypsiferous soils, the crystal water content must be 

subtracted from the total oven-dry water content. The AD/OD ratio is corrected to a crystal 

water basis when the gypsum content of the soil is >1%. Gypsum content of the soil is 

determined in procedure 4E2a1a1. 

132
3. Interferences 

Traditionally, the most frequently used definition for a dry soil is the soil mass after it 

has come to a constant weight at a temperature of 100 to 110°C (American Society for Testing 

and Materials, 2004). Many laboratory ovens are not capable of maintaining this prescribed 

temperature range. Temperatures that are >50°C may promote oxidation or decomposition of 

some forms of organic matter. 

Samples may not reach a constant weight with overnight drying. Do not add moist 

samples to an oven with drying samples unless the drying samples have been in the oven for at 

least 12 to 16 h. Soil samples may adsorb significant amounts of moisture from the atmosphere 

after cooling. Prompt weighing, i.e., <30 min after samples have cooled, helps to eliminate this 

problem. During the weighing or drying processes, the non-uniform weight of weighing 

vessels, sample contamination, or sample loss may lead to erroneous results. 

The removal of structural water, most commonly in gypsum, can produce a positive 

error. When reporting the water content of gypsiferous soils, the crystal water content must be 

subtracted from the total oven-dry water content. Gypsum, hydrous oxides, and amorphous 

material may be affected. 

4. Safety

Use heat resistant gloves to remove weighing containers from a hot oven. No other 

significant hazard is associated with this procedure. Follow standard laboratory procedures. 

5. Equipment

5.1 Electronic balance, ± 1-mg sensitivity 

5.2 Oven, thermostatically controlled, 110 ± 5°C 

5.3 Thermometer, 0 to 200°C 

5.4 Tin dishes, 4.5-cm diameter x 3-cm height, with covers 

6. Reagents 

No reagents are required for this determination. 

7. Procedure 

7.1 Tare the moisture dishes. Record each sample number and associated dish number. 

7.2 Add 10 to 20 g <2mm or fine-grind, air-dry soil to each moisture dish for AD/OD 

determination. For FM/OD determination, add enough <2mm or fine-grind, moist soil to 

achieve ≈ 10 to 20 g sample of air-dry soil. Weigh the dish plus the sample and record the 

weight to the nearest 1mg. Place the sample dish in a drying oven set at 110 ± 5°C. Allow the 

sample to remain in the oven overnight (12 to 16 h). 

7.3 Remove the sample dish and allow it to cool before re-weighing. Record the oven-dry 

weight to the nearest 1mg. 

7.4 Do not allow the sample dish to remain at room temperature for >30 min before reweighing. 

7.5 Discard the sample. 

7.6 Refer to the calculations for the correction for crystal water of gypsum in gypsiferous soils. 

8. Calculations 

Calculations 8.1 – 8.2 for AD/OD ratio (procedure 3D1) are as follows: 

133
8.1 AD/OD ratio = AD/OD 

where: 

AD = (Air-dry weight) – (Tin tare weight) 

OD = (Oven-dry weight) – (Tin tare weight) 

8.2 H2O = [(AD – OD) x 100]/OD 

where: 

H2O = % Water content 

AD = (Air-dry weight) – (Tin tare weight) 

OD = (Oven-dry weight) – (Tin tare weight) 

Calculations 8.3 – 8.4 for FM/OD ratio (procedure 3D2) are as follows: 

8.3 FM/OD ratio = FD/OD 

where: 

FM = (Field-moist weight) – (Tin tare weight) 

OD = (Oven-dry weight) – (Tin tare weight) 

8.4 H2O = [(FM – OD) x 100]/OD 

where: 

FM = (Field-moist weight) – (Tin tare weight) 

OD = (Oven-dry weight) – (Tin tare weight) 

Calculations 8.5 – 8.6 for gypsum H2O correction (procedure 3D3) are as follows: 

8.5 (AD/OD)c = (AD/OD)uc /[1 + (Gypsum x 0.001942)] 

where: 

AD/ODc = Air-dry/oven-dry ratio, corrected basis, gypsiferous soils 

AD/ODuc = Air-dry/oven-dry ratio, uncorrected basis 

Gypsum = % Gypsum uncorrected (procedure 4E2a1a1) 

8.6 H2Oc = [H2Ouc - (Gypsum x 0.1942)]/ [1 + (Gypsum x 0.001942)] 

where: 

H2Oc = % Water content, corrected basis, gypsiferous soils 

H2Ouc = % Water content, uncorrected basis (calculation 8.2) 

Gypsum= % Gypsum uncorrected (procedure 4E2a1a1) 

AD/OD Data Use 

The following equation is used to calculate the weight of air-dry soil needed to provide a given 

weight of oven-dry soil for other analytical procedures. 

8.7 AD = (ODr)/[1-(H2O/100)] 

where: 

AD = Required weight of air-dry soil 

ODr = Desired weight of oven-dry soil 

H2O = Percent water determined from AD/OD (calculation 8.2) 

134
9. Report 

Report the AD/OD and/or FM/OD ratio as a dimensionless value to the nearest 0.01 

unit. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Nelson, R.E. 1982. Carbonate and gypsum. p. 159-165. In A.L. Page, R.H. Miller, and 

D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Nelson, R.E., L.C. Klameth, and W.D. Nettleton. 1978. Determining soil content and 

expressing properties of gypsiferous soils. Soil Sci. Soc. Am. J. 42:659-661. 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

Coefficient of Linear Extensibility (COLE) (3D4) 

Coefficient of linear extensibility (COLE) is a derived value that denotes the fractional 

change in the clod dimension from a moist to a dry state (Franzmeier and Ross, 1968; 

Grossman et al., 1968; Holmgren, 1968). COLE may be used to make inferences about shrinkswell capacity and clay mineralogy. The COLE concept does not include irreversible 

shrinkage such as that occurring in organic and some andic soils. Certain soils with relatively 

high contents of smectite clay have the capacity to swell significantly when moist and to shrink 

and crack when dry. This shrink-swell potential is important for soil physical qualities (large, 

deep cracks in dry seasons) as well as for genetic processes and soil classification (Buol et al., 

1980). 

COLE can also be expressed as percent, i.e., linear extensibility percent (LEP). LEP = 

COLE x 100. The LEP is not the same as LE. In soil taxonomy (Soil Survey Staff, 1999), 

linear extensibility (LE) of a soil layer is the product of the thickness, in centimeters, multiplied 

by the COLE of the layer in question. The LE of a soil is defined as the sum of these products 

for all soil horizons (Soil Survey Staff, 1999). Refer to Soil Survey Staff (1999) for additional 

discussion of LE. 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

Coefficient of Linear Extensibility (COLE) (3D4) 

Air-Dry or Oven-Dry to 33-kPa Tension (3D4a) 

The SSL calculates the COLE for the whole soil (air-dry or oven-dry WRN3D

suction) by procedure 3D4a. The COLE value is reported in cm cm-1. Calculate &2/(

when coarse fragments are present as follows: 

8.1 COLEws = {1/[Cm x (Db33<2mm/Dbd<2mm) + (1 - Cm)]}1/3 - 1 

where: 

COLEws = Coefficient of linear extensibility on a whole-soil base. 

Db/33<2mm = Bulk density at 33-kPa water content on a <2-mm base (g cc-1). 

Dbd<2mm = Bulk Density, oven-dry or air-dry, on a <2-mm base (g cc-1). 

135
Cm = Coarse fragment (moist) conversion factor. 

8.2 If no coarse fragments, Cm = 1. If coarse fragments are present, calculate Cm as follows: 

Cm = Vol<2mm /Volwhole

where: 

Vol<2mm = Volume moist <2-mm fabric (cm3) 

Volwhole = Volume moist whole soil (cm3) 

OR (alternatively) 

8.3 Cm = (100 – Vol>2mm)/100 

where: 

Vol>2mm = Volume percentage of the >2-mm fraction 

8.4 If no coarse fragments, Cm = 1, the previous equation reduces as follows: 

COLEws = (Dbd<2mm/Db33<2mm)

1/3 – 1 

where: 

COLEws = Coefficient of linear extensibility on a whole-soil base 

Dbd<2mm = Bulk Density, oven-dry or air-dry, on a <2-mm base (g cc-1) 

Db33<2mm = Bulk Density at 33-kPa water content on a <2-mm base (g cc-1) 

References 

Buol, S.W., F.D. Hole, and R.J. McCracken. 1980. Soil genesis and classification. 2nd ed. Iowa 

State Univ. Press, Ames IA. 

Franzmeier, D.P., and S.J. Ross, Jr. 1968. Soil swelling: Laboratory measurement and relation 

to other soil properties. Soil Sci. Soc. Amer. Proc. 32:573-577. 

Grossman, R.B., B.R. Brasher, D.P. Franzmeier, and J.L. Walker. 1968. Linear extensibility as 

calculated from natural-clod bulk density measurements. Soil Sci. Soc. Am. Proc. 32:570-

573. 

Holmgren, George G.S. 1968. Nomographic calculation of linear extensibility in soils 

containing coarse fragments. Soil Sci. Soc. Amer. Proc. 32:568-570. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys. Agric. Handb. No. 436. 2nd ed USDA-NRCS. Govt. Print. Office, 

Washington, DC. 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

Water Retention Difference (WRD) (3D5) 

The calculation of the water retention difference (WRD) is considered the initial step in 

the approximation of the available water capacity (AWC). WRD does not allow for restriction 

of roots from the soil layer or osmotic pressure. Usually the volume of rock fragments is 

considered a diluent containing no water between the suctions that define WRD. WRD is a 

calculated value that denotes the volume fraction for water in the whole soil that is retained 

between 1500-kPa suction and an upper limit of usually 33 or 10-kPa suction. The upper limit 

(lower suction) is selected so that the volume of water retained approximates the volume of 

water held at field capacity. The 10-, 33- and 1500-kPa gravimetric water contents are then 

converted to a whole soil volume basis by multiplying by the bulk density (Db33) and adjusting 

downward for the volume fraction of rock fragments, if present in the soil. The lower suctions, 

e.g., 10 or 5-kPa, are used for coarse materials. Refer to Soil Survey Staff Division Staff 

136
(1993) and Grossman et al. (1994) for additional discussion on coarse materials and the 

significance of soil water content at lower suctions, e.g., 5 and 10 kPa, as well as suggestions 

for the selection of these lower suctions for the determination of water retention difference 

(WRD). 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

Water Retention Difference (WRD) (3D5) 

Between 33-kPa and 1500-kPa Tension (3D5a) 

The SSL calculates the WRD between 33 and 1500-kPa suctions in the whole soil by 

procedure 3D5a. The WRD is reported as centimeters of water per centimeter of depth of soil 

(cm cm-1), but the numbers do not change when other units, e.g., in in-1 or ft ft-1 are needed. 

The WRD with W33 as the upper limit is reported as cm cm-1. This WRD is calculated on a 

whole-soil base as follows: 

WRDws = [(W33<2mm - W1500<2mm) x (Db33<2mm) x Cm]/ (Pw x 100) 

where: 

WRDws = Volume fraction (cm3

 cm-3) of water retained in the whole soil between 33-kPa 

 and 1500-kPa suction reported in cm cm-1. 

W33<2mm = Weight percentage of water retained at 33-kPa suction on a <2-mm soil basis. 

W1500<2mm = Weight percentage of water retained at 1500-kPa suction on a <2-mm soil basis. 

 If available, moist 1500-kPa (procedure 3C2a1b) is the first option in the WRD 

 calculation; otherwise, dry 1500-kPa (procedure 3c2a1a) is used. 

Db33<2mm = Bulk density at 33-kPa water content on a <2-mm base (g cm-3). 

Pw = Density of water (1 g cm-3). 

Cm = Coarse fragment material conversion factor. If no coarse fragments, Cm = 1. If 

 coarse fragments are present, calculate Cm as follows: 

Cm = Vol<2mm/Volwhole

where: 

Vol<2mm = Volume moist <2mm fabric (cm3) 

Volwhole = Volume moist whole soil (cm3) 

OR (alternatively) 

Cm = (100 - Vol>2mm)/100 

 

where: 

Vol>2mm = Volume percentage of the >2-mm fraction. 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

Water Retention Difference (WRD) (3D5) 

Between 10-kPa and 1500-kPa Tension (3D5b) 

The SSL also calculates the WRD between 10-kPa (W10) and 1500-kPa suctions (W1500) 

by procedure 3D5b. This WRD value can be calculated by substituting the W10 in place of W33

in the equation for procedure 3D5a. The W10 may be used as the upper limit of plant available 

water for coarse soil materials. 

137
Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

Water Retention Difference (WRD) (3D5) 

Between 33-kPa Rewet and 1500-kPa (Air-Dry) Tension (3D5c) 

The SSL also calculates the WRD between 33-kPa rewet (Wr) and W15 by procedure 

3D5c. This WRD value can be calculated by substituting the Wr in place of W33 in the equation 

for 3D5a. The Wr is used for organic materials. 

References 

Grossman, R.B., T. Sobecki, and P. Schoeneberger. 1994. Soil interpretations for resource soil 

scientists. Soil Water. Tech. Workbook. USDA-SCS, Lincoln, NE. 

Soil Survey Division Staff. 1993. Soil survey manual. USDA. Handb. No. 18. U.S. Govt. Print. 

Office, Washington, DC. 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

1500-kPa Water Content/Total Clay (3D6) 

Divide the 1500-kPa water retention (procedure 3C2a) by the total clay percentage 

(procedure 3A1a). This ratio is reported as a dimensionless value. In the past, the ratios of 

1500-kPa water:clay have been reported as g g-1. For more detailed information on the 

application of this ratio, refer to Soil Survey Staff (1995, 1999). 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

Total Silt Fraction (3D7) 

Total silt is a soil separate with 0.002- to 0.05-mm particle diameter. The SSL 

determines the fine silt separate by pipet analysis and the coarse silt separate by difference 

(3A1a). Total silt is reported as a weight percentage on a <2-mm basis (3D7). For more 

information on these data, refer to Soil Survey Staff (1995). 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

Total Sand Fraction (3D8) 

Total sand is a soil separate with 0.05- to 2.0-mm particle diameter. The SSL 

determines the sand fractions by sieve analysis (3A1a). Total sand is the sum of the very fine 

sand (VFS), fine sand (FS), medium sand (MS), coarse sand (CS), and very coarse sand 

fractions VCS). The rationale for five subclasses of sand and the expansion of the texture 

classes of sand, e.g., sandy loam and loamy sand, is that the sand separates are the most visible 

to the naked eye and the most detectable by "feel" by the field soil scientist. Total sand is 

reported as a weight percentage on a <2-mm basis (3D8). For more information on the 

application of these data, refer to Soil Survey Staff (1995). 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

2- to 5- mm Fraction (3D9) 

The SSL determined coarse fraction with 2- to 5-mm particle diameter by procedures 

outlined in 3A2. The 2- to 5-mm divisions correspond to the size of opening of the No. 10 and 

No. 4 screen (4.76 mm), respectively, used in engineering. Coarse fractions with 2- to 5- mm 

particle-diameter correspond to the rock-fragment division, fine pebbles (Soil Survey Staff, 

138
1993). Coarse frations with 2- to 5- mm particle diameter are reported as a weight percentage 

on a <75-mm basis (3D9). For more information on coarse fraction with >2-mm particle 

diameters. For more information on these data, refer to Soil Survey Staff (1995). 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

5- to 20-mm Fraction (3D10) 

The SSL determined coarse fraction with 5 to 20-mm particle diameter by procedures 

outlined in 3A2. The 5- to 20-mm divisions correspond to the size of opening of the No. 4 

screen (4.76 mm) and the 3⁄4-in screen (19.05 mm), respectively, used in engineering. Coarse 

fractions with 5- to 20- mm particle-diameter correspond to the rock fragment division, 

medium pebbles (Soil Survey Staff, 1993). Coarse frations with 5- to 20- mm particle-diameter 

are reported as a weight percentage on a <75-mm basis (3D10). For more information on these 

data, refer to Soil Survey Staff (1995). 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

20- to 75-mm Fration (3D11) 

The SSL determined coarse fraction with 20 to 75-mm particle diameter by procedures 

outlined in 3A2. The 20- to 75-mm divisions correspond to the size of opening of the 3⁄4-in 

screen (19.05 mm) and the 3-in screen (76.1 mm), respectively, used in engineering. Coarse 

fractions with 20- to 75- mm particle-diameter correspond to the rock fragment division, coarse 

pebbles (Soil Survey Staff, 1993). Coarse frations with 20- to 75- mm particle diameter are 

reported as a weight percentage on a <75-mm basis (3D11). For more information on these 

data, refer to Soil Survey Staff (1995). 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

0.1 to 75-mm Fraction (3D12) 

The SSL determines coarse fractions with 0.1 to 75-mm particle diameter by procedures 

outlined in 3A1a and 3A2. The 75-mm division corresponds to the size of opening in the 3-in 

screen (76.1 mm) used in engineering. These data are listed for taxonomic placement for 

particle-size class, i.e., to distinguish loamy and silty family particle-size classes. Refer to Soil 

Survey Staff (1995, 1999) for additional discussion on particle-size classes. Coarse fractions 

with 0.1 to 75-mm particle diameter are reported as a weight percentage on a <75-mm basis 

(3D12). 

Ratios and Estimates Related to Particle-Size Analysis, Bulk Density, and 

Water Retention (3D) 

>2-mm Fraction (3D13) 

The SSL determine coarse fractions with >2-mm particle diameter by procedure 

outlined in 3A2. Coarse fractions with >2-mm particle diameter are reported as a weight 

percent on a whole-soil basis (3D13). For more information on these data, refer to Soil Survey 

Staff (1993, 1995, 1999). 

References 

Soil Survey Division Staff. 1993. Soil survey manual. USDA. Handb. No. 18. U.S. Govt. Print. 

Office, Washington, DC. 

Soil Survey Staff. 1995. Soil survey laboratory information manual. Version No. 1.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, DC 

139
Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys. 2nd ed. Agric. Handb. No. 436. USDA-NRCS. U.S. Govt. Print. 

Office, Washington, DC. 

Micromorphology (3E) 

Thin Sections (3E1) 

Preparation (3E1a) 

1. Application 

Micromorphology is used to identify fabric types, skeleton grains, weathering intensity, 

illuviation of argillans, and to investigate genesis of soil or pedological features. 

2. Summary of Method 

In this procedure (3E1a), a soil clod is impregnated with a polymer resin (Innes and 

Pluth, 1970). A flat surface of the soil sample is glued to a glass slide. The soil sample is cut 

and ground to a thickness of ≈ 30 μm. The thin section is examined with a petrographic 

microscope (Anon. 1987; Cady, et al., 1986). 

3. Interferences 

Impregnation of the soil sample must be complete, or the sample will disintegrate 

during processing. Air bubbles interfere with petrographic examination. Bubbles are avoided 

by using proper temperature, pressure, and technique. The final, 30-μm thickness is estimated 

by examining the slide under polarized light. If the quartz interference colors are of first order, 

i.e., white, gray, and pale yellow, the sample is ≈ 30 μm (Anon. 1987). 

4. Safety 

Use adequate ventilation when mixing, heating, and applying the resins. Use tongs or 

heat resistant gloves when handling hot slides or resins. 

5. Equipment 

5.1 Petro-thin, thin sectioning system, Buehler, Lake Bluff, IL 

5.2 Metallographic polisher with cast-iron laps 

5.3 Diamond saw 

5.4 Electric oven 

5.5 Hot plate with temperature control or a petrographic slide warmer 

5.6 Polarizing microscope 

5.7 Vacuum, 0.8 bars (80 kPa) 

5.8 Desiccator 

5.9 Porcelain crucibles 

5.10 Standard petrographic slides 

5.11 Cover glass 

5.12 Silicon carbide abrasives 

5.13 Squares of thick, rough-textured plate glass, 305 mm 

5.14 Metal probes or dissecting needles 

5.15 Small forceps 

5.16 Art brush 

5.17 Razor blade 

5.18 Small chisel, probe (ice pick), ordinary hacksaw, or jeweler's hacksaw 

6. Reagent

6.1 Scotchcast resin, Industrial Electric Products Division, 3M Company, 3M Center, St. 

Paul, MN 55101. 

6.2 Epoxide. The SSL uses EPO-MIX from Buehler. 

6.3 Ethylene glycol, automotive coolant/anti-freeze 

140
7. Procedure 

Sample Collection

7.1 Collect samples by any procedure that does not disturb the natural structure. Core samplers 

are commonly used. A satisfactory procedure for some soils is to use a knife or trowel to carve 

a clod that fits in bulk density box cells, a tin box, matchbox, or a round ice-cream container. 

7.2 Place clods in an upright position in the container. Mark the top of clod with a thumb tack, 

staple, or pin to ensure proper orientation. 

7.3 Select clods from bulk samples if orientation is of no interest. Avoid coated clods with 

Saran or other plastic because coatings interfere with the grinding after the clod is sectioned. 

7.4 Place clods in small plastic bags to avoid contamination from other samples during transit. 

Pack irregular clods in box cells or containers with light weight material to avoid breakage. 

Unless fragility is affected, the prevention of moisture loss is usually unnecessary as most 

samples are usually dried before impregnation. 

7.5 The whole core or clod can be impregnated, but better results are generally obtained with 

specimens that are 5 cm3

 or smaller. Remove specimens from the sample with a small chisel, a 

probe (ice pick), an ordinary hacksaw, or a jeweler's hacksaw. 

Sample Preparation

7.6 Place the soil sample in a disposable heat- and chemical-resistant beaker and place in a 

glass desiccator. Evacuate the air from the desiccator and dry the sample overnight at 80°C. 

The natural structure of the soil samples is better preserved by the technique of freeze-drying. 

Impregnation of the freeze-dried samples may be an improvement over oven-dried samples. In 

preparation for the proceeding step, bring the freeze-dried or oven-dried sample to ≈ 80°C. 

Mixing plastic solution

7.7 Many good resins are on the market. The NSSL uses Scotchcast. Add two parts of part A 

by weight to three parts of part B. For best results, raise part A and part B to ≈ 80°C before 

mixing. Weigh parts to an accuracy of 2% before mixing. Mix until a uniform color is 

obtained. 

Impregnation 

7.8 Open the desiccator which contains the dry samples, add the heated plastic solution, and 

evacuate all the air from the sample. Release the vacuum and again evacuate the air. Do not 

mistake boiling solution under evacuated conditions for escaping air bubbles from the sample 

material. 

7.9 Cure the impregnated soil overnight in the oven at 110°C. After curing, the block is ready 

for sectioning. Disposable containers can be cut with the cooled samples during sectioning. 

Cutting and Rough Grinding

7.10 With a diamond saw blade, cut the sample block into 13-mm thick chips that are small 

enough to fit on a regular petrographic slide. 

7.11 With a slurry of successively finer abrasives, grind one surface smooth on the revolving 

lap until the surface is highly polished. Experience is required to determine the mixture of 

abrasive and water that gives the best results for each grade of abrasive. If the sample surface 

tends to pull apart or to react with water, dry and re-impregnate the small chip or polish it by 

141
hand on a glass plate. Alternatively, grind the block with an abrasive and lubricate with 

ethylene glycol. 

7.12 Clean the sample free of all abrasive material. An ultrasonic bath is recommended. Dry 

thoroughly. 

Mounting

7.13 Burnish petrographic slides to a uniform thickness. 

7.14 Firmly attach the chip to the burnished slide with a strong, transparent bonding agent. Use 

a thermoplastic cement or epoxide. Mix the resin and hardener according to the product 

instructions. Allow entrapped air to rise to the top. Apply a thin layer of epoxide to the slide 

and to the chip. Place the chip obliquely on the slide and lower slowly. Move the chip back 

and forth with moderate pressure to remove entrapped air bubbles and excess epoxide. Clamp 

with a spring clamp and cure at ~ 50°C for 1 h. 

Final Grinding

7.15 Consult the Petro-thin operation and maintenance instructions for proper operation. 

7.16 Clean the glass of excess cement. 

7.17 Use the Petro-thin to cut off the excess sample and grind the sample to ≈ 30 μm with the 

diamond lap. Examine the section frequently under a polarizing microscope during the final 

stages of grinding. If quartz is present in the sample, use it to judge thickness. If the sample is 

≈ 0.030 mm thick, the quartz interference colors are of the first order, i.e., white, gray, and pale 

yellow. 

7.18 If a Petro-thin is not available, trim the mounted sample with a diamond saw blade to a 

thickness of 50 to 100 μm. Begin with the coarse abrasive and lap by hand until the sample is 

relatively thin. Use successively finer abrasives. 

7.19 Care and considerable practice are needed to develop the dexterity required to handle an 

almost finished section without over-grinding. Use the finest abrasive to finish grinding on 

ground-glass plates. Wash the section free of abrasive and dry thoroughly. 

Seating Cover Glass

7.20 Heat the finished section and the cover slip to ≈ 40°C. Spread a small quantity of epoxide 

over the surface of the thin section and the cover slip. Wait a few seconds for the air bubbles to 

escape. Place the cover glass obliquely on one end of the section and lower very slowly. If any 

air bubbles remain, remove them by pressing lightly on the cover glass with a soft eraser. As 

the section cools, but before the plastic hardens, remove excess epoxy with a razor blade. After 

the epoxy hardens, remove the final thin film with a razor blade. A thick film may cause the 

slide to break when the epoxy is removed. 

7.21 Very dense soils and soils with clay fractions that have 30% or more montmorillonite 

require special handling. Use either a dry-grinding technique or a more penetrating 

impregnation procedure. Without using water, cut the sample to the appropriate size. Sprinkle 

a coarse abrasive (American Optical No. 190) on the ground-glass plate and commence to drygrind one face of the sample by hand. Use a figure "8" or a counterclockwise motion for best 

results. Use successively finer abrasives and continue to grind until the surface is highly 

polished. Proceed with the standard mounting technique. 

7.22 Aroclor 5460, a thermoplastic chlorinated diphenyl resin (Monsanto), seems to give better 

impregnation of dense soils. Place pieces of air-dry soil material in xylene and evacuate. 

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Submerge the xylene-saturated soil material in molten Aroclor 5460. Hold the sample in the 

Aroclor at ≈ 200°C for 1 to 2 days. Remove impregnated soil material, allow to cool, and 

prepare thin sections by dry-grinding. 

8. Calculations 

None 

9. Report

Describe the thin section as outlined in procedure 3E1b. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Anon. 1987. Petrographic sample preparation for micro-structural analysis. Buehler 

Digest, Vol. 24, No.1. 

Cady, J.G., L.P. Wilding, and L.R. Drees. 1986. Petrographic microscope techniques. 

p. 198-204. In A. Klute (ed.) Methods of soil analysis. Part 1. Physical and 

mineralogical methods. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Innes, R.P., and D.J. Pluth. 1970. Thin section preparation using an epoxy 

impregnation for petrographic and electron microprobe analysis. Soil Sci. Soc. 

Am. Proc. 34:483-485. 

Micromorphology1 (3E) Thin Sections (3E1) 

Interpretation (3E1b) 

Application 

Background: Micromorphology may be defined as the study of soils or regolith 

samples in their natural undisturbed arrangement using microscopic techniques (Cady, 1986; 

Stoops, 2003). This technique is also termed microfabric analysis and entails descriptive 

terminology that has been developed over the past 50 years. The science and terminology of 

microfabric analysis was initially documented by Kubiena (1938) and important publications 

documenting terminology since have included Brewer (1964); Fitzpatrick (1984, 1993); 

Bullock et al. (1985); and Stoops (2003). Methodological descriptions for producing thin 

sections can be found in Cady et al. (1986); Fitzpatrick (1984); Murphy (1986); Fox et 

al.(1993); and Fox and Parent (1993). An excellent book on examination of mineral 

weathering in thin sections is Delvigne (1998) and the Soil Science Society of America has a 

collection of images on a CD that illustrates many features of microfabrics (SSSA, 1993). 

Examination of thin sections with a polarizing light microscope can be considered an 

extension of field morphological studies. The level of resolution increases from field 

examination to optical microscopic examination and finally to submicroscopic techniques 

(electron microscopy), but this sequence of techniques increasingly sacrifices field of view 

(Cady et al., 1986). Thus, the results of micromorphological studies are most useful when they 

are combined with other field (landscape description, pedon morphological description) and 

laboratory data (Cady, 1965). Micromorphology is used to identify types and sequences of 

active processes occurring in soils via identification of argillans, fabric types, skeleton grains, 

weathering intensity. It is an ideal tool to investigate genesis of soil or pedological features. 

1

 W. Dennis Nettleton, Research Soil Scientist (retired) and Michael A.Wilson, Research Soil 

Scientist, NSSC, NRCS, Lincoln, NE, wrote the procedure for description and interpretation of 

soil micromorphology as seen in thin sections. 

143
Initially, the investigator should scan the overall features of a thin section and determine 

those features that require emphasis. This initial scanning may include all the thin sections 

from a soil profile or all those related to a particular problem. Different kinds of illumination 

should be used with each magnification. Strong convergent light with crossed polarizers 

elucidates structures in dense or weakly birefringent material that may appear opaque or 

isotropic. Structures in translucent specimens become more clearly visible if plain light is 

used, and the condensers are stopped down. Everything should be viewed in several positions 

of the stage or during slow rotation with crossed polarized light. 

A thin section is a two-dimensional slice through a three-dimensional body. The shapes 

of mineral grains and structural features are viewed in one plane, and the true shapes must be 

inferred. A grain that appears needle-shaped may be a needle or the edge of a flat plate. An 

elliptical pore may be an angular slice through a tube. A circular unit is probably part of a 

sphere. With a three-dimensional perspective in mind as well as an awareness of section 

thickness, repeated viewing of similar features that appear to be cut at different angles is the 

best way to accustom oneself to a volume rather than a planar interpretation of shape. A wellprepared section is 20- to 30-μm thick. Grains smaller in thickness are stacked and cannot be 

viewed as individual grains. Similarly, pores smaller than 20 to 30 μm cannot be seen clearly. 

A pore size of 20-μm diameter equates to a soil moisture tension of 15 kPa (0.15 bar) (Rode, 

1969) so that visible pores in thin section are mostly drained at water contents below field 

capacity. 

Sand and silt grains in thin sections are identified by standard methods presented in 

petrography texts. The general analytical approach is the same for grain studies (procedure 

7B1) as it is for thin sections. However, in grain studies, the refractive index is used only as a 

relative indicator, and other optical and morphological properties are more important. 

Furthermore, in thin sections, a concern with minerals that occur in small quantities or an 

attempt to quantify mineralogical analysis is seldom necessary. The separate particle-size 

fractions should be used for the identification and mineralogical analyses that are important to a 

study, whereas the thin sections should be used mainly for information about component 

arrangement. Recognition of aggregates, concretions, secondary pseudomorphs, and weathered 

grains is more important in thin section studies than in sand and silt petrography. Recognition 

of these components in thin section are easier because interior structures are exposed. 

Although grain studies are important in soil genesis studies, the arrangement of components is 

destroyed or eliminated by sample preparation procedures that separate the sand, silt, and clay. 

In the United States, emphasis in micromorphology has been on clay arrangement. 

Clay occurs not only in the form of aggregates but also in massive interstitial fillings, coatings, 

bridges, and general groundmass. Even though the clay particles are submicroscopic, they can 

be described, characterized and sometimes identified, e.g., the 1:1 and 2:1 lattice clays can be 

distinguished. Completely dispersed, randomly arranged clay of less than 1 μm exhibits no 

birefringence and appears isotropic in crossed polarized light. Clay in a soil is seldom all 

random and isotropic. Clay develops in oriented bodies, either during formation or as a result 

of pressure or translocation. If enough plate-shaped particles are oriented together in a body 

that is large enough to see, birefringence can be observed. 

With the exception of halloysite, the silicate clay minerals in soils are platy. The a and 

b crystallographic axes are within the plane of the plate, and the c axis is almost perpendicular 

to this plane. Even though the crystals are monoclinic, the minerals are pseudohexagonal, as 

the distribution of stems along the a and b axes is so nearly the same, and the c axis is so nearly 

perpendicular to the other axes. The optical properties, crystal structure, and general habit of 

clay are analogous to those of the micas, which can be used as models to analyze and describe 

clay properties. 

The speed of light that travels in the direction of the c axis and vibrates parallel to the a 

axis is almost the same as that light that vibrates parallel to the b axis. Therefore, the refractive 

indices are very close, and the interference effects in crossed polarized light are small when 

observed along the c axis. Light that vibrates parallel to the c axis travels faster than in other 

directions. Hence, the refractive index is lower. If the edge of the crystal or aggregate of 

144
crystals is viewed along the a-b plane between crossed polarizers, two straight extinction 

positions are viewed, and interference colors are manifested in other positions. If a clay 

concentration is organized so that most of the plates are parallel, the optical effects can be 

observed. The degree and quality of optical effects depend on the purity, continuity, and the 

orientation process of the clay body. 

Kaolinite has low birefringence and has refractive indices slightly higher than quartz. 

In the average thin section, interference colors for kaolinite are gray to pale yellow. In residual 

soils that are derived from coarse-grained igneous rocks, kaolinite occurs as book-like and 

accordion-like aggregates of silt and sand size. 

Even though halloysite can form oriented aggregates, it should not show birefringence 

because of its tubular habit. Halloysite may show very faint, patternless birefringence, which is 

caused by impurities or by refraction of light at the interfaces between particles. 

The 2:1 lattice minerals (Fig. 1) have high birefringence and show bright, intermediateorder, interference colors if the edges of aggregates are viewed. In the clay-size range, 

distinctions among smectite, mica, vermiculite, and chlorite in thin section are seldom possible. 

These clay minerals are usually mixed in the soil and seldom occur pure. In many soils, these 

clay minerals are stained and mixed with iron oxide and organic matter. 

Residual clay has been in place since its formation by weathering. Although it may 

have been transported within fragments of weathered material, it remains in place relative to 

the fabric of these fragments. This clay may be random, have no orientation, and thus be 

isotropic; however, more often, it shows some birefringence. In transported materials, silt-size 

flakes and other small aggregates are common. In many residual materials, clay is arranged 

either in forms that are pseudomorphs of rock minerals or in definite bodies of crystal 

aggregates, e.g., vermicular or accordion-like kaolin books. The regular, intact arrangement of 

these materials is usually diagnostic of residual material. 

Clay rearrangement may result from differentially applied stress that produces shear 

(Fig. 2). Platy particles become oriented by slippage along a plane, e.g., slickenside faces in a 

Vertisol or in clayey layers. Platy particles also are oriented inside the blocks. Root pressure, 

mass movement, slump, and creep can produce stress orientation. If the faces on structural 

units are smooth and do not have separate coatings, stress orientation can be inferred. 

Otherwise, in plain light, stress orientation cannot be observed. In plain light, clay in the thin 

section may be homogeneous and featureless. In crossed polarized light, the orientation pattern 

is reticulate, consisting of bright lines showing aggregate birefringence, often intersecting at 

regular angles. The effect is that of a network in a plaid pattern. There may be numerous sets 

of these slippage planes, which appear in different positions as the stage is turned. Stressoriented clay may be near rigid bodies, e.g., quartz grains, or along root channels. Stressoriented clay is often strongly developed on ped faces. Stress can also orient mica flakes and 

any other small platy grains. 

Location features that distinguish translocated clay from residual clay are its occurrence 

in separate bodies, usually with distinct boundaries, and its location on present or former pore 

walls, channel linings, or ped faces. Translocated clay may have a different composition than 

matrix clay, especially if its origin is another horizon. This clay is more homogeneous and is 

usually finer than the matrix clay. Translocated clay displays lamination, indicating deposition 

in successive increments, and manifests birefringence and extinction, indicating that these 

translocated clay bodies are oriented aggregates. If these bodies are straight, they have parallel 

extinction. If these bodies are curved, a dark band is present wherever the composite c axis and 

the composite a and b axes are parallel to the vibration planes of the polarizers. When the stage 

is rotated, these dark bands sweep through the clay aggregate. 

Other substances such as goethite, gibbsite, carbonate minerals (Fig. 3), and gypsum 

may form pore linings and ped coatings. These substances can be identified by their 

mineralogical properties. 

Amorphous coatings of organic matter, with or without admixed Fe and Al, are 

common, especially in spodic horizons. This material is dark brown to black, isotropic or 

faintly birefringent, and often flecked with minute opaque grains. Amorphous coatings of 

145
organic matter occur as the bridging and coating material in B horizons of sandy Spodosols and 

as thin coatings or stains on pore and ped faces in other soils. 

2. Procedure 

Description of Microfabrics

Terms have been defined for distribution patterns of the components of soil thin 

sections (Brewer, 1964 and 1976; Stoops and Jongerius, 1975; Brewer et al., 1983; Bullock et 

al., 1985; and Stoops, 2003). As these terms have become more widely adopted in the 

literature, the SSL increasingly uses them in Soil Survey Investigations Reports (SSIR's) and in 

soil project correspondence. Micromorphological descriptions often contain terminology from 

different sources to describe properties of the fabric. 

Related Distribution Patterns: The five "coarse-fine related distribution patterns" of 

Stoops and Jongerius (1975) are in common usage. The nomenclature of these distribution 

patterns, as described by Stoops and Jongerius (1975), are intended to be broadly defined. 

There are no restrictions on material type, absolute size, orientation, granulation, or origin. The 

system may be used to describe the distribution of primary particles, e.g., quartz grains, as well 

as compound units, e.g., humic micro-aggregates. The coarser particles may be silt, sand, or 

gravel, whereas the finer material may be clay, silt, or sand. Figure 4 shows the average 

textures, linear extensibilities (LE), and drained pore to filled pore (DP/FP) ratios of some 

related distribution patterns of a number of U.S. soils. 

The monic type (granic type of Brewer et al., 1983) consists of fabric units of only one 

size group, e.g., pebbles, sand, lithic fragments (coarse monic) or clays (fine monic). In the 

gefuric type, the coarser units are linked by bridges of finer material but are not surrounded by 

this material. In the chitonic type (chlamydic type of Brewer et al., 1983), the coarser units are 

surrounded by coatings of finer material. In the enaulic type, the larger units support one 

another, and the interstitial spaces are partially filled with finer material. The enaulic fabric 

consists of material finer than is found in either the gefuric or chitonic type but is not so fine as 

is found in the porphyric type. In the end member of the sequence, the porphyric type, the 

large fabric units occur in a dense groundmass of smaller units, and there is an absence of 

interstitial pores. This type is equivalent to the earlier porphyroskelic class of Brewer (1964) 

or to the current porphyric class (Brewer et al., 1983). The class may be divided into types 

based on the spacing of the coarser units. 

Plasma Fabrics: Brewer (1976) divided soil materials into three groups for descriptive 

purposes: peds, pedological features, and s-matrices. Peds are the basic units in soils that 

contain organized structural units and are composed of skeletal grains, plasma, and pedological 

features. The s-matrix is the material within which pedological features occur, having no 

definite boundary, size, shape, or orientation (Brewer, 1976). Skeleton grains of a soil material 

are individual grains larger than colloidal size. The soil plasma includes all the colloidal size 

material as well as relatively soluble material not bound in skeleton grains. 

The description of plasmic fabrics is based on the interpretations of optical properties 

under crossed-polarized light, especially extinction phenomena. Plasma concentrated or 

crystallized into pedological features is not included in the description of plasmic fabrics. In 

general, the descriptive terms for the s-matrix are those as defined by Brewer (1976). The smatrix plasma fabrics are divided into two groups, the asepic and sepic types. Asepic fabrics

are those with anisotropic plasma in which the domains, i.e., the plasma separations, are not 

oriented relative to each other. Sepic fabrics are those with anisotropic domains with various 

orientation patterns visible under cross-polarized light. Figure 5 shows some plasma fabrics 

and their clay, silt + clay, and linear extensibility averages of a number of U.S. soils. 

Eswaran (1983) characterized the <25-μm2

 size domains of monomineralic soils using a 

scanning electron microscope (SEM). These features are smaller than some domains described 

by Brewer (1976). However, these small features provide the detail expected of the 

interparticle relationships present in the larger separations. The domains in allophanic soils are 

composed of globular aggregates. The halloysitic soils differ in that the halloysite tubes 

146
generally may be seen as protrusions from globular forms. The domains in micaceous soils 

retain the face-to-face packing that is common in micas and may retain some of the book-like 

forms as well. The domains in montmorillonitic soils are bent to conform to the shape of 

skeletan grains. However, the packing is essentially face-to-face and, upon drying, the fabric is 

very dense and compact. In kaolinitic soils, the domains frequently are present as booklets that 

are packed face-to-face, unless iron hydrous oxide has disrupted the platelets, in which case, 

the platelets may still be packed face-to-face in subparallel stacks. 

Asepic plasmic fabrics are subdivided into two groups, argillasepic and silasepic types. 

Argillasepic fabrics are dominated by anisotropic clay minerals and have a random orientation 

pattern of clay-size domains. Overall, asepic fabrics have flecked extension patterns. Silasepic 

fabrics have a wider range of particle sizes than argillasepic types. However, a careful 

observer may view silt-size domains or plasma bodies that give the matrix an overall flecked 

extinction pattern (Fig. 6). 

The sepic plasmic fabrics have recognizable domains with various patterns of 

orientation. Internally, the domains, i.e., plasma separations, have striated extinction patterns. 

Brewer (1964) recognizes seven kinds, most of which are widely adopted. Insepic fabrics

consist of isolated, striated plasma domains within a flecked plasma matrix (Fig. 7). Mosepic 

fabrics consist of plasma domains with striated orientation that may adjoin each other or be 

separated by small plasma areas with flecked orientation that are not oriented relative to each 

other (Fig. 8). The fabric is vosepic when the plasma separations with striated orientation are 

associated with channel or pore (void) walls. The fabric is skelsepic when the plasma 

separations occur at the skeleton grain-matrix contact (Fig. 9). 

The remaining three sepic plasmic fabrics are most common in fine-textured soils. In 

masepic fabrics, the plasma separations occur as elongated zones within the s-matrix and 

apparently are not associated with void walls or skeleton grains (Fig. 10). The striations have 

parallel orientations to zone length. Lattisepic fabrics are similar to masepic fabrics except that 

the acicular and prolate domains occur in lattice-like patterns. In omnisepic fabrics, all of the 

plasma has a complex striated orientation pattern. 

Three other kinds of plasmic fabrics are characteristic of particular minerals or kinds of 

soils. Undulic plasmic fabrics have practically isotropic extinction patterns at low 

magnification, and the domains are indistinct even at high magnification. Isotic plasmic fabrics

have isotropic plasma, even at highest magnifications with high light intensity. The crystic 

plasmic fabrics have anisotropic plasma with recognizable crystals, usually of soluble 

materials. 

Pedological Features, Cutans: The term, cutan, and definitions of its respective types 

(Brewer, 1964) have been widely adopted by soil scientists. Cutan is defined by Brewer as a 

modification of the texture, structure, or fabric at natural surfaces in soil materials due to the 

concentration of particular soil constituents or as in-place modification of the plasma (Fig. 11). 

Generally, the cutans are subdivided on the basis of their location, composition, and internal 

fabric. Cutan locations are surfaces of grains, peds, channels, or voids. The mineralogical 

nature of cutans is characterized, e.g., argillans, ferri-argillans, or organo-argillans. Argillans

are composed dominantly of clay minerals, ferri-argillans have iron oxides as a significant part 

of their composition, and organo-argillans have significant color addition by inclusion of 

organic matter. 

Sesquan is a general term used for a cutan of sesquioxides or hydroxides. Sesquans that 

are specific for goethite, hematite, or gibbsite are called goethans, hematans, or gibbsans, respectively. Similarly, cutans of gypsum, carbonate, calcite, halite, quartz, silica, and 

chalcedony are called gypsans, calcans, calcitans, halans, quartzans, silans, and chalcedans, respectively. Skeleton grains that adhere to the cutanic surface are called skeletans. Pedological Features, Glaebules: Glaebules (Brewer, 1964) are three dimensional 

pedological units (e.g., Fe oxide or carbonate nodules) within the s-matrix whose morphology 

is incompatible with the composition of the present matrix material. (The name is derived from 

the Latin term glaebula, meaning a small lump or aggregate of earth.) They are usually prolate 

to equant. A glaebule is recognized as a unit either because of a greater concentration of a 

147
constituent, or difference from the s-matrix fabric, or because of the presence of distinct 

boundaries of a constituent within the enclosing s-matrix. Glaebules include papules, nodules, 

concretions, and pedodes. Papules are pedogenic features composed of clay minerals with 

continuous and/or laminar fabric, sharp external boundaries, and commonly prolate to equant, 

somewhat rounded shapes. Nodules (Fig. 12) are pedological features with undifferentiated 

internal fabric. Concretions are pedological features with concentrically laminated structures 

about a center. Pedodes are pedological features with hollow interiors, often lined with 

crystals. 

Pedological Features, Voids: Voids are the empty spaces within the s-fabric. Those 

voids with diameters of 20 μm to > 2 mm can be studied and measured in thin section. Brewer 

(1976) classifies these voids as follows: (1) simple packing voids (empty spaces due to random 

packing of single skeleton grains); (2) compound packing voids (Fig. 13) (empty spaces 

between peds or other compound individuals); (3) vughs (Fig. 14) (relatively large spaces that 

are not formed by packing of skeleton grains; (4) vesicles (Fig. 15) (relatively large empty 

spaces with smooth, regular outlines); (5) chambers (empty spaces with smooth, regular 

outlines that connect to other voids); (6) joint planes (plane-shaped, empty spaces that traverse 

the s-matrix in a regular pattern); (7) skew planes (plane-shaped, empty spaces that traverse the 

s-matrix in an irregular pattern); (8) craze planes (plane-shaped, empty spaces that traverse the 

s-matrix in a highly irregular pattern of short flat or curved planes); and (9) channels (mostly 

cylindrical-shaped, empty spaces that are larger than packing voids). 

Interpretations 

Related Distribution Patterns: Usually, the basic descriptive terms for soil fabrics do 

not imply any specific genesis of the feature. However, modifiers commonly are added when 

fabric descriptions are complete enough to understand the means of formation, i.e., stress 

cutan, or in-place plasma modification, is the result of differential forces, e.g., shearing, 

whereas an illuviation cutan is formed by movement of material in solution or suspension and 

later deposited (Brewer, 1964). 

The average properties of some related distributions we have described are given in 

Figure 4. In an experimental study of soil microfabrics by anisotropic stresses of confined 

swelling and shrinking, Jim (1986) showed that with an increase in the activity and proportion 

of the clay fraction, the related distribution patterns alter from dominantly matrigranic (monic, 

with the units being aggregates) to matrigranodic (enaulic) to porphyric. Similarly our data for 

some U.S. soils show that the relative pore volumes at 30 kPa for some soil coarse-fine 

distributions increase from enaulic through open porphyric (Fig. 16). 

Some monic fabrics are inherited, and include soil fabrics formed in sand dunes, sandy 

sediments deposited by streams and rivers, beach deposits, and gruss. Fauna can produce 

monic fabrics that are mostly fecal pellets. Monic fabrics also can form by fracturing and 

flaking of organic coatings in the upper B horizons of the Spodosols (Flach, 1960) and by 

freezing and thawing (Brewer and Pawluk, 1975). 

Several kinds of finer material (plasma) can bridge the coarser particles (skeleton 

grains) to form gefuric related distribution patterns. Gefuric patterns are common in weakly 

developed argillic and spodic horizons and in duripans. Silicate clays can bridge skeleton 

grains in some argillic horizons; the organic matter, iron, and aluminum complexes in some 

kinds of spodic horizons; and the amorphous silica in some kinds of duripans. 

In soils that are slightly more developed than those with gefuric patterns, chitonic 

related distribution patterns form. These are common in argillic and spodic horizons and in 

duripans. Bridges as well as complete coatings of skeleton grains are present. Usually, the 

cement or plasma is material that adheres to skeleton grains. These cements have covalent 

bonds and commonly include silica (Fig. 17) , iron, aluminum, and organic matter (Chadwick 

and Nettleton, 1990). 

The enaulic related distribution patterns are more common in soil material in which the 

cement bonds to itself more strongly than to skeleton grains. In sandy soils, ionic-bonded 

calcite and gypsum tend to bond to themselves more strongly than to skeleton grains (Fig. 3), 

148
thereby producing open porphyric related distribution patterns (Chadwick and Nettleton, 1990). 

Even though organic matter has covalent bonds and usually surrounds grains, organic material 

forms pellets in void spaces between skeleton grains in some spodic horizons. 

Porphyric related patterns form from the normal packing of grains in materials with a 

high proportion of fine material. These patterns can be the end member of several kinds of 

sequences (Brewer et al., 1983). In porphyric related patterns, there may or may not be 

skeleton grains of primary minerals, pedorelicts, organics, lithic fragments of shale, sandstone, 

or other rocks. In the porphyric related patterns, the material consists of silt and clay, and the 

interstices tend to be filled with minimal formation of coatings. In precursors of the porphyric 

related distribution patterns, the silt to clay ratio is used to identify the kind of sequences by 

which the porphyric pattern forms (Brewer et al., 1983). The porphyric patterns are common in 

loessial soils, especially in argillic and petrocalcic horizons, duripans, and ortstein. 

Plasmic Fabrics: The asepic plasmic fabrics differ in composition mainly in silt to clay 

ratios. Argillasepic fabrics have the higher clay contents, usually <30 percent but may have as 

much as 70 percent (Brewer et al., 1983). Organic matter or iron stains, resulting in a flecked 

distribution pattern mask the birefringence of the plasma. Argillasepic fabrics are important 

fabrics in many fine-textured B horizons. Silasepic plasmic fabrics have low clay contents and 

have more silt than clay. The silasepic fabrics are common in porphyric related distribution 

patterns in A and B horizons of Solonetz, Solodized Solonetz and Solodic Soils, Soloths, Red 

Podzolic Soils, Lateritic Podzolic Soils, and are also associated with some sedimentary deposits 

(Brewer et al., 1983). Silasepic plasma fabrics are common in A and B horizons of loessial 

soils in association other kinds of plasma separations. Even if there is high clay content, the 

horizons with asepic plasmic fabrics have low effective linear extensibilities (LE) either 

because the clays are low-swelling types or because the soils do not dry enough to undergo the 

full range of laboratory-measured LE. 

In soils that form in the same climate, the kind of sepic plasmic fabrics form a sequence 

relative to increasing linear extensibility (Nettleton et al., 1969; Holzhey et al., 1974). In 

increasing order of shrink-swell stress, the plasmic fabric sequence is insepic, mosepic, 

lattisepic, omnisepic, and masepic. Using X-ray diffraction (Clark, 1970) and scanning 

electron microscopy (Edil and Krizek, 1976), observations of deformation experiments indicate 

that the degree of clay orientation increases with an increase in applied stress. In an 

experimental study of soil microfabrics by anisotropic stresses of confined swelling and 

shrinking, Jim (1986) shows that with an increase in the activity and content of the clay 

fraction, there is an increase in the long and narrow plasma separations, i.e., a progression from 

insepic to mosepic to masepic plasmic fabrics. 

Insepic plasmic fabrics are very common in finer-grained porphyric B horizons of a 

wide range of soil groups (Brewer et al., 1983). Soil horizons with insepic fabrics generally 

have a LE of <4 percent. In some insepic plasmic fabrics, the plasma islands or papules are 

pseudomorphs of some weatherable mineral, whereas in other insepic fabrics, the papules are 

clay skin fragments or are eolian sand-size clay aggregates (Butler, 1974). In some samples, 

the pseudomorphs do not disperse well in particle-size distribution analysis (PSDA). 

Mosepic plasmic fabrics commonly have more clay than insepic fabrics do because they 

contain more islands of plasma. However, in mosepic plasmic fabrics, LE also remains low. 

Shrink-swell forces have not been sufficient or have not operated long enough to have 

homogenized the islands of plasma into the soil matrix. 

Vosepic plasmic fabrics occur in soil horizons that have undergone stress either due to 

shrink-swell forces or to tillage. Even though root growth is adequate to increase the 

percentage of oriented clay near the root-soil interface (Blevins et al., 1970), root growth does 

not appear adequate to form vosepic or other highly stressed plasmic fabrics. Usually, vosepic 

fabrics are present in soil horizons in which the main fabric type is masepic or skelsepic. The 

vosepic plasmic fabric rarely occurs as the only fabric in a soil horizon. 

There are at least two types of origins for orientation of plasma on sands. One is a 

result of clay illuviation. By definition, this type would not be included with skelsepic fabric. 

The related distribution patterns associated with this fabric commonly are monic, gefuric, or 

149
enaulic. The other origin is commonly the porphyric related distribution patterns with LE's that 

are >4 percent for dryland soils, i.e., soils in aridic, xeric, or ustic soil moisture regimes. These 

are the true skelsepic fabrics. Shrink-swell forces have been involved in their formation as 

shown by relatively few papules or clay skins remaining, and there are vosepic areas. 

Masepic, lattisepic, and omnisepic plasmic fabrics are evidence of stress >4 percent in 

dryland soils. Clay contents are usually >35 percent, but the threshold amount is dependent on 

clay mineral type and on degree of dryness common to the environment. In masepic, lattisepic, 

and omnisepic plasmic fabrics, papules and clay skins rarely are found, but areas of skelsepic

and vosepic areas commonly are present. 

Undulic plasmic fabrics seem to be associated with basic parent materials, especially 

basalt, and with moderate to strong weathering (Brewer et al., 1983). The fabric commonly is 

stained deeply by iron minerals, and kaolinite and halloysite are the important clay minerals. 

Clays in these horizons do not disperse well in PSDA, but high 1500-kPa (15 bar) water 

contents suggest that the horizons belong in clayey families. Some papules and clay skins 

commonly are present, but these plasma separations also are stained deeply by iron. 

Isotic plasmic fabrics are common in spodic horizons and in Andisols. The clays in 

these horizons are amorphous and disperse poorly in PSDA. The water-holding capacities of 

these soil horizons are relatively high. Some unweathered volcanic ash may be present. 

Crystic plasmic fabrics are common in B horizons of soils formed in dryland areas. In 

soil horizons with large areas of interlocking crystals, there is restricted soil permeability, 

increased unconfined compressive strength, and limited particle dispersion, depending on the 

degree of cementation. 

Cutans and Pedogenic features: Most argillans (Fig. 11) are formed, at least in part, 

by illuviation. The content of strongly oriented clay (usually argillans plus papules), in 

texture-contrast soils (soils with argillic horizons) is usually <5 percent of the soil volume 

(Brewer et al., 1983). In some sandy soils that are low in silt, the argillans and papules are as 

much as 30 percent of the soil material (Brewer et al., 1983). The measured illuviated clay 

rarely accounts for the difference in clay content between the A and B horizons. Some of the 

clay may originate from weathering in place and some from a destruction of argillans and 

papules. 

If argillans and papules are present in argillic horizons in dryland soils, the soil LE is 

usually <4 percent (Nettleton et al., 1969). In some humid environments, argillans and papules 

may be present even where the LE is >4 percent. As soils in humid environments do not dry to 

the same degree as those in the desert, the clay skins may survive because only part of the 

linear extensibility is effective. 

Papules may originate by the weathering of primary minerals, the isolation of clay skins 

by the channel and void migration within the soil matrix (Nettleton et al., 1968; Nettleton et al., 

1990) or by the introduction of eolian sands and silts that are composed of clays (Butler, 1974; 

Brewer and Blackmore, 1976). The comparison of size and shape of papules and minerals, as 

well as of parent material, may help to determine if the papules are pseudomorphs of one of the 

primary minerals. Internal fabric resemblances and residual parts of the primary mineral within 

the papules help to determine if a papule is a pseudomorph. 

The determination of whether or not a papule is an illuvial feature is important for 

classification purposes. Arcuate forms and laminar internal fabrics are evidence that the 

feature is illuvial. If the feature partially surrounds an oval body of silt, illuvial origin of the 

feature is relatively certain (Nettleton et al., 1968). 

The origin of the papule as eolian may be determined by studying its size and shape, its 

internal fabric, and the number and degree of its alterations relative to other particles. 

Microlaminae may suggest an origin as sediment. Unlike soil pedorelicts or rock fabrics 

(lithorelicts), nodules, or glaebules rich in soluble plasma, probably form by accretion (Brewer, 

1976). Most concretions, as well as pedodes, are accretionary and usually form in place. 

A study of soil voids may be useful in predicting the clay activity and shrink-swell 

behavior of soils. In an experimental study of soil microfabrics by anisotropic stresses of 

confined swelling and shrinking, Jim (1986) shows that with an increase in the activity and 

150
content of the clay fraction, there is a drastic decrease in void volume, especially the >30μm. 

Furthermore, the void shapes change from compound packing voids to planar voids and vughs. 

With an increase in stress from shrink-swell forces, aggregates become flattened at contacts, 

resulting in more angular and eventually fused compound units. 

A possible objective of micromorphological studies may be the measurement of 

porosity and the prediction not only of soil water content at various suctions but also of 

hydraulic conductivity. In thin section studies of voids in sands and sandy soils, there is a close 

correlation between microscopic and suction methods (Swanson and Peterson, 1942). 

However, in those soils whose volumes change with changes in water content, pore size 

distribution is undefined, and no constant void size distribution exists (Brewer, 1976). 

Furthermore, there are several invalidated assumptions that commonly are made in relating 

porosity to permeability (Nielsen et al., 1972 p. 11). The assumptions that especially relate to 

soil fabric are that no pores are sealed off, pores are distributed at random, and pores are 

generally uniform in size. A more serious difficulty may be that a thin section, even if reduced 

to a 20-μm thickness, may make the examination of the <20-μm diameter pores impossible, if 

these pores pass through the section at an angle of <45°. This means that many voids that are 

involved in unsaturated water flow in soils will not be visible in thin section (Baver, 1956 p. 

271). 

The size, shape, and arrangement of skeleton grains determine the nature of simple 

packing voids, but the origin of compound packing voids is not so straightforward. The 

unaccommodated peds of the compound packing voids may be formed by faunal excreta, 

shrink-swell action, man's activities, or by other unknown causes. 

Vughs usually occur in soil materials with a wide range in size of particles, including 

silicate clays. Some vughs form by the weathering and removal of carbonate, and others form 

by faunal activity or the normal packing of plasma and skeleton grains. The very regular 

outline of vesicles is of interest (Nettleton and Peterson, 1983). Lapham (1932) states that in 

Sierozems (Aridisols), the vesicles that are near the surface are the result of air entrapment by 

rainfall following dry dusty periods. Laboratory studies verify this phenomenon (Springer, 

1958). If high silt soils are allowed to dry before each irrigation, the vesicle size increases with 

the number of irrigations (Miller, 1971). As a result of studies of infiltration rates and sediment 

production in rangeland in central and eastern Nevada, Blackburn and Skau (1974) and 

Rostagno (1989) conclude that the infiltration rates are the lowest and the sediment yields are 

the highest on sites that have vesicular surface horizons. The failure of most vesicles to 

connect to other voids and the low strength of the crust in which vesicles occur help to explain 

the low infiltration rates and the high sediment yields that commonly are found on these soils. 

Joint planes (Fig. 18) are produced in relatively uniform fine-textured soils by a 

relatively regular system of cracking upon drying (Brewer, 1976). Once formed, these joint 

planes tend to open in the same place during successive drying cycles. Skew planes are 

produced in more heterogeneous materials or by irregular drying (Brewer, 1976). Craze planes

often occur in Chernozems (Mollisols), possibly as a result of the high humic acid content 

(Brewer, 1976). Because of their size, cross-sectional shape, and kind of branching pattern, 

channels probably form by faunal activity, plant root systems, or by certain geological 

processes (Brewer and Sleeman, 1963). 

3. References 

Baver, L.D. 1956. Soil physics. 3rd ed. John Wiley & Sons, Inc., NY. 

Blackburn, W.H., and C.M. Skau. 1974. Infiltration rates and sediment production of 

selected plant communities in Nevada. J. Range Manage. 27:476-480. 

Blevins, R.L., N. Holowaychuk, and L.P. Wilding. 1970. Micromorphology of soil fabric 

at tree root-soil interface. Soil Sci. Soc. Am. Proc. 34:460-465Brewer, R. 1964. Fabric 

and mineral analysis of soils. John Wiley & Sons Inc., NY. 

Brewer, R. 1964. Fabric and mineral analysis of soils. John Wiley & Sons Inc., NY. 

Brewer, R. 1976. Fabric and mineral analysis of soils. Reprint of 1964 ed., with suppl. 

material. Robert E. Cringer Publ. Co., Huntington, NY. 

151
Brewer, R., and A. V. Blackmore. 1976. Relationships between subplasticity rating, 

optically oriented clay, cementation and aggregate stability. Aust. J. Soil Res. 14:237-

248. 

Brewer, R., and S. Pawlak. 1975. Investigations of some soils developed in hummocks of 

the Canadian sub-artic and southern-arctic regions. I. Morphology and 

micromorphology. Can. J. Soil Sci. 55:301-319. 

Brewer, R., and J.R. Sleeman. 1963. Pedotubules: their definition, classification and 

interpretation. J. Soil Sci. 15:66-78. 

Brewer, R., J.R. Sleeman, and R.C. Foster. 1983. The fabric of Australian soils. p. 439-

476. In Division of soils, CSIRO (ed.) Soils: an Australian viewpoint. CSIRO: 

Melbourne/Academic Press, London. 

Bullock, P., N. Fedoroff, and A. Jongerius, G. Stoops, T. Tursina, and others. 1985. 

Handb. for soil thin section description. Waine Res. Publ., Walverhampton, England. 

Butler, B.E. 1974. A contribution towards the better specification of parna and some other 

aeolian clays in Australia. Z. Geomorph. N.F. Suppl. Bd. 20:106-116. Berlin, Germany. 

Cady, J.G. 1965. Petrographic microscope techniques. In C.A. Black, D.D. Evans, J.L. 

White, L.E. Ensminger, and F.E. Clark (eds.) Methods of soil analysis. Part 1. Physical 

and mineralogical properties, including statistics of measurement and sampling. 1st ed. 

Agron. 9:604-631. 

Cady, J.G., L.P. Wilding, and L.R. Drees. 1986. Petrograhic microscope techniques. In A. 

Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical properties. 2nd 

ed. Agron. 9:185-218. 

Chadwick, O.A., and W.D. Nettleton. 1990. Micromorphologic evidence of adhesive and 

cohesive forces in soil cementation. p. 207-212. In L.A. Douglas (ed.) Developments in 

Soil Sci. 19. Soil micromorphology: a basic and applied science. Elsevier Sci. Publ., 

NY. 

Clark, B.R. 1970. Mechanical formation of preferred orientation in clays. Am. J. Sci. 

269:250-266. 

Delvigne, J.E. 1998. Atlas of micromorphology of mineral alteration and weathering. 

Canadian Miner Special Pub. 3. Miner. Assoc. of Canada. Ontario. 

Edil, T.B., and R.J. Krizek. 1976. Influence of fabric and soil suction on the mechanical 

behavior of a kaolinitic clay. Geoderma. 15:323-341. 

Eswaran, H. 1983. Characterization of domains with the scanning electron microscope. 

Pedology 33:41-54. 

FitzPatrick, E.A. 1984. Micromorphology of soils. Chapman and Hall, Ltd., London. 

FitzPatrick, E.A. 1993. Soil microscopy and micromorphology. John Wiley and Sons, 

New York. 

Flach, K.W. 1960. Sols bruns acides in the northeastern United States. Genesis, 

morphology, and relationships to associated soils. Unpubl. Ph.D. Thesis, Cornell, NY. 

Fox, C.A., R.K. Guertin, E. Dickson, S. Sweeney, R. Protz, and A.R. Mermut. 1993. 

Micromorphology methodology for inorganic soils. p. 683-709. In M.R. Carter (ed.) 

Soil sampling and methods of Analysis. Lewis Publishers., Boca Raton. 

Fox, C.A., and L.E. Parent. 1993. Micromorphology methodology for organic soils. p. 

473-485. In M.R. Carter (ed.) Soil sampling and methods of Analysis. Lewis 

Publishers., Boca Raton. 

Holzhey, C.S., W.D. Nettleton, and R.D. Yeck. 1974. Microfabric of some argillic 

horizons in udic, xeric, and torric soil environments of the United States. p. 747-760. In

G.K. Rutherford (ed.) Soil Microscopy. Proc. of 4th Int. Working-meeting on Soil 

Micromorphology. Limestone Press, Kingston, Ontario, Canada. 

Kubiena, W.L. 1938. Micropedology. Collegiate Press, Ames, IA. 

Jim, C.Y. 1986. Experimental study of soil microfabrics induced by anistropic stresses of 

confined swelling and shrinking. Geoderma. 37:91-112. 

Lapham, M.H. 1932. Genesis and morphology of desert soils. Am. Soil Surv. Assoc. Bull. 

13:34-52. 

152
Miller, D.E. 1971. Formation of vesicular structure in soil. Soil Sci. Soc. Am. J. 35:635-

637. 

Murphy, C.P. 1986. Thin section preparation of soils and sediments. Academic 

Publishers, Great Britain. 

Nettleton, W.D., K.W. Flach, and B.R. Brasher. 1969. Argillic horizons without clay 

skins. Soil Sci. Soc. Am. Proc. 33:121-125. 

Nettleton, W.D., R.B. Grossman, and B.R. Brasher. 1990. Concept of argillic horizons in 

Aridisols-taxonomic implications. p. 167-176. In J.M. Kimble and W.D. Nettleton 

(eds.) Proc. of 4th Int. Soil Correlation Meeting (ISCOM). Characterization, 

classification, and utilization of Aridisols in Texas, New Mexico, Arizona, and 

California, October 3-17, 1987. Part A: Papers. 

Nettleton, W.D., R.J. McCracken, and R.B. Daniels. 1968. Two North Carolina Coastal 

Plain catenas. II. Micromorphology, composition, and fragipan genesis. Soil Sci. Soc. 

Am. Proc. 32:582-587. 

Nettleton, W.D., and F.F. Peterson. 1983. Aridisols. p. 165-215. In L.P. Wilding, N.E. 

Smeck, and G.F. Hall (eds.). Pedogenesis and soil taxonomy. II. The soil orders. 

Elsevier, NY. 

Nielsen, D.R., R.D. Jackson, J.W. Cary, and D.D. Evans (eds). 1972. Soil water. Am. Soc. 

Agron., Madison, WI. 

Rode, A.A. 1969. Theory of soil moisture. Vol. 1. Moisture properties of soils and 

movement of soil moisture. (In English, translated from Russian.) Israel Prog. for 

Scientific Translations, Jerusalem. p. 38. 

Rostagno, C.M. 1989. Infiltration and sediment production as affected by soil surface 

conditions in a shrubland of Patagonia, Argentina. J. Range Manage. 42:383-385. 

Soil Science Society of America. 1993. A reference collection for soil micromorphology. 

CD Rom. ASA and SSSA, Madison, WI. 

Springer, M.E. 1958. Desert pavement and vesicular layer of some soils of the desert of the 

Lahontan Basin, Nevada. Soil Sci. Soc. Am. Proc. 22:63-66. 

Stoops, G., and A. Jongerius. 1975. Proposal for micromorphological classification in soil 

materials. I. A classification of the related distribution of coarse and fine particles. 

Geoderma. 13:189-200. 

Swanson, C.L.W., and J.B. Peterson. 1942. The use of micrometric and other methods for 

the evaluation of soil structure. Soil Sci. 53:173-183. 

153
Figure 1. Large biotite grain undergoing expansion from weathering. Note the 

high birefringence due to the orientation of the grain in thin section. Frame width = 

1.0 mm. (Series name not designated; Fremont Co., WY, Pedon 98P0456, Bt2 

horizon under crossed polarized light). 

Figure 2. Horizons with high percentage of clay of expandable aluminosilicate claysized minerals become aligned through shrink-swell processes. This alignment 

results in preferred orientation of clay particles, making the plasma anisotropic 

(visible under crossed polarized light. This process results in a loss of argillans 

along ped faces in many soils. Frame width = 0.9 mm. (White House pedon, 

Cochise Co., AZ, Pedon 40A001, BCtk horizon under crossed polarized light). 

154
Figure 3. Calcium carbonate around skeletal (sand-sized) grains in a coarse-textured 

matrix. These carbonate coatings are referred to as calcitans (Brewer, 1976). Their 

formation illustrates attraction to and deposition of carbonates on mineral surfaces 

(e.g., quartz or feldspar grains) accessible to percolating water. Frame width = 0.9 

mm. ( Cax pedon, San Bernardino, Co., CA, Pedon 97P0420, Bkg2 horizon under 

crossed polarized light). 

Figure 4. Kinds of related distribution patterns and a listing of their physical 

properties. Frame width of each idealized kind of fabric is 0.5mm. The lower size 

limit of coarse material in the C/Fpatterns was set at about 50 μm for most of the 

slides. 

155
Figure 5. Kinds of plasma fabrics and a listing of their physical properties. Frame 

width of each idealized kind of fabric is 0.5 mm. 

Figure 6. Silasepic plasma fabric. Frame width = 1.3 mm. (Southridge pedon, 

Allamakee Co., IA; 87P0075 Ap horizon under crossed polarized light). 

156
Figure 7. Insepic plasma fabric. Frame width = 1.3 mm. (Mexico pedon, Macon 

Co., MO, 87P0771, BE horizon under crossed polarized light). 

Figure 8. Mosepic plasma fabric. Frame width = 1.3 mm. (Leonard pedon, Macon 

Co., MO, 87P0770, 2Btg3 horizon under crossed polarized light). 

157
Figure 9. Skelsepic plasma fabric. Frame width = 1.3 mm. (Redding pedon, San 

Diego Co., CA, 40A2847, Bt horizon under crossed polarized light). 

Figure 10. Masepic plasma fabric. Frame width = 1.3 mm. (Gloria pedon, 

Monterey Co., CA, , 40A2845, Bt horizon under crossed polarized light). 

158
Figure 11. Oriented illuvial clay (argillans) surrounding skeletal grains. Frame 

width = 1.1 mm (Paxon pedon, New York Co., NY, 00P0001, 2Cd1 horizon under 

plane polarized light) 

. 

Figure 12. Fe oxide nodule from an Andisol in Blue Mountains of eastern Oregon. 

Frame width = 2.5 mm. (Tower pedon, Umatilla Co., OR, 97P0547, Bw1 horizon 

under plane polarized light). 

159
Figure 13. Compound packing voids, surrounded by illuvial clay (argillans). Clay 

lining channels is anisotropic due to orientation during deposition, while clay 

(plasma) in the s-matrix is partially anisotropic due to stress orientation (shrinkswell processes). Frame width = 1.0 mm. (Endlich pedon, 99P0001, Bt1 horizon 

under crossed polarized light). 

Figure 14. Void that has smooth edges and is elongated. This void type is described 

by Brewer (1976) as a vugh. Frame width = 1.0 mm. (Troutville pedon, Gunnison 

Co., CO, 99P0002, E&Bt horizon under cross polarized light). 

160
Figure 15. The walls consisting of “smooth, simple curves” indicates that this void 

is a vesicle. These vesicles were formed in the thin, surface crust of a Typic 

Haplargid. Frame width = 3.2 mm (Dera pedon, Juab Co., UT, 81P0610, A1 

horizon under crossed polarized light). 

Figure 16. Relative pore volumes at 30 kPa for soil fabric coarse-fine distributions 

for some U.S. soils. 

161
Figure 17. Horizon with duripan exhibiting silica cementation. Fabric has an opal 

and chalcedony laminar cap. The matrix above and below is composed of 

durinodes (non-crystalline silica) surrounded by moderately-oriented silicate clays. 

Clay can provide the initial absorption surface for silica in soil solution. The 

absorption of silica onto established silica phases leads to formation of nodules. 

Frame width = 1.0 mm. (Series name not designated, Jefferson Co., OR, Pedon 

87P0513, 2Bkqm horizon under plane polarized light). 

Figure 18. Joint planes (platy structure) formed in the surface horizon of a soil. 

Frame width = 2.5 mm. (Frisite pedon, Fremont County, WY, 98P0453, A horizon 

under cross polarized light). 

162
Wet Aggregate Stability (3F) 

Wet-Sieving (3F1) 

Air-dry, 2 to 1 mm, 2- to 0.5-mm Aggregates Retained (3F1a1a) 

1. Application 

An aggregate is a group of primary particles that cohere to each other more strongly 

than to other surrounding soil particles (Soil Science Society of America, 1997). 

Disaggregration of soil mass into aggregates requires the application of a disrupting force. 

Aggregate stability is a function of whether the cohesive forces between particles can withstand 

the applied disruptive force. The analysis of soil aggregation can be used to evaluate or predict 

the effects of various agricultural techniques, e.g. tillage and organic-matter additions, and 

erosion by wind and water (Nimmo and Perkins, 2002). The measurement can serve as a 

predictor of infiltration and soil erosion potential. This method provides a measure of aggregate 

stability following a disruption of initially air-dry aggregates by abrupt submergence followed 

by wet sieving. This procedure was developed for use by the Natural Resources Conservation 

Service, Soil Survey field offices. 

2. Summary of Method 

This method (3F1a1a) measures the retention of air-dry aggregates (2 to 1 mm) on a 

0.5-mm sieve after sample has been submerged in RO water overnight followed by agitation of 

sample. 

3. Interferences 

Air bubbles in the sieve can create tension in the water, thereby reducing the percentage 

of aggregates that are retained on the 0.5-mm sieve. Variation in the moisture content of airdry soils can affect results. A correction should be made for the sand > 0.5 mm resistant to 

dispersion in sodium hexametaphosphate. 

4. Safety

If ovens are used, hot surfaces can be a hazard. Follow standard laboratory safety 

precautions. 

5. Equipment 

5.1 Bowls, Rubbermaid or equivalent, 1800 mL 

5.2 Electronic balance, ±0.01-g sensitivity and 500-g capacity 

5.3 Sieves, square-hole 

5.3.1 0.5 mm, stainless steel, no.35, 125-mm diameter, 50-mm height 

5.3.2 1 mm, brass, 203-mm diameter, 50-mm height 

5.3.3 2 mm, brass, 203-mm diameter, 50-mm height 

5.4 Oven, 110°C 

5.5 Camping plate, Coleman, stainless steel, 152-mm diameter, Peak 1, Model 8553-462. 

5.6 Aluminum foil dish, 57-mm diameter x 15-mm deep, with lifting tab 

6. Reagents 

6.1 Reverse osmosis (RO) water 

6.2 Sodium hexametaphosphate solution. Dissolve 35.7 g of sodium hexametaphosphate 

(Na4P2O7) and 7.94 g of sodium carbonate (Na2CO3) in 1 L of RO water. Alternatively, 

use Calgon, water softener. 

7. Procedure

7.1 Use natural fabric (NF) samples in pint containers. Assemble a 2-mm sieve on top of a 1-

mm sieve. Crush the NF sample by hand or with mortar and pestle. Crush sample so as to pass 

the 2-mm sieve with a minimum reduction in size. Sieve entire NF sample. 

163
7.2 Place the material that is retained on 1-mm sieve in pint container and discard the 

remaining material. 

7.3 Sieve the material again with 1-mm sieve to remove dust and other small particles. Weigh 

a 3.00 ± 0.05-g sample of the 2- to 1-mm material in aluminum foil dishes. 

7.4 Place 0.5-mm sieve in plastic bowl and fill bowl so that the water level is at a 20-mm height 

above the base of screen. Remove air bubbles with a syringe. 

7.5 Distribute the 3.00-g sample (2 to 1 mm) on the 0.5-mm sieve. Aggregates should not 

touch. Allow sample to sit overnight. 

7.6 Agitate the sample by raising and lowering the sieve in the water bowl 20 times in 40 s. On 

the upward strokes, drain sieve but do not raise so high that air enters to beneath the sieve. 

7.7 Remove sieve from water bowl, place on Coleman plate, and dry in oven for 2 to 2.5 h at 

110°C. During drying process, the plate retains the soil that drops through the sieve. 

7.8 Remove the sample from the oven. Weigh sieve, plate, and sample. Sample is those 

aggregates retained on 0.5-mm sieve. Record weight. If no sand (>0.5 mm) is present, discard 

sample from sieve and plate by brushing. Weigh sieve and plate. Record weight. 

7.9 Calculate the Sw from the particle-size data (procedure 3A1). If there is sand (>0.5 mm) 

and no particle-size data, discard sample on plate and disperse that retained on the sieve with 

sodium hexametaphosphate solution. Alternatively, place 3 g of Calgon in plastic bowl and 

stir until dissolved. Place the 0.5-mm sieve with sample in sodium hexametaphosphate (or 

Calgon) solution so that the solution line is at a 35-mm height above the base of screen.. 

Gently triturate the dispersing solution with the fingers to remove soft <0.5 mm material 

adhering to the > 0.5 mm. Remove sieve from sodium hexametaphosphate (or Calgon) solution 

and rinse with RO water until all sodium hexametaphosphate (or Calgon) solution has passed 

through sieve, and only the sand (>0.5 mm) is left on sieve. Place sieve on Coleman plate, 

place in oven, and dry for 2 to 2.5 h at 110°C. 

7.10 Remove sample from oven. Weigh the sieve, plate, and sample. Record weight. Discard 

sample and brush sieve and plate. Weigh sieve and plate. Record weight. Alternatively, 

calculate the Sw from the particle-size data (procedure 3A1). 

7.11 Thoroughly wash sieve and plate with RO water, especially those sieves with sodium 

hexametaphosphate solution. 

8. Calculations

Aggregates (%) = [(WR - SW)/(3.00 – Sw)] x 100 

where: 

WR = Total weight of aggregates retained on 0.5-mm sieve 

SW = Weight of 2- to 0.5-mm sand 

9. Report

Report aggregate stability as a percentage of aggregates (2- to 0.5-mm) retained after 

wet sieving. Do not report determinations if the 2- to 0.5-mm fraction is >50% of the 2- to 1-

mm sample. 

164
10. Precision and Accuracy

Precision and accuracy data are available from the SSL upon request. 

11. References

Nimmo, J.R., and K.S. Perkins. 2002. Aggegate stabililty and size distribution. p. 317-328. 

In J.H. Dane and G.C. Topp (eds.). Part 4. Physical methods. Soil Sci. Am. Book Series 

No. 5. ASA and SSSA, Madison, WI. 

Soil Science Society of America. 1997. Glossary of soil science terms. Soil Sci. Soc. Am., 

Madison, WI. 

Particle Density (3G) 

Pycnometer Gas Displacement (3G1) 

Oven-dry, <2 mm (3G1a1) 

Oven-dry, >2 mm (3G1a2) 

1. Application 

Density is defined as mass per unit volume. Particle density refers to the density of the 

solid particles collectively (Flint and Flint, 2002). Particle density is required for sedimentation 

analysis; calculating soil volume or mass; and for mathematically correcting bulk soil samples 

containing significant amounts of rock fragments so as to determine fine-soil density, water 

content, or other soil properties affected by volume displacement of rock fragments (Flint and 

Childs, 1984). 

2. Summary of Method 

This method (3G1) determines particle density by the pycnometer gas displacement 

procedure. This is accomplished by employing Archimedes’ principle of fluid displacement to 

determine the volume. The displaced fluid is a gas that can penetrate the finest pores, thereby 

assuring maximum accuracy (Quantachrome Instruments, 2003). Helium gas is the most 

commonly recommended gas since its small atomic dimensions assures penetration into 

crevices and pores approaching one Angstrom (10-10m) in dimension, and its behavior as an 

ideal gas is also desirable. 

3. Interferences 

Sample should be dry. Displacement gas will evaporate water molecules and create 

additional partial pressure (Flint and Flint, 2002). Temperature should be relatively constant 

since the method uses the ideal gas equation of state. Instrument should be calibrated when 

environmental conditions change. 

4. Safety 

No significant hazards are associated with this procedure. Follow standard laboratory 

safety practices. 

5. Equipment 

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Oven, 110°C 

5.3 Gas pycnometer, Penta-pycnometer, Quantachrome Instruments, Boynton Beach, FL 

6. Reagents 

6.1 Helium gas 

7. Procedure 

 

7.1 Oven-dry the soil sample at 110°C overnight. 

165
7.2 Allow the instrument to warm up for least 30 min prior to use. 

 

7.3 Set the regulator pressure to slightly over 20 PSIG. 

7.4 Validate the calibration by determining the volume of the calibration sphere. 

7.5 If volumes are outside specification range, recalibrate the instrument per instruction 

manual. 

7.6 Select the largest sample cell size of 135, 50, or 10 cc. The sample should fill at least half 

of the sample cell volume. 

7.7 Weigh the sample cell to the nearest 0.01g. Place sample in the sample cell and reweigh to 

the nearest 0.01 g. The difference is the sample weight. Record the weight. 

7.8 Place the sample cells into the sample cell holder. Properly seal the cell holder with the 

cover. 

7.9 Define each cell with sample cell size, weight, and sample identification number. 

7.10 Set the instrument to multi run and enter the number of runs between 3 and 5. 

7.11 Set the purge mode to 3 pulse cycles. 

7.12 Start the sample run. 

7.13 Record the average volume for each sample. 

7.14 Calculate the particle density. 

8. Calculations 

Particle density (g cm-3) = Sample weight (g)/Sample volume 

9. Report 

Report particle density (g cm-3) to the nearest 0.01 unit on either the <2-mm or >2-mm 

particle-size fraction. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Flint, A.L., and S. Childs. 1984. Development and calibration of an irregular hole bulk density sampler. Soil Sci. Soc. Am. J. 48:374-378. Flint, A.L., and L.E. Flint. 2002. Particle density. p. 229-240. In J.H. Dane and G.C. Topp 

 (eds.) Methods of soil analysis, Part 4. Physical methods. Soil Sci. Am. Book Series 

 No. 5. ASA and SSSA, Madison, WI. Quantachrome Corporation. 2003. Penta-pycnometer instruction manual. Quantachrome 

 Corporation, Boynton Beach, FL 

166
Atterberg Limits (3H) 

Liquid Limit (LL) (3H1) 

Air-Dry, <0.4 mm (3H1a1) 

Field-Moist, <0.4 mm (3H1b1) 

Liquid Limit (LL) is the percent water content of a soil at the arbitrarily defined 

boundary between the liquid and plastic states. This water content is defined as the water 

content at which a pat of soil placed in a standard cup and cut by a groove of standard 

dimensions will flow together at the base of the groove for a distance of 13 mm (1/2 in) when 

subjected to 25 shocks from the cup being dropped 10 mm in a standard LL apparatus operated 

at a rate of 2 shocks s-1. Refer to ASTM method D 4318 (American Society for Testing and 

Materials, 2004). The LL is reported as percent water on a <0.4-mm basis (40-mesh) 

(procedure 3H1). 

Atterberg Limits (3H) 

Plasticity Index (3H2) 

Air-Dry, <0.4 mm (3H2a1) 

Field-Moist, <0.4 mm (3H2b1) 

The PI is the range of water content over which a soil behaves plastically. Numerically, 

the PI is the difference in the water content between the LL and the plastic limit (PL). Refer to 

procedure +1 for the definition of LL. The PL is the percent water content of a soil at 

the boundary between the plastic and brittle states. The boundary is the water content at which 

a soil can no longer be deformed by rolling into 3.2-mm (1/8-in) threads without crumbling. 

Refer to ASTM method D 4318 (American Society for Testing and Materials, 2004). The PL is 

reported as percent water on a <0.4-mm basis (procedure 3H2). 

References 

American Society for Testing and Materials. 2004. Standard tests for liquid limit, plastic limit, 

and plasticity index for soils. D 4318. Annual book of ASTM standards. Construction. 

Section 4. Soil and rock; dimension stone; geosynthesis. Vol. 04.08. ASTM, Philadelphia, 

PA. 

SOIL AND WATER CHEMICAL EXTRACTIONS AND ANALYSES (4) 

Acid Standardization (4A) 

1. Application 

The process by which the concentration of a solution is accurately ascertained is known 

as standardization (Dean, 1995). Commonly a solution is standardized by a titration in which it 

reacts with a weighed portion of a primary standard. The reaction between the titrant and the 

substance selected as a primary standard should fulfill the requirements for titrimetric analysis. 

In addition, a primary standard should be in a state of known high purity (typically <0.1 to 

0.2% impurities), stable (easy to dry, not very hydroscopic, or lose weight upon exposure to 

air), and have a reasonably high equivalent weight in order to minimize the consequences of 

errors in weighing (Day and Underwood, 1980). For acid-base titrations, it is customary to 

prepare solutions of an acid and base of approximately the desired concentration and then to 

standardize one of the solutions against a primary standard. The solution thus standardized can 

be used a secondary standard to obtain the normality of the other solution. Some widely used 

primary standards are as follows: 

167
Benzoic acid - (C6H5CO2H). Molecular weight = 122.123. Dissolve about 0.5 g in 50% 

ethanol and titrate to phenolphthalein end point. 

Borax - (Na2B4O7·10H2O). Molecular weight = 381.360. Methyl red indicator. Dissolve in 

water. Weak acid. 

Mercuric oxide - (HgO) Molecular weight = 216.599. Bromthymol blue indicator. Dissolve 

0.5 g with 15 g of KBr in 25 mL of reverse osmosis deionized (RODI) water, excluding CO2. 

Potassium bicarbonate - (KHCO3). Molecular weight = 100.116. Bromcresol green indicator, 

first tint of green end point. 

Potassium biodate - (KH(IO3)2). Molecular weight = 389.912. Bromthymol blue end biodate 

point. Strong acid. Low solubility. 

Potassium biphthalate - (KHC8H4O4). Molecular weight = 204.224. Phenolphthalein 

indicator. Weak acid. 

Potassium bitatrate - (KHC4H4O6). Molecular weight = 188.178. Phenolphthalein bitatrate 

indicator. Molding problem. 

Sodium carbonate - (Na2CO3). Molecular weight = 105.988 Bromocresol green indicator, 

first green end point. 

Refer to Table 1 for a list of some common acids and bases. 

2. Summary of Method 

Dissolve a known amount of the primary standard (e.g., Na2CO3) in reverse osmosis 

deionized (RODI) water. Prepare 10 of these Na2CO3 solutions plus 8 blanks and titrate with 

the acid to be standardized (e.g., HCl, H2SO4). Calculate the normality of the acid from the 

mean blank and titers. Report the normality and standard deviation for the acid standardization. 

3. Interferences 

Clean the glass electrode by rinsing with distilled water. Wiping the electrode dry with 

a cloth, laboratory tissue, or similar material may cause electrode polarization. 

Slow electrode response may cause the end point to be overshot. Cleaning the electrode 

with detergent solution may decrease the response time. If all else fails, change the electrode. 

Dry primary standards and store in a dessicator to prevent hydration. Contamination of 

the primary standard may occur when drying, storing, or weighing the reagent. Use gloves to 

weigh the primary standard in weighing vessel. 

4. Safety 

Wear protective clothing and eye protection when preparing reagents. Dispense 

concentrated acids in a fume hood. Thoroughly wash hands after handling reagents. Be 

prepared to use safety showers and eyewash stations if necessary. Use sodium bicarbonate and 

water to neutralize and dilute spilled acids. Follow the manufacturer’s safety precautions when 

using the automatic titrator. Review Material Safety Data Sheets (MSDS) for reagents. 

5. Equipment 

5.1 Electronic balance, ±0.10-mg sensitivity 

5.2 Oven, 110ο

C 

5.3 Weighing vessel, 40 x 50mm 

5.4 Desiccator 

168
5.5 Automatic titrator, with control unit, sample changer, and dispenser, Metrohm Ltd., 

Brinkmann Instruments, Inc. 

5.6 Combination pH-reference electrode, Metrohm Ltd., Brinkmann Instruments, Inc. 

5.7 Computer, with Titrino Workcell software, Metrohm Ltd., Brinkman Instruments, Inc., and 

printer 

5.8 Titration beakers, 250 mL, borosilicate, Metrohm Ltd., Brinkman Instruments Inc. 

6. Reagents

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 pH buffers (4.00, 7.00, 9.18) 

6.3 Sodium carbonate, anhydrous, 99.8% pure 

6.4 Calcium sulfate (anhydrous) or equivalent desiccant 

7. Procedure 

7.1 Place a weighing vessel containing ≈ 10 g of the Na2CO3 in an oven at 110οC overnight. 

Let cool in a desiccator to room temperature (≈ 30 min). 

7.2 Refer to Acid Standardization Form. Weigh the weighing vessel plus the Na2CO3

designated in Section 7.1 to the nearest 0.1mg (VW1a). 

7.3 Tare a 250-mL titration beaker on the electronic balance. Add 0.15 - 0.55 g Na2CO3 to the 

beaker. Record the weight of the Na2CO3 to the nearest 0.1mg (SW1). 

7.4 Verify the weighed SW1 as follows: 

7.4.1 Re-weigh the weighing vessel plus Na2CO3 designated in Section 7.1 to the nearest 0.1mg 

(VW1b). 

 7.4.2 Calculate SWC1 as follows: VW1a – VW1b = SWC1. 

7.4.3 If SWC1 calculated in Section 7.4b is within 0.5 mg of the weighed SW1 determined in 

Section 7.3, proceed to Section 7.5, but if not, return to Section 7.2 and begin again. 

7.5 Prepare nine more Na2CO3 solutions (SW2 ...SW10) by this same procedure (Sections 7.2 -

7.4). 

7.6 Add 100 mL of RODI water to each of the SW1......SW10 and to eight empty beakers for 

blanks (B1....8) and gently swirl to facilitate dissolution of the salt. 

7.7 Prepare the titration system according to the manufacture’s instructions. Calibrate the pH 

electrode with 4.00, 7.00, and 9.18 pH buffers. Recalibrate electrode if R2 <0.950. 

 

7.8 Set-up the automatic titrator to set end point titration mode. The "Set" pH parameters are 

listed as follows: 

Parameter Value

Measured value pH 

Titration rate normal 

Stop volume 100.0 mL 

Stop End Point 9 

Stop Potential 4.2 pH 

Sensitivity High 

169
Fixed End Point 4.6 pH 

Signal Drift 25 

Equilibration time 5 s 

7.9 Titrate each of the SW1......SW10 and B1......8 and record the titres. 

8. Calculations 

 

8.1 Bmean = Bsum/n 

where: 

B = Blank mean (mL) 

Bsum = Sum of blank titres (mL) 

n = Number of blanks (n = 8) 

8.2 TCS1.....10 = TS1......10 – Bm

where: 

TCS1......10 = Corrected sample titre (mL) 

TS1......10 = Sample titre (mL) 

Bm = Blank mean (mL) 

8.3 N1.......10 = [(SW1.....10 x 0.0188698 mole HCl/g Na2CO3) / (TCS1......10 x 10-3 L ml-1)] = 

(SW1....10 x 18.8698)/ TCS1......10 

where: 

N1.......10 = Normality calculated from titre (number of equivalents of solute per liter) 

SW1.....10 = Na2CO3 weight (g) 

8.4 Nmean = Nsum/n 

where: 

Nmean = Normality mean 

Nsum = Sum of normalities 

n = Number of samples (n = 10) 

8.5 Calculate standard deviation (Std) for Nmean. If the NStd is < 0.0005, record Nmean to four 

decimals to left of decimal. If NStd > 0.0005, discard no more than two suspicious values and 

return again to Sections 7.2 to 8.5 until 10 (n = 10) are achieved. 

9. Report 

Report the mean normality of acid (Nmean), standard deviation, and date of 

standardization. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

 

10. References 

Day, R.A., Jr. and, A.L. Underwood. 1980. Quantitative analysis. Prentice-Hall, Inc., 

Englewood Cliffs, NJ. 

Dean, J.A. 1995. Analytical chemistry handbook. McGraw Hill, Inc., New York, NY. 

170
STANDARDIZATION OF ACIDS 

Table 1. Common commercial strengths of acids and bases. 

Name Molecular 

Weight 

Moles per 

Liter 

Grams per 

Liter 

Percent by 

Weight 

Specific 

Gravity 

Acetic acid 60.05 17.4 1045 99.5 1.05 

Glacial acetic acid 60.05 6.27 376 36 1.045 

Butyric acid 88.1 10.3 912 95 0.96 

Formic acid 46.02 23.4 

5.75 

1080 

264 

90 

25 

1.20 

1.06 

Hydriodic acid 127.9 7.57 

5.51 

0.86 

969 

705 

110 

57 

47 

10 

1.70 

1.50 

1.1 

Hydrobromic acid 80.92 8.89 

6.82 

720 

552 

48 

40 

1.50 

1.38 

Hydrochloric acid 36.5 11.6 

2.9 

424 

105 

36 

10 

1.18 

1.05 

Hydrocyanic acid 27.03 25 

0.74 

676 

19.9 

97 

2 

0.697 

0.996 

Hydrofluoric acid 20.01 32.1 

28.8 

642 

578 

55 

50 

1.167 

1.155 

Hydrofluosilic 

acid 

144.1 2.65 382 30 1.27 

Hypophosphorus 

acid 

66.0 9.47 

5.14 

1.57 

625 

339 

104 

50 

30 

10 

1.25 

1.13 

1.04 

Lactic acid 90.1 11.3 1020 85 1.2 

Nitric acid 63.02 15.99 

14.9 

1008 

938 

837 

71 

67 

61 

1.42 

1.40 

1.37 

Perchloric acid 100.5 11.65 

9.2 

1172 

923 

70 

60 

1.67 

1.54 

Phosphoric acid 98 14.7 1445 85 1.70 

Sulfuric acid 98.1 18.0 1766 96 1.84 

Sulfurous acid 82.1 0.74 61.2 6 1.02 

Ammonia water 17.0 14.8 252 28 0.898 

Potassium 

hydroxide 

56.1 13.5 

1.94 

757 

109 

50 

10 

1.52 

1.09 

Sodium carbonate 106.0 1.04 110 10 1.10 

Sodium hydroxide 40 19.1 

2.75 

763 

111 

50 

10 

1.53 

1.11 

______________________________________________________________________________________ 

 

171
Acid Standardization 

Acid:_____________ Date:_______ Technician: 

_________ 

Vessel Weight Sample 

Weight 

Sample Titer Blanks CorrectedS

ample Titer

 #1 Beginning Weight VW1a SW1 TS1 B1 TCS1

 Ending Weight VW1b B2

 #2 Beginning Weight VW2a SW2 TS2 B3 TCS2

 Ending Weight VW2b B4

 #3 Beginning Weight VW3a SW3 TS3 B5 TCS3

 Ending Weight VW3b B6

 #4 Beginning Weight VW4a SW4 TS4 B7 TCS4

 Ending Weight VW4b SW5 B8

 #5 Beginning Weight VW5a SW5 TS5 Bsum TCS5

 Ending Weight VW5b Bmean

 #6 Beginning Weight VW6a SW6 TS6 TCS6

 Ending Weight VW6b

 #7 Beginning Weight VW7a SW7 TS7 TCS7

 Ending Weight VW7b

 #8 Beginning Weight VW8a SW8 TS8 TCS8

 Ending Weight VW8b

 #9 Beginning Weight VW9a SW9 TS9 TCS9

 Ending Weight VW9b

 #10 Beginning Weight VW10a SW10 TS10 TCS10

 Ending Weight VW10b

N1....10

NStd

 

172
SOIL AND WATER CHEMICAL EXTRACTIONS AND ANALYSES (4) 

Ion Exchange and Extractable Cations (4B) 

Ion exchange is a reversible process by which one cation or anion held on the solid 

phase is exchanged with another cation or anion in the liquid phase, and if two solid phases are 

in contact, ion exchange may also take place between two surfaces (Tisdale et al., 1985). In 

most agricultural soils, the cation exchange capacity (CEC) is generally considered to be more 

important than anion exchange (AEC), with the anion molecular retention capacity of these 

soils usually much smaller than the CEC (Tisdale et al., 1985). Some soils with abundant 

goethite and gibbsite, as do some oxic horizons or subsoils of Oxisols (Soil Survey Staff, 

1999), may have a CEC to AEC ratio approaching 1.0 (net charge of zero) or a small positive 

charge (Foth and Ellis, 1988). 

Soil mineral and organic colloidal particles have negative valence charges that hold 

dissociable cations, and thus are "colloidal electrolytes" (Jackson, 1958). The CEC is a 

measure of the quantity of readily exchangeable cations that neutralize negative charges in the 

soil (Rhoades, 1982). CEC is a reversible reaction in soil solution, dependent upon negative 

charges of soil components arising from permanently charged or pH-dependent sites on organic 

matter and mineral colloid surfaces. The mechanisms for these negative charges are isomorphic 

substitution within layered silicate minerals; broken bonds at mineral edges and external 

surfaces; dissociation of acidic functional groups in organic compounds; and preferential 

adsorption of certain ions on particle surfaces (Rhoades, 1982). Isomorphic substitution 

produces permanent charge. The other charge mechanisms produce variable charge which is 

dependent on the soil solution phase as affected by soil pH, electrolyte level, valence of 

counter-ions, dielectric constant, and nature of anions (Rhoades, 1982). As a result of the 

variable charge in soils, the CEC is a property dependent on the method and conditions of 

determination. The method of determination is routinely reported with CEC data. 

CEC is a measure of the total quantity of negative charges per unit weight of the 

material and is commonly expressed in units of milliequivalents per 100 g of soil (meq 100 g-1) 

or centimoles per kg of soil (cmol(+) kg-1). The SSL reports cmol(+) kg-1 on <2-mm base. The 

CEC can range from less than 1.0 to greater than 100 cmol(+) kg-1 soil. The term equivalent is 

defined as "1 gram atomic weight of hydrogen or the amount of any other ion that will combine 

with or displace this amount of hydrogen". The milliequivalent weight of a substance is one 

thousandth of its atomic weight. Since the equivalent weight of hydrogen is about 1 gram, the 

term milliequivalent may be defined as "1 milligram of hydrogen or the amount of any other 

ion that will combine with or displace it" (Tisdale et al., 1985). 

Common CEC values for some soil components (NSSL, 1975) are as follows: 

Soil Component cmol(+) kg-1

Organic Matter 200 to 400 

“Amorphous” Clay 160 (at pH 8.2) 

Vermiculite 100 to 150 

Montmorillonite 60 to 100 

Halloysite 4H2O 40 to 50 

Illlite 20 to 40 

Chlorite 10 to 40 

Kaolinite 2 to 16 

Halloysite 2H20 5 to 10 

Sesquioxides 0 

These very broad CEC ranges are intended only as general guidelines. More narrow groupings 

of CEC values are possible as data are continually collected and correlated, e.g., the CEC of 

173
organic matter in Mollisols in the western United States ranges from 100 to 300 cmol (+) kg-1

(average 200), and the CEC of organic matter in Histosols ranges from 125 to 185 cmol (+) kg-1

and increases with decomposition of the organic matter (NSSL Staff, 1975). 

Many procedures have been developed to determine CEC. These CEC measurements 

vary according to the nature of the cation employed, concentration of salt, and the equilibrium 

pH. The CEC measurement should not be thought of as highly exact but rather as an 

equilibrium measurement under the conditions selected (Jackson, 1958). Knowledge of the 

operational definition (procedure, pH, cation, and concentration) is necessary before evaluating 

the CEC measurement (Sumner and Miller, 1996). The more widely adopted methods of CEC 

determination are classified (Rhoades, 1982) as follows: 

(1) cation summation 

(2) direct displacement 

(3) displacement after washing 

(4) radioactive tracer 

The SSL performs a number of CEC methods, using several different reagents and pH 

levels. The CEC’s most commonly reported by the SSL are CEC-7 (4B1a1a1a1), CEC-8.2 

(4B4b1), and effective cation exchange capacity (ECEC) (4B4b2). As a general rule, the CEC8.2 > CEC-7 > ECEC. Cation Exchange Capacity: NH4OAc, pH 7.0 (CEC-7) 

The CEC-7 is a commonly used method (4B1a1a1a1) and has become a standard 

reference to which other methods are compared (Peech et al., 1947). Displacement after 

washing is the basis for this procedure. The CEC is determined by saturating the exchange 

sites with an index cation (NH4

+

) using a mechanical vacuum extractor (Holmgren et al., 1977); 

washing the soil free of excess saturated salt; displacing the index cation (NH4

+

) adsorbed by 

the soil; and measuring the amount of the index cation (NH4

+

). An advantage of using this 

method is that the extractant is highly buffered so that the extraction is performed at a constant 

and known pH (pH 7.0). In addition, the NH4

+

 on the exchange complex is easily determined. 

CEC-7 is an analytically determined value and is usually used in calculating the CEC-7/clay 

ratios, although many SSL Primary Characterization Data Sheets predating 1975 show CEC8.2/clay. 

Cation Exchange Capacity: Sum of Cations (CEC-8.2) CEC-8.2 is calculated (4B4b1) by summing the NH4OAc extractable bases (4B1a1b1-4) 

plus the BaCl2-TEA extractable acidity (4B2a1a1 or 4B2b1a1). Cation summation is the basis 

for this procedure. The CEC-8.2 minus the CEC-7 is considered the pH dependent charge from 

pH 7.0 to pH 8.2. The CEC-8.2 is not reported if significant quantities of soluble salts or 

carbonates are present in the soil. CEC-8.2 is calculated as follows: 

CEC-8.2 = NH4OAc extractable bases + Extractable acidity 

Effective Cation Exchange Capacity: NH4OAc Extractable Bases + Aluminum: 

CEC can be measured by extraction with an unbuffered salt, which measures the 

effective cation exchange capacity (ECEC), i.e., CEC at the normal soil pH (Coleman et al., 

1958). Since the unbuffered salt solution, e.g., 1 N KCl, only affects the soil pH one unit or 

less, the extraction is determined at or near the soil pH and extracts only the cations held at 

active exchange sites at the particular pH of the soil. Neutral NH4OAc extracts the same 

amounts of Ca2+, Mg2+, Na+, K+ as KCl and therefore extractable bases by NH4OAc is used at 

the SSL in place of KCl-extractable bases. 

ECEC may be determined by extracting one soil sample with neutral normal NH4OAc 

to determine the exchangeable basic cations (Ca2+, Mg2+, Na+, and K+) and by extracting 

another sample of the same soil with 1.0 N KCl to determine the exchangeable Al. The 1 N

174
KCl-extractable Al approximates exchangeable Al and is a measure of "active" acidity present 

in soils with a 1:1 pH <5.5. Aluminum is non-exchangeable at pH >5.5 due to hydrolysis, 

polymerization, and precipitation. For soils with pH <7.0, the ECEC should be less than the 

CEC measured with a buffered solution at pH 7.0. The ECEC is not reported for soils with 

soluble salts. ECEC (4B4b2a) is calculated by summing the NH4OAc bases (4B1a1b1-4) plus 

the KCl extractable Al (4Ba1a1) as follows: 

ECEC = NH4OAc extractable bases + KCl-extractable Al

Effective Cation Exchange Capacity: NH4Cl (ECEC) 

The CEC using a neutral unbuffered salt (NH4Cl) is also an analytically determined 

value (4B1b1a1a1). The CEC by NH4Cl provides an estimate of the ECEC of the soil (Peech et 

al., 1947). For a soil with a pH of <7.0, the ECEC value should be < CEC measured with a 

buffered solution at pH 7.0. The NH4Cl CEC is ≈ equal to the NH4OAc extractable bases plus 

the KCl extractable Al for noncalcareous soils. This ECEC method is less commonly used at 

the SSL. 

References 

Coleman, T.R., E.J. Kamprath, and S.B. Weed. 1958. Liming. Adv. Agron. 10:475. 

Foth, H.D., and B.G. Ellis. 1988. Soil fertility. John Wiley & Sons, Inc., NY. 

Holmgren, G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically controlled variable 

rate leaching device. Soil Sci. Am. J. 41:1207-1208. 

Jackson, M.L. 1958. Soil chemical analysis. Prentice-Hall, Inc., Englewood Cliffs, NJ. 

National Soil Survey Laboratory Staff. 1975. Proposed tables for soil survey reports. RSSIU, 

USDA-SCS, Lincoln, NE 

Peech, M., L.T. Alexander, L.A. Dean, and J.F. Reed. 1947. Methods of soils analysis for soil 

fertility investigations. USDA Circ. 757, 25 pp. 

Rhoades, J.D. Cation exchange capacity. 1982. p. 149-157. In A.L. Page, R.H. Miller, and D.R. 

Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological properties. 

2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Sumner, M.E., and W.P. Miller. 1996. Cation exchange capacity and exchange coefficients. p. 

1201-1229. In D.L. Sparks (ed.) Methods of soil analysis. Part 3. Chemical methods. No. 5. 

ASA and SSSA, Madison, WI. 

Tisdale, S.L., W.L. Nelson, and J.D. Beaton. 1985. Soil fertility and fertilizers. 4th ed. 

Macmillan Publ. Co., NY. 

Ion Exchange and Extractable Cations (4B) 

Displacement after Washing, NH4OAc, pH 7 (4B1a) Automatic Extractor, 2 M KCl Rinse (4B1a1a) 

Steam Distillation, HCl Titration (4B1a1a1a) 

Cation Exchange Capacity (CEC-7) (4B1a1a1a1) 

Air-dry or Field-Moist, <2 mm (4B1a1a1a1a-b1) 

1. Application 

The cation exchange capacity (CEC) determined with 1 N NH4OAc buffered at pH 7.0 

(CEC-7), is a commonly used method and has become a standard reference to which other 

methods are compared (Peech et al., 1947). The advantages of using this method are that the 

extractant is highly buffered so that the extraction is performed at a constant, known pH (7.0) 

and that the NH4

+

 on the exchange complex is easily determined. 

2. Summary of Method 

Displacement after washing is the basis for this procedure. The CEC is determined by 

saturating the exchange sites with an index cation (NH4

+

); washing the soil free of excess 

saturated salt; displacing the index cation (NH4

+

) adsorbed by the soil; and measuring the 

amount of the index cation (NH4

+

). A sample is leached using 1 N NH4OAc and a mechanical 

175
vacuum extractor (Holmgren et al., 1977). The extract is weighed and saved for analyses of the 

cations. The NH4

+

 saturated soil is rinsed with ethanol to remove the NH4

+

 that was not 

adsorbed. The soil is then rinsed with 2 M KCl. This leachate is then analyzed by steam 

distillation and titration to determine the NH4

+

 adsorbed on the soil exchange complex. The 

CEC by NH4OAc, pH 7 is reported in meq 100 g-1 or (cmol (+) kg-1) soil in procedure 

4B1a1a1a1. 

3. Interferences 

Incomplete saturation of the soil with NH4

+

 and insufficient removal of NH4

+

 are the 

greatest interferences to this method. Ethanol removes some adsorbed NH4

+

 from the exchange 

sites of some soils. Isopropanol rinses have been used for some soils in which ethanol removes 

adsorbed NH4

+

. Soils that contain large amounts of vermiculite can irreversibly "fix" NH4

+

. Soils that contain large amounts of soluble carbonates can change the extractant pH and/or can 

contribute to erroneously high cation levels in the extract. This method overestimates the 

“field” CEC of soils with pH <7 (Summer and Miller, 1996) 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

and bases. Dispense concentrated acids and bases in a fume hood. Thoroughly wash hands 

after handling reagents. Use the safety showers and eyewash stations to dilute spilled acids and 

bases. Use sodium bicarbonate and water to neutralize and dilute spilled acids. Nessler's 

reagent contains mercury which is toxic. Proper disposal of the Nessler's reagent and clean-up 

of equipment in contact with the reagent is necessary. 

Ethanol is flammable. Avoid open flames and sparks. Standard laboratory equipment 

includes fire blankets and extinguishers for use when necessary. Follow the manufacturer's 

safety precautions when using the vacuum extractor and the Kjeltec Auto Analyzers. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Mechanical vacuum extractor, 24-place, SAMPLETEX, MAVCO Industries, Lincoln, NE 

(Fig. 1 and 2) 

5.3 Tubes, 60-mL, polypropylene, for extraction (0.45-μm filter), reservoir, and tared 

extraction tubes 

5.4 Rubber tubing, 3.2 ID x 1.6 OD x 6.4 mm (1/8 ID x 1/16 OD x 1 in) for connecting 

syringe barrels. 

5.5 Kjeltec Auto 2300 Sampler System, Tecator, Perstorp Analytical

5.6 Digestion tubes, straight neck, 250 mL 

5.7 Syringe filters, 0.45 μm, Whatman 

5.8 Wash bottles 

5.9 Vials, plastic 

5.10 Centrifuge, Centra, GP-8, Thermo IEC, Needham Heights, MA 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Ammonium acetate solution (NH4OAc), 1 N, pH 7.0. Add 1026 mL of glacial acetic acid 

(CH3COOH) to 15 L RODI water. Add 1224 mL of concentrated ammonium hydroxide 

(NH4OH). Cool. Allow to stand one day to equilibrate to room temperature. Mix and 

adjust to pH 7.0 with CH3COOH (typically, ≈ 40 mL) or NH4OH and dilute with RODI 

water to 18 L. 

6.3 Ethanol (CH3CH2OH), 95%, U.S.P. 

6.4 Nessler's reagent. Add 4.56 g of potassium iodide (KI) to 30 mL RODI water. Add 5.68 g 

of mercuric iodide (HgI2). Stir until dissolved. Dissolve 10 g of sodium hydroxide 

(NaOH) in 200 mL of RODI water. Transfer NaOH solution to a 250-mL volumetric flask 

176
and slowly add K-Hg-I solution. Dilute to volume with RODI water and thoroughly mix. 

Solution should not contain a precipitate. Solution can be used immediately. Store in 

brown bottle to protect from light. 

6.5 Potassium chloride solution, 2 M. Add 1341.9 g of KCl reagent in 8 L RODI water. 

Allow solution to equilibrate to room temperature. Dilute to 9 L with RODI water. 

6.6 Boric acid, 4% (w:v), with bromcresol green-methyl red indicator (0.075 % bromcresol 

green and 0.05% methyl red), Chempure 

6.7 Hydrochloric acid (HCl), 0.1 N, standardized. Dilute 167 mL of concentrated HCl in 20 L 

of RODI water. Refer to procedure for Standardization of Acids. 

6.8 NaOH, 1 M. Add 500 mL of 50% NaOH solution to 8 L of RODI water. Dilute to 9 L with 

RODI water. 

7. Procedure 

Extraction of Bases 

7.1 Weigh 2.5 g of <2-mm, air-dry soil to the nearest mg and place in a labeled extraction tube 

(ET). If sample is fine-grind, weigh 1 g to the nearest mg. If sample is moist, weigh enough 

soil to achieve ≈ 2.5 or 1g, respectively, of air-dry soil. Prepare one quality control check 

sample per 24 samples. 

7.2 Place labeled ET on extractor and connect to corresponding tared extraction tube 

(TETNH4OAc) with rubber tubing. 

7.3 Use wash bottle to rinse inside of ET with NH4OAc. All soil should be wetted and no air 

bubbles. Shaking, swirling, or stirring may be required to wet organic samples. Fill ET to the 

20-mL mark with NH4OAc solution (≈ 10 mL). 

7.4 Secure reservoir tube (RT) to top of ET tube and let stand for 30 min. Extract at 30-min rate 

the NH4OAc solution until 2 mL of this solution remains above soil level. Turn off extractor. 

Do not let soil dry. 

7.5 Add 40 mL of NH4OAc solution to the RT. Set extractor for an overnight (12h) extraction. 

Extractor will turn off automatically. 

7.6 Next day, remove RT from top of extractor and place in a clean container. Carefully 

remove TETNH4OAc. Leave the rubber tubing on the ET. Weigh each TETNH4OAc containing the 

NH4OAc extract to the nearest mg. 

7.7 Mix the extract in each TETNH4OAc by manually shaking. Fill a labeled plastic vial with 

extract solution and cap. Discard the excess properly. The solution in the vial is reserved for 

analyses of extracted cations (procedure 4B1a1b1-4) on the atomic absorption 

spectrophotometer (AAS). Some samples may be cloudy and need to be filtered prior to 

analysis on the AA. If extracts are not to be determined immediately after collection, then store 

samples at 4°C in plastic tubes. 

Removal of Excess Ammonium Acetate 

7.8 Re-connect the TETNH4OAc with paired ET. Use a wash bottle to rinse the sides of the ET 

with ethanol to remove any remaining NH4OAc or soil particles adhering to the ET. All soil 

should be wetted and no air bubbles. Fill ET to the 20-mL mark with ethanol. Secure RT to top 

of ET tube and let stand for 30 min. 

7.9 Extract at the 30-min extraction rate the ethanol solution until 2 mL of this solution remains 

above the soil level. Turn off the extractor. Do not let soil dry. 

177
7.10 Add 45 mL of ethanol to the RT. Extract (≈ 45 min) the ethanol until 2 mL of this 

solution remains above the soil level. Turn off the extractor. Do not let soil dry. Disconnect 

the TETNH4OAc from the ET and discard the ethanol properly. 

7.11 Re-connect the TETNH4OAc to the ET and add 55 mL of ethanol to the RT. Set the extractor 

for 45 min. Turn off the extractor. Remove the TETNH4OAc, leaving the tubing connected to the 

ET. Discard the ethanol properly. 

7.14 After the final ethanol wash, collect a few drops of ethanol extract from the ET on a spot 

plate. Test for NH4

+

 by using Nessler's reagent. A yellow, red to reddish brown precipitate is a 

positive test. If the test is positive, repeat the ethanol wash and retest with Nessler's reagent. 

Repeat until a negative test is obtained. 

2 M KCl Rinse 

7.15 Connect a new labeled extraction tube (ETKCl) with rubber tubing to ET on extractor. 

7.16 Use a wash bottle to rinse inside of ET with 2 M KCl to remove any remaining ethanol or 

soil particles adhering to the ET. All soil should be wetted and no air bubbles. Fill ET to the 

20-mL mark with KCl solution and let stand for 30. 

7.17 Extract at the 30-min rate the KCl solution until 2 mL of this solution remains above soil 

level. Turn off extractor. Do not let soil dry.

7.18 Secure RT to top of ET tube. Add 40 mL KCl solution to RT and set the extract for 45 

min. Remove the ET and ETKCl from the extractor. 

Steam Distillation: Setup, Operation, and Analysis 

7.19 Transfer the contents of the ETKCl to a 250-mL digestion tube. If extracts are not to be 

determined immediately after collection, then store samples at 4°C. 

7.20 Refer to the manufacturer’s manual for operation of the distillation unit. The following are 

only very general guidelines for instrument conditions. 

Program: Kjeldahl 1 

Receiving solution (boric acid): 30 mL 

Water: 0 mL 

Alkali (NaOH): 20 mL 

Mode: Delay 

Time: 1 s 

Distillation: Volume 

Tube Drain: Yes 

7.21 When using new reagents, e.g., boric acid, reagent blanks are distilled in 2 sets of 6, one 

set per Kjeltec machine. Each set of 6 is averaged and recorded on bench worksheet and 

manually set on each machine. During the steam distillation, the mean reagent blank titer is 

automatically subtracted from the sample titer. 

7.22 Record the normality of standardized acid. 

7.23 Connect the tube to the distillation unit. Close the safety door. Distillation and titration 

are performed automatically. Record the titer in mL of titrant. 

178
8. Calculations 

CEC = [Titer x N x 100 x R]/[Sample Weight (g)] 

where: 

CEC = Cation Exchange Capacity (meq 100 g-1) 

Titer = Titer of sample (mL) 

N = Normality of HCl titrant 

100 = Conversion factor to 100-g basis 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

9. Report 

Report CEC-7 to the nearest 0.1 meq 100 g-1 (cmol (+) kg-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Holmgren, G.G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically controlled 

variable rate leaching device. Soil Sci. Am. J. 41:1207-1208. 

Peech, M., L.T. Alexander, L.A. Dean, and J.F. Reed. 1947. Methods of soil analysis for 

soil fertility investigations. USDA Circ. 757, 25 pp. 

Sumner, M.E., and W.P. Miller. 1996. Cation exchange capacity and exchange 

coefficients. p. 1201-1229. In D.L. Sparks (ed.) Methods of soil analysis. Part 3. 

Chemical methods. No. 5. ASA and SSSA, Madison, WI. 

179
Fig.1. Mechanical vacuum extractor, 

SAMPLETEX, MAVCO Industries, Lincoln, NE. 

Fig. 2. Mechanical vacuum extractor used at the USDA-NRCS Soil Survey Laboratory 

for chemical extractions and analyses, e.g., cation exchange capacity, NH4OAc, pH 7. 

180
Ion Exchange and Extractable Cations (4B) er Washing, NH Cl (4B1b) Autom

he cation exchange capacity (CEC) determined with a neutral cation unbuffered salt, 

Cl, is an estimate of the “effective” CEC (ECEC) of the soil (Peech et al., 1947). 

For a s

); washing the soil free of excess 

saturate

ses of the 

cations The NH4 saturated soil is rinsed with ethanol to remove the NH4 that was not 

il is then rinsed with 2 M KCl. This leachate is then analyzed by steam +

 adsorbed on the soil exchange complex. The 

uration of the soil with NH and insufficient removal of NH are the 

hange 

sites of some soils. Isopropanol rinses have been used for some soils in which ethanol removes 

eversibly "fix" NH4

+

. arbonates can change the extractant pH and/or can 

els in the extract. 

ves) and eye protection 

ace shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

ense concentrated acids and bases in a fume hood. Thoroughly wash hands 

ids and 

reage toxic. Proper disposal of the Nessler's reagent and clean-up 

 necessary. 

includ s 

safety

5. E

5.1 E

 NE 

(

e

s

5.5 Kjeltec Auto 2300 Sampler System, Tecator, Perstorp Analytical 

Displacement aft 4

atic Extractor, 2 M KCl Rinse (4B1b1a) Steam Distillation, HCl Titration (4B1b1a1a) 

Cation Exchange Capacity (4B1b1a1a1) 

Air-dry or Field-Moist, <2 mm (4B1b1a1a1a-b1) 

1. Application 

T

e.g., 1 N NH4

oil with a pH of <7.0, the ECEC values should be <CEC measured with a buffered 

solution at pH 7.0. The NH4Cl CEC is approximately equal to the NH4OAc extractable bases 

plus the KCl extractable Al for noncalcareous soils. 

2. Summary of Method 

Displacement after washing is the basis for this procedure. The CEC is determined by 

saturating the exchange sites with an index cation (NH4

+

d salt; displacing the index cation (NH4

+

) adsorbed by the soil; and measuring the 

amount of the index cation (NH4

+

). A sample is leached using 1 N NH4Cl and a mechanical 

vacuum extractor (Holmgren et al., 1977). The extract is weighed and saved for analy + + . 

adsorbed. The so

distillation and titration to determine the NH4

CEC by NH4Cl is reported as meq 100 g-1 -1 or (cmol (+) kg ) soil in procedure 4B1b1a1a1. 

3. Interferences 

Incomplete sat + + 4 4

greatest interferences to this method. Ethanol removes some adsorbed NH4

+

 from the exc

adsorbed NH4

+

. Soils that contain large amounts of vermiculite can irr

Soils that contain large amounts of soluble c

contribute to erroneously high cation lev

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and glo

(f

and bases. Disp

after handling reagents. Use the safety showers and eyewash stations to dilute spilled ac

bases. Use sodium bicarbonate and water to neutralize and dilute spilled acids. Nessler's 

nt contains mercury which is

of equipment in contact with the reagent is

Ethanol is flammable. Avoid open flames and sparks. Standard laboratory equipment 

es fire blankets and extinguishers for use when necessary. Follow the manufacturer'

 precautions when using the vacuum extractor and the Kjeltec Auto Analyzers. 

quipment 

lectronic balance, ±1.0-mg sensitivity 

5.2 Mechanical Vacuum Extractor, 24-place, SAMPLETEX, MAVCO Industries, Lincoln,

See Fig. 1 and 2, procedure 4B1a1a1a1) 

5.3 Tubes, 60-mL, polypropylene, for extraction (0.45-μm filter), reservoir, and tared 

xtraction tubes 

5.4 Rubber tubing, 3.2 ID x 1.6 OD x 6.4 mm (1/8 ID x 1/16 OD x 1 in) for connecting 

yringe barrels. 

181
5.6 Digestion tubes, straight neck, 250 mL 

5.7 Syringe filters, 0.45 μm, Whatman 

.8 Wash bottles 

 .10 Centrifuge, Centra, GP-8, Thermo IEC, Needham Heights, MA 

DI 

0 L. 

.3 Ethanol (CH CH OH), 95%, U.S.P. 

dd 5.68 g 

tir until dissolved. Dissolve 10 g of sodium hydroxide 

(NaOH) in 200 mL of RODI water. Transfer NaOH solution to a 250-mL volumetric 

ghly 

5 Potassium chloride solution, 2 N. Add 1341.9 g of KCl reagent in 8 L RODI water. 

.05% methyl red), Chempure. 

.7 Hydrochloric acid (HCl), 0.1 N, standardized. Dilute 167 mL of concentrated HCl in 20 

aOH solution to 8 L of RODI water. Dilute to 9 L 

with RODI water. 

Extraction of Bases 

ube 

heck 

n extractor and connect to corresponding tared extraction tube 

(TETNH4Cl) with rubber tubing. 

he 

.4 Secure reservoir tube (RT) to top of ET tube and let stand for 30 min. Extract at 30-min rate 

on. 

.6 Next day, remove RT from top of extractor and place in a clean container. Carefully 

.7 Mix the extract in each TETNH4Cl by manually shaking. Fill a labeled plastic vial with 

extract solution and cap. Discard the excess properly. The solution in the vial is reserved for 

5

5.9 Vials, plastic

5

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Ammonium chloride solution (NH4Cl), 1 N. Dissolve 535 g of NH4Cl reagent in RO

water and dilute to 1

6 3 2

6.4 Nessler's reagent. Add 4.56 g of potassium iodide (KI) to 30 mL RODI water. A

of mercuric iodide (HgI2). S

flask and slowly add K-Hg-I solution. Dilute to volume with RODI water and thorou

mix. Solution should not contain a precipitate. Solution can be used immediately. Store

in brown bottle to protect from light. 

6.

Allow solution to equilibrate to room temperature. Dilute to 9 L with RODI water. 

6.6 Boric acid, 4% (w:v), with bromcresol green-methyl red indicator (0.075 % bromcresol 

green and 0

6

L of RODI water. Refer to procedure for Standardization of Acids. 

6.8 NaOH, 1 M. Add 500 mL of 50% N

7. Procedure 

7.1 Weigh 2.5 g of <2-mm, air-dry soil to the nearest mg and place in a labeled extraction t

(ET). If sample is fine-grind, weigh 1 g to the nearest mg. If sample is moist, weigh enough 

soil to achieve ≈ 2.5 or 1g, respectively, of air-dry soil. Prepare one quality control c

sample per 24 samples. 

7.2 Place labeled ET o

7.3 Use wash bottle to rinse inside of ET with NH4Cl. All soil should be wetted and no air 

bubbles. Shaking, swirling, or stirring may be required to wet organic samples. Fill ET to t

20-mL mark with NH4Cl solution (≈ 10 mL). 

 

7

the NH4Cl solution until 2 mL of this solution remains above soil level. Turn off extractor. Do 

not let soil dry. 

7.5 Add 40 mL of NH4Cl solution to the RT. Set extractor for an overnight (12h) extracti

Extractor will turn off automatically. 

7

remove TETNH4Cl. Leave the rubber tubing on the ET. Weigh each TETNH4Cl containing the 

NH4Cl extract to the nearest mg. 

7

182
analyses of extracted cations (procedure 4B1b1b1-4) on the atomic absorption (AA) 

spectrophotometer. Some samples may be cloudy and need to be filtered prior to analysis on 

the AA. If extracts are not to be determined immediately after collection, then store samples a

4°C in plastic tubes. 

t 

Removal of Excess Ammonium Chloride 

ith ethanol to remove any remaining NH Cl or soil particles adhering to the ET. All soil 

.9 Extract at 30-min rate the ethanol solution until 2 mL of this solution remains above the soil 

.10 Add 45 mL of ethanol to the RT. Extract (≈ 45 min) the ethanol until 2 mL of this 

t 

rly. 

7.11 Re-connect the Set the extractor 

e 

w, red to reddish brown precipitate is a 

ositive test. If the test is positive, repeat the ethanol wash and retest with Nessler's reagent. 

Repeat until a negative test is obtained. 

2 M KCl Rinse 

7.13 Connect a new labeled extraction tube (ETKCl) with rubber tubing to ET on extractor. 

7.14 Use a wash bottle to rinse inside of ET with 2 M KCl to remove any remaining ethanol or 

soil particles adhering to the ET. All soil should be wetted and no air bubbles. Fill ET to the 

20-mL mark with KCl solution and let stand for 30 min. 

7.15 Extract at the 30-min extraction rate the KCl solution until 2 mL of this solution remains 

above soil level. Turn off extractor. Do not let soil dry.

7.16 Secure RT to top of ET tube. Add 40 mL KCl solution to RT and set the extract for 45 

min. Remove the ET and ETKCl from the extractor. 

Steam Distillation: Setup, Operation, and Analysis 

7.17 Transfer the contents of the ETKCl to a 250-mL digestion tube. If extracts are not to be 

determined immediately after collection, then store samples at 4°C. 

7.18 Refer to the manufacturer’s manual for operation of the distillation unit. The following are 

only very general guidelines for instrument conditions. 

7.8 Re-connect the TETNH4Cl with paired ET. Use a wash bottle to rinse the sides of the ET 

w 4

should be wetted and no air bubbles. Fill ET to the 20-mL mark with ethanol. Secure RT to top

of ET and let stand for 30 min. 

7

level. Turn off the extractor. Do not let soil dry. 

7

solution remains above the soil level. Turn off the extractor. Do not let soil dry. Disconnec

the TETNH4Cl from the ET and discard the ethanol prope

TETNH4Cl to the ET and add 55 mL of ethanol to the RT.

for 45 min. Turn off the extractor. Remove the TETNH4Cl, leaving the tubing connected to th

ET. Discard the ethanol properly. 

7.12 After the final ethanol wash, collect a few drops of ethanol extract from the ET on a spot 

plate. Test for NH4

+

 by using Nessler's reagent. A yello

p

183
Program: Kjeldahl 1 

Receiving Solution (boric acid): 30 mL 

Water: 0 mL 

Alkali (NaOH):20 mL 

Mode: Delay 

Time: 1 s 

Distillation: Volume 

Tube Drain: Yes 

7.19 When using new reagents, e.g., boric acid, reagent blanks are distilled in 2 sets of 6, one 

set per Kjeltec machine. Each set of 6 is averaged and recorded on bench worksheet and 

manually set on each machine. During the steam distillation, the mean reagent blank titer is 

automatically subtracted from the sample titer. 

7.20 Record the normality of standardized acid. 

7.21 Connect the tube to the distillation unit. Close the safety door. Distillation and titration 

are performed automatically. Record the titer in mL of titrant. 

8. Calculations 

CEC = [Titer x N x 100 x R]/[Sample Weight (g)] 

where: 

CEC = Cation Exchange Capacity (meq 100 g-1) 

Titer = Titer of sample (mL) 

N = Normality of HCl titrant 

100 = Conversion factor to 100-g basis 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

9. Report 

Report neutral salts CEC to the nearest 0.1 meq 100 g-1 (cmol (+) kg-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Holmgren, G.G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically controlled 

variable rate leaching device. Soil Sci. Am. J. 41:1207-1208. 

Peech, M., L.T. Alexander, L.A. Dean, and J.F. Reed. 1947. Methods of soil analysis for 

soil fertility investigations. USDA. Agric. Circ. 757, 25 pp. 

Ion Exchange and Extractable Cations (4B) 

Displacement after Washing, NH4OAc, pH 7 (4B1a) Automatic Extractor (4B1a1) 

Atomic Absorption Spectrophotometer (4B1a1b) 

Calcium, Magnesium, Potassium, and Sodium (4B1a1b1-4) Air-dry or Field-Moist, <2-mm (4B1a1b1-4a-b1) 

1. Application 

The extractable bases (Ca2+, Mg2+, K+, and Na+) from the NH4OAc extraction 

(procedure 4B1a1) are generally assumed to be those exchangeable bases on the cation 

exchange sites of the soil. The term extractable rather than exchangeable bases is used because 

184
any additional source of soluble bases influences the results. The abundance of these cations 

usually occurs in the sequence of Ca2+ > Mg2+ > K+ > Na+. Deviation from this usual order 

signals that some factor or factors, e.g., free CaCO3 or gypsum, serpentine (high Mg2+), or 

natric material (high Na+), have altered the soil chemistry. The most doubtful cation 

extractions with this method are Ca2+ in the presence of free CaCO3 or gypsum and K+ in soils 

that are dominated by mica or vermiculite (Thomas, 1982). 

2. Summary of Method 

The NH4OAc extract from procedure 4B1a1 is diluted with an ionization suppressant 

(La2O3). The analytes are measured by an atomic absorption spectrophotometer (AAS). The 

analyte is measured by absorption of the light from a hollow cathode lamp. An automatic 

sample changer is used to aspirate a series of samples. The AAS converts absorption to analyte 

concentration. Data are automatically recorded by a microcomputer and printer. The NH4OAc 

extracted cations, Ca2+, Mg2+, K+, and Na+, are reported in meq 100 g-1 soil or (cmol (+) kg-1) in 

procedures 4B1a1b1-4, respectively. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

analyses of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. Do not use borosilicate tubes because of potential leaching of 

analytes. 

4. Safety 

Wear protective clothing and safety glasses. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Thoroughly wash hands after handling these metal salts. 

Follow standard laboratory procedures when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene gas is highly flammable. Avoid 

open flames and sparks. Standard laboratory equipment includes fire blankets and 

extinguishers for use when necessary. Follow the manufacturer's safety precautions when 

using the AAS. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Atomic absorption spectrophotometer (AAS), double-beam optical system, AAnalyst, 

300, Perkin-Elmer Corp., Norwalk, CT 

5.3 Autosampler, AS-90, Perkin-Elmer Corp., Norwalk, CT 

5.4 Computer, with AA WinLab software, Perkin-Elmer Corp., Norwalk, CT, and printer 

5.5 Single-stage regulator, acetylene 

5.6 Digital diluter/dispenser, with syringes 10000 and 1000 μL, gas tight, MicroLab 500, 

Hamilton Co., Reno, NV 

5.7 Plastic test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer 

5.8 Containers, polyethylene 

5.9 Peristaltic pump 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Hydrochloric acid (HCl), concentrated 12 N

6.3 HCl, 1:1 HCl:RODI, 6 N. Carefully mix 1 part of concentrated HCl to 1 part RODI 

water. 

6.4 NH4OH, reagent-grade, specific gravity 0.90 

6.5 Glacial acetic acid, 99.5% 

6.6 Ammonium acetate solution (NH4OAc), 1 N, pH 7.0. Add 1026 mL of glacial acetic 

acid (CH3COOH) to 15 L RODI water. Add 1224 mL of concentrated ammonium 

185
hydroxide (NH4OH). Cool. Allow to stand one day to equilibrate to room temperature. 

Mix and adjust to pH 7.0 with CH3COOH (typically, ≈ 40 mL) or NH4OH and dilute 

with RODI water to 18 L. The NH4OAc solution is used for extraction of cations 

(procedure 4B1a1). 

6.7 NH4OAc solution, 2.0 N, pH 7.0. Mix 228 mL of glacial acetic acid in 1200 mL of 

RODI water. While stirring, carefully add 272 mL of concentrated NH4OH. Cool. 

Allow to stand one day to equilibrate to room temperature. Mix and adjust pH 7.0 using 

CH3COOH or NH4OH. Dilute to 2 L with RODI water. 

6.8 Stock lanthanum ionization suppressant solution (SLISS), 65,000 mg L-1. Wet 152.4 g 

lanthanum oxide (La2O3) with 100 mL RODI water. Slowly and cautiously add 500 mL 

of 6 N HCl to dissolve the La2O3. Cooling the solution is necessary. Dilute to 2 L with 

RODI water. Filter solution. Store in polyethylene container. 

6.9 Working lanthanum ionization suppressant solution (WLISS), 2000 mg L-1. Dilute 61.5 

mL of SLISS with 1800 mL of RODI water (1:10). Dilute to final volume of 2-L with 

RODI water. Store in polyethylene container. 

6.10 Primary stock standards solutions (PSSS), high purity, 1000 mg L-1: Ca, Mg, K, and Na. 

6.11 Working stock mixed standards solution (WSMSS), High, Medium, Low, Very Low, 

and Blank. In five 500-mL volumetric flasks, add 250 mL of 2 N NH4 OAc and the 

following designated amounts of Ca PSSS, Mg PSSS, K PSSS, and Na PSSS. Dilute to 

volume with RODI. Invert to thoroughly mix. Store in polyethylene containers. 

Prepare fresh weekly. Store in the refrigerator. Allow to equilibrate to room 

temperature before use. Prepare WSMSS as follows: 

6.11.1 High Standard WSMSS: 90 mL Ca PSSS, 7.5 mL Mg PSSS, 20.0 mL K PSSS, and 

100.0 mL Na PSSS = 180 mg L-1 Ca, 15 mg L-1 Mg, 40 mg L-1 K, and 200 mg L-1 Na 

6.11.2 Medium Standard WSMSS: 60 mL Ca PSSS, 5.0 mL Mg PSSS, 10.0 mL K PSSS, and 

50.0 mL Na PSSS = 120 mg L-1 Ca, 10 mg L-1 Mg, 20 mg L-1 K, and 100 mg L-1 Na 

6.11.3 Low Standard WSMSS: 30 mL Ca PSSS, 2.5 mL Mg PSSS, 5.0 mL K PSSS, and 10.0 

mL Na PSSS = 60 mg L-1 Ca, 5 mg L-1 Mg, 10 mg L-1 K, and 20 mg L-1 Na 

6.11.4 Low/Low Standard WSMSS: 12.5 mL Ca PSSS, 0.25 mL Mg PSSS, 0.125 mL K PSSS, 

and 5.0 mL Na PSSS = 25 mg L-1 Ca, 0.5 mg L-1 Mg, 0.25 mg L-1 K, and 10 mg L-1 Na 

6.11.5 Blank WSMSS = 0 mL of Ca, Mg, K, and Na PSSS. 

6.12 Mixed calibration standard solutions (MCSS), High, Medium, Low, Very Low, and 

Blank. Dilute 1 part WSMSS with 19 parts of WLISS (1:20) dilution with resulting 

concentrations for MCSS as follows: 

6.12.1 MCSS High Standard: 9.0 mg L-1 Ca, 0.75 mg L-1 Mg, 2.0 mg L-1 K, and 10.0 mg L-1

Na 

6.12.2 MCSS Medium Standard: 6.0 mg L-1 Ca, 0.5 mg L-1 Mg, 1.0 mg L-1 K, and 5.0 mg L-1

Na 

6.12.3 MCSS Low Standard: 3.0 mg L-1 Ca, 0.25 mg L-1 Mg, 0.5 mg L-1 K, and 1.0 mg L-1 Na 

6.12.4 MCSS Very Low Standard: 1.25 mg L-1 Ca, 0.025 mg L-1 Mg, 0.125 K, and 0.5 mg L-1

Na 

6.12.5 Blank = 0 mg L-1 Ca, Mg, K, and Na 

186
6.13 Compressed air with water and oil traps. 

6.14 Acetylene gas, purity 99.6%. 

7. Procedure 

Dilution of Calibration Standards and Sample Extracts 

7.1 The 10-mL syringe is for diluent (WLISS). The 1-mL syringe is for the MCSS and 

NH4OAc extracts (procedure 4B1a1). Set the digital diluter at a 1:20 dilution. See reagents for 

preparation of the MCSS (High, Medium, Low, Very Low, Blank). Dilute 1 part NH4OAc 

sample extract with 19 parts of WLISS (1:20 dilution). 

 

7.2 Dispense the diluted sample solutions into test tubes which have been placed in the sample 

holders of the sample changer. 

AAS Set-up and Operation 

7.3 Refer to the manufacturer's manual for operation of the AAS. The following are only very 

general guidelines for instrument conditions for the various analytes. 

Analyte Conc. Burner Wavelength Slit Fuel/Oxidant 

 (mg L-1) & angle (nm) (mm) (C2H2/Air) 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Ca 9.0 10 cm @ 0° 422.7 0.7 1.5/10.0 

Mg 0.75 10 cm @ 0° 285.2 0.7 1.5/10.0 

K 2.0 10 cm @ 0° 766.5 0.7 1.5/10.0 

Na 10.0 10 cm @ 30° 589.0 0.2 1.5/10.0 

7.4 Use the computer and printer to set instrument parameters and to collect and record 

instrument readings. 

AAS Calibration and Analysis 

7.5 Calibrate the instrument by using the MCSS (High, Medium, Low, Very Low, Blank). The 

data system will then associate the concentrations with the instrument responses for each 

MCSS. Rejection criteria for MCSS, if R2

 <0.99.

7.6 If sample exceeds calibration standard, the sample is diluted 1:5, 1:20, 1:100, etc., with 1 N

NH4OAc followed by 1:20 dilution with WLISS. 

7.7 Perform one quality control (QC) (Low Standard MCSS) every 12 samples. If reading is 

not within 10%, the instrument is re-calibrated and QC re-analyzed. 

7.8 Record analyte readings to 0.01 unit. 

8. Calculations 

The instrument readings for analyte concentration are in mg L-1. These analyte concentrations 

are converted to meq 100 g-1 as follows: 

Soil Analyte Concentration (meq 100 g-1) = [A x [(B1 - B2)/B3] x C x R x 100]/[1000 x E x F] 

where: 

A = Analyte (Ca, Mg, K, Na) concentration in extract (mg L-1) 

B1 = Weight of extraction syringe and extract (g) 

B2 = Weight of tared extraction syringe (g) 

B3 = Density of 1 N NH4OAc at 20°C (1.0124 g cm-3) 

187
C = Dilution, if performed 

100 = Conversion factor (100-g basis) 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = mL L-1

E = Soil sample weight (g) 

F = Equivalent weight (mg meq-1) 

where: 

Ca+2 = 20.04 mg meq-1

Mg+2 = 12.15 mg meq-1

Na+1 = 22.99 mg meq-1

K+1 = 39.10 mg meq-1

9. Report 

Report the extractable Ca2+, Mg2+, Na+, and K+ to the nearest 0.1 meq 100 g-1 (cmol (+) 

kg-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Thomas, G.W. 1982. Exchangeable cations. p. 159-165. In A.L. Page, R.H. Miller, and 

D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Ion Exchange and Extractable Cations (4B) 

Displacement after Washing, NH4Cl (4B1b) Automatic Extractor (4B1ba) 

Atomic Absorption Spectrophotometer (4B1b1b) 

Calcium, Magnesium, Potassium, and Sodium (4B1b1b1-4) Air-dry or Field-Moist, <2-mm (4B1b1b1-4a-b1) 

1. Application 

The extractable bases (Ca2+, Mg2+, Na+, and K+) from the NH4Cl extraction (procedure 

4B1b1) are generally assumed to be those exchangeable bases on the cation exchange sites of 

the soil. The abundance of these cations usually occurs in the sequence of Ca2+ > Mg2+ > K+

 > 

Na+. Deviation from this usual order signals that some factor or factors, e.g., free CaCO3 or 

gypsum, serpentine (high Mg2+), or natric material (high Na+), have altered the soil chemistry. 

The most doubtful cation extractions with this method are Ca2+ in the presence of free CaCO3

or gypsum and K+ in soils that are dominated by mica or vermiculite (Thomas, 1982). 

2. Summary of Method 

The NH4Cl extract from procedure 4B1b1 is diluted with an ionization suppressant 

(La2O3). The analytes are measured by an atomic absorption spectrophotometer (AAS). The 

analyte is measured by absorption of the light from a hollow cathode lamp. An automatic 

sample changer is used to aspirate a series of samples. The AAS converts absorption to analyte 

concentration. Data are automatically recorded by a microcomputer and printer. The NH4Cl 

extracted cations, Ca2+, Mg2+, K+, and Na+, are reported in meq 100 g-1 soil or (cmol (+) kg-1) in 

procedures 4B1b1b1-4, respectively. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

analyses of these cations. These interferences vary in importance, depending upon the 

188
particular analyte selected. Do not use borosilicate tubes because of potential leaching of 

analytes. 

4. Safety 

Wear protective clothing and safety glasses. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Thoroughly wash hands after handling these metal salts. 

Follow standard laboratory procedures when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene gas is highly flammable. Avoid 

open flames and sparks. Standard laboratory equipment includes fire blankets and 

extinguishers for use when necessary. Follow the manufacturer's safety precautions when 

using the AAS. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Atomic absorption spectrophotometer (AAS), double-beam optical system, AAnalyst, 

300, Perkin-Elmer Corp., Norwalk, CT 

5.3 Autosampler, AS-90, Perkin-Elmer Corp., Norwalk, CT 

5.4 Computer, with AA WinLab software, Perkin-Elmer Corp., Norwalk, CT, and printer 

5.5 Single-stage regulator, acetylene 

5.6 Digital diluter/dispenser, with syringes 10000 and 1000 μL, gas tight, MicroLab 500, 

Hamilton Co., Reno, NV 

5.7 Plastic test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer 

5.8 Containers, polyethylene 

5.9 Peristaltic pump 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Hydrochloric acid (HCl), concentrated 12 N

6.3 HCl, 1:1 HCl:RODI, 6 N. Carefully mix 1 part of concentrated HCl to 1 part RODI 

water. 

6.4 Ammonium chloride solution (NH4Cl), 1 N. Dissolve 535 g of NH4Cl reagent in RODI 

water and dilute to 10 L. 

6.5 Stock lanthanum ionization suppressant solution (SLISS), 65,000 mg L-1. Wet 152.4 g 

lanthanum oxide (La2O3) with 100 mL RODI water. Slowly and cautiously add 500 mL 

of 6 N HCl to dissolve the La2O3. Cooling the solution is necessary. Dilute to 2 L with 

RODI water. Filter solution. Store in polyethylene container. 

6.6 Working lanthanum ionization suppressant solution (WLISS), 2000 mg L-1. Dilute 61.5 

mL of SLISS with 1800 mL of RODI water (1:10). Dilute to final volume of 2-L with 

RODI water. Store in polyethylene container. 

6.7 Primary stock standards solutions (PSSS), high purity, 1000 mg L-1: Ca, Mg, K, and Na. 

6.8 Working stock mixed standards solution (WSMSS), High, Medium, Low, Very Low, 

and Blank. In five 500-mL volumetric flasks, add 250 mL of 2 N NH4Cl and the 

following designated amounts of Ca PSSS, Mg PSSS, K PSSS, and Na PSSS. Dilute to 

volume with RODI. Invert to thoroughly mix. Store in polyethylene containers. 

Prepare fresh weekly. Store in the refrigerator. Allow to equilibrate to room 

temperature before use. Prepare WSMSS as follows: 

6.8.1 High Standard WSMSS: 90 mL Ca PSSS, 7.5 mL Mg PSSS, 20.0 mL K PSSS, and 

100.0 mL Na PSSS = 180 mg L-1 Ca, 15 mg L-1 Mg, 40 mg L-1 K, and 200 mg L-1 Na 

6.8.2 Medium Standard WSMSS: 60 mL Ca PSSS, 5.0 mL Mg PSSS, 10.0 mL K PSSS, and 

50.0 mL Na PSSS = 120 mg L-1 Ca, 10 mg L-1 Mg, 20 mg L-1 K, and 100 mg L-1 Na 

189
6.8.3 Low Standard WSMSS: 30 mL Ca PSSS, 2.5 mL Mg PSSS, 5.0 mL K PSSS, and 10.0 

mL Na PSSS = 60 mg L-1 Ca, 5 mg L-1 Mg, 10 mg L-1 K, and 20 mg L-1 Na 

6.8.4 Low/Low Standard WSMSS: 12.5 mL Ca PSSS, 0.25 mL Mg PSSS, 0.125 mL K PSSS, 

and 5.0 mL Na PSSS = 25 mg L-1 Ca, 0.5 mg L-1 Mg, 0.25 mg L-1 K, and 10 mg L-1 Na 

6.8.5 Blank WSMSS = 0 mL of Ca, Mg, K, and Na PSSS 

6.9 Mixed calibration standard solutions (MCSS), High, Medium, Low, Very Low, and 

Blank. Dilute 1 part WSMSS with 19 parts of WLISS (1:20) dilution with resulting 

concentrations for MCSS as follows: 

6.9.1 MCSS High Standard: 9.0 mg L-1 Ca, 0.75 mg L-1 Mg, 2.0 mg L-1 K, and 10.0 mg L-1

Na 

6.9.2 MCSS Medium Standard: 6.0 mg L-1 Ca, 0.5 mg L-1 Mg, 1.0 mg L-1 K, and 5.0 mg L-1

Na 

6.9.3 MCSS Low Standard: 3.0 mg L-1 Ca, 0.25 mg L-1 Mg, 0.5 mg L-1 K, and 1.0 mg L-1 Na 

6.9.4 MCSS Very Low Standard: 1.25 mg L-1 Ca, 0.025 mg L-1 Mg, 0.125 K, and 0.5 mg L-1

Na 

6.9.5 Blank = 0 mg L-1 Ca, Mg, K, and Na 

6.10 Compressed air with water and oil traps. 

6.11 Acetylene gas, purity 99.6%. 

7. Procedure 

Dilution of Calibration Standards and Sample Extracts 

7.1 The 10-mL syringe is for diluent (WLISS). The 1-mL syringe is for the MCSS and NH4Cl 

extracts (procedure 4B1b). Set the digital diluter at a 1:20 dilution. See reagents for 

preparation of the MCSS (High, Medium, Low, Very Low, Blank). Dilute 1 part NH4Cl sample 

extract with 19 parts of WLISS (1:20 dilution). 

7.2 Dispense the diluted sample solutions into test tubes which have been placed in the sample 

holders of the sample changer. 

AAS Set-up and Operation 

7.3 Refer to the manufacturer's manual for operation of the AAS. The following are only very 

general guidelines for instrument conditions for the various analytes. 

Analyte Conc. Burner Wavelength Slit Fuel/Oxidant 

 (mg L-1) & angle (nm) (mm) (C2H2/Air) 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Ca 9.0 10 cm @ 0° 422.7 0.7 1.5/10.0 

Mg 0.75 10 cm @ 0° 285.2 0.7 1.5/10.0 

K 2.0 10 cm @ 0° 766.5 0.7 1.5/10.0 

Na 10.0 10 cm @ 30° 589.0 0.2 1.5/10.0 

7.4 Use the computer and printer to set instrument parameters and to collect and record 

instrument readings. 

190
AAS Calibration and Analysis 

7.5 Calibrate the instrument by using the MCSS (High, Medium, Low, Very Low, Blank). The 

data system will then associate the concentrations with the instrument responses for each 

MCSS. Rejection criteria for MCSS, if R2 <0.99.

7.6 If sample exceeds calibration standard, the sample is diluted 1:5, 1:20, 1:100, etc., with 1 N

NH4Cl followed by 1:20 dilution with WLISS. 

7.7 Perform one quality control (QC) (Low Standard MCSS) every 12 samples. If reading is 

not within 10%, the instrument is re-calibrated and QC re-analyzed. 

7.8 Record analyte readings to 0.01 unit. 

8. Calculations 

The instrument readings for analyte concentration are in mg L-1. These analyte concentrations 

are converted to meq 100 g-1 as follows: 

Soil Analyte Concentration (meq 100 g-1) = [A x [(B1 - B2)/B3] x C x R x 100]/[1000 x E x F] 

where: 

A = Analyte (Ca, Mg, K, Na) concentration in extract (mg L-1) 

B1 = Weight of extraction syringe and extract (g) 

B2 = Weight of tared extraction syringe (g) 

B3 = Density of 1 N NH4Cl at 20°C (1.0166 g cm-3) 

C = Dilution, if performed 

100 = Conversion factor (100-g basis) 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = mL L-1

E = Soil sample weight (g) 

F = Equivalent weight (mg meq-1) 

where: 

Ca+2 = 20.04 mg meq-1

Mg+2 = 12.15 mg meq-1

Na+1 = 22.99 mg meq-1

K+1 = 39.10 mg meq-1

9. Report 

Report the extractable Ca2+, Mg2+, K+

, and Na+ to the nearest 0.1 meq 100 g-1 (cmol (+) 

kg-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Thomas, G.W. 1982. Exchangeable cations. p. 159-165. In A.L. Page, R.H. Miller, and 

D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

191
BaCl2-Triethanolamine, pH 8.2 Extraction (4B2) Automatic Extractor (4B2a) 

Automatic Titrator (4B2a1) 

Back Titration with HCl (4B2a1a) 

Extractable Acidity (4B2a1a1) 

Air-Dry or Field-Moist, <2 mm (4B2a1a1a-b1) 

1. Application 

The extractable acidity is the acidity released from the soil by a barium chloridetriethanolamine (BaCl2-TEA) solution buffered at pH 8.2 and includes all the acidity generated 

by replacement of the H and Al from permanent and pH dependent exchange sites. Extractable 

acidity may be measured at any pH, and a variety of methods have been used to measure it. 

The Soil Conservation Service adopted a pH of 8.2 because it approximates the calculated pH 

of a soil containing free CaCO3 in equilibrium with the normal CO2 content (0.03%) of the 

atmosphere. A pH of 8.2 also closely corresponds to the pH of complete neutralization of soil 

hydroxy-Al compounds. Although other pH values are valid for some types of soils, and the 

BaCl2-TEA, pH 8.2 method (4B2a1a1) may not always accurately reflect the nature of soils as 

they occur in the environment, this method has become a standard reference to which other 

methods are compared. 

2. Summary of Method 

A soil sample is leached with a BaCl2-TEA solution buffered at pH 8.2. Sample is 

allowed to stand overnight and extracted using a mechanical vacuum extractor (Holmgren et 

al., 1977). The extract is back-titrated with HCl. The difference between a blank and the 

extract is the extractable acidity. Extractable acidity is reported in meq 100 g-1 soil or (cmol (+) 

kg-1). 

3. Interferences 

No significant interferences are known to exist with this method. However, for some 

very acid soils, the buffer capacity of the BaCl2-TEA solution may be exceeded. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

and bases. Dispense concentrated acids in a fume hood. Thoroughly wash hands after 

handling reagents. Use the safety showers and eyewash stations to dilute spilled acids and 

bases. Use sodium bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Mechanical vacuum extractor, 24 place, SAMPLETEX, MAVCO Industries, Lincoln, NE 

5.3 Pipettes or dispenser, adjustable volume to 20 mL 

5.4 Titration beakers, 250-mL, plastic, Metrohm Ltd., Brinkmann Instruments Inc. 

5.5 Automatic titrator, with control unit, sample changer, and dispenser, Metrohm Ltd., 

Brinkmann Instruments, Inc. 

5.6 Combination pH-reference electrode, Metrohm Ltd., Brinkmann Instruments, Inc. 

5.7 Computer, with Titrino Workcell software, Metrohom Ltd., Brinkmann Instruments, Inc., 

and printer

5.8 Titration beakers, 250-mL, plastic, Metrohm Ltd., Brinkmann Instruments Inc. 

5.9 Tubes, 60-mL, polypropylene, for extraction, with 0.45-μm filter 

5.10 Rubber tubing, 3.2 ID x 6.4 OD x 25.4 mm, (1/8 ID x 1/16 OD x 1 in) for connecting 

syringe barrels 

192
6. Reagents 

6.1 Reverse osmosis deionized (RODI) water 

6.2 Reverse osmosis (RO) water 

6.3 Hydrochloric acid (HCl), concentrated, 12 N 

6.4 HCl, 0.13 N, standardized. Dilute 193 mL of concentrated HCl to 16-L volume with 

RODI water. 

6.5 Buffer solution [0.5 N BaCl2, 0.2 N Triethanolamine (TEA), pH 8.2]. Dissolve 977 g 

of BaCl2·2H2O in 8 L of RODI water. Dissolve 477 g of TEA in 4 L of RODI water. 

Mix two solutions and bring to nearly 16-L volume with RODI water. Adjust to pH 

8.2 with ≈ 33 mL of concentrated HCl or barium hydroxide. Bring to 16-L volume 

with RODI water. 

6.6 Replacement solution. Dissolve 977 g of BaCl2·2H2O in 8 L of RODI water. Add 80 

mL of buffer solution and dilute 16-L volume with RODI water. 

7. Procedure 

Extraction of Acidity 

7.1 Weigh 2.5 g of <2-mm or fine-grind, air-dry soil to the nearest mg and place in a labeled 

extraction (ET1). If sample is moist, weigh enough soil to achieve ≈ 2.5 g of air-dry soil. 

Prepare at least one reagent blank (no sample in syringe) and one quality control check sample 

per 24 samples. 

7.2 Place labeled ET on extractor and connect to corresponding extraction tube (ETAcidity) with 

rubber tubing. 

7.3 Use a dispenser to add 20.00 mL of BaCl2-TEA solution to the ET1. During the addition, 

wash the sides of the tube and wet the sample. For organic soils, shaking, swirling, or stirring 

may be required to wet the sample. 

 

7.4 Let ET1 tube stand overnight. 

7.5 Set the extractor for a 30-min extraction rate. Extract solution to a 0.5- to 1.0-cm height 

above the sample. Turn off the extractor. Do not allow the sample to become dry. 

7.6 Use a dispenser to add 20.00 mL of replacement solution to ET1. Extract the sample at 30-

min rate, pulling the solution almost completely through the sample. 

7.7 Add a second 20.00-mL aliquot of replacement solution to ET1. Extract at 30-min rate until 

all the solution has been drawn through the sample. 

7.8 Carefully remove ETAcidity. Leave rubber tubing on the ET1. 

Titration of BaCl2-TEA Extract 

7.9 Transfer the BaCl2-TEA extract from the ETAcidity to a 250-mL polyethylene titration 

beaker. 

7.10 Add 100 mL of RO water to the beaker. The solution is ready to be titrated. 

 

7.11 Refer to manufacturer's manual for operation of the automatic titrator. 

7.12 Calibrate automatic titrator with with 9.18, 7.00 and 4.00 pH buffers. Set-up the automatic 

titrator to set end point titration mode. The "Set" pH parameters are listed as follows: 

193
Parameter Value

Ep1 pH 4.60 

Dyn change pH 1.5 units 

Drift 0.4 mV s-1

Time delay 10 s 

Drift 0.4 mV s-1

Temp 25°C 

Stop Volume 75 mL 

 

7.13 If pre-titration pH is 0.3 units lower than the average pH of the blanks, re-run using a 0.25 

g sample 

7.14 Record the titer to the nearest 0.01 mL. Record the normality of the HCl solution. 

Average the titer of the reagent blanks and record. 

8. Calculations 

Extractable acidity (meq 100 g-1) = {[(B – T) x N x R]/C} x 100 

where: 

B = Average reagent blank titer (mL) 

T = Sample titer (mL) 

N = Normality of HCl 

C = Sample Weight (g) 

100 = Conversion factor (100-g basis) 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

9. Report 

Report extractable acidity to the nearest 0.1 meq 100 g-1 (cmol (+) kg-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Holmgren, G.G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically 

controlled variable rate leaching device. Soil Sci. Am. J. 41:1207-1208. 

BaCl2-Triethanolamine, pH 8.2 Extraction (4B2) Centrifuge (4B2b) 

Automatic Titrator (4B2b1) 

Back Titration with HCl (4B2b1a) 

Extractable Acidity (4B2b1a1) 

Air-Dry or Field-Moist, <2 mm (4B2b1a1a-b1) 

1. Application 

The extractable acidity is the acidity released from the soil by a barium chloridetriethanolamine (BaCl2-TEA) solution buffered at pH 8.2 and includes all the acidity generated 

by replacement of the H and Al from permanent and pH dependent exchange sites. Extractable 

acidity may be measured at any pH, and a variety of methods have been used to measure it. 

The Soil Conservation Service adopted a pH of 8.2 because it approximates the calculated pH 

of a soil containing free CaCO3 in equilibrium with the normal CO2 content (0.03%) of the 

atmosphere. A pH of 8.2 also closely corresponds to the pH of complete neutralization of soil 

hydroxy-Al compounds. Although other pH values are valid for some types of soils, and the 

194
BaCl2-TEA, pH 8.2 method (4B2b1a1) may not always accurately reflect the nature of soils as 

they occur in the environment, this method has become a standard reference to which other 

methods are compared. 

2. Summary of Method 

A soil sample is leached with a BaCl2-TEA solution buffered at pH 8.2. Sample is 

allowed to stand overnight, shaken, and centrifuged. The extract is back-titrated with HCl. The 

difference between a blank and the extract is the extractable acidity. Extractable acidity is 

reported in meq 100 g-1 soil or (cmol (+) kg-1). 

3. Interferences 

No significant interferences are known to exist with this method. However, for some 

very acid soils, the buffer capacity of the BaCl2-TEA solution may be exceeded. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

and bases. Dispense concentrated acids in a fume hood. Thoroughly wash hands after 

handling reagents. Use the safety showers and eyewash stations to dilute spilled acids and 

bases. Use sodium bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Pipettes or dispenser, adjustable volume to 40 mL 

5.3 Vortexer, mini, Analog, VRW Scientific Products 

5.4 Centrifuge tubes, 50-mL, polyethylene 

5.5 Centrifuge, Centra, GP-8, Thermo IEC, Needham Heights, MA 

5.6 Titration beakers, 250-mL, plastic, Metrohm Ltd., Brinkmann Instruments Inc. 

5.7 Automatic titrator, with control unit, sample changer, and dispenser, Metrohm Ltd., 

Brinkmann Instruments, Inc. 

5.8 Combination pH-reference electrode, Metrohm Ltd., Brinkmann Instruments, Inc. 

5.9 Computer, with Titrino Workcell software, Metrohom Ltd., Brinkmann Instruments, Inc., 

and printer

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water 

6.2 Hydrochloric acid (HCl), concentrated, 12 N 

6.3 HCl, 0.13 N, standardized. Dilute 193 mL of concentrated HCl to 16-L volume with RODI 

water. 

6.4 Buffer solution (0.5 N BaCl2, 0.2 N Triethanolamine (TEA), pH 8.2). Dissolve 977 g of 

BaCl2·2H2O in 8 L of RODI water. Dissolve 477 g of TEA in 4 L of RODI water. Mix 

two solutions and bring to nearly 16-L volume with RODI water. Adjust to pH 8.2 with ≈

33 mL of concentrated HCl or barium hydroxide. Bring to 16-L volume with RODI water. 

6.5 Replacement solution. Dissolve 977 g of BaCl2·2H2O in 8 L of RODI water. Add 80 

mL of buffer solution and dilute to 16-L volume with RODI water. 

7. Procedure 

Extraction of Acidity 

7.1 Weigh 5 g of <2-mm or fine-grind, air-dry soil to the nearest mg and place in a centrifuge 

tube. If sample is moist, weigh enough soil to achieve ≈ 5 g of air-dry soil. Prepare at least two 

reagent blanks (no sample in tube) and one quality control check sample per 21 samples. 

195
7.2 Add 40.00 mL of BaCl2-TEA solution to sample. Cap the tube and shake to ensure all soil 

is wetted. Place tube in a rack. 

 

7.3 Place tube rack on its side and gently shake to stratify the mixture lengthwise along the 

tube. Allow to stand overnight on its side. 

7.4 Centrifuge sample at 2000 rpm for 5 min. 

7.5 Decant extract into numbered titration beakers. 

7.6 Add 40 mL of replacement solution to sample. 

7.7 Cap tube and use a vortexer to loosen soil. Manually shake. 

7.8 Repeat Sections 7.4 – 7.7. 

7.9 Repeat Sections 7.4 – 7.5. Total volume in titration beaker should be ≈ 120 mL. 

Titration of BaCl2-TEA Extract 

7.10 Place titration beakers on automatic sample changer. 

7.11 Refer to the manufacturer’s manual for operation of the automatic titrator. 

7.12 Calibrate the titrator meter with 9.18, 7.00 and 4.00 pH buffers. Set-up the automatic 

titrator to sent end point mode. The “Set” pH parameters are listed as follows: 

Parameter Value

Ep1 pH 4.60 

Dyn change pH 1.5 units 

Drift 0.4 mV s-1

Time delay 10 s 

Drift 0.4 mV s-1

Temp 25°C 

Stop Volume 75 mL 

7.13 If pre-titration pH is 0.3 units lower than the average pH of the blanks, re-run using a 0.5-g 

sample. 

7.14 Record the titer to the nearest 0.01 mL. Record the normality of the HCl solution. 

Average the titer of the reagent blanks and record. 

8. Calculations 

Extractable acidity (meq 100 g-1) = {[(B – T) x N x R]/C} x 100 

where: 

B = Average reagent blank titer (mL) 

T = Sample titer (mL) 

N = Normality of HCl 

C = Sample Weight (g) 

100 = Conversion factor (100-g basis) 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

196
9. Report 

Report extractable acidity to the nearest 0.1 meq 100 g-1 (cmol (+) kg-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Holmgren, G.G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically 

controlled variable rate leaching device. Soil Sci. Am. J. 41:1207-1208. 

1 N KCl Extraction (4B3) Automatic Extractor (4B3a) 

Inductively Coupled Plasma Atomic Emission Spectrophotometer (4B3a1) Radial Mode (4B3a1a) 

Al and Mn (4B3a1a1-2) 

Air-Dry or Field-Moist, <2 mm (4B3a1a1-2a-b1) 

1. Application 

The Al extracted by 1 N KCl approximates exchangeable Al and is a measure of the 

"active" acidity present in soils with a 1:1 water pH <5.5. Above pH 5.5, precipitation of Al 

occurs during analysis. This method does not measure the acidity component of hydronium 

ions (H3O+

). If Al is present in measurable amounts, the hydronium is a minor component of 

the active acidity. Because the 1 N KCl extractant is an unbuffered salt and usually affects the 

soil pH one unit or less, the extraction is determined at or near the soil pH. The KCl 

extractable Al is related to the immediate lime requirement and existing CEC of the soil. The 

"potential" acidity is better measured by the BaCl2-TEA method (procedure 4B2a1a1) 

(Thomas, 1982). The use of NH4Cl in place of KCl is useful where a single exttractant for 

exchangeable bases and Al is preferred since NH4

+

 is as effective as K at displacing Al (Lee et 

al., 1985: Bertsch and Bloom, 1996). The Mn extracted by 1 N KCl approximates exchangeable 

Mn. Mn is an essential trace metal for plant nutrition. Soil analysis for Mn is of interest from 

both deficiency and toxicity perspectives (Gambrell, 1996). 

2. Summary of Method 

In this procedure (4B3a1a1-2), a soil sample is leached with 1 N KCl using the 

mechanical vacuum extractor (Holmgren et al., 1977). The extract is weighed. The KCl 

extracted solution is diluted with 0.5 N HCl. The analytes are measured by inductively coupled 

plasma atomic emission spectrophotometer (ICP-AES). The Mn and Al are reported in mg kg-1

and cmol(+) kg-1, respectively, in the soil. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

ICP-AES analyses of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. 

The soil:extractant ratio must remain constant. A soil:extractant ratio of 1:10 (w:v) for 

batch procedures is most commonly used. Using a leaching technique, a 1:20 (w:v) ratio gives 

comparable results. If the sample size is changed, the amount of extractable Al is changed. No 

other significant interferences have been identified for this procedure. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Follow standard laboratory practices when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Follow the manufacturer's safety 

precautions when using the ICP-AES. 

197
5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Mechanical vacuum extractor, 24-place, SAMPLETEX, MAVCO Industries, Lincoln, NE 

(See Fig.1 - 2, procedure 4B1a1a1a1) 

5.3 Tubes, 60-mL, polypropylene, for extraction (0.45-μm filter), reservoir, and tared 

extraction tubes 

5.4 Rubber tubing, 3.2 ID x 1.6 OD x 6.4 mm (1/8 ID x 1/16 OD x 1 in) for connecting 

syringe barrels. 

5.5 Dispenser, 10 mL 

5.6 Inductively coupled plasma atomic emission spectrophotometer (ICP-AES), Perkin-Elmer 

Optima 4300 Dual View (DV), Perkin-Elmer Corp., Norwalk, CT. 

5.7 Scott spray chamber with end cap and gem cone x-flow nebulizer

5.8 Torch coupler at -3 position 

5.9 RF generator, floor mounted power unit, 45 MHz free running, Perkin-Elmer 

Corp.,Norwalk, CT. 

5.10 Computer, with WinLab software ver. 4.1, Perkin-Elmer Corp., Norwalk, CT, and printer 

5.11 Recirculating chiller, Neslab, CFT Series 

5.12 Autosampler, AS-93, Perkin-Elmer Corp., Norwalk, CT. 

5.13 Single-stage regulator, high-purity, high-flow, argon 

5.14 Pipettes, electronic digital, 10000 and 1000 μL, with tips 10000 and 1000 μL 

5.15 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer 

5.16 Containers, polyethylene 

5.17 Vortexer, mini, MV1, VWR Scientific Products 

5.18 Disposable tubes, glass, 10 mL 

6. Reagents

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Potassium chloride solution (KCl), 1.0 N. Dissolve 1341.9 g of KCl reagent in 16 L 

RODI water. Allow solution to equilibrate to room temperature. Dilute to 18 L with 

RODI water. Use 1.0 N KCl for Al and Mn extraction. 

6.3 Potassium chloride solution (KCl), 2.0 N. Dissolve 298.2 g of KCl reagent in 1.5 L RODI 

water. Allow solution to equilibrate to room temperature. Dilute to 2 L with RODI 

water. Use 2.0 N KCl for standards. 

6.4 HCl, 0.5 N. In a 1-L volumetric, add 41.67 mL concentrated HCl 12 N to RODI water 

and dilute to volume with RODI water. 

6.5 Primary Stock Standard Solution (PSSS), high purity, 1000 mg L-1: Al and Mn. 

6.6 Mixed calibration standards solution (MCSS) for Al and Mn as follows: 

6.6.1 MCSS High: In 1-L volumetric flask, mix 40 mL Al PSSS, 5 mL Mn PSSS, 14.91 g KCl, 

and 33.3 mL concentrated HCl and dilute to volume with RODI water. Invert to 

thoroughly mix. Final concentration = 40 and 5 mg L-1 Al and Mn, respectively. Store in 

polyethylene containers. Prepare fresh weekly. Store in the refrigerator. Allow to 

equilibrate to room temperature before use. 

6.6.2 MCSS Medium: In 1-L volumetric flask, mix 20 mL Al PSSS, 2 mL Mn PSSS, 14.91 g 

KCl, and 33.3 mL concentrated HCl and dilute to volume with RODI water. Invert to 

thoroughly mix. Final concentration = 20 and 2 mg L-1 Al and Mn, respectively. Store in 

polyethylene containers. Prepare fresh weekly. Store in the refrigerator. Allow to 

equilibrate to room temperature before use. 

6.6.3 MCSS Low: In 1-L volumetric flask, mix 10 mL Al PSSS, 1mL Mn PSSS, 14.91 g KCl 

and 33.3 mL concentrated HCl and dilute to volume with RODI water. Invert to 

thoroughly mix. Final concentration = 10 and 1 mg L-1 Al and Mn, respectively. Store in 

198
polyethylene containers. Prepare fresh weekly. Store in the refrigerator. Allow to 

equilibrate to room temperature before use. 

6.6.4 MCSS Blank: In 1-L volumetric flask, mix 500 RODI water, 33.3 mL concentrated HCl, 

and 14.91 g KCl and dilute to volume with RODI water. Invert to thoroughly mix. Store 

in polyethylene containers. Prepare fresh weekly. Store in the refrigerator. Allow to 

equilibrate to room temperature before use. 

 6.7 Argon gas, purity 99.9% 

7. Procedure 

Extraction of Al and Mn

7.1 Weigh 2.5 g of <2-mm, air-dry soil to the nearest mg and place in a labeled extraction tube 

(ET). If sample is fine-grind, weigh 1.25 g to the nearest mg. If sample is moist, weigh enough 

soil to achieve ≈ 2.5 or 1.25 g, respectively, of air-dry soil. Prepare one quality control sample 

per 24 samples. 

7.2 Place labeled ET on extractor and connect to corresponding tared extraction tube (TETKCl) 

with rubber tubing. 

7.3 Use a dispenser and add 10 mL of 1 N KCl to the ET. All soil should be wetted and no air 

bubbles. Shaking, swirling, or stirring may be required to wet organic samples. 

7.4 Secure reservoir tube (RT) to top of ET tube and let stand for 30 min. Extract at 30-min 

rate the KCl soultion until 2 mL of this solution remains above soil level. Turn off extractor. 

Do not let soil dry. 

7.5 Add 45 mL of KCl solution to the RT if sample weight is 2.5 g. Add 17.5 mL of KCl 

solution to the RT if sample weight is 1.25 g. Set extractor for 45-min extraction. Extractor 

will turn off automatically. 

7.6 Remove RT from top of extractor. Carefully remove TETKCl. Leave the rubber tubing on 

the ET. Weigh each TETKCl containing the KCl extract to the nearest mg. 

7.7 Mix the extract in each TETKCl by manually shaking. Fill a disposable tube with extract 

solution and discard the excess properly. This solution is reserved for extractable Al and Mn 

analyses. If extracts are not be determined immediately after collection, then store samples at 

4°C. 

Dilution of Extracts 

7.8 Dilute samples (1:5 dilution). Dilute 1 part KCl sample extract with 4 parts 0.5 N HCl. Use 

Vortexer to mix sample. 

7.9 Place the diluted sample solutions into test tubes and place in the sample holder of the 

sample changer. 

ICP-AES Set-up and Operation 

7.10 Refer to the manufacturer's manual for operation of the ICP-AES. The following 

parameters are only very general guidelines for instrument conditions for the analytes. 

199
Parameter Value

View Radial 

Wavelength Al 396.153 

Wavelength Mn 257.610 

Background Correction “ON” 2-Point 

Gas Flow 

 Torch Gas 15.0 L min-1

 Auxiliary Gas Flow 0.5 L min-1

 Nebulizer Flow 0.80 L min-1

Power 1450 W 

Peristaltic Pump 

 Sample Flow Rate 1.25 mL min-1

 Flush Rate 35 s 

 Relaxation Time 15 s 

 Pump Tubing Type Solvflex black/black, 2-stop, 0.030 ID for sample 

 Solvflex red/red, 2-stop, 0.045 ID for rinse 

 ICP-AES Calibration and Analysis

7.11 Calibrate the instrument by using the MCSS. The data system will then associate the 

concentrations with the instrument responses for each MCSS. Rejection criteria for MCSS, if 

R2

 <0.99. 

7.12 If sample exceeds calibration standard, the sample is diluted 1:10 with 1 N KCl followed 

by 1:5 0.5 HCl. 

7.13 Perform one quality control (QC) (Low MCSS) every 12 samples. If reading is not within 

10%, the instrument is re-calibrated and QC re-analyzed. 

7.14 Record analyte readings to 0.01 mg L-1. 

8. Calculations 

The instrument readings are the analyte concentration (mg L-1 Al and Mn). Use these values to 

calculate the analyte concentration in meq 100 g-1 and mg kg-1 for Al and Mn, respectively. 

8.1 Al (meq 100 g-1) = [A x [(B1 - B2)/B3] x C1 x C2 x R x 100]/[1000 x E x F]

where: 

A = Al concentration in extract (mg L-1) 

B1 = Weight of extraction syringe and extract (g) 

B2 = Weight of tared extraction syringe (g) 

B3 = Density of 1 N KCl at 20°C (1.0412 g mL-1) 

C1 = Dilution, required (1:5) 

C2 = Dilution, if performed 

100 = Conversion factor (100-g basis) 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = mL L-1 

E = Soil sample weight (g) 

F = Equivalent weight (Al3+ = 8.99 mg meq-1) 

 

8.2 Mn (mg kg-1) = [A x [(B1 - B2)/B3] x C1 x C2 x R x 1000]/[1000 x E]

200
where: 

A = Mn concentration in extract (mg L-1) 

B1 = Weight of extraction syringe and extract (g) 

B2 = Weight of tared extraction syringe (g) 

B3 = Density of 1 N KCl at 20°C (1.0412 g mL-1) 

C1 = Dilution ratio, required (1:5) 

C2 = Dilution ratio, if needed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor in numerator to kg-basis 

1000 = Factor in denominator (mL L-1) 

E = Soil sample weight (g) 9. Report

Report KCl extractable Al to the nearest 0.1 meq 100 g-1 (cmol(+) kg-1) and Mn to the 

nearest mg kg-1. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Gambrell, R. P. 1996. Manganese. p. 665-682. In D.L. Sparks (ed.) Methods of soil 

Analysis . Part 3. Chemical Methods. . Soil Sci. Am. Book Series No. 5. ASA and SSA, 

Madison WI. 

Holmgren, George G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically 

controlled variable rate leaching device. Soil Sci. Soc. Am. J. 41:1207-1208. 

Bertsch, P.M., and P.R. Bloom. 1996. Aluminum. p. 517-530. In D.L. Sparks (ed.) 

Methods of soil analysis. Part 3. Chemical methods. No. 5. ASA and SSSA, Madison, 

WI. 

Lee, R., B.W. Bache, M.J. Wilson, and G.S. Sharp. 1985. Aluminum release in relation to 

the determination of cation exchange capacity of some podzolized New Zealand soils. J. 

Soil Sci. 36:239-253. 

Thomas, G.W. 1982. Exchangeable cations. p. 159-165. In A. Klute (ed.) Methods of soil 

analysis. Part 2. Chemical and microbiological properties. 2nd ed. Agron. Monogr. 9. 

ASA and SSSA, Madison, WI. 

Ratios and Estimates Related to Ion Exchange and Extractable Cations 

(4B4) 

Sum of Extractable Bases (4B4a) 

Sum of Extractable Bases by NH4OAc, pH 7 (4B4a1) 

4OAc, pH 7, Calculated (4B4a1a) 

Sum the NH4OAc, pH 7 extractable bases (Ca2+, Mg2+, K+, and Na+) (4B4a1a) obtained 

by procedure 4B1a1 and analyzed in procedures 4B1a1b1-4, respectively. This value is 

reported as meq 100 g-1 (cmol (+) kg-1). 

Ratios and Estimates Related to Ion Exchange and Extractable Cations 

(4B4) 

Sum of Extractable Bases (4B4a) 

Sum of Extractable Bases by NH4Cl (4B4a2) 

4Cl, Calculated (4B4a2a) 

Sum the NH4Cl extractable bases (Ca2+, Mg2+, K+, and Na+) (4B4a2a) obtained by 

procedure 4B1b1 and analyzed in procedures 4B1b1b1-4, respectively. This value is reported 

as meq 100 g-1 (cmol (+) kg-1). 

201
Ratios and Estimates Related to Ion Exchange and Extractable Cations 

(4B4) 

Cation Exchange Capacity (CEC) (4B4b) 

CEC-8.2 (Sum of Cations) (4B4b1) 

CEC-8.2, Calculated (4B4b1a) 

CEC-8.2, Not Calculated (4B4b1b) 

Calculate the CEC-8.2 (4B4b1a) by adding the sum of the NH4OAc extractable bases 

(4B4a1) plus the BaCl2-TEA extractable acidity (4B2a1a1 or 4B2b1a1). This value is reported 

as meq 100 g-1 (cmol (+) kg-1). Cation summation is the basis for this procedure. The CEC-8.2 

minus the CEC-7 is considered the pH dependent charge from pH 7.0 to pH 8.2. The CEC-8.2 

is not calculated (4B4b1b) if significant quantities of soluble salts or carbonates are present in 

the soil. CEC-8.2 is calculated as follows: 

CEC-8.2 = NH4OAc Bases + BaCl2-TEA Acidity 

Ratios and Estimates Related to Ion Exchange and Extractable Cations 

(4B4) 

Cation Exchange Capacity (CEC) (4B4b) 

Effective Cation Exchange Capacity (ECEC) (4B4b2) Sum of NH4OAc Extractable Bases + 1 N KCl Extractable Aluminum, Calculated (4B4b2a) 

Sum of NH4OAc Extractable Bases + 1 N KCl Extractable Aluminum, Not Calculated (4B4b2b) 

Calculate the ECEC (4B4b2a) by adding the sum of the NH4OAc extractable bases 

(4B4a1) plus the 1 N KCl extractable Al (4B3a1a1). This value is reported as meq 100 g-1

(cmol (+) kg-1). The ECEC is not calculated (4B4b2b) if significant quantities of soluble salts 

or carbonates are present in the soil. ECEC by NH4OAc extractable bases and 1 N KCl Al is 

calculated as follows: 

ECEC = NH4OAc Bases + 1 N KCl Al 

Ratios and Estimates Related to Ion Exchange and Extractable Cations 

(4B4) 

Base Saturation (4B4c) 

Base Saturation by NH4OAc, pH 7 (CEC-7) (4B4c1) Base Saturation by CEC-7, Calculated (4B4c1a) 

Base Saturation by CEC-7, Set to 100% (4B4c1b) 

Calculate the base saturation (4B4c1a) by dividing by the sum of NH4OAc extractatable 

(4B4a1) bases by CEC-7 (4B1a1a1a1) and multiplying by 100. This value is reported as meq 

100 g-1 (cmol (+) kg-1). If a soil has significant quantities of soluble salts or carbonates, this 

value is set to 100% (4B4c1b). In soil taxonomy, base saturation determined by CEC-7 is used 

in mollic, umbric, and eutro-dystro criteria (Soil Survey Staff, 1999). Calculate base saturation 

by CEC-7 as follows: 

Base Saturation (%) = (NH4OAc Bases/CEC-7) x 100 

202
References 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. Print. Office, 

Washington, DC. 

Ratios and Estimates Related to Ion Exchange and Extractable Cations 

(4B4) 

Base Saturation (4B4c) 

Base Saturation by NH4Cl (4B4c2) 

4Cl, Calculated (4B4c2a) 

4Cl, Set to 100% (4B4c2b) 

Calculate the base saturation (4B4c2a) by dividing the sum of the NH4Cl extractatable 

(4B4a2) bases by CEC by NH4Cl (4B1b1a1a1) and multiplying by 100. This value is reported 

as meq 100 g-1 or cmol (+) kg-1.If a soil has significant quantities of soluble salts or carbonates,

this value is set to 100% (4B4c2b). Calculate base saturation by 1+&O as follows: 

Base Saturation (%) = (NH4Cl Bases/CEC by NH4Cl) x 100 

Ratios and Estimates Related to Ion Exchange and Extractable Cations 

(4B4) 

Base Saturation (4B4c) 

Base Saturation by CEC-8.2 (Sum of Cations) (4B4c3) 

Base Saturation by CEC-8.2, Calculated (4B4c3a) Base Saturation by CEC-8.2, Not Calculated (4B4c3b) 

Calculate the base saturation (4B4c3a) by dividing the sum of the NH4OAc extractable 

bases (4B4a1) by CEC-8.2 (4B4b1a) and multiplying by 100. This value is reported as meq 100 

g

-1 or cmol (+) kg-1. If a soil has signficant quantities of soluble salts or carbonates, this value 

is not calculated (4B4c3b). Calculate base saturation by CEC-8.2 (Sum of Cations) as follows: 

Base Saturation (%) = [NH4OAc Bases/(NH4OAc Bases + BaCl2-TEA Acidity)] x 100 

References 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. Print. Office, 

Washington, DC. 

Ratios and Estimates Related to Ion Exhange and Extractable Cations (4B4) Base Saturation (4B4c) 

Base Saturation by Effective Cation Exchange Capacity (ECEC) (4B4c4) Base Saturation by Sum of NH4OAc Extractable Bases + 1 N KCl 

Extractable Aluminum, Calculated (4B4c4a) 

Base Saturation by Sum of NH4OAc Extractable Bases + 1 N KCl 

Extractable Aluminum, Not Calculated (4B4c4b) 

Calculate the base saturation (4B4c4a) by dividing the sum of NH4OAc extractable 

bases (4B4a1) by the ECEC (4B4b2a) and multiplying by 100. If a soil has signficant quantities 

of soluble salts or carbonates, this value is not calculated (4B4c4b). Calculate base saturation 

by ECEC as follows: 

203
Base Saturation (%) = (NH4OAc Bases/NH4OAc Bases + 1 N KCl Al) x 100 

Ratios and Estimates Related to Ion Exchange and Extractable Cations 

(4B4) 

Aluminum Saturation (4B4d) 

Aluminum Saturation by Effective Cation Exchange Capacity (ECEC) (4B4d1) 

Aluminum Saturation by Sum of NH4OAc Extractable Bases + 1 N KCl 

Extractable Aluminum, Calculated (4B4d1a) 

Aluminum Saturation by Sum of NH4OAc Extractable Bases + 1 N KCl 

Extractable Aluminum, Not Calculated (4B4d1b) 

Calculate the Al saturation (4B4d1a) by dividing the 1 N KCl extractable Al (4B3a1a1) 

by ECEC (4B4b2a) and multiplying by 100. If a soil has signficant quantities of soluble salts 

or carbonates, this value is not calculated (4B4d1b). Calculate Al saturation as follows: 

Al Saturation (%) = [1 N KCl Al/(NH4OAc Bases + 1 N KCl Al)]

Ratios and Estimates Related to Ion Exchange and Extractable Cations 

(4B4) 

Activity (4B4e) 

CEC-7FOD\%H 

Divide the &(& (procedure %DDD) by FOD\ 7 (procedure $D).This ratio is

reported as a dimensionless value. In the past, the ratios of CEC:clay have been

reported as meq g-1. For more detailed information on the application of 

this ratio, refer to Soil Survey Staff (1995, 1999). 

Reaction (4C) 

Soil Suspensions (4C1) 

Electrode (4C1a) 

Standard Glass Body Combination (4C1a1) 

Digital pH/Ion Meter (4C1a1a) 

Soil pH is one of the most frequently performed determinations, and one of the most 

indicative measurements of soil chemical properties (McLean, 1982). Soil pH tells more about 

a soil than merely indicating whether it is acidic or basic but also the availability of essential 

nutrients and toxicity of other elements can be estimated because of their known relationship 

with pH (Thomas, 1996). Soil pH is affected by many factors, e.g., nature and type of inorganic 

and organic matter; amount and type of exchangeable cations and anions; soil:solution ratio; 

salt or electrolyte content; and CO2 content (McLean, 1982). The acidity, neutrality, or basicity 

of a soil influences the solubility of various compounds; the relative ion bonding to exchange 

sites; and microbial activities. Depending on the predominant clay type, the pH may be used as 

a relative indicator of base saturation (Mehlich, 1934). Soil pH is also a critical factor in the 

availability of most essential elements for plants. 

The SSL performs several pH determinations. These methods include but are not 

limited to as follows: NaF (1 N pH 7.5 to 7.8) (4C1a1a1); saturated paste pH (4C1a1a2); 

oxidized pH (4C1a1a3); 1:1 water and 1:2 CaCl2 (final solution: 0.01 M CaCl2) (4C1a2a1-2, 

respectively); 1 N KCl, procedure 4C1a2a3; and organic materials, CaCl2 (final solution ≈ 0.01 

M CaCl2) (4C1a1a4). 

An increase in the soil:water ratio or the presence of salts generally results in a decrease 

in the soil pH. The soluble salt content of the soil can be overcome by using dilute salt 

204
solutions, e.g., CaCl2 or KCl, instead of distilled water. The use of dilute salt solutions is a 

popular method for masking seasonal variation in soil pH. The pH readings are usually less 

with dilute salt solutions than with distilled water but may be equal to or greater in highly 

weathered tropical soils, i.e., soils with a high anion exchange capacity. When the pH values of 

various soils are compared, determination by the same method is important (Foth and Ellis, 

1988). 

The 1 N KCl is an index of soil acidity and is more popular in those regions with 

extremely acid soils and in which KCl is used as an extractant of exchangeable Al. The KCl pH 

indicates the pH at which Al is extracted. Similar to the 1:2 CaCl2 pH, the 1 N KCl pH readings 

also tend to be uniform regardless of time of year. 

The saturated paste pH is popular in regions with soils with soluble salts. The water 

content varies with soil water storage characteristics. The saturated paste pH may be more 

indicative of the saturated, irrigated soil pH than is the soil pH measurement at a constant 

soil:water ratio. The saturated paste pH is also that pH at which the saturation extract is 

removed for salt analysis, and hence, is the pH and the dilution at which the sodium adsorption 

ratio (SAR) is computed (procedure 4E4b). 

The 1 N NaF pH may be used as an indicator that amorphous material dominates the 

soil exchange complex. The oxidized pH may be used to assess the activities of soil 

microorganisms. In soil taxonomy, the CaCl2 pH is used to distinguish two family reaction 

classes in Histosols (Soil Survey Staff, 1999). 

References 

Foth, H.D., and B.G. Ellis. 1988. Soil fertility. John Wiley and Sons. New York, NY. 

McLean, E.O. 1982. Soil pH and lime requirement. p. 199-224. In A.L Page, R.H. Miller, and 

D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Mehlich, A. 1943. The significance of percentage of base saturation and pH in relation to soil 

differences. Soil Sci. Soc. Am. Proc. 7:167-174. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. Print. Office, 

Washington, DC. 

Thomas, G.W. 1996. Soil pH and soil acidity. p. 475-490. In D.L. Sparks (ed.) Methods of soil 

analysis. Part 3. Chemical methods. No. 5. ASA and SSSA, Madison, WI. 

Reaction (4C) 

Soil Suspensions (4C1) 

Electrode (4C1a) 

Standard Glass Body Combination (4C1a1) 

Digital pH/Ion Meter (4C1a1a)

1 N NaF, pH 7.5 – 7.8 (4C1a1a1) Air-Dry or Field-Moist, <2 mm (4C1a1a1a-b1) 

1. Application 

The action of NaF upon noncrystalline (amorphous) soil material releases hydroxide 

ions (OH-) to the soil solution and increases the pH of the solution. The amount of amorphous 

material in the soil controls the release of OH- and the subsequent increase in pH (Fields and 

Perrott, 1966). The following reactions illustrate this action and form the basis of this 

procedure. 

Al(OH)3 + 3 F- >> AlF3 + 3 OHSi(OH)4 + 4 F-

 >> SiF4 + 4 OH205
Most soils contain components that react with NaF and release OH-

. However, a NaF 

pH >9.4 is a strong indicator that amorphous material dominates the soil exchange complex. 

Amorphous material is usually an early product of weathering of pyroclastic materials in a 

humid climate. Amorphous material appears to form in spodic horizons in the absence of 

pyroclastics. 

2. Summary of Method 

A 1-g sample is mixed with 50 mL of 1 N NaF and stirred for 2 min. While the sample 

is being stirred, the pH is read at exactly 2 min in the upper 1/3 of the suspension (4C1a1a1). 

3. Interferences 

The difference in the sediment and supernatant pH is called the suspension effect 

(McLean, 1982). To maintain uniformity in pH determination, measure the pH just above the 

soil sediment. Clays may clog the KCl junction and slow the electrode response. Clean the 

electrode by rinsing with distilled water and patting it dry with tissue. Wiping the electrode dry 

with a cloth, laboratory tissue, or similar material may cause electrode polarization. Use high 

purity (99%) NaF. 

Soils with a 1:1 water pH >8.2 do not give a reliable NaF pH. Free carbonates in a soil 

result in a high NaF pH. In general, soils with a 1:1 water pH <7.0 are not affected. 

4. Safety 

The NaF is poisonous. Avoid eye contact and ingestion. Skin penetration and irritation 

are moderately hazardous. Do not eat or drink while using NaF. Thoroughly wash hands after 

use. Wear protective clothing, e.g., coats, aprons, and gloves, and eye protection, e.g., safety 

glasses or goggles, when using NaF. Use the fume hood when using NaF. Follow standard 

laboratory safety practices. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Paper cup, 120 mL (4 fl. oz.), disposable, Solo Cup Co., No. 404 

5.3 Titration beakers, polyethylene, 250 mL 

5.4 Automatic titrator, Metrohm Titroprocessors, Control Units, Sample Changers, and 

Dosimats, Metrohm Ltd., Brinkmann Instruments, Inc. 

5.5 Combination pH-reference electrode, Metrohm, Brinkmann Instruments, Inc. 

6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

6.2 Borax pH buffers, pH 4.00, pH 7.00, and pH 9.18, for electrode calibration, Beckman, 

Fullerton, CA. 

6.3 Phenolphthalein 

6.4 Sodium fluoride (NaF), 99% purity, EM Science 

6.5 Sodium fluoride (NaF), 1.0 N solution. In a plastic bottle, add 400 g NaF in 8 L of 

distilled water. Let stand for 3 days. On the third day, after excess NaF has settled, 

measure 50 mL of the solution and read pH. The pH should be between 7.5 and 7.8. 

Add 3 to 5 drops 0.25% phenolphthalein and titrate to pink end point (pH 8.2 to 8.3). If 

pH is outside the 7.5 and 7.8 range, then adjust pH with either HF or NaOH. If solution 

has a pH >8.2 or if the titratable acidity is >0.25 meq L-1, use another source of NaF. 

7. Procedure 

7.1 Weigh 1 g of <2-mm or fine-grind, air-dry soil to the nearest 1 mg and place in a 120-mL 

(4-oz) paper cup. If sample is moist, weigh enough soil to achieve ≈ 1 g of air-dry soil. 

7.2 Calibrate the titrator with pH 4.00, 7.00, and 9.18 buffer solutions. 

206
7.3 Sample stirring, waiting interval for readings, addition of NaF solution, pH readings, and 

rinsing of electrode are controlled by computer. 

7.4 The general sequence used by the automated system is as follows: 

7.4.1 The sample is lifted so that the pH electrode is positioned above the soil sediment. 

Stirring begins immediately and is maintained during each sample cycle. 

7.4.2 A 50-mL solution is added to sample. 

7.4.3 After 2 min, NaF pH is read. Record pH to the nearest 0.01 unit. 

7.4.4 The sample is lowered, and the electrode and stirrer are rinsed with RO water. 

7.4.5 The next sample is positioned for analysis. 

7.4.6 The cycle is repeated until all samples have been analyzed. 

7.5 Discard the solution and cup in safe containers. The paper cup with the NaF solution leaks 

in about 15 min. 

8. Calculations 

No calculations are required for this procedure. 

9. Report 

Report NaF pH to the nearest 0.1 pH unit. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Fields, M., and K.W. Perrott. 1966. The nature of allophane in soils. Part 3. Rapid field and 

laboratory test for allophane. N.Z. J. Sci. 9:623-629. 

McLean, E.O. 1982. Soil pH and lime requirement. p. 199-224. In A.L. Page, R.H. Miller, 

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison,

Reaction (4C) 

Soil Suspensions (4C1) 

Electrode (4C1a) 

Standard Glass Body Combination (4C1a1) 

Digital pH/Ion Meter (4C1a1a)

Saturated Paste pH (4C1a1a2) 

Air-Dry, <2 mm (4C1a1a2a1) 

1. Application 

When making interpretations about the soil, the saturated paste pH is usually compared 

to the 1:1 water pH and the 1:2 CaCl2 pH. The usual pH sequence is as follows: 1:1 water pH > 

1:2 CaCl2 pH > saturated paste pH. If saturated paste pH is > 1:2 CaCl2 pH, the soil is not 

saline. If the saturated paste pH > 1:1 water pH, the soil may be Na saturated and does not 

have free carbonates. 

Because of the interrelations that exist among the various soil chemical determinations, 

the saturated paste pH value may be used as a means of cross-checking salinity data for internal 

207
consistency and reliability (U.S. Salinity Laboratory Staff, 1954). Some rules of thumb that 

apply to the saturated paste pH are as follows: 

a. Soluble carbonates are present only if the pH is >9. 

b. Soluble bicarbonate seldom >3 or 4 meq L-1, if the pH is <7. 

c. Soluble Ca2+ and Mg2+ seldom >2 meq L-1, if the pH is >9. 

d. Gypsiferous soils seldom have a pH >8.2. 

2. Summary of Method 

The saturated paste is prepared (4F2), and the pH of paste is measured with a calibrated 

combination electrode/digital pH meter (4C1a1a2). 

3. Interferences 

The difference in the sediment and supernatant pH is called the suspension effect 

(McLean, 1982). To maintain uniformity in pH determination, measure the pH just beneath the 

surface of saturated paste. Clays may clog the KCl junction and slow the electrode response. 

Clean the electrode by rinsing with RO water and patting it dry with tissue. Wiping the 

electrode dry with a cloth, laboratory tissue, or similar material may cause electrode 

polarization. 

4. Safety 

No significant hazards are associated with this procedure. Follow standard laboratory 

safety practices. 

5. Equipment 

5.1 Digital pH/ion meter, Accumet Model AR15, Fisher Scientific 

5.2 Electrode, standard glass body combination, Accu-flow, Fisher Scientific 

6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

6.2 Borax pH Buffers, pH 4.00, pH 7.00 and pH 9.18, for electrode calibration, Beckman, 

Fullerton, CA. 

7. Procedure 

7.1 Prepare a saturated paste (procedure 4F2). 

7.2 Calibrate the pH meter with pH 4.00, 7.00 and 9.18 buffer solutions. 

7.3 After equipment calibration, gently wash the electrode with RO water. Dry the electrode. 

Do not wipe the electrode with a tissue as this may cause a static charge on the electrode. 

7.4 Gently lower the electrode in the saturated paste until the KCl junction of the electrode is 

beneath the surface of saturated paste. 

7.5 Allow the pH meter to stabilize before recording the pH. Record pH to the nearest 0.01 

unit. 

7.6 Gently raise the pH electrode from the paste and wash all particles adhering to the electrode 

with a stream of RO water. 

208
8. Calculations 

No calculations are required for this procedure. 

9. Report 

Report saturated paste pH to the nearest 0.1 pH unit. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

McLean, E.O. 1982. Soil pH and lime requirement. p. 199-224. In A.L. Page, R.H. Miller, 

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. USDA Handb. 60. U.S. Govt. Print. Office, Washington, DC. 

Reaction (4C) 

Soil Suspensions (4C1) 

Electrode (4C1a) 

Standard Glass Body Combination (4C1a1) 

Digital pH/Ion Meter (4C1a1a)

Oxidized pH (4C1a1a3) 

1. Application 

Sulfidic material is waterlogged mineral, organic, or mixed soil material with a pH of 

3.5 or higher, containing oxidizable sulfur compounds, and which if incubated as a 1-cm thick 

layer under moist, aerobic conditions (field capacity) at room temperature, shows a drop in pH 

of 0.5 or more units to a pH value of 4.0 or less (1:1 by weight in water or in a minimum of 

water to permit measurement) within 8 wk (Van Breemen, 1982; Soil Survey Staff, 1999). The 

intent of the method described herein is to determine if known or suspected sulfidic materials 

will oxidize to form a sulfuric horizon (Soil Survey Staff, 1999). Identification of H2S in a soil 

by a “rotten-egg” smell or FeS in a saturated soil by its blue-black color indicates that sulfidic 

materials may be present. If such soils are drained and oxidized, the soil pH could drop to 3.5 

or less, making the soil unsuitable for many uses. A field test for FeS is to add 1 N HCl and 

note the odor of H2S. 

2. Summary of Method 

Transfer enough soil to fill a plastic cup one-half to two-thirds full. Add a little water if 

needed to make a slurry. Stir the slurry thoroughly to introduce air. Determine pH 

immediately. Place cup in a closed container with openings (inlet and outlet) providing 

humidified air. Keep at room temperature. After 24 h, open the container, stir the sample 

thoroughly, and determine the soil pH. Repeat the procedure for a minimum of 10 days until 

the pH reaches a steady state of < 0.1 units over a 2-day period. Record daily pH readings 

(4C1a1a3). 

3. Interferences 

Samples should be shipped in watertight containers completely filled with water from 

the ambient soil solution to prevent potential oxidation of sulfides and reduction in soil pH. 

Extended time in stirring of sample and/or in reading the pH may result in the 

introduction of sufficient O2 into the mixture to change the pH reading. Quickly stirring the 

mixture and reading the pH reduce this error. 

Clean the electrode by rinsing with reverse osmosis (RO) water and patting it dry with 

tissue. Wiping the electrode dry with a cloth, laboratory tissue, or similar material may cause 

electrode polarization. 

209
4. Safety 

No significant hazard has been identified with this procedure. Follow standard 

laboratory safety precautions. 

5. Equipment 

5.1 Cups, plastic 

5.2 Closed container, with openings (inlet and outlet) providing for humidified airflow. A tube 

from the inlet of this closed container is connected to the outlet of a stoppered 2.5-L 

container full of RO water. A pump supplies air to a bubbling stone placed near the 

bottom of the 2.5-L container (Fig. 1). 

Fig. 1. Apparatus for measuring oxidized pH. 

.4 Electrode, standard glass body combination, Accu-flow, Fisher Scientific 

.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

A. 

. Procedure 

rate the pH meter with pH 4.00 and pH 7.00 buffer solutions. 

e. 

e. 

er 

Stir the slurry thoroughly to introduce air. 

brane are in contact with the mixture. 

1 

H unit.

7.6 Aft n a closed container with openings 

(inlet and outlet) providing for humidified airflow. A tube from the inlet of this closed 

connected to the outlet of a stoppered 2.5-L container full of RO water. A pump 

5.3 Digital pH/ion meter, Accumet Model AR15, Fisher Scientific 

5

6. Reagents 

6

6.2 Borax pH buffers, pH 4.00 and pH 7.00 for pH meter calibration, Beckman, Fullerton, C

7

7.1 Calib

7.2 After equipment calibration, gently wash the electrode with RO water. Dry the electrod

Do not wipe the electrode with a tissue as this may cause a static charge on the electrod

7.3 Transfer enough soil to fill a small plastic cup one-half to two-thirds full. Add a little wat

if needed to make a slurry. 

7.4 Determine immediately the pH of sample by carefully placing the electrode into the soil 

mixture. Ensure that the KCl junction and sensor mem

7.5 Allow the pH meter to stabilize before recording the pH. Record the pH to the nearest 0.0

p

er pH determination, immediately place sample i

container is 

210
supplies air to a bubbling stone placed near the bottom of the 2.5-L container. Keep at room 

.7 Stir the sample and record pH daily. Note any bubbling. After pH determination, 

e sample back in closed container. 

7.8 Rec

temperature (20 to 25°C). 

7

immediately plac

ord the pH for a minimum of 10 days until the change is <0.1 pH units for two days. 

8. C

. Report 

initial pH and the oxidized pH (end pH) to the nearest 0.1 pH unit. 

e SSL upon request. 

classification of acid sulfate soils in 

ins. p. 95-108. In J.A. Kittrick, D.S. Fanning, and L.R. Hossner (eds.) Acid 

Soil S

Organic Materials CaCl2 pH, Final Solution ≈ 0.01 M CaCl2 (4C1a1a4) 

1. Ap

osols 

he control section. 

) of the prepared sample in a 30-mL plastic container and add 4 

mL of 0.015 M CaCl2, i.e., yields final concentration of ≈ 0.01 M CaCl2 with most packed, 

ic materials. Mix, cover, and allow to equilibrate at least 1 h. Uncover and 

measur

3. Interferences 

f organic soil material can be used in field offices. Since it is not practical in 

rmination on a dry sample weight, moist soil is used. The specific 

cking of material must be 

il Survey Staff, 

 the pH electrode by rinsing with reverse osmosis (RO) water and patting it dry 

g the electrode dry with a cloth, laboratory tissue, or similar material may 

ause electrode polarization. 

alculations 

No calculations are required for this procedure. 

9

Report the 

10. Precision and Accuracy 

Precision and accuracy data are available from th

11. References 

Van Breemen, N. 1982. Genesis, morphology, and 

Coastal Pla

sulfate weathering. Soil Soc. Am. Spec. Publ. No.10. ASA and SSSA, Madison, WI. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd. ed. U.S. Govt. 

Print. Office, Washington, DC. 

Reaction (4C) uspensions (4C1) Electrode (4C1a) 

Standard Glass Body Combination (4C1a1) 

Digital pH/Ion Meter (4C1a1a)

plication 

This pH is used in soil taxonomy to distinguish two family reaction classes in Hist

(Soil Survey Staff, 1999). Dysic families have a pH <4.5 in 0.01 M CaCl2 in all parts of the 

organic materials in the control section. Euic families have a pH >4.5 in 0.01 M CaCl2 in some 

part of t

2. Summary of Method 

Place 2.5 mL (2.5 cm3

moist organ

e pH with pH paper or pH meter (4C1a1a4). 

This test o

the field to base a dete

volume of moist material depends on how it is packed. Therefore, pa

standardized in order to obtain comparable results by different soil scientists (So

1999). 

Clean

with tissue. Wipin

c

211
4. Safety 

No signifcant hazard has been identifed with this procedure. Follow standard 

laboratory safety precautions. 

. Equipment 

0 mL 

5.2 Digital pH/ion meter, Accumet Model AR15, Fisher Scientific 

. Reagents

 water 

.2 Calcium chloride (CaCl ), 0.015 M. Dissolve 1.10 g of CaCl ·2H O in RO water and 

for pH meter calibration, Beckman, Fullerton, CA. 

7. Procedure

s dry, add water and let stand to saturate. Place 50 to 60 

L of a representative sample on a paper towel in a linear mound. Roll the towel around the 

ed 

g segments. 

yrophosphate (5B), and pH (4C1a1a4). 

.5 cm3

) of the prepared sample in a 30-mL polycon and add 4 mL of 0.015 

M CaC ly 0.01 M CaCl2 with most packed 

moist organic materials. 

7.6 Mix

easure pH. Rinse electrode with RO water. 

7.8 Alternatively, place pH strip on top of sample so that it wets from the bottom. Close cover 

librate approximately 5 min. Remove pH strip with tweezers. Use a wash 

bott

referen

quired for this procedure. 

nit. 

5

5.1 Polycons, 3

5.3 Electrode, standard glass body combination, Accu-flowt, Fisher Scientific 

5.4 Half-syringe, 6 mL. Cut plastic syringe longitudinally to form a half-cylinder measuring 

device. 

5.5 Metal spatula 

6

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent

6 2 2 2

dilute to 500 mL. 

6.3 Borax pH buffers, pH 4.00 and 7.00, 

Sample Preparation

7.1 Prepare soil material. If the soil i

m

sample and express water if necessary. Use additional paper towels as external blotters. 

Remove the sample and place on a fresh paper towel. The sample should be firm but saturat

with water. 

7.2 Use scissors to cut sample into 0.5- to 1.0-cm lon

7.3 Randomly select sample segments for determination of fiber (5C), solubility in 

p

 

pH Determination

7.4 Use a metal spatula to pack a half-syringe that is adjusted to the 5-mL mark or 2.5-mL (2.5-

cm3

) volume with the moist sample. 

7.5 Place 2.5 mL (2

l2, i.e. yields a final concentration of approximate

, cover, and allow to equilibrate at least 1 h. 

7.7 Uncover, mix again, immerse electrode, and m

and allow to equi

le to gently wash soil from bottom of strip. Compare color of active segment (center) with

ce segments and with pH scale on box to determine pH. 

8. Calculations 

No calculations are re

9. Report

Report the 0.01 M CaCl2 pH to the nearest 0.1 pH u

212
10. Precision and Accuracy

Precision and accuracy data are available from the SSL upon request. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

eting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. 

a) Comb

ry or Field-Moist, <2 mm (4C1a2a1a-b1) 1:2 0.01 M CaCl pH (4C1a2a2) , < 2mm (4C1a2a2a-b1) 

l soil pH is generally less than the 

1:1 wat

d and 

onacid) in families of Entisols and Aquepts (Soil Survey Staff, 1999). The acid class is <5.0 

 (2:1) or ≈ 5.5 in 1:1 water. The nonacid class is >

11. References

and interpr

Print. Office, Washington, DC. 

Reaction (4C) 

Soil Suspensions (4C1) 

Electrode (4C1 ination pH-Reference Electrode (4C1a2) Automatic Titrator (4C1a2a) 

1:1 Water pH (4C1a2a1) 

Air-D

2

Air-Dry or Field Moist

1. Application 

The 1:1 water pH (4C1a2a1) and 1:2 0.01 M CaCl2 pH (4C1a2a2) determinations are 

two commonly performed soil pH measurements. The CaC 2

er pH. The combination of exchange and hydrolysis in salt solutions (0.1 to 1 M) can 

lower the measured pH from 0.5 to 1.5 units, compared to the pH measured in RO water (Foth 

and Ellis, 1988). 

In soil taxonomy, these pH values are used as a criterion for reaction classes (aci

n

pH in 0.01 M CaCl2 5.0 pH in 0.01 M CaCl

(2:1). 

lly measured in water and then measured in CaCl . With the 

additio he 

ccasional stirring. The sample is allowed to stand 1 h with occasional stirring. The sample is 

 s, and the 1:1 water pH is measured. The 0.02 M CaCl (20mL) is added to soil 

suspen

. Interfernces 

ill vary between the supernatant and soil sediment (McLean, 1982). Measure 

rmity. Clays may clog the KCl junction 

trode dry with cloth, 

trode polarization. Rinse the electrode with 

 soil:water mixture. Closed containers and 

ion, 

the p considered, if doing critical work. 

4. S

No significant hazards are associated with the procedure. Follow standard laboratory 

. 

2

 2. Summary of Method 

The pH is measured in soil-water (1:1) and soil-salt (1:2 CaCl2) solutions. For 

convenience, the pH is initia 2

n of an equal volume of 0.02 M CaCl2 to the soil suspension that was prepared for t

water pH, the final soil-solution ratio is 1:2 0.01 M CaCl2. A 20-g soil sample is mixed with 20 mL of reverse osmosis (RO) water (1:1 w:v) with 

o

stirred for 30 2

sion, the sample is stirred, and the 1:2 0.01 M CaCl2 pH is measured (4C1a2a2). 

3

The pH w

the pH just above the soil sediment to maintain unifo

and slow the electrode response. Clean the electrode. Wiping the elec

laboratory tissue or similar material may cause elec

distilled water and pat dry. 

Atmospheric CO2 affects the pH of the

nonporous materials will not allow equilibration with CO2. At the time of pH determinat

artial pressure of CO2 and the equilibrium point must be

afety 

safety practices

213
5. Equipment 

5.1 Measuring scoop, handmade, ≈ 20-g capability 

5.3 Dispenser, 0 to 30 mL, Repipet or equivalent 

.4 Beverage stirring sticks, wood 

akers, polyethylene, 250 mL 

.6 Automatic titrator, Metrohm Titroprocessors, Control Units, Sample Changers, and 

210.100, Brinkmann 

Instruments, Inc. 

. Reagents 

e of reagent water 

.2 Borax pH buffers, pH 4.00, pH 7.00, and pH 9.18, for electrode calibration, Beckman, 

loride (CaCl2), 0.02 M. Dissolve 23.52 g of CaCl2·2H2O in RO water and 

dilute to 8 L. 

. Procedue 

.1 Use a calibrated scoop to measure ≈ 20 g of <2-mm or fine-grind, air-dry soil. If sample is 

.2 Place the sample in a 120-mL (4-oz) paper cup. 

.3 Dispense 20 mL of RO water into sample and stir. 

.4 Place paper cup with sample in 250-mL titration beaker, allow to stand for 1 h, stirring 

eadings, and 

nsing of electrode are controlled by computer. 

.8 The general sequence used by the automated system is as follows: 

.8.1 The sample is lifted so that the pH electrode is positioned above the soil sediment. 

s stirred for 30 s. 

.8.3 After 1 min, 1:1 water pH is read. Record pH to the nearest 0.01 unit. 

7.8.4 T

 pH is read. Record pH to the nearest 0.01 unit. 

.8.6 The sample is lowered, and the electrode and stirrer are rinsed with RO water. 

7.8.7

7.8.8 The cycle is repeated until all samples have been analyzed. 

5.2 Paper cup, 120 mL (4 fl. oz.), disposable, Solo Cup Co., No. 404 

5

5.5 Titration be

5

Dosimats, Metrohm Ltd., Brinkmann Instruments, Inc. 

5.7 Combination pH-reference electrode, Metrohm part no. 6.0

6

6.1 Reverse osmosis (RO) water, ASTM Type III grad

6

Fullerton, CA. 

6.3 Calcium ch

7

7

moist, use calibrated scoop to achieve ≈ 20 g of air-dry soil. 

7

7

7

occasionally. 

7.5 Load beakers into sample changer. 

7.6 Calibrate the pH meter using the pH 9.18, 7.00 and pH 4.00 buffer solutions. 

7.7 Sample stirring, waiting interval for readings, addition of CaCl2 solution, pH r

ri

7

7

7.8.2 The sample i

7

he 20 mL of 0.02 M CaCl2 are added to sample. The sample is stirred for 30 s. 

7.8.5 After 1 min, the 1:2 CaCl2

7

 The next sample is positioned for analysis. 

214
8. C

9. R

uracy 

ata are available from the SSL upon request. 

iley and Sons. NY, NY. 

 lime requirement. p. 199-224. In A.L. Page, R.H. Miller, 

ical and microbiological 

A, Madison, WI. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

eting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. 

4C) oil Suspensions (4C1) 

Comb

H (4C1a2a3) ir-Dry or Field-Moist, <2 mm (4C1a2a3a-b1) 

1. Ap

 in the 

 of Method 

A 20-g soil sample is mixed with 20 mL of 1 N KCl. The sample is allowed to stand for 

asional stirring. The sample is stirred for 30 s, and after 1 min, the KCl pH is read 

(4C1a2

. Interferences 

ence in the sediment and supernatant pH is called the suspension effect 

in determination, measure the pH just above the soil 

ponse. Clean the 

ter and patting it dry with tissue. Wiping the 

al may cause electrode 

4. S

 standard laboratory 

afety practices. 

5.2 Paper cup, 120 mL (4 fl. oz.), disposable, Solo Cup Co., No. 404 

.4 Beverage stirring sticks, wood, FSN 7340-00-753-5565 

akers, polyethylene, 250 mL 

alculations 

No calculations are required for this procedure. 

eport 

Report the 1:1 water pH and the 1:2 0.01 M CaCl2 pH to the nearest 0.1 pH unit. 

10. Precision and Acc

Precision and accuracy d

11. References 

Foth, H.D., and B.G. Ellis. 1988. Soil fertility. John W

McLean, E.O. 1982. Soil pH and

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chem

properties. 2nd ed. Agron. Monogr. 9. ASA and SSS

and interpr

Print. Office, Washington, DC. 

Reaction (

S

Electrode (4C1a) ination pH-Reference Electrode (4C1a2) Automatic Titrator (4C1a2a) 

1 N KCl p A

plication 

The 1 N KCl pH is an index of soil acidity. If KCl pH is <5, significant amounts of Al 

are expected in the solution, and if the pH is very much below 5, almost all the acidity is

form of Al. 

2. Summary

1 h with occ

a3). 

3

The differ

(McLean, 1982). To maintain uniformity 

sediment. Clays may clog the KCl junction and slow the electrode res

electrode by rinsing with reverse osmosis (RO) wa

electrode dry with a cloth, laboratory tissue, or similar materi

polarization. 

afety 

No significant hazards are associated with the procedure. Follow

s

5. Equipment 

5.1 Measuring scoop, handmade, ≈ 20 g 

5.3 Dispenser, 0 to 20 mL, Repipet or equivalent 

5

5.5 Titration be

215
5.6 Automatic titrator, Metrohm Titroprocessors, Control Units, Sample Changers, and 

ents, Inc. 

.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

ullerton, 

CA. 

 L. 

. Procedure 

.1 Use a calibrated scoop to measure ≈ 20 g of <2-mm or fine-grind, air-dry soil. If sample is 

.3 Dispense 20 mL of 1 N KCl into sample and stir with wooden beverage stirrer. 

.4 Place paper cup with sample in 250-mL titration beaker, allow to stand 1 h, stirring 

r table. 

s. 

 are 

ontrolled by computer. 

.8 The general sequence used by the automated system is as follows: 

.8.1 The sample is lifted so that pH electrode is positioned above the soil sediment. 

7.8.2 T

 min, the KCl pH is read. Record pH to the nearest 0.01 unit. 

 

.8.4 The sample is lowered, and the electrode and stirrer are rinsed with RO water. 

7.8.5 T

7.8.6 The cycle is repeated until all samples have been analyzed. 

8. Calculations 

No calculations are required for this procedure. 

9. Report 

Report KCl pH to the nearest 0.1 pH unit. 

10. Precision and Accuracy 

Precision and accuracy data are available upon request from the SSL. 

Dosimats, Metrohm Ltd., Brinkmann Instruments, Inc. 

5.7 Combination pH-reference electrode, Brinkmann Instrum

6. Reagents 

6

6.2 Borax pH buffers, pH 4.00, 7.00, and 9.18 for electrode calibration, Beckman, F

6.3 Potassium chloride (KCl), 1.0 N. Dissolve 74.56 g of KCl in RO water. Dilute to 1

7

7

moist, use calibrated scoop to achieve ≈ 20 g of air-dry soil. 

7.2 Place the sample in a 120-mL (4-oz) paper cup. 

7

7

occasionally. 

7.5 Load beakers into sample change

7.6 Calibrate the pH meter using the pH 4.00, 7.00, and 9.18 buffer solution

7.7 Sample stirring, waiting interval for reading, pH reading, and rinsing of electrode

c

7

7

he sample is stirred for 30 s. 

7.8.3 After 1

7

he next sample is positioned for analysis. 

216
11. References 

McLean, E.O. 1982. Soil pH and lime requirement. p. 199-224. In A.L. Page, R.H. Miller, 

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Soil Test Analyses (4D) 

For more than 30 years, soil testing has been widely used as a basis for determining 

lime and fertilizer needs (Soil and Plant Analysis Council, 1999). In more recent years, some of 

these tests have been employed in more diverse agronomic and environmental uses (SERAIEG, 2000). It is for these reasons that the SSL has expanded its suite of soil test analyses to 

more completely characterize the inorganic and organic N fractions and to provide a number P 

analyses for a broad spectrum of soil applications. 

Methods development in soil P characterization (Bray and Kurtz, 1945; Olsen et al., 

1954; Chang et al., 1957) has been instrumental in developing principles and understanding of 

the nature and behavior of P in soils (Olsen et al., 1982). Amounts, forms, and distribution of 

soil P vary with soil-forming factors (Walker, 1974; Stewart DQG7LHVVHQ, 1987); level and kind of 

added P (Barrow, 1974; Tisdale et al., 1985; Sharpley et al., 1996 ); other soil and land 

management factors (Haynes, 1982; Sharpley, 1985); and soil P-sorption characteristics 

(GoldberJ and Sposito, 1984; Van Riemsdijk et al., 1984; Polyzopoulos et al., 1985; Frossard et 

al., 1993). Knowledge of these factors and their impact upon the fate and transport of soil P has 

been used in developing soil P interpretations for such broad and diverse application as fertility, 

taxonomic classification, genesis and geomorphology models, and environmental studies (Burt 

et al., 2002). 

To characterize the P in the soil system requires the selection of an appropriate method 

of determination. This selection is influenced by many factors, e.g., objectives of study; soil 

properties; sample condition or environment; accuracy; and reproducibility (Olsen and 

Sommers, 1982). Most soil P determinations have two phases, i.e., preparation of a solution 

that contains the soil P or fraction thereof and the quantitative determination of P in the 

solution. Most P analyses of soil solutions have been colorimetric procedures, as they are 

sensitive, reproducible, and lend themselves to automated analysis, accommodating water 

samples, digest solutions, and extracts (SERA-IEG 17, 2000). Inductively coupled plasma 

(ICP) spectrophotometry can also be used for P determination, with the popularity of this 

procedure increasing due to the use of multi-element soil extractants (SERA-IEG 17, 2000). 

Results from colorimetric analyses are not always comparable to those from ICP because ICP 

estimates the total amount of P in solution while the colorimetric procedures measure P that can 

react with the color developing reagent (SERA-IEG 17, 2000). 

The selected colorimetric method for P determination depends on the concentration of 

solution P; concentration of interfering substances in the solution to be analyzed; and the 

particular acid system involved in the analytical procedure (Olsen and Sommers, 1982). The 

SSL determines a number of P analyses, mostly colorimetrically, with the exception of the 

multi-element extractant Mehlich No. 3 (4D6a1a1-18). These P analyses include but are not 

limited to as follows: anion-resin extractable (4D1a1a1a1-2); water soluble (4D2a1a1); Bray P1 (4D3a1); Olsen sodium-bicarbonate (4D5a1); Mehlich No. 3 (4D6a1); citric acid soluble 

(4D7a1); and New Zealand P Retention (4D8a1). The procedures for total P analysis 

(4H1a1a1a1-20, 4H1b1a1a1-11) are described in another section of this manual entitled “Total 

Analysis”. 

Nitrogen is ubiquitous in the environment as it is continually cycled among plants, soil 

organisms, soil organic matter, water and the atomosphere (National Research Council, 1993). 

Nitrogen is one of the most important plant nutrients and forms some of the most mobile 

compounds in the soil-crop system, and as such, is commonly related to water-quality 

problems. Total N includes both organic and inorganic forms. The SSL procedure for total N 

(4H2a2) is described in another section of this manual entitled “Total Analysis”. 

Inorganic N in soils is predominately NO3 and NH4, with nitrite seldom found in 

detectable amounts except in neutral to alkalilne soils receiving NH4 or NH4-producing 

217
fertilizers (Maynard and Kalra, 1993; Mulvaney, 1996). There is considerable diversity among 

laboratories in the extraction and determination of NO3 and NH4 (Maynard and Kalra, 1993). 

Nitrate is water soluble and a number of soil solutions including water have been used as 

extractants, with the most common being KCl (refer to Maynard and Kalra, 1993; and 

Mulvaney, 1996 for review of extractants). The SSL determines inorganic N (nitrate-nitrite) by 

KCl extraction, with a flow injection automated ion analyzer used to measure the soluble 

inorganic nitrate (NO3

-

) (4D9a1a1-2). The nitrate is quantitatively reduced to nitrite by passage 

of the sample through a copperized cadmium column. The nitrite (reduced nitrate plus original 

nitrite) is then determined by diazotizing with sulfanilamide followed by coupling with N-1-

naphthylethylenediamine dihydrochloride. The resulting water soluble dye has a magenta color 

which is read at 520 nm. 

The concept of an organic N fraction that is readily mineralized has been used to assess 

soil N availability in cropland, forests, and waste-disposal sites (Campbell et al, 1993). 

Incubation-leaching techniques have been used to quantify the mineralizable pool of soil 

organic N. These techniques may be aerobic or anerobic. The SSL determines mineralizable N 

(N as NH3) by anaerobic incubation (4D10a1a1). In addition, the SSL also determines 

mineralizable N after fumigation incubation (6B2a1a1), described in another section of this 

manual entitled “Soil Biological and Plant Analyses”. 

References 

Barrow, N.J. 1974. Effect of previous additions of phosphate on phosphate adsorption by soils. 

Soil Sci. 118:82-89. 

Bray, R.H., and L.T. Kurtz. 1945. Determination of total, organic, and available forms of 

phosphorus in soils. Soil Sci. 59:39-45. 

Burt, R., M..D. Mays, E.C. Benham, and M.A. Wilson. 2002. Phosphorus characterization and 

correlation with properties of selected benchmark soils of the United States. Commun. Soil 

Sci. Plant Anal. 33:117-141. 

Campbell, C.A., B.H. Ellert, and Y.W. Jame. 1993. Nitrogen mineralilzation potential in soils. 

p. 341-357. In Martin R. Carter (ed.) Soil sampling and methods of analysis. Can. Soc. Soil 

Sci. Lewis Publ., Boca Raton, FL. 

Chang, S.C., and M.L. Jackson. 1957. Fractionation of soil phosphorus. Soil Sci. 84:133-144. 

Frossard, E., C. Feller, H. Tiessen, J.W.B. Stewart, J.C. Fardeau, and J.L. Morel. 1993. Can an 

isotopic method allow for the determination of phosphate-fixing capacity of soils? Commun. 

Soil Sci. Plant Anal. 24:367-377. 

Haynes, H.R. 1982. Effects of liming on phosphate availability in acid soils. Plant Soil. 63:289-

308. 

Goldberg, S., and G. Sposito. 1984. A chemical model of phosphate adsorption by soils. II. 

Noncalcareous soils. Soil Sci. Soc. Am. J. 48:779-783. 

Maynard, D.G., and Y.P. Kalra. 1993. Nitrate and exchangeable ammonium nitrogen. p. 25-38. 

In Martin R. Carter (ed.) Soil sampling and methods of analysis. Can. Soc. Soil Sci. Lewis 

Publ., Boca Raton, FL. 

Mulvaney, R.L. 1996. Nitrogen – Inorganic forms. p. 1123-1184. In In D.L. Sparks (ed.) 

Methods of soil analysis. Part 3. Chemical methods. No. 5. ASA and SSSA, Madison, WI. 

National Research Council. 1993. Soil and water quality. An agenda for agriculture. Committee 

on long-range soil and water conservation. Natl. Acad. Press, Washington, DC 

Olsen, S.R., and C.V. Cole, F.S. Watanabe, and L.A. Dean. 1954. Estimation of available 

phosphorus in soils by extraction with sodium bicarbonate. USDA Circ. 939. U.S. Govt. 

Print. Office, Washington, DC. 

Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. p. 403-430. In A.L. Page, R.H. Miller, and 

D.R. Kenney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Polyzopoulos, N.A., V.Z. Keramidas, and H. Koisse. 1985. Phosphate sorption by some 

Alfisols as described by commonly used isotherms. Soil Sci. Soc. Am. J. 49:81-84. 

218
SERA-IEG 17. 2000. Methods of phosphorus analysis for soils, sediments, residuals, and 

waters. In G. M. Pierzynski (ed.) Southern Cooperative Series Bull. No. XXX. USDACSREES Regional Committee: Minimizing Agricultural Phosphorus Losses for Protection 

of the Water Resource. 

Sharpley, A.N. 1985. Depth of surface soil-runoff interaction as affected by rainfall, soil, 

slopoe, and management. Soil Sci. Soc. Am. J. 49:1010-1015. 

Sharpley, A.N. 1996. Availability of residual phosphorus in manured soils. Soil Sci. Soc. Am. 

J. 60:1459-1466. 

Stewart, J.W.B, and H. Tiessen. 1987. Dynamics of soil organic phosphorus. Biogeochemistry. 

4:41-60. 

Tisdale, S.L., W.L. Nelson, J.D. Beaton. 1985. Soil fertililty and fertilizers. 4th ed. Macmillan 

Publ. Co., New York, NY. 

Van Riemsdijk, W.H., A.M.A. Van der Linden, and L.J.M. Boumans. 1984. Phosphate sorption 

by soils. III. The diffusioin-precipitation model tested for three acid sandy soils. Soil Sci. 

Soc. Am. J. 48:545-548. 

Walker, T.W. 1974. Phosphorus as an index of soil development. Trans. Int. Congr. Soil Sci. 

10:451-457. 

Soil Tests (4D) 

Anion Resin Extraction (4D1) 

Two-Point Extraction (4D1a) 

1-h, 24-h, 1 M NaCl (4D1a1a1) UV-Visible Spectrophotometer, Dual-Beam (4D1a1a1a) 

Phosphorus, Two points (4D1a1a1a1-2) 

Air-dry or Field-Moist, <2 mm (4D1a1a1a1-2a-b1) 

1. Application 

Anion resins remove P from soils without chemical alterations and only minor pH 

changes. Amounts of P released from soil and adsorbed by resins have been used as a measure 

of available P; an assessment of the availability of residual phosphates; estimation of release 

characteristics and runoff P for agricultural land (Elrashidi, et al., 2003); and the buffer 

capacity of soils (Olsen and Sommers, 1982). 

Plotting g log of extraction periods (0.25, 0.50, 1, 2, 4, 8, 24, 48 h) against amounts of P 

released (mg kg-1) showed a linear relationship in 24 U.S. benchmark soils (Elrashidi et al., 

2003). Two extraction periods (1 and 24 h) are sufficient to develop linear equations that 

predict P release characteristics (PRC), describing the whole relationship between the 

extraction time (1 min to 48 h) and amount of P released (mg kg-1) for soils (Elrashidi et al., 

2003). The method describes a two-point measurement (1 and 24 h extraction). 

2. Summary of Method A 2-g soil sample and 4-g resin bag are shaken with 100 mL of reverse osmosis 

deionized water for 1 h. Soil suspension is shaken again with another 4-g resin bag for 23 h. 

Phosphorus released from soil during shaking is adsorbed by resin. To remove P from resin, 

resin bags are shaken for 1 h in 1 M NaCl solution. Concentrated HCl is added to sample 

extracts. A 1-mL aliquot is diluted with 4 mL of ascorbic acid molybdate solution. Absorbance 

of the solution is read using a spectrophotometer at 882 nm. Data are reported as mg P kg-1 soil 

(4D1a1a1a1-2). 

 

3. Interferences 

The Mo blue methods, which are very sensitive for P, are based on the principle that in 

an acid molybdate solution containing orthophosphate ions, a phosphomolybdate complex 

forms that can be reduced by ascorbic acid, SnCl2, and other reducing agents to a Mo color. 

The intensity of blue color varies with the P concentration but is also affected by other factors 

219
such as acidity, arsenates, silicates, and substances that influence the oxidation-reduction 

conditions of the system (Olsen and Sommers, 1982). 

 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated H2SO4 and HCl to a fume 

hood. Use safety showers and eyewash stations to dilute spilled acids and bases. Use sodium 

bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Mechanical reciprocating shaker, 100 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Bottles, polyethylene, 250, 125, and 60 mL 

5.4 Funnel, 60° angle, long stem, 50-mm diameter 

5.5 Filter paper, Whatman 42, 150 mm 

5.6 Cups, plastic 

5.7 Dispenser, 50 mL 

5.8 Pipettes, electronic digital, 2500 μL and 10 mL, with tips 2500 μL and 10 mL 

5.9 Cuvettes, plastic, 4.5-mL, 1-cm light path, Daigger Scientific 

5.10 Spectrophotometer, UV-Visible, Dual-View, Varian, Cary 50 Conc, Varian Australia Pty 

Ltd. 

5.11 Computer, with Cary WinUV software, Varian Australia Pty Ltd., and printer 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Anion exchange resin (AER), DOWEX Marathon, type II, 510-610 μm spherical beads 

(DOW Chemical Company), converted to bicarbonate form by soaking bags overnight in 

1.0 M NaHCO3 solution and washing out excess salt with RODI water. Store in RODI 

water in refrigerator. 

6.3 Nitex nylon fabric, 300-μm pores, and nylon thread, Sefar America, Inc., for making and 

sewing resin bags 

6.4 Hydrochloric acid (HCl), concentrated, 12 N, trace pure grade 

6.5 NaCl solution. Dissolve 58.4 g NaCl in 1000 mL RODI water. 

6.6 Sulfuric-tartarate-molybdate solution (STMS). Dissolve 60 g of ammonium molybdate 

tetrahydrate [(NH4)6Mo7O24·4H2O] in 200 mL of boiling RODI water. Allow to cool to 

room temperature. Dissolve 1.455 g of antimony potassium tartarate (potassium 

antimony tartarate hemihydrate [K(SbO)C4H4O6·1/2H2O] in the ammonium molybdate 

solution. Slowly and carefully add 700 mL of concentrated H2SO4. Cool and dilute to 1 

L with RODI water. Store in a dark bottle in the refrigerator. 

6.7 Ascorbic acid solution. Dissolve 13.2 g of ascorbic acid in RODI water and dilute to 100 

mL with RODI water. Make fresh daily. 

6.8 Working ascorbic acid molybdate solution (WAMS). Mix 25 mL of STMS solution with 

800 mL of RODI water. Add 10 mL of ascorbic acid solution and dilute to 1 L with 

RODI water. Allow to stand at least 1 h before using. Prepare fresh daily. 

6.9 Working stock standard P solution (WSSPS), 100.0 mg P L-1. In a 1-L volumetric flask, 

dissolve 0.4394 g primary standard grade anhydrous potassium dihydrogen phosphate 

(KH2PO4) that has been dried for 2 h at 110°C in about 800 mL 1.0 M NaCl. Dilute to 

volume with NaCl solution and invert to mix thoroughly. Store in a polyethylene bottle. 

Make fresh weekly. Store in a refrigerator. 

220
6.10 Standard P calibration solutions (SPCS) or working standards, 4.0, 3.0, 2.0, 1.0, 0.5, 0.25, 

and 0.0 mg P L-1. Prepare fresh weekly. Store in a refrigerator. Allow to equilibrate to 

room temperature before use. To seven 100-mL volumetric flasks add as follows: 

6.10.1 4.0 mg P L-1 = 4.0 mL WSSPS 

6.10.2 3.0 mg P L-1 = 3.0 mL WSSPS

6.10.3 2.0 mg P L-1 = 2.0 mL WSSPS 

6.10.4 1.0 mg P L-1 = 1.0 mL WSSPS 

6.10.5 0.5 mg P L-1 = 0.5 mL WSSPS 

6.10.6 0.25 mg P L-1 = 0.25 mL WSSPS 

6.10.7 0.0 mg P L-1 = 0.0 mL WSSPS 

Add 70 mL of 1.0 M NaCl solution and 4.0 mL of concentrated HCl to each SPCS. Allow to 

cool and dilute to mark with 1.0 M NaCl solution. Invert to mix thoroughly. 

6.11 Quality Control Samples: 0.1 mg L-1 solution made from SSPS; blanks; selected SPCS; 

and SSL standard. 

7. Procedure 

7.1 Weigh 2 g of <2-mm or fine-grind, air-dry soil to nearest mg on an electronic balance and 

place in a 250-mL polyethylene bottle. Add 100 mL RODI water to bottle. Use two replicates 

for each soil sample in addition to a control treatment where all steps of the extraction process 

are performed in the absence of soil. 

7.2 Place 4-g resin bag in the soil suspension and control sample. Transfer sample to shaker. 

Shake for 1 h at 100 oscillations min-1 at room temperature (20°C ± 2°C). After shaking, 

remove P from resin as described in Section 7.4 and then proceed with Sections 7.5 – 7.14. 

7.3 Place another 4-g resin bag in the soil suspension and control sample. Transfer sample to 

shaker. Shake for 23 h at 100 oscillations min-1 at room temperature (20°C ± 2°C). After 

shaking, remove P from resin as described in Section 7.4 and then proceed with Sections 7.5 – 

7.14. 

7.4 Remove P from resin by lifting resin bag out of soil suspension and rinsing with 5 mL 

RODI water to remove attached soil particles. Add RODI water to soil suspension. If 

necessary, keep soil suspension for the next extraction. 

7.5 Place resin bag in a 125-mL polyethylene bottle containing 50 mL of 1.0 M NaCl solution. 

7.6 Transfer bottle to shaker and shake for 1 h at 100 oscillations min-1 at room temperature (20 

°C± 2°C). 

7.7 Transfer extracting solutions to 60-mL polyethylene bottles. Filter if soil particles are 

observed in the extract. Add 2 mL concentrated HCl to each bottle. If extracts are not to be 

determined immediately after collection, then store samples at 4°C. Analyze samples within 72 

h. 

7.8 Use the pipette to transfer a 1-mL aliquot of the sample to a plastic cup. Also transfer a 1-

mL aliquot of the each SPCS to a plastic cup. Use a clean pipette tip for each sample and 

SPCS. 

221
7.9 Dispense 4 mL of the WAMS to sample aliquot and to each SPCS. Swirl to mix. The color 

reaction requires a minimum of 20 min before analyst records readings. Complete all readings 

within 2-h period since blue color may fade after this period. 

7.10 Transfer sample extract and SPCS to cuvettes. 

7.11 Set the spectrophotometer to read at 882 nm. Autozero with calibration blank. 

7.12 Calibrate the instrument using the SPCS. The data system will then associate the 

concentrations with the instrument responses for each SPCS. Rejection criteria for SPCS, if R2

<0.99. 

7.13 Run samples using calibration curve. Sample concentration is calculated from the 

regression equation. Rejection criteria for batch, if blanks as samples >0.01: If SPCS as 

samples >±20%; and if SSL standard >± 20% mean. Record results to the nearest 0.01unit for 

the sample extract and each SPCS. 

7.14 If samples are outside the calibration range, dilute sample extracts with extracting solution 

and re-analyze. 

8. Calculations 

Convert extract P (mg L-1) to soil P (mg kg-1) as follows: 

Soil P (mg kg -1) =[ (A x B x C x R x 1000)/E] 

where: 

A = Sample extract reading (mg L-1) 

B = Extract volume (L) (0.055) 

C = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report 

Report data to the nearest 0.1 mg P kg-1 soil. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Elrashidi, M.A., M.D. Mays, and P.E. Jones. 2003. A technique to estimate release 

characteristics and runoff phosphorus for agricultural land. Commun. Soil Sci. and Plant 

Anal. 34:1759-1790. 

Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. p. 403-430. In A.L. Page, R.H. Miller, 

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

222
Soil Tests (4D) 

Aqueous Extraction (4D2) 

Single-Point Extraction (4D2a) 

1:10, 30 min (4D2a1) 

UV-Visible Spectrophotometer, Dual-Beam (4D2a1a) 

Phosphorus (4D2a1a1) 

Air-dry or Field-Moist, <2 mm (4D2a1a1a-b1) 

 

1. Application 

Phosphorus occurs in soil in both the solution and solid phase. These forms are well 

documented but questions still remain concerning the exact nature of the constituents and ionic 

forms found in water, soils, and sediments (National Research Council, 1993). These forms 

influence P availability in relation to root absorption and plant growth; runoff and water quality 

problems; and P loadings. 

Water soluble P has been defined as P measured in water, dilute salt extracts (e.g., O.01

M CaCl2), displaced soil solutions, or saturation paste extracts (Olsen and Sommers, 1982). 

Even though the water soluble fraction principally consists of inorganic orthophosphate ions, 

there is evidence that some organic P is also included (Rigler, 1968). 

The water or dilute salt extracts represent an attempt to approximate the soil solution P 

concentration. As an index of P availability, the objectives of this method are (1) to determine 

the P concentration level in the soil extract that limits plant growth (Olsen and Sommers, 1982) 

and (2) to determine the composition of the soil solution so that the chemical environment of 

the plant roots may be defined in quantitative terms (Adams, 1974). The sum of water soluble 

P and pH 3 extractable P has also been defined as the available P in runoff (Jackson, 1958). 

2. Summary of Method A 2.5-g sample of <2-mm, air-dry soil is mechanically shaken for 30 min in 25-mL of 

reverse osmosis deionized water. The sample is then centrifuged until solution is free of soil 

mineral particles, and then filtered until clear extracts are obtained. Absorbance of the solution 

is read using a spectrophotometer at 882 nm. Data are reported as mg P kg-1 soil (4D2a1a1). 

3. Interferences 

The Mo blue methods, which are very sensitive for P, are based on the principle that in 

an acid molybdate solution containing orthophosphate ions, a phosphomolybdate complex 

forms that can be reduced by ascorbic acid, SnCl2, and other reducing agents to a Mo color. 

The intensity of blue color varies with the P concentration but is also affected by other factors 

such as acidity, arsentes, silicates, and substances that influence the oxidation-reduction 

conditions of the system (Olsen and Sommers, 1982). 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated H2SO4 and HCl to a fume 

hood. Use safety showers and eyewash stations to dilute spilled acids and bases. Use sodium 

bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Centrifuge tubes, 50-mL, polyethylene 

5.4 Filter paper, Whatman No. 42, 150 mm 

5.5 Funnel, 60° angle, long stem, 50-mm diameter 

223
5.6 Centrifuge, Centra GP-8, Thermo IEC, Needham Heights, MA 

5.7 Volumetric flasks, 2-L, 100-mL, and 25-mL 

5.8 Bottles, plastic, dark, 2-L 

5.9 Pipettes, electronic digital, 2500 μL and 10 mL, with tips 2500 μL and 10 mL 

5.10 Cups, plastic 5.11 Cuvettes, plastic, 4.5-mL, 1-cm light path, Daigger Scientific 

5.12 Dispenser, 30 mL or 10 mL 

5.13 Spectrophotometer, UV-Visible, Varian, Cary 50 Conc, Varian Australia Pty Ltd. 

5.14 Computer, with Cary WinUV software, Varian Australia Pty Ltd., and printer 

6. Reagents

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Sulfuric acid (H2SO4), concentrated, 36 N, trace pure grade 

6.3 Molybdate solution. Dissolve 12.0 g ammonium molybdate tetrahydrate 

[(NH4)6Mo7O24·4H2O] in approximately 250 mL RODI water. Dissolve 0.2908 potassium 

antimony tartarate [K(SbO)C4H4O6·1/2H2O] in 100 mL RODI water. Add these two 

dissolved reagents to 1-L 5 N H2SO4 (141 mL conc. H2SO4 diluted to 1-L), mix 

thoroughly, and dilute with RODI water to 2-L. Store in dark bottle and refrigerate 

(reagent A). 

6.4 Ascorbic acid: Dissolve 2.112 g of ascorbic acid in 400 mL of reagent A and mix 

(reagent B). Prepare fresh daily. 

6.5 Stock standard P solution (SSPS), 100.0 mg P L-1. In a 1-L volumetric flask, dissolve 

0.4394 g primary standard grade anhydrous potassium dihydrogen phosphate (KH2PO4) 

that has been dried for 2 h at 110°C in about 800 mL RODI water. Dilute to volume with 

RODI water and invert to thoroughly mix. Store in polyethylene containers. Make fresh 

weekly. Store in a refrigerator. 

6.6 Working stock standard P solution (WSSPS), 10.0 mg P L-1. In a 1-L volumetric flask, 

pipet 100 mL SSPS and in 700 mL RODI water. Dilute to volume with RODI water and 

invert to thoroughly mix. Make fresh daily. 6.7 Standard P calibration solutions (SPCS) or working standards, 0.8, 0.6, 0.4, 0.2, and 0.0 

mg P L-1. Make fresh daily. To five 25-mL volumetric flasks add as follows: 

6.7.1 0.8 mg P L-1 = 2.0 mL WSSPS 

6.7.2 0.6 mg P L-1 = 1.5 mL WSSPS 

6.7.3 0.4 mg P L-1 = 1.0 mL WSSPS 

6.7.4 0.2 mg P L-1 = 0.5 mL WSSPS 

6.7.5 0.0 mg P L-1 = 0.0 mL WSSPS (blank) 

Add 4 mL reagent B, dilute each SPCS to mark with RODI water (extracting solution), and 

invert to thoroughly mix. 

6.8 Quality Control Samples: 0.1 mg L-1 solution made from SSPS; blanks; and selected 

SPCS. In addition, SSL soil standard is routinely included in a batch for quality control. 

7. Procedure 

7.1 Weigh 2.5 g of <2-mm or fine-grind, air-dry soil to nearest mg on an electronic balance and 

place into a 50-mL centrifuge flask. If sample is moist, weigh enough soil to achieve ≈ 2.5 g of 

air-dry soil. 

7.2 Add 25.0 mL of RODI water to sample. Place the sample in shaker and shake for 30 min at 

200 oscillations min-1 at room temperature (20°C± 2°C). 

224
7.3 Remove the sample from the shaker. Centrifuge at 3000 rpm for 20 min, decant, filter, and 

collect extract in receiving cup. If extracts are not to be determined immediately after 

collection, then store samples at 4°C. Analyze samples within 24 h. 

7.4 Pipet 2-mL of sample extract into plastic cup, add 4-mL reagent B and 19 mL RODI water. 

Color is stable for 24 h. Maximum intensity develops in 10 min. 

7.5 Transfer SPCS and sample extracts into 4.5-mL cuvettes. 

7.6 Set spectrophotometer to 882 nm. Autozero with calibration blank. 

7.7 Calibrate the instrument using the SPCS. The data system will then associate the 

concentrations with the instrument responses for each SPCS. Rejection criteria for SPCS, if R2

<0.99.

7.8 Run samples using calibration curve. Sample concentration is calculated from the 

regression equation. Rejection criteria for batch, if blanks as samples > 0.01; if SPCS as 

samples > ± 20%; and if SSL standard > ± 20% mean. Record results to the nearest 0.01 unit 

for the sample extract and each SPCS. 

7.9 If samples are outside the calibration range, dilute samples with extracting solution and rerun. 

 

8. Calculations 

Convert extract P (mg L-1) to soil P (mg kg-1) as follows: 

Soil P (mg kg-1) = [(A x B x C1 x C2 x R x 1000)/E] 

where: 

A = Sample extract reading (mg kg-1) 

B = Extract volume (L) 

C1 = Dilution, required 

C2 = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report 

Report data to the nearest 0.1 mg P kg-1 soil. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Adams, F. 1974. Soil solution. p. 441-481. In E.W. Carson (ed.) The plant root and its 

environment. Univ. Press of Virginia, Charlottesville, VA. 

Jackson, M.L. 1958. Soil chemical analysis. Prentice-Hall, Inc., Englewood Cliffs, N.J. 

National Research Council. 1993. Soil and water quality. An agenda for agriculture. 

Committee on long-range soil and water conservation. Natl. Acad. Press, Washington, 

DC. 

Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. p. 403-430. In A.L. Page, R.H. Miller, 

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

225
Rigler, F.W. 1968. Further observations inconsistent with the hypothesis that the 

molybdenum blue method measures orthophosphate in lake water. Limnology and 

Oceanography 13:7-13. 

Sharpley, A.N., and R.G. Menzel. 1987. The impact of soil and fertilizer phosphorus on 

the environment. Adv. Agron. 41:297-324. 

U.S. Department of Interior, U.S. Geological Survey. 1993. Methods for determination of 

inorganic substances in water and fluvial sediments. Book 5. Chapter Al. Method I2601-78. 

U.S. Environmental Protection Agency. 1983. Methods for chemical analysis of water and 

wastes. EPA-600/4-79-020. Revised March, 1983, Method 365.1. 

Soil Tests (4D) 

Aqueous Extraction (4D2) 

Single-Point Extraction (4D2a) 

1:10, 30 min (4D2a1) 

Flow Injection, Automated Ion Analyzer (4D2a1b) 

Phosphorus (4D2a1b1) 

Air-Dry or Field-Moist, < 2 mm (4D2a1b1a-b1) 

1. Application 

Phosphorus occurs in soil in both the solution and solid phase. These forms are well 

documented but questions still remain concerning the exact nature of the constituents and ionic 

forms found in water, soils, and sediments (National Research Council, 1993). These forms 

influence P availability in relation to root absorption and plant growth; runoff and water quality 

problems; and P loadings. 

Water soluble P has been defined as P measured in water, dilute salt extracts (e.g., 0.01

M CaCl2), displaced soil solutions, or saturation paste extracts (Olsen and Sommers, 1982). 

Even though the water soluble fraction principally consists of inorganic orthophosphate ions, 

there is evidence that some organic P is also included (Rigler, 1968). 

The water or dilute salt extracts represent an attempt to approximate the soil solution P 

concentration. As an index of P availability, the objectives of this method are (1) to determine 

the P concentration level in the soil extract that limits plant growth (Olsen and Sommers, 1982) 

and (2) to determine the composition of the soil solution so that the chemical environment of 

the plant roots may be defined in quantitative terms (Adams, 1974). The sum of water soluble 

P and pH 3 extractable P has also been defined as the available P in runoff (Jackson, 1958). 

2. Summary of Method A 2.5-g sample of <2-mm, air-dry soil is mechanically shaken for 30 min in 25-mL of 

reverse osmosis deionized water (RODI). The sample is then centrifuged until solution is free 

of soil mineral particles, and then filtered until clear extracts are obtained. 

A flow injection automated ion analyzer is used to measure the orthophosphate ion 

(PO4

3-). This ion reacts with ammonium molybdate and antimony potassium tartrate under 

acidic conditions to form a complex. This complex is reduced with ascorbic acid to form a blue 

complex which absorbs light at 880 nm. Absorbance is proportional to the concentration of 

PO4

3- in the sample. Data are reported as mg P kg-1 soil (4D2a1b1). 

3. Interferences 

Silica forms a pale blue complex which also absorbs at 880 nm. This interference is 

generally insignificant as a Si concentration of approximately 30 mg SiO2 L-1 would be 

required to produce a 0.005 mg P L-1 positive error in orthophosphate (LACHAT, 1993). 

Glassware contamination is a problem in low-level P determinations. Glassware should 

be washed with 1:1 HCl and rinsed with deionized water. Commercial detergents should rarely 

be needed but, if they are used, use P-free preparation for lab glassware (LACHAT, 1993). 

226
Concentrations of ferric ion >50 mg L-1 will cause a negative error due to competition 

with the complex for the reducing agent ascorbic acid. Samples high in Fe can be pretreated 

with sodium bisulfite to eliminate this interference. Treatment with bisulfite will also remove 

the interference due to arsenates (LACHAT, 1993). 

4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated H2SO4 and HCl to a fume 

hood. Use safety showers and eyewash stations to dilute spilled acids and bases. Use sodium 

bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Centrifuge tubes, 50-mL, polyethylene 

5.3 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.4 Centrifuge, Centra GP-8, Thermo IEC, Needham Heights, MA 

5.5 Filter paper, Whatman No. 42, 150 mm 

5.6 Funnel, 60° angle, long stem, 50-mm diameter 

5.7 Volumetric flasks, 1-L and 250-mL 

5.8 Bottles, plastic, dark, 1-L 

5.9 Cups, plastic 

5.10 Flow Injection Automated Ion Analyzer, QuikChem AE, LACHAT Instruments, 

Milwaukee, WI, with computer and printer 

5.11 XYZ Sampler, LACHAT Instruments, Milwaukee, WI 

5.12 Reagent Pump, LACHAT Instruments, Milwaukee, WI 

5.13 Automated Dilution Station, LACHAT Instruments, Milwaukee, WI 

5.14 Sample Processing Module (SPM) or channel, QuikChem Method (10-115-01-1-A, 

orthophosphate in waters, 0.01 to 2.0 mg P L-1), LACHAT Instruments, Milwaukee, WI 

5.15 Computer, with QuikChem software, LACHAT Instruments, Milwaukee, WI, and printer 

5.16 Pipettes, electronic digital, 2500 μL and 10 mL, with tips, 2500 μL and 10 mL 

5.17 Vials, plastic, 25-mL (standards) 

5.18 Culture tubes, glass, 10-mL (samples) 

5.19 Dispenser, 30 mL or 10 mL 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Helium, compressed gas 

6.3 Sulfuric acid (H2SO4), concentrated, 36 N, trace pure grade 

6.4 Stock ammonium molybdate solution. In 1-L volumetric flask dissolve 40.0 g ammonium 

molybdate tetrahydrate [(NH4)6Mo7O24·4H2O] in approximately 800 mL RODI water. 

Dilute to the mark with RODI water and invert to thoroughly mix. Stir for 4 h. Store in 

plastic and refrigerate. 

6.5 Stock antimony potassium tartrate solution. In 1-L flask, dissolve 3.0 g antimony 

potassium tartrate (potassium antimony tartrate hemihydrate [K(SbO)C4H4O6·1/2H2O] in 

approximately 800 mL RODI water. Dilute to the mark and invert to thoroughly mix. 

Store in dark bottle and refrigerate. 

6.6 Molybdate color reagent. In 1 L volumetric flask, add about 500 mL RODI water, then 

add 35.0 mL concentrated sulfuric acid (CAUTION: The solution will get very hot!). 

Swirl to mix. When it can be comfortably handled, add 72 mL stock antimony potassium 

tartrate solution and 213 mL stock ammonium molybdate solution. Dilute to volume 

with RODI water and invert three times. Degas with helium ≈ 5 min. 

227
6.7 Ascorbic acid reducing solution. In l-L volumetric flask, dissolve 60.0 g ascorbic acid in 

about 700 mL RODI water. Dilute to volume with RODI water and invert three times. 

Degas with helium ≈ 5 min. Optional: After dilution to volume and degassing, dissolve 

1.0 g dodecyl sulfate (CH3(CH2)11OSO3Na). Prepare fresh weekly. 

6.8 Sodium hydroxide - EDTA rinse. Dissolve 65 g sodium hydroxide (NaOH) and 6 g 

tetrasodium ethylenediamine tetraacetic acid (Na4EDTA) in 1.0 L RODI water. 

6.9 Stock standard P solution (SSPS), 100.0 mg P L-1 (ppm). In a 1-L volumetric flask, 

dissolve 0.4394 g primary standard grade anhydrous potassium dihydrogen phosphate 

(KH2PO4) that has been dried for 2 h at 110°C in about 800 mL RODI water. Dilute to 

volume and invert to thoroughly mix. Do not degas. Store in polyethylene containers. 

Make fresh weekly. Store in a refrigerator. 

6.10 Working stock standard P solution (WSSPS), 10.0 mg P L-1. In a 1-L volumetric flask, 

dilute 100.0 mL SSPS to mark with RODI water. Invert to thoroughly mix. Make fresh 

daily. 

6.11 Standard P calibration solutions (SPCS) or working standards, 2.0, 1.0, 0.5, 0.20, 0.05, 

0.01, and 0.00 mg P L-1. Make fresh daily. To seven 250-mL volumetric flasks add as 

follows: 

6.11.1 2.0 mg P L-1 = 50.0 mL WSSPS 

6.11.2 1.0 mg P L-1 = 25.0 mL WSSPS 

6.11.3 0.5 mg P L-1 = 12.5 ml WSSPS 

6.11.4 0.20 mg P L-1 = 5.0 mL WSSPS 

6.11.5 0.05 mg P L-1 = 1.25 mL WSSPS 

6.11.6 0.01 mg P L-1 = 0.25 mL WSSPS 

6.11.7 0.00 mg P L-1= 0 mL WSSPS (blank) 

Dilute each SPCS to the mark with RODI water and invert to thoroughly mix. Do not degas. 

7. Procedure 

7.1 Weigh 2.5 g of <2-mm or fine-grind, air-dry soil to nearest mg on an electronic balance and 

place into a 50-mL centrifuge tube. If sample is moist, weigh enough soil to achieve ≈ 2.5 g of 

air-dry soil. 

7.2 Add 25.0 mL of RODI water to sample. Transfer the sample to the shaker. Shake for 30 

min at 200 oscillations min-1 at room temperature (20°C± 2°C). 

7.3 Remove the sample from the shaker. Centrifuge at 2000 rpm for 10 min decant, filter, and 

collect extract in receiving cup. 

7.4 Transfer sample extracts into culture tubes and place in XYZ sample trays marked 

"Samples". If extracts are not to be determined immediately after collection, then store samples 

at 4°C. Analyze samples within 24 h. 

7.5 Transfer SPCS standards into plastic vials and place in descending order in XYZ sample 

trays marked "Standards". 

7.6 Refer to the operating and software reference manuals for LACHAT set-up and operation. 

7.7 Turn main power switch "ON" and allow 15 min for heater module to warm up to 37°C. 

7.8 On reagent pump, set speed to 35. Pump RODI water through system for 20 min. 

228
7.9 On computer main menu, select "Methods" and then "Analysis Select and Download". On 

method list, select water soluble P method. System unit receives the downloaded method and 

initializes it. 

7.10 Pump reagents into manifold. Continue this step and observe baseline. A good baseline 

needs to be smooth and at zero absorbance. Scatter is indicative of air bubbles and irregular 

reagent flow. Also observe for any back-pressure in manifold tubing. 

7.11 On computer main menu, select "Samples", "Tray Definition and Submit", and then "Edit" 

to create new sample tray followed by "Submit" to run new sample tray. 

7.12 Method parameters specific to water soluble P are defined within the "Method Definition" 

menu. Some of these parameters have been modified from the QuikChem Method 10-115-01-

1-A, orthophosphate in waters (U.S. Environmental Protection Agency, 1983; LACHAT 

Instruments, 1993; U.S. Department of Interior, Geological Survey 1993). Modifications are 

primarily related to the criteria and strategies for calibration standards and to injection timing. 

7.13 Some of the method parameters as they relate to calibration standards are as follows: 

7.13.1 There are 7 calibration standards (2.00, 1.00, 0.50, 0.20, 0.05, 0.01, and 0.00 mg P L-1) 

with a data format of ####.###, i.e., data rounded to 3 places. 

7.13.2 The segments/boundaries for the calibration standards are A - D (2.0 to 0.20 mg P L-1) 

and D - G (0.20 to 0.00 mg P L-1). 

7.13.3 The protocol (replications) for the calibration standards is as follows: AA BB CCC 

DDDD EEEE FFFF GG 

7.13.4 The check standard is 2.0 mg P L-1. Maximum number of consecutive trays between 

check standard is one; maximum number of consecutive samples between check standard is 60; 

and maximum elapse time between check standards is 2 h. 

7.13.5 Calibration strategy for segments A - D and D - G are normal. The normal strategy 

requires a minimum correlation coefficient of 0.99. Both segments require a maximum 

standard deviation in slope of 50%. A calibration passes only when both criteria are met. 

Strategies are user designated. In addition, calibration strategies are based on the full chord. 

Chord 0 is full chord, and chord 1 - 5 are sections of peak from start of peak to end of peak. 

7.13.6 The instrument is calibrated with the injection of SPCS. The data system then associates 

the concentrations with the instrument response for each SPCS. 

7.14 Method parameters in relation to timing are as follows: 

7.14.1 Cycle period: 40 s 

7.14.2 Inject to start of peak period: 18 s. To see if peaks are being timed correctly, scan across 

correlation coefficients for all chords 1 - 5. The most peak area should be between chords 2 - 4 

with the most signal-to-noise ratio in chords 1 and 5. 

7.14.3 Inject to end of peak period: 52 s 

7.14.4 Automatic timing, where standard assumptions are in effect; no manual timing. 

7.15 Method parameters in relation to data presentation are as follows: 

229
7.15.1 Top Scale Response: 0.50 abs 

7.15.2 Bottom Scale Response: 0.00 abs 

7.16 Method parameters in relation to data results are as follows: 

7.16.1 Set Default Chord to 3. This change must be made to both the sample and the 

calibration RDF's. 

7.17 Refer to the "Method Definition" for water soluble P for other method parameters not 

discussed here. 

7.18 Run samples using calibration curve. Sample concentration is calculated from the 

regression equations. Report results to the nearest 0.01 unit for the sample extract and each 

SPCS. 

7.19 If samples are outside calibration range, dilute samples with extracting solution and reanalyze. 

7.20 Upon completion of run, place the transmission lines into the NaOH - EDTA solution. 

Pump the solution for approximately 5 min to remove any precipitated reaction products. Then 

place these lines in RODI water and pump for an additional 5 min and proceed with the normal 

"Shut-down" procedure. 

8. Calculations 

Convert extract P (mg L-1) to soil P (mg kg-1) as follows: 

Soil P (mg kg-1) = [(A x B x C x R x 1000/E] 

where: 

A = Sample extract reading (mg L-1) 

B = Extract volume (L) 

D = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report 

Report data to the nearest 0.1 mg P kg-1 soil. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Adams, F. 1974. Soil solution. p. 441-481. In E.W. Carson (ed.) The plant root and its 

environment. Univ. Press of Virginia, Charlottesville. 

Jackson, M.L. 1958. Soil chemical analysis. Prentice-Hall, Inc., Englewood Cliffs, NJ. 

LACHAT Instruments. 1993. QuikChem method 10-115-01-1-A, orthophosphate in 

waters, 0.02 to 2.0 mg P L-1. LACHAT Instruments, 6645 West Mill Rd., Milwaukee, 

WI. 

230
National Research Council. 1993. Soil and water quality. An agenda for agriculture. 

Committee on long-range soil and water conservation. Natl. Acad. Press, Washington, 

DC. 

Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. p. 403-430. In A.L. Page, R.H. Miller, 

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Rigler, F.W. 1968. Further observations inconsistent with the hypothesis that the 

molybdenum blue method measures orthophosphate in lake water. Limnology and 

Oceanography 13:7-13. 

Sharpley, A.N., and R.G. Menzel. 1987. The impact of soil and fertilizer phosphorus on 

the environment. Adv. Agron. 41:297-324. 

 

Soil Tests (4D) 

Bray P-1 Extraction (4D3) 

UV-Visible Spectrophotometer, Dual-Beam (4D3a) 

Phosphorus (4D3a1) 

Air-Dry or Field-Moist, <2 mm (4D3a1a-b1) 

1. Application 

The Bray P-1 procedure is widely used as an index of available P in the soil. Bray and 

Krutz (1945) originally designed the Bray P-1 extractant to selectively remove a portion of the 

adsorbed form of P with the weak, acidified ammonium fluoride solution. Adsorbed 

phosphorus is the in the anion form adsorbed by different charged surface functional groups 

that have varying degrees of adsorption affinity. In general, this method has been most 

successful on acid soils (Olsen and Sommers, 1982). The acid solubilizes calcium and 

aluminum phosphates, and partially extracts iron phosphates compounds. The NH4F 

complexes the aluminum in solution and limits readsorption of P on iron oxides (Kuo, 1996). 

The Bray P-1 has limited ability to extract P in calcareous soils due to the neutralization of the 

dilute acid by carbonates. 

2. Summary of Method A 2.5-g soil sample is shaken with 25 mL of Bray P-1 extracting solution for 15 min. 

The sample is centrifuged until solution is free of soil mineral particles, and then filtered until 

clear extracts are obtained. A 2-mL aliquot is diluted with 8-mL of ascorbic acid molybdate 

solution. Absorbance of the solution is read using a spectrophotometer at 882 nm. Data are 

reported as mg P kg-1 soil (4D3a1). 

3. Interferences 

Many procedures may be used to determine P. Studies have shown that incomplete or 

excessive extraction of P to be the most significant contributor to interlaboratory variation. The 

Bray P-1 procedure is sensitive to the soil/extractant ratio, shaking rate, and time. This 

extraction uses the ascorbic acid-potassium antimony-tartarate-molybdate method. The FiskeSubbarrow method is less sensitive but has a wider range before dilution is required (North 

Central Regional Publication No. 221, 1988). For calcareous soils, the Olsen method is 

preferred. An alternative procedure for calcareous soils is to use the Bray P-1 extracting 

solution at a 1:50 soil:solution ratio. This procedure has been shown to be satisfactory for 

some calcareous soils (Smith et al., 1957; North Central Regional Publication No. 221, 1988). 

231
4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated H2SO4 and HCl to a fume 

hood. Use safety showers and eyewash stations to dilute spilled acids and bases. Use sodium 

bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±0.10-mg sensitivity 

5.2 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Centrifuge tubes, 50-mL, polyethylene 

5.4 Funnel, 60° angle, long stem, 50-mm diameter 

5.5 Filter paper, Whatman 42, ashless, 9-cm diameter 

5.6 Centrifuge, Centra GP-8, Thermo IEC, Needham Heights, MA 

5.7 Pipettes, electronic digital, 2500 μL and 10 mL, with tips 2500 μL and 10 mL 

5.8 Cups, plastic 

5.9 Cuvettes, plastic, 4.5-mL, 1-cm light path, Daigger Scientific 

5.10 Dispenser, 30 mL or 10 mL 

5.11 Spectrophotometer, UV-Visible, Dual-View, Varian, Cary 50 Conc, Varian Australia Pty 

Ltd. 

5.12 Computer, with Cary WinUV software, Varian Australia Pty Ltd., and printer 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Hydrochloric acid (HCl), concentrated, 12 N, trace pure grade 

6.3 HCl, 1 N. Carefully add 83.33 mL of concentrated HCl to RODI water and dilute to 1-L 

volume. 

6.4 Sulfuric acid (H2SO4), concentrated, 36 N 6.5 Bray No. 1 Extracting solution, 0.025 N HCl and 0.03 N NH4F. Dissolve 8.88 g of NH4F 

in 4 L RODI water. Add 200 mL of 1.0 N HCl and dilute to 8 L with RODI water. The 

solution pH should be 2.6 ± 0.5. Store in a polyethylene bottle. 

6.6 Sulfuric-tartarate-molybdate solution (STMS). Dissolve 60 g of ammonium molybdate 

tetrahydrate [(NH4)6Mo7O24·4H2O] in 200 mL of boiling RODI water. Allow to cool to 

room temperature. Dissolve 1.455 g of antimony potassium tartarate (potassium 

antimony tartarate hemihydrate [K(SbO)C4H4O6·1/2H2O] in the ammonium molybdate 

solution. Slowly and carefully add 700 mL of concentrated H2SO4. Cool and dilute to 1 

L with RODI water. Store in the dark in the refrigerator. 

6.7 Ascorbic acid solution. Dissolve 6.6 g of ascorbic acid in RODI water and dilute to 50 

mL with RODI water. Make fresh daily. 

6.8 Working ascorbic acid molybdate solution (WAMS). Mix 25 mL of STMS solution with 

800 mL of RODI water. Add 10 mL of ascorbic acid solution and dilute to 1 L with 

RODI water. Allow to stand at least 1 h before using. Prepare fresh daily. 

6.9 Working stock standard P solution (WSSPS), 100.0 mg P L-1. In a 1-L volumetric flask, 

dissolve 0.4394 g primary standard grade anhydrous potassium dihydrogen phosphate 

(KH2PO4) that has been dried for 2 h at 110°C in about 800 mL extracting solution. 

Dilute to 1-L volume with extracting solution water and invert to thoroughly mix. Store 

in polyethylene containers. Make fresh weekly. Store in a refrigerator. 

6.10 Standard P calibration solutions (SPCS) or working standards, 5.0, 4.0, 2.0, 0.8, 0.4, 0.0 

mg P L-1. Make fresh weekly. Store in a refrigerator. Allow to equilibrate to room 

temperature before use. To six 250-mL volumetric flasks add as follows: 

6.10.1 5.0 mg P L-1 = 12.5 mL WSSPS 

232
6.10.2 4.0 mg P L-1 = 10.0 mL WSSPS 

6.10.3 2.0 mg P L-1 = 5.0 mL WSSPS

6.10.4 0.8 mg P L-1 = 2.0 mL WSSPS 

6.10.5 0.4 mg P L-1 = 1.0 mL WSSPS 

6.10.6 0.0 mg P L-1 = 0 mL WSSPS (blank) 

Dilute each SPCS to the mark with extracting solution and invert to thoroughly mix. 

6.11 Quality Control Samples: 0.1 mg L-1 solution made from SSPS; blanks; and selected 

SPCS. In addition, SSL soil standard and WEPAL ISE’s (Wageningen Evaluating 

Programmes for Analytical Laboratories, International Soil Exchange) from The 

Netherlands are routinely included in a batch for quality control. 

7. Procedure 

7.1 Weigh 2.5 g of <2-mm or fine-grind, air-dry soil to nearest mg on an electronic balance and 

place into a 50-mL centrifuge tube. If sample is moist, weigh enough soil to achieve ≈ 2.5 g of 

air-dry soil. 

7.2 Dispense 25.0 mL of extracting solution to tube. 

7.3 Transfer the sample in the shaker. Shake for 15 min at 200 oscillations min-1 at room 

temperature (20°C). 

7.4 Remove the sample from the shaker. Centrifuge at 2000 rpm for 10 min, decant, filter, and 

collect extract in receiving cup. If extracts are not to be determined immediately after 

collection, then store samples at 4°C. Analyze samples within 72 h. 

7.5 Use the pipette to transfer a 2-mL aliquot of the sample to a plastic cup. Also transfer a 2-

mL aliquot of each SPCS to a plastic cup. Use a clean pipette tip for each sample and SPCS. 

7.6 Dispense 8 mL of the WAMS to sample aliquot and to each SPCS. Swirl to mix. The color 

reaction requires a minimum of 20 min before analyst records readings. 

7.7 Transfer sample extract and SPCS to cuvettes. 

7.8 Set the spectrophotometer to read at 882 nm. Autozero with calibration blank. 

7.9 Calibrate the instrument using the SPCS. The data system will then associate the 

concentrations with the instrument responses for each SPCS. Rejection criteria for SPCS, if R2

<0.99. 

7.10 Run samples using calibration curve. Sample concentration is calculated from the 

regression equation. Rejection criteria for batch, if blanks as samples > 0.01; If SPCS as 

samples > ± 20%; if SSL standard > ± 20% mean; and if ISE > (3 x MAD), where MAD = 

median of absolute deviations. Record results to the nearest 0.01 unit for the sample extract and 

each SPCS. 

7.11 If samples are outside the calibration range, dilute sample extracts with extracting solution 

and re-analyze. 

8. Calculations 

Convert the extract P (mg L-1) to soil P (mg kg-1) as follows: 

233
Soil P (mg kg-1) = =[(A x B x C x R x 1000)/E]

where: 

A = Sample extract reading (mg L-1) 

B = Extract volume (L) 

C = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report 

Report data to the nearest 0.1 mg P kg-1 soil. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Bray, R.H., and L.T. Kurtz. 1945. Determination of total, organic, and available forms of 

phosphorus in soils. Soil Sci. 59:39-45. 

Kuo, S. 1996. Phosphorus. p. 869-919. In D.L. Sparks (ed.) Methods of soil analysis. Part 

3. Chemical methods. No. 5. ASA and SSSA, Madison, WI. 

North Central Regional Publication No. 221. 1988. Recommended chemical soil test 

procedures for the North Central region. Agric. Exp. Stn. of IL, IN, IA, KS, MI, MN, 

MS, NE, ND, OH, SD, WI, and USDA cooperating. 

Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. p. 403-430. In A.L. Page, R.H. Miller, 

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Smith, F.W., B.G. Ellis, and J. Grava. 1957. Use of acid-fluoride solutions for the 

extraction of available phosphorus in calcareous soils and in soils to which rock 

phosphate has been added. Soil Sci. Soc. Am. Proc. 21:400-404. 

Soil Tests (4D) 

Bray P-1 Extraction (4D3) 

Flow-Injection, Automated Ion-Analyzer (4D3b) 

Phosphorus (4D3b1) 

Air-Dry or Field-Moist, <2 mm (4D3b1a-b1) 

1. Application 

The Bray P-1 procedure is widely used as an index of available P in the soil. Bray and 

Krutz (1945) originally designed the Bray P-1 extractant to selectively remove a portion of the 

adsorbed form of P with the weak, acidified ammonium fluoride solution. Adsorbed 

phosphorus is the in the anion form adsorbed by different charged surface functional groups 

that have varying degrees of adsorption affinity. In general, this method has been most 

successful on acid soils (Olsen and Sommers, 1982). The acid solubilizes calcium and 

aluminum phosphates, and partially extracts iron phosphates compounds. The NH4F complexes 

the aluminum in solution and limits readsorption of P on iron oxides (Kuo, 1996). The Bray P1 has limited ability to extract P in calcareous soils due to the neutralization of the dilute acid 

by carbonates. For most soils, Bray P-1 and Mehlich No. 3 are nearly comparable in their 

abilities to extract native P but exceed Olsen sodium-bicarbonate method by two- to three-fold, 

indicating that predictive models for Bray P-1, Mehlich No. 3, and Olsen sodium-bicarbonate 

are closely associated with pH buffering of extractant (acid versus alkaline) (Burt et al., 2002). 

234
2. Summary of Method 

A 2.5-g soil sample is mechanically shaken for 15 min in 25-mL of Bray P-1 extracting 

solution. The sample is then centrifuged until solution is free of soil mineral particles, and then 

filtered until clear extracts are obtained. 

A flow injection automated ion analyzer is used to measure the orthophosphate ion 

(PO4

3-). This ion reacts with ammonium molybdate and antimony potassium tartrate under 

acidic conditions to form a complex. This complex is reduced with ascorbic acid to form a blue 

complex which absorbs light at 660 nm. Absorbance is proportional to the concentration of 

PO4

3- in the sample. Data are reported as mg P kg-1 soil (4D3b1). 

3. Interferences 

Silica forms a pale blue complex which also absorbs at 660 nm. This interference is 

generally insignificant as a silica concentration of approximately 4000 mg L-1 would be 

required to produce a 1 mg L-1 positive error in orthophosphate (LACHAT Instruments, 1989). 

Concentrations of ferric iron greater than 50 mg L-1 will cause a negative error due to 

competition with the complex for the reducing agent ascorbic acid. Samples high in iron can 

be pretreated with sodium bisulfite to eliminate this interference. Treatment with bisulfite will 

also remove the interference due to arsenates (LACHAT Instruments, 1989). 

The determination of phosphorus is sensitive to variations in acid concentrations in the 

sample since there is no buffer. With increasing acidity, the sensitivity of the method is 

reduced. Samples, standards, and blanks should be prepared in a similar matrix. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated HCl, NH4F, and H2SO4 to a 

fume hood. Use safety showers and eyewash stations to dilute spilled acids and bases. Use 

sodium bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Centrifuge tubes, 50-mL, polyethylene 

5.3 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.4 Centrifuge, Centra GP-8, Thermo IEC, Needham Heights, MA 

5.5 Filter paper, Whatman No. 42, 150 mm 

5.6 Funnel, 60° angle, long stem, 50-mm diameter 

5.7 Volumetric flasks, 1-L and 250-mL 

5.8 Bottles, plastic, dark, 1-L 

5.9 Cups, plastic 

5.10 Dispenser, 30 mL or 10 mL 

5.11 Flow Injection Automated Ion Analyzer, QuikChem AE, LACHAT Instruments, 

Milwaukee, WI, with computer and printer 

5.12 XYZ Sampler, LACHAT Instruments, Milwaukee, WI 

5.13 Reagent Pump, LACHAT Instruments, Milwaukee, WI 

5.14 Automated Dilution Station, LACHAT Instruments, Milwaukee, WI 

5.15 Sample Processing Module (SPM) or channel, QuikChem Method (12-115-01-1-A, 

orthophosphate in waters, 0.4 to 20 mg P L-1), LACHAT Instruments, Milwaukee, WI 

5.16 Computer, with QuikChem software, LACHAT Instruments, Milwaukee, WI, and printer 

5.17 Pipettes, electronic digital, 2500 μL and 10 mL, with tips 2500 μL and 10 mL 

5.18 Vials, plastic, 25-mL (standards) 

5.19 Culture tubes, glass, 10-mL (samples) 

235
6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Helium, compressed gas 

6.3 Hydrochloric acid (HCl), concentrated, 12 N, trace pure grade 

6.4 Sulfuric acid (H2SO4), concentrated, 36 N, trace pure grade 

6.5 HCl, 1 N. Carefully add 83.33 mL of concentrated HCl to RODI water and dilute to 1-L 

volume. 

6.6 Bray No. 1 Extracting Solution. 0.025 M HCl, and 0.03 M NH4F. Dissolve 8.88 g of 

NH4F in 4 L RODI water. Add 200 mL of 1.0 N HCl and dilute to 8 L with RODI water. 

The solution pH should be 2.6 ± 0.05. Store in a polyethylene bottle. 

6.7 Stock ammonium molybdate solution. In 1-L volumetric flask dissolve 40.0 g ammonium 

molybdate tetrahydrate [(NH4)6Mo7O24·4H2O] in approximately 800 mL RODI water. 

Dilute to the mark with RODI water and invert to thoroughly mix. Stir for 4 h. Store in 

plastic and refrigerate. 

6.8 Stock antimony potassium tartrate solution. In 1-L flask, dissolve 3.0 g antimony 

potassium tartrate (potassium antimony tartrate hemihydrate [K(SbO)C4H4O6·1/2H2O] in 

approximately 800 mL RODI water. Dilute to the mark and invert to thoroughly mix. 

Store in dark bottle and refrigerate. 

6.9 Molybdate color reagent. In 1 L volumetric flask, add 72 mL stock antimony potassium 

tartrate solution and 213 mL stock ammonium molybdate solution. Dilute to volume 

with RODI water and invert to thoroughly mix. Degas with helium ≈ 15 min. 

6.10 Ascorbic acid reducing solution. In l-L volumetric flask, dissolve 60.0 g ascorbic acid in 

about 700 mL RODI. Dilute to volume with RODI water and invert to thoroughly mix. 

Degas with helium ≈ 5 min. After dilution to volume and degassing, dissolve 1.0 g 

dodecyl sulfate (CH3(CH2)11OSO3Na). Prepare fresh daily. 

6.11 0.8 M H2SO4 Carrier. To 1-L container, add 44.4 mL concentrated H2SO4 and bring 

volume with RODI water. (CAUTION: The solution will get very hot!) Invert to 

thoroughly mix. Degas with helium ≈ 5 min. 

6.12 Sodium hydroxide - EDTA rinse. Dissolve 65 g sodium hydroxide (NaOH) and 6 g 

tetrasodium ethylenediamine tetraacetic acid (Na4EDTA) in 1.0 L RODI water. 

6.13 Working stock standard P solution (WSSPS), 100.0 mg P L-1. In a 1-L volumetric flask, 

dissolve 0.4394 g primary standard grade anhydrous potassium dihydrogen phosphate 

(KH2PO4) that has been dried for 2 h at 110°C in about 800 mL extracting solution. 

Dilute to 1-L volume with extracting solution and invert to thoroughly mix. Store in 

polyethylene containers. Make fresh weekly. Store in a refrigerator. 

6.14 Standard P calibration solutions (SPCS) or working standards, 20.00, 12.00, 4.00, 0.800, 

and 0.000 mg P L-1 as PO4

3-. Make fresh weekly. Store in refrigerator. Allow to 

equilibrate to room temperature before use. To five 250-mL volumetric flasks add as 

follows: 

6.14.1 20.00 mg P L-1 = 50 mL WSSPS 

6.14.2 12.00 mg P L-1 = 30 mL WSSPS 

6.14.3 4.00 mg P L-1 = 10 ml WSSPS 

6.14.4 0.80 mg P L-1 = 2 mL WSSPS 

6.14.5 0.00 mg P L-1= 0 mL WSSPS (blank) 

Dilute each SPCS to the mark with extracting solution and invert to thoroughly mix. Do not 

degas. 

7. Procedure 

7.1 Weigh 2.5 g of <2-mm or fine-grind, air-dry soil to nearest mg on an electronic balance and 

place into a 50-mL centrifuge tube. If sample is moist, weigh enough soil to achieve ≈ 2.5 g of 

air-dry soil. 

236
7.2 Dispense 25.0 mL of extracting solution to tube. 

 

7.3 Transfer the sample to the shaker. Shake for 15 min at 200 oscillations min-1 at room 

temperature (20°C± 2°C). 

7.4 Remove the sample from the shaker. Centrifuge at 2000 rpm for 10 min, decant, filter, and 

collect extract in receiving cup. If extracts are not to be determined immediately after 

collection, then store samples at 4°C. Analyze samples within 72 h. 

7.5 Transfer sample extracts into culture tubes and place in XYZ sample trays marked 

"Samples". 

7.6 Transfer SPCS standards into plastic vials and place in descending order in XYZ sample 

trays marked "Standards". 

7.7 Refer to the operating and software reference manuals for LACHAT set-up and operation. 

7.8 Turn main power switch "ON" and allow 15 min for heater module to warm up to 60°C. 

7.9 On reagent pump, set speed to 35. 

7.10 On computer main menu, select "Methods" and then "Analysis Select and Download". On 

method list, select Bray P-1 Method. System unit receives the downloaded method and 

initializes it. 

7.11 Pump reagents into appropriate chambers of the manifold. Continue this step and observe 

baseline. A good baseline needs to be smooth and at zero absorbance. Scatter is indicative of 

air bubbles and irregular reagent flow. Also observe for any back-pressure in manifold tubing. 

7.12 On computer main menu, select "Samples", "Tray Definition and Submit", and then "Edit" 

to create new sample tray followed by "Submit" to run new sample tray. 

7.13 Method parameters specific to Bray P-1 are defined within the "Method Definition" menu. 

Some of these parameters have been modified from the QuikChem Method 12-115-01-1-A, 

orthophosphate in soils (U.S. Environmental Protection Agency, 1983; LACHAT Instruments, 

1989; U.S. Department of Interior, Geological Survey, 1993). Modifications are primarily 

related to the criteria and strategies for calibration standards and to injection timing. 

7.14 Some of the method parameters as they relate to calibration standards are as follows: 

7.14.1 There are 5 calibration standards (20.00, 12.00, 4.00, 0.80, and 0.00 mg P L-1) with a 

data format of ####.###, i.e., data rounded to 3 places. 

7.14.2 The segments/boundaries for the calibration standards are A - C (20.0 to 4.0 mg P L-1); 

C - E (4.0 to 0.0 mg P L-1). 

7.14.3 The protocol (replications) for the calibration standards is as follows: AA BB CC DDD 

EEE. 

7.14.4 The check standard is 20.0 mg P L-1. Maximum number of consecutive trays between 

check standard is one; maximum number of consecutive samples between check standard is 60; 

and maximum elapse time between check standards is 2 h. 

237
7.14.5 Calibration strategy for segments A – C and C - E are normal. The normal strategy 

requires a minimum correlation coefficient of 0.99. Both segments require a maximum 

standard deviation in slope of 50%. A calibration passes only when both criteria are met. 

Strategies are user designated. In addition, calibration strategies are based on the full chord. 

Chord 0 is full chord, and chord 1 - 5 are sections of peak from start of peak to end of peak. 

7.14.6 The instrument is calibrated with the injection of SPCS. The data system then associates 

the concentrations with the instrument response for each SPCS. 

 

7.15 Method parameters in relation to timing are as follows: 

7.15.1 Cycle period: 40 s 

7.15.2 Inject to start of peak period: 18 s. To see if peaks are being timed correctly, scan across 

correlation coefficients for all chords 1 - 5. The most peak area should be between chords 2 - 4 

with the most signal-to-noise ratio in chords 1 and 5. 

7.15.3 Inject to end of peak period: 46 s 

7.15.4 Automatic timing, where standard assumptions are in effect. Manual timing may be 

helpful in this method. 

7.16 Method parameters in relation to data presentation are as follows: 

7.16.1 Top Scale Response: 0.50 abs 

7.16.2 Bottom Scale Response: 0.00 abs 

7.17 Refer to the "Method Definition" for Bray P-1 for other method parameters not discussed 

here. 

7.18 Run samples using calibration curve. Sample concentration is calculated from the 

regression equations. Report results to the nearest 0.01 unit for the sample extract and each 

SPCS. 

7.19 If samples are outside calibration range, dilute samples with extracting solution and reanalyze. 

 

7.20 Upon completion of run, place the transmission lines into the NaOH - EDTA solution. 

Pump the solution for approximately 5 min to remove any precipitated reaction products. Then 

place these lines in RODI water and pump for an additional 5 min and proceed with the normal 

"Shut-down" procedure. 

8. Calculations 

Convert extract P (mg L-1) to soil P (mg kg-1) as follows: 

Soil P (mg kg-1) = [(A x B x C x R x 1000)/E] 

where: 

A = Sample extract reading (mg L-1) 

B = Extract volume (L) 

C = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

238
1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report 

Report data to the nearest 0.1 mg P kg–1 soil. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Bray, R.H., and L.T. Kurtz. 1945. Determination of total, organic, and available forms of 

phosphorus in soils. Soil Sci. 59:39-45. 

Burt, R., M..D. Mays, E.C. Benham, and M.A. Wilson. 2002. Phosphorus characterization 

and correlation with properties of selected benchmark soils of the United States. 

Commun. Soil Sci. Plant Anal. 33:117-141. 

Kuo, S. 1996. Phosphorus. p. 869-919. In D.L. Sparks (ed.) Methods of soil analysis. Part 

3. Chemical methods. No. 5. ASA and SSSA, Madison, WI. 

LACHAT Instruments. 1989. QuikChem method 12-115-01-1-A, phosphorus as 

orthophosphate, 0.4 to 20 mg P L-1. LACHAT Instruments, 6645 West Mill Rd., 

Milwaukee, WI. 

Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. p. 403-430. In A.L. Page, R.H. Miller, 

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

U.S. Department of the Interior, U.S. Geological Survey. 1993. Methods for determination 

of inorganic substances in water and fluvial sediments. Book 5. Chapter Al. Method I2601-78. 

U.S. Environmental Protection Agency. 1983. Methods for chemical analysis of water and 

wastes. EPA-600/4-79-020. Revised March, 1983, Method 353.2. 

Bray P-2 Extraction (4D4) 

UV-Visible Spectrophotometer, Dual-Beam (4D4a) 

Phosphorus (4D4a1) 

Air-Dry or Field-Moist, <2 mm (4D4a1a-b1) 

1. Application 

The Bray P-2 procedure functions to extract a portion of the plant available P in the soil. 

It has a similar composition to Bray P-1 extraction solution. The difference is a slightly higher 

concentration of HCl (0.025 N to 0.1 N) in the Bray P-2. It was originally designated by Bray 

and Kurtz (1945) to extract the easily acid soluble P a well as a fraction of adsorbed 

phosphates. The HCl solublizes calcium and aluminum phosphates, and partially extracts iron 

phosphate compounds. The NH4F complexes the aluminum in solution and limits readsorption 

of P on iron oxides (Kuo, 1996). The higher acid concentration of the Bray P-2 should allow 

greater extraction of P in calcareous soils compared to Bray P-1, but it is not as widely used by 

soil testing laboratories as Bray P-1. 

2. Summary of Method 

A 2.5-g soil sample is shaken with 25 mL of Bray P-2 extracting solution for 15 min. 

The sample is centrifuged until solution is free of soil mineral particles, and then filtered until 

clear extracts are obtained. A 2-mL aliquot is diluted with 8-mL of ascorbic acid molybdate 

solution. Absorbance of the solution is read using a spectrophotometer at 882 nm. Data are 

reported as mg P kg-1 soil (4D4a1). 

239
3. Interferences 

Many procedures may be used to determine P. Studies have shown that incomplete or 

excessive extraction of P to be the most significant contributor to interlaboratory variation. The 

Bray procedure is sensitive to the soil/extractant ratio, shaking rate, and time. This extraction 

uses the ascorbic acid-potassium antimony-tartarate-molybdate method. The Fiske-Subbarrow 

method is less sensitive but has a wider range before dilution is required (North Central 

Regional Publication No. 221, 1988). For calcareous soils, the Olsen method is preferred. An 

alternative procedure for calcareous soils is to use the Bray P-1 extracting solution at a 1:50 

soil:solution ratio. This procedure has been shown to be satisfactory for some calcareous soils 

(Smith et al., 1957; North Central Regional Publication No. 221, 1988). The higher acid 

concentration of the Bray P-2 should allow greater extraction of P in calcareous soils compared 

to Bray P-1, but it is not as widely used by soil testing laboratories as Bray P-1. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated H2SO4 and HCl to a fume 

hood. Use safety showers and eyewash stations to dilute spilled acids and bases. Use sodium 

bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±0.10-mg sensitivity 

5.2 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Centrifuge tubes, 50-mL, polyethylene 

5.4 Funnel, 60° angle, long stem, 50-mm diameter 

5.5 Filter paper, Whatman 42, ashless, 9-cm diameter 

5.6 Centrifuge, Centra GP-8, Thermo IEC, Needham Heights, MA 

5.7 Pipettes, electronic digital, 2500 μL and 10 mL, with tips 2500 μL and 10 mL 

5.8 Cups, plastic 

5.9 Cuvettes, plastic, 4.5-mL, 1-cm light path, Daigger Scientific 

5.10 Dispenser, 30 mL or 10 mL 

5.11 Spectrophotometer, UV-Visible, Dual-View, Varian, Cary 50 Conc, Varian Australia Pty 

Ltd. 

5.12 Computer, with Cary WinUV software, Varian Australia Pty Ltd., and printer 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Hydrochloric acid (HCl), concentrated, 12 N, trace pure grade 

6.3 HCl, 1 N. Carefully add 83.33 mL of concentrated HCl to RODI water and dilute to 1-L 

volume. 

6.4 Sulfuric acid (H2SO4), concentrated, 36 N 

6.5 Bray No. 2 Extracting solution, 0.1 N HCl and 0.03 N NH4F. Dissolve 8.88 g of NH4F in 

4 L RODI water. Add 800 mL of 1.0 N HCl and dilute to 8 L with RODI water. Store in 

a polyethylene bottle. 

6.6 Sulfuric-tartarate-molybdate solution (STMS). Dissolve 60 g of ammonium molybdate 

tetrahydrate [(NH4)6Mo7O24·4H2O] in 200 mL of boiling RODI water. Allow to cool to 

room temperature. Dissolve 1.455 g of antimony potassium tartarate (potassium 

antimony tartarate hemihydrate [K(SbO)C4H4O6·1/2H2O] in the ammonium molybdate 

solution. Slowly and carefully add 700 mL of concentrated H2SO4. Cool and dilute to 1 

L with RODI water. Store in the dark in the refrigerator. 

6.7 Ascorbic acid solution. Dissolve 6.6 g of ascorbic acid in RODI water and dilute to 50 

mL with RODI water. Make fresh daily. 

240
6.8 Working ascorbic acid molybdate solution (WAMS). Mix 25 mL of STMS solution with 

800 mL of RODI water. Add 10 mL of ascorbic acid solution and dilute to 1 L with 

RODI water. Allow to stand at least 1 h before using. Prepare fresh daily. 

6.9 Working stock standard P solution (WSSPS), 100.0 mg P L-1. In a 1-L volumetric flask, 

dissolve 0.4394 g primary standard grade anhydrous potassium dihydrogen phosphate 

(KH2PO4) that has been dried for 2 h at 110°C in about 800 mL extracting solution. 

Dilute to 1-L volume with extracting solution water and invert to thoroughly mix. Store 

in polyethylene containers. Make fresh weekly. Store in a refrigerator. 

6.10 Standard P calibration solutions (SPCS) or working standards, 5.0, 4.0, 2.0, 0.8, 0.4, 0.0 

mg P L-1. Make fresh weekly. Store in a refrigerator. Allow to equilibrate to room 

temperature before use. To six 250-mL volumetric flasks add as follows: 

6.10.1 5.0 mg P L-1 = 12.5 mL WSSPS 

6.10.2 4.0 mg P L-1 = 10.0 mL WSSPS 

6.10.3 2.0 mg P L-1 = 5.0 mL WSSPS

6.10.4 0.8 mg P L-1 = 2.0 mL WSSPS 

6.10.5 0.4 mg P L-1 = 1.0 mL WSSPS 

6.10.6 0.0 mg P L-1 = 0 mL WSSPS (blank) 

Dilute each SPCS to the mark with extracting solution and invert to thoroughly mix. 

6.11 Quality Control Samples: 0.1 mg L-1 solution made from SSPS; blanks; and selected 

SPCS. In addition, SSL soil standard and WEPAL ISE’s (Wageningen Evaluating 

Programmes for Analytical Laboratories, International Soil Exchange) from The 

Netherlands are routinely included in a batch for quality control. 

7. Procedure 

7.1 Weigh 2.5 g of <2-mm or fine-grind, air-dry soil to nearest mg on an electronic balance and 

place into a 50-mL centrifuge tube. If sample is moist, weigh enough soil to achieve ≈ 2.5 g of 

air-dry soil. 

7.2 Dispense 25.0 mL of extracting solution to tube. 

7.3 Transfer the sample in the shaker. Shake for 15 min at 200 oscillations min-1 at room 

temperature (20°C). 

7.4 Remove the sample from the shaker. Centrifuge at 2000 rpm for 10 min, decant, filter, and 

collect extract in receiving cup. If extracts are not to be determined immediately after 

collection, then store samples at 4°C. Analyze samples within 72 h. 

7.5 Use the pipette to transfer a 2-mL aliquot of the sample to a plastic cup. Also transfer a 2-

mL aliquot of each SPCS to a plastic cup. Use a clean pipette tip for each sample and SPCS. 

7.6 Dispense 8 mL of the WAMS to sample aliquot and to each SPCS. Swirl to mix. The color 

reaction requires a minimum of 20 min before analyst records readings. 

7.7 Transfer sample extract and SPCS to cuvettes. 

7.8 Set the spectrophotometer to read at 882 nm. Autozero with calibration blank. 

7.9 Calibrate the instrument using the SPCS. The data system will then associate the 

concentrations with the instrument responses for each SPCS. Rejection criteria for SPCS, if R2

<0.99. 

241
7.10 Run samples using calibration curve. Sample concentration is calculated from the 

regression equation. Rejection criteria for batch, if blanks as samples > 0.01; If SPCS as 

samples > ± 20%; if SSL standard > ± 20% mean; and if ISE > (3 x MAD), where MAD = 

median of absolute deviations. Record results to the nearest 0.01 unit for the sample extract and 

each SPCS. 

7.11 If samples are outside the calibration range, dilute sample extracts with extracting solution 

and re-analyze. 

9. Calculations 

Convert the extract P (mg L-1) to soil P (mg kg-1) as follows: 

Soil P (mg kg-1) = [(A x B x C x R x 1000)/E]

where: 

A = Sample extract reading (mg L-1) 

B = Extract volume (L) 

C = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report 

Report data to the nearest 0.1 mg P kg-1 soil. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Bray, R.H., and L.T. Kurtz. 1945. Determination of total, organic, and available forms of 

phosphorus in soils. Soil Sci. 59:39-45. 

Kuo, S. 1996. Phosphorus. p. 869-919. In D.L. Sparks (ed.) Methods of soil analysis. Part 

3. Chemical methods. No. 5. ASA and SSSA, Madison, WI. 

North Central Regional Publication No. 221. 1988. Recommended chemical soil test 

procedures for the North Central region. Agric. Exp. Stn. of IL, IN, IA, KS, MI, MN, 

MS, NE, ND, OH, SD, WI, and USDA cooperating. 

Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. p. 403-430. In A.L. Page, R.H. Miller, 

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Smith, F.W., B.G. Ellis, and J. Grava. 1957. Use of acid-fluoride solutions for the 

extraction of available phosphorus in calcareous soils and in soils to which rock 

phosphate has been added. Soil Sci. Soc. Am. Proc. 21:400-404. 

Soil Tests (4D) 

Olsen Sodium-Bicarbonate Extraction (4D5) 

UV-Visible Spectrophotometer, Dual-Beam (4D5a) 

Phosphorus (4D5a1) 

Air-Dry or Field-Moist, <2 mm (4D5a1a-b1) 

1. Application 

Olsen extractant is 0.5 M sodium bicarbonate solution at pH 8.5. This extractant is most 

applicable to neutral to calcareous soils (Buurman et al., 1996). Solubility of Ca-phosphate in 

242
calcareous, alkaline, or neutral soils in increased because of the precipitation of Ca++ as CaCO3 

(Soil and Plant Analysis Council, 1999). Olsen extractant correlates with Mehlich No. 3 on 

calcareous soils (R2= 0.918), even though the quantity of Mehlich No. 3 extractable P is 

considerably higher (Soil and Plant Analysis Council, 1999). While Mehlich No. 3, Bray P-1, 

and Olsen sodium-bicarbonate are linearly related, relationships developed between some P 

tests (e.g., Olsen P, Mehlich No. 3) may have limited predictive capability with increasing soil 

P content (Burt et al. 2000). 

2. Summary of Method A 1.0-g soil sample is shaken with 20 mL of Olsen sodium-bicarbonate extracting 

solution for 30 min. The sample is centrifuged until solution is free of soil mineral particles, 

and then filtered until clear extracts are obtained. Dilute 5-mL of sample extract with 5-mL of 

color reagent. The absorbance of the solution is read using a spectrophotometer at 882 nm. 

Data are reported as mg P kg-1 soil (4D5a1). 

3. Interferences 

The Mo blue methods, which are very sensitive for P, are based on the principle that in 

an acid molybdate solution containing orthophosphate ions, a phosphomolybdate complex 

forms that can be reduced by ascorbic acid, SnCl2, and other reducing agents to a Mo color. 

The intensity of blue color varies with the P concentration but is also affected by other factors 

such as acidity, arsenates, silicates, and substances that influence the oxidation-reduction 

conditions of the system (Olsen and Sommers, 1982). 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated H2SO4 and HCl to a fume 

hood. Use safety showers and eyewash stations to dilute spilled acids and bases. Use sodium 

bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Centrifuge tube, 50 mL, polyethylene 

5.4 Funnel, 60° angle, long stem, 50-mm diameter 

5.5 Filter paper, Whatman 42, 150 mm 

5.6 Centrifuge, Centra, GP-8, Thermo IEC, Thermo IEC, Needham Heights, MA. 

5.7 Pipettes, electronic digital, 1000μL and 10 mL, with tips, 1000μL and 10 mL 

5.8 Cups, plastic 

5.9 Dispenser, 30 mL or 10 mL 

5.10 Cuvettes, plastic, 4.5-mL, 1-cm light path, Daigger Scientific 

5.11 Spectrophotometer, UV-Visible, Dual-View, Varian, Cary 50 Conc, Varian Australia Pty 

Ltd. 

5.12 Computer, with Cary WinUV software, Varian Australia Pty Ltd., and printer 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Sulfuric acid (H2SO4), concentrated, 36 N, trace pure grade

6.3 Sulfuric acid (H2SO4), 4 M. To 250-mL volumetric, carefully add 56 mL concentrated 

H2SO4 to 150 mL RODI water. Allow to cool. Make to final volume with RODI water. 

Invert to thoroughly mix. 

6.4 NaOH, 1 M. Dissolve 4 g NaOH in 100 mL RODI water. 

243
6.5 Olsen Sodium Bicarbonate Extracting solution ( 0.5 M NaHCO3). To 6-L container, 

dissolve 252 g NaHCO3 in RODI water. Adjust the pH to 8.5 with 1M NaOH. Make to 

final volume. Mix thoroughly. Check pH every day. 

6.6 Ammonium molybdate, 4%. Dissolve 4 g of [(NH4)6Mo7O24·4H2O] in 100-mL 

volumetric with RODI water. Dilute to volume with RODI water. Store in the dark in the 

refrigerator. 

6.7 Potassium antimony – (III) oxide tartarate, 0.275%. Dissolve 0.275 g 

[K(SbO)C4H4O6·1/2H2O] in 100 mL RODI water. 

6.8 Ascorbic acid, 1.75%. Dissolve 1.75 g ascorbic acid in 100 mL RODI water. Prepare 

fresh daily. 

6.9 Color developing reagent. To a 500-mL bottle, add 50 mL 4 M H2SO4, 15 mL 4% 

ammonium molybdate, 30 mL 1.75% ascorbic acid, 5 mL 0.275% potassium antimony – 

(III) oxide tartarate, and 200 mL RODI water. Mix well after each addition. Prepare 

fresh daily. 

6.10 Stock standard P solution (SSPS), 100.0 mg P L-1. In a 1-L volumetric flask, dissolve 

0.4394 g primary standard grade anhydrous potassium dihydrogen phosphate (KH2PO4) 

that has been dried for 2 h at 110°C in about 800 mL extracting solution. Dilute to 1-L 

volume with extracting solution and invert to thoroughly mix. Store in polyethylene 

containers. Make fresh weekly. Store in a refrigerator. 

6.11 Working stock standard P solution (WSSPS), 4.0 mg P L-1. Pipet 10 mL of 100 mg P L-1

SSPS to 250-mL volumetric flask. Dilute to 250-mL volume with extracting solution and 

invert to thoroughly mix. Make fresh weekly. Store in the refrigerator. 

6.12 Standard P calibration solution (SPCS), or working standards, 2.0, 1.6, 1.2, 0.8, 0.4, and 

0.0 mg P L-1. Make fresh weekly. Store in the refrigerator. Allow to equilibrate to room 

temperature before use. To six 50-mL volumetric flasks, add as follows: 

6.12.1 2.0 mg P L-1= 25 mL WSSPS 

6.12.2 1.6 mg P L-1 = 20 mL WSSPS 

6.12.3 1.2 mg P L-1 = 15 mL WSSPS 

6.12.4 0.8 mg P L-1 = 10 mL WSSPS 

6.12.5 0.4 mg P L-1 = 5 mL WSSPS 

6.12.6 0.0 mg P L-1 = 0 mL WSSPS (blank) 

Dilute each SPCS to mark with extracting solution and invert to thoroughly mix. 

6.13 Quality Control Samples: 0.1mg P L-1 solution made from SSPS; blanks; and selected 

SPCS. In addition, SSL soil standard and WEPAL ISE’s (Wageningen Evaluating 

Programmes for Analytical Laboratories, International Soil Exchange) from The 

Netherlands are routinely included in a batch for quality control. 

7. Procedure 

7.1 Weigh 1.0 g of <2mm or fine-grind, air-dry soil to the nearest mg into a 50-mL centrifuge 

tube. If sample is moist, weigh enough soil to achieve ≈ 1.0 g of air-dry soil. 

7.2 Dispense 20.0 mL of extracting solution to tube. 

7.3 Transfer the sample to the shaker. Shake for 30 min at 200 oscillations min-1 at room 

temperature (20°C± 2°C). 

7.4 Remove the sample from the shaker. Centrifuge at 2000 rpm for 10 min, decant, filter, and 

collect extract in receiving cup. If extracts are not to be determined immediately after 

collection, then store samples at 4°C. Analyze samples within 72 h. 

244
7.5 Use the pipette to transfer a 5-mL aliquot of the sample to a plastic cup. Also transfer a 5-

mL aliquot of each SPCS to a plastic cup. Use a clean pipette tip for each sample and SPCS. 

7.6 Dispense 5 mL of color developing reagent to sample aliquot and to each SPCS. Swirl to 

mix. Do not place sample cups close together as carbon dioxide is released and solution will 

bubble. The color reaction requires a minimum of 20 min before analyst records readings. 

Allowing 1 h for color development usually improves results. Color will remain stable for 24 

h. 

7.7 Transfer sample extract and SPCS to cuvettes. 

7.8 Set the spectrophotometer to read at 882 nm. Autozero with calibration blank. 

7.9 Calibrate the instrument using the SPCS. The data system will then associate the 

concentrations with the instrument responses for each SPCS. Rejection criteria for SPCS, if R2

<0.99. 

7.10 Run samples using calibration curve. Sample concentration is calculated from the 

regression equation. Rejection criteria for batch, if blanks as samples > 0.01; if SPCS as 

samples > ± 20%; if SSL standard > ± 20% mean; and if ISE > (3 x MAD), where MAD = 

median of absolute deviations. Record results to the nearest 0.01 unit for the sample extract and 

each SPCS. 

7.11 If samples are outside calibration range, dilute sample extracts with extracting solution 

and re-analyze. 

8. Calculations 

8.1 Convert the extract P (mg L-1) to soil P (mg kg –1) as follows: 

Soil P (mg kg-1) = [(A x B x C x R x 1000)/E] 

where: 

A = Sample extract reading (mg L-1) 

B = Extract volume (L) 

C = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report 

Report data to the nearest 0.1 mg P kg-1 soil. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Buurman, P, B. van Lagen, and E.J. Velthorst. 1996. Manual for soil and water analysis. 

Backhuys Publ., Leiden, The Netherlands. 

Burt, R., M..D. Mays, E.C. Benham, and M.A. Wilson. 2002. Phosphorus characterization 

and correlation with properties of selected benchmark soils of the United States. 

Commun. Soil Sci. Plant Anal. 33:117-141. 

245
Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. p. 403-430. In A.L. Page, R.H. Miller, 

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Soil and Plant Analysis Council. 1999. Handbook on reference methods for soil analysis. 

Council on Soil Testing and Plant Analysis, CRC Press, Boca Raton, FL. 

Soil Tests (4D) 

Mehlich No. 3 Extraction (4D6) 

UV-Visible Spectrophotometer, Dual-Beam (4D6a) 

Phosphorus (4D6a1) 

Air-Dry or Field-Moist, < 2 mm (4D6a1a-b1) 

1. Application 

Mehlich No. 3 was developed by Mehlich (1984) as a multielement soil extraction (Ca, 

Mg, K, Na, P). In the Mehlich No. 3 procedure, P is extracted by reaction with acetic acid and 

Fl compounds. Mehlich No. 3 is a used an index of available P in the soil. Extraction of P by 

Mehlich No. 3 is designed to be applicable across a wide range of soil properties ranging in 

reaction from acid to basic (Mehlich, 1984). Mehlich No. 3 correlates well with Bray P-1 on 

acid to neutral (R2

 = 0.966) but does not correlate with Bray P-1 on calcareous soils (Soil and 

Plant Analysis Council, 1999). Mehlich No. 3 correlates with Olsen extractant on calcareous 

soils (R2= 0.918), even though the quantity of Mehlich No. 3 extractable P is considerably 

higher (Soil and Plant Analysis Council, 1999). The Mehlich No. 3 extractant is neutralized 

less by carbonate compounds in soil than the double acid (Mehlich No. 1) and the Bray P-1, 

and is less aggressive towards apatite or other Ca-phosphate than the double acid and Bray P-2 

extractants (Tran and Simard, 1993). Mehlich No. 3 can also be used to extract Ca, Mg, K, and 

Na in a wide range of soils and correlates well with Mehlich No. 1, Mehlich No. 2, and 

NH4OAc (Soil and Plant Analysis Council, 1999). 

2. Summary of Method A 2.5-g soil sample is shaken with 25 mL of Mehlich No. 3 extracting solution for 5 

min. The sample is centrifuged until solution is free of soil mineral particles, and then filtered 

until clear extracts are obtained. Dilute 0.5-mL of sample extract with 13.5-mL of working 

solution. Absorbance of the solution is read using a spectrophotometer at 882 nm. Data are 

reported as mg P kg-1 soil (4D6a1). 

3. Interferences 

 The Mo blue methods, which are very sensitive for P, are based on the principle that in 

an acid molybdate solution containing orthophosphate ions, a phosphomolybdate complex 

forms that can be reduced by ascorbic acid, SnCl2, and other reducing agents to a Mo color, 

with ascorbic acid most commonly used by agricultural laboratories (Murphy and Riley, 1962). 

The intensity of blue color varies with the P concentration but is also affected by other factors 

such as acidity, arsenates, silicates, and substances that influence the oxidation-reduction 

conditions of the system (Olsen and Sommers, 1982). 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated H2SO4 and HCl to a fume 

hood. Use safety showers and eyewash stations to dilute spilled acids and bases. Use sodium 

bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

246
5.2 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Centrifuge tubes, 50-mL, polyethylene 

5.4 Funnel, 60° angle, long stem, 50-mm diameter 

5.5 Filter paper, Whatman 42, 150 mm 

5.6 Centrifuge, Centra, GP-8, Thermo IEC, Needham Heights, MA 

5.7 Pipettes, electronic digital, 1000 μL and 10 mL, with tips, 1000 μL and 10 mL 

5.8 Dispenser, 30 mL or 10 mL 

5.9 Cups, plastic 

5.10 Cuvettes, plastic, 4.5-mL, 1-cm light path, Daigger Scientific 

5.11 Spectrophotometer, UV-Visible, Dual-View, Varian, Cary 50 Conc, Varian Australia Pty 

Ltd. 

5.12 Computer with Cary WinUV software, Varian Australia Pty Ltd., and printer 

6. Reagents

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Sulfuric acid (H2SO4), concentrated, 36 N, trace pure grade 

6.3 Mehlich No. 3 Extracting solution (0.2 N CH3COOH; 0.25 N NH4NO3; 0.015 N NH4F; 

0.13 N HNO3; 0.001 M EDTA). Premixed Mehlich No. 3 Extractant, Special-20, Hawk 

Creek Laboratory, Rural Route 1, Box 686, Simpson Road, Glen Rock, PA, 17327. 

6.4 Sulfuric-tartarate-molybdate solution (STMS). Dissolve 100 g of ammonium molybdate 

tetrahydrate [(NH4)6Mo7O24·4H2O] in 500 mL of RODI water. Dissolve 2.425 g of 

antimony potassium tartarate (potassium antimony tartarate hemihydrate 

[K(SbO)C4H4O6·1/2H2O] in the ammonium molybdate solution. Slowly and carefully 

add 1400 mL of concentrated H2SO4 and mix well. Cool and dilute to 2 L with RODI 

water. Store in the dark in the refrigerator. 

6.5 Ascorbic acid solution. Dissolve 8.8 g of ascorbic acid in RODI water and dilute to 100-

mL with RODI water. Make fresh daily. 

6.6 Working ascorbic acid molybdate solution (WAMS). Dilute 20 mL of STMS solution and 

10 mL of the ascorbic acid solution with RODI water to make 1-L. Allow solution to 

come to room temperature before using. Prepare fresh daily. 

6.7 Working stock standard P solution (WSSPS), 100.0 mg P L-1. In a 1-L volumetric flask, 

dissolve 0.4394 g primary standard grade anhydrous potassium dihydrogen phosphate 

(KH2PO4) (dried for 2 h at 110°C) in about 800 mL extracting solution. Dilute to 1-L 

volume with extracting solution and invert to thoroughly mix. Store in polyethylene 

containers. Make fresh weekly. Store in a refrigerator. 

6.8 Standard P calibration solutions (SPCS) or working standards, 12.0, 10.0, 8.0, 4.0, 2.0, 

1.0, 0.8, 0.4 and 0.0 mg P L-1. Prepare fresh weekly. Store in a refrigerator. Allow to 

equilibrate to room temperature before use. In nine 250-mL volumetric flasks add as 

follows: 

6.8.1 12.0 mg P L-1 = 30 mL WSSPS 

6.8.2 10.0 mg P L-1 = 25 mL WSSPS 

6.8.3 8.0 mg P L-1 = 20 mL WSSPS 

6.8.4 4.0 mg P L-1 = 10 mL WSSPS 

6.8.5 2.0 mg P L-1 = 5 mL WSSPS 

6.8.6 1.0 mg P L-1 = 2.5 mL WSSPS 

6.8.7 0.8 mg P L-1 = 2 mL WSSPS 

6.8.8 0.4 mg P L-1 = 1 mL WSSPS 

6.8.9 0.0 mg P L-1 = 0 mL WSSPS (blank) 

Dilute each SPCS to the mark with extracting solution and invert to thoroughly mix. 

 

247
6.9 Quality Control Samples: 0.1 mg P L -1 solution made from SSPS; blanks; and selected 

SPCS. In addition, SSL soil standard and WEPAL ISE’s (Wageningen Evaluating 

Programmes for Analytical Laboratories, International Soil Exchange) from The 

Netherlands are routinely included in a batch for quality control. 

7. Procedure 

7.1 Weigh 2.5 g of <2-mm or fine-grind, air-dry soil to the nearest mg into a 50-mL centrifuge 

tube. If sample is moist, weigh enough soil to achieve ≈ 2.5 g of air-dry soil. 

7.2 Dispense 25.0 mL of extracting solution to the tube. 

7.3 Transfer the sample to the shaker. Shake for 5 min at 200 oscillations min-1 at room 

temperature (20°C± 2°C). 

7.4 Remove the sample from the shaker. Centrifuge at 2000 rpm for 10 min, decant, filter, and 

collect extract in receiving cups. If extracts are not to be determined immediately after 

collection, then store samples at 4°C. Analyze samples within 72 h. 

7.5 Use the pipette to transfer a 1 mL (or 0.5-mL) aliquot of the sample to a plastic cup. Also 

transfer a 1 mL (or 0.5-mL) aliquot of each SPCS to a plastic cup. Use a clean pipette tip for 

each sample and SPCS. 

7.6 Dispense 27 mL (or 13.5 mL) of the WAMS to sample aliquot and to each SPCS. Swirl to 

mix. The color reaction requires a minimum of 20 min before analyst records readings. 

Allowing 1 h for color development usually improves results. Color will remain stable for 6 h. 

7.7 Transfer sample extract and SPCS to cuvettes. 

7.8 Set the spectrophotometer to read at 882 nm. Autozero with calibration blank. 

7.9 Calibrate the instrument by using the SPCS. The data system will then associate the 

concentrations with the instrument responses for each SPCS. Rejection criteria for SPCS, if R2

<0.99.

7.10 Run samples using calibration curve. Sample concentration is calculated from the 

regression equation. Rejection criteria for batch, if blanks as samples > 0.01; if SPCS as 

samples > ± 20%; if SSL standard > ± 20% mean; and if ISE > (3 x MAD), where MAD = 

median of absolute deviations. Record results to the nearest 0.01 unit for the sample extract and 

each SPCS. 

7.11 If samples are outside calibration range, dilute sample extracts with extracting solution 

and re-analyze. 

8. Calculation 

8.1 Convert extract P (mg L-1) to soil P (mg kg-1) as follows: 

Soil P (mg kg -1) = [(A x B x C x R x 1000)/E] 

where: 

A = Sample extract reading (mg L-1) 

B = Extract volume (L) 

C = Dilution, if performed 

248
R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report 

Report data to the nearest 0.1mg P kg –1 soil. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Mehlich, A. 1984. Mehlich 3 soil text extractant: A modification of Mehlich 2 extractant. 

Commun. Soil Sci. Plant Anal. 15:1409-1416. 

Murphy, J., and J.R. Riley. 1962. A modified single solution method for the determination 

of phosphate in natural waters. Anal. Chem. Acta. 27:31-36. 

Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. p. 403-430. In A.L. Page, R.H. Miller, 

and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Soil and Plant Analysis Council, Inc. 1999. Handbook on reference methods for soil 

analysis. Council on Soil Testing and Plant Analysis. CRC Press, Boca Raton, FL. 

Tran, T.S., and R.R. Simard. 1993. Mehlich III-extractable elements. p. 43-50. In M.R. 

Carter (ed.) Soil sampling and methods of analysis. Can. Soc. Soil Sci. Lewis Publ., 

Boca Raton, FL. 

Mehlich No. 3 Extraction (4D6) 

Inductively Coupled Plasma Atomic Emission Spectrophotometer (4D6b) Axial Mode (4D6b1) 

Ultrasonic Nebulizer (4D6b1a) 

Aluminum, Arsenic, Barium, Calcium, Cadmium, Cobalt, Chromium, Copper, Iron, Potassium Magnesium, Manganese, Sodium, Nickel, Phosphorus, Lead, Selenium, and Zinc (4D6b1a1-18) 

Air-Dry or Field-Moist (4D6b1a1-18a-b1) 

1. Application 

Mehlich No. 3 was developed by Mehlich (1984) as a multielement soil extraction (Ca, 

Mg, K, Na, P). In the Mehlich No. 3 procedure, P is extracted by reaction with acetic acid and 

Fl compounds. Mehlich No. 3 is a used an index of available P in the soil. Extraction of P by 

Mehlich No. 3 is designed to be applicable across a wide range of soil properties ranging in 

reaction from acid to basic (Mehlich, 1984). Mehlich No. 3 correlates well with Bray P-1 on 

acid to neutral (R2

 = 0.966) but does not correlate with Bray P-1 on calcareous soils (Soil and 

Plant Analysis Council, 1999). Mehlich No. 3 correlates with Olsen extractant on calcareous 

soils (R2= 0.918), even though the quantity of Mehlich No. 3 extractable P is considerably 

higher (Soil and Plant Analysis Council, 1992). The Mehlich No. 3 extractant is neutralized 

less by carbonate compounds in soil than the double acid (Mehlich No. 1) and the Bray P-1, 

and is less aggressive towards apatite or other Ca-phosphate than the double acid and Bray P-2 

extractants (Tran and Simard, 1993). Mehlich No. 3 can also be used to extract Ca, Mg, K, and 

Na in a wide range of soils and correlates well with Mehlich No. 1, Mehlich No. 2, and 

NH4OAc (Soil and Plant Analysis Council, 1999). Additionally, Mehlich No. 3 can be used to 

extract Al, Cd, Cu, Fe, Mn, Ni, Pb, and Zn (Elrashidi et al., 2003). 

2. Summary of Method 

A 2.5-g soil sample is shaken with 25 mL of Mehlich No. 3 extracting solution for 5 

min. The sample is centrifuged until solution is free of soil mineral particles, and then filtered 

until clear extracts are obtained. Calibration standards are prepared for elemental analysis. A 

249
blank of Mehlich No. 3 is prepared. An inductively coupled plasma atomic emission 

spectrophotometer (ICP-AES) is used for analysis. The concentration of Al, As, Ba, Ca, Cd, 

Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Se, and Zn are determined by an inductively coupled 

plasma atomic emission spectrophotometer (ICP-AES) in radial mode. Data by this procedure 

(4D6b1a1-18) are reported as mg kg-1 soil. 

3. Interferences 

Spectral and matrix interferences exist. Interferences are corrected or minimized by 

using both an internal standard and inter-elemental correction factors. Also, careful selection 

of specific wavelengths for data reporting is important. Background corrections are made by 

ICP-AES software. Samples and standards are matrix-matched to help reduce interferences. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated acids to a fume hood. Use 

safety showers and eyewash stations to dilute spilled acids and bases. Use sodium bicarbonate 

and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 5.2 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Centrifuge tubes, 50-mL, polyethylene 

5.4 Funnel, 60° angle, long stem, 50-mm diameter 

5.5 Filter paper, Whatman 42, 150 mm 

5.6 Centrifuge, Centra, GP-8, Thermo IEC, Needham Heights, MA 

5.7 Pipettes, electronic digital, 1000 μL and 10 mL, with tips, 1000 μL and 10 mL 

5.8 Dispenser, 30 mL or 10 mL 

5.9 Cups, plastic 

5.10 Inductively coupled plasma atomic emission spectrophotometer (ICP-AES), Perkin-Elmer 

Optima 3300 Dual View (DV), Perkin-Elmer Corp., Norwalk, CT. 

5.11 RF generator, floor mounted power unit, 45 MHz free running, Perkin-Elmer Corp., 

Norwalk, CT. 

5.12 Computer, with WinLab software ver. 4.1, Perkin-Elmer Corp., Norwalk, CT, and printer 

5.13 Recirculating chiller, Neslab, CFT Series 

5.14 Compressed gasses, Argon (minimum purity=99.996%) and Nitrogen (minimum 

purity=99.999%) 

5.15 Autosampler, AS-90, Perkin-Elmer Corp., Norwalk, CT. 

5.16 Quartz torch, Part No. N069-1662; alumina injector (2.0 mm id), Part No. N069-5362 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Mehlich No. 3 Extracting solution (0.2 N CH3COOH; 0.25 N NH4NO3; 0.015 N NH4F; 

0.13 N HNO3; 0.001 M EDTA). Premixed Mehlich No. 3 Extractant, Special-20, Hawk 

Creek Laboratory, Rural Route 1, Box 686, Simpson Road, Glen Rock, PA, 17327. 

6.3 Primary standards, 1000 mg L-1: of Al, Fe, Ca, Mg, Na, K, Mn, P, As, Ba, Cd, Co, Cr, Cu, 

Ni, Pb, Se, and Zn, High Purity Standards, Charleston, SC. 

6.4 Mixed Standard High A, 100, 100, 100, 20, 40, 20, and 10 mg L-1 of Ca, Mg, Al, K, Fe, 

Na, Cr, respectively: To a 500-mL volumetric, add 50, 50, 50, 10, 20, 10, and 5 mL of the 

1000 mg L-1 Ca, Mg, Al, K, Fe, Na (Section 6.3) and dilute to volume with Mehlich No. 3 

(Section 6.2) extracting solution. Invert to thoroughly mix. Store in a polyethylene 

container. Make fresh weekly. Store in a refrigerator. 

250
6.5 Mixed Standard Medium A, 50, 50, 50, 10, 20, 10, and 5 mg L-1 of Ca, Mg, Al, K, Fe, Na, 

and Cr, respectively: To a 100-mL volumetric, add 50 mL of Mixed Standard High A and 

dilute to volume with Mehlich No. 3 extracting solution. Invert to thoroughly mix. Store 

in polyethylene container. Make fresh weekly. Store in a refrigerator. 

6.6 Mixed Standard Low A, 5, 5, 5, 1, 2, 1, and 0.5 mg L-1 of Ca, Mg, Al, K, Fe, Na, and Cr, 

respectively: To a 100-mL volumetric, add 10 mL of Mixed Standard Medium A and 

dilute to volume with Mehlich No. 3 extracting solution. Invert to thoroughly mix. Store 

in polyethylene container. Make fresh weekly. Store in a refrigerator. 

6.7 Mixed Standard Very Low A, 0.5, 0.5, 0.5, 0.1, 0.2, 0.1 and 0.05 mg L-1 of Ca, Mg, Al, 

K, Fe, Na, and Cr, respectively: To a 100-mL volumetric, add 10 mL of Mixed Standard 

Low A and dilute to volume with Mehlich No. 3 extracting solution. Invert to thoroughly 

mix. Store in a polyethylene container. Make fresh weekly. Store in a refrigerator. 

6.8 Mixed Standard High B, 250, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10 mg L-1 of P, As, Ba, 

Cd, Co, Cu, Mn, Ni, Se, Zn, and Pb, respectively: To a 100-mL volumetric, add 25, 1, 1, 

1, 1, 1, 1, 1, 1, 1, and 1 mL of the 1000 mg L-1 of P, As, Ba, Cd, Co, Cu, Mn, Ni, Se, Zn, 

and Pb (Section 6.3) and dilute to volume with Mehlich No. 3 (Section 6.2) extracting 

solution. Invert to thoroughly mix. Store in a polyethylene container. Make fresh weekly. 

Store in a refrigerator. 

6.10 Mixed Standard Medium B, 25, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 mg L-1 of P, As, Ba, Cd, Co, Cu, 

Mn, Ni, Pb, Se, and Zn, respectively: To a 100-mL volumetric, add 10 mL of Mixed 

Standard High B and dilute to volume with Mehlich No. 3 extracting solution. Invert to 

thoroughly mix. Store in polyethylene container. Make fresh weekly. Store in a 

refrigerator. 

6.11 Mixed Standard Low B, 2.5, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1 mg L-1 of P, As, 

Ba, Cd, Co, Cu, Mn, Ni, Pb, Se, and Zn, respectively: To a 100-mL volumetric, add 10 

mL of Mixed Standard Medium B and dilute to volume with Mehlich No. 3 extracting 

solution. Invert to thoroughly mix. Store in polyethylene container. Make fresh weekly. 

Store in a refrigerator. 

6.12 Mixed Standard Very Low B, 0.25, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 

0.01 mg L-1 of P, As, Ba, Cd, Co, Cu, Mn, Ni, Pb, Se, and Zn, respectively: To a 100-mL 

volumetric, add 10 mL of Mixed Standard Low B and dilute to volume with Mehlich No. 

3 extracting solution. Invert to thoroughly mix. Store in polyethylene container. Make 

fresh weekly. Store in a refrigerator. 

6.13 Blanks: To a 100-mL volumetric, Mehlich No. 3 extracting solution. Invert to thoroughly 

mix. Store in polyethylene container. Make fresh weekly. Store in a refrigerator. 

7. Procedure 

Extraction of Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Se, and Zn 

7.1 Weigh 2.5 g of <2-mm or fine-grind, air-dry soil to the nearest mg into a 50-mL centrifuge 

tube. If sample is moist, weigh enough soil to achieve ≈ 2.5 g of air-dry soil. 

7.2 Dispense 25.0 mL of extracting solution to the tube. 

7.3 Transfer the sample to the shaker. Shake for 5 min at 200 oscillations min-1 at room 

temperature (20°C± 2°C). 

7.4 Remove the sample from the shaker. Centrifuge at 2000 rpm for 10 min, decant, filter, and 

collect extract in receiving cups. If extracts are not to be determined immediately after 

collection, then store samples at 4°C. Analyze samples within 72 h. 

ICP-AES Set-up and Operation 

7.5 Use the ICP-AES in axial mode to analyze elements. Use ultrasonic nebulization of 

sample. No initial dilutions of samples are necessary prior to analysis. Perform instrument 

251
checks (Hg alignment; BEC and %RSD of 1 mg L-1 Mn solution) prior to analysis as discussed 

in operation manual of instrument. Check instrument alignment and gas pressures to obtain 

optimum readings with maximum signal to noise ratio. 

Analyses are generally performed at two or more wavelengths for each element. The selected 

wavelengths are as follows (reported wavelength listed first and in boldface): 

 Element Wavelength 

 ----------- nm --------- Al 308.215, 396.153 

 Fe 259.939, 238.204 

 Ca 315.887, 317.932 Mg 280.271, 279.075 

 Na 589.592, 588.995 

 K 766.490 

 Mn 260.570 257.608 

 P 178.221, 214.915 

 As 193.69 

 Ba 233.525 455.507 

 Cd 226.501, 214.435 

 Co 228.614 

 Cr 267.710 205.558 

 Cu 324.753, 327.396 

 Ni 232.003, 231.604, 

 Pb 220.353, 216.998 

 Se 196.026 

 Zn 213.857, 206.197 

7.6 Use the Mehlich No. 3 extracting solution to dilute those samples with concentrations 

greater than the high standard. Rerun all elements and use only the data needed from the 

diluted analysis. 

7.7 Establish detection limits using the blank standard solution. The instrumental detection 

limits are calculated by using 3 times the standard deviation of 10 readings of the blank. These 

values establish the lower detection limits for each element. Analyzed values lower than the 

detection limits are reported as "ND" or non-detected. The fraction digested needs to be 

identified with each sample. 

8. Calculations 

The calculation of mg kg-1 of an element in the soil from mg L-1 in solution is as follows: 

Analyte concentration in soil (mg kg-1) = [A x B x C x R x 1000]/E 

A = Sample extract reading (mg L-1) 

B = Extract volume (L) 

C = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (3D2) 

1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report

Data are reported to the nearest 0.1mg kg-1. 

252
10. Precision and Accuracy 

Precision and accuracy and precision data are available from the SSL upon request. 

11. References 

Elrashidi, M.A., M.D. Mays, and C.W. Lee. 2003. Assessment of Mehlich3 and 

ammonium bicarbonate−DTPA extraction for simultaneous measurement of fifteen 

elements in soils. Commun. Soil Sci. and Plant Anal. 34:2817-2838. 

Mehlich, A. 1984. Mehlich 3 soil text extractant: A modification of Mehlich 2 extractant. 

Commun. Soil Sci. Plant Anal. 15:1409-1416. 

Murphy, J., and J.R. Riley. 1962. A modified single solution method for the determination 

of phosphate in natural waters. Anal. Chem. Acta. 27:31-36. 

Olsen, S.R., and L.E. Sommers. 1982. p. 403-430. In A.L. Page, R.H. Miller, and D.R. 

Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Soil and Plant Analysis Council, Inc. 1999. Handbook on reference methods for soil 

analysis. Council on Soil Testing and Plant Analysis. CRC Press, Boca Raton, FL. 

Tran, T.S., and R.R. Simard. 1993. Mehlich III-extractable elements. p. 43-50. In M.R. 

Carter (ed.) Soil sampling and methods of analysis. Can. Soc. Soil Sci. Lewis Publ., 

Boca Raton, FL. 

Soil Tests (4D) 

Citric Acid Soluble (4D7) 

UV-Visible Spectrophotometer, Dual-Beam (4D7a) 

Phosphorus (4D7a1) 

Air-Dry or Field-Moist, <2 mm (4D7a1a-b1) 

1. Application 

In soil taxonomy, citric acid soluble P2O5 is a criterion for distinguishing between 

mollic (<250 ppm P2O5) and anthropic epipedons (>250 ppm P2O5) (Soil Survey Staff, 1999). 

Additional data on anthropic epipedons from several parts of the world may permit 

improvements in this definition (Soil Survey Staff, 1999). 

Phosphorus (citrate-soluble, Method 960.01) and phosphorus (citrate insoluble, Method 

963.03) are recognized methods in the Official Methods of Analysis by the Association of 

Analytical Communities (AOAC) International (AOAC, 2000). The AOAC citrate-soluble P 

method considers the recovery of phosphite source materials as available phosphorus, even 

though the Association of American Plant Food Control Officials does not recognize phosphite 

as a source of available phosphorus. The procedure described herein is used by N.A.A.S. 

(England and Wales) and is based on the method developed by Dyer (1894). 

2. Summary of Method 

A sample is checked for CaCO3 equivalent. Sufficient citric acid is added to sample to 

neutralize the CaCO3 plus bring the solution concentration of citric acid to 1%. A 1:10 

soil:solution is maintained for all samples. The sample is shaken for 16 h and filtered. 

Ammonium molybdate and stannous chloride are added. Absorbance is read using a 

spectrophotometer at 660 nm. Data are reported as mg P2O5 kg-1 soil (4D7a1). 

3. Interferences 

Unreacted carbonates interfere with the extraction of P2O5. Sufficient citric acid is 

added to sample to neutralize the CaCO3. However, a high citrate level in sample may interfere 

with the molybdate blue test. If this occurs, the method can be modified by evaporating the 

extract and ashing in a muffle furnace to destroy the citric acid. 

Positive interferences in the analytical determination of P2O5 are silica and arsenic, if 

the sample is heated. Negative interferences in the P2O5 determination are arsenate, fluoride, 

253
thorium, bismuth, sulfide, thiosulfate, thiocyanate, or excess molybdate. A concentration of Fe 

>1000 ppm interferes with P2O5 determination. Refer to Snell and Snell (1949) and Metson 

(1956) for additional information on interferences in the citric acid extraction of P2O5. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

and bases. Dispense concentrated acids and bases in fume hood. Use the safety showers and 

eyewash stations to dilute spilled acids and bases. Use sodium bicarbonate and water to 

neutralize and dilute spilled acids. Follow standard laboratory procedures. 

5. Equipment 

5.1 Electronic balance, ±0.10-mg sensitivity 

5.2 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Centrifuge tubes, 50-mL, graduated, polyethylene 

5.4 Bottles, with gas release caps 

5.5 Filter paper, Whatman 42, 150 mm 

5.6 Funnel, 60° angle, long-stem, 50-mm diameter 

5.7 Pipettes, electronic digital, 1000 μL and 10 mL, with tips, 1000 μL and 10 mL 

5.8 Dispenser, 30-mL or 10-mL 

5.9 Cuvettes, plastic, 4.5-mL, 1-cm light path, Daigger Scientific 

5.10 Spectrophotometer, UV-Visible, Dual-View, Varian, Cary 50 Conc, Varian Australia Pty 

Ltd. 

5.11 Computer, with Cary WinUV software, Varian Australia Pty Ltd., and printer 

6. Reagents 

6.1 Reverse osmosis deonized (RODI) water 

6.2 Hydrochloric acid (HCl), concentrated, 12 N, trace pure grade 

6.3 Citric acid solution, 10%. In a 1-L volumetric, dissolve 100 g of anhydrous citric acid 

(C6H8O7) in RODI water and bring to volume with RODI water. 

6.4 Citric acid solution, 1%. Dilute 100.0 mL of 10% citric acid solution to 1-L with RODI 

water 

6.5 Ammonium molybdate solution, 1.5%. Dissolve 15.0 g of ammonium molybdate 

[(NH4)6MO7O24·4H2O] in 300 mL of distilled water. Transfer to a 1-L volumetric flask 

and carefully add 310 mL of concentrated HCl. Allow to cool. Make to 1-L volume with 

RODI water. Store in brown bottle in the dark in a refrigerator. Solution is stable for ≈ 3 

months. 

6.6 Stock stannous chloride solution (SSCS). Dissolve 10 g of stannous chloride 

(SnCl2·2H2O) in 100 mL of concentrated HCl. Invert to mix thoroughly. Make fresh 

weekly. Store in a refrigerator. 

6.7 Working stannous chloride solution (WSCS). Dilute 2 mL of SSCS with 100 mL of 

RODI water. Use immediately as solution is only stable for ≈ 4 h. 

6.8 Stock standard P2O5 solution (SSPS), 250 mg L-1 P. Dissolve 1.099 g of potassium 

dihydrogen orthophosphate (KH2PO4) that has been dried for 2 h at 110°C with RODI 

water in 1-L volumetric flask. Add 5 ml of 2 N HCl. Make to 1-L volume with RODI 

water. Invert to mix thoroughly. Store in polyethylene bottles. Make fresh weekly. Store 

in a refrigerator. 

6.9 Working stock standard P2O5 solution (WSSPS), 2.5 mg L-1 P. Pipet 10.0 mL of SSPS 

and dilute to 1-L in a volumetric flask with RODI water. Invert to mix thoroughly. Make 

fresh daily. 

6.10 Standard P2O5 calibration solutions (SPCS). Pipet 0.0, 1.0, 2.0, 3.0, 4.0, and 5.0 mL of 

WSSPS into 50-mL tubes, add 1 ml of 1% citric acid solution, 4 mL of ammonium 

molybdate solution, and dilute to 25-mL with RODI water. Add 2 mL of the working 

254
stannous chloride solution (WSCS). Final concentrations are 0.0, 0.10, 0.20, 0.30, 0.40, 

and 0.50 mg L-1, respectively. Invert to mix thoroughly. Prepare fresh weekly. Store in a 

refrigerator. Allow to equilibrate to room temperature before use. 

6.11 Quality Control Samples: 0.1 mg P L -1 solution from SSPS; blanks; selected SPCS; and 

SSL soil standard are routinely included in a batch for quality control. 

7. Procedure 

7.1 Weigh 3 g of <2-mm or fine-grind, air-dry soil to the nearest mg into a bottle with gas 

release tops. If sample is moist, weigh enough soil to achieve ≈ 3 g of air-dry soil. If the soil 

does not contain free carbonates, proceed to step 7.3. 

7.2 If the soil contains free CaCO3, refer to Table 1 to determine the amount of 10% citric acid 

solution required to neutralize the CaCO3. Add required volume of 10% citric acid into a 

graduated cylinder and bring to a volume of 30-mL with RODI water. Add this solution to the 

soil. Place the bottle in a mechanical shaker and shake the bottle for 6 h at 200 oscillations 

min-1 at room temperature (20°C ± 2°C) to dissolve and neutralize the CaCO3. Proceed to step 

7.4. 

Table 1. Volume of 10% citric acid (mL) required to decompose CaCO3 (%) and to bring 

to solution concentration to 1% in a final volume of 30 mL for 3-g sample. 

____________________________________________________________________________________________________________

%CC1 mL CA2 % CC mL CA % CC mL CA %CC mL CA 

0 3.0 16 9.1 32 15.3 48 21.4 

1 3.4 17 9.5 33 15.7 49 21.8 

2 3.8 18 9.9 34 16.1 50 22.2 

3 4.2 19 10.3 35 16.4 51 22.6 

4 4.5 20 10.7 36 16.8 52 23.0 

5 4.9 21 11.1 37 17.2 53 23.3 

6 5.3 22 11.4 38 17.6 54 23.7 

7 5.7 23 11.8 39 18.0 55 24.1 

8 6.1 24 12.2 40 18.4 56 24.5 

9 6.5 25 12.6 41 18.7 57 24.9 

10 6.8 26 13.0 42 19.1 58 25.3 

11 7.2 27 13.4 43 19.5 59 25.6 

12 7.6 28 13.7 44 19.9 60 26.0 

13 8.0 29 14.1 45 20.3 61 26.4 

14 8.4 30 14.5 46 20.7 62 26.8 

15 8.8 31 14.9 47 21.0 63 27.2 ____________________________________________________________________________________________________________ 

1

%CC = percent calcium carbonate in a sample 

2

CA = ml of 10% citric acid needed to be diluted to 30-ml volume with RODI water and added 

to sample 

7.3 If the soil contains no free CaCO3, add 30 mL of 1% citric acid solution to the sample. 

7.4 Cap the bottles, place in a mechanical shaker and shake for 16 h at 200 oscillations min- at 

room temperature (20°C ± 2°C). 

7.5 Remove the sample from shaker and filter. Collect extract. If extracts are not to be 

determined immediately after collection, then store samples at 4° C. Analyze samples within 

72 h. 

255
7.6 Pipet 1 mL of sample extract into a plastic cup. Samples are treated the same as SPCS 

(Section 6.10). Add 4 mL of ammonium molybdate solution to all samples and SPCS, and 

diluted to 25-mL with RODI water. Add 2 mL working stannous chloride solution (WSCS). 

Swirl to mix and allow to stand 20 min for color development. 

7.7 Transfer sample extract and SPCS to cuvettes. 

7.8 Set the spectrophotometer to read at 660 nm. Autozero with calibration blank. A blank has 

all reagents contained in the sample extract except the soil. 

7.9 Calibrate the instrument by using the SPCS. The data system will then associate the 

concentrations with the instrument responses for each SPCS. Rejection criteria for SPCS, if R2

<0.99. 

7.10 Run samples using calibration curve. Run samples using calibration curve. Sample 

concentration is calculated from the regression equation. Rejection criteria for batch, if blanks 

as samples > 0.01; if SPCS as samples > ± 20%; and if SSL standard > ± 20% mean. 

Record results to the nearest 0.01 unit for the sample extract and each SPCS. 

7.11 If samples are outside calibration range, dilute sample extracts with extracting solution 

and re-analyze. 

8. Calculations 

Convert the extract P2O5 (mg L-1) to soil P2O5 (mg kg-1) as follows: 

Soil P2O5 (mg kg-1) = [A x B x C1 x C2 x R x 1000 x 2.29]/E 

where: 

A = P2O5 in sample extract (mg L-1) 

B = Extract volume (L) (0.03) 

C1 = Automatic dilution (1:25) 

C2 = Dilution, if necessary 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor to kg-basis 

2.29 = Conversion factor P to P2O5

E = Sample weight (g) 

9. Report 

Report the 1% citrate acid extractable P2O5 in mg kg-1 to nearest whole number. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

American Association of Analytical Communities (AOAC), International. 2000. 

Phosphorus (Citrate-Soluble) in Fertilizers and Phosphorus (Citrate-Insoluble) in 

Fertilizers, Methods 960.01 and 963.03, respectively. Official Methods of Analysis. 

Dyer. 1894. Trans. Chem. Soc. 65:115-167. 

Metson, A.J. 1956. Methods of chemical analysis for soil survey samples. Soil Bur. Bull. 

No. 12. N.Z. Dept. Sci. and Industrial Res. 

Snell, F.D., and C.T. Snell. 1949. Colorimetric methods of analysis. Phosphorus. Vol 2. 

3rd ed. p.630-681. D. Van Nostrand Co., Inc. 

256
Soil Survey Staff. 1999. Soil taxonomy. A basic system of soil classification for making 

and interpreting soil surveys. 2nd ed. USDA-NRCS. Govt. Print. Office, Washington 

DC. 

Soil Tests (4D) 

New Zealand P Retention (4D8) 

UV-Visible Spectrophotometer, Dual-Beam (4D8a) 

Phosphorus (4D8a1) 

Air-Dry or Field-Moist, <2 mm (4D8a1a-b1) 

1. Application 

In soil taxonomy, the P retention of soil material is a criterion for andic soil properties 

(Soil Survey Staff, 1999). Andisols and other soils that contain large amounts of allophane and 

other amorphous minerals have capacities for binding P (Gebhardt and Coleman, 1984). The 

factors that affect soil P retention are not well understood. However, allophane and imogolite 

have been considered as major materials that contribute to P retention in Andisols (Wada, 

1985). Phosphate retention is also called P adsorption, sorption, or fixation. 

2. Summary of Method 

A 5-g soil sample is shaken in a 25-mL aliquot of a 1000 mg L-1 P solution for 24 h. 

The mixture is centrifuged at 2000 rpm for 15 min. An aliquot of the supernatant is transferred 

to a colorimetric tube to which nitric vanadomolybdate acid reagent (NVAR) is added. 

Absorbance of the solution is read using a spectrophotometer at 466 nm. This absorbance 

correlates to the concentration of the non–adsorbed P that remains in the sample solution. The 

New Zealand P retention (Blakemore et al., 1987) is the initial P concentration minus the P 

remaining in the sample solution and is reported as percent P retained (4D8a1). 

3. Interferences 

No significant problems are known to affect the P retention measurement. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated HNO3 to a fume hood. Use 

safety showers and eyewash stations to dilute spilled acids and bases. Use sodium bicarbonate 

and water to neutralize and dilute spilled acids. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity

5.2 Mechanical reciprocating shaker, 100 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Digital diluter/dispenser with syringes, 10000 and 1000 μL, gas tight, Microlab 500, 

Reno, NV 

5.4 Centrifuge, Centra GP-8 

5.5 Centrifuge tubes, 50 mL, polyethylene 

5.6 Cups, plastic 

5.7 Pipettes, electronic digital, 1000 μL and 10 mL, with tips, 1000 μL and 10 mL 

5.8 Dispenser, 30 mL or 10 mL 

5.9 Filter paper, Whatman 42, 150 mm 

5.11 Cuvettes, plastic, 4.5-mL, 1-cm path, Daigger Scientific 

5.12 Spectrophotometer, UV-Visible, Varian, Cary 50 Conc, Varian Australia Pty Ltd. 

5.13 Computer, with Cary WinUV software, Varian Australia Pty Ltd., with printer 

257
6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Superfloc 16, 0.2%, 2 g L-1 RODI water 

6.3 Nitric acid (HNO3), concentrated, 16 N

6.4 P retention solution (PRS), 1000 mg L-1 P. Dissolve 35.2 g of KH2PO4 that has been 

dried for 2 h at 110°C and 217.6 g of sodium acetate trihydrate (CH3COONa·3H2O) in 

RODI water. Add 92 mL of glacial acetic acid. Dilute to 8 L with RODI water. The 

solution pH should range between 4.55 and 4.65. 

6.5 Nitric acid solution. Carefully and slowly dilute 200 mL of concentrated HNO3 to 2 L of 

RODI water. Add the acid to the water. 

6.6 Molybdate solution. Dissolve 32 g of ammonium molybdate [(NH4)6Mo7O24·4H2O] in 

50°C RODI water. Allow the solution to cool to room temperature and dilute to 2 L with 

RODI water. 

6.7 Nitric vanadomolybdate acid reagent (NVAR), vanadate solution. Dissolve 1.6 g of 

NH4VO3 in 500 mL of boiling RODI water. Allow the solution to cool to room 

temperature. Carefully and slowly add 12 mL of concentrated HNO3. Dilute to 2 L with 

RODI water. Mix the nitric acid solution with the vanadate solution and then add the 

molybdate solution. Mix well. Note: This solution needs to be made in this order. 

6.8 Diluent for Standard P calibration solutions (DSPCS). Add 54.4 g of sodium acetate 

trihydrate (CH3COONa·3H2O) and 23 mL of glacial acetic acid and dilute to 2 L with 

RODI water. 

6.9 Standard P calibration solutions (SPCS), 100, 80, 60, 40, 20, and 0% P retained. Make 

fresh weekly. Store in a refrigerator. Allow to equilibrate to room temperature before 

use. To six 100-mL volumetric flasks add the appropriate amount of PRS (1000 mg L-1) 

and bring to volume with DSPCS solution as follows: 

6.9.1 100% SPCS = (0 mg L-1) = Bring to 100-mL volume with DSPCS solution. 

6.9.2 80% SPCS = 1: 20 (200 mg L-1) = Add 20 mL PRS and bring to 100-mL volume with 

DSPCS solution. 

6.9.3 60% SPCS = 1:10 (400 mg L-1) = Add 40 mL PRS and bring to 100-mL volume with 

DSPCS solution. 

6.9.4 40% SPCS = 3:20 (600 mg L-1) = Add 60 mL PRS and bring to 100-mL volume with 

DSPCS solution. 

6.9.5 20% SPCS = 1:5 (800 mg L-1) = Add 80 mL PRS and bring to 100-mL volume with 

DSPCS solution. 

6.9.6 0% SPCS = 1:4 (1000 mg L-1) = Add 100 mL PRS to a 100-mL volumetric. 

 

6.10 Quality Control: SSL soil standard is routinely included in every batch of 24 samples for 

quality control. 

7. Procedure 

7.1 Weigh 5g of <2-mm or fine-grind, air-dry soil to the nearest mg into a 50-mL centrifuge 

tube. If sample is moist, weigh enough soil to achieve ≈ 5 g of air-dry soil. No fine-grind 

material is used for this procedure. 

7.2 Use the dispenser to add 25.0 mL of P-retention solution to centrifuge tube. 

258
7.3 Transfer the sample to the shaker. Shake for 24 h at 100 oscillations min-1 at room 

temperature (20°C± 2°C). 

7.4 Remove sample from the shaker. Add 2 to 3 drops of Superfloc, 0.02% w/v to each tube. 

Centrifuge at 2000 rpm for 15 min, decant, filter, and collect extract in receiving cup. If 

extracts are not to be determined immediately after collection, then store samples at 4°C. 

Analyze samples within 72 h. 

7.5 Use the digital diluter to add the nitric vanadomolybdate acid reagent (NVAR) to each 

sample supernatant and to each SPCS. To fill a 4.5-mL cuvette, use a dilution of 1:20 sample 

dilution. 

7.6 The color reaction requires a minimum of 30 min before the analyst records readings. 

7.7 Set the spectrophotometer to read at 466 nm. Auto zero with the calibration blank. 

7.8 Calibrate the instrument using the SPCS. The data system will then associate the % P 

retained with the instrument responses. Rejection criteria for SPCS, if R2

 <0.99. 

7.9 Run samples using calibration curve. Sample P retention is calculated from the regression 

equation, i.e., the absorbance is equated to the SPCS. Rejection criteria for batch, if blanks as 

samples > 0.01; if SPCS as samples > ± 20%; and if SSL standard > ± 20% mean. Record 

results to the nearest 0.01 unit for the sample extract and each SPCS. 

7.10 If samples are outside calibration range, dilute sample extracts with extracting solution 

and re-analyze. 

8. Calculations 

None.for this proce 

9. Report

Report the percent New Zealand P retention to the nearest whole number. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Blakemore, L.C., P.L. Searle, and B.K. Daly. 1987. Methods for chemical analysis of soils. 

43 p. NZ Bureau Scientific Report 80, NZ Soil Bur. Lower Hutt, NZ. 

Gebhardt, H., and N.T. Coleman. 1984. Anion adsorption of allophanic tropical soils: III. 

Phosphate adsorption. p. 237-248. In K.H. Tan (ed.) Anodosols. Benchmark papers in 

soil science series. Van Nostrand Reinhold, Co., Melbourne, Australia. 

Soil Survey Staff. 1999. Soil taxonomy. A basic system of soil classification for making 

and interpreting soil surveys. 2nd ed. USDA-NRCS. Govt. Print. Office, Washington 

DC. 

Wada, K. 1985. The distinctive properties of Andosols. p. 173-229. In B.A. Stewart (ed.) 

Advances in Soil Science. Springer-Verlag, New York, NY. 

259
Soil Tests (4D) 

1 M KCl Extraction (4D9) Cadmium-Copper Reduction (4D9a) 

Sulfanilamide N-1-Naphthylethylenediamine Dihydrochloride (4D9a1) Flow-Injection, Automated Ion Analyzer (4D9a1a) 

Nitrate-Nitrite (4D9a1a1-2) 

Air-Dry or Field-Moist, <2 mm (4D9a1a1-2a-b1) 

1. Application 

The inorganic combined N in soils is predominantly NH4

+

 and NO3

-

 (Keeney and 

Nelson, 1982). Nitrogen in the form of ammonium ions and nitrate are of particular concern 

because they are very mobile forms of nitrogen and are most likely to be lost to the 

environment (National Research Council, 1993). All forms of nitrogen, however, are subject to 

transformation to ammonium ions and nitrate as part of the nitrogen cycle in agroecosystems 

and all can contribute to residual nitrogen and nitrogen losses to the environment (National 

Research Council, 1993). 

2. Summary of Method A 2.5-g soil sample is mechanically shaken for 30 min in 25 mL of 1 M KCl solution. 

The sample is then filtered through Whatman No. 42 filter paper. A flow injection automated 

ion analyzer is used to measure the soluble inorganic nitrate (NO3

-

). The nitrate is 

quantitatively reduced to nitrite by passage of the sample through a copperized cadmium 

column. The nitrite (reduced nitrate plus original nitrite) is then determined by diazotizing with 

sulfanilamide followed by coupling with N-1-naphthylethylenediamine dihydrochloride. The 

resulting water soluble dye has a magenta color which is read at 520 nm. Absorbance is 

proportional to the concentration of NO3

-

 in the sample. Data are reported as mg N kg-1 soil as 

NO3

-

 and/or NO2

-

 (4D9a1a1-2, respectively). 

3. Interferences 

Low results can be obtained for samples that contain high concentration of Fe, Cu, or 

other metals. In this method, EDTA is added to the buffer to reduce this interference 

(LACHAT, 1993). 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of NH4OH and concentrated HCl to a fume 

hood. Use safety showers and eyewash stations to dilute spilled acids and bases. Use sodium 

bicarbonate and water to neutralize and dilute spilled acids. Cadmium is toxic and 

carcinogenic. Wear gloves and follow the precautions described on the Material Safety Data 

Sheet. If repacking the cadmium-copper reduction column, do all transfers over a special tray 

or beaker dedicated to this purpose. Preferably, send the cadmium-copper column to LACHAT 

for repacking. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Centrifuge tubes, 25 mL, polyethylene, Oak Ridge 

5.3 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.4 Centrifuge, 50-mL, polyethylene 

5.5 Pipettes, electronic digital, 2500 μL and 10 mL, with tips, 2500 μL and 10 mL 

5.6 Filter paper, Whatman No. 42, 150 mm 

5.7 Funnel, 60° angle, long stem, 50-mm diameter 

260
5.8 Volumetric flasks, 1-L and 250-mL 

5.9 Bottles, plastic, dark, 1-L 

5.10 Cups, plastic 

5.11 Dispenser, 30 mL or 10 mL 

5.12 Flow Injection Automated Ion Analyzer, QuikChem AE, LACHAT Instruments, 

Milwaukee, WI, with computer and printer 

5.13 XYZ Sampler, LACHAT Instruments, Milwaukee, WI 

5.14 Reagent Pump, LACHAT Instruments, Milwaukee, WI 

5.15 Automated Dilution Station, LACHAT Instruments, Milwaukee, WI 

5.16 Sample Processing Module (SPM) or channel, QuikChem Method (12-107-04-1-B, 

nitrate/nitrite in 1 M KCl 0.02 to 20.0 mg N L-1), LACHAT Instruments, Milwaukee, WI 

5.17 Computer, with QuikChem software, LACHAT Instruments, Milwaukee, WI, and printer 

5.18 Vials, plastic, 25-mL (standards) 

5.19 Culture tubes, glass, 10-mL (samples) 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Helium, compressed gas 

6.3 15 M NaOH. In a 500-mL container, add 250 ml RODI water. Slowly add 300 g NaOH. 

(CAUTION: The solution will get very hot!) Swirl until dissolved. Cool and store in a 

plastic bottle. Used to adjust ammonium chloride buffer to pH 8.5 (reagent 6.4). 

6.4 Ammonium chloride buffer, pH 8.5. In a hood, add 500 mL RODI to a 1-L volumetric 

flask. Add 105 mL concentrated HCl, 95 mL ammonium hydroxide (NH4OH) and 1.0 g 

disodium EDTA. Dissolve and dilute to mark. Invert to mix. Degas with helium ≈ 5 

min. 

6.5 Sulfanilamide color reagent. To a 1-L volumetric flask, add 600 mL RODI H2O followed 

by 100 mL 85 percent phosphoric acid (H3PO4), 40.0 g sulfanilamide, and 1.0 g N-1-

naphthylethylenediamine dihydrochloride (NED). Shake to wet and stir to dissolve 20 

min. Dilute to mark, invert to thoroughly mix. Degas with helium ≈ 5 min. Store in dark 

bottle and discard when pink. 

6.6 1 M KCl extracting solution, carrier and standards diluent. Dissolve 74.5 g potassium 

chloride (KCl) in 800 mL RODI water. Dilute to mark and invert to thoroughly mix. 

The extracting solution is used also as the carrier and a component of the N standards. 

Degas with helium ≈ 5 min. 

6.7 The following are standards preparation for a 1 channel system determining NO2

-

 + NO3

-

or NO2

-

 and a 2 channel system where one channel is used for NO2

-

 + NO3

-

 and the other 

channel is used for determining NO2

-

. For the 1 channel system, either NO2

-

 or NO3

-

standards may be used. It is recommended that when running a 1 channel method for 

NO2

-

 + NO3

-

 that NO3

-

 standards are used. For the 2 channel system, the use of both NO2

-

+ NO3

-

 standard sets are recommended. 

6.7.1 Stock standard nitrate solution (SSNO3S), 200.0 mg N L-1 as NO3

-

 in 1 M KCl. In a 1-L 

volumetric flask, dissolve 1.444 g potassium nitrate (KNO3) dried in an oven for 2 h at 

110° C and 74.5 g KCl in 600 mL RODI water. Dilute to mark with RODI water and 

invert to thoroughly mix. Store in polyethylene containers. Make fresh weekly. Store in 

a refrigerator. 

6.7.2 Working stock standard nitrate solution (WSSNO3S), 20.0 mg N L-1 as NO3

-

 in 1 M KCl. 

To a 1-L volumetric flask, add 100 ml SSNO3S. Dilute to mark with 1 M KCl and invert 

to thoroughly mix. Make fresh daily. 

6.7.3 Standard nitrate calibration standards (SNO3CS) or working standards, 10.00, 2.00, 0.80, 

0.08, and 0.00 mg N L-1 as NO3

-

 in 1 M KCl. Make fresh daily. To five 250-mL 

volumetric flasks add as follows: 

6.7.3.1 10.00 mg N L-1 = 125.0 mL WSSNO3S 

6.7.3.2 2.00 mg N L-1 = 25.0 mL WSSNO3S 

261
6.7.3.3 0.80 mg N L-1 = 10.0 mL WSSNO3S 

6.7.3.4 0.08 mg N L-1 = 1.00 mL WSSNO3S 

6.7.3.5 0.00 mg N L-1 = 0.0 mL WSSNO3S (blank) 

Dilute each SNO3CS to the mark with 1 M KCl and invert to thoroughly mix. Do not degas. 

6.7.4 Stock standard nitrite solution (SSNO2S), 200.0 mg N L-1 as NO2

-

 in 1 M KCl. In a 1-L 

volumetric flask, dissolve 0.986 g sodium nitrite (NaNO2) or 1.214 g potassium nitrite 

(KNO2), and 74.5 g KCl in 800 mL RODI water. Dilute to mark with RODI water and 

invert to thoroughly mix. Store in polyethylene containers. Make fresh weekly. Store in a 

refrigerator. 

6.7.5 Working stock standard nitrite solution (WSSNO2S), 20.0 mg N L-1 as NO2

-

 in 1 M KCl. 

To a 1-L volumetric flask, add 100 ml SSNO2S. Dilute to mark with 1 M KCl and invert 

to thoroughly mix. Make fresh daily. 

6.7.6 Standard nitrite calibration standards (SNO2CS) or working standards, 10.00, 2.00, 0.80, 

0.08, and 0.00 mg N L-1 as NO3

-

 in 1 M KCl. Make fresh daily. To five 250-mL 

volumetric flasks add as follows: 

6.7.6.1 10.00 mg N L-1 = 125.0 mL WSSNO2S 

6.7.6.2 2.00 mg N L-1 = 25.0 mL WSSNO2S 

6.7.6.3 0.80 mg N L-1 = 10.0 mL WSSNO2S 

6.7.6.4 0.08 mg N L-1 = 1.00 mL WSSNO2S 

6.7.6.5 0.00 mg N L-1 = 0.0 mL WSSNO2S (blank) 

Dilute each SNO2CS to the mark with 1 M KCl and invert to thoroughly mix. Do not degas. 

7. Procedure 

Extraction 

7.1 Weigh 2.5 g of <2-mm or fine-grind, air-dry soil to the nearest mg and place into a 50-mL 

centrifuge tube. If sample is moist, weigh enough soil to achieve ≈ 2.5 g of air-dry soil. 

7.2 Add ≈ 25 mL of 1 M KCl to sample. Transfer the sample to a shaker. Shake for 30 min at 

200 oscillations min-1 at room temperature (20°C ± 2°C). 

7.3 Remove the sample from the shaker. Decant, filter, and collect extract in receiving cups. If 

extracts are not to be determined immediately after collection, then store samples at 4°C. 

Analyze samples within 24 h. 

Flow Injection Set-up and Operation 

7.4 Transfer sample extracts into culture tubes and place in XYZ sample trays marked 

"Samples". 

7.5 Transfer WNCS standards into plastic vials and place in descending order in XYZ sample 

trays marked "Standards". 

7.6 Refer to the operating and software reference manuals for LACHAT for set-up and 

operation. 

 

7.7 Turn main power switch "ON". 

7.8 Before inserting cadmium-copper reduction column, pump all reagents into manifold. Turn 

pump off. On the column, disconnect the center tubing from one of the union connectors and 

immediately connect to the outlet tubing of the buffer mixing coil. Connect the open tubing on 

262
the column to the tee fitting where the color reagent is added. Do not let air enter the column. 

Return the pump to normal speed. If air is introduced accidentally, connect the column into the 

manifold, turn the pump on maximum, and tap column, working up the column until all air is 

removed. Average life of column is approximately 600 samples. Upon degradation, the 

column needs to be replaced. 

7.9 On computer main menu, select "Methods" and then "Analysis Select and Download". On 

method list, select 1 M KCl N method. System unit receives the downloaded method and 

initializes it. On computer main menu, select "Samples", "Tray Definition and Submit", and 

then "Edit" to create new sample tray followed by "Submit" to run new sample tray. 

7.10 Upon connection of cadmium column and downloading of 1 M KCl Method, continue to 

pump reagents into manifold. Continue this step and observe baseline. A good baseline needs 

to be smooth and at zero absorbance. Scatter is indicative of air bubbles and irregular reagent 

flow. Also observe for any back-pressure in manifold tubing. 

7.11 Method parameters specific to 1 M KCl N are defined within the "Method Definition" 

menu. Some of these parameters have been modified from the QuikChem Method 12-107-04-

1-B, nitrate-nitrite in 2 M (1 M) KCl soil extracts (U.S. Environmental Protection Agency, 

1983; LACHAT Instruments, 199; U.S. Department of Interior, Geological Survey, 1993). 

7.12 Some of the method parameters as they relate to calibration standards (nitrate - nitrite) are 

as follows: 

7.12.1 There are 5 calibration standards (10.00, 2.00, 0.80, 0.08, and 0.00 mg N L-1), with a 

data format of ####.###, i.e., data rounded to 3 places. 

7.12.2 The segments/boundaries for the calibration standards are A - C (10.0 to 0.8 mg N L-1) 

and C - E (0.8 to 0.0 mg N L-1). 

7.12.3 The protocol (replications) for the calibration standards is as follows: AA BB CCC DDD 

EE. 

7.12.4 Check standard is 10.0 mg N L-1. Maximum number of consecutive trays between 

check standard is one; maximum number of consecutive samples between check standard is 60; 

and maximum elapse time between check standards is 2 h. 

7.12.5 Calibration strategy for segments A - C and C - E are normal. The normal strategy 

requires a minimum correlation coefficient of 0.99. Both segments require a maximum 

standard deviation in slope of 50%. A calibration passes only when both criteria are met. 

Strategies are user designated. In addition, calibration strategies are based on the full chord. 

Chord 0 is full chord, and chord 1 - 5 are sections of peak from start of peak to end of peak. 

7.12.6 The instrument is calibrated with the injection of SNO3CS and/or SNO2CS. The data 

system is calibrated with the injection of SNO3CS and/or SNO2CS. The data system then 

associates the concentrations with the instrument response for each SNO3CS and/or SNO2CS. 

7.13 Method parameters in relation to timing are as follows: 

7.13.1 Cycle period: 40 s 

7.13.2 Inject to start of peak period: 27 s. To see if peaks are being timed correctly, scan across 

correlation coefficients for all chords 1 - 5. The most peak area is supposed to be in chords 2 - 

4 with the most signal-to-noise ratio in chords 1 and 5. 

263
7.13.3 Inject to end of peak period: 63 s 

7.13.4 Automatic timing, where standard assumptions are in effect; no manual timing. 

7.14 Method parameters in relation to data presentation are as follows: 

7.14.1 Top Scale Response: 0.50 abs 

7.14.2 Bottom Scale Response: 0.00 abs 

7.15 Refer to the "Method Definition" for 1 M KCl nitrate for other method parameters not 

discussed here. 

7.16 Run samples using calibration curve. Sample concentration is calculated from the 

regression equations. Report results to the nearest 0.01 unit for the sample extract and each 

SPCS. 

7.17 If samples are outside calibration range, dilute samples with extracting solution and reanalyze. 

7.18 Upon completion of run, place the transmission lines into RODI water and pump for 

approximately 20 min and proceed with the normal "Shut-down" procedure. 

7.19 The accumulation of 1 M KCl in the manifold tubing and the fittings may cause clogs over 

time. Upon completion of analysis, the valves and fittings need to be washed with RODI 

water. Some fittings may need to be soaked overnight or placed in a sonic bath for 10 to 15 

min to remove any KCl accumulations. 

8. Calculations 

Convert extract N (mg L-1) to soil N (mg kg-1) as follows: 

Soil N = [ (A x B x C x R x 1000)/E] 

where: 

A = Sample extract reading (mg N L-1) 

B = Extract volume (L) 

C = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report 

Report data to the nearest 0.1mg N kg-1 soil as NO3

-

 and/or NO2

-

. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Keeney, D.R., and D.W. Nelson. 1982. p. 643-698. Nitrogen - inorganic forms. In A.L. 

Page, R.H. Miller, and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical 

and microbiological properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, 

WI. 

264
LACHAT Instruments. 1992. QuikChem method 12-107-04-1-B, nitrate in 2 M (1 M) KCl 

soil extracts, 0.02 to 20.0 mg N L-1. LACHAT Instruments, 6645 West Mill Rd., 

Milwaukee, WI. 

National Research Council. 1993. Soil and water quality. An agenda for agriculture. 

Committee on long-range soil and water conservation. Natl. Acad. Press, Washington, 

DC. 

U.S. Department of Interior, U.S. Geological Survey. 1993. Methods for determination of 

inorganic substances in water and fluvial sediments. Book 5. Chapter Al. Method I2601-78. 

U.S. Environmental Protection Agency. 1983. Methods for chemical analysis of water and 

wastes. EPA-600/4-79-020. Revised March, 1983, Method 353.2. 

Soil Tests (4D) 

Aerobic Incubation (4D10) 

2 M KCl Extraction (4D10a) 

Ammonia –Salicylate (4D10a1) 

Flow Injection, Automated Ion Analyzer (4D10a1a) 

N as NH3 (Mineralizable N) (4D10a1a1) Air-Dry or Field-Moist, <2 mm (4D10a1a1a-b1) 

1. Application 

The most satisfactory methods currently available for obtaining an index for the 

availability of soil N are those involving the estimation of the N formed when soil is incubated 

under conditions which promote mineralization of organic N by soil microorganisms 

(86Environmental Protection Agency, 1992). The method described herein for estimating 

mineralizable N is one of anaerobic incubation and is suitable for routine analysis of soils. This 

method involves estimation of the ammonium produced by a 1-week period of incubation of 

soil at 40°C (Keeney and Bremner, 1966) under anaerobic conditions to provide an index of N 

availability. 

2. Method Summary 

An aliquot of air-dry homogenized soil is placed in a test tube with water, stoppered, 

and incubated at 40°C for 1 week. The contents are rinsed with 2 M KCl. A flow injection 

automated ion analyzer is used to measure the ammonium produced in the soil after incubation. 

Absorbance of the solution is read at 660 nm. Data are reported as mg N kg-1 soil as NH3 by 

procedure 4D10a1a1. 

3. Interferences 

The temperature and incubation period must remain constant for all samples. The test 

can be performed on field-moist or air-dry soil samples. Soil extracts can contain sufficient 

concentrations of calcium and magnesium to cause precipitation during analysis. EDTA is 

added to eliminate this problem (Keeney and Nelson, 1982). 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

and bases. Dispense concentrated acids and bases in a fume hood. Thoroughly wash hands 

after handling reagents. Use the safety showers and eyewash stations to dilute spilled acids and 

bases. Use sodium bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Test tubes, 16-mm x 150-mm 

5.3 PVC stoppers 

265
5.4 Incubator, Model 10-140, Quality Lab Inc., Chicago, IL 

5.5 Centrifuge, 50-mL, polyethylene 

5.6 Filter paper, Whatman No. 42, 150 mm 

5.7 Funnel, 60° angle, long stem, 50-mm diameter 

5.8 Flow Injection Automated Ion Analyzer, QuikChem AE, LACHAT Instruments, 

Milwaukee, WI 

5.9 XYZ Sampler, LACHAT Instruments, Milwaukee, WI 

5.10 Reagent Pump, LACHAT Instruments, Milwaukee, WI 

5.11 Automated Dilution Station, LACHAT Instruments, Milwaukee, WI 

5.12 Sample Processing Module (SPM) or channel, QuikChem Method (12-107-06-2-A, 

ammonia (salicylate) in 2 M KCl soil extracts, 0.05 to 10.0 mg P L-1), LACHAT 

Instruments, Milwaukee, WI 

5.13 Computer, with QuikChem software, LACHAT Instruments, Milwaukee, WI, and printer 

5.14 Vials, plastic, 25-mL (standards) 

5.15 Culture tubes, glass, 10-mL (samples) 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Helium, compressed gas 

6.3 Potassium chloride (KCl), 2 M, carrier and standards diluent. Dissolve 150 g KCl in 

RODI water and dilute to 1-L volume. Mix thoroughly. Degas with helium. 

6.4 EDTA (ethylene tetraacetic acid disodium salt dihydrate), 6% solution. Dissolve 66 g 

EDTA in 900 mL RODI water. Dilute to 1-L and invert to mix thoroughly. Degas with 

helium. 

6.5 NaOH, buffer. Dissolve 28.0 g NaOH and 50.0 g sodium phosphate dibasic heptahydrate 

(Na2HPO4·7H20) in 900 mL RODI water. Dilute to 1-L and invert to mix thoroughly. 

Degas with helium. 

6.6 Salicylate-Nitroprusside Color Reagent. Dissolve 150 g sodium salicylate [salicylic acid 

sodium salt (C6H4(OH)(COO)Na)], and 1.0 g sodium nitroprusside [sodium 

nitroferricyanide dihydrate (Na2Fe(CN)5NO·2H2O)] in 800 mL RODI water. Dilute to 1-

L and invert to mix thoroughly. Degas with helium. Store in dark bottle in a refrigerator. 

6.7 Hypochlorite Reagent. In a 500-mL volumetric, dilute 250 mL of 5.25% sodium 

hypochlorite (NaOCl) to mark with RODI water. Invert to mix thoroughly. Degas with 

helium. 

6.8 Stock standard N solution (SSNS), 100.0 mg N L-1. In a 1-L volumetric flask, dissolve 

150 g potassium chloride (KCl) and 0.3819 g of ammonium chloride (NH4Cl) that has 

dried for 2 h at 110°C in about 800 mL RODI water. Dilute to volume with RODI water 

and invert to thoroughly mix. Do not degas with helium. Store in polyethylene 

containers. Make fresh weekly. Store in a refrigerator. 

6.9 Standard N calibration solutions (SNCS) or working standards, 20.0, 8.00, 2.00, 0.50, 

0.10, 0.00 mg N L-1. Make fresh daily. To six 250-mL volumetric flasks add as follows: 

6.9.1 20.00 mg P L-1 = 50.0 mL SSNS 

6.9.2 8.00 mg P L-1 = 20.0 mL SSNS 

6.9.3 2.00 mg P L-1 = 5.0 ml SSNS 

6.9.4 0.50 mg P L-1 = 1.25 mL SSNS 

6.9.5 0.10 mg P L-1 = 0.25 mL SSNS 

6.9.6 0.00 mg P L-1= 0.0 mL SSNS (blank) 

Dilute to mark with 2 M KCl. Invert to mix thoroughly. 

266
7. Procedure 

Anaerobic Incubation of Soil Sample

7.1 Weigh 5 g of <2 mm, air-dry soil to the nearest mg into a 16-mm x 150-mm test tube. If 

soil is fine-grind, weigh 1.25 g. If sample is moist, weigh enough soil to achieve ≈ 5 or 1.25 g, 

respectively, of air-dry soil. 

7.2 Add 12.5 ±1 mL of RODI water. Do not add ethanol to overcome any wetting difficulties 

as ethanol may act as an interference with microbial activity. Stopper the tube, shake, and 

place in a 40°C constant-temperature incubator for 7 days. Refer to the manufacturer's 

instructions for set-up and operation of the incubator. 

7.3 At the end of 7 days, remove the tube and shake for 15 s. 

7.4 Transfer the contents of the test tube to another test tube. Complete the transfer by rinsing 

the tube with 3 times with 4 ml of 2 M KCl, using a total of 12.5 ±1 mL of the KCl. Filter 

contents into a centrifuge tube. If extracts are not to be determined immediately after collection, 

then store samples at 4°C. Analyze samples within 24 h. Ammonia is volatile and will leave 

the sample slowly, even though contained in polyethylene bottles. 

Flow Injection Set-up and Operation 

7.5 Transfer sample extracts into culture tubes and place in XYZ sample trays marked 

“Samples”. 

7.6 Transfer WNCS standards into plastic vials and place in descending order in XYZ sample 

trays marked "Standards". 

7.7 Refer to the operating and software reference manuals for LACHAT for set-up and 

operation. 

 

7.8 Turn main power switch "ON" and allow 15 min for heater module to warm up to 60°C. 

7.9 On reagent pump, set speed to 35. 

7.10 On computer main menu, select "Methods" and then "Analysis Select and Download". On 

method list, select Mineralizable N Method. System unit receives the downloaded method and 

initializes it. 

7.11 Pump reagents (6.4, 6.5, 6.6, 6.7) into appropriate chambers of the manifold. Continue 

this step and observe baseline. A good baseline needs to be smooth and at zero absorbance. 

Scatter is indicative of air bubbles and irregular reagent flow. Also observe for any backpressure in manifold tubing. 

7.12 On computer main menu, select "Samples", "Tray Definition and Submit", and then "Edit" 

to create new sample tray followed by "Submit" to run new sample tray. 

7.13 Method parameters specific to mineralizable N are defined within the "Method Definition" 

menu. Some of these parameters have been modified from the QuikChem Method 12-107-06-

2-A, ammonia (salicylate) in 2 M KCl soil extracts (U.S. Environmental Protection Agency, 

1979; LACHAT Instruments, 2001). Modifications are primarily related to the criteria and 

strategies for calibration standards and to injection timing. 

7.14 Some of the method parameters as they relate to calibration standards are as follows: 

267
7.14.1 There are 6 calibration standards (20.00, 8.00, 2.00, 0.50, 0.10, and 0.00 mg P L-1) with 

a data format of ####.###, i.e., data rounded to 3 places. 

7.14.2 The segments/boundaries for the calibration standards are A - C (20.0 to 2.00 mg P L-1); 

C - F (2.00 to 0.00 mg P L-1). 

7.14.3 The protocol (replications) for the calibration standards is as follows: AA BB CC DD 

EE FF. 

7.14.4 The check standard is 20 mg P L-1. Maximum number of consecutive trays between 

check standard is one; maximum number of consecutive samples between check standard is 60; 

and maximum elapse time between check standards is 2 h. 

7.14.5 Calibration strategy for segments A – C and C - F are normal. The normal strategy 

requires a minimum correlation coefficient of 0.99. Both segments require a maximum 

standard deviation in slope of 50%. A calibration passes only when both criteria are met. 

Strategies are user designated. In addition, calibration strategies are based on the full chord. 

Chord 0 is full chord, and chord 1 - 5 are sections of peak from start of peak to end of peak. 

7.14.6 The instrument is calibrated with the injection of SNCS. The data system the associates 

the concentrations with the instrument response for each SNCS. 

7.15 Method parameters in relation to timing are as follows: 

7.15.1 Cycle period: 40 s 

7.15.2 Inject to start of peak period: 25 s. To see if peaks are being timed correctly, scan across 

correlation coefficients for all chords 1 - 5. The most peak area should be between chords 2 - 4 

with the most signal-to-noise ratio in chords 1 and 5. 

7.1.5.3 Inject to end of peak period: 46 s 

7.15.4 Automatic timing, where standard assumptions are in effect. Manual timing may be 

helpful in this method. 

7.16 Method parameters in relation to data presentation are as follows: 

7.16.1 Top Scale Response: 0.50 abs 

7.16.2 Bottom Scale Response: 0.00 abs 

7.17 Refer to the "Method Definition" for Mineralizable N for other method parameters not 

discussed here. 

7.18 Run samples using calibration curve. Sample concentration is calculated from the 

regression equations. Report results to the nearest 0.01 unit for the sample extract and each 

SNCS. 

7.19 If samples are outside calibration range, dilute samples with extracting solution and reanalyze. 

 

7.20 Upon completion of run, place the transmission lines into the 1 M HCl. Pump the solution 

for approximately 5 min to remove any precipitated reaction products. Then place these lines in 

268
RODI water and pump for an additional 5 min and proceed with the normal "Shut-down" 

procedure. 

8. Calculations 

Convert extract N (mg L-1) to soil N (mg kg-1) as follows: 

Soil N = [(A x B x C x R x 1000)/E]

where: 

A = Analyte reading (mg L-1) 

B = Extract volume (L) 

C = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report 

Report data to the nearest mg N kg-1 soil as NH3. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References Keeney, D.R., and J.M. Bremner. 1966. Comparison and evaluation of laboratory methods 

of obtaining an index of soil nitrogen availability. Agron. J. 58:498-503. 

Keeney, D.R., and D.W. Nelson. 1982. Nitrogen – inorganic forms. p. 643-698. In A.L. 

Page, R.H. Miller, and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical 

and microbiological properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, 

WI. 

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Carbonate and Gypsum (4E) 

3 N HCl Treatment (4E1) CO2 Analysis (4E1a) Manometer, Electronic (4E1a1) 

Calcium Carbonates (4E1a1a1) 

Air-Dry, <2 mm (4E1a1a1a1) 

Air-Dry, <20 mm (4E1a1a1a2) 

1. Application 

The distribution and amount of CaCO3 are important for fertility, erosion, available 

water-holding capacity, and genesis of the soil. Calcium carbonate provides a reactive surface 

for adsorption and precipitation reactions, e.g., phosphate, trace elements, and organic acids 

(Loeppert and Suarez, 1996; Amer et al., 1985; Talibudeen an Arambarri, 1964; Boischot et al., 

1950). The determination of calcium carbonate (CaCO3) equivalent is a criterion in soil 

taxonomy (Soil Survey Staff, 1999). Carbonate content of a soil is used to define carbonatic, 

particle-size, and calcareous soil classes and to define calcic and petrocalcic horizons (Soil 

Survey Staff, 1999). The formation of calcic and petrocalcic horizons has been related to a 

269
variety of processes, some of which include translocation and net accumulation of pedogenic 

carbonates from a variety of sources as well as the alteration of lithogenic (inherited) carbonate 

to pedogenic carbonate (soil-formed carbonate through in situ dissolution and reprecipitation of 

carbonates) (Rabenhorst et al., 1991). The CaCO3 equivalent is most commonly reported on the 

<2-mm base. However, in some soils with hard carbonate concretions, carbonates are 

determined on both the <2-mm (4E1a1a1a1) and the 2- to 20-mm basis (4E1a1a1a2). 

2. Summary of Method 

The amount of carbonate in the soil is measured by treating the samples with HCl. The 

evolved CO2 is measured manometrically. The amount of carbonate is then calculated as 

percent CaCO3. 

3. Interferences 

Chemical interference is the reaction by the acid with other carbonates, e.g., carbonates 

of Mg, Na, and K, that may be present in soil sample. The calculated CaCO3 is only a 

semiquantitative measurement (Nelson, 1982). 

Analytical interference may be caused by temperature changes within the reaction 

vessel. When sealing the vessel, the analyst should not hold the vessel any longer than 

necessary to tighten the cap. The internal pressure must be equalized with the atmosphere. 

After the septum has been pierced with a needle, ≈ 5 to 10 s are required to equalize the internal 

pressure of the bottle. With extensive use, the septa leak gas under pressure. The septa should 

be replaced at regular intervals. The analyst should not touch the glass of the vessel when 

reading the pressure. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when handling acids. Thoroughly wash hands after 

handling acids. Use the fume hood when diluting concentrated HCl. Use the safety showers 

and eyewash stations to dilute spilled acids. Use sodium bicarbonate and water to neutralize 

and dilute spilled acids. 

The gelatin capsule may leak acid while being filled. Keep other personnel away from 

the area when filling capsules. 

High pressure may develop inside the bottle if there is a large amount of calcareous 

sample. Do not use more than 2 g of any sample in the bottles. If high pressure develops in the 

bottle, release the pressure by venting the gas with a syringe needle. Some bottles may break 

without shattering. Discard any bottle with hairline cracks or obvious defects. 

5. Equipment 

5.1 Electronic balance, ±0.10-mg sensitivity 

5.2 Electronic balance, ±1mg-sensitivity

5.3 Threaded weighing bottles, wide-mouth, clear glass, standard, 120 mL (4 fl. oz.), 48-mm 

neck size. For best results, grind rim of bottle with 400-600 grit sandpaper on a flat glass 

plate. 

5.4 Machined PVC caps for threaded 120-mL (4 fl. oz.) weighing bottles, 54-mm diameter 

with 12.7-mm diameter hole drilled in center, O-ring seal. 

5.5 O-rings, 3.2 x 50.8 x 57.2 mm (1/8 x 2 x 2 1/4 in) 

5.6 Flanged stopper No. 03-255-5, Fisher Scientific. Place in machined cap. 

5.7 Manometer, hand-held gauge and differential pressure, PCL-200 Series, Omega 

Engineering, Stanford, CT.

5.8 Hypodermic needle, 25.4 mm (1 in), 23 gauge. Connect needle to pressure tubing on 

transducer. 

5.9 Mechanical rotating shaker, 140 rpm, Eberbach 6140, Eberbach Corp., Ann Arbor, MI. 

270
6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Methyl red indicator 

6.3 Hydrochloric acid (HCl), concentrated, 12 N

6.4 HCl, 3 N. Dilute 500 mL of concentrated HCl with 1500 mL RODI water. Add a few 

crystals of methyl red indicator. Methyl red indicator will turn yellow if HCl is consumed 

by sample. If this reaction occurs, adjust the sample size (smaller). 

6.5 Gelatin capsule, 10 mL, size 11, Torpac Inc., Fairfield, NJ. 

6.6 Gylcerine, USP. Put the gylcerine in a small squeeze bottle and use as a lubricant for the 

O- rings. 

6.7 CaCO3, Ultrex, assay dried basis 100.01%, 

7. Procedure 

Manometer Calibration 

7.1 Calibrate the manometer quarterly or whenever equipment changes (e.g., old rubber septum 

replaced). Calibrate by weighing three replicates of CaCO3 standards (0, 0.025, 0.05, 0.1, 0.2, 

0.3, 0.4, 0.5, 0.75 g). Weigh to the nearest 0.1mg. Dry the standard samples in the oven for 2 h 

at 110°C. Remove samples from oven, place in desiccator and cool to ambient temperature. 

Proceed as outlined in Sections 7.4 through 7.9. 

<2-mm Basis 

7.2 A CaCl2 pH >6.95 is generally used as an indicator of the presence of carbonates. The 

presence of carbonates (effervescence with HCl) is also checked during lab preparation 

(procedure 1B1b2b5). 

7.3 Weigh 0.5 to 2 g of fine-grind, air-dry soil sample to the nearest mg and place in a 120-mL, 

wide-mouth bottle. Run 3 blanks and a quality control check sample with every batch of 24 

samples. The quality control check sample serves as a single point check. Vary the sample 

weight according to the CaCO3 content based on effervescence of sample (procedure 1B1b2b5) 

as follows: 

7.3.1 Use a 2-g sample weight if effervescence is None, Very Slight, or Slight. 

7.3.2 Use a 1-g sample weight, if effervescence is Strong. 

7.3.3 Use a 0.5-g sample weight, if effervescence is Violent. 

7.4 Lubricate the O-ring of bottle cap with gylcerine from a squeeze bottle. 

7.5 Dispense 10 mL of 3 N HCl into a gelatin capsule and carefully place the top on the 

capsule. The HCl may squirt or leak out of capsule. If this happens, discard the capsule. 

7.6 Place the capsule in bottle and cap bottle immediately. 

7.7 Release any pressure in the bottle by piercing the stopper with a hypodermic needle. 

Remove the needle after ≈ 5 to 10 s. 

7.8 After 5 to 10 min, the HCl dissolves through the capsule. Shake the bottle at a rate of 140 

rpm on the shaker for the first 10 min and last 10 min of a 1-h interval at room temperature 

(20°C ± 2°C). After this 1 h, measure the pressure in the bottle by piercing the stopper of the 

cap with a hypodermic needle connected to the manometer. 

271
7.9 Auto-zero the manometer before taking readings. Record the manometer readings (mm 

Hg). 

<20-mm Basis 7.10 Determine carbonate content of the 2- to 20-mm fraction on a fine-grind (<180 μm) airdry sample by the above method. 

7.11 The carbonate in the 2- to 20-mm fraction and in the <2-mm fraction are combined and 

converted to a <20-mm soil basis. 

8. Calculations 

8.1 Correct the manometer readings as follows: 

CR = (MR – BR) 

where: 

CR = Corrected reading 

MR = Manometer reading 

BR = Blank reading 

Three blanks are run with each batch of 24 samples. The average of three blanks is used as BR. 

8.2 Calculate the regression equation for the corrected manometer readings. Use the CaCO3

weights as the dependent variable (regressed or predicted values) and the corresponding 

manometer readings as the independent variable. 

8.3 Use the corrected (CR) linear regression (slope, intercept) equation to estimate % CaCO3 in 

the sample as follows: 

8.4 CCE = [(CR x Slope + Intercept) /Sample Weight (g)] x AD/OD 

where: 

CCE = Calcium Carbonate Equivalent (%) in <2-mm fraction or 2- to 20-mm fraction 

CR = Corrected manometer reading 

AD/OD = Air-dry/oven-dry ratio (procedure 3D1) 

8.5 Carbonate = (A x B) + [C x (1-B)] 

where: 

Carbonate = Carbonate as CaCO3 on a <20-mm basis (%) 

A = CaCO3 in <2-mm fraction (%) 

B = Weight of the <20-mm fraction minus the weight of the 2- to 20-mm fraction 

divided by the weight of <20-mm fraction (procedures 1B2b2f and 3A2). 

C = CaCO3 in 2- to 20-mm fraction (%) 

9. Report

Report CaCO3 equivalent as a percentage of oven-dry soil to the nearest whole number. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

272
11. References 

Amer, F.A., A. Mahmoud, and V. Sabel. 1985. Zeta potential and surface area of calcium 

carbonate as related to phosphate sorption. Soil Sci. Soc. Am. J. 49:1137-1142. 

Boischot, P, M. Coppenet, and J. Hebert. 1950. Fixation de l’acide phosphorique sur le 

calcaire des sols. Plant Soil 2:311-322. 

Loeppert, R. H., and D. L. Suarez. 1996. Carbonate and gypsum. p. 437-474. In D.L. 

Sparks (ed.) Methods of Soil Analysis. Part 3 – Chemical methods. Soil Sci. Am. Book 

Series No. 5. ASA and SSSA, Madison, WI. 

Nelson, R.E. 1982. Carbonate and gypsum. p. 181-197. In A.L. Page, R.H. Miller, and 

D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Rabenhorst, M.C., L.T. West, and L.P. Wilding. 1991. Genesis of calcic and petrocalcic 

horizons in soils over carbonate rocks. p. 61-74. In W.D. Nettleton (ed.) Occurrence, 

characteristics, and genesis of carbonate, gypsum, and silica accumulations in soils. Soil 

Sci. Soc. Am. Spec. Publ. No. 26. ASA and SSSA, Madison, WI. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. 

Print. Office, Washington, DC. 

Talibudeen, O., and P. Arambarri. 1964. The influence of the amount and the origin of 

calcium carbonates on the isotopically-exchangeable phosphate in calcareous soils. J. 

Agric. Sci. 62:93-97. 

Carbonate and Gypsum (4E) 

Aqueous Extraction (4E2) 

Precipitation in Acetone (4E2a) 

Conductivity Bridge (4E2a1) 

Electrical Conductivity (4E2a1a) 

Gypsum, Qualitative and Quantitative (4E2a1a1) Air-Dry, < 2 mm (4E2a1a1a1) 

Air-Dry, < 20 mm (4E2a1a1a2) 

1. Application 

If the electrical conductivity of a soil sample >0.50 dS cm-1 by procedure 4F1a1a1, 

gypsum content is determined. Gypsum content of a soil is a criterion for gypsic and 

petrogypsic horizons and for mineralogical class at the family level (Soil Survey Staff, 1999). 

Soil subsidence through solution and removal of gypsum can crack building foundations, break 

irrigation canals, and make roads uneven. Failure can be a problem in soils with as little as 

1.5% gypsum (Nelson, 1982). The gypsum content in the soil may be used to determine if 

reclamation of sodic soils requires chemical amendments. Corrosion of concrete is also 

associated with soil gypsum. 

Gypsum formation by precipitation of calcium sulfate (CaSO4) is usually highest at the 

surface layers. Gypsum from deposits high in gypsum are usually highest in the lower part of 

the soil profile. However, leaching may disrupt this sequence. Gypsum is reported on both the 

<2- and the <20-mm base. 

2. Summary of Method 

A soil sample is mixed with water to dissolve gypsum. Acetone is added to a portion of 

the clear extract to precipitate the dissolved gypsum. After centrifuging, the gypsum is 

redissolved in water. The electrical conductivity (EC) of the solution is read. The EC reading 

is used to estimate the gypsum content in meq 100 g-1. 

In procedure 4E2a1a1, gypsum content (meq 100 g-1) is converted to percent gypsum 

(uncorrected). The percent gypsum (uncorrected) is used to calculate percent gypsum 

(corrected). The percent gypsum (corrected) is used to correct the AD/OD (air-dry/oven-dry 

ratio). The AD/OD and corrected AD/OD are determined in procedures 3D1 and 3D3, 

273
respectively. The corrected AD/OD uses the correction for the crystal water of gypsum. 

Gypsum content on a <2-mm basis is reported in procedure 4E2a1a1a1. 

Gypsum content may also be determined on the 2- to 20-mm fraction prepared by 

procedure 1B1b2f1a1. The gypsum determined on the 2- to 20-mm fraction and the gypsum 

determined on the fine earth (prepared by procedure 1B1b2d2) are combined and converted to a 

<20-mm soil basis. Gypsum on a <20-mm basis is reported in procedure 4E2a1a1a2. 

3. Interferences 

Loss of the precipitated gypsum is the most significant potential error. Care in handling 

the precipitated gypsum is required. Incomplete dissolution of gypsum is also possible. In 

soils with large gypsum crystals, use fine-ground samples to reduce sampling errors. 

When present in sufficiently high concentrations, the sulfates of Na and K are also 

precipitated by acetone. The concentration limits for sulfates of Na and K are 50 and 10 meq 

L-1, respectively. 

4. Safety 

Acetone is highly flammable. Avoid open flames and sparks. Use a nonsparking 

centrifuge. Standard laboratory equipment includes fire blankets and extinguishers for use 

when necessary. Proper use and appropriate load balance of the centrifuge is required. Follow 

standard laboratory safety precautions. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity

5.2 Bottles, 250 mL, with caps, Wheaton. 

5.3 Mechanical reciprocating shaker, 200 oscillations min-1, Eberbach 6000, Eberbach Corp., 

Ann Arbor, MI 5.4 Dispenser, 100 mL and 10 mL 

5.5 Pipette, 20 mL, solvent, Pistolpet, Manostat 

5.6 Pipette, 10 mL, electronic digital, with tips, polypropylene, 10 mL, 

5.7 Centrifuge, Sorvall, GLC-1, General Laboratory Centrifuge 

5.8 Centrifuge tubes, 15 mL, plain, conical 

5.9 Thermometer, 0° to 100°C 

5.10 Conductivity bridge and conductivity cell, Markson Model 1056, Amber Science, 

Eugene, OR 

5.11 Filter paper, folded, 185-mm diameter, Whatman No. 2V 

5.12 Funnel, 90 cm 

5.13 Flask, Erhlenmeyer, 250 mL 

5.14 Vortexer, mini, MV1, VWR Scientific Products 

6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

6.2 Potassium chloride (KCl), 0.010 N. Dry KCl overnight or at least 4 h in oven (105°C). 

Dissolve 0.7456 g of dry reagent grade KCl in RO water and bring to 1-L volume. 

Conductivity at 25°C is 1.41 mmhos cm-1. 

6.3 Acetone, purity 99% 

7. Procedure 

7.1 Weigh 5.0 g of fine-grind, air-dry soil into a 500-mL Wheaton bottle to the nearest mg. If a 

trace of gypsum is present, a 20-g sample size may be used. If the EC reading is >0.85 mmhos 

cm-1, repeat the procedure using a smaller sample size (2.5, 1, 0.5. 0.25, or 0.1 g). 

7.2 Use a dispenser to add 100 mL of RO water to sample and 1 blank. 

274
7.3 Cap the bottle and shake at an oscillating rate of 200 oscillations min-1 for 30 min at room 

temperature (20°C ± 2°C). 

7.4 Filter the suspension. The first few mL of filtrate is usually cloudy and should be 

discarded. Collect the clear filtrate in a 250-mL flask. 

7.5 Pipet 5 mL of filtrate into 15-mL conical centrifuge tube. 

7.6 Use a solvent dispenser to add 5 mL acetone. 

7.7 Cap tube with a polyethylene stopper and mix. 

7.8 Carefully release pressure within tube by loosening the stopper. 

7.9 Let stand for at least 10 min to allow the precipitate to flocculate. 

7.10 Use acetone (1 or 2 mL) to rinse stopper and inside rim of tube to prevent gypsum loss. 

7.11 Remove stopper and centrifuge at 2200 rpm for 5 min. 

7.12 Decant and discard supernatant. Invert and drain the tube on filter paper or on towel for 5 

min. 

7.13 Add 5 mL of acetone to the tube. Replace stopper. Use Vortexer to shake sample. 

7.14 Carefully remove stopper and rinse it and the inside rim of tube with acetone (1 or 2 mL). 

7.15 Centrifuge the sample tube at 2200 rpm for 5 min. 

7.16 Discard supernatant. Drain tube upside down for 5 min. 

7.17 Use a dispenser to add 10 mL of RO water to tube. 

7.18 Stopper and shake with Vortexer until the precipitate dissolves. 

7.19 Calibrate the EC meter and cell by drawing the 0.010 N KCl solution into the cell. 

7.20 Flush the cell and fill with RO water. Digital reading should be 0.00. 

7.21 Read the EC of dissolved precipitate by drawing up solution into cell and flush at least 

once. 

7.22 If the EC reading is >0.85 mmhos cm-1, repeat the procedure using a smaller sample 

weight. 

8. Calculations 

8.1 Calculate % Gypsumuc (Gypsum uncorrected) by using Table 1 to convert EC reading 

(mmhos/cm) to gypsum content (meq/100 g) and proceeding with the following the equation. 

% Gypsumuc = [Gypsum x Water x 0.08609 x AD/OD]/[Sample Weight (g) x 5]

where: 

% Gypsumuc= % Gypsum in <2 mm fraction or 2 to 20-mm fraction 

275
Gypsum = Gypsum (meq L-1). Refer to Table 1. 

Water = Volume RO water (100 mL) to dissolve gypsum 

0.08609 = Conversion factor (gypsum % = meq 100 g-1 x 0.08609) 

AD/OD = Air-dry/oven-dry ratio, (procedure 3D1) 

5 = Filtrate (5 mL) 

8.2 Table 1 converts EC (mmhos cm-1) to gypsum (meq L-1) for the above calculations. Enter 

Table 1 using both the x and y axis for the EC reading to determine gypsum content (meq L-1). 

8.3 Alternatively to using Table 1, calculate % Gypsumuc from the following equation: 

Result = (Exp (2.420384 + 1.1579713 x Log (EC – blank)) x Water x 0.08609 x ADOD)/(Sample Weight x 5) 

8.4 The following equation for calculation of % Gypsumc (gypsum corrected) assumes the 

crystal-water content of gypsum is 19.42% (Nelson et al., 1978) as opposed to the theoretical 

water content (20.21%). 

% Gypsumc = [% Gypsumuc]/[1 + 0.001942 x % Gypsumuc] 

8.5 Use the % Gypsumuc to recalculate the AD/OD (procedure 3D1). The corrected AD/OD 

(procedure 6F3) uses the correction for the crystal water of gypsum. 

8.6 Calculate gypsum on <20-mm basis (procedure 4E2a1a1) as follows: 

(%) Gypsum = A x B + [C x (1 - B)] 

where: 

A = Gypsum (%) in <2-mm fraction 

B = Weight of the <20-mm fraction minus the 20- to 2-mm fraction divided by the weight of 

the <20-mm fraction 

C = Gypsum (%) in the 20- to 2-mm fraction 

9. Report 

Report gypsum as a percent to the nearest whole unit. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Nelson, R.E. 1982. Carbonate and gypsum. p. 181-197. In A.L. Page, R.H. Miller, and 

D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Nelson, R.E., L.C. Klamath, and W.D. Nettleton. 1978. Determining soil gypsum content 

and expressing properties of gypsiferous soils. Soil Sci. Soc. Am. J. 42:659-661. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. 

Print. Office, Washington, DC. 

276
Table 1. Convert EC reading (mmhos cm-1) to gypsum content (meq L-1) 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

EC | 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 

0.0 | 0.40 

0.1 | 0.80 0.89 0.98 1.10 1.22 1.31 1.40 1.50 1.60 1.70 

0.2 | 1.80 1.90 2.00 2.10 2.20 2.30 2.40 2.50 2.60 2.70 

0.3 | 2.80 2.90 3.00 3.10 3.20 3.30 3.40 3.50 3.60 3.72 

0.4 | 3.85 3.98 4.10 4.22 4.35 4.48 4.60 4.70 4.80 4.90 

0.5 | 5.00 5.12 5.25 5.38 5.50 5.62 5.75 5.88 6.00 6.12 

0.6 | 6.25 6.35 6.45 6.58 6.70 6.82 6.95 7.05 7.15 7.28 

0.7 | 7.40 7.52 7.65 7.78 7.90 8.04 8.18 8.32 8.45 8.58 

0.8 | 8.70 8.82 8.95 9.05 9.15 9.28 9.40 9.55 9.70 9.85 

0.9 |10.00 10.12 10.25 10.38 10.50 10.62 10.75 10.88 11.00 11.15 

1.0 |11.30 

Electrical Conductivity and Soluble Salts (4F)

Aqueous Extraction (4F1) 

1:2 Extraction (4F1a) 

Conductivity Bridge (4F1a1) 

Electrical Conductivity (4F1a1a) 

Salt Prediction (4F1a1a1) 

Air-Dry, <2 mm (4F1a1a1a1) 

1. Application 

Salt prediction is used not only to predict which soils have measurable amounts of 

soluble salts but also to predict the quantity and the appropriate dilutions for salt analyses of 

those soils. If salt prediction or conductivity is <0.25 mmhos cm-1 (dS cm-1) soils are 

considered nonsalty, and generally, no other salt analyses are performed on these soils by the 

SSL. 

2. Summary of Method 

A soil sample is mixed with water and allowed to stand overnight. The electrical 

conductivity (EC) of the mixture is measured using an electronic bridge. The EC by this 

method (4F1a1a1) is used to indicate the presence of soluble salts (U.S. Salinity Laboratory 

Staff, 1954). 

3. Interferences 

Reverse osmosis deionized water is used to zero and flush the conductivity cell. The 

extract temperature is assumed to be 25°C. If the temperature deviates significantly, a 

correction may be required. 

Provide airtight storage of KCl solution and samples to prevent soil release of alkaliearth cations. Exposure to air can cause gains and losses of water and dissolved gases 

significantly affecting EC readings. 

4. Safety 

No significant hazards are associated with this procedure. Follow standard laboratory 

safety practices. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Conductivity bridge and conductivity cell, with automatic temperature adjustment, 25 ±

0.1°C, Markson Model 1056, Amber Science, Eugene, OR 

5.3 Plastic cups, 30 mL (1 fl. oz.), with lids, Sweetheart Cup Co. Inc., Owings Mills, MD 

5.4 Dispenser, Repipet or equivalent, 0 to 10 mL 

277
6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

6.2 Potassium chloride (KCl), 0.010 N. Dry KCl overnight in oven (110°C). Dissolve 0.7456 

g of KCl in RODI water and bring to 1-L volume. Conductivity at 25°C is 1.412 mmhos 

cm

-1. 

7. Procedure 

7.1 Weigh 5.0 g of <2-mm, air-dry soil in a 30-mL (1-oz) condiment cup. 

7.2 Add 10 mL of RO water to sample using a Repipet dispenser. 

7.3 Swirl to mix, cap, and allow to stand overnight. 

7.4 Standardize the conductivity bridge using RO water (blank) and 0.010 N KCl (1.41 mmhos 

cm

-1). 

7.5 Read conductance of supernatant solution directly from the bridge. 

7.6 Record conductance to 0.01 mmhos cm-1. 

8. Calculations 

8.1 No calculations are required for this procedure. 

8.2 Use the following relationship to estimate the total soluble cation or anion concentration 

(meq L-1) in the soil. 

EC (mmhos cm-1) x 10 = Cation or Anion (meq L-1) 

8.3 Use the following relationship to estimate the total soluble cation or anion concentration 

(meq g-1 oven-dry soil) in the soil. 

EC (mmhos cm-1) x 20 = Cation (meq g-1 soil) 

EC (mmhos cm-1) x 20 = Anion (meq g-1 soil) 

9. Report 

Report prediction conductance to the nearest 0.01 mmhos cm-1 (dS m-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. 160 p. USDA Handb. 60. U.S. Govt. Print. Office, Washington, 

DC. 

Electrical Conductivity and Soluble Salts (4F)

Saturated Paste (4F2) 

Salt-affected soils, i.e., excessive amounts of soluble salts and/or exchangeable sodium 

(ES), are common in, though not restricted to, arid and semi-arid regions. These soils are 

278
usually described and characterized in terms of the soluble salt concentrations, i.e., major 

dissolved inorganic solutes (Rhoades, 1982). Salt composition and distribution in the soil 

profile affect the plant response, i.e., osmotic stress, specific ion effects, and nutritional 

imbalances. Soil texture and plant species also are factors in this plant response to saline soils. 

Traditionally, the classification of salt-affected soils has been based on the soluble salt 

concentrations in extracted soil solutions and on the exchangeable sodium percentage (ESP) in 

the associated soil (Bohn et al., 1979). In general, saline soils have been defined as having a 

salt content >0.1% or an EC >4 mmhos cm-1; alkali soils have an ESP of >15%; and salinealkali soils have properties of both saline and alkali soils (U.S. Salinity Laboratory Staff, 1954). 

In soil taxonomy, the ESP and the Na-adsorption ratio (SAR) have been used as criteria for 

natric horizons (Soil Survey Staff, 1999). The ESP and SAR are calculated in procedures 

4F3a1 and 4F3b, respectively. 

The measurable absolute and relative amounts of various solutes are influenced by the 

soil:water ratio at which the soil solution extract is made. Therefore, this ratio is standardized 

to obtain results that can be applied and interpreted universally. Soil salinity is conventionally 

defined and measured on aqueous extracts of saturated soil pastes (U.S. Salinity Laboratory 

Staff, 1954). This soil:water ratio is used because it is the lowest reproducible ratio at which 

the extract for analysis can be readily removed from the soil with common laboratory 

equipment, i.e., pressure or vacuum, and because this soil:water ratio is often related in a 

predictable manner to field soil water contents (Rhoades, 1982). Soil solutions obtained at 

lower soil moisture conditions are more labor intensive and require special equipment. 

The SSL measures salinity on aqueous extracts of saturated soil pastes. The saturated 

paste is prepared (4F2), and the saturation percentage (SP) determined (4F2a1). The saturated 

paste extract is obtained with an automatic extractor (4F2c1). Electrical conductivity and soil 

resistivity of saturated paste are measured in procedures 4F2b1 and 4F2b2, respectively. The 

saturated paste pH is measured in procedure 4C1a1a2. The water-soluble cations of Ca2+, Mg2+, K+

, and Na+ are measured by atomic absorption spectrophotometry in procedures 

4F2c1a1-4, respectively. The water-soluble anions of Br, CH3COO-, Cl-, F-, NO3

-

, NO2

-

, PO4

3-, and SO4

2- are measured by ion chromatography in procedures 4F2c1b1a1-8, respectively. The 

carbonate and bicarbonate concentrations are determined by acid titration procedures 

4F2c1c1a1-2, respectively. Estimated total salt is calculated in procedure 4F3c. The SSL also 

performs a salt prediction test (procedure 4F1a1a1) which is used not only to predict those soils 

that have measurable amounts of soluble salts but also to predict the quantity and the 

appropriate dilutions for salt analyses of those soils. If salt predictions or conductances are 

<0.25 mmhos cm-1, soils are considered nonsalty, and generally, no other salt analyses are 

performed on these soils by the SSL. 

The SP, i.e., the amount of moisture in the saturated paste, is an important 

measurement. An experienced analyst should be able to repeat the saturated paste preparation 

to an SP within 5%. The SP can be related directly to the field moisture range. Measurements 

on soils, over a considerable textural range, (U.S. Salinity Laboratory Staff, 1954) indicate the 

following general rules of thumb. 

SP ≈ 4 x 15-bar water 

SP ≈ 2 x upper end field soil moisture content 

AWC ≈ SP/4 

where: 

Sp = Saturation percentage 

AWC = Available water capacity 

279
Therefore, at the upper (saturated) and lower (dry) ends of the field moisture range, the salt 

concentration of the soil solution is ≈ 4x and 2x the concentration in the saturation extract, 

respectively. 

If the soil texture is known, and the 15-bar water content has been measured, the 

preceding SP relationships may be redefined (U.S. Salinity Laboratory Staff, 1954) as follows: 

15 Bar 

Water % 

Texture Relationship 

2.0 to 6.5 Coarse SP ≈ 6 1/3 x 15 bar 

6.6 to 15 Medium SP ≈ 4 x 15 bar 

>15 Fine SP ≈ 3 1/4 x 15 bar 

>15 Organic SP ≈ 3 2/3 x 15 bar 

The electrical conductivity of the saturated paste (ECs) is measured and is commonly 

reported as resistivity (Rs). The ECs measurement requires more time, i.e., preparation of 

saturated soil paste, than the Rs measurement. However, the ECs is the easier measurement 

from which to make interpretations, i.e., ECs is more closely related to plant response (U.S. 

Salinity Laboratory Staff, 1954). Furthermore, there is a limited correlation between ECs and 

Rs, as the relationship is markedly influenced by variations in SP, salinity, and soil mineral 

conductivity. The ECs has been related to Rs (U.S. Laboratory Staff, 1954) by the equation as 

follows: 

ECs ≈ 0.25/Rs

where: 

0.25 = Constant for Bureau of Soils electrode cup 

Historically, the ECs is adjusted to 60°F (15.5°C) basis before interpretative use. The 

ECs and Rs increase ≈ 2% per °C. The SSL determines the ECs and Rs in procedures )E and

4F2b2, respectively. The unit EC x 103 is called mmhos cm-1. The ECs (mmhos cm-1) may be used to estimate the salt percentage (Psw) in solution 

(U.S. Salinity Laboratory Staff, 1954) as follows: 

Psw ≈ 0.064 x ECs (mmhos cm-1) 

The preceding equation may be used to estimate the salt percentage in the soil (Pss) 

(U.S. Salinity Laboratory Staff, 1954) as follows: 

Pss ≈ (Psw x SP)/100 

The ECs (mmhos cm-1) may be used to estimate the osmotic potential (OP) in 

atmospheres of a solution (U.S. Salinity Laboratory Staff, 1954) as follows: 

OP ≈ 0.36 x ECs (mmhos cm-1) 

The ECs (mmhos cm-1) may be used to estimate the total cation or anion concentration 

(meq L-1) of the solution (U.S. Salinity Laboratory Staff, 1954) as follows: 

Total cations ≈ 10 x ECs (mmhos cm-1) 

Total anions ≈ 10 x ECs (mmhos cm-1) 

280
where: 

ECs at 25°C 

A means of cross-checking chemical analyses for consistency and reliability is provided 

by the interrelations that exist among the various soil chemical determinations (U.S. Salinity 

Laboratory Staff, 1954). The saturated paste pH is the apparent pH of the soil:water mixture 

and is a key indicator in many of these interrelations. The saturated paste pH is dependent 

upon the dissolved CO2 concentration; moisture content of the mixture; exchangeable cation 

composition; soluble salt composition and concentration; and the presence and amount of 

gypsum and alkaline-earth carbonates. Some rules of thumb that apply to the saturated paste 

(U.S. Salinity Laboratory Staff, 1954) are as follows: 

Total Cation and Anion Concentrations

Total cations ≈ Total anions, expressed on equivalent basis 

pH and Ca and Mg Concentrations

Concentrations of Ca2+ and Mg2+ are seldom >2 meq L-1 at pH >9. 

pH and Carbonate and Bicarbonate Concentrations

Carbonate concentration (meq L-1) is measurable only if pH >9. 

Bicarbonate concentration is rarely >10 meq L-1 in absence of carbonates. 

Bicarbonate concentration is seldom >3 or 4 meq L-1 if pH <7. 

Gypsum

Gypsum is rarely present if pH >8.2. 

Gypsum has variable solubility in saline solutions (20 to 50 meq L-1). 

Check for the presence of gypsum if Ca concentration >20 meq L-1 and pH <8.2. 

pH, ESP, and Alkaline-Earth Carbonates

Alkaline-earth CO3

-

 and ESP >15 are indicated if pH >8.5. 

ESP <15 may or may not be indicated if pH <8.5. 

No alkaline-earth CO3

-

 are indicated if pH <7.5. 

pH and Exchangeable Acidity

Significant amounts of exchangeable acidity are indicated if pH <7.0. 

The commonly determined soluble cations and anions in the saturation extract include 

calcium, magnesium, sodium, potassium, chloride, sulfate, nitrate, fluoride, carbonate, 

bicarbonate, and nitrite. The less commonly analyzed cations and anions include iron, 

aluminum, manganese, lithium, strontium, rubidium, cesium, hydronium, phosphate, borate, 

silicate, bromide, selenate, selenite, arsenate, and arsenite. 

281
The effect of soluble cations upon the exchangeable cation determination is to increase 

the cation concentration in the extracting solution, i.e., NH4OAc, buffered at pH 7.0 (procedure 

4B1a1b1-4). The dissolution of salts by the extractant necessitates an independent 

determination of soluble cations and a correction to the exchangeable cations. Therefore, in 

soils with soluble salts or carbonates, the soluble cations (meq L-1 solution) must be measured 

separately and the results subtracted from the extractable bases for determination of 

exchangeable bases as follows: 

Exchangeable = Extractable - Soluble 

The presence of alkaline-earth carbonates prevents accurate determination of exchangeable Ca 

and Mg. Refer to procedures 4E3c1a1-4. 

References 

Bohn, H.L., McNeal, B.L., and O'Connor, G.A. 1979. Soil chemistry. John Wiley & Sons, New 

York, NY. 

Rhoades, J.D. 1982. Soluble salts. p. 167-179. In A.L Page, R.H. Miller, and D.R. Keeney 

(eds.) Methods of soil analysis. Part 2. Chemical and microbiological properties. 2nd ed. 

Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of saline 

and alkali soils. 160 p. USDA Handb. 60. U.S. Govt. Print. Office, Washington, DC. 

Electrical Conductivity and Soluble Salts (4F) 

Saturated Paste (4F2) 

Gravimetric (4F2a) 

Water Percentage (4F2a1) 

Air-Dry, <2 mm (4F2a1a1) 

1. Application 

The saturated soil paste is a particular mixture of soil and water, i.e. the soil paste 

glistens as it reflects light; flows slightly when the container is tipped; and slides freely and 

cleanly from a spatula except for those soils with high clay content. This soil:water ratio is 

used because it is the lowest reproducible ratio for which enough extract for analysis can be 

readily removed from the soil with pressure or vacuum, and because this ratio is often related in 

a predictable manner to the field soil water content (U.S. Salinity Laboratory Staff, 1954). 

Upon preparation of a saturated paste, an aqueous extract is obtained, which is used in a series 

of chemical analyses, e.g., electrical conductivity and concentrations of the major solutes. 

2. Summary of Method 

A saturated paste is prepared (4F2) by adding water to a soil sample while stirring the 

mixture until the soil paste meets the saturation criteria, i.e. the soil paste glistens as it reflects 

light; flows slightly when the container is tipped; and slides freely and cleanly from a spatula 

except for those soils with high clay content. The mixture is covered and allowed to stand 

overnight. The saturation criteria are then rechecked. If the mixture fails to meet these criteria, 

more water or soil is added until criteria are met. A saturated paste sub-sample is used to 

determine the moisture content, i.e., saturation percentage (SP) by procedure 4F2a1. 

3. Interferences 

Special precautions must be taken for peat and muck soils and very fine or very coarsetextured soils (Rhoades, 1982). Dry peat and muck soils, especially if coarse textured or 

woody, require an overnight wetting to obtain a definite end point for the saturated paste. After 

the first wetting, pastes of these soils usually stiffen and lose their glisten. However, upon 

adding water and remixing, the paste usually retains the saturated paste characteristics. With 

fine-textured soils, enough water should be added immediately, with a minimum of mixing, to 

282
bring the sample nearly to saturation. Care also should be taken not to overwet coarse-textured 

soils. The presence of free water on the surface of the paste after standing is an indication of 

oversaturation in the coarse-textured soils (Rhoades, 1982). 

4. Safety 

Use heat-resistant gloves to remove hot moisture cans from the oven. No other 

significant hazards are associated with this procedure. Follow standard laboratory safety 

practices. 

5. Equipment 

5.1 Aluminum cans, drying 

5.2 Spatulas, stainless steel, hardwood handles 

5.3 Electronic balance, ±1-mg sensitivity 

5.4 Oven, thermostatically controlled, 110°C 

5.5 Thermometer, 0° to 200°C 

5.6 Plastic food containers, 1920 mL (16 fl. oz.) capacities with recessed lids, Sweetheart 

Products Group, Owings Mills, MD 

6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

7. Procedure 

Saturated Soil Paste Preparation (4F2) 

7.1 Place a <2-mm, air-dry, 250-g soil sample in the food container. This sample size is 

convenient to handle with the 1920-mL (16-oz) food containers and provides enough extract 

for most purposes. The sample size varies with the number of determinations to be made upon 

the paste or saturation extract. 

7.2 Add enough RO water to bring the sample nearly to saturation. To reduce soil puddling 

and to obtain a more definite end point of the saturation criteria, mix with a minimum of 

stirring. Soils puddle easily when worked at a moisture content near field capacity. If the paste 

becomes too wet, add more dry soil. 

7.3 Occasionally tap the container on the workbench to consolidate the soil:water mixture. At 

saturation, the soil paste glistens as it reflects light; flows slightly when the container is tipped; 

and slides freely and cleanly off the spatula except for those soils with high clay content. 

7.4 Cover the container and allow the sample to stand overnight. 

7.5 Recheck saturation criteria, i.e., ordinarily, free water should not collect on the soil surface; 

paste should not stiffen markedly; and paste should not lose its glisten upon standing. 

7.6 If the paste does not meet the saturation criteria, remix the paste with more RO water or dry 

soil. Allow to stand for at least 4 h and recheck the saturation criteria. 

Saturation Percentage Determination (4F2a1)

7.7 Tare a moisture can and cover. Label each moisture can with the appropriate sample 

number. 

7.8 Add ≈ 20 to 40 g of the saturated soil paste to the moisture can. 

7.9 Cover the can, weigh the can plus sample, and record the weight to the nearest mg. 

283
7.10 Remove the can cover, place the can in a vented drying oven at 110°C, and leave in the 

oven overnight (12 to 16 h). A drying period of 24 h or longer is recommended. Do not place 

moist samples in the oven with other samples that are drying, unless these samples have been in 

the oven at least 12 to 16 h. Do not overcrowd the drying oven with samples. 

7.11 Remove the cans from the oven and cover immediately. Allow the cans to cool for 1 h. 

7.12 Weigh the oven-dry paste sample and record the weight. Before calculating the SP, 

subtract the tare weights from the saturated paste and oven-dry weights. Do not use the SP subsample for other analyses. 

8. Calculations 

 

SP= [(WtSP - WtOD)/ (WtOD)] x 100 

where: 

SP = Saturation percentage 

WtSP = Weight of saturated paste 

WtOD = Weight of oven-dry soil 

9. Report 

Report the saturation percentage to the nearest 0.1%. 

10. Precision and Accuracy 

Precision and accuracy are available from the SSL upon request. 

11. References 

Rhoades, J.D. 1982. Soluble Salts. p. 167-179. In A.L. Page, R.H. Miller, and D.R. Keeney 

(eds.) Methods of soil analysis. Part 2. Chemical and microbiological properties. 2nd 

ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

U.S. Salinity Laboratory Staff, 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. 160 p. USDA Handb. 60, U.S. Govt. Print Office, Washington 

DC. 

Electrical Conductivity and Soluble Salts (4F) 

Saturated Paste (4F2) 

Conductivity Bridge (4F2b) 

Electrical Conductivity (4F2b1) 

Air-Dry, <2 mm (4F2b1a1) 

1. Application 

The electrical conductivity of the saturation extract (ECs) is used as a criterion for 

classifying a soil as saline. Other uses of this measurement include the estimation of the total 

cation concentration in the extract, salt percentage in solution (Psw), salt percentage in soil (Pss), 

and osmotic pressure (OP). The unit EC x 103 is called the mmhos cm-1. For solutions with a 

low ECs, i.e., dilute solutions, the ECs (mmhos cm-1) x 10 ≈ cation concentration (meq L-1) 

(U.S. Salinity Laboratory Staff, 1954). The ECs (mmhos cm-1) x 0.064 ≈ (Psw); the (Psw x 

SP)/100 ≈ Pss; and the ECs (mmhos cm-1) x 0.36 ≈ OP in atmospheres (U.S. Salinity Laboratory 

Staff, 1954). 

2. Summary of Method 

The ECs of the saturation extract that is prepared in procedure 4F2 is measured using a 

conductivity cell and a direct reading digital bridge (4F2b1). The cell constant is set using a 

standard solution. 

284
3. Interferences 

Reverse osmosis deionized water is used to zero and flush the conductivity cell. The 

extract temperature is assumed to be 25°C. If the temperature deviates significantly, a 

correction may be required. 

Provide airtight storage of KCl solution and samples to prevent soil release of alkaliearth cations. Exposure to air can cause gains and losses of water and dissolved gases 

significantly affecting EC readings. 

4. Safety 

No significant hazards are associated with this procedure. Follow standard laboratory 

safety procedures. 

5. Equipment 

5.1 Conductivity bridge and conductivity cell, with automatic temperature adjustment, 25±

0.1°C, Markson Model 1096, Amber Science, Eugene, OR 

6. Reagents 

6.1 Reverse osmosis (RODI) water, ASTM Type I grade of reagent water, for rinse and KCl 

preparation 

6.2 Potassium chloride (KCl), 0.010 N. Dry KCl overnight in oven (110°C). Dissolve 0.7456 

g of KCl in RODI water and bring to 1-L volume. Conductivity at 25°C is 1.412 mmhos 

cm-1. 

7. Procedure 

7.1 Calibrate the conductivity meter and cell by drawing the 0.010 N KCl solution into the cell. 

7.2 Set the meter to "D" Scale and adjust the digital reading to "1.41". 

7.3 Flush the cell and fill with RODI water. Verify that digital reading is "0.00". 

7.4 Read the electrical conductivity of saturation extract (ECs) by drawing up the extract into 

the cell and flush at least once if the cell has not been dried. Draw up extract a second time. 

Reading is started on the "C" Scale. Higher readings may require the use of the "D" or "E" 

Scales. 

7.5 When the reading has stabilized, record the ECs. Rinse the cell with RODI water and 

ensure that the conductivity reading falls to zero. 

8. Calculations 

No calculations are required for this procedure. 

9. Report

Report ECs to the nearest 0.01 mmhos cm-1 (dS m-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the Soil Survey upon request. 

11. References 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. 160 p. USDA Handb. 60. U.S. Govt. Print. Office, Washington, 

DC. 

285
Electrical Conductivity and Soluble Salts (4F) 

Saturated Paste (4F2) 

Conductivity Bridge (4F2b) 

Resistivity (4F2b2) 

Air-Dry, <2 mm (4F2b2a1) 

1. Application 

The resistivity of the soil paste is mainly used to estimate the salt content in the soil. 

The apparatus is simple and rugged, the measurements can be made quickly, and the results are 

reproducible. Many agencies use the Bureau of Soils electrode cup to estimate the soluble salt 

content in soils (Davis and Bryan, 1910; Soil Survey Staff, 1951). 

There is no simple method to convert saturation extract electrical conductivity to soil 

paste resistivity or vice versa. There is a limited correlation between ECs and Rs, as the 

relationship is markedly influenced by variations in SP, salinity, and soil mineral conductivity. 

2. Summary of Method 

A saturated paste that is prepared in procedure 4F2 is placed in an electrode cup. The 

resistance is measured (procedure 4F2b2). The temperature of the paste is measured. The 

resistance (ohms) is converted to a 60°F (15.5°C) basis using a fourth order equation (Benham, 

2003). 

3. Interferences 

No significant interferences are known to affect the saturated paste resistivity 

measurement. 

4. Safety 

No significant hazards are associated with this procedure. Follow standard laboratory 

safety practices. 

5. Equipment 

5.1 Conductivity bridge, Standard Wheatstone, Model RC 16B2, Beckman Instruments, Inc. 

5.2 Soil cup cell holder, soil cup Cel-M, Industrial Instruments, Inc. 

5.3 Bureau of Soils electrode cup, cell constant is defined as 0.25. 

5.4 Thermometer, 0 to 100°C 

6. Reagents 

No reagents or consumables are used in this procedure. 

7. Procedure 

7.1 Fill the electrode cup with the saturated paste that is prepared in procedure 4F2. Gently tap 

the cup to remove air bubbles. Level the soil paste by striking off the excess with a spatula. 

7.2 Place the cup in the cell holder. Make sure that the surfaces of the cup and holder are clean 

and bright. Use steel wool or fine sandpaper to carefully clean the surfaces. 

7.3 Set the conductivity meter to 1000 cycles s-1 and adjust the multiplier range and the dial 

control to obtain the most distinct butterfly pattern on the fluorescent tube. 

7.4 Measure resistivity. Adjustment of the sensitivity control also may be necessary. 

7.5 Record the resistivity. 

286
7.6 Place a thermometer in the saturated paste. When the temperature is stabilized, record the 

temperature. 

8. Calculations 

Use Table 1 to convert measured resistance to specific resistance at 60°F (15.5°C). 

Resistivity (ohms cm-1) = ohms @ 60° F x electrode cup cell factor. 

Alternatively, the following equation may be used reducing soil paste resistance readings to 

values at 60°F with final results reported to 4 significant figures. 

A = (-0.013840786 + 0.028627073B - 0.00037976971B2 + 3.7891593e-06B3 -1.2020657e-08B4) x 

C x D x E 

Where: 

A = Resistance (ohms) corrected to 60oF 

B = Temperature (oF) at which the resistance was measured 

C = Resistance (ohms) measured at temperature B 

D = Electrode cup cell factor 

E = Scale (range multiplier) 

9. Report 

Report saturated paste resistivity in units of ohms at 60°F (15.5°C) to the nearest whole 

number. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Benham, E.C. 2003. Soil resistivity temperature correction. USDA-NRCS, Lincoln, NE. 

Davis, R.O., and H. Bryan. 1910. The electrical bridge for the determination of soluble 

salts in soils. USDA, Bur. Soils Bull. 61, 36 pp. 

Soil Survey Staff. 1951. Soil survey manual. USDA-SCS. Govt. Print. Office, Washington, 

DC. 

Whitney, M., and T.H. Means. 1897. An electrical method of determining the soluble salt 

content of soils. USDA, Div. Soils Bul. 8, 30 pp., illus. 

287
---------------------------------------------------------------------------------------------------------------- 

°F. 1000 2000 3000 4000 5000 6000 7000 8000 9000

 

40 735 1470 2205 2940 3675 4410 5145 5880 6615

42 763 1526 2289 3052 3815 4578 5341 6104 6867

44 788 1576 2364 3152 3940 4728 5516 6304 7092

46 814 1628 2442 3256 4070 4884 5698 6512 7326

48 843 1686 2529 3372 4215 5058 5901 6744 7587

50 867 1734 2601 3468 4335 5202 6069 6936 7803

52 893 1786 2679 3572 4465 5358 6251 7144 8037

54 917 1834 2751 3668 4585 5502 6419 7336 8253

56 947 1894 2841 3788 4735 5682 6629 7576 8523

58 974 1948 2922 3896 4870 5844 6818 7792 8766

60 1000 2000 3000 4000 5000 6000 7000 8000 9000

62 1027 2054 3081 4108 5135 6162 7189 8216 9243

64 1054 2108 3162 4216 5270 6324 7378 8432 9486

66 1081 2162 3243 4324 5405 6486 7567 8648 9729

68 1110 2220 3330 4440 5550 6660 7770 8880 9990

70 1140 2280 3420 4560 5700 6840 7980 9120 10260

72 1170 2340 3510 4680 5850 7020 8190 9360 10530

74 1201 2402 3603 4804 6005 7206 8407 9608 10809

76 1230 2460 3690 4920 6150 7380 8610 9840 11070

78 1261 2522 3783 5044 6305 7566 8827 10088 11349

80 1294 2588 3882 5176 6470 7764 9058 10352 11646

82 1327 2654 3981 5308 6635 7962 9289 10616 11943

84 1359 2718 4077 5436 6795 8154 9513 10872 12231

86 1393 2786 4179 5572 6965 8358 9751 11144 12537

88 1427 2854 4281 5708 7135 8562 9989 11416 12843

90 1460 2920 4380 5840 7300 8760 10220 11680 13140

92 1495 2990 4485 5980 7475 8970 10465 11960 13455

94 1532 3064 4596 6128 7660 9192 10724 12256 13788

96 1570 3140 4710 6280 7850 9420 10990 12560 14130

9666 11277 12888 14499

--------------------------------------------------------------------------------------------------------- 

Table 1. Bureau of soils data for reducing soil paste resistance readings to values at 

60°F (Whitney and Means, 1897). 

---------------------------------------------------------------------------------------------------------------- Temp Ohms 

98 1611 3222 4833 6444 8055

288
Electrical Conductivity and Soluble Salts (4F) 

Saturated Paste (4F2) 

Saturated Paste Extraction (4F2c) 

Automatic Extractor (4F2c1) 

1. Application 

The saturated paste is operationally defined so that it may be reproduced by a trained 

analyst using limited equipment. The saturated paste extract derived from the saturated paste is 

an important aqueous solution because many soil properties have been related to the 

composition of the saturation extract, e.g., soluble salt composition and electrical conductivity. 

These soil properties or characteristics are related in turn to the plant response to salinity (U.S. 

Salinity Laboratory Staff, 1954). 

2. Summary of Method 

The saturated paste (prepared in 4F2) is transferred to a plastic filter funnel fitted with 

filter paper. The funnel is placed on a mechanical vacuum extractor (Holmgren et al., 1977), 

and the saturated paste is extracted (4F2c1). The extract is used in subsequent chemical 

analyses, e.g., water-soluble cations (procedure 4F2c1a1-4) and water-soluble anions 

(procedures 4F2c1b1a1-8 and 4F2c1c1a1-2). 

3. Interferences 

Some saturated pastes are difficult to extract, i.e., soil dispersion and puddling. 

Repeated extractions may be necessary to obtain sufficient extract. High speed centrifuging or 

filtration of the extract also may be necessary. If the extract is to be stored for an extended 

period, sodium hexametaphosphate may be added to prevent calcium carbonate precipitation in 

the extract. 

4. Safety

No significant hazards are associated with this procedure. Follow standard laboratory 

procedures. 

5. Equipment 

5.1 Mechanical vacuum extractor, 24-place, SAMPLETEX, MAVCO Industries, Lincoln, NE 

5.2 Paste extraction cups, 9-cm diameter, for mechanical vacuum extractors 

5.3 Syringes, disposable, 60 mL, polypropylene, for extraction 

5.4 Rubber tubing, 3.2 ID x 1.6 OD x 6.4 mm (1/8 ID x 1/16 OD x 1 in) 

5.5 Polycons, Richards Mfg. Co. 

5.6 Syringe filters, 0.45-μm diameter, Whatman, Cliffton, NJ 

5.7 Filter paper, 3 and 9-cm diameter, Whatman No. 40 or equivalent 

6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

7. Procedure 

7.1 Prepare the saturated paste extract cup to receive the saturated paste (procedure 4E3) by 

placing a 3-cm diameter filter paper circle over the center of the cup followed by two 9-cm 

diameter filter paper circles. Slightly moisten the filter paper to ensure that it remains in place. 

Ensure there is no trapped air between the two 9-cm filter paper circles. 

7.2 Place the extraction syringe on the lower disk of the mechanical vacuum extractor. 

289
7.3 Use a clamp to close rubber tubing on the bottom of the paste extraction cup. Carefully 

transfer the saturated paste into the extraction cup. Gently tap the cup to remove entrapped air 

in the paste. Place cups on the extractor, connect the syringe and remove the clamp. 

7.4 When all cups are ready to extract, place a plastic cover over the extraction cup to retard 

evaporation. 

7.5 Turn on the extractor. Set the extraction time to ≈ 1 h. 

7.6 When the extractor stops, turn off the power. 

7.7 If sufficient extract has been obtained, pull the plunger of the syringe down. Do not pull 

plunger from the barrel of the syringe. Carefully remove the syringe containing the extract. 

Leave the rubber tubing on the sample tube. 

7.8 If insufficient extract has been obtained, re-extract by repositioning the extractor to its 

starting configuration. Remove excess air in the syringe and restart the extractor. Slowing the 

extraction time to an overnight extraction may be necessary to obtain sufficient extract. 

Alternate methods are to extract any "unused" saturated paste in a new extraction cup or to reextract by removing the top "moist" paste from the extraction cup, mixing with any "unused" 

paste, and re-extracting with a clean extraction cup or centrifuging. 

7.9 Filtering the saturation extract is recommended to prevent the development of 

microorganisms. Connect the syringe to a 0.45 μm diameter syringe filter and express the 

extract into a polycon. If extracts are not to be determined immediately after collection, then 

store samples at 4°C. 

8. Calculations

No calculations are required for this procedure. 

9. Report

None. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Holmgren, George G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically 

controlled variable rate leaching device. Soil Sci. Am. J. 41:1207-1208. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. 160 p. USDA Handb. 60. U.S. Govt. Print. Office, Washington, 

DC. 

Electrical Conductivity and Soluble Salts (4F) 

Saturated Paste (4F2) 

Saturated Paste Extraction (4F2c) 

Automatic Extractor (4F2c1) 

Atomic Absorption Spectrophotometry (4F2c1a) 

Calcium, Magnesium, Potassium, and Sodium (4F2c1a1-4) Air-Dry, <2 mm (4F2c1a1-4a1) 

1. Application 

The commonly determined soluble cations are Ca2+, Mg2+, K+, and Na+. In soils with a 

low saturation pH, measurable amounts of Fe and Al may be present. Determination of soluble 

 

290
cations is used to obtain the relations between total cation concentration and other properties of 

saline solutions such as electrical conductivity and osmotic pressure (U.S. Salinity Laboratory 

Staff, 1954). The relative concentrations of the various cations in the soil-water extracts also 

provide information on the composition of the exchangeable cations in the soil. Complete 

analyses of the soluble ions provide a means to determine total salt content of the soils and salt 

content at field moisture conditions. 

2. Summary of Method 

The saturation extract from procedure 4F2c1 is diluted with an ionization suppressant 

(La2O3). The analytes are measured by an atomic absorption spectrophotometer (AA). The 

data are automatically recorded by a computer and printer. The saturation extracted cations, 

Ca2+, Mg2+, K+, and Na+, are reported in meq L-1 (mmol (+) L-1) in procedures 4F2c1a1-4, 

respectively. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

analysis of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. Do not use borosilicate tubes because of potential leaching of 

analytes. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Thoroughly wash hands after handling these metal salts. 

Follow standard laboratory procedures when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene is highly flammable. Avoid open 

flames and sparks. Standard laboratory equipment includes fire blankets and extinguishers for 

use when necessary. Follow the manufacturer's safety precautions when using the AA. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Atomic absorption spectrophotometer (AAS), double-beam, AAnalyst 300, PerkinElmer Corp., Norwalk, CT 

5.3 Autosampler, AS-90, Perkin-Elmer Corp., Norwalk, CT 

5.4 Computer, with AA WinLab software, Perkin-Elmer Corp., Norwalk, CT, and printer 

5.5 Single-stage regulator, acetylene 

5.6 Digital diluter/dispenser, with syringes 10000 and 1000 μL, gas tight, MicroLab 500, 

Hamilton Co., Reno, NV 

5.7 Plastic test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer 

5.8 Containers, polyethylene 

5.9 Peristaltic pump 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Hydrochloric acid (HCl), concentrated 12 N

6.3 HCl, 1:1 HCl:RODI, 6 N. Carefully mix 1 part of concentrated HCl to 1 part RODI 

water. 

6.4 Stock lanthanum ionization suppressant solution (SLISS), 65,000 mg L-1. Wet 152.4 g 

of lanthanum oxide (La2O3) with 100 mL RODI water. Slowly and cautiously add 500 

mL of 6 N HCl to dissolve the La2O3. Cooling the solution is necessary. Dilute to 2 L 

with RODI water. Filter solution. Store in polyethylene container. 

6.5 Working lanthanum ionization suppressant solution (WLISS), 2000 mg L-1. Dilute 61.5 

mL of SLISS with 1800 mL of RODI water (1:10). Make up to volume with RODI 

water. Invert to mix thoroughly. Store in polyethylene container. 

291
6.6 Primary stock standards solution (PSSS), high purity, 1000 mg L-1: Ca, Mg, K, and Na. 

6.7 Working stock mixed standards solution (WSMSS) for Ca, Mg, and K. In a 500-mL 

volumetric flask, add 250 mL Ca PSSS, 25 mL Mg PSSS, and 100 mL K PSSS = 500 

mg L-1 Ca, 50 mg L-1 Mg, and 200 mg L-1 K. Dilute to volume with RODI water. Invert 

to thoroughly mix. Store in polyethylene containers. Prepare fresh weekly. Store in the 

refrigerator. 

6.8 Mixed calibration standards solution (MCSS), High, Medium, Low, Very Low, and 

Blank as follows: 

6.8.1 MCSS High Standard (1:100): Dilute WSMSS 1:100 with WLISS. Invert to mix 

thoroughly mix. Store in polyethylene containers. Prepare fresh weekly. Store in a 

refrigerator. Allow to equilibrate to room temperature before use. Final concentration = 

5 mg L-1 Ca, 0.5 mg L-1 Mg, and 2 mg L-1 K. 

6.8.2 MCSS Medium Standard (1:200): To a 100-mL volumetric flask, add 50 mL of 

WSMSS and bring to volume with RODI water. Dilute 1:100 with WLISS. Invert to 

thoroughly mix. Store in polyethylene containers. Prepare fresh weekly. Store in a 

refrigerator. Allow to equilibrate to room temperature before use. Final concentration 

=2.5 mg L-1 Ca, 0.25 mg L-1 Mg, and 1 mg L-1 K. 

6.8.3 MCSS Low Standard (1:400): To a 100-mL volumetric flask, add 25 mL of WSMSS 

and bring to volume with RODI water. Dilute 1:100 with WLISS. Invert to mix 

thoroughly. Store in polyethylene containers. Prepare fresh weekly. Store in a 

refrigerator. Allow to equilibrate to room temperature before use. Final concentration = 

1.25 mg L-1 Ca, 0.125 mg L-1 Mg, and 0.5 mg L-1 K. 

6.8.4 MCSS Very Low Standard (1:600): To a 100-mL volumetric flask, add 16.65 mL of 

WSMSS and bring to volume with RODI water. Dilute 1:100 with WLISS. Invert to 

mix thoroughly. Store in polyethylene containers. Prepare fresh weekly. Store in a 

refrigerator. Allow to equilibrate to room temperature before use. Final concentration = 

0.83 mg L-1 Ca, 0.08 mg L-1 Mg, and 0.33 mg L-1 K. 

6.8.5 MCSS Blank = 0 mL of Ca, Mg, and K. Dilute RODI water 1:100 with WLISS. 

6.9 Na Calibration Standards Solution (NaCSS), High, Medium, Low, and Very Low as 

follows: 

6.9.1 NaCSS High Standard (1:100): Dilute Na PSMSS (1000 mg L-1) 1:100 with WLISS. 

Invert to thoroughly mix. Store in polyethylene containers. Prepare fresh weekly. Store 

in a refrigerator. Allow to equilibrate to room temperature before use. Final 

concentration = 10 mg L-1 Na. 

6.9.2 NaCSS Medium Standard (1:200): In a 50-mL volumetric, add 25 mL of Na PSMSS 

and bring to volume with RODI water. Dilute 1:100 with WLISS. Invert to mix 

thoroughly. Store in polyethylene containers. Prepare fresh weekly. Store in a 

refrigerator. Allow to equilibrate to room temperature before use. Final concentration = 

5 mg L-1 Na. 

6.9.3 NaCSS Low Standard (1:400): In a 50-mL volumetric flask, add 12.5 mL of PSMSS 

and bring to volume with RODI water. Dilute 1:100 with WLISS. Invert to thoroughly 

mix. Store in polyethylene containers. Prepare fresh weekly. Store in a refrigerator. 

Allow to equilibrate to room temperature before use. Final concentration = 2.5 mg L-1

Na. 

292
6.9.4 NaCSS Very Low Standard (1:600) In a 50-mL volumetric flask, add 8.35 mL of 

PSMSS Na (1000 ppm) and bring to volume with RODI water. Dilute 1:100 with 

WLISS. Invert to thoroughly mix. Store in polyethylene containers. Prepare fresh 

weekly. Store in a refrigerator. Allow to equilibrate before use. Final concentration = 

1.67 mg L-1 Na. 

6.9.5 NaCSS Blank = 0 mL Na PSMSS. Dilute RODI water 1:100 with WLISS. 

6.10 Compressed air with water and oil traps. 

6.11 Acetylene gas, purity 99.6%. 

7. Procedure 

Dilution of Calibration Standards and Sample Extracts 

7.1 The 10-mL syringe is for diluent (WLISS). The 1-mL syringe is for the MCSS and 

saturation sample extracts (procedure 4F2c1). Set the digital diluter at a 1:100 dilution. See 

regeants for the preparation of the MCSS and the NaCSS. Dilute the saturation extract sample 

with 100 parts of WLISS (1:100). 

7.2 Dispense the diluted sample solutions into test tubes which have been placed in the sample 

holders of the sample changer. 

AAS Set-up and Operation 

7.3 Refer to the manufacturer's manual for operation of the AAS. The following are only very 

general guidelines for instrument conditions for the various analytes. 

Analyte Conc. Burner Wavelength Slit Fuel/Oxidant 

 (mg L-1) & angle (nm) (mm) (C2H2/Air) ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Ca 5.0 10 cm @ 0° 422.7 0.7 1.5/10.0 

Mg 0.5 10 cm @ 0° 285.2 0.7 1.5/10.0 

K 2.0 10 cm @ 0° 766.5 0.7 1.5/10.0 

Na 10.0 10 cm @ 30° 589.0 0.2 1.5/10.0 

7.4 Use the computer and printer to set instrument parameters and to collect and record 

instrument readings. 

AAS Calibration and Analysis 

7.5 Calibrate the instrument by using the MCSS and NaCSS. The data system will then 

associate the concentrations with the instrument responses fore each MCSS. Rejection criteria 

for MCSS, if R2

 <0.99. 

7.6 If sample exceeds calibration standard, the sample is diluted 1:5, 1:20, 1:100, etc., with 

RODI water followed by 1:100 dilution with WLISS. 

7.7 Perform one quality control (QC) (Low Standard) for every 12 samples. If reading is not 

within 10%, the instrument is re-calibrated and QC re-analyzed. 

7.8 Record analyte readings to 0.01 mg L-1. 

293
8. Calculations 

The instrument readings for analyte concentration are in mg L-1. These analyte concentrations 

are converted to meq L-1 as follows: 

Analyte Concentration in Soil (meq L-1) = (A x B)/C 

where: 

A = Analyte (Ca2+, Mg2+, K+, Na+) concentration in extract (mg L-1) 

B = Dilution ratio, if needed 

C = Equivalent weight 

where: 

Ca+2 = 20.04 mg meq-1

Mg+2 = 12.15 mg meq-1

Na+1 = 22.99 mg meq-1

K+1 = 39.10 mg meq-1

9. Report 

Report the saturation extraction cations of Ca2+, Mg2+, Na+, and K+ to the nearest 0.1 

meq L-1 (mmol (+) L-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. 160 p. USDA Handb. 60. U.S. Govt. Print. Office, Washington, 

DC. 

Electrical Conductivity and Soluble Salts (4F) 

Saturated Paste (4F2) 

Saturated Paste Extraction (4F2c) 

Automatic Extractor (4F2c1) 

Ion Chromatograph 4F2c1b 

Conductivity Detector (4F2c1b1) 

Self-Regeneration Suppressor (4F2c1b1a) 

Bromide, Acetate, Chloride, Fluoride, Nitrate, Nitrite, Phosphate, and Sulfate (4F2c1b1a1-8) 

Air-Dry, <2 mm (4F2c1b1a1-8a1) 

1. Application 

The soluble anions that are commonly determined in saline and alkali soils are 

carbonate, bicarbonate, sulfate, chloride, nitrate, nitrite, fluoride, phosphate, silicate, bromide, 

and borate (Khym, 1974; U.S. Salinity Laboratory Staff, 1954). Carbonate and bicarbonate are 

determined by titration. Phosphate, silicate, bromide, borate, and aluminate are found only 

occasionally in measurable amounts in soils. Chloride, sulfate, nitrate, fluoride, and nitrite are 

measured in solution by chromatography. In saline and alkali soils, carbonate, bicarbonate, 

sulfate, and chloride are the anions that are found in the greatest abundance. In general, soluble 

sulfate is usually more abundant than soluble chloride. 

2. Summary of Method 

The soil saturation extract is diluted according to its electrical conductivity (ECs). The 

diluted sample is injected into the ion chromatograph, and the anions are separated. A 

294
conductivity detector is used to measure the anion species and content. Standard anion 

concentrations are used to calibrate the system. A calibration curve is determined, and the 

anion concentrations are calculated. A computer program automates these actions. The 

saturation extract anions, Br-, CH3COO-, Cl-, F-, NO3

-

, NO2

-

, PO4

3-, and SO42- are reported in 

meq L-1 (mmol (-) L-1) in procedures 4F2c1b1a1-8, respectively. This same method may also 

be used for water analysis. 

3. Interferences 

Some saturation extracts contain suspended solids. Filtering after dilution removes the 

particles. Saturation extracts of acid soils that contain Fe and/or Al may precipitate and clog 

the separator column. Saturation extracts of very high pH may contain organic material which 

may clog or poison the column. Low molecular weight organic anions will co-elute with 

inorganic anions from the column. 

4. Safety 

Wear protective clothing and safety glasses. When preparing reagents, exercise special 

care. Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash 

hands after handling these metal salts. Follow the manufacturer's safety precautions when 

using the chromatograph. 

5. Equipment 

5.1 Ion chromatograph, double-column, conductivity detection, Dionex DX-120, Dionex 

Corp., Sunnyvale, CA 

5.2 Guard column, IonPac AG14, 4 x 50 mm, Dionex Corp., Sunnyvale, CA 

5.3 Analytical column, IonPac AS14, 4 x 250 mm, Dionex Corp., Sunnyvale, CA 

5.4 Self-regeneration suppressor, ASRS – ULTRA, 4 mm, Dionex Corp., Sunnyvale, CA 

5.5 Autosampler, AS40, Dionex Corp., Sunnyvale, CA 

5.6 Computer with PeakNet software and printer 

5.7 Digital diluter/dispenser, with syringes 10000 and 1000 μL, gas tight, MicroLab 500, 

Hamilton Co., Reno, NV 

5.8 Poly-vials with caps, 5 mL, Dionex Corp., Sunnyvale, CA 

6. Reagents 

6.1 Reverse osmosis deionized filtered (RODI), ASTM Type I grade of reagent water 

6.2 Helium gas 

6.3 Eluent solution. Solution A: Mix 5.30 g of Na2CO3 with RODI water in a 500-mL 

volumetric and make to volume with RODI water. Solution B: Mix 4.20 g of NaHCO3

with RODI water in a 500-mL volumetric and make to volume with RODI water. Add 

35 mL of Solution A and 10 mL of Solution B in a 1-L volumetric and make to volume 

with RODI water for a final concentration is 0.024 M Na2CO3 and 0.025 M NaHCO3. 

Make 2 L of eluent solution if chromatograph is to run overnight. Place eluent in eluent 

tank and degas with helium 15 min L-1 eluent (30 min total). Make fresh daily. 

6.4 Primary stock standards solutions, (PSSS1000), high purity, 1000 mg L-1: Cl-, SO4

2-, F, 

NO3

-

, NO2

-

, Br-, CH3COO-, and PO4

3-. 

6.5 Primary stock standards solutions (PSSS100), 100 mg L-1: F-, NO3

-

, NO2

-

, Br-, and PO4

3-. 

Prepare fresh weekly. In five 250-mL volumetric flasks add as follows: 

6.5.1 F- PSSS100 = 25 mL F- PSSS1000

6.5.2 Br- PSSS100 = 25 mL of Br- PSSS1000 

6.5.3 NO2

-

 PSSS100 = 25 mL NO2

-

 PSSS1000 

6.5.4 NO3

-

 PSSS100 = 25 mL NO3

-

 PSSS1000 

6.5.5 PO4

3- PSSS100 = 25 mL PO43- PSSS1000 

295
Dilute each PSSS100 to volume with RODI water and invert to thoroughly mix. Store in the 

refrigerator. 

6.6 Mixed calibration standards solutions (MCSS), A, B, C, D, E, and Blank as follows: 

6.6.1 MCSSA = In a 250-mL volumetric flask, add as follows 

12.5 mL Cl- PSSS1000 = 50 mg L-1

25 mL SO4

2

 PSSS1000 = 100 mg L-1

12.5 mL F- PSSS100 = 5 mg L-1

20 mL NO3

-

 PSSS100 = 8 mg L-1

20 mL NO2

-

 PSSS100 = 8 mg L-1

22 mL Br- PSSS100 = 8.8 mg L-1

20 mL CH3COO- PSSS1000 = 80 mg L-1

24 mL PO4

3- PSSS100 = 9.6 mg L-1

Dilute to volume with RODI water and invert to thoroughly mix. Store in glass containers. 

Store in the refrigerator. Prepare fresh weekly. 

6.6.2 MCSSB = In a 100-mL volumetric flask, add 40 mL MCSSA and dilute to volume with 

RODI water. Final concentration = 20, 40, 2, 3.2, 3.2, 3.52, 30.4, and 3.52 mg L-1 Cl-

, 

SO4

2-, F-

, NO3

-

, NO2

-

, Br-, CH3COO-, and PO4

3-, respectively. Invert to thoroughly mix. 

Store in glass containers. Prepare fresh weekly. Store in the refrigerator. 

6.6.3 MCSSC = In a 100-mL volumetric flask, add 20 mL MCSSA and dilute to volume with 

RODI water. Final concentration = 10, 20, 1, 1.6, 1.6, 1.76, 15.2, and 1.76 mg L-1 Cl-, SO4

2-, F-

, NO3

-

, NO2

-

, Br-, CH3COO-, and PO4

3-, respectively. Invert to thoroughly mix. 

Store in glass containers. Prepare fresh weekly. Store in the refrigerator. 

6.6.4 MCSSD = In a 250-mL volumetric flask, add 25 mL MCSSA and dilute to volume with 

RODI water. Invert to thoroughly mix. Final concentration = 5, 10, 0.5, 0.8, 0.8, 0.88, 

7.6, and 0.88 mg L-1 Cl-, SO4

2-, F- , NO3-

, NO2

-

, Br-, CH3COO-, and PO4

3-, respectively. 

Store in glass containers. Prepare fresh weekly. Store in the refrigerator. 

6.6.5 MCSSE = In a 250-mL volumetric flask, add 5 mL MCSSA and dilute to volume with 

RODI water. Final concentration = 1, 2, 0.1, 0.16, 0.16, 0.176, 1.52, and 0.176 mg L-1

Cl-, SO4

2-, F- , NO3-

, NO2

-

, Br-, CH3COO-, and PO4

3-, respectively. Invert to thoroughly 

mix. Store in glass containers. Prepare fresh weekly. Store in the refrigerator. 

6.6.6 MCSS Blank = 0 mL of Cl-

, SO4

2-, F-

, NO3

-

, NO2

-

, Br-, CH3COO-, and PO4

3-. Dilute 

RODI water to volume. 

7. Procedure 

Dilution of sample extracts 

7.1 To estimate the total soluble anion concentration (meq L-1), multiply the ECs (procedure 

4F2b1) by 10. Subtract the CO3

2- and HCO3-

 concentrations (procedures 4F2c1c1a1-2) from 

the total anion concentration. The remainder is the ≈ concentration (meq L-1) of anions to be 

separated by ion chromatography. 

Anion concentration (meq L-1) = ECs x 10 - (HCO3

-

 + CO3

2-) 

296
7.2 Dilute the saturation extract with the RODI water as follows: 

ECs (dS cm-1) Dilution Factor

 0.00 to 0.55 4 

 0.56 to 0.65 5 

 0.66 to 0.75 6 

 0.76 to 0.85 7 

 0.86 to 0.95 8 

 0.96 to 1.05 9 

 1.06 to 1.20 10 

 1.21 to 1.40 15 

 1.41 to 1.50 25 

 1.51 to 1.60 30 

 1.61 to 1.80 40 

 1.81 to 2.00 50 

 2.01 to 2.30 60 

 2.31 to 2.60 70 

 2.61 to 3.10 80 

 3.11 to 3.55 90 

 3.56 to 4.05 100 

 4.06 to 4.60 120 

 4.61 to 5.20 140 

 5.21 to 5.85 150 

 5.86 to 6.55 160 

 6.56 to 7.30 180 

 7.31 to 8.00 200 

 8.01 to 9.00 225 

 9.01 to 10.00 240 

 10.01 to 11.50 270 

 11.51 to 13.00 280 

 13.01 to 14.50 300 

 14.51 to 16.00 320 

 16.01 to 17.00 360 

 17.01 to 18.00 400 

 18.01 to 20.00 450 

 20.01 to 21.00 480 

 21.01 to 23.00 500 

 23.01 to 24.00 540 

 24.01 to 25.00 560 

 25.01 to 27.00 600 

 27.01 to 28.00 640 

 28.01 to 30.00 680 

 30.01 to 32.00 700 

 32.01 to 33.00 720 

 33.01 to 36.00 800 

 36.01 to 40.00 900 

 40.01 to 44.00 1000 

297
7.3 Place the MCSS (B, C, D, E, Blank) and diluted extract samples in the Poly-vials and cap 

with filtercaps. 

Set-up and Operation of Ion Chromatograph (IC) 

7.4 Refer to the Manufacturer's manual for the operation of chromatograph. Because any 

number of factors may cause a change in IC operating conditions, only a general set-up of the 

Dionex DX-120 ion chromatograph is presented. Individual analysts may modify some or all 

of the operating conditions to achieve satisfactory results. Ranges and/or (typical settings) are 

as follows: 

Parameter Range and/or (Typical Setting) 

Calibration Peak Height or (Area) 

Flow Setting 0.5 to 4.5 mL min-1 (1.63 mL min-1) 

Pressure 0 to 4000 psi (2200 to 2400 psi) 

Detection Suppressed conductivity 

Total Conductivity 0 to 999.9 μS 

Injection Volume 10 μL 

Auto Offset -999.9 to 999.9 μS (ON) 7.5 Load the sample holder cassettes with the capped samples, standards, and check samples. 

7.6 Use the computer and printer to set instrument parameters and to collect and record 

instrument readings. 

IC Calibration and Analysis 

7.7 Calibrate the instrument by using the MCSS (B, C, D, E, Blank). The data system will then 

associate the concentrations with the instrument responses for each MCSS. Rejection criteria 

for MCSS, R2

 <0.99. 

7.8 If samples are outside calibration, dilute sample extracts with RODI water solution and reanalyze. 

7.9 Perform one quality control (QC) (Low Standard MCSS, Standard C) for every 12 samples. 

If reading is not within tolerance limits (10 to 15%, based on analyte), the instrument is recalibrated and QC re-analyzed. 

7.10 Record analyte readings to 0.01 mg L-1. 

8. Calculations 

The instrument readings for analyte concentration are in mg L-1. These analyte concentrations 

are converted to meq L-1 as follows: 

Analyte Concentration in Soil (meq L-1) = (A x B)/C 

where: 

A = Analyte (Br-, CH3COO-, Cl-, F-, NO3

-

, NO2

-

, PO4

3-, SO42-) concentration in extract (mg L-1) 

B = Dilution ratio, if needed 

C = Equivalent weight 

where: 

Cl- = 35.45 mg meq-1

SO4

2- = 48.03 mg meq-1

298
F-

 = 19.00 mg meq-1

NO3

-

 = 62.00 mg meq-1

NO2

-

 = 46.00 mg meq-1

Br- = 79.90 mg meq-1

CH3COO- = 59.05 mg meq-1

PO4

3- = 31.66 mg meq-1

9. Report 

Report the saturation extraction anions (Cl-, SO4

2-, F-

, NO3

-

, NO2

-

, Br-, CH3COO-, and 

PO4

3-) to the nearest 0.1 meq L-1 (mmol (-) L-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Khym, J.X. 1974. Analytical ion-exchange procedures in chemistry and biology: Theory, 

equipment, techniques. Prentice-Hall, Inc., Englewood Cliffs, NJ. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. USDA Agric. Handb. 60. U.S. Govt. Print. Office, Washington, 

DC. 

Electrical Conductivity and Soluble Salts (4F) 

Saturated Paste (4F2) 

Saturated Paste Extraction (4F2c) 

Automatic Extractor (4F2c1) 

Automatic Titrator (4F2c1c) 

Combination pH-Reference Electrode (4F2c1c1) Acid Titration, H2SO4 (4F2c1c1a) Carbonate and Bicarbonate (4F2c1c1a1-2) 

Air-Dry, < 2 mm (4F2c1c1a1-2a1)

1. Application 

The water soluble anions that usually are determined in saturation extracts are 

carbonate, bicarbonate, sulfate, chloride, nitrate, nitrite, fluoride, phosphate, silicate, bromide, 

and borate. Carbonate and bicarbonate are analyzed by titration. In saturation extracts, 

carbonate is measurable if the pH >9 (U.S. Salinity Laboratory Staff, 1954). The bicarbonate 

concentration is seldom >10 meq L-1 in the absence of carbonate anions (U.S. Salinity 

Laboratory Staff, 1954). The bicarbonate concentration at pH <7 seldom exceeds 3 or 4 meq L1

 (U.S. Salinity Laboratory Staff, 1954). 

The total dissolved ion amounts generally increase with increasing soil moisture 

content. While some ions increase, some ions may decrease. The carbonate and bicarbonate 

anions are among those ions which are most dependent upon soil moisture. Therefore, in 

making interpretations about carbonate and bicarbonate in soil solution, there must be careful 

consideration about the chemistry of the soil and the soil solution. 

2. Summary of Method 

An aliquot of the saturation extract (procedure 4F2c) is titrated on an automatic titrator 

to pH 8.25 and pH 4.60 end points. The carbonate and bicarbonate are calculated from the 

titers, aliquot volume, blank titer, and acid normality (procedures 4F2c1c1a1-2, respectively). 

Carbonate and bicarbonate are reported in meq L-1 (mmol (+) L-1). 

299
3. Interfernces 

Clean the electrode by rinsing with distilled water and patting it dry with tissue. Wiping 

the electrode dry with a cloth, laboratory tissue, or similar material may cause electrode 

polarization. 

Slow electrode response time may cause over shooting the end point. A combination of 

slowing the buret speed and increasing the time delay may help. Cleaning the electrode with 

detergent may decrease the response time. If all else fails, changing the electrode generally 

solves the problem. Blanks may not titrate properly because some sources of reverse osmosis 

(RO) water have a low pH. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise care. 

Thoroughly wash hands after handling reagents. Restrict the use of concentrated H2SO4 to the 

fume hood. Use showers and eyewash stations to dilute spilled acids. Use sodium bicarbonate 

and water to neutralize and dilute spilled acids. Follow the manufacturer's safety precautions 

when operating the automatic titrator. 

5. Equipment 

5.1 Automatic titrator, Metrohm 670 Titroprocessor, with control unit, sample changer, and 

dispenser, Metrohm Ltd., Brinkmann Instruments, Inc. 

5.2 Combination pH-reference electrode, Metrohm Ltd., Brinkmann Instruments, Inc. 

5.3 Pipettes, electronic digital, 2500 μL and 10 mL, with tips, 2500 μL and 10 mL 

6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

6.2 Helium gas 

6.3 Sulfuric acid (H2SO4), concentrated, 36 N

6.3 H2SO4, 0.0240 N standardized. Carefully dilute 2.67 mL of concentrated H2SO4 in 4 L of 

RODI degassed water (≈ 15 min). Re-standardize the acid at regular intervals. Refer to 

the procedure for standardization of acids. 

6.4 Borax pH buffers, pH 4.00, pH 7.00, and pH 9.18, for titrator calibration, Beckman, 

Fullerton, CA. 

7. Procedure 

7.1 Pipet 3 mL of the fresh saturation extract (procedure 4E3c) into a 250-mL titration beaker. 

7.2 Add 72 mL of RO water into a titration beaker. Final volume is 75 mL for blanks and 

samples. Run 8 to 12 blanks of RO water through the titration procedure. 

7.3 Refer to manufacturer's manual for operation of the automatic titrator. 

7.4 Calibrate automatic titrator with 9.18, 7.00 and 4.00 pH buffers. Set-up the automatic 

titrator to set end point titration mode. The "Set" pH parameters are listed as follows: 

Parameter Value

Ep1 pH 8.25 

Dyn change pH 1.5 units 

Drift 0.4 mV s-1

Time delay 10 s 

Ep2 pH 4.60 

Dyn change pH 1.5 units 

Drift 0.4 mV s-1

300
Temp 25°C 

Stop Volume 35 mL 

7.5 Place the 250-mL titration beakers in the sample changer. 

7.6 Press "Start". 

7.7 If the titrator is operating properly, no other analyst intervention is required. The titers and 

other titration parameters are recorded on the Titroprocessor printer. 

8. Calculations 

8.1 CO3

2- (meq L-1) =(2 T1 x N x 1000)/Aliquot 

8.2 HCO3

-

 (meq L-1) = [(T2 + T1) - Blank – (2 x T1) x N x 1000]/Aliquot 

where: 

T1 = Titer of CO3

2- (mL) 

T2 = Titer of HCO3

-

 (mL) 

N = Normality of H2SO4

Blank = Average titer of blank solutions (mL) 

Aliquot = Volume of saturation extract titrated (mL) 

1000 = Conversion factor to meq L-1

9. Report

Report saturation extract CO3

2- and HCO3-

 to the nearest 0.1 meq L-1 (mmol (-) L-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. USDA Handb. 60. U.S. Govt. Print. Office, Washington, DC. 

Ratios and Estimates Related to Soluble Salts (4F3) 

Exchangeable Sodium Percentage (ESP), NH4OAc, pH 7.0(4F3a) ESP, Calculated without Saturated Paste Extraction (4F3a1) 

Compute the exchangeable sodium percentage (ESP) by dividing the exchangeable 

sodium (ES) by the CEC by NH4OAc, pH 7.0 (CEC-7) and multiplying by 100 (procedure 

4F3a1). The ES is calculated by subtracting the water soluble Na+

 determined in procedure 

4E3c1a4 from the NH4OAc extractable Na+ determined in procedure 4B1a1b4 (U.S. Salinity 

Laboratory Staff, 1954). The CEC-7 is determined in procedure 4B1a1a1a1. In soil taxonomy, 

an ESP >15% is a criterion for natric horizons (Soil Survey Staff, 1999). When the saturation 

extract is not prepared, the ESP is calculated as follows: 

ESP = (ES/CEC-7) x 100 

where: 

ESP = Exchangeable sodium percentage 

ES = Extractable sodium (NH4OAc extractable Na+, (cmol (+) kg-1)). 

CEC-7 = CEC by NH4OAc, pH 7.0 (cmol (+) kg-1). 

301
Ratios and Estimates Related to Soluble Salts (4F3) 

Exchangeable Sodium Percentage (ESP), NH4OAc, pH 7.0(4F3a) ESP, Calculated with Saturated Paste Extraction (4F3a2) 

Exchangeable Na is computed with acceptable accuracy unless salt contents > 20 

mmhos cm-1 (dS m-1) at 25 C. Exchangeable Na equals extractable Na minus saturation 

extract Na multiplied by saturation percentage. Saturation percentage is the water percentage 

in the saturated paste divided by 1000. Exchangeable Na can be determined with greater 

accuracy than the other cations in the presence of gypsum or carbonates. If exchangeable K is 

negligible compared to exchangeable Ca and Mg then exchangeable Ca plus Mg equals CEC 

(NH4OAc, pH 7.0) minus exchangeable Na. This approximation is suitably reproducible for 

comparison between soils and for soil classification. Exchangeable Ca can be computed in the 

same manner as exchangeable Na. Results are not so satisfactory for exchangeable Ca when 

computed in the presence of carbonates or large amounts of gypsum. 

When the saturation extract is prepared, the SSL calculates the ESP by procedure 4F3a2 

as follows: 

ESP = 100 x [Naex - (Naws x (H2Ows/1000))]/CEC-7 

where: 

ESP = Exchangeable sodium percentage 

Naex = Extractable Na (NH4OAc extractable Na+

, (cmol (+) kg-1)) 

Naws = Water-soluble Na (mmol (+) L-1) 

H2Ows = Water saturation percentage 

CEC-7 = CEC by NH4OAc, pH 7.0 (cmol (+) kg-1) 

1000 = Conversion factor to (cmol (+) kg-1) 

100 = Conversion factor to percent 

Ratios and Estimates Related to Soluble Salts (4F3) 

Sodium Adsorption Ratio (SAR) (4F3b) 

Compute the sodium adsorption ratio (SAR) by dividing the molar concentration of the 

monovalent cation Na+ by the square root of the molar concentration of the divalent cations 

Ca2+ and Mg2+ (U.S. Salinity Laboratory Staff, 1954). The water soluble Ca2+, Mg2+, and Na+

are determined in procedures 4F2c1a1, 4F2c1a2, and 4F2c1a4, respectively. The SAR was 

developed as a measurement of the quality of irrigation water, particularly when the water is 

used for irrigating soils that are salt or Na affected (U.S. Salinity Laboratory Staff, 1954). In 

soil taxonomy, a SAR >13 is a criterion for natric horizons (Soil Survey Staff, 1999). The SSL 

calculates the SAR by procedure 4F3b. The SAR is calculated as follows: 

 

SAR = 

 

[Na ] +

[Ca Mg ] [ ] + + + + +

2 

SAR = Sodium Adsorption Ratio 

Na+

 = Water soluble Na+ (mmol (+) L-1). 

Ca2+ = Water soluble Ca2+ (mmol (+) L-1). 

Mg2+ = water soluble Mg2+ (mmol (+) L-1). 

302
References 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys. USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. Print. Office, 

Washington, DC. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of saline 

and alkali soils. USDA Agric. Handb. 60. U.S. Govt. Print. Office, Washington, DC. 

Ratios and Estimates Related to Soluble Salts (4F3) 

Estimated Total Salt (4F3c) 

Use the charts and graphs available in U.S. Salinity Laboratory Staff (1954) to estimate 

total salt content (4F3c) from the electrical conductivity (ECs) of the saturation extract 

(procedure 4F2b1). The essential relations are summarized in the equations as follows: 

Total Salt in soil (ppm) = (-4.2333 + (12.2347 X Ecs) + (0.058 x Ecs

2 ) - (0.0003 x Ecs3

)) x 

0.000064 x SP 

where: 

ECs = Electrical conductivity of saturation extract 

SP = Saturation percentage of saturation paste

Previous equations used to estimate total salt content are as follows: 

Log total salt in soil (ppm) = 0.81 + 1.08 x Log ECs (mmhos cm-1) + Log SP 

where: 

ECs = Electrical conductivity of saturation extract 

SP = Saturation percentage of saturation paste

Total salt in soil (%) = Total salt (ppm) x 10-4

These equations are applicable to saturation extracts with an ECs <20 mmhos cm-1. 

Deviations occur at higher salt concentrations. 

References 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys. USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. Print. Office, 

Washington, DC. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of saline 

and alkali soils. 160 p. U.S. Dept. of Agric. Handb. 60. U.S. Govt. Print. Office, 

Washington, DC. 

Selective Dissolutions (4G) 

Background: Over the years, various terms have been used to describe broad groupings 

of soil components, e.g., crystalline phyllosilicates, amorphous, poorly crystalline, 

paracrystalline, noncrystalline, allophane, imogolite, and short-range-order minerals 

(SROMs), etc (Jackson, 1986). These groupings have been related, in part, to various 

laboratory analyses, and thereby, have been operationally defined quantitatively and 

semiquantitatively by these analyses (Jackson, 1986). Some of these analytical procedures 

include X-ray diffraction analysis and selective chemical dissolutions, e.g., dithionite-citrate, 

sodium pyrophosphate, and ammonium oxalate extractions. These terms have not been used 

consistently in the literature. In addition, there is not always a clear delineation between 

dissolution data, either conceptually or operationally. For more detailed discussion of these 

303
various soil terms and the application of selective chemical extractions, refer to Wada (1989) 

and Soil Survey Staff (1995). 

Selective dissolution data have been used extensively in the study of the noncrystalline 

material content of soils and sediments. However, there are limitations in using these data. In 

general, there exists a continuum of crystalline order, ranging from no long-range order to 

paracrystalline to poorly crystalline to well crystalline (Follet et al., 1965). Selective 

dissolution data are necessary for independent determinations of various inorganic constituents 

of soils because of the difficulty with many physical analytical methods in estimating or even 

recognizing the presence of noncrystalline and paracrystalline free oxides or aluminosilicates 

mixed with crystalline soil components (Jackson et al., 1986). In general, the crystalline free 

oxides and phyllosilicates of soils can be identified qualitatively and estimated 

semiquantitatively by X-ray diffraction analysis. Those soils containing hydroxyls (-OH 

groups), e.g., kaolinite, gibbsite, and goethite, can sometimes be determined quantitatively by 

differential thermal analysis (DTA), differential scanning colorimetry (DCS), and 

thermogravimetric analysis (TGA). Refer to additional discussion on X-ray diffraction and 

thermal analysis in the mineralogy section (7) of this manual. 

With selective chemical dissolution data, there are difficulties in the adequate 

assessment of the portion that is extracted by particular reagents, e.g., dithionite-citrate, sodium 

pyrophosphate, and ammonium oxalate. In principle, it cannot be expected that chemical 

methods are able to perfectly distinguish the degrees of crystallinity, and some caution is 

required in the interpretation of these analytical data (van Wambeke, 1992). Refer to (Wada, 

1989) for the dissolution of Al, Fe, and Si in various clay constituents and organic complexes 

by treatment with different reagents. The SSL routinely performs three selective chemical 

dissolutions as follows: dithionite-citrate (4G1a1-3); ammonium oxalate (4G2a1a1-5); and 

sodium pyrophosphate (4G3a1-3). 

Dithionite-Citrate Extraction: The original objectives of the dithionite-citrate 

extraction were to determine the free Fe oxides and to remove the amorphous coatings and 

crystals of free Fe oxide, acting as cementing agents, for subsequent physical and chemical 

analysis of soils, sediments, and clay minerals (Weaver et al., 1968; Jackson, 1969; Jackson et 

al., 1986). Dithionite-citrate extractable Fe (Fed) is considered a measure of "free iron" in soils 

and, as such, is pedogenically significant. Dithionite-citrate extractable Fe data are of interest 

in soil genesis-classification studies because of its increasing concentration with increasing 

weathering, and its effect on soil colors (Schwertmann, 1992). "Free iron" is also considered 

an important factor in P-fixation and soil aggregate stability. 

Sodium Pyrophosphate Extraction: Sodium pyrophosphate extracting solutions tend 

to selectively extract mainly Fe and Al associated with organic compounds while the dithionitecitrate extractions tend to extract these compounds plus the free oxides (McKeague et al., 

1971). At one time, sodium pyrophosphate extractable Fe and Al in conjunction with 

dithionite-citrate data were used to help identify translocated Al and Fe humus complexes in 

spodic horizons (Soil Survey Staff, 1975). Numerous evaluations of pyrophosphate extracts 

have indicated that the pyrophosphate extraction does not necessarily correlate with organicbound Fe and Al (Schuppli et al., 1983; Kassim et al., 1984; Parfitt and Childs, 1988; Birkeland 

et al., 1989) as commonly thought (Schwertmann and Taylor, 1977; Parfitt and Childs, 1988). 

Pyrophosphate not only extracts organic-bound Fe but also peptizes solid particles of 

ferrihydrite and in some instances even goethite (Yuan et al., 1993). The use of sodium 

pyrophosphate extract data in conjunction with dithionite-citrate data as chemical requirements 

for spodic horizons have been replaced by other criteria (Soil Survey Staff, 1999) and, at one 

time, were referred to as spodic horizon criteria on the SSL data sheets. 

Ammonium Oxalate Extraction: In general, ammonium oxalate allowed to react in 

darkness has been considered to be a selective dissolution for noncrystalline materials 

(McKeague and Day, 1966; Higashi and Ikeda, 1974; Fey and LeRoux, 1976; Schwertmann 

and Taylor, 1989; Hodges and Zelazny, 1980). The ammonium oxalate procedure removes 

most noncrystalline and paracrystalline materials (allophane and imogolite) from soils (Higashi 

and Ikeda, 1974; Hodges and Zelazny, 1980) as well as short-range-ordered oxides and 

304
hydroxides of Al, Fe, and Mn (Schwertmann, 1959, 1964; McKeague and Day, 1966; 

McKeague et al., 1971; Fey and LeRoux, 1976). In addition, this method is assumed to extract 

Al + Fe humus. Opaline Si is not dissolved by this method (Wada, 1977). This procedure has 

been reported to dissolve very little hematite and goethite and small amounts of magnetite 

(Baril and Bitton, 1969; McKeague et al., 1971; Walker, 1983). There have been conflicting 

data on the effect of this procedure on clay minerals, but in general, the ammonium oxalate 

treatment is considered to have very little effect on phyllosilicates (kaolinite, montmorillonite, 

illite) or gibbsite. The ammonium oxalate extraction is assumed to dissolve selectively "active" 

Al and Fe components that are present in noncrystalline materials as well as associated or 

independent poorly crystalline silica. The method also extracts allophane, imogolite, Al + Fe 

humus complexes, and amorphous or poorly crystallized oxides and hydroxides. 

The intent of the ammonium oxalate procedure is to measure the quantities of poorly 

crystalline materials in the soil. At the present time, the ammonium oxalate extraction is 

considered the most precise chemical method for measuring these soil components. However, 

in principle it cannot be expected that chemical methods are able to perfectly distinguish 

degrees of crystallinity, and some caution is to be exercised in the interpretation of the 

analytical data (van Wambeke, 1992). A more reliable and accurate estimation of soil 

properties and a better understanding of noncrystallinity are provided when ammonium oxalate 

extraction is used in conjunction with other selective dissolution procedures, thermal 

techniques, and chemical tests (Jackson, 1986). 

Application, Ratios, and Estimates: In a general way, the Fed is considered to be a 

measure of the total pedogenic Fe, e.g., goethite, hematite, lepidocrocite, and ferrihydrite, while 

the ammonium oxalate extractable Fe (Feo) (probably ferrihydrite) is a measure of the 

paracrystalline Fe (Birkeland et al., 1989). The Feo/Fed ratio is often calculated because it is 

considered an approximation of the relative proportion of ferrihydrite in soils (Schwertmann, 

1985). 

The Mnd is considered the "easily reducible Mn". The Ald and Alo are pedogenically 

significant. The Ald represents the Al substituted in Fe oxides, which can have an upper limit 

of thirty-three mole percent substitution (Schwertmann et al., 1977; Schwertmann and Taylor, 

1989). The Alo is generally an estimate of the total pedogenic Al in soils dominated by 

allophane, imogolite, and organically-bound Al (Wada, 1977; Childs et al., 1983). Unlike Fed, the Ald extract is commonly less than the Alo (Childs et al., 1983; Birkeland et al., 1989) and so 

does not necessarily represent the total pedogenic Al (Wada, 1977). 

Allophane in soils can be estimated from the Alo and Sio and the pyrophosphate 

extractable Al (Alp) (Parfitt and Henmi, 1982; Parfitt and Wilson, 1985; Parfitt, 1990). The Alo

represents the Al dissolved from allophane, imogolite, and Al-humus complexes, and the Alp is 

the Al from the Al-humus complexes alone (Parfitt and Kimble, 1989). The Alo minus the Alp

gives an estimate of the Al in allophane and imogolite, whereas the Sio gives an estimate of the 

Si in allophane and imogolite. The (Alo - Alp)/Sio times the molar ratio (28/27) is an estimate 

of the Al/Si ratio of allophane and imogolite in the soil. The values of 28 and 27 represent the 

atomic weights of Si and Al, respectively. 

Selective chemical dissolution data are used as taxonomic criteria for mineralogy 

classes, e.g., ammonium oxalate Fe and Si for the amorphic and ferrihydritic mineralogy 

classes and dithionite-citrate Fe for the ferritic mineralogy class. The optical density of 

ammonium oxalate extract (ODOE) of >0.25 is used as a chemical criterion for spodic 

materials (Soil Survey Staff, 1999). An increase in ODOE is used as an indicator of the 

accumulation of translocated organic materials in an illuvial horizon (Soil Survey Staff, 1999). 

Ammonium oxalate extractable Alo plus 0.5 Feo is also used as a taxonomic criterion for andic 

soil properties (Soil Survey Staff, 1999). The weight of Fe atoms is approximately twice that 

of Al atoms. In evaluating the relative proportion of Fe and Al atoms solubilized by 

ammonium oxalate, the weight percent of Fe must be divided by two, i.e., Alo + 1⁄2 Feo. Refer 

to the Soil Survey Staff (1995, 1999) for more detailed discussion of these taxonomic criteria. 

305
References: 

Baril, R., and G. Bitton. 1969. Teneurs elevees de fer libre et identification taxonomique de 

certain sols due Quebec contenant de la magnetite. Can. J. Soil Sci. 49:1-9. 

Birkeland, P.W., R.M. Burke, and J.B. Benedict. 1989. Pedogenic gradients of iron and 

aluminum accumulation and phosphorus depletion in arctic and alpine soils as a function of 

time and climate. Quat. Res. 32:193-204. 

Fey, M.V., and J. LeRoux. 1976. Quantitative determinations of allophane in soil clays. Proc. 

Int. Clay Conf. 1975 (Mexico City). 5:451-463. Appl. Publ. Ltd., Wilmette, IL. 

Follet, E.A.C., W.J. McHardy, B.D. Mitchell, and B.F.L. Smith. 1965. Chemical dissolution 

techniques in the study of soil clays. I. & II. Clay Miner. 6:23-43. 

Higashi, T., and H. Ikeda. 1974. Dissolution of allophane by acid oxalate solution. Clay Sci. 

4:205-212. 

Hodges, S.C., and L.W. Zelazny. 1980. Determination of noncrystalline soil components by 

weight difference after selective dissolution. Clays Clay Miner. 28:35-42. 

Jackson, M.L. 1969. Soil chemical analysis. Adv. 2nd ed. Univ. Wisconsin, Madison, WI. 

Jackson, M.L., C.H. Lim, and L.W. Zelazny. 1986. Oxides, hydroxides, and aluminosilicates. 

In A. Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd 

ed. Agron. 9:101-150. 

Kassim, J.K., S.N. Gafoor, and W.A. Adams. 1984. Ferrihydrite in pyrophosphate extracts of 

podzol B horizons. Clay Miner. 19:99-106. 

McKeague, J.A., J.E. Brydon, and N.M. Miles. 1971. Differentiation of forms of extractable 

iron and aluminum in soils. Soil Sci. Soc. Am. Proc. 35:33-38. 

McKeague, J.A., and J.H. Day. 1966. Dithionite- and oxalate-extractable Fe and Al as aids in 

differentiating various classes of soils. Can. J. Soil Sci. 46:13-22. 

Parfitt, R.L. 1990. Allophane in New Zealand - A review. Aust. J. Soil Res. 28:343-360. 

Parfitt, R.L., and C.W. Childs. 1988. Estimation of forms of Fe and Al: a review of and 

analysis of contrasting soils by dissolution and Moessbauer methods. Aust. J. Soil. Res. 

26:121-144. 

Parfitt, R.L., and T. Henmi. 1982. Comparison of an oxalate-extraction method and an infrared 

spectroscopic method for determining allophane in soil clays. Soil Sci. Nutr. 28:183-190. 

Parfitt, R.L., and J.M. Kimble. 1989. Conditions for formation of allophane in soils. Soil Sci. 

Soc. Am. J. 53:971-977. 

Parfitt, R.L. and A.D. Wilson. 1985. Estimation of allophone and halloysite in three sequences 

of volcanic soils, New Zealand. Catena Suppl. 7:1-9. 

Schuppli, P.A., G.J. Ross, and J.A. McKeague. 1983. The effective removal of suspended 

materials from pyrophosphate extracts of soils from tropical and temperate regions. Soil Sci. 

Soc. Am. J. 47:1026-1032. 

Schwertmann, U. 1959. Die fraktionierte Extraktion der freien Eisenoxide in Boden, ihre 

mineralogischen Formen und ihre Entstehungsweisen. Z. Pflanzenernahr. Dueng. Bodenk. 

84:194-204. 

Schwertmann, U. 1964. The differentiation of iron oxides in soil by extraction with ammonium 

oxalate solution. Z. Pflanzenernaehr. Bodenkd. 105:194-202. 

Schwertmann, U. 1985. The effect of pedogenic environments on iron oxide minerals. Adv. 

Soil Sci. i, 172-200. 

Schwertmann, U. 1992. Relations between iron oxides, soil color, and soil formation. In J.M. 

Bigham and E.J. Ciolkosz (eds.). Soil color. SSSA Spec. Publ. No. 31. Soil Sci. Soc. Am., 

Madison, WI. 

Schwertmann, U., R.W. Fitzpatrick, and J.LeRoux. 1977. Al substitution and differential 

disorder in soil hematites. Clays Clay Miner. 25:373-374. 

Schwertmann, U., and R.M. Taylor. 1977. Iron oxides. In J.B. Dixon and S.B. Weed (eds.). 

Minerals in soil environment. Soil Sci. Soc. Am. No. 1:145-180. 

Schwertmann, U., and R.M. Taylor. 1989. Iron oxides. In J.B. Dixon and S.B. Weed (eds.). 

Minerals in soil environment. 2nd ed. Soil Sci. Soc. Am. No. 1:370-438. 

306
Survey Staff. 1975. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys, USDA-SCS Agric. Handb. No. 436. U.S. Govt. Print. Office, 

Washington, DC. 

Soil Survey Staff. 1995. Soil survey laboratory information manual. Version No. 1.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, DC. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys. USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. Print. Office, 

Washington, DC. 

van Wambeke, A. 1992. Soils of the tropics: properties and appraisal. McGraw-Hill, Inc., NY. 

Wada, K. 1977. Allophane and imogolite. In J.B. Dixon and S.B. Weed (eds.). Minerals in soil 

environment. 1st ed. Soil Sci. Soc. Am. No. 1:603-638. 

Wada, K. 1989. Allophane and imogolite. In J.B. Dixon and S.B. Weed (eds.). Minerals in soil 

environment. 2nd ed. Soil Sci. Soc. Am. No. 1: 1051-1087. 

Walker, A.L. 1983. The effects of magnetite on oxalate- and dithionite-extractable iron. Soil 

Sci. Soc. Am. J. 47:1022-1025. 

Weaver, R.M., J.K. Syers, and M.L. Jackson. 1968. Determination of silica in citratebicarbonate-dithionite extracts of soils. Soil Sci. Soc. Am. Proc. 32:497-501. 

Yuan, G., L.M. Lavkulich, and C. Wang. 1993. A method for estimating organic-bound iron 

and aluminum contents in soils. Commun. Soil Sci. Plant Anal. 24(11&12), 1333-1343. 

Selective Dissolutions (4G) 

Dithionite-Citrate Extraction (4G1) 

Atomic Absorption Spectrophotometer (4G1a) 

Aluminum, Iron, Manganese (4G1a1-3) 

Air-Dry or Field Moist, <2 mm (4G1a1-3a-b1) 

1. Application 

Dithionite-citrate (CD) is used as a selective dissolution extractant for organically 

complexed Fe and Al, noncrystalline hydrous oxides of Fe and Al, and amorphous 

aluminosilicates (Wada, 1989). The CD solution is a poor extractant of crystalline hydrous 

oxides of Al, allophane, and imogolite. The CD solution does not extract opal, Si, or other 

constituents of crystalline silicate minerals (Wada, 1989).

This extraction is also sometimes referred to as citrate-dithionite or sodium citratedithionite. The method (4G1a1-3) described herein is not the same extraction as described in 

the Soil Survey Investigations Report (SSIR) No. 1 (1972), method 6C3. This obsolete SSL 

method (6C3) incorporated sodium bicarbonate as a buffer (pH 7.3) in the dithionite-citrate 

method, resulting in a buffered neutral citrate-bicarbonate-dithionite (Aguilera and Jackson, 

1953; Mehra and Jackson, 1960; and Jackson, 1969), commonly referred to as the CBD 

method. 

2. Summary of Method 

A soil sample is mixed with sodium dithionite, sodium citrate, and reverse osmosis 

deionized (RODI) water, and shaken overnight. Solution is centrifuged, and a clear extract 

obtained. The CD extract is diluted with RODI water. The analytes are measured by an atomic 

absorption spectrophotometer (AAS). The data are automatically recorded by a computer and 

printer. The AAS converts absorption to analyte concentration. The percent CD extractable Al, 

Fe, and Mn are reported in procedures 4G1a1-3, respectively. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

AA analyses of these elements. These interferences vary in importance, depending upon the 

particular analyte selected. 

307
The redox potential of the extractant is dependent upon the pH of the extracting solution 

and the soil system. Sodium citrate complexes the reduced Fe and usually buffers the system to 

a pH of 6.5 to 7.3. Some soils may lower the pH, resulting in the precipitation of Fe sulfides. 

Filtered extracts can yield different recoveries of Fe, Mn, and Al, relative to unfiltered 

extracts. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves); eye protection (face 

shields, goggles, or safety glasses); and a breathing filter when handling dry sodium dithionite. 

Sodium dithionite may spontaneously ignite if allowed to become moist, even by atmospheric 

moisture. Keep dithionite in a fume hood. 

Follow standard laboratory practices when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene gas is highly flammable. Avoid 

open flames and sparks. Standard laboratory equipment includes fire blankets and 

extinguishers for use when necessary. Follow the manufacturer's safety precautions when 

using the AA. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Atomic absorption spectrophotometer (AAS), double-beam optical system, AAnalyst, 

300, Perkin-Elmer Corp., Norwalk, CT, with computer and printer 

5.4 Autosampler, AS-90, Perkin-Elmer Corp., Norwalk, CT 

5.5 Peristaltic pump 

5.6 Single-stage regulators, acetylene and nitrous oxide 

5.7 Centrifuge, Centra, GP-8, Thermo IEC, Needham Heights, MA 

5.8 Digital diluter/dispenser, with syringes 10000 and 1000 μL, gas tight, MicroLab 500, 

Hamilton Co., Reno, NV 

5.9 Dispenser, 30 mL 

5.10 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer 

5.11 Containers, polypropylene

5.12 Volumetrics, Class A, 100, 250, and 1000-mL 

5.13 Measuring scoop, handmade, 0.4 g calibrated 

5.14 Centrifuge tubes, 50-mL 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Sodium dithionite (Na2S2O4), purified powder 

6.3 Sodium citrate dihydrate (Na3C6H507·2H2O), crystal, reagent. Dissolve 336 g sodium 

citrate in approximately 1 L RODI water, followed by diluting to 2 L with RODI water. 

Final concentration is 0.57 M sodium citrate. 

6.4 Sulfuric acid (H2SO4), concentrated. 

6.5 Phosphoric acid (H3PO4), concentrated (85%). For Fe analysis, samples are diluted 1:50 

prior to analysis. A diluting solution for Fe analysis (for a final concentration of 0.5% 

H3PO4 in samples) may be made by adding 6.12 mL of concentrated H3PO4 to 500 mL 

volume of RODI water, diluting to 1000 mL and mixing thoroughly. (Note: 1:5 sample 

dilutions for Al and Mn are in RODI water.) 

6.6 Primary Stock Standard Solution (PSSS), high purity, 1000 mg L-1: Fe, Mn, and Al. 

6.7 Calibration standards for Fe (Section 6.8): To each 100 mL volume of blank, 

calibration, and quality control (QC) standards, add 25 mL of the following matrix 

matching mixture. This mixture is made by combining 20 mL Na citrate extracting 

solution, 0.21 mL H2SO4, and 6 mL H3PO4 and diluting to 250 mL volume with RODI 

308
water. Invert to mix thoroughly. (Note: Matrix of standards is prepared to match a 1:50 

dilution of samples. Also, H2SO4 substitutes for dithionite). 

6.8 Standard Fe calibration solutions (SFeCS) or working standards (25.0, 20.0, 15.0, 10.0, 

5.0, 1.0, and 0.0 mg Fe L-1) and QC (12.5 mg L-1). Prepare fresh weekly. In seven 100-

mL volumetric flasks add as follows: 

6.8.1 25.0 mg Fe L-1 = 2.5 mL PSSSFe

6.8.2 20.0 mg Fe L-1 = 2.0 mL PSSSFe

6.8.3 15.0 mg Fe L-1 = 1.5 mL PSSSFe

6.8.4 10.0 mg Fe L-1 = 1.0 mL PSSSFe

6.8.5 5.0 mg Fe L-1 = 0.5 mL PSSSFe

6.8.6 1.0 mg Fe L-1 = 0.1 mL PSSSFe

6.8.7 0.0 mg Fe L-1 = 0.0 mL PSSSFe (blank) 

6.8.8 12.5 m Fe L-1 = 1.25 mL PSSSFe (QC) 

Fill to volume with RODI water and invert to mix thoroughly. After dissolution, transfer 

solution to a plastic bottle. 

6.9 Calibration standards for Mn (Section 6.10): To each 100 mL volume of blank, 

calibration, and quality control (QC) standards, add 25 mL of the following matrix 

matching mixture. This mixture is made by combining 200 mL Na citrate extracting 

solution, 2.1 mL H2SO4, and diluting to 250-mL volume with RODI water. Invert to 

mix thoroughly. (Note: Matrix of standards is prepared to match a 1:5 dilution of 

samples. Also, H2SO4 substitutes for dithionite). 

6.10 Standard Mn calibration solutions (SMnCS) or working standards (15.0, 10.0, 5.0, 2.5, 

1.5, and 0.0 mg Mn L-1) and QC (6.5 mg L-1). Prepare fresh weekly. In six 100-mL 

volumetric flasks add as follows: 

6.10.1 15.0 mg Mn L-1 = 1.5 mL PSSSMn

6.10.2 10.0 mg Mn L-1 = 1.0 mL PSSSMn

6.10.3 5.0 mg Mn L-1 = 0.5 mL PSSSMn

6.10.4 2.5 mg Mn L-1 = 0.25 mL PSSSMn

6.10.5 1.5 mg Mn L-1 = 0.15 mL PSSSMn

6.10.6 0.0 mg Mn L-1 = 0.0 mL PSSSMn (blank) 

6.10.7 6.5 mg Mn L-1 = 0.65 mL PSSSMn (QC) 

Fill to volume with RODI water and invert to mix thoroughly. After dissolution, transfer 

solution to a plastic bottle. 

6.11 Calibration standards for Al (Section 6.12): To each 100 mL volume of blank, 

calibration, and quality control (QC) standards, add 25 mL of the following matrix 

matching mixture. This mixture is made by combining 200 mL Na citrate extracting 

solution, 2.1 mL H2SO4, and then diluting to 250-mL volume with RODI water. Invert 

to mix thoroughly. (Note: Matrix of standards is prepared to match a 1:5 dilution of 

samples (same as with Mn). Also, H2SO4 substitutes for dithionite). 

6.12 Standard Al calibration solutions (SAlCS) or working standards (100.0, 80.0, 60.0, 

40.0, 20.0, 10.0, and 0.0 mg Al L-1) and QC (50.0 mg L-1). Prepare fresh weekly. In 

seven 100-mL volumetric flasks add as follows: 

6.12.1 100.0 mg Al L-1 = 10.0 mL PSSSAl

6.12.2 80.0 mg Al L-1 = 8.0 mL PSSSAl

6.12.3 60.0 mg Al L-1 = 6.0 mL PSSSAl

309
6.12.4 40.0 mg Al L-1 = 4.0 mL PSSSAl

6.12.5 20.0 mg Al L-1 = 2.0 mL PSSSAl

6.12.6 10.0 mg Al L-1 = 1.0 mL PSSSAl 

6.12.7 0.0 mg Al L-1 = 0.0 mL PSSSAl (blank) 

6.12.8 50.0 mg Al L-1 = 5.0 mL PSSSAl (QC) 

Fill to volume with RODI water and invert to mix thoroughly. After dissolution, transfer 

solution to a plastic bottle.

6.13 Acetylene gas, purity 99.6% 

6.14 Nitrous oxide, USP 

6.15 Compressed air with water and oil traps 

7. Procedure 

Extraction of Al, Fe, and Mn 

7.1 Weigh 0.75 g of <2-mm or fine-grind, air-dry soil sample to the nearest mg and place in an 

50-mL centrifuge tube. If sample is moist, weigh enough soil to achieve ≈ 0.75 g of air-dry soil. 

7.2 Add 0.4 g of sodium dithionite (use one calibrated scoop) and 25 mL of sodium citrate 

solution. 

7.3 Cap tubes and shake briefly by hand to dislodge soil from tube bottom. Place tubes in rack. 

7.4 Place rack in shaker and shake overnight (12 to 16 h) at 200 oscillations min-1 at room 

temperature (20°C ± 2°C). 

7.5 Remove tubes from shaker and manually shake tubes to dislodge any soil from cap. Allow 

samples to sit overnight. 

7.6 The following day, centrifuge at 4000 rpm for 15 min. The Fe, Mn, and Al are determined 

on the AA from a clear aliquot of solution. 

Dilution of Sample Extracts 

7.7 No ionization suppressant is required as the Na in the extractant is present in sufficient 

quantity. For a 1:50 dilution of samples for Fe analysis, use the H3PO4 diluting solution (see 

Section 6.5). The dilution of Fe results in a final solution concentration of 0.5% H3PO4. Dilute 

1 part CD sample extract with 49 parts of H3PO4 diluting solution (1:50 dilution). 

7.8 A 1:5 dilution in RODI water is used for Al and Mn. Dilute 1 part CD sample extract with 

4 parts RODI water. 

7.9 Dispense the diluted sample solutions into test tubes that have been placed in the holders of 

the sample changer. 

AAS Set-up and Operation 

7.10 Refer to the manufacturer’s manual for operation of the AAS. The following are only 

very general guidelines for instrument conditions for the various analytes. 

310
Analyte Conc. Wavelength Burner Head Slit Fuel/Oxidant 

 (mg L-1) (nm) (mm) 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Fe 25.0 248.8 10-cm parallel 0.2 3.0 C2H2/15.7 Air 

Mn 15.0 279.8 10-cm parallel 0.2 3.0 C2H2/15.7 Air 

Al 100.0 309.3 5-cm parallel 0.7 8.5 C2H2/15.7 N2O 

Typical read delay is 3 s, and integration time is 3 s but can vary depending on soil type. Three 

replicates are average for each sample. 

7.11 Use the computer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.12 The instrument readings are programmed to display analyte concentration in mg L-1

(ppm). 

AAS Calibration and Analysis

7.13 Each element is analyzed during separate runs on the AAS. Use the calibration reagent 

blank and calibration standards to calibrate the AAS. Calibrations are linear with calculated 

intercept. 

7.14 Use the QC after every 12th sample. It must pass within 15% to continue. If it fails, 

recalibrate and reread the QC. The QC is also read at the end of each run. 

7.15 If samples are outside the calibration range, a serial dilution is performed. A 1:5 dilution 

of the sample using the calibration blank, followed by the typical dilution (1:5 dilution with 

RODI water for Al and Mn, and 1:50 dilution with the H3PO4 diluting solution for Fe). 

Maintain matrix match between standards and diluted samples by performing this extra dilution 

with calibration blank. 

7.16 Record analyte readings to 0.01 unit. 

8. Calculations 

Convert analyte concentrations (mg L-1) to percent in soil as follows: 

Soil Fe, Al, Mn (%) = (A x B x C x R x 100)/ (E x 1000) 

where: 

A = Sample extract reading (mg L–1) 

B = Extract Volume (L) 

C = Dilution, required 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

E = Sample weight (g) 

100 = Conversion factor to 100-g basis 

1000 = mg g-1

9. Report

Report percent CD extractable Al, Fe, and Mn to the nearest 0.1 of a percent. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

311
11. References 

Wada, K. 1989. Allophane and imogolite. p. 1051-1087. In J.B. Dixon and S.B. Weed 

(eds.). Minerals in soil environment. 2nd ed. Soil Sci. Am. Book Series No. 1. ASA and 

SSSA, Madison, WI. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. 

Print. Office, Washington, DC. 

Selective Dissolutions (4G) 

Ammonium Oxalate Extraction (4G2) 

Automatic Extractor (4G2a) 

Inductively Coupled Plasma Atomic Emission Spectrophotometer (4G2a1) Radial Mode (4G2a1a) 

Aluminum, Iron, Manganese, Phosphorus, and Silicon (4G2a1a1-5) Air-Dry or Field-Moist, <2 mm (4G2a1a1-5a-b1) 

UV-Visible Spectrophotometer, Dual Beam (4G2a2) 

Transmittance (4G2a2a) 

Optical Density (4G2a2a1) 

Air-Dry or Field-Moist, <2 mm (4G2a2a1a-b1) 

1. Application 

Ammonium oxalate is used as a selective dissolution extractant for organically 

complexed Fe and Al, noncrystalline hydrous oxides of Fe and Al, allophane, and amorphous 

aluminosilicates (Wada, 1989). Ammonium oxalate is a poor extractant of imogolite and layer 

silicates and does not extract crystalline hydrous oxides of Fe and Al, opal, or crystalline 

silicate (Wada, 1989). A more reliable and accurate estimation of soil properties and a better 

understanding of soil exchange complex is provided when ammonium oxalate extraction is 

used in conjunction with other selective dissolution procedures, thermal techniques, and 

chemical tests. In soil taxonomy, ammonium oxalate extractable Fe and Al are criteria for 

andic soil properties (Soil Survey Staff, 1999). This extraction is also sometimes referred to as 

acid ammonium oxalate, acid oxalate, oxalate-oxalic acid, or oxalic acid-ammonium oxalate. 

2. Summary of Method 

A soil sample is extracted with a mechanical vacuum extractor (Holmgren et al., 1977) 

in a 0.2 M ammonium oxalate solution buffered at pH 3.0 under darkness. The ammonium 

oxalate extract is weighed. The ammonium oxalate extract is diluted with reverse osmosis 

deionized water. The analytes are measured by a inductively coupled plasma atomic emission 

spectrophotometer (ICP-AES). Data are automatically recorded by a computer and printer. 

The ammonium oxalate extractable Al, Fe, Mn, P, and Si are reported in procedures 4G2a1a1-

5, respectively. All these data are reported in percent except Mn and P, which are reported in 

mg kg-1. In procedure 4G2a2a1, the optical density of the extract is measured with a UV 

spectrophotometer at 430 nm. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

ICP analyses of these elements. These interferences vary in importance, depending upon the 

particular analyte chosen. 

The ammonium oxalate buffer extraction is sensitive to light, especially UV light. The 

exclusion of light reduces the dissolution effect of crystalline oxides and clay minerals. If the 

sample contains large amounts of amorphous material (>2% Al), an alternate method should be 

used, i.e., shaking with 0.275 M ammonium oxalate, pH 3.25, 1:100 soil:extractant. 

312
4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Follow standard laboratory practices when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Follow the manufacturer's safety 

precautions when using the UV spectrophotometer and ICP. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Mechanical vacuum extractor, 24 place, SAMPLETEX, MAVCO Industries, 

Lincoln, NE 

5.3 Tubes, 60-mL, polypropylene, for extraction (0.45-μm filter), reservoir, and tared 

extraction tubes 

5.4 Rubber tubing, 3.2 ID x 1.6 OD x 6.4 mm, (1/8 ID x 1/16 OD x 1 in) for connecting 

syringe barrels 

5.5 Dispenser, 30-mL 

5.6 Pipettes, electronic digital, 10000 and 1000 μL, with tips 10000 and 1000 μL 

5.7 Containers, polyethylene 

5.8 Inductively coupled plasma atomic emission spectrophotometer (ICP-AES), dual-view, 

with high-solids nebulizer, alumina or quartz injector, Optima 4300 DV, Perkin-Elmer 

Corp., Norwalk, CT. 

5.9 Automsampler, AS-93, Perkin-Elmer Corp., Norwalk, CT 

5.10 Computer, with WinLab32TM software, and printer 

5.11 Single-stage regulator, high-purity, high-flow, argon 

5.12 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer, Fisher 

Scientific 

5.13 Vortexer, mini, MV1, VWR Scientific Products 

5.14 Spectrophotometer, UV-Visible, Varian, Cary 50 Conc, Varian Australia Pty Ltd. 

5.15 Computer with Cary WinUV software, Varian Australia Pty Ltd., and printer 

5.16 Cuvettes, plastic, 4.5-mL, 1-cm light path, Daigger Scientific 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Ammonium oxalate buffer solution, 0.2 M, pH 3.0. Solution A (base): Dissolve 284 g of 

(NH4)2C2O4·2H2O in 10 L of DDI water. Solution B (acid): Dissolve 252 g of 

H2C2O4·H2O in 10 L of DDI water. Mix 4 parts solution A with 3 parts solution B. 

Adjust ammonium oxalate solution pH by adding either acid or base solution. Store in a 

polypropylene bottle. 

6.3 Borax pH buffers, pH 4.00, 7.00, and 9.18 for electrode calibration, Beckman, Fullerton, 

CA. 

6.4 Primary Fe standard, 1000 mg L-1. Certified Reference Solution, Fisher Chemical 

Scientific Co., Fairlawn, N.J. 

6.5 Primary Al standard, 1000 mg L-1. Certified Reference Solution, Fisher Chemical 

Scientific Co., Fairlawn, N.J. 

6.6 Primary Si standard, 1000 mg L-1. Certified Reference Solution, Fisher Chemical 

Scientific Co., Fairlawn, N.J. 

6.7 Primary Mn standard, 1000 mg L-1. Certified Reference Solution, Fisher Chemical 

Scientific Co., Fairlawn, N.J. 

6.8 Primary P standard, 1000 mg L-1. Certified Reference Solution, Fisher Chemical 

Scientific Co., Fairlawn, N.J. 

6.9 High mixed calibration standard. Mix 60 mL of each primary standard (Si, Fe, and Al) 

with 10 mL of primary Mn standard and 20 mL of primary P standard in 1 L volumetric 

flask. Add 100 mL of 0.2 M ammonium oxalate solution and make to 1-L volume with 

RODI water. The elements are added in the order (Si, Fe, Al, Mn, P) to avoid element 

precipitation. Resulting solution contains 60 mg L-1 each of Si, Fe, and Al, 10 mg L-1

313
Mn, and 20 mg L-1 P. Invert to mix thoroughly. Store in a polyethylene bottle. Make 

fresh weekly. Store in a refrigerator. 

6.10 Medium mixed calibration standard. Mix 30 mL of each primary standard (Si, Fe, and 

Al) with 5 mL of primary Mn standard and 10 mL of primary P standard in 1 L 

volumetric flask. Add 100 mL of 0.2 M ammonium oxalate solution and make to 1-L 

volume with RODI water. The elements are added in the order (Si, Fe, Al, Mn, P) to 

avoid element precipitation. Resulting solution contains 30 mg L-1 each of Si, Fe, and Al, 

5 mg L-1 Mn, and 10 mg L-1 P. Invert to mix thoroughly. Store in a polyethylene bottle. 

Make fresh weekly. Store in a refrigerator. 

6.11 Low mixed calibration standard. Mix 10 mL of each primary standard (Si, Fe, and Al) 

with 2 mL of primary Mn standard, and 3 mL primary P standard in 1 L volumetric flask. 

Add 100 mL of 0.2 M ammonium oxalate solution and make to 1-L volume with RODI 

water. The elements are added in the order (Si, Fe, Al, Mn, P) to avoid element 

precipitation. Resulting solution contains 10 mg L-1 each of Si, Fe, and Al, 2 mg L-1 Mn, 

and 3 mg L-1 P. Invert to mix thoroughly. Store in a polyethylene bottle. Make fresh 

weekly. Store in a refrigerator. 

6.12 Low Si calibration standard. Mix 5 mL of Si primary standard in 1-L volumetric flask. 

Add 100 mL of 0.2 M ammonium oxalate solution and make to 1-L volume with RODI 

water. Resulting solution contains 5 mg L-1 Si. Invert to mix thoroughly. Store in 

polyethylene bottle. Make fresh weekly. Store in a refrigerator. 

6.13 Very Low Si calibration standard. Mix 2 mL of Si primary standard in 1-L volumetric 

flask. Add 100 mL of 0.2 M ammonium oxalate solution and make to 1-L volume with 

RODI water. Resulting solution contains 2 mg L-1 Si. Invert to mix thoroughly. Store in 

polyethylene bottle. Make fresh weekly. Store in a refrigerator. 

6.14 Calibration reagent blank solution. Add 100 mL of 0.2 M ammonium oxalate solution 

and make to 1-L volume with RODI water. Store in polyethylene bottle. Make fresh 

weekly. Store in a refrigerator. 

6.15 Argon gas, purity 99.9% 

6.16 Nitrogen, purity 99.9% 

7. Procedure 

Extraction of Fe, Mn, Al, Si, and P 

7.1 Weigh 0.5 g of <2-mm, air-dry or fine-grind soil the nearest mg and place in sample tube. 

If sample is moist, weigh enough soil to achieve ≈ 0.5 g. Prepare two reagent blanks (no sample 

in tube) per set of 48 samples. 

7.2 Place labeled ET on extractor and connect to corresponding tared extraction tube 

(TETOxalate) with rubber tubing. 

7.3 Use a dispenser to add 15.00 mL of ammonium oxalate buffer to the ET. Make sure that 

the sample is thoroughly wetted. During the addition, wash sides of the tube and wet the 

sample. Shaking, swirling, or stirring may be required to wet organic samples. Allow sample 

to stand for at least 30 min. Cover samples with black plastic bag to exclude light. 

7.4 Secure reservoir tube (RT) to top of ET tube. Set extractor for 30-min extraction rate and 

extract until the ammonium oxalate buffer solution is at a 0.5 to 1.0-cm height above sample. 

Turn off extractor. 

7.5 Add 35 mL of ammonium oxalate buffer to the RT. 

7.6 Cover the extractor with a black plastic bag to exclude light. Adjust the extraction rate for a 

12-h extraction. 

314
7.7 After the extraction, shut off the extractor. Carefully remove TETOxalate. Leave the rubber 

tubing on the ET. 

7.8 Weigh each syringe containing ammonium oxalate extract to the nearest mg. 

7.9 Mix extract in each TETOxalate by manually shaking. Fill a disposable tube with extract 

solution. This solution is reserved for determinations of Fe, Mn, Al, Si, and P. If optical 

density is to be measured, fill a disposable cuvette with extract solution. Discard excess 

solution properly. If extracts are not to be determined immediately after collection, then store 

samples at 4°C. 

Determination of Optical Density of Extract

7.10 Place 4 mL of ammonium oxalate extract in disposable cuvette. 

7.11 Place 4 mL of ammonium oxalate reagent blank in disposable cuvette. 

7.12 On the spectrophotometer, select a 430-nm wavelength. Select normal slit width and 

height. Refer to manufacturer’s manual for operation of the spectrophotometer. 

7.13 Use the ammonium oxalate extract reagent blank to zero spectrophotometer. 

7.14 Record optical density of ammonium oxalate extract to nearest 0.000 unit. 

Dilution of Sample Extracts and Standards

7.15 Dilute ammonium oxalate extracts (1:10) with RODI water. Add 1 part ammonium 

oxalate sample extract with 9 parts dilution solution. Pipet 0.7 mL of extract and 6.3 mL RODI 

water. Vortex. Calibration reagent blanks and calibration standards are not diluted. 

7.16 Dispense the diluted solutions into test tubes that have been placed in the sample holder of 

the sample changer. 

ICP-AES Set-up and Operation

7.17 Refer to the manufacturer's manual for operation of the ICP-AES. The following 

parameters are only very general guidelines for instrument conditions for the various analytes. 

Parameter Value

Plasma 

 Source Equilibration Delay 20 sec 

 Plasma Aerosol Type Wet 

 Nebulizer Start-up Conditions Gradual 

 Plasma 15 L min-1

 Auxiliary 0.5 L min-1

 Nebulizer 0.85 L min-1

 Power 1450 Watts 

 View Dist 15.0 

 Plasma View Radial 

Peristaltic Pump 

 Sample Flow Rate 2.00 L min-1

 Sample Flush Time 35 sec 

 

315
Wash Parameters Between samples 

Wash Rate 2.00 mL min-1

Wash Time 30 sec 

Background Correction 2 point (all elements) 

Read Delay 2 sec 

Replicates 2 

Nebulizer pressure depends on the type of nebulizer that is being used, i.e., low flow nebulizer 

requires a higher nebulizer pressure whereas a higher flow nebulizer requires a lower nebulizer 

pressure. To check for correct nebulizer pressure, aspirate with 1000.0 mg L-1 yttrium. Adjust 

pressure to correct yttrium bullet. 

7.18 Analyte data are reported at the following wavelengths. 

 Element Wavelength 

 ----------- nm --------- 

 Fe 259.94 

 Al 308.22 

 Si 251.61 

 Mn 257.61 

 P 213.61 

7.19 Use the computer and printer to set instrument parameters and to collect and record 

instrument readings. The instrument readings are programmed in mg L-1. 

ICP-AES Calibration and Analysis 

7.20 Use a multipoint calibration for ICP-AES analysis of ammonium oxalate extracts. The 

ICP calibrates the blank first, low standard, medium standard, followed by the high standard. 

Prepare a quality control (QC) standard with analyte concentration between the high and low 

calibration standards. The ICP reads the QC after the high standard. If the QC falls within the 

range set by operator (±10%), the instrument proceeds to analyze the unknowns. If the QC is 

outside the range, the instrument restandardizes. The QC is analyzed approximately every 12 

samples. 

7.21 If sample exceeds calibration standard, dilute 1:5 (1 mL of sample extract with 4 mL 0.02 

M ammonium oxalate extracting solution), followed by a 1:10 (1 mL of 1:5 solution with 9 mL 

RODI water). This makes for a 1:50 dilution. 

7.22 Record analyte readings to the nearest 0.01 unit. 

8. Calculations (Al, Fe, Si)

The instrument readings are the analyte concentration (mg L-1 Fe, Mn, Al, Si, and P). Use these 

values to calculate the analyte concentration in percent in the soil for Fe, Al, and Si and mg kg-1

for Mn and P as follows: 

8.1 Soil Fe, Al, Si (%) = [A x [(B1 – B2)/B3] x C1 x C2 x R x 100]/(E x 1000 x 1000) 

where: 

A = Sample extract reading (mg L-1) 

316
B1 = Weight of syringe + extract (g) 

B2 = Tare weight of syringe (g) 

B3 = Density of 0.2 M ammonium oxalate solution at 20° C (1.007 g mL-1) 

C1 = Dilution, required 

C2 = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

E = Sample weight (g) 

100 = Conversion factor to 100-g basis 

1000 = Factor in denominator (mL L-1) 

1000 = Factor in denominator (mg g-1) 

8.2 Soil Mn, P (mg kg-1) = [ A x [(B1 – B2)/B3] x C1 x C2 x R x 1000]/(E x 1000) 

where: 

A = Sample extract reading (mg L-1) 

B1 = Weight of syringe + extract (g) 

B2 = Tare weight of syringe (g) 

B3 = Density of 0.2 M ammonium oxalate solution at 20° C (1.007 g mL-1) 

C1 = Dilution, required 

C2 = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor in numerator to kg-basis 

1000 = Factor in denominator (mL L-1) 

E = Sample weight (g) 

9. Report 

Report the percent ammonium oxalate extractable Al, Fe, and Si to the nearest 0.01%. 

Report the concentration of ammonium oxalate extractable Mn and P to the nearest mg kg-1

soil. Report the optical density of the ammonium oxalate extract to the nearest 0.01 unit. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

10. References 

Aguilera, N.H., and M.L. Jackson. 1953. Iron oxide removal from soils and clays. Soil Sci. 

Soc. Am. Proc. 17:359-364. 

Holmgren, G.G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically controlled 

variable rate leaching device. Soil Sci. Am. J. 41:1207-1208. 

Jackson, M.L. 1979. Soil chemical analysis-advance course. 2nd ed., 11th Printing. 

Published by author, Madison, WI. 

Mehra, O.P., and M.L. Jackson. 1960. Iron oxide removal from soils and clays by a 

dithionite-citrate system buffered with sodium bicarbonate. Clays Clay Miner. 7:317-

327. 

Soil Survey Staff. 1999. Soil taxonomy. A basic system of soil classification for making 

and interpreting soil surveys. 2nd ed. USDA-NRCS. Govt. Print. Office, Washington 

DC. 

Wada, K. 1989. Allophane and imogolite. p. 1051-1087. In J.B. Dixon and S.B. Weed 

(eds.). Minerals in soil environment. 2nd ed. Soil Sci. Soc. Am. Book Series No. 1. 

ASA and SSSA, Madison. 

317
Selective Dissolutions (4G) 

Ammonium Oxalate (4G2) 

Ratios and Estimates Related to Ammonium Oxalate Extraction (4G2b) Al + 1⁄2 Fe (4G2b1) 

The ratio using ammonium oxalate extractable Al plus 1⁄2 Fe determined in procedure 

4G2a1a1-5 are used as taxonomic criterion for andic soil properties. Refer to Soil Survey Staff 

(1995, 1999) for more detailed information on the application of this ratio. 

References 

Soil Survey Staff. 1995. Soil survey laboratory information manual. Version No. 1.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, DC. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys. USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. Print. Office, 

Washington, DC. 

Selective Dissolutions (4G) 

Sodium Pyrophosphate Extraction (4G3) 

Atomic Absorption Spectrophotometry (4G3a) 

Aluminum, Iron, and Manganese (4G3a1-3) 

Air-Dry or Field-Moist, <2 mm (4G3a1-3a-b1) 

Acid Digestion (4G3b) 

K2Cr2O7 + (H2SO4 + H3PO4 Digestion)(4G3b1) CO2 Evolution, Gravimetric (4G3b1a) Organic Carbon (4G3b1a1) 

Air-Dry or Field-Moist, <2 mm (4G3b1a1a-b1) 

1. Application 

Sodium pyrophosphate (0.1 M Na4P2O7) is used as a selective dissolution extractant for 

organically complexed Fe and Al (Wada, 1989). The Na4P2O7 solution is a poor extractant for 

allophane, imogolite, amorphous aluminosilicates, and noncrystalline hydrous oxides of Fe and 

Al. The Na4P2O7 solution does not extract opal, crystalline silicates, layer silicates, and 

crystalline hydrous oxides of Fe and Al (Wada, 1989). Sodium pyrophosphate extractable 

organic C, Fe, and Al were former criteria for spodic placement in soil taxonomy (Soil Survey 

Staff, 1975). 

2. Summary of Method 

The soil sample is mixed with 0.1 M Na4P2O7 and shaken overnight. The solution is 

then allowed to settle overnight before centrifuging and filtering to obtain a clear extract. The 

analytes (Al, Fe, Mn) are measured by an atomic absorption spectrophotometer (AAS). The 

data are automatically recorded by a computer and printer. The AAS converts absorption to 

analyte concentration. Percent sodium pyrophosphate extractable Al, Fe, and Mn are reported 

in procedures 4G3a1-3, respectively. The organic C in the sodium pyrophosphate extract is 

wet oxidized in a fume hood and gravimetrically measured in procedure 4G3b1a1. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

AA analyses of these elements. These interferences vary in importance, depending upon the 

particular analyte selected. 

There are several problems with this procedure, especially the peptization and 

dispersion of microcrystalline iron oxide by pyrophosphate (Jeanroy and Guilet, 1981). The 

quantity of Fe extracted with pyrophosphate decreases with increasing centrifugation 

(McKeague and Schuppli, 1982); therefore uniform high-speed centrifugation or micropore 

filtration treatments are required (Schuppli et al., 1983; Loveland and Digby, 1984). Sodium 

318
pyrophosphate extraction works best at pH 10 (Loeppert and Inskeep, 1996). The concentration 

of Na4P2O7 solution must be close to 0.1 M. Variable amounts of Fe, Al, Mn, and organic C 

may be extracted by varying the pyrophosphate concentration. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Thoroughly wash hands after handling these metal salts. 

Follow standard laboratory procedures when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene is highly flammable. Avoid open 

flames and sparks. Standard laboratory equipment includes fire blankets and extinguishers for 

use when necessary. Follow the manufacturer's safety precautions when using the atomic 

absorption spectrophotometer (AAS). 

5. Equipment 

5.1 Electronic balance, ±0.1-mg sensitivity 

5.2 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Atomic absorption spectrophotometer (AAS), double-beam optical system, AAnalyst 

300, Perkin-Elmer Corp., Norwalk, CT 

5.4 Autosampler, AS-90, Perkin-Elmer Corp., Norwalk, CT 

5.5 Peristaltic pump 

5.6 Single-stage regulators, acetylene and nitrous oxide 

5.7 Centrifuge, Centra, GP-8, Thermo IEC, Needham Heights, MA 

5.8 Digital diluter/dispenser, with syringes 10000 and 1000 μL, gas tight, MicroLab 500, 

Hamilton Co., Reno, NV 

5.9 Dispenser, 40 mL 

5.10 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer 

5.11 Containers, polypropylene 

5.12 Volumetrics, Class A, 100, 250, and 1000-mL 

5.13 Centrifuge tubes, 50-mL 

5.14 Funnel, 60° angle, long stem, 50-mm diameter 

5.15 Filter paper, Whatman 42, 150 mm 

5.16 Absorption bulb, Nesbitt with stopper 

5.17 Absorption bulb, Stetser-Norton 

5.18 Flask, boiling, round bottom, short neck 

5.19 Condenser, Allihn 

5.20 Funnel, separatory, cylindrical, open top, with stopcock 

5.21 Tube, drying, Schwartz 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water 

6.2 Hydrochloric acid (HCl), concentrated, 12 N

6.3 Sodium pyrophosphate solution, 0.1 M. Dissolve 446.05 g of Na4P2O7·10H2O in 10 L of 

RODI water. pH solution to 10.0 with either HCl or NaOH. 

6.4 Primary Fe standard, 1000 mg L-1. Certified Reference Solution, Fisher Chemical 

Scientific Co., Fairlawn, N.J. 

6.5 Primary Al standard, 1000 mg L-1. Certified Reference Solution, Fisher Chemical 

Scientific Co., Fairlawn, N.J. 

6.6 Primary Mn standard, 1000 mg L-1. Certified Reference Solution, Fisher Chemical 

Scientific Co., Fairlawn, N.J. 

6.7 Mixed Calibration Standards (MCS), Fe, Al, Mn. To six 250-mL volumetrics, add the 

following amounts of Primary Standards (1000 mg L-1) as follows. The elements are 

added in the order (Fe, Al, Mn) to avoid element precipitation. 

319
6.7.1 25, 100, and 15 mg L-1 Fe, Al, and Mn = 6.25, 25.00, and 3.75 mL Fe, Al, and Mn, 

respectively. 

6.7.2 20, 80, and 10 mg L-1 Fe, Al, and Mn = 5.00, 20.00, and 2.50 mL Fe, Al, and Mn, 

respectively. 

6.7.3 10, 40, and 5 mg L-1 Fe, Al, and Mn = 2.50, 10.00, and 1.25 mL Fe, Al, and Mn, 

respectively. 

6.7.4 5, 20, and 2.50 mg L-1 Fe, Al, and Mn = 1.25, 5.00, and 0.625 mL Fe, Al, and Mn, 

respectively. 

6.7.5 1, 10, and 1.5 mg L-1 Fe, Al, and Mn = 0.25, 2.50, 0.375 mL Fe, Al, and Mn, 

respectively. 

6.7.6 0, 0, and 0 mg L-1 Fe, Al, and Mn = 0.0, 0.0, and 0.0 mL Fe, Al, and Mn, respectively. 

Add 50 mL of 0.1 M Na4P2O7 to each MCS and make to volume with RODI water. Final 

concentration of MCS is 0.02 M Na4P2O7. Quality control (QC) is the MCS with 10, 40, and 5 

mg L-1 Fe, Al, and Mn, respectively. 

 

6.8 Potassium dichromate (K2Cr2O7) reagent. 

6.9 Potassium iodide solution. Dissolve 100 g of KI in 100 mL of RODI water. 

6.10 Silver sulfate, saturate aqueous solution 

6.11 Digestion acid mixture: Mix 600 mL of concentrated H2SO4 and 400 mL of 85% H3PO4

6.12 Indicarb or Mikohibite 

6.13 Soda lime 

6.14 Zinc granules, 300 mesh 

6.15 Anhydrone 

6.16 Acetylene gas, purity 99.6% 

6.17 Nitrous oxide gas, compressed 

6.18 Compressed air with water and oil traps 

7. Procedure 

Extraction of Al, Fe, and Mn

7.1 Weigh 0.5 g <2-mm or fine-grind, air-dry soil to the nearest mg sample and place in a 50-

mL centrifuge tube. If sample is moist, weigh enough soil to achieve ≈ 0.5 g of air-dry soil. 

7.2 Add 30-mL of 0.1 M Na4P2O7, pH 10.0 solution to centrifuge tube. 

7.3 Cap tube and shake briefly by hand to dislodge soil from tube bottom. Place tube in rack. 

7.4 Place rack in shaker and shake overnight (12 to 16 h) at 200 oscillations min-1 at room 

temperature (20°C ± 2°C). 

7.5 Remove tubes from shaker and manually shake tubes to dislodge any soil from cap. Allow 

samples to sit overnight. 

7.6 Next day centrifuge sample at 4000 rpm for 15 min. The Fe, Mn, and Al are determined 

from a clear aliquot of solution. Filter if necessary. 

320
Dilution of Sample Extracts and Standards

7.7 No ionization suppressant is required as the Na in the extractant is present in sufficient 

quantity. Dilute samples 1:5 with RODI water. Samples have a final concentration of 0.02 M

Na4P2O7. 

7.8 Dispense the MCS and diluted sample solutions into test tubes that have been placed in the 

sample holder of the sample changer. 

AAS Set-up and Operation 

7.9 The following are only very general guidelines for instrument conditions for the various 

analytes. 

Analyte Conc. Wavelength Burner Head Slit Fuel/Oxidant 

 (mg L-1) (nm) (mm) 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Fe 25.0 248.3 10-cm parallel 0.2 3.0 C2H2/15.2 Air 

Mn 15.0 279.8 10-cm parallel 0.2 3.0 C2H2/15.7 Air 

Al 100.0 309.3 5-cm parallel 0.7 7.0 C2H2/3.5 N2O 

Typical read delay is 3 s and integration time is 3 s but can vary depending on soil type. Three 

replicates are averaged for each sample. 

7.10 Use the computer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.11 If sample exceeds calibration standard, dilute the sample 1:10 with 0.1 M Na4P2O7 and 

then 1:5 with RODI water. 

AAS Calibration

7.12 Each element is analyzed during separate runs on the AAS. Use the calibration reagent 

blank and calibration standards to calibrate the AAS. Calibrations are linear with calculated 

intercept. 

7.13 Use the QC after every 12th sample. It must pass within 15% to continue. If it fails, 

recalibrate and reread the QC. The QC is also read at the end of each run. 

7.14 If samples are outside the calibration range, dilute 

7.15 Record analyte readings to 0.01 unit. 

Organic C Determination

7.16 Pipet 100 mL of the extract into a 100-ml flask. 

7.17 Evaporate the extract to near dryness using a 50°C water bath and a gentle stream of clean, 

filtered air. 

7.18 Construct the wet combustion apparatus. Refer to Fig. 1 for the apparatus for gravimetric 

organic C determination. 

7.19 Add 1 to 2 g of potassium dichromate. 

7.20 Wash the neck of the flask with 3 mL of RODI H2O and connect to condenser. 

321
7.21 Attach a weighed Nesbitt bulb to the system and open the valve at the top. 

7.22 Pour 25 mL of digestion-acid mixture into the funnel. Add the mixture to the flask and 

immediately close the stopcock. Use the digestion-acid mixture to lubricate the stopcock. 

7.23 The tip of the air-delivery tube should be ≈ 0.5 cm below the digestion-acid mixture. 

Adjust the flow of the "carrier stream" to maintain 1 to 2 bubble s-1 rate throughout the 

digestion. Apply suction on the outlet side of the Nesbitt bulb. Gentle air pressure and needle 

valve on the air-pressure line aids flow-adjustment. 

7.24 With a gas flame or a variable power-heating mantle, gently heat the flask until the 

mixture boils (≈ 3 to 4 min). Continue a gentle boiling for 10 min. Heating is too rapid if 

white fumes of SO2 are visible above the second bulb of the reflux condenser. 

7.25 Remove the heat and allow to aerate for 10 additional min at a rate of 6 to 8 bubbles s-1. 

7.26 Close the stopcock on the Nesbitt bulb, disconnect the bulb from the system, and weigh to 

the nearest 0.0001g. 

8. Calculations 

8.1 Soil Fe, Al, Mn (%) = (A x B x C1 x C2 x R x 100)/(E x 1000 x 1000) 

where: 

A = Analyte concentration reading (mg L-1) 

B = Extract volume (L) 

C1 = Dilution, required 

C2 = Dilution, if performed 

322
R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 3D2) 

E = Sample weight (g) 

100 = Conversion factor to 100-g basis 

1000 = Factor in denominator (mg g-1) 

1000 = Factor in denominator (mL L-1) 

8.2 Organic C (%) = [(WtF - WtI) x 27.3 x Volume x R]/(Sample Weight (g) x 236.6) 

where: 

WtF = Nesbitt bulb weight after digestion (g) 

WtI = Nesbitt bulb weight before digestion (g) 

Volume = Extract volume digested (mL) 

R = Air-dry/oven-dry ratio (procedure 3D1) or field-moist/oven-dry ratio (procedure 

3D2) 

27.3 = Conversion factor 

236.6 = Total extract volume (mL) 

9. Report

Report sodium pyrophosphate extractable Fe, Mn, and Al to the nearest 0.1 of a percent. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Jeanroy, E., and B. Guillet. 1981. The occurrence of suspended ferruginous particles in 

pyrophosphate extracts of some soil horizons. Geoderma 26:95-105. 

Loeppert, R. H., and W.P. Inskeep. 1996. Iron. p. 639-664. In D.L. Sparks (ed.) Methods 

of Soil Analysis. Part 3 – Chemical methods. Soil Sci. Am. Book Series No. 5. ASA 

and SSSA, Madison, WI. 

Loveland, P.J., and P. Digby. 1984. The extraction of Fe and Al by 0.1M pyrophosphate 

solutions: A comparison of some techniques. J. Soil Sci. 35:243-250. 

McKeague, J.A., and P.A. Schuppli. 1982. Changes in concentration of iron and aluminum 

in pyrophosphate extracts of soil and composition of sediment resulting from 

ultracentrifugation in relation to spodic horizon criteria. Soil Sci. 134:265-270. 

Schuppli, P.A. P.A., G.J. Ross, and J.A. McKeague. 1983. The effective removal of 

suspended materials from pyrophosphate extracts of soils from tropical and temperate 

regions. Soil Sci. Soc. Am. J. 47:1026-1032. 

Soil Survey Staff. 1975. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. USDA-SCS Agric. Handb. 436. U.S. Govt. Print. Office, 

Washington, DC. 

Wada, K. 1989. Allophane and imogolite. p. 1051-1087. In J.B. Dixon and S.B. Weed 

(eds.). Minerals in soil environment. 2nd ed. Soil Sci. Am. Book Series No. 1. ASA and 

SSSA, Madison, WI. 

323
Total Analysis (4H) 

Acid Digestion (4H1) 

HNO3 + HCl Digestion (4H1a) Microwave (4H1a1) 

Inductively Coupled Plasma Atomic Emission Spectrophotometer (4H1a1a) Axial Mode (4H1a1a1) 

Ultrasonic Nebulizer (4H1a1a1a) 

Silver, Arsenic, Barium, Beryllium, Cadmium, Cobalt, Chromium, Copper, Manganese, Molybdenum, Nickel, Phosphorus, Lead, Antimony, Tin, Strontium, Thallium, Vanadium, Tungsten, and Zinc (4H1a1a1a1-20) Air-Dry, <2 mm (4H1a1a1a1-20a1) 

1. Application 

The term of trace elements is widely applied to a variety of elements that are generally 

present in plants, soils, and water in low concentrations or what is termed background levels. 

Knowledge of these levels is important in understanding the consequences of increasing levels 

of trace elements in ecosystems (Tiller, 1989; Holmgren et al., 1992). These elements may 

become elevated in concentration due to natural (e.g., magmatic activity, mineral weathering, 

translocation through the soil or landscape) or through human-induced activities (e.g., 

pesticides, mining, smelting, manufacturing). The relative reactivity or bioavailability of these 

elements in soils is governed by a variety of chemical factors such as pH, redox potential, 

organic concentrations, and oxides (Pierzynski and Schwab, 1993; Gambrell, 1994; Keller and 

Vedy, 1994; Burt et al., 2002). Uses of elemental data in soil survey applications are broad and 

diverse, ranging from understanding natural (Wilcke and Amelung, 1996; Jersak et al., 1997) to 

human-induced distributions (Wilcke et al., 1998). Knowledge of the elemental amounts and 

distribution in soils and their relationships with other soil properties can enhance the 

understanding of the fate and transport of anthropogenic elements, thereby expanding the utility 

and application of soil survey knowledge in areas of environmental concern such as urban, 

mine spoil reclamation, smelter emissions, and agricultural waste applications (Burt et al., 

2003). 

2. Summary of Method 

The approach of this digestion methodology is to maximize the extractable 

concentration of elements in digested soils while minimizing the matrix interferences such as 

found in digestion procedures that use HF acid. This method (4H1a1) follows EPA Method 

3051A. A 500-mg <2-mm soil separate which has been air-dried and ground to < 200 mesh (75 

μm) is weighed into a 100-ml Teflon (PFA) sample digestion vessel. To the vessel, 9.0 mL 

HNO3 and 3.0 mL HCl are added. The vessel is inserted into a protection shield and covered, 

and placed into a rotor with temperature control. Following microwave digestion, the rotor and 

samples are cooled, and digestate quantitatively transferred into a 50-ml glass volumetric high 

purity reverse osmosis deionized water. The volumetrics are allowed to stand overnight, filled 

to volume, and samples transferred into appropriate acid-washed polypropylene containers for 

analysis. The concentration of Ag, As, Ba, Be, Cd, Co, Cr, Cu, Mn, Mo, Ni, P, Pb, Sb, Sn, Sr, 

Tl, V, W, and Zn are determined using an inductively coupled plasma atomic emission 

spectrophotometer (ICP-AES) in axial mode by procedures 4H1a1a1a1-20, respectively. 

Mercury is analyzed by a cold-vapor atomic absorption spectrophotometer (CVASS) 

(4H1a1c1), and As and Se are determined by flow through hydride-generation and atomic 

absorption spectrophotometer (HGAAS) (4H1a1b1a1-2), respectively. 

3. Interferences 

Organic constituents may contain metals and are difficult to digest if present in high 

concentrations. Certain elements are subject to volatile losses during digestion and transfer. 

Certain soil minerals (e.g., quartz, feldspars) are not soluble in HNO3 + HCl. 

324
Spectral and matrix interferences exist. Interferences are corrected or minimized by 

using both an internal standard and inter-elemental correction factors. Also, careful selection 

of specific wavelengths for data reporting is important. Background corrections are made by 

ICP software. Samples and standards are matrix-matched to help reduce interferences. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated acids to the fume hood. Wash hands thoroughly after 

handling reagents. Filling the digestion vessel to greater than 25 percent of the free volume or 

adding organic reagents or oxidizing agents to the cup may result in explosion of the digestion 

microwave system. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Pipet(s) capable of delivering 3 and 9 mL, Omnifit Corp. manufacturers variable volume, 

(10-ml maximum) pipettes suitable for HNO3 and HCl delivery from 2.5 L bottles 

5.3 Volumetric flasks, class A glass, 50 mL 

5.4 Polypropylene bottles, 60 mL, with cap 

5.5 Electronic balance, (±0.1 mg sensitivity) 

5.6 Microwave oven, CEM Mars 5, 14 position-HP500 Plus vessel and rotor (vessels 

composed of PFA, sleeves composed of advanced composite) 

5.7 Volumetrics, 500, 250, and 50-mL class A glass 

5.8 Containers, 500-mL, polypropylene, with screw caps 

5.9 Pipettes, electronic digital, 250 μL and 10 mL, Rainin Instrument Co., Woburn, MA 

5.10 Inductively coupled plasma atomic emission spectrophotometer (ICP-AES), Perkin-Elmer 

Optima 3300 Dual View (DV), Perkin-Elmer Corp., Norwalk, CT 

5.11 RF generator, floor mounted power unit, 45 MHz free running, Perkin-Elmer Corp., 

Norwalk, CT. 

5.12 Computer, with WinLab software ver. 4.1, Perkin-Elmer Corp., Norwalk, CT, and printer 

5.13 Recirculating chiller, Neslab, CFT Series 

5.14 Compressed gasses, argon (minimum purity = 99.996%) and nitrogen (minimum purity = 

99.999%) 

5.15 Autosampler, AS-90, Perkin-Elmer Corp., Norwalk, CT. 

5.16 Quartz torch, Part No. N069-1662; alumina injector (2.0 mm id), Part No. N069-5362 

5.17 Ultrasonic nebulizer, Model U-5000AT+ , CETAC Corp., Omaha, NE 

5.18 Peristaltic pump (for automatic injection of internal standard) 

6. Reagents 

6.1 

6.2 

6.3 

6.4 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.5 Concentrated hydrochloric acid (HCl), 12 N, trace pure grade 

6.6 Concentrated nitric acid (HNO3), 16 N, trace pure grade 

6.7 Primary standards: 1000 mg L-1, from High Purity Standards, Charleston, SC. Single 

elemental standards are manufactured in dilute HNO3, HNO3 + HF, or H2O 

325
7. Procedure 

Microwave Acid Digestion 

7.1 About 500 mg of fine-earth (<2-mm) or a specific particle size separate ground to <200-

mesh (75 μm) is weighed to the nearest 0.1 mg in a 100-mL digestion vessel. 

7.2 Note: If sample is principally composed of organic materials (organic C > 15%), perform a 

preliminary digestion in the muffle furnace in an digestion crucible: 250°C for 15 min, 450°C 

for 15 min, followed by 550°C for 1 h. 

7.3 Pipet 9.0 mL HNO3 and 3.0 mL HCl into the sample and allow to completely wet. Add 

acids in the fume hood. Allow acids to react and vent in uncovered vessels for about 30 min. 

7.4 Place covered vessels in protective sleeve, cover and place into rotor. 

7.5 Place digestion rotor in the microwave oven and insert the temperature probe into the 

reference vessel. Attach the probe cable into the fitting in the top of the microwave. Connect 

the pressure monitor to the vessel. 

7.6 Microwave settings are as follows: 

1200 watts at 100% power for 5.5 min until 175°C 

Hold at 175°C for 4.5 min 

Cool for 5 min 

7.7 After cooling, disconnect temperature probe and pressure sensor from microwave. 

7.8 Remove rotor from oven, and place in fume hood. 

7.9 Open each vessel carefully and then quantitatively transfer contents of vessel to a 50-mL 

volumetric flask with RODI water.

7.10 Cap flask and mix well by inverting. Allow to stand overnight. Finish filling to volume 

with RODI water. 

7.11 Decant contents into a labeled 60-mL polypropylene container. 

7.12 Prepare working standards of a blank, reference soil sample from the SSL repository, 

NIST or other standard reference material, and blank by the same digestion method. Run two 

of these standards or blank with each set of 14 samples. 

ICP-AES Calibration Standards, Set-Up, and Operation 

7.13 A primary mixed calibration standard (PMCS) is prepared from the respective primary 

elemental standards (1000 mg L-1) to a 500-mL final volume. From this PMCS, three working 

calibration standards (WCS) are prepared. In addition, a single element standard for Tl (STl1) 

is prepared separately from a 1000 μg L-1 stock standard to a 50-mL final volume. Also, prior 

to diluting to volume, add 90 mL HNO3 and 30 mL HCl to the PMCS and 9 mL HNO3 and 3 

326
mL HCl to the STl1. Use RODI water to dilute to final volume for PMCS and STl1. Invert to 

mix thoroughly. Store in polyethylene container in refrigerator. Make fresh on a routine basis. 

The amount of the primary standards (1000 mg L-1) to make the PMCS, amount of the1000 μg 

L-1 Tl stock standard to make the STl1 and the final elemental concentrations of the PMCS and 

STl1 are as follows: 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Element Concentration Primary Standard Required

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 -μg L-1- ---- mL ---- 

As 2,000 1 

Ni 4,000 2 

P 60,000 30 

Cr 4,000 2 

Mn 40,000 20 

Cu 20,000 10 

Zn 20,000 10 

Cd 2,000 1 

Pb 4,000 2 

Co 4,000 2 

Ag 400 0.2 

Ba 120,000 60 

Be 600 0.3 

Sb 400 0.2 

Sr 60,000 30 

Mo 400 0.2 

V 20,000 10 

Sn 8,000 4 

Tl 500 25 

W 2,000 1 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

7.14 The WCS are made from dilution of the PMCS with the exception of single element Tl 

(STl2), which is made up separately. The three WCS (Low, Medium, and High) require 0.625, 

6.25, and 62.5 ml PMCS diluted to 250-mL final volume, respectively. Also, prior to diluting to 

volume, add 44.89, 43.88, and 33.75 mL HNO3 and 14.96, 14.63, and 11.25 mL HCl to the 

WCS (Low, Medium, High, respectively). The STl2 requires 0.5, 5, and 50 mL of the STl1

diluted to a 50-mL final volume. Also, prior to diluting to volume, add 8.91 and 8.1 mL HNO3

and 2.97 and 2.7 mL HCl for the Low and Medium ST12, respectively. Use RODI water to 

dilute to final volume for WCS and STl2. Invert to mix thoroughly. Store in polyethylene 

container in a refrigerator. Make fresh on a routine basis. The elemental concentrations of the 

Low, Medium, and High WCS and the ST12 are as follows: 

327
⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 ---------------- Concentration -------------- 

Element Low Medium High 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 ------------------- μg L-1 -------------------- 

Ni 10 100 1000 

P 150 1500 15000 

Cr 10 100 1000 

Mn 100 1000 10000 

Cu 50 500 5000 

Zn 50 500 5000 

Cd 5 50 500 

Pb 10 100 1000 

Co 10 100 1000 

Ag 1 10 100 

Ba 300 300 3000 

Be 1.5 15 150 

Sb 1.0 10 100 

Sr 150 1500 15,000 

Mo 1 10 100 

V 50 500 5000 

Sn 20 200 2000 

Tl 5 50 500 

W 5 50 500 

As 5 50 500 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

7.15 Single element primary standards (1000 mg L-1, Al, Fe, Mo, V, Mn) are required to create 

the inter-elemental correction (IEC) factors. These are prepared in the matrix of the digests and 

are combined into one solution for routine calibration. The single element IEC standards 

(SEIECS) are required to determine the IEC’s. The mixed IEC standard (MIECS) is required 

for routine calibration. The SEIECS is based on a 50-mL final volume and the MIECS is based 

a 250-mL final volume. Use RODI water to dilute to final volume for SEIECS and MIECS. 

Invert to mix thoroughly. Store in polyethylene container in a refrigerator. Make fresh on 

routine basis. The amount of the primary standard (1000 mg L-1) to make the SEIECS and 

MIECS solutions and the final elemental concentration of these IEC solutions are as follows: 

 IEC Solution --------Primary Standard-------- 

Element Concentration --------------Required ------------ 

 MIECS SEIECS 

 --mg L-1-- ------------------mL--------------- 

Al 100 25.00 5.0 

Fe 100 25.00 5.0 

Mo 5 1.25 0.25 

V 10 2.50 0.50 

Mn 10 2.50 0.50 

 

 

7.16 To MIECS, add 45 and 15 mL HNO3 and HCl, respectively. To SEIECS, add 9 and 3 mL 

HNO3 and HCl, respectively. Use RODI water to dilute to final volume for MIECS and 

SEIECS. 

328
7.17 The elements chosen for IEC factors are based on established spectral interferences with 

chosen analyte wavelengths. The SEIECS should initially be prepared in separate 50-mL 

volumetrics for establishment of IEC factors and then prepared (MIECS) in a single 250-mL 

volumetric for routine analysis. IEC factors are established via a procedure in the WinLab 

software in which the amount of interference on the analyte (in μg L-1) is measured for each mg 

L-1 of interferent concentration in the digest. 

7.18 A 10 mg L-1 Lu internal standard (read at 291.138 nm) is added to the blank, all 

calibration standards, and samples. It is prepared by adding 5.0 mL Lu primary standard (1000 

mg L-1) and 10 ml conc. HNO3 to 500-mL volumetric flask, and diluting to volume with RODI 

water.Internal standard is automatically injected via the peristaltic pump and mixing block. 

7.19 Use the ICP-AES in axial mode and ultrasonic nebulization to analyze sample. Internal 

standard is added via an external peristaltic pump at 15% pump speed using 0.44 mm id. pump 

tubing. Internal standard and samples or standards are mixed via a mixing block and coil prior 

to entering the ultrasonic nebulizer. No initial dilutions of samples are necessary prior to 

analysis.Perform instrument checks (Hg alignment; BEC and %RSD of 1 mg L-1 Mn solution) 

prior to analysis as discussed in operation manual of instrument. Check instrument alignment 

and gas pressures to obtain optimum readings with maximum signal to noise ratio. 

7.20 Analyses are generally performed at two or more wavelengths for each element. The 

selected wavelengths are as follows: (reported wavelength listed first and in boldface): 

 Element Wavelength 

 ----------- nm --------- 

 Al 237.312 308.215 

 Fe 302.107 238.203 

 Mn 260.570 203.844 

 P 178.221, 213.620 

 Cr 267.710, 205.558 

 Cu 324.753, 327.396 

 Ni 232.003, 231.604, 

 Zn 213.857, 206.197 

 Cd 228.802, 226.501 

 Pb 220.353, 216.998 

 Co 228.614

 Sb 217.582, 206.833 

 Sr 460.733, 407.771 

 Ba 233.525, 455.507 

 Be 313.104, 313.046 

 As 188.979

 Ag 328.068, 338.287 

Mo 202.031, 203.845 

 V 292.402, 310.230 

 Sn 189.927, 235.485 

 W 207.912, 224.876 

 Tl 190.801, 276.787 

 Lu 291.138 (Internal Standard) 

 Al (IEC) 237.312 

 Fe (IEC) 302.107

 Mo (IEC) 202.031

 V (IEC) 292.402

 Mn (IEC) 260.568 

329
7.21 Use the blank standard solution to dilute those samples with concentrations greater than 

the high standard. Rerun all elements and use only the data needed from the diluted analysis. 

7.22 Establish detection limits using the blank standard solution. The instrumental detection 

limits are calculated by using 3 times the standard deviation of 10 readings of the blank. These 

values establish the lower detection limits for each element. Analyzed values lower than the 

detection limits are reported as "ND" or non-detected. 

7.23 The extract obtained in this procedure (4H1a1) is used in procedure 4H1a1c1 for Hg 

analysis and in procedures 4H1a1b1a1-2 for As and Se analysis, respectively. 

8. Calculations 

The calculation of mg kg-1 of an element in the soil from μg L-1 in solution is as follows: 

Analyte concentration in soil (mg kg-1) = [A x B x C x R x 1000]/E x 1000 

A = Sample extract reading (μg L-1) 

B = Extract volume (L) 

C = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) 

1000 = Conversion factor in numerator to kg-basis 

E = Sample weight (g) 

1000 = Factor in denominator (μg mg

-1) 

9. Report 

Analyses are generally performed at two or more wavelengths for each element, with 

the one selected wavelength for reporting purposes. The particle-size fraction digested needs to 

be identified with each sample. Data are reported to the nearest 0.01 mg kg-1. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

10. References 

Burt, R., M.A. Wilson, T.J. Keck, B.D. Dougherty, D.E. Strom, and J.A. Lindhal. 2002. 

Trace element speciation in selected smelter-contaminated soils in Anaconda and Deer 

Lodge Valley, Montana, USA. Adv. Environ. Res. 8:51-67. 

Burt, R., M.A. Wilson, M.D. Mays, and C.W. Lee. 2003. Major and trace elements of 

selected pedons in the USA. J. Environ. Qual. 32:2109-2121. 

Gambrell, R.P. 1994. Trace and toxic metals in wetlands–A review. J. Environ. Qual. 

23:883-891. 

Holmgren, G.G.S., M.W. Meyer, R.L. Chaney, and R.B. Daniels. 1993. Cadmium, lead, 

zinc, copper, and nickel in agricultural soils of the United States of America. J. 

Environ. Qual. 22:335-348. 

Jersak, J., R. Amundson, and G. Brimhall, Jr. 1997. Trace metal geochemistry in 

Spodosols of the Northeastern United States. J. Environ. Qual. 26:551-521. 

Keller, C., and J.C. Vedy. 1994. Distribution of copper and cadmium fractions in two 

forest soils. J. Environ. Qual. 23:987-999. 

Pierzynski, G.M., and A. P. Schwab. 1993. Bioavailability of zinc, cadmium, and lead in 

a metal-contaminated alluvial soil. J. Environ. Qual. 22:247-254. 

Tiller, K.G. 1989. Heavy metals in soils and their environmental significance. In B.A. 

Stewart (ed.) Adv. Soil Sci. 9:113-142. 

Wilcke, W., and W. Amelung. 1996. Small-scale heterogeneity of aluminum and heavy 

metals in aggregates along a climatic transect. Soil Sci. Soc. Am. Proc. 60:1490-1495. 

330
Wilcke, W., S. Muller, N. Kanchanakool, and W. Zech. 1998. Urban soil contamination 

in Bangkok: Heavy metal and aluminum partitioning in topsoils. Geoderma 86:211-

228. 

Total Analysis (4H) 

Acid Digestion (4H1) 

HNO3 + HCl Digestion (4H1a) Microwave (4H1a1) 

HCl Digestion (4H1a1b) 

Water Bath (4H1a1b1) 

Flow Through Hydride-Generation and Atomic Absorption Spectrophotometer (4H1a1b1) 

Arsenic and Selenium (4H1a1b1a1-2) 

Air-Dry, <2 mm (4H1a1b1a1-2a1) 

1. Application 

Arsenic is an extremely toxic element that is occurs in both organic and inorganic forms 

in soils. It is typically found in low concentrations, but has been widely applied to soils as a 

component in pesticides and herbicides and also via industrial pollution and smelting 

operations. The element is used in drugs, soaps, dyes, and metals, though 90% of industrial As 

in the U.S. is used in wood preservatives (Pinsker, 2001). Concerns exist for both short-term 

(acute) and long-term (chronic) soil exposure. Primary route for exposure is via soil ingestion 

or inhalation of air-borne particles. Data from As measurements in groundwater by U.S. 

Geological Survey and Environmental Protection Agency has suggested that most As in 

groundwater is related to natural sources (Ryker, 2001), i.e., from mineral dissolution from 

minerals in geologic formations and soils. For example, As released via pyrite oxidation is in 

part responsible for groundwater As levels in Bangladesh ranging between 50 and 2,500 ug/L 

in many wells. Soil applied As is generally immobile, with soil chemistry similar to 

phosphorus. The element occurs as arsenate (As5+) and arsenite (As3+), and in soils, is in the 

form of the oxyanion, AsO4

3-. The weathering of limestone and biological accumulation of the 

element by aquatic organisms is responsible for the high levels in wetland soils of Florida 

(Chen et. al., 2002) 

Selenium is a naturally occurring element in rocks, but is especially concentrated in 

certain geologic formations, such as Mancos Shale in Colorado and Wyoming and in the shales 

of the Moreno and Kreyenhagen Formations of California (Martens and Suarez, 1997). 

Selenium occurs in four species (related to valance states): selenate (Se6+), selenite (Se4+), 

elemental Se (Se0), and selenide (Se2-). The bioavailability and toxicity is related to speciation. 

The oxidized species are more commonly found in soils and water. The element is important 

due to both deficiency (forages for animals) and toxicity (bioaccumulation) concerns (Huang 

and Fujii, 1996). 

2. Summary of Method 

A soil sample is digested with HNO3 and HCl in a microwave oven (procedure 4H1a1). 

Following extraction, samples are diluted with water to a final 50-mL volume. A 6-mL aliquot 

of the digestate is combined with 6 mL concentrated H2SO4 and heated at 180 C for 5 min in 

the microwave oven to eliminate the HNO3. Then, the extract is combined with 14 mL of 

water and 20 mL of concentrated HCl and boiled for 30 min. Sample extracts are allowed to 

cool. Potassium iodide is added as a pre-reduction step for As analysis, with a final 

concentration of 1% in analysis solutions. Solutions are allowed to stand 1 h before analyzed 

for total As and/or Se, using flow through hydride-generation and atomic absorption 

spectrophotometer (HGAAS). Under acidic conditions, sodium borohydride (NaBH4) reduces 

As and Se to form gaseous products that can be detected by atomic adsorption. For example: 

3NaBH4 + 4H2SeO3 Æ 4H2Se(g) + 3H3BO4 + 3NaOH 

331
 The data are automatically recorded by a computer and printer. The As and Se 

concentrations are reported as mg kg-1 in the soil by procedure 4H1a1b1a1-2, respectively. 

3. Interferences 

Oxidizing acids (e.g., nitric) can produce interferences, and inter-element interferences 

(e.g., Cu, Sn, Ni, Fe, Cr, Pb, Co) can affect determinations. Even small amounts of nitric acid 

produce suppressed, erratic absorbance signals and low recoveries, more so for As than Se. 

This interference can be effectively eliminated with either (1) addition of urea before the 

potassium iodide pre-reduction step, or (2) boiling the samples with H2SO4. Alternatively, if 

samples are boiled in HCl, the quantity of nitric acid can be sufficiently reduced to eliminate 

the need for urea. Hydride-forming elements may exist in more than one oxidation-state, 

affecting the signal. In general, As5+ methods produce a signal that may be 20 to 50% of that 

produced by As3+. There are typically more inter-element interferences for As5+ methods than 

for As3+. Inter-element inteferences can be reduced by using the lowest possible concentration 

of sodium borohydride. Best results can be obtained for difficult samples containing high 

concentrations of metals if the sodium borohydride concentration is reduced to 0.3% w/v. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves); eye protection (face 

shields, goggles, or safety glasses); and a breathing filter when handling As and Se solutions. 

These elements are extremely toxic. 

Follow standard laboratory practices when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene gas is highly flammable. Avoid 

open flames and sparks. Standard laboratory equipment includes fire blankets and 

extinguishers for use when necessary. Follow the manufacturer's safety precautions when 

using the AA. 

5. Equipment 

5.1 Electronic balance, ±0.1-mg sensitivity 

5.2 Atomic absorption spectrophotometer (AAS), PE Model Analyst 300, Perkin-Elmer Corp., 

Norwalk, CT 

5.3 System 2 Electrodeless Discharge Lamp (EDL) Power Supply, with lamps for As and Se, 

Perkin-Elmer Corp., Norwalk, CT 

5.4 Autosampler, Model 90A, Perkin-Elmer Corp., Norwalk, CT 

5.5 WinLab Software, Ver. 4.1, Perkin-Elmer Corp., Norwalk, CT 

5.6 Computer, Dell Optiplex GXM 333 MHz Pentium, Dell Computer Corp., 17 in color 

monitor 

5.7 Printer, Hewlett-Packard LaserJet 880A 

5.8 Single-stage regulator, acetylene service, part number E11-0-N511A, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 

5.9 Double-stage regulator, argon service 

5.10Varian Vapor Generation Accessory, Model VGA-77 

5.11Tubes, 50-mL for calibration standards 

5.12Test tubes, 50-mL, Corning Pyrex, for sample digestion 

5.13Test tubes, 25-mL, 16 mm x 100, for sample dilution and autosampler 

5.14 100, 250, and 1000-mL volumetrics, class A.

5.15Containers, polypropylene and glass

5.16Water bath, 95°C-capability

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Sulfuric acid (H2SO4), 36 M, trace metal purity 

6.3 Sodium hydroxide (NaOH⋅3H20) 

332
6.4 Sodium borohydride (NaBH4) pellets 

6.5 Hydrochloric acid (HCl), 12 M, trace metal purity, assay 35-38% 

6.6 Acetylene gas, purity 99.6%. 

6.7 Compressed air with water and oil traps 

6.8 Compressed Argon 

6.9 Primary standards, 1000 mg L-1As and 1000 mg L-1 Se, High Purity Standards, Inc. 

6.10Primary mixed working standard (PMWS), 1000 μg L-1 As and Se: Add 500 mL RODI 

water to a 1-L volumetric. Add 1 mL of 1000 mg L-1 As, 1 mL of 1000 mg L-1 Se, and 10 

mL concentrated HCl . Fill to volume with RODI water. Invert to mix thoroughly. Final 

concentration is ≈ 1% HCl. Store in polyethylene container in a refrigerator. Make fresh 

weekly. 

6.11Mixed Calibration Standards (MCS), 150, 100, 75, 50, 25, 12, and 0 μg L-1: To seven 250-

mL volumetrics, add PMWS and concentrated HCl as follows: 

6.11.1 150 μg L-1 = 37.5 mL PMWS + 106 mL HCl 

6.11.2 100 μg L-1 = 25.0 mL PMWS + 113 mL HCl 

6.11.3 75 μg L-1 = 18.75 mL PMWS + 116 mL HCl 

6.11.4 50 μg L-1 = 12.5 mL PMWS + 119 mL HCl 

6.11.5 25 μg L-1 = 6.25 mL PMWS + 122 mL HCl 

6.11.6 12 μg L-1 = 3.0 mL PMWS + 124 mL HCl 

6.11.7 0 μg L-1 = 0 mL PMWS + 125 mL HCl 

6.12Bring to volume with RODI water and invert to mix thoroughly. Store in polyethylene 

container in a refrigerator. Standards will keep for 2 to 3 days with refrigeration. Quality 

Control (QC) check is MCS 100 μg L-1. Final concentration of MCS and QC check is ≈ 6 

M HCl. 

6.13Acid Carrier, 6 M HCl: Add 200 mL RODI water to a 500-mL volumetric. Carefully add 

250 mL concentrated HCl and fill to volume with RODI water. Invert to mix thoroughly. 

6.14Reductant, 0.5% NaOH - 0.3% NaBH4: Add 200 mL RODI water to a 500-mL volumetric. 

Always stabilize the solution by first adding the NaOH. Add 2.5 g NaOH and mix until 

dissolved. Add 1.5 g of NaBH4, mix until dissolved, and fill to volume. Invert to mix 

thoroughly. Degas for 10 min. Make fresh daily. 

6.15 Potassium iodide (KI) (10%) – ascorbic acid solution (10%): To a 500-mL volumetric, 

add 250 mL of RODI water. Dissolve 50 g of KI and 50 g of ascorbic acid and dilute to 

volume with RODI water. Invert to mix thoroughly. Make fresh daily. (Procedure requires 

1-mL per sample.) 

6.16 Diluent, 6 M HCl, for samples: Add 400 mL RODI water to a 1-L volumetric. Carefully 

add 500 mL concentrated HCl and fill to volume with RODI water. Invert to mix 

thoroughly. 

6.17QC Soil Standards: Loam C (certified reference material, purchased from High purity 

Standards) and NIST SRM 2710 (National Institute of Standards and Technology, 

Standard Reference Material), all prepared to < 200 mesh (75 μm). 

7. Procedure 

Digestion of acid (HNO3 + HCl) extract 

7.1 Prepare soil samples, soil standards, blanks, and spikes prepared in procedure 4H1a1 as 

follows: Pipette 6mL of acid (HNO3 + HCl) extract and 6mL concentrated H2SO4 into a 50-mL 

Pyrex tube. Place in a glass beaker (4 tubes into each 250-mL beaker; maximum of 3 beakers, 

i.e., 12 samples, in microwave at one time). Heating program for microwave is as follows: 

333
Parameter Value

Stage 1 

Max. Power (watts) 600 

Heating Power (%) 100 

Program Ramp (min) 5:00 

Pressure (psi) 800 

Temperature (°C) 180 

Hold (min) 30:00 

Place thermocouple (in thermowell) into one sample. Heat microwave until 180° C is reached 

for 5 minutes. At that time, fuming (loss of HNO3) should cease. Allow samples to cool and 

vent in the microwave for 5 minutes prior to removal. 

7.2 To the microwave digested soil samples and MCS, pipette 15 mL of RODI water + 20 mL 

of concentrated HCl. Include one QC soil standard and blank in each sample rack. Soil 

samples and QC soil standards have a final concentration of ≈ 6 M HCl. 

7.3.Digest the open tubes (do not cover) in a sample rack by submerging up to the neck of the 

tubes in a water bath (95° C). Heat for 30 min and remove to cool. 

7.4 Remove tubes, cool, fill to volume and cap. Mix well by inverting. (Note: digested soil 

samples and QC soil standards can be analyzed the same day, or placed into the refrigerator 

overnight for subsequent analysis the following day.) For As analysis, proceed to Section 7.5. 

For Se analysis, proceed to Section 7.7. 

7.5 Arsenic (MCS): Pipette 36 mL of digested MCS + 4 mL of KI-ascorbic acid solution into 

test tubes that have been placed in the sample holder of the sample changer. Allow to stand 1 h 

before As analysis. Do not allow MCS to stand greater than 2 h before As analysis. For every 

sample extract rack, do a set of MCS. 

7.6 Arsenic (sample extracts): Pipette 9 mL of sample extract + 1 mL of KI-ascorbic acid 

solution into test tubes that have been placed in the sample holder of the sample changer. Allow 

to stand 1 h before As analysis. Do not allow samples to stand longer than 2 h before As 

analysis. 

 

7.7 Selenium (sample extracts and MCS): Pour sample extract and MCS (without KI-ascorbic 

acid solution) into test tubes that have been placed in the sample holder of the sample changer. 

HGAAS Set-up and Operation

7.8 Each element is analyzed separately on the atomic absorption spectrometer. Refer to 

manufacturer's manual for operation of AAS. Connect EDL power supply to AAS. Allow 

EDL to warm up 20 to 30 minutes. Follow the manufacturer’s operating procedures for AA 

EDL settings, warm-up, and adjustments to settings. Connect vapor generation accessory 

to AA. Follow the manufacturer’s operating procedures for appropriate gas and liquid 

flow. Instrumental parameters for each element are as follows: 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Element Wavelength Slit Width EDL Current 

 nm mA 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Arsenic 193.7 0.7 380 

Selenium 196.0 2.0 250 

334
The flame is required only for heating the gas flow tube and is maintained as a low temperature 

as possible. Use an air/C2H2 mixture of 6.5 and 0.2 L min-1. 

7.9 For automated analysis (using the autosampler), the analysis is performed using atomic 

absorption with background correction, time average mode, with a read delay of 48 s, BOC 

time of 5 s, and read time of 2 s. Rinse for 30 s between samples. Reported values are the 

average of five replications. 

7.10 Use the computer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.11 The instrument readings are programmed to display analyte concentration in μg L-1 (ppb). 

HGAAS Calibration

7.12 Each element is analyzed during separate runs on the AA. Use the calibration reagent 

blank and calibration standards to calibrate the AAS. Detection limits are 5 and 10 μg L-1 for 

As and Se, respectively. 

7.13 Use the QC standards after every 12th sample. The QC is 100 μg L-1 for As and Se, 

respectively, with + 30% rejection criteria. If QC fails after three attempts, recalibrate and 

reread the QC. The QC is read at the end of each run. 

7.14 If samples are outside the calibration range, a 1:5 serial dilution is performed using 6 M

HCl. The QC soil standards (Loam C and SRM 2710) have As contents of 47±3 and 626±38, 

mg kg-1 soil, respectively, as consensus/certified values. These QC soil standards have 

automatic dilutions of 1:10 and 1:100, respectively. 

Clean-up and Maintenance 

7.15 Soak the absorption cell in dilute HNO3 acid (0.1% w/v) for 30 min, rinse thoroughly with 

RODI water, and allow to dry. 

7.16 If gas/liquid separator and tubing (including autosampler sipper) has been exposed to 

contamination with KI, pump a freshly prepared 1% sodium thiosulfate solution through the 

system for 10 min. The sodium thiosulfate solution must be removed by pumping RODI water 

through the system for 10 min. 

7.17 If gas/liquid separator and tubing have not been exposed to contamination with KI, pump 

RODI water through the system for 10 min. 

8. Calculations 

Convert extract As and Se (μg L-1) to soil As and Se (mg kg-1) as follows: 

Soil As (mg kg -1) = [A x B x C x R x 1000]/E x 1000 

where: 

A = Sample extract reading (μg L-1) 

B = Extract volume (L) (0.05) 

C = Dilution, if performed 

1000 = Conversion factor in numerator to kg-basis 

1000 = Factor in denominator (μg mg-1) 

R = Air-dry/oven-dry ratio (procedure 3D1) 

E = Sample weight (g) (0.5) 

335
Soil Se (mg kg -1) = [A x B x C x R x 1000]/E x 1000 

where: 

A = Sample extract reading (μg L-1) 

B = Extract volume (L) (0.05) 

C = Dilution, if performed 

1000 = Conversion factor in numerator to kg-basis 

1000 = Factor in denominator (μg mg

-1) 

R = Air-dry/oven-dry ratio (procedure 3D1) 

E = Sample weight (g) (0.5) 

9. Report 

Report As and Se to the nearest 0.1 mg kg-1 soil. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Anawar, H.M., J. Akai, K.M.G. Mostofa, S. Safiullah, and S.M. Tareq. 2002. Arsenic 

poisoning in groundwater: Health risk and geochemical sources in Bangladesh. 

Environ. Int. 27:597-604. 

Chen, M., L.Q. Ma, and W.G. Harris. 2002. Arsenic concentrations in Florida surface 

soils: influence of soil type and properties. Soil Sci. Soc. Am. J. 66:632-640. 

Huang, P.M., and R. Fujii. 1996. Selenium and arsenic. p. 793-831. In D.L. Sparks (ed.) 

Methods of soil analysis. Part 3 – Chemical Analysis. Soil Sci. Soc. Am. Book Series 

No. 5. ASA and SSSA, Madison, WI. 

Martens, D.A., and D.L. Suarez. 1997. Selenium speciation of marine shales, alluvial 

soils, and evaporation basin soils of California. J. Environ. Qual. 26:424-432. 

Office of Environmental Health Assessment Services. 1999. Hazards of short-term 

exposure to arsenic contaminated soil. State of Washington. Olympia, WA. 

Pinsker, L.M. 2001. Health hazards: Arsenic. Geotimes. Nov. p. 32-33. 

Ryker, S.J. 2001. Mapping arsenic in groundwater: a real need, but a hard problem. 

Geotimes. Nov. p. 34-36. 

Total Analysis (4H) 

Acid Digestion (4H1) 

HNO3 + HCl Digestion (4H1a) 

Microwave (4H1a1) 

Cold Vapor Atomic Absorption Spectrophotometer (4H1a1c) 

Mercury (4H1a1c1) 

Air-Dry, <2-mm (4H1a1c1a1) 

1. Application 

Mercury is highly toxic to both plants and animals, and enters the food chain primarily 

through atmospheric deposition (smelting, coal combustion, volcanic activity) and pesticide 

usage (Pais and Jones, 1997). Due to the absorption of Hg by both organic and inorganic soil 

components, many studies have been performed which have examined soil-Hg interactions 

(MacNaughton and James, 1974; Barrow and Cox, 1992; Yin et al., 1996) and ecosystem 

distributions (Hall et al., 1987; Inacio et al., 1998). 

2. Summary of Method 

Soil digests (HNO3 + HCl) from procedure 4H1a1 are analyzed for Hg using cold-vapor 

atomic absorption spectroscopy (CVAAS). This method is based on absorption of radiation at 

253.7 nm wavelength by Hg vapor. The digest is mixed with stannous chloride to reduce Hg to 

336
the elemental state. Using argon as a carrier gas, the solution is passed over a gas-liquid 

separator in a closed system to separate the gaseous Hg from solution. The Hg vapor passes 

through a cell positioned in the light path of an atomic absorption spectrophotometer. 

Absorbance (peak height) is measured as a function of mercury concentration. Mercury data 

are reported as μg kg-1 soil by procedure 4H1a1c1. 

3. Interferences 

Copper, chlorides, and certain volatile organic materials may be interferences. 

4. Safety 

Soil digests contain acid and must be handled appropriately. Procedure uses a primary 

Hg standard that is diluted for working standards. Use gloves and avoid skin contact. Gasses 

exhausting from the Hg analyzer cabinet, prior to passing through the Hg vapor trap may 

contain Hg vapor. Do not run the instrument unless the exhaust gas is properly scrubbed or 

removed. 

5. Equipment 

5.1 Cold-vapor atomic absorption spectrophotometer (CVAAS), CETAC M-6000A Mercury 

Analyzer, CETAC Corp., Omaha, NE 

5.2 Autosampler, CETAC ASX-500 Model 510, CETAC Corp., Omaha, NE 

5.3 Autodilutor Accessory, CETAC ADX-500, CETAC Corp., Omaha, NE 

5.4 Nafion drying tube, CETAC Corp., Omaha, NE 

5.5 Peristaltic Pump, CETAC Corp., Omaha, NE 

5.6 Computer, Microsoft Windows 97, CETAC M-6000A Software, CETAC, Corp., Omaha, 

NE, and printer 

5.7 Pipettors, electronic digital, Rainin Instrument Co., Woburn, MA, 2500 μL and 10 mL 

5.8 Compressed argon gas 

5.9 Calcium sulfate (anhydrous) or equivalent desiccant 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Concentrated hydrochloric acid (HCl), 12 N. Use trace pure HCl. 

6.3 Concentrated nitric acid (HNO3), 16 N. Use trace pure HNO3. 6.4 Primary standard: 1000 mg L-1 Hg, High-Purity Standards, Charleston, SC. 

6.5 Stock standard, 500 μg L-1: Add 0.25 mL primary standard to 500 mL volumetric and 

dilute to mark with RODI water and invert to mix thoroughly. 

6.6 Standard Hg calibration solutions or working standards are 4.0, 3.0, 2.5, 1.0, 0.5, and 0.0 ug 

L-1. To six 50-mL volumetric flasks add as follows: 

6.6.1 0.0 ug L-1 = 9 mL HNO3 + 3 mL HCl 

6.6.2 0.5 ug L-1 = 0.05 mL stock standard + 9 mL HNO3 + 3 mL HCl 

6.6.3 1.0 ug L-1 = 0.1 mL stock standard + 9 mL HNO3 + 3 mL HCl 

6.6.4 2.5 ug L-1 = 0.25 mL stock standard + 9 mL HNO3 + 3 mL HCl 

6.6.5 3.0 ug L-1 = 0.3 mL stock standard + 9 mL HNO3 + 3 mL HCl 

6.6.6 4.0 ug L-1 = 0.4 mL stock standard + 9 mL HNO3 + 3 mL HCl 

Dilute each working standard to mark with RODI water and invert to mix thoroughly. These 

working standards are used for Normal and High Throughput Ranges. 

6.7 Stannous chloride, reducing agent 10% stannous chloride solution (SnCl2 in 7% HCl). Add 

50 g of stannous chloride and 97.2 mL concentrated HCl to 500 mL volumetric and dilute to 

mark with RODI water. Invert to mix thoroughly. 

 

337
6.8 Diluent: Add 90 mL concentrated HNO3 and 30 mL concentrated HCl to 500 mL 

volumetric and dilute to mark with RODI water. Invert to mix thoroughly. 

6.9 Rinse (5% HNO3): Add 71.4 mL HNO3 to 1-L volumetric and dilute to mark with RODI 

water. Invert to mix thoroughly. 

 

6.10 Potassium permanganate, solid, crystalline, fills safety trap for Hg vapor exhaust. 

6.11 Glass wool. Fine glass wool only. 

7. Procedure 

 

7.1. Oven radiator temperature must be at 125°C to maintain the actual gas temperature of 50° C. Argon gas carrier must be supplied at 100 psig (6.9 bar). Liquid flow is always set at fixed 

flow of 4.0 mL min-1 (sample) and 0.8 mL min-1 (reagent). 

7.2. Turn mercury analyzer and mercury lamp for warm-up (90 min) prior to analysis. Ensure 

integrity of lamp (there is some loss of performance at 13 mA but replace at 15 mA). 

7.3. Turn on computer and choose Worksheet Template appropriate to range of analysis. Three 

ranges of analysis (Highest Sensitivity, Normal, and High Throughput) have been developed on 

the CETAC Mercury Analyzer. Method parameters for each of these ranges are saved on a 

different Worksheet Template. General parameters are as follows: 

High Throughput Range: 

Sampling Times: 

 Integration 1 s 

 Read Delay 35 s 

Auto-Adjust Integration 

 Replicates 4 

Instrument Control 

 Gas Flow 300 mL min-1

Autosampler Setup 

 Sip Duration 20 s 

 Rinse Time 20 s 

 Repeats 1 

Sample Matrix: Liquid 

Reslope Frequency: 0 

Reslope Standard: Standard No. 3 (check standard) 

Detection Limit: 0.050 μg L-1

Baseline Correction: 1 point 

Normal Range: 

Sampling Times: 

 Integration 1 s 

 Read Delay 50 s 

Auto-Adjust Integration 

 Replicates 4 

338
Instrument Control 

 Gas Flow 85 mL min-1

Autosampler Setup 

 Sip Duration 30 s 

 Rinse Time 45 s 

 Repeats 1 

Sample Matrix: Liquid 

Reslope Frequency: 0 

Reslope Standard: Standard No. 3 (check standard) 

Detection Limit: 0.015 μg L-1

Baseline Correction: 1 point 

Highest Sensitivity Range: 

Sampling Times: 

 Integration 1 

 Read Delay 50 

Auto-Adjust Integration 

 Replicates 4 

Instrument Control 

 Gas Flow 40 mL min-1

Autosampler Setup 

 Sip Duration 60 s 

 Rinse Time 140 s 

 Repeats 1 

Sample Matrix: Liquid 

Reslope Frequency: 0 

Reslope Standard: Standard No. 3 (check standard) 

Detection Limit: 0.001 μg L-1

Baseline Correction: 2 point 

7.4.Prior to analysis ensure that the gas-liquid separator (GLS) post is fully wetted as follows: 

7.4.1 Check the bottle supplying the ASX-500 rinse station is full of 5% HNO3. 

7.4.2 Use quick release mechanism and fully release clamp tension on lower two tube channels 

of peristaltic pump (drain channels). 

7.4.3 Use sample and reagent tubes and pump 5% HNO3 and stannous chloride reagent, 

respectively. 

7.4.4 With drain pump tubes unclamped, GLS should begin to fill with 5% HNO3. 

7.4.5 Allow GLS to fill until liquid level reaches top of GLS center post or until gas bubble 

propels a meniscus upward to wet post all along its length, including apex. 

7.4.6 Upon wetting, immediately reengage quick-release clamps on drain pump tubes. 

7.4.7 Do not let liquid level overflow GLS into Nafion drying tube. 

339
7.4.8 With drain tube clamps properly reengaged and pump running, liquid level normally stops 

rising and goes back down 

7.4.9 Once GLS has emptied, leave pump running (keep liquid flowing) 

7.5 Zero analyzer to compensate for baseline offsets (due to microscopic dust buildup on the 

optics, dirty sample windows, and thermal drift). 

7.6 Define Time Profile using Signal Profile Chart (sample time, and 1st and 2nd baseline 

correction points) as follows: 

7.6.1 Current sample time on chart will start at dark green vertical line and stop at light red 

vertical line. 

7.6.2 Using mouse, define sample time by clicking on chart and dragging to right. 

7.6.3 Integration times will automatically be recalculated based on new total sample time. 

7.6.4 Current 1st baseline correction point will start at light blue vertical line and stop at dark 

red line. 

7.6.5 Use mouse and shift key and change point times by clicking on chart and dragging to 

right. 

7.6.6 To do this, press and hold shift key. 

7.6.7 Click with left mouse button on left limit of part of signal to be used on baseline 

correction point. 

7.6.8 Light blue vertical cursor line will appear. 

7.6.9 Without releasing shift key or left mouse button, drag mouse to right until portion of 

signal to be used as baseline correction point is between light blue and dark red cursor lines. 

7.6.10 Release shift and mouse key and chart will update baseline times in worksheet. 

7.6.11 Current 2nd baseline correction point on chart will start at light green vertical line and 

stop at purple line. 

7.6.12 Use mouse and control key, change point times by clicking on chart and dragging to 

right. 

7.7 Enter sample numbers, final volume, and weights in “Labels”. 

7.8 Run calibration and analysis in “Analysis”. 

7.9 After completion of analytical run, run RODI water through sample sipper tube and 

stannous chloride reagent lines. Pump all lines dry after rinsing. 

7.10 Perform shutdown: turn off mercury lamp, argon gas, ASX-500, pump, M-6000 main 

power, close the M-6000A Software, and turn off the computer. 

 

340
8. Calculations 

Analytical data is reported by the instrument in μg mL-1 in solution. It is converted to μg kg-1 in 

soil as follows: 

Hg in soil (μg kg-1) = [A x B x C x R x 1000]/E 

where: 

A = Sample extract reading (μg L-1) 

B = Extract volume (mL) 

C = Dilution, if performed 

1000 = Conversion factor in numerator to kg-basis 

R = Air-dry/oven-dry ratio (procedure 3D1) 

E = Sample weight (g) 

9. Report

Hg data are reported to the nearest 0.1 μg kg-1. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Barrow, N.J., and V.C. Cox. 1992. The effects of pH and chloride concentration on 

mercury sorption: I. By goethite. J. Soil Sci. 43:295-304. 

Hall, A., A.C. Duarte, M.T. Caldeeira, and M.F. Lucas, M.F. 1987. Sources and sinks of 

mercury in the coastal lagoon of Aveiro, Portugal. Sci. Total Environ. 64:75-87. 

Inacio, M.M., V. Pereira, and M.S. Pinto. 1998. Mercury contamination in sandy soils 

surrounding an industrial emission source (Estarreja, Portugal). Geoderma 85:325-339. 

MacNaughton, M.G., and R.O. James. 1974. Adsorption of aqueous mercury (II) 

complexes at the oxide/water interface. J. Colloid Interface Sci. 47:431-440. 

Pais, Istvan, and J.B. Jones, Jr. 1997. The handbook of trace elements. St. Lucie Press. 

Boca Raton, FL. 223 pp. 

Yin, Y., H.E. Allen, Y. Li, C.P. Huang, and P.F. Sanders. 1996. Adsorption of mercury(II) 

by soil: Effects of pH, chloride, and organic matter. J.

Total Analysis (4H) 

Acid Digestion (4H1) 

HF + HNO3 + HCl Digestion (4H1b) Microwave (4H1b1) 

Boric Acid (4H1b1a) 

Inductively Coupled Plasma Atomic Emission Spectrophotometer (4H1b1a1a1-11) 

Radial Mode (4H1b1a1a) 

Aluminum, Calcium, Iron, Potassium, Magnesium, Manganese, Sodium, Phosphorus, Silicon, Zirconium, and Titanium (4H1b1a1a1-11) Air-Dry, <2 mm (4H1b1a1a1-11a1) 

Oven-Dry, <2 μm (4H1b1a1a1-11b2) 

1. Application 

Prior to the development of modern analytical techniques, e.g., X-ray diffraction and 

thermal analysis, identification of minerals was based on elemental analysis and optical 

properties (Washington, 1930; Bain and Smith, 1994). Chemical analysis is still essential to 

determine mineral structural formulas and to identify and quantify specific mineral species 

through elemental allocation to minerals. Many clay mineral groups are subdivided based on 

composition. 

341
Analysis of the entire fine-earth (<2-mm) fraction or specific particle-size separates 

provides information on parent material uniformity, pedon development, and mineral 

weathering within or between pedons. This interpretation is determined from differences 

between horizons or pedons in elemental concentrations, elemental ratios such as Si/Al, 

Si/Al+Fe, or Ti/Zr, or from differences in total elemental concentrations compared to 

concentrations determined by selective dissolution techniques. 

The inherent fertility of a soil derived from its parent material can be examined by 

determination of the basic cations relative to the Si or Al content. Phosphorus fertility of a soil 

and potential water quality problems can be better understood by measurements of total P, 

especially when compared to other P measurements, such as water-soluble or Bray-1 

extractable P. 

Hydrofluoric acid (HF) is efficient in the digestion and dissolution of silicate minerals 

for elemental dissolution (Bernas, 1968; Sawhney and Stilwell, 1994). HNO3 + HCl aids in the 

digestion of soil components, especially the organic fraction. Procedure 4H1b1a is a digestion 

of 100 mg of dried clay suspension, the fine-earth (<2-mm) fraction, or other particle size 

separate with HF + HNO3 + HCl. Samples are placed in Teflon digestion vessels and heated in 

a microwave. Elemental concentration of the digestate is determined using an inductively 

coupled plasma atomic emission spectrometer (ICP-AES). Procedure 4H1b1 follows EPA 

method 3052. 

2. Summary of Method 

A 250-mg <2-mm or other particle-size soil separate which has been oven-dried and 

ground to < 200 mesh (75 μm) is weighed into a 100-ml Teflon (PFA) sample digestion vessel. 

In addition, dried clay (<0.002 mm) may be used or a clay suspension (procedure 7A1a1) 

containing approximately 250 mg of clay material is pipeted into a digestion container and 

dried at 110°C. A equal amount of suspension is pipeted into a tared aluminum-weighing dish 

and dried at 110°C to obtain a dried sample weight. The P and Na content of the clay fraction is 

not measurable when the soil is dispersed in sodium hexametaphosphate (procedure 7A1a1). 

To the vessel, 9.0 mL HNO3, 3.0 mL HCl, and 4 mL HF are added. The vessel is 

inserted into a protection shield and covered, and placed into a rotor with temperature control. 

Following microwave digestion, the rotor and samples are cooled, and 20 ml of 4.5% boric acid 

solution is added (4H1b1a). The samples are then covered and heated in the microwave. The 

digestate then quantitatively transferred onto a 100-ml polypropylene volumetric with boric 

acid solution to achieve a final boric acid concentration of 2.1%. The volumetrics are allowed 

to stand overnight, filled to volume, and approximately 60 mL saved for analysis. The 

concentration of Al, Ca, Fe, K, Mg, Mn, Na, P, Si, Ti, and Zr are determined by ICP-AES by 

procedures 4H1b1a1a1-11, respectively. 

3. Interferences 

Insoluble fluorides of various metals may form. Formation of SiF4 results in gaseous 

losses of Si, but additions of boric acid retards formation of this molecule as well as dissolves 

other metal fluorides. Spectral and matrix interferences exist. Careful selection of specific 

wavelengths for data reporting is important. Background corrections are made by ICP-AES 

software. Samples and standards are matrix matched to reduce interferences where possible. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated acids to the fume hood. Keep HF acid refrigerated and 

avoid contact with skin of all acids. Wash hands thoroughly after handling reagents. Filling 

the digestion vessel to greater than 25 percent of the free volume or adding organic reagents or 

oxidizing agents to the cup may result in explosion of the digestion microwave system. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity

342
5.2 Pipet(s) capable of delivering 3, 4, and 9 ml. Omnifit Corp. manufacturers variable 

volume, (10-ml maximum) pipettes suitable for HNO3 and HCl delivery from 2.5 L 

bottles. 

5.3 Volumetric flasks, nalgene, 100 mL 

5.4 Polypropylene bottles, 60 mL, with cap 

5.5 Electronic balance, (±0.1 mg sensitivity) 

5.6 Microwave, CEM Mars 5, 14 position-HP500 Plus vessel and rotor (vessels composed of 

PFA, sleeves composed of advanced composite). 

5.7 Desiccator 

5.8 Disposable aluminum-weighing dishes 

5.9 Volumetrics, 500-mL, polypropylene 

5.10 Containers, 500-mL, polypropylene, with screw caps 

5.11 Pipettes, electronic digital, 2500 μL and 10 mL, Rainin Instrument Co., Woburn, MA 

5.12 Inductively coupled plasma atomic emission spectrophotometer (ICP-AES), Perkin-Elmer 

Optima 3300 Dual View (DV), Perkin-Elmer Corp., Norwalk, CT. 

5.13 RF generator, floor mounted power unit, 45 MHz free running, Perkin-Elmer Corp., 

Norwalk, CT. 

5.14 Computer, with WinLab software, ver. 4.1, Perkin-Elmer Corp., Norwalk, CT, and printer 

5.15 Recirculating chiller, Neslab, CFT Series 

5.16 Compressed gasses, argon (minimum purity = 99.996%) and nitrogen(minimum purity = 

99.999%) 

5.17 Autosampler, AS-90, Perkin-Elmer Corp., Norwalk, CT. 

5.18 Quartz torch, Part No. N069-1662; alumina injector (2.0 mm id), Part No. N069-5362; 

Ryton 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Calcium sulfate (anhydrous) or equivalent desiccant 

6.3 Hydrofluoric acid (HF), 48%, low trace metal content 

6.4 Concentrated hydrochloric acid (HCl), 12 N, trace pure grade 

6.5 Concentrated nitric acid (HNO3), 16 N, trace pure grade 

6.6 Boric acid solution, 4.5 percent. Dissolve 45.0 g low trace metal, granular boric acid 

(H3BO3) in 1000 mL RODI water. 

6.7 Boric acid solution, 1.9 percent. Dissolve 19.0 g low trace metal, granular boric acid 

(H3BO3) in 1000 mL RODI water. 

6.8 Primary standards: 1000 mg L-1, from High Purity Standards, Charleston, SC. Single 

elemental standards in dilute HNO3, HNO3 + HF, or H2O 

7. Procedure 

Microwave Acid Digestion 

7.1 Fine-earth (<2-mm) or a specific particle size separate ground to <200-mesh (75 μm) is 

used. A 250 mg sample is weighed to the nearest 0.1 mg in a 100-ml TFM vessel. If a clay 

suspension is used, proceed to section 7.2 to 7.5. If using dried specimen, proceed to section 

7.6. (Note: samples are typically prepared in sets of 14, as the digestion rotor accommodates 

that number of samples; If sample is principally composed of organic materials (organic C > 

15%), perform a preliminary digestion in the muffle furnace in an digestion crucible: 250°C for 

15 min, 450°C for 15 min, followed by 550°C for 1 h. 

7.2 Prepare Na-saturated clay as in procedure 7A1a1, (Preparation of Clay Suspension, 

Sections 7.8 to 7.19). Clay dispersion by this method eliminates quantitative analysis of Na 

and P in the clay due to dispersion by sodium hexametaphosphate. Digestion of the entire fine 

earth (<2-mm) fraction or any fraction not derived by dispersion with sodium 

hexametaphosphate (or other Na and P-containing dispersing agents) can be quantitatively 

343
analyzed for Na and P. Dispersion of clays and cleaning of test tubes and dishware should be 

with RODI water. 

7.3 Pipet a known aliquot of clay suspension containing approximately 250 mg clay into a 100-

mL TFM vessel. The volume of required suspension depends on the clay concentration in the 

suspension, but is generally from 6 to 10 mL. More dilute suspensions should be partially 

evaporated under a fume hood to concentrate the clay prior to transfer to the Teflon container. 

7.4 Pipet a duplicate aliquot of suspension (as used in section 7.3) into a tared Al weighing 

dish, dry at 110°C, cool in a desiccator, and weigh to the nearest 0.1 mg. Use this value as the 

sample weight in the calculations. 

7.5 Dry the Teflon container and clay suspension in an oven for 4 h or until the aqueous portion 

of the suspension is completely evaporated. Remove from oven and cool on the bench top or in 

a fume hood. Cooling in a desiccator is not required. 

7.6 Pipet 9.0 mL HNO3 and 3.0 mL HCl into the sample and allow to completely wet and then 

pipet 4 mL HF into sample. Add acids in the fume hood. 

7.7 Place covered Teflon digestion vessels in protective sleeve, cover, and place into rotor. 

7.8 Place digestion rotor in the microwave oven and insert the temperature probe into the 

reference vessel. Attach the probe cable into the fitting in the top of the microwave. Connect 

the pressure monitor to the vessel. 

7.9 Microwave settings are as follows: 

1200 Watts, 100% power for 10 min (350 psi) to approximately 180°C 

1200 Watts, 70% power for 9.5 min (350 psi), holding at 180°C 

Cool (Vent) for 15 min 

7.10 After venting, disconnect temperature probe from microwave. 

7.11 Remove rotor from oven and place in fume hood. 

7.12 Open each vessel carefully, add 20 mL 4.5 percent boric acid (H3BO3) solution, then 

cover vessels and re-digest in microwave at: 1200 Watts, 100% power (350 psi) to 160°C, at 

160°C for 10 min. Cool (vent) for 15 min. 

7.13 Transfer contents of digestion vessel to a 100-mL nalgene volumetric flask and adjust to 

near volume with 1.9% boric acid, achieving a final concentration of 2.1 percent H3BO3.

7.14 Cap flask and mix well by inverting. Allow to stand overnight to dissolve any metal 

fluorides. Finish filling to volume with 1.9% boric acid. 

7.15 Invert the volumetric flask to mix and decant approximately 60 mL into a labeled 

polypropylene container. 

7.16 Prepare working standards of a blank, reference soil sample from the SSL repository, and 

a National Institute of Standards and Technology (NIST) standard reference or other reference 

material by the same digestion method. Run one of these standards with each set of 14 

samples. 

344
ICP-AES Calibration Standards, Set-up, and Operation 

7.17 Instrument calibration standards for analysis are limited to specific combinations of 

elements because of chemical incompatibilities of certain elements. Each working standard is 

used in two concentrations, high and low. The concentrations of elements in the low standards 

(CALO, ALLO, and SILO) are 50 percent of the concentrations in the high standards (CAHI, 

ALHI, and SIHI). The amounts of primary standards (1000 mg L-1) to make 500-mL volume 

of the low and high calibration standards, at the specified concentrations, for ICP-AES analysis 

are as follows: 

7.17.1 CALO is 75, 25, 20, and 10 mg L-1 of Ca, K, Mg, and Mn, respectively. To a 500- mL 

volumetic flask, add 37.5, 12.5, 10.0, and 5.0 mL of the Ca, K, Mg, and Mn primary 

standards (1000 mg L-1), respectively. 

7.17.2 CAHI is 150, 50, 40, and 20 mg L-1 of Ca, K, Mg, and Mn, respectively. To a 500-mL 

volumetric flask, add 75.0, 25.0, 20.0, and 10.0 mL of the Ca, K, Mg, and Mn primary 

standards (1000 mg L-1), respectively. 

7.17.3 ALLO is 100, 75, 5, 5, and 25 mg L-1 of Al, Fe, Ti, Zr, and Na, respectively. To a 500-

mL volumetric flask, add 50.0, 37.5, 2.5, 2.5, and 12.5 of the Al, Fe, Ti, Zr, and Na 

primary standards (1000 mg L-1), respectively. 

7.17.4 ALHI is 200, 150, 10, 10, and 50 mg L-1 of Al, Fe, Ti, Zr, and Na, respectively. To a 

500-mL volumetric flask, add 100.0, 75.0, 5.0, 5.0, and 25.0 mL of the Al, Fe, Ti, Zr, 

and Na primary standards (1000 mg L-1), respectively. 

7.17.5 SILO is 225 and 5 mg L-1 of Si and P, respectively. To a 500-mL volumetric flask, add 

112.5 and 2.5 mL of the Si and P primary standards (1000 mg L-1), respectively. 

7.17.6 SIHI is 450 and 10 mg L-1 of Si and P, respectivley. To a 500-mL volumetric flask, add 

225.0 and 5.0 mL of the Si and P primary standards (1000 mg L-1), respectivley. 

7.18 To the calibration standards and a blank, also add the following chemicals: 20.0 mL HF; 

45.0 mL HNO3; 15.0 mL HCl; and 10.90 g granular Boric Acid. Make all standards and the 

blank to a final 500-mL volume with RODI water. 

7.19 Use the ICP-AES in radial mode and analyze for the following elements: Fe, Mn, Al, Ca, 

Mg, Na, K, P, Si, Zr, and Ti. No initial dilutions of samples are necessary prior to analysis. 

Perform instrument checks (Hg alignment, BEC, %RSD of Mn solution) prior to analysis as 

discussed in operation manual of instrument. Check instrument alignment and gas pressures to 

obtain optimum readings with maximum signal to noise ratio. 

7.20 Analyses are generally performed at two or more wavelengths for each element. The 

selected wavelengths are as follows: (reported wavelength listed first and in bold): 

 Element Wavelength 

 ----------- nm --------- 

 

 Al 308.215, 396.157 

 Ca 315.887, 317.932 

 Fe 259.939, 238.205 

 K 766.490 

 Mg 280.271, 279.075 

 Mn 257.610, 260.570 

 Na 589.592, 588.995 

 P 178.221, 213.620 

 Si 212.412, 251.612 

 Ti 334.940, 368.522 

 Zr 339.197, 343.818 

 

345
7.21 Use the blank standard solution to dilute those samples with concentrations greater than 

the high standard. Rerun all elements and use only the data needed from the diluted analysis. 

7.22 Establish detection limits using the blank standard solution. These instrumental detection 

limits are calculated by using 3 times the standard deviation of 10 readings of the blank. These 

values establish the lower detection limits for each element. Analyzed values lower than the 

detection limits are set equal to zero. 

8. Calculations 

8.1 The calculation of mg kg-1 of an element in the soil from mg L-1 in solution is as follows: 

Analyte concentration in soil (mg kg-1) = [A x B x C x R x 1000]/E 

A = Sample extract reading (mg L-1) 

B = Extract volume (L) 

C = Dilution, if performed 

R = Air-dry/oven-dry ratio (procedure 3D1) 

1000 = Conversion factor in numerator to kg-basis 

E = Sample weight (g) 

8.2 Data are recorded on an elemental basis. Often users request data in an oxide form. The 

factor for converting from an elemental form to an oxide form is based on the atomic weights 

of the element and oxygen. An example is as follows: 

Atomic weight Si = 28.09 

Atomic Weight O = 16.0 

Molecular weight SiO2= 60.09 

Calculate percent Si in SiO2 as follows: 

Si (%) = (28.09/60.09) x 100 = 46.7 % 

There is 46.7 percent Si in SiO2. To convert from mg/kg Si to percent Si oxide (SiO2) in the 

soil, divide by 10,000 to convert from mg kg-1 to %, then divide the percent Si by 0.467 or 

multiply by the inverse of this value. The element, oxide form, and the elemental percent in the 

oxide form are as follows: 

Element Oxide Elemental 

 Form % 

 

Si SiO2 46.7 

Al Al2O3 52.9 

Fe Fe2O3 69.9 

Mg MgO 60.3 

Mn MnO 77.4 

K K2O 83.0 

Ti TiO2 59.9 

Ca CaO 71.5 

Zr ZrO2 74.0 

P P2O5 43.6 

Na Na2O 74.2 

346
9. Report

Analyses are generally performed at two or more wavelengths for each element, with 

the one selected wavelength for reporting purposes. The particle-size fraction digested needs to 

be identified with each sample. Data are reported to the nearest mg kg-1. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Bain, D.C., and B.F.L. Smith. 1994. Chemical analysis. p. 300-332. In M.J. Wilson (ed.) 

Clay mineralogy: Spectroscopic and chemical determinative methods. Chapman and 

Hall, Inc. London, England. 

Bernas, B. 1968. A new method for decomposition and comprehensive analysis of silicates 

by atomic absorption spectrometry. Anal. Chem. 40:1682-1686. 

Sawhney, B.L., and D.E. Stilwell. 1994. Dissolution and elemental analysis of minerals, 

soils, and environmental samples. p. 49-82. In J.E. Amonette and L.W. Zelazny (eds.) 

Quantitative methods in soil mineralogy. Soil Sci. Soc. Am. Misc. Publ. SSSA, 

Madison, WI. 

Washington, H.S. 1930. The chemical analysis of rocks. 4th ed. John Wiley and Sons, Inc., 

NY, NY. 

Total Analysis (4H) 

Dry Combustion (4H2) 

Thermal Conductivity Detector (4H2a) 

Total Carbon, Nitrogen, and Sulfur (4H2a1-3) 

Air-Dry, <2 mm (4H2a1-3a1) 

1. Application 

Organic Matter and Organic Carbon: Soil organic matter has been defined as the 

organic fraction of the soil exclusive of undecayed plant and animal residues and has been used 

synonymously with "humus" (Soil Science Society of America, 1987). However, for 

laboratory analyses, the soil organic matter generally includes only those organic materials that 

accompany soil particles through a 2-mm sieve (Nelson and Sommers, 1982). The organic 

matter content influences many soil properties, e.g., water retention capacity; extractable bases; 

capacity to supply N, P, and micronutrients; stability of soil aggregates; and soil aeration 

(Nelson and Sommers, 1996). 

Organic C is a major component of soil organic matter. Organic C consists of the cells 

of microorganisms; plant and animal residues at various stages of decomposition; stable 

"humus" synthesized from residues; and nearly inert and highly carbonized compounds, e.g., 

charcoal, graphite, and coal (Nelson and Sommers, 1982). As organic C is the major 

component of soil organic matter, a measurement of organic C can serve as an indirect 

determination of organic matter. Organic C determination is either by wet or dry combustion. 

In the past, the SSL used the wet combustion method, Walkley-Black modified aciddichromate digestion, FeSO4 titration, automatic titrator (6A1c, method obsolete, Soil Survey 

Staff, 1996). 

Values for organic C are multiplied by the "Van Bemmelen factor" of 1.724 to calculate 

organic matter. This factor is based on the assumption that organic matter contains 58% 

organic C. The proportion of organic C in soil organic matter for a range of soils is highly 

variable. Any constant factor that is selected is only an approximation. Studies have indicated 

that subsoils have a higher factor than surface soils (Broadbent, 1953). Surface soils rarely 

have a factor <1.8 and usually range from 1.8 to 2.0. The subsoil factor may average ≈ 2.5. 

The preference is to report organic C rather than to convert the organic C to organic matter 

through use of an approximate correction factor. 

347
The SSL also uses a direct determination of soil organic matter. The organic matter is 

destroyed, after which the loss in weight of the soil is taken as a measure of the organic matter 

content (5A). The percent organic matter lost on ignition (400°C) can be used in place of 

organic matter estimates by the Walkley-Black organic C method. 

Total Carbon: Total C is the sum of organic and inorganic C. Most of the organic C is 

associated with the organic matter fraction, and the inorganic C is generally found with 

carbonate minerals. The organic C in mineral soils generally ranges from 0 to 12% (Nelson 

and Sommers, 1996). 

Total C is quantified by two basic methods, i.e., wet or dry combustion. The SSL uses 

dry combustion (4H2a1). In total C determinations, all forms of C in a soil are converted to 

CO2 followed by a quantification of the evolved CO2. Total C can be used to estimate the 

organic C content of a soil. The difference between total and inorganic C is an estimate of the 

organic C. The inorganic C should be approximately equivalent to carbonate values measured 

by CO2 evolution with strong acid (Nelson and Sommers, 1996). In the SSL procedure 

4E1a1a1, the amount of carbonate in a soil is determined by treating a sample with HCl 

followed by manometrically measuring the evolved CO2. The amount of carbonate is then 

calculated as a CaCO3 equivalent basis. Organic C defines mineral and organic soils. In soil 

taxonomy, organic C is also used at lower taxonomic levels, e.g., ustollic and fluventic 

subgroups (Soil Survey Staff, 1999). 

Total Nitrogen: Total N includes organic and inorganic forms. The total N content of 

the soil may range from <0.02% in subsoils, 2.5% in peats, and 0.06 to 0.5% in surface layers 

of many cultivated soil (Bremmer and Mulvaney, 1982). The total N data may be used to 

determine the soil C:N ratio, the soil potential to supply N for plant growth, and the N 

distribution in the soil profile. The C:N ratio generally ranges between 10 to 12. Variations in 

the C:N ratio may serve as an indicator of the amount of soil inorganic N. Uncultivated soils 

usually have higher C:N ratios than do cultivated soils. 

Soils with large amounts of illites or vermiculties can “fix” significant amounts of N 

compared to those soils dominated by smectites or kaolinites (Young and Aldag, 1982; 

Nommik and Vahtras, 1982). Since the organic C of may soils diminishes with depth while the 

level of “fixed” N remains constant or increases, the C:N ratio narrows (Young and Aldag, 

1982). The potential to “fix” N has important fertility implications as the “fixed” N is slowly 

available for plant growth. 

Two methods of analysis of total N have gained acceptance for the determination of 

total N in soils. These include the Kjeldahl (1883) method, which is essentially a wet oxidation 

procedure and the Dumas (1831) method, which is fundamentally a dry oxidation (i.e., 

combustion) procedure (Bremmer, 1996). The SSL uses the combustion technique for analysis 

of total N (4H2a2).

Total Sulfur: Organic and inorganic S forms are found in soils, with the organic 

fraction accounting for >95% of the total S in most soils from humid and semi-humid 

(Tabatabai, 1996). Mineralization of organic S and its conversion to sulfate by chemical and 

biological activity may serve as a source of plant-available S. Total S typically ranges from 

0.01 to 0.05% in most mineral soils. In organic soils, total S may be >0.05%. The proportion 

of organic and inorganic S in a soil sample varies widely according to soil type and depth of 

sampling (Tabatabai, 1996). 

In well-drained, well-aerated soils, most of the inorganic S normally occurs as sulfate. 

In marine tidal flats, other anaerobic marine sediments, and mine spoils, there are usually large 

amounts of reduced S compounds that oxidize to sulfuric acid upon exposure to the air. In arid 

regions, significant amounts of inorganic S are found as sulfates such as gypsum and barite 

(Tabatabai, 1996). 

The typical use of total S is an index of the total reserves of this element, which may be 

converted to plant-available S. The SSL uses the combustion technique for analysis of total S 

(4H2a3). Extractable sulfate S (SO4

2-S) is an index of readily plant-available S. Reagents that 

have been used for measuring SO4

2-S include water, hot water, ammonium acetate, sodium 

carbonate and other carbonates, ammonium chloride and other chlorides, potassium phosphate 

348
and other phosphate, and ammonium fluoride (Bray-1). Extractable SO4

2-S does not include 

the labile fraction of soil organic S that is mineralized during the growing season (Tabatabai, 

1996). Extraction reagents for organic S include hydrogen peroxide, sodium bicarbonate, 

sodium hydroxide, sodium oxalate, sodium peroxide, and sodium pyrophosphate. There are 

other methods available for determination of S, especially for total S and SO4

2-S. The 

investigator may refer to the review by Beaton et al., (1968). 

For detailed discussion of the application of total C, N, and S, refer to Soil Survey Staff 

(1995). 

2. Summary of Method 

An air-dry (80 mesh, <180 μm) sample is packed in a tin foil, weighed, and analyzed 

for total C, N, and S by an elemental analyzer (procedures 4H2a1-3, respectively). The 

elemental analyzer works according to the principle of catalytic tube combustion in an 

oxygenated CO2 atmosphere and high temperature. The combustion gases are freed from 

foreign gases. The desired measuring components (N2, CO2, and SO2) are separated from each 

other with the help of specific adsorption columns and determined in succession with a thermal 

conductivity detector, with helium as the flushing and carrier gas. Percent total C, N, and S are 

reported by methods 4H2a1-3a1, respectively. 

3. Interferences 

Contamination through body grease or perspiration must be avoided in sample packing. 

Substance loss after weighing should be avoided by exact folding of the sample into the tin foil. 

Air in the sample material should be minimized (falsifying the N value) by compressing the 

sample packing. Insufficient O2 dosing reduces the catalysts, decreasing their effectiveness and 

durability. Burnt sample substance that remains in ash finger falsifies the results of subsequent 

samples. WO3 is used as sample additive and combustion filling to aid combustion or bind 

interfering substances (alkaline or earth-alkaline elements, avoid non-volatile sulfates). 

4. Safety 

Exhaust gas pipes should lead into a ventilated fume hood. Aggressive combustible 

products should not be analyzed. Before working on electrical connections (adsorption 

columns) or before changing reaction tubes, the instrument must be cooled down and cooled 

off. Gloves and safety glasses should be worn at all times during operation and maintenance of 

instrument. 

5. Equipment 

5.1 Elemental analyzer with on-line electronic balance (0.1± mg sensitivity) and automatic 

sample feeder, Elementar varioEL and Elementar varioEL III, Elementar 

Analysensysteme GmbH, Hanau-Germany, and combustibles (Elementar Americas, 

Inc., Mt. Laurel, NJ; Alpha Resources Inc., Stevensville, MI) as follows: 

5.1.1 Quartz ash finger, quartz

5.1.2 Quartz bridge

5.1.3 Combustion tube 

5.1.4 Reduction tube

5.1.5 Gas purification (U-tube, GL 18)

5.1.6 Support tube (65 mm)

5.1.7 Protective tube

5.1.8 O2 lance (150 mm rapid N)

5.1.9 Tin boats (4 x 4 x 11 mm)

5.1.10 Tin foil cups

5.2 Computer, with varioEL software, Elementar Analysensysteme GmbH, HanauGermany, and printer

349
6. Reagents 

6.1 Sulfanilic acid, calibration standard, 41.6% C, 4.1% H, 8.1 % N, 27.7% O, and 18.5% S 

6.2 Copper sticks 

6.3 Corundum balls, high purity, alumina spheres, 3 – 5 mm 

6.4 Cerium dioxide, 1 – 2 mm 

6.5 Tungsten oxide powder, sample additive

6.6 Tungsten trioxide granulate, combustion tube filling

6.7 Quartz wool

6.8 Silver wool

6.9 Phosphorus pentoxide, Sicapent, Elementar Americas, Inc., Mt. Laurel, NJ

6.10 Helium, carrier gas, 99.996% purity 

6.11 Oxygen, combustion gas, 99.995% purity 

7. Procedure 

Elemental Analyzer Set-up and Operation 

7.1 Refer to the manufacturer's manual for operation and maintenance of the elemental 

analyzer. Conditioning of the elemental analyzer and determination of factor and blank value 

limit are part of the daily measuring routine. The following are only very general guidelines for 

instrument parameters for the various analytes in the CNS mode. 

Temperature 

 Furnace 1 1140° C 

 Furnace 2 850 ° C 

 Furnace 3 0 ° C 

CO2 Column 85 ° C 

SO2 Column 210 ° C 

SO2 Col. Standby 140 ° C 

Timing 

 Flush 5 s 

 Oxygen Delay 10 s 

 Auto Zero Delay 30 s 

 Integrator Reset Delay 50 s 

 Peak Anticipation N 70 s 

 Peak Anticipation C 125 s 

 Peak Anticipation S 70 s 

Integrated Reset Delay for S 60 s 

Thresholds 

 N Peak 3 mV 

 C Peak 3 mV 

 S Peak 3 mV 

O2 Dosing 

 Index 1 150 s 

 Index 2 1 s 

 Index 3 90 s 

 Index 4 120 s 

 Index 5 180 s 

350
Elemental Analyzer Calibration and Analysis 

7.2 A calibration that covers the desired working range of each element is performed. The test 

substances sulfanilic acid with each given element content and different weights is analyzed. 

The PC program automatically computes the calibration function (linear, polynomial, or 

mixed). Calibration will typically remain stable for at least 6 months. Re-calibration is 

recommended when the daily factor is outside the range of 0.9 to 1.1 or if components that 

influence the results (e.g., detector or adsorption column) have been exchanged. Changing the 

desorption temperature of adsorption columns can also require a re-calibration. . 

7.3 Add 0.100 g of tungsten oxide in tin foil and tare. An homogenized fine-grind, air-dry soil 

sample is then packed in this tin foil, weighed (0.100 to 0.05 g), and placed into the carousel of 

the automatic sample feeder of elemental analyzer. Sample weight is based on visual 

observation of the sample, related to element content, homogeneity, and combustion behavior 

of the sample. The sample weight is entered in the PC from an on-line electronic balance via an 

interface. A quality control (QC) sample is performed at a minimum of every 35 to 40 

samples. 

8. Calculations 

C (%) = Ci x AD/OD 

where: 

C (%) = C (%), oven-dry basis 

Ci = C (%) instrument 

AD/OD = Air-dry/oven-dry ratio (procedure 3D1) 

N (%) = Ni x AD/OD 

where: 

N (%) = N (%), oven-dry basis 

Ni = N (%) instrument 

AD/OD = Air-dry/oven-dry ratio (procedure 3D1) 

S (%) = Si x AD/OD 

where: 

S (%) = S (%) on oven-dry basis 

Si = S (%) instrument 

AD/OD = Air-dry/oven-dry ratio (procedure 3D1) 

9. Report

Report total C and S percentage to the nearest 0.01% and total N to the nearest 0.001%. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Beaton, James D., G.R. Burns, and J. Platou. 1968. Determination of sulphur in soils and 

plant material. Tech. Bull. No. 14. The Sulfur Inst., Washington, DC. 

Bremmer, J.M. 1996. Nitrogen – Total. p. 1085 – 1121. In D.L. Sparks (ed.) Methods of 

soil analysis. Part 3. Chemical methods. No. 5. ASA and SSSA, Madison, WI. 

Bremmer, J.M., and C.S. Mulvaney. 1982. Nitrogen - Total. p. 595-624. In A.L. Page, 

R.H. Miller, and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and 

microbiological properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

351
Broadbent, F.E. 1953. The soil organic fraction. Adv. Agron. 5:153-183. 

Dumas, J.B.A. 1831. Procedes de l’analyse organique. Ann. Chim. Phys. 247:198-213. 

Kjeldahl, J. 1883. Neue Methode zur Bestimmung des Stickstoffs in organischen Korpern. 

Z. Anal. Chem. 22:366-382. 

Nelson, D.W., and L.E. Sommers. 1996. Total carbon, organic carbon, and organic matter. 

p. 961-1010. In D.L. Sparks (ed.) Methods of soil analysis. Part 3. Chemical methods. 

No. 5. ASA and SSSA, Madison, WI. 

Nommik, H., and K. Vahtras. 1982. Retention and fixation of ammonium and ammonia in 

soils. P. 123-171. In F.J. Stevenson (ed.) Nitrogen in agricultural soils. Agronomy 22, 

ASA and SSSA, Madison, WI. 

Soil Science Society of America. 1987. Glossary of soil science terms. Rev. ed. Soil Sci. 

Soc. Am., Madison, WI. 

Soil Survey Staff. 1996. Soil survey laboratory methods manual. Version No. 3.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, 

DC. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. 

Print. Office, Washington, DC. 

Tabatabai, M.A. 1996. Sulfur. p. 921-960. In D.L. Sparks (ed.) Methods of soil analysis. 

Part 3. Chemical methods. No. 5. ASA and SSSA, Madison, WI. 

Young, J.L., and R.W. Aldag. 1982. Inorganic forms of nitrogen in soil. p. 43-66. In F.J. 

Stevenson (ed.) Nitrogen in agricultural soils. Agronomy 22. ASA and SSSA, Madison, 

WI. 

Ground and Surface Water Analysis (4I) 

Reaction (4I1) 

Electrode (4I1a) 

Standard Glass Body Combination (4I1a1) 

Digital pH/Ion Meter (4I1a1a) 

pH (4I1a1a1) 

1. Application 

 The pH of a water sample is a commonly performed determination and one of the most 

indicative measurements of water chemical properties. The acidity, neutrality, or basicity is a 

key factor in the evaluation of water quality. 2. Summary of Method 

The pH of the water sample is measured with a calibrated combination electrode/digital 

pH meter (procedure 4I1a1a1). 

3. Interfernces 

Water pH needs to be measured immediately upon arrival at the laboratory in order to 

maintain optimal preservation of sample (Velthorst, 1996). 

4. Safety 

No significant hazards are associated with the procedure. Follow standard laboratory 

safety practices. 

5. Equipment 

5.1 Syringe filters, 0.45-μm diameter, Whatman, Cliffton, NJ 

5.2 Tubes, 50-mL, with caps 

5.3 Digital pH/ion meter, Accumet Model AR 15, Fisher Scientific 

5.4 Electrode, standard glass body combination, Accu-flow, Fisher Scientific 

352
6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

6.2 Borax pH buffers, pH 4.00, pH 7.00, and pH 9.18, for electrode calibration, Beckman, 

Fullerton, CA. 

7. Procedure 

7.1 Water sample is filtered into a 50-mL tube. If extracts are not to be determined 

immediately after collection, then store samples at 4° C. Analyze samples within 72 h. 

7.2 Calibrate the pH meter with pH 4.00, 7.00, and 9.18 buffer solutions. 

7.3 After equipment calibration, gently wash the electrode with RO water. Dry the electrode. 

Do not wipe the electrode with a tissue as this may cause a static charge on the electrode. 

7.4 Gently lower the electrode in the water sample until the KCl junction of the electrode is 

beneath the water surface. 

7.5 Allow the pH meter to stabilize before recording the pH. Record pH to the nearest 0.01 

unit. 

7.6 Gently raise the pH electrode and wash the electrode with a stream of RO water. 

8. Calculations 

No calculations are required for this procedure. 

9. Report 

Report the pH of the water sample to the nearest 0.1 pH unit. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

 Velthorst, E.J. 1996. Water analysis. p. 121-242. In P. Buurman, B. van Lagen, and E.J. 

Velthorst (eds.) Manual for soil and water analysis. Backhuys Publ. Leiden. 

Ground and Surface Water Analyses (4I) 

Electrical Conductivity and Salts (4I2) Conductivity Bridge and Cup (4I2a) 

Electrical Conductivity (4I2a1) 

1. Application 

Measuring electrical conductivity (EC) and total dissolved salts (TDS) is 

straightforward, but it is not in soils because salinity is significantly affected by the prevailing 

moisture content. A primary source of salts is chemical weathering of the minerals present in 

soils and rocks, with the most important including dissolution, hydrolysis, carbonation, 

acidification, and oxidation-reduction (National Research Council, 1993). All of these 

reactions contribute to an increase in the dissolved mineral load in the soil solution and in 

waters. 

2. Summary of Method 

The electrical conductivity of the water sample is measured using an electronic bridge 

(4I2a1). 

353
3. Interferences 

Reverse osmosis water is used to zero and flush the conductivity cell. The extract 

temperature is assumed to be 25°C. If the temperature deviates significantly, a correction may 

be required. 

Provide airtight storage of KCl solution and samples to prevent soil release of alkaliearth cations. Exposure to air can cause gains and losses of water and dissolved gases 

significantly affecting EC readings. 

4. Safety 

No significant hazards are associated with this procedure. Follow standard laboratory 

safety practices. 

5. Equipment 

5.1 Syringe filters, 0.45-μm diameter, Whatman, Cliffton, NJ 

5.2 Tubes, 50-mL, with caps 

5.3 Conductivity bridge and conductivity cell, with automatic temperature adjustment, 25 ±

0.1°C, Markson Model 1056, Amber Science, Eugene, OR 

6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

6.2 Potassium chloride (KCl), 0.010 N. Dry KCl overnight in oven (110°C). Dissolve 0.7456 

g of KCl in RODI water and bring to 1-L volume. Conductivity at 25°C is 1.412 mmhos 

cm-1. 

7. Procedure 

7.1 Water sample is filtered into a 50-mL tube and capped. If extracts are not to be determined 

immediately after collection, then store samples at 4° C. Analyze samples within 72 h. 

7.2 Standardize the conductivity bridge using RO water (blank) and 0.010 N KCl (1.41 mmhos 

cm

-1). 

7.3 Read conductance of water sample directly from the bridge. 

7.4 Record conductance to 0.01 mmhos cm-1. 

8. Calculations 

8.1 No calculations are required for this procedure. 

8.2 Use the following relationship to estimate the total soluble cation or anion concentration 

(meq L-1) in the water. 

EC (mmhos cm-1) x 10 = Cation or Anion (meq L-1) 

9. Report 

Report prediction conductance to the nearest 0.01 mmhos cm-1

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

354
11. References 

National Research Council. 1993. Soil and water quality. An agenda for agriculture. Natl. 

Acad. Press, Washington, DC. 

Ground and Surface Water Analyses (4I) 

Electrical Conductivity and Salts (4I2) Atomic Absorption Spectrophotometer (4I2b) 

Calcium, Magnesium, Potassium, and Sodium (4I2b1-4) 

1. Application 

Nutrients (nitrogen and phosphorus), sediments, pesticides, salts, or trace elements in 

ground and surface water affect soil and water quality (National Research Council, 1993). This 

procedure is developed for the analysis of ground or surface water. 

2. Summary of Method 

The water sample is filtered and diluted with an ionization suppressant (La2O3). The 

analytes are measured by an atomic absorption spectrophotometer (AAS). The data are 

automatically recorded by a computer and printer. The saturation extracted cations, Ca2+, 

Mg2+, K+, and Na+ are reported in meq L-1 (mmol (+) L-1) in procedures 4I2b1-4, respectively. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

analysis of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. Do not use borosilicate tubes because of potential leaching of 

analytes. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Thoroughly wash hands after handling these metal salts. 

Follow standard laboratory procedures when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene is highly flammable. Avoid open 

flames and sparks. Standard laboratory equipment includes fire blankets and extinguishers for 

use when necessary. Follow the manufacturer's safety precautions when using the AAS. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Syringe filters, 0.45-μm diameter, Whatman , Cliffton, NJ 

5.3 Tubes, 50-mL, with caps 

5.4 Atomic absorption spectrophotometer (AAS), double-beam, AAnalyst 300, Perkin-Elmer 

Corp., Norwalk, CT 

5.5 Autosampler, AS-90, Perkin-Elmer Corp., Norwalk, CT 

5.6 Computer, with AA WinLab software, Perkin-Elmer Corp., Norwalk, CT, and printer 

5.7 Single-stage regulator, acetylene 

5.8 Digital diluter/dispenser, with syringes 10000 and 1000 μL, gas tight, MicroLab 500, 

Hamilton Co., Reno, NV 

5.9 Plastic test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer 

5.10 Containers, polyethylene 

5.11 Peristaltic pump 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 Hydrochloric acid (HCl), concentrated 12 N

355
6.3 HCl, 1:1 HCl:RODI, 6 N. Carefully mix 1 part of concentrated HCl to 1 part RODI 

water. 

6.4 Stock lanthanum ionization suppressant solution (SLISS), 65,000 mg L-1. Wet 152.4 g of 

lanthanum oxide (La2O3) with 100 mL RODI water. Slowly and cautiously add 500 mL 

of 6 N HCl to dissolve the La2O3. Cooling the solution is necessary. Dilute to 2 L with 

RODI water. Filter solution. Store in polyethylene container. 

6.5 Working lanthanum ionization suppressant solution (WLISS), 2000 mg L-1. Dilute 61.5 

mL of SLISS with 1800 mL of RODI water (1:10). Make to 2-L volume with RODI 

water. Invert to mix thoroughly. Store in polyethylene container. 

6.6 Primary stock standards solution (PSSS), high purity, 1000 mg L-1: Ca, Mg, K, and Na. 

6.7 Working stock mixed standards solution (WSMSS) for Ca, Mg, and K. In a 500-mL 

volumetric flask, add 250 mL Ca PSSS, 25 mL Mg PSSS, and 100 mL K PSSS = 500 

mg L-1 Ca, 50 mg L-1 Mg, and 200 mg L-1 K. Dilute to volume with RODI water. Invert 

to thoroughly mix. Store in polyethylene containers. Prepare fresh weekly. Store in the 

refrigerator. 

6.8 Mixed calibration standards solution (MCSS), High, Medium, Low, Very Low, and Blank 

as follows: 

6.8.1 MCSS High Standard (1:100): Dilute WSMSS 1:100 with WLISS. Invert to mix 

thoroughly mix. Store in polyethylene containers. Prepare fresh weekly. Store in a 

refrigerator. Allow to equilibrate to room temperature before use. Final concentration = 5 

mg L-1 Ca, 0.5 mg L-1 Mg, and 2 mg L-1 K. 

6.8.2 MCSS Medium Standard (1:200): To a 100-mL volumetric flask, add 50 mL of WSMSS 

and bring to volume with RODI water. Dilute 1:100 with WLISS. Invert to thoroughly 

mix. Store in polyethylene containers. Prepare fresh weekly. Store in a refrigerator. 

Allow to equilibrate to room temperature before use. Final concentration =2.5 mg L-1 Ca, 

0.25 mg L-1 Mg, and 1 mg L-1 K. 

6.8.3 MCSS Low Standard (1:400): To a 100-mL volumetric flask, add 25 mL of WSMSS and 

bring to volume with RODI water. Dilute 1:100 with WLISS. Invert to mix thoroughly. 

Store in polyethylene containers. Prepare fresh weekly. Store in a refrigerator. Allow to 

equilibrate to room temperature before use. Final concentration = 1.25 mg L-1 Ca, 0.125 

mg L-1 Mg, and 0.5 mg L-1 K. 

6.8.4 MCSS Very Low Standard (1:600): To a 100-mL volumetric flask, add 16.65 mL of 

WSMSS and bring to volume with RODI water. Dilute 1:100 with WLISS. Invert to 

mix thoroughly. Store in polyethylene containers. Prepare fresh weekly. Store in a 

refrigerator. Allow to equilibrate to room temperature before use. Final concentration = 

0.83 mg L-1 Ca, 0.08 mg L-1 Mg, and 0.33 mg L-1 K. 

6.8.5 MCSS Blank = 0 mL of Ca, Mg, and K. Dilute RODI water 1:100 with WLISS. 

6.9 Na Calibration Standards Solution (NaCSS), High, Medium, Low, and Very Low as 

follows: 

6.9.1 NaCSS High Standard (1:100): Dilute Na PSMSS (1000 mg L-1) 1:100 with WLISS. 

Invert to thoroughly mix. Store in polyethylene containers. Prepare fresh weekly. Store 

in a refrigerator. Allow to equilibrate to room temperature before use. Final concentration 

= 10 mg L-1 Na. 

6.9.2 NaCSS Medium Standard (1:200): In a 50-mL volumetric, add 25 mL of Na PSMSS and 

bring to volume with RODI water. Dilute 1:100 with WLISS. Invert to mix thoroughly. 

356
Store in polyethylene containers. Prepare fresh weekly. Store in a refrigerator. Allow to 

equilibrate to room temperature before use. Final concentration = 5 mg L-1 Na. 

6.9.3 NaCSS Low Standard (1:400): In a 50-mL volumetric flask, add 12.5 mL of PSMSS and 

bring to volume with RODI water. Dilute 1:100 with WLISS. Invert to thoroughly mix. 

Store in polyethylene containers. Prepare fresh weekly. Store in a refrigerator. Allow to 

equilibrate to room temperature before use. Final concentration = 2.5 mg L-1 Na. 

6.9.4 NaCSS Very Low Standard (1:600) In a 50-mL volumetric flask, add 8.35 mL of PSMSS 

Na (1000 ppm) and bring to volume with RODI water. Dilute 1:100 with WLISS. Invert 

to thoroughly mix. Store in polyethylene containers. Prepare fresh weekly. Store in a 

refrigerator. Allow to equilibrate before use. Final concentration = 1.67 mg L-1 Na. 

6.9.5 NaCSS Blank = 0 mL Na PSMSS. Dilute RODI water 1:100 with WLISS. 

6.10 Compressed air with water and oil traps. 

6.11 Acetylene gas, purity 99.6%. 

7. Procedure 

7.1 Water sample is filtered into a 50-mL tube and capped. If extracts are not to be determined 

immediately after collection, then store samples at 4° C. Analyze samples within 72 h. 

Dilution of Calibration Standards and Sample Extracts 

7.2 The 10-mL syringe is for diluent (WLISS). The 1-mL syringe is for the MCSS and water 

sample. Set the digital diluter at a 1:100 dilution. See Sections 6.8 and 6.9 for preparation of 

the MCSS and NaCSS. Dilute the saturation extract sample with 100 parts of WLISS (1:100). 

7.3 Dispense the diluted sample solutions into test tubes which have been placed in the sample 

holders of the sample changer. 

AAS Set-up and Operation 

7.4 Refer to the manufacturer's manual for operation of the AAS. The following are only very 

general guidelines for instrument conditions for the various analytes. 

Analyte Conc. Burner Wavelength Slit Fuel/Oxidant 

 (mg L-1) & angle (nm) (mm) (C2H2/Air) ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Ca 5.0 10 cm @ 0° 422.7 0.7 1.5/0.0 

Mg 0.5 10 cm @ 0° 285.2 0.7 1.5/10.0 

K 2.0 10 cm @ 0° 766.5 0.7 1.5/10.0 

Na 10.0 10 cm @ 30° 589.0 0.2 1.5/10.0 

7.5 Use the computer and printer to set instrument parameters and to collect and record 

instrument readings. 

AAS Calibration and Analysis 

7.6 Calibrate the instrument by using the MCSS and NaCSS. The data system will then 

associate the concentrations with the instrument responses fore each MCSS and NaCSS. 

Rejection criteria for MCSS and NaCSS, if R2

 <0.99. 

7.7 If sample exceeds calibration standard, the sample is diluted 1:5, 1:20, 1:100, etc., with 

RODI water followed by 1:100 dilution with WLISS. 

357
7.8 Perform one quality control (QC) (Low Standard) for every 12 samples. If reading is not 

within 10%, the instrument is re-calibrated and QC re-analyzed. 

7.9 Record analyte readings to 0.01 mg L-1. 

8. Calculations 

The instrument readings for analyte concentration are in mg L-1. These analyte concentrations 

are converted to meq L-1 as follows: 

Analyte Concentration in Soil (meq L-1) = (A x B)/C 

where: 

A = Analyte (Ca, Mg, K, Na) concentration in extract (mg L-1) 

B = Dilution ratio, if needed 

C = Equivalent weight 

where: 

Ca+2 = 20.04 mg meq-1

Mg+2 = 12.15 mg meq-1

K+1 = 39.10 mg meq-1 

Na+1 = 22.99 mg meq-1

9. Report 

Report the saturation extraction cations of Ca2+, Mg2+, K+, and Na+ to the nearest 0.1 

meq L-1 (mmol (+) L-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

National Research Council. 1993. Soil and water quality. An agenda for agriculture. Natl. 

Acad. Press, Washington, DC. 

Ground and Surface Water Analyses (4I) 

Electrical Conductivity and Salts (4I2) Ion Chromatograph (4I2c) 

Conductivity Detector (4I2c1) 

Self-Regeneration Suppressor (4I2c1a) 

Bromide, Acetate, Chloride, Fluoride, Nitrate, Nitrite, Phosphate, and Sulfate (4I2c1a1-8) 

1. Application 

Nutrients (nitrogen and phosphorus), sediments, pesticides, salts, or trace elements in 

ground and surface water affect soil and water quality (National Research Council, 1993). This 

procedure is developed for the analysis of ground or surface water. 

2. Summary of Method 

The water sample is filtered and is diluted according to its electrical conductivity (ECs). 

The diluted sample is injected into the ion chromatograph, and the anions are separated. A 

conductivity detector is used to measure the anion species and content. Standard anion 

concentrations are used to calibrate the system. A calibration curve is determined, and the 

anion concentrations are calculated. A computer program automates these actions. The water 

358
anions, Br-

, CH3COO-, Cl-, F-, NO3

-

, NO2

-

, PO4

3-, SO42- are reported in meq L-1 (mmol (-) L-1) 

by procedure 4I2c1a1-8, respectively. 

3. Interferences 

Some water samples contain suspended solids and require filtering. Low molecular 

weight organic anions will co-elute with inorganic anions from the column. 

4. Safety 

Wear protective clothing and safety glasses. When preparing reagents, exercise special 

care. Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash 

hands after handling these metal salts. Follow the manufacturer's safety precautions when 

using the chromatograph. 

5. Equipment 

5.1 Syringe filters, 0.45-μm diameter, Whatman, Cliffton, NJ 

5.2 Tubes, 50-mL, with caps 

5.3 Guard column, IonPac AG14, 4 x 50 mm, Dionex Corp., Sunnyvale, CA 

5.4 Analytical column, IonPac AS14, 4 x 250 mm, Dionex Corp., Sunnyvale, CA 

5.5 Self-regeneration suppressor, ASRS – ULTRA, 4 mm, Dionex Corp., Sunnyvale, CA 

5.6 Autosampler, AS40, Dionex Corp., Sunnyvale, CA 

5.7 Computer with PeakNet software and printer 

5.8 Digital diluter/dispenser, with syringes 10000 and 1000 μL, gas tight, MicroLab 500, 

Hamilton Co., Reno, NV 

5.9 Poly-vials with caps, 5 mL, Dionex Corp., Sunnyvale, CA 

6. Reagents 

6.1 Reverse osmosis deionized filtered (RODI), ASTM Type I grade of reagent water 

6.2 Helium gas 

6.3 Eluent solution. Solution A: Mix 5.30 g of Na2CO3 with RODI water in a 500-mL 

volumetric and make to volume with RODI water. Solution B: Mix 4.20 g of NaHCO3

with RODI water in a 500-mL volumetric and make to volume with RODI water. Add 

35 mL of Solution A and 10 mL of Solution B in a 1-L volumetric and make to volume 

with RODI water for a final concentration is 0.024 M Na2CO3 and 0.025 M NaHCO3. Make 2 L of eluent solution if chromatograph is to run overnight. Place eluent in eluent 

tank and degas with helium 15 min L-1 eluent (30 min total). Make fresh daily. 

6.4 Primary stock standards solutions, (PSSS1000), high purity, 1000 mg L-1: Cl-, SO4

2-, F-

, 

NO3

-

, NO2

-

, Br-, CH3COO-, and PO4

3-. 6.5 Primary stock standards solutions (PSSS100), 100 mg L-1: F-

, NO3

-

, NO2

-

, Br-, and PO4

3-. 

Prepare fresh weekly. In five 250-mL volumetric flasks add as follows: 

6.5.1 F- PSSS100 = 25 mL F- PSSS1000

6.5.2 Br- PSSS100 = 25 mL Br- PSSS1000 

6.5.3 NO2

-

 PSSS100 = 25 mL NO2

-

 PSSS1000 

6.5.4 NO3

-

 PSSS100 = 25 mL NO3

-

 PSSS1000 

6.5.5 PO4

3- PSSS100 = 25 mL PO43- PSSS1000 

Dilute each PSSS100 to volume with RODI water and invert to thoroughly mix. Store in the 

refrigerator. 

6.6 Mixed calibration standards solutions (MCSS), A, B, C, D, E, and Blank as follows: 

6.6.1 MCSSA = In a 250-mL volumetric flask, add as follows 

359
12.5 mL Cl-

 PSSS1000 = 50 mg L-1

25 mL SO4

2

 PSSS1000 = 100 mg L-1

12.5 mL F- PSSS100 = 5 mg L-1

20 mL NO3

-

 PSSS100 = 8 mg L-1

20 mL NO2

-

 PSSS100 = 8 mg L-1

22 mL Br- PSSS100 = 8.8 mg L-1

20 mL CH3COO- PSSS1000 = 80 mg L-1

24 mL PO4

3- PSSS100 = 9.6 mg L-1

Dilute to volume with RODI water and invert to thoroughly mix. Store in glass containers. 

Store in the refrigerator. Prepare fresh weekly. 

6.6.2 MCSSB = In a 100-mL volumetric flask, add 40 mL MCSSA and dilute to volume with 

RODI water. Final concentration = 20, 40, 2, 3.2, 3.2, 3.52, 30.4, and 3.52 mg L-1 Cl-, SO4

2-, F-

, NO3

-

, NO2

-

, Br-, CH3COO-, and PO4

3-, respectively. Invert to thoroughly mix. 

Store in glass containers. Prepare fresh weekly. Store in the refrigerator. 

6.6.3 MCSSC = In a 100-mL volumetric flask, add 20 mL MCSSA and dilute to volume with 

RODI water. Final concentration = 10, 20, 1, 1.6, 1.6, 1.76, 15.2, and 1.76 mg L-1 Cl-

, 

SO4

2-, F-

, NO3

-

, NO2

-

, Br-, CH3COO-, and PO4

3-, respectively. Invert to thoroughly mix. 

Store in glass containers. Prepare fresh weekly. Store in the refrigerator. 

6.6.4 MCSSD = In a 250-mL volumetric flask, add 25 mL MCSSA and dilute to volume with 

RODI water. Invert to thoroughly mix. Final concentration = 5, 10, 0.5, 0.8, 0.8, 0.88, 

7.6, and 0.88 mg L-1 Cl-

, SO4

2-, F- , NO3-

, NO2

-

, Br-, CH3COO-, and PO4

3-, respectively. 

Store in glass containers. Prepare fresh weekly. Store in the refrigerator. 

6.6.5 MCSSE = In a 250-mL volumetric flask, add 5 mL MCSSA and dilute to volume with 

RODI water. Final concentration = 1, 2, 0.1, 0.16, 0.16, 0.176, 1.52, and 0.176 mg L-1

Cl-, SO4

2-, F- , NO3-

, NO2

-

, Br-, CH3COO-, and PO4

3-, respectively. Invert to thoroughly 

mix. Store in glass containers. Prepare fresh weekly. Store in the refrigerator. 

6.6.6 MCSS Blank = 0 mL of Cl-, SO4

2-, F-

, NO3

-

, NO2

-

, Br-, CH3COO-, and PO4

3-. Dilute 

RODI water to volume. 

7. Procedure 

7.1 Water sample is filtered into a 50-mL tube and capped. If extracts are not to be determined 

immediately after collection, then store samples at 4° C. Analyze samples within 72 h. 

Dilution of sample extracts 

7.2 To estimate the total soluble anion concentration (meq L-1), multiply the EC (procedure 

4I2a1) by 10. Subtract the CO3

2- and HCO3-

 concentrations (procedures 4I2d1a1-2) from the 

total anion concentration. The remainder is the ≈ concentration (meq L-1) of anions to be 

separated by ion chromatography. 

Anion concentration (meq L-1) = ECs x 10 - (HCO3

-

 + CO3

2-) 

7.2 Dilute the saturation extract with the RODI water as follows: 

360
ECs (dS cm-1) Dilution Factor

 0.00 to 0.55 4 

 0.56 to 0.65 5 

 0.66 to 0.75 6 

 0.76 to 0.85 7 

 0.86 to 0.95 8 

 0.96 to 1.05 9 

 1.06 to 1.20 10 

 1.21 to 1.40 15 

 1.41 to 1.50 25 

 1.51 to 1.60 30 

 1.61 to 1.80 40 

 1.81 to 2.00 50 

 2.01 to 2.30 60 

 2.31 to 2.60 70 

 2.61 to 3.10 80 

 3.11 to 3.55 90 

 3.56 to 4.05 100 

 4.06 to 4.60 120 

 4.61 to 5.20 140 

 5.21 to 5.85 150 

 5.86 to 6.55 160 

 6.56 to 7.30 180 

 7.31 to 8.00 200 

 8.01 to 9.00 225 

 9.01 to 10.00 240 

 10.01 to 11.50 270 

 11.51 to 13.00 280 

 13.01 to 14.50 300 

 14.51 to 16.00 320 

 16.01 to 17.00 360 

 17.01 to 18.00 400 

 18.01 to 20.00 450 

 20.01 to 21.00 480 

 21.01 to 23.00 500 

 23.01 to 24.00 540 

 24.01 to 25.00 560 

 25.01 to 27.00 600 

 27.01 to 28.00 640 

 28.01 to 30.00 680 

 30.01 to 32.00 700 

 32.01 to 33.00 720 

 33.01 to 36.00 800 

 36.01 to 40.00 900 

 40.01 to 44.00 1000 

361
7.3 Place the MCSS (B, C, D, E, Blank) and diluted extract samples in the Poly-vials and cap 

with filtercaps. 

Set-up and Operation of Ion Chromatograph (IC) 

7.4 Refer to the Manufacturer's manual for the operation of chromatograph. Because any 

number of factors may cause a change in IC operating conditions, only a general set-up of the 

Dionex DX-120 ion chromatograph is presented. Individual analysts may modify some or all 

of the operating conditions to achieve satisfactory results. Ranges and/or (typical settings) are 

as follows: 

Parameter Range and/or (Typical Setting) 

Calibration Peak Height or (Area) 

Flow Setting 0.5 to 4.5 mL min-1 (1.63 mL min-1) 

Pressure 0 to 4000 psi (2200 to 2400 psi) 

Detection Suppressed conductivity 

Total Conductivity 0 to 999.9 μS 

Injection Volume 10 μL 

Auto Offset -999.9 to 999.9 μS (ON) 7.5 Load the sample holder cassettes with the capped samples, standards, and check samples. 

7.6 Use the computer and printer to set instrument parameters and to collect and record 

instrument readings. 

IC Calibration and Analysis 

7.7 Calibrate the instrument by using the MCSS (B, C, D, E, Blank). The data system will then 

associate the concentrations with the instrument responses for each MCSS. Rejection criteria 

for MCSS, R2

 <0.99. 

7.8 If samples are outside calibration, dilute sample extracts with RODI water solution and reanalyze. 

7.9 Perform one quality control (QC) (Low Standard MCSS, Standard C) for every 12 

samples. If reading is not within tolerance limits (10 to 15%, based on analyte), the instrument 

is re-calibrated and QC re-analyzed. 

7.10 Record analyte readings to 0.01 mg L-1. 

8. Calculations 

The instrument readings for analyte concentration are in mg L-1. These analyte concentrations 

are converted to meq L-1 as follows: 

Analyte Concentration in Soil (meq L-1) = (A x B)/C 

where: 

A = Analyte (Br-, CH3COO-, Cl-, F-, NO3

-

, NO2

-

, PO4

3-, SO42-) concentration in extract (mg L-1) 

B = Dilution ratio, if needed 

C = Equivalent weight 

where: 

Cl- = 35.45 mg meq-1

SO4

2- = 48.03 mg meq-1

362
F-

 = 19.00 mg meq-1

NO3

-

 = 62.00 mg meq-1

NO2

-

 = 46.00 mg meq-1

Br- = 79.90 mg meq-1

CH3COO- = 59.05 mg meq-1

PO4

3- = 31.66 mg meq-1

9. Report 

Report the saturation extraction anions (Br-, CH3COO-, Cl-, F-, NO3

-

, NO2

-

, PO4

3-, SO42

) 

to the nearest 0.1 meq L-1 (mmol (-) L-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

National Research Council. 1993. Soil and water quality. An agenda for agriculture. Natl. 

Acad. Press, Washington, DC. 

Ground and Surface Water Analyses (4I) 

Electrical Conductivity and Salts (4I2) Automatic Titrator (4I2d) 

Combination pH-Reference Electrode (4I2d1) 

Acid Titration, H2SO4 (4I2d1a) Carbonate and Bicarbonate (4I2d1a1-2) 

1. Application 

Nutrients (nitrogen and phosphorus), sediments, pesticides, salts, or trace elements in 

ground and surface water affect soil and water quality (National Research Council, 1993). This 

procedure is developed for the analysis of ground or surface water. 

2. Summary of Method The water sample is filtered and aliquot titrated on an automatic titrator to pH 8.25 and 

pH 4.60 end points. The carbonate and bicarbonate are calculated from the titers, aliquot 

volume, blank titer, and acid normality. Carbonate and bicarbonate are reported in meq L-1

(mmol (-) L-1) by procedures 4I2d1a1-2, respectively. 

3. Interferences 

Clean the electrode by rinsing with distilled water and patting it dry with tissue. Wiping 

the electrode dry with a cloth, laboratory tissue, or similar material may cause electrode 

polarization. 

Slow electrode response time may cause over shooting the end point. A combination of 

slowing the buret speed and increasing the time delay may help. Cleaning the electrode with 

detergent may decrease the response time. If all else fails, changing the electrode generally 

solves the problem. Blanks may not titrate properly because some sources of reverse osmosis 

(RO) water have a low pH. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise care. 

Thoroughly wash hands after handling reagents. Restrict the use of concentrated H2SO4 to the 

fume hood. Use showers and eyewash stations to dilute spilled acids. Use sodium bicarbonate 

and water to neutralize and dilute spilled acids. Follow the manufacturer's safety precautions 

when operating the automatic titrator. 

363
5. Equipment 

5.1 Syringe filters, 0.45-μm diameter, Whatman, Cliffton, NJ 

5.2 Tubes, 50-mL, with caps 

5.3 Automatic titrator, Metrohm 670 Titroprocessor, with control unit, sample changer, and 

dispenser, Metrohm Ltd., Brinkmann Instruments, Inc. 

5.4 Combination pH-reference electrode, Metrohm Ltd., Brinkmann Instruments, Inc. 

5.5 Pipettes, electronic digital, 2500 μL and 10 mL, with tips, 2500 μL and 10 mL 

6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

6.4 Helium gas 

6.3 Sulfuric acid (H2SO4), concentrated, 36 N

6.5 H2SO4, 0.0240 N standardized. Carefully dilute 2.67 mL of concentrated H2SO4 in 4 L of 

RODI degassed water (≈ 15 min). Re-standardize the acid at regular intervals. Refer to 

the procedure for standardization of acids. 

6.4 Borax pH buffers, pH 4.00, pH 7.00, and pH 9.18, for titrator calibration, Beckman, 

Fullerton, CA. 

7. Procedure 

7.1 Water sample is filtered into a 50-mL tube and capped. If extracts are not to be determined 

immediately after collection, then store samples at 4° C. Analyze samples within 72 h. 

7.2 Pipet 3 mL of the water sample into a 250-mL titration beaker. 

7.3 Add 72 mL of RO water into a titration beaker. Final volume is 75 mL for blanks and 

samples. Run 8 to 12 blanks of RO water through the titration procedure. 

 

7.4 Refer to manufacturer's manual for operation of the automatic titrator. 

7.5 Calibrate automatic titrator with 9.18, 7.00 and 4.00 pH buffers. Set-up the automatic 

titrator to set end point titration mode. The "Set" pH parameters are listed as follows: 

Parameter Value

Ep1 pH 8.25 

Dyn change pH 1.5 units 

Drift 0.4 mV s-1

Time delay 10 s 

Ep2 pH 4.60 

Dyn change pH 1.5 units 

Drift 0.4 mV s-1

Temp 25°C 

Stop Volume 35 mL 

7.6 Place the 250-mL titration beakers in the sample changer. 

7.7 Press "Start". 

7.8 If the titrator is operating properly, no other analyst intervention is required. The titers and 

other titration parameters are recorded on the Titroprocessor printer. 

364
8. Calculations 

8.1 CO3

2- (meq L-1) =(2 T1 x N x 1000)/Aliquot 

8.2 HCO3

-

 (meq L-1) = [(T2 + T1) - Blank – (2 x T1) x N x 1000]/Aliquot 

where: 

T1 = Titer of CO3

2- (mL) 

T2 = Titer of HCO3

-

 (mL) 

N = Normality of H2SO4

Blank = Average titer of blank solutions (mL) 

Aliquot = Volume of saturation extract titrated (mL) 

1000 = Conversion factor to meq L-1

9. Report

Report saturation extract CO3

2- and HCO3-

 to the nearest 0.1 meq L-1 (mmol (-) L-1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

National Research Council. 1993. Soil and water quality. An agenda for agriculture. Natl. 

Acad. Press, Washington, DC. 

Ground and Surface Water Analyses (4I) 

Total Analysis (4I3) 

Inductively Coupled Plasma Atomic Emission Spectrophotometer (4I3a) Axial Mode (4I3a1) 

Ultrasonic Nebulizer (4I3a1a) Aluminum, Iron, Manganese, Phosphorus, and Silicon (4I3d1a1-5) 

1. Application 

Nutrients (nitrogen and phosphorus), sediments, pesticides, salts, or trace elements in 

ground and surface water affect soil and water quality (National Research Council, 1993). This 

procedure is developed for the analysis of ground or surface water. This procedure is developed 

for the analysis of the elemental content of ground or surface water. 

2. Summary of Method 

The water is filtered and acidified with HCl. Two calibration standards plus a blank are 

prepared for elemental analysis. An inductively coupled plasma atomic emission 

spectrophotometer (ICP-AES) in axial mode is used to determine the concentration of Al, Fe, 

Mn, P, and Si (mg L-1) by procedures 4I3d1a1-5, respectively. 

3. Interferences 

Spectral and matrix interferences exist. Interferences are corrected or minimized by 

using an internal standard. Also, careful selection of specific wavelengths for data reporting is 

important. Samples and standards are matrix matched to help reduce interferences. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated acids to the fume hood. Wash hands thoroughly after 

handling reagents. 

365
5. Equipment 

5.1 Syringe filters, 0.45-μm diameter, Whatman, Cliffton, NJ

5.2 Tubes, 50-mL, with caps 

5.3 Volumetrics, 500-mL and 200 ml, class A glass 

5.4 Containers, 500-mL, polypropylene, with screw caps 

5.5 Pipettors, electronic digital, Rainin Instrument Co., Woburn, MA, 2500 μL and 10 mL 

5.6 Inductively coupled plasma atomic emission spectrophotometer (ICP-AES), Perkin-Elmer 

Optima 3300 Dual View (DV), Perkin-Elmer Corp., Norwalk, CT. 

5.7 Computer, with WinLab software, ver. 4.1, Perkin-Elmer Corp., Norwalk, CT, and 

printer 

5.8 Compressed gasses, Argon (minimum purity=99.996%) and Nitrogen (minimum 

purity=99.999%) 

5.9 Autosampler, AS-90, Perkin-Elmer Corp., Norwalk, CT. 

5.10 Quartz torch, alumina injector (2.0 mm id), Ultrasonic Nebulizer, Model U-5000AT+ , 

CETAC Corp., Omaha, NE 

6. Reagents 

6.1 Deionized, reverse osmosis (RODI) water, ASTM Type 1 grade of reagent water 

6.2 Concentrated hydrochloric acid (HCl), 12 N. Use trace-pure grade that contains low 

levels of impurities. 

6.3 Primary standards:1000 mg L-1, High Purity Standards, Charleston, SC. Single elemental 

standards are manufactured in dilute HNO3, HNO3 + HF, or H2O 

6.4 Internal standard: HNO3, trace pure 

7. Procedure 

7.1 Water sample is filtered into a 50-mL tube and capped. If extracts are not to be determined 

immediately after collection, then store samples at 4° C. Analyze samples within 72 h. 

7.2 The working calibration standards (WCS) are made from dilution of the primary standards. 

The low and high WCS for Al and Si are prepared as follows: 

7.2.1 ALLO is 0.5, 2.5, and 2.5 mg L-1 of Al, Fe, and Mn, respectively. To a 500-mL 

volumetric flask, add 0.25, 1.25, and 1.25 mL of the Al, Fe, and Mn primary standard 

(1000 mg L-1), respectively. 

7.2.2 ALHI is is 1.0, 5.0, and 5.0 mg L-1 of Al, Fe, and Mn, respectively. To a 500-mL 

volumetric flask, add 0.50, 2.50, and 2.50 mL of the Al, Fe, and Mn primary standard 

(1000 mg L-1), respectively. 

7.2.3 SILO is 0.5 and 0.5 mg L-1 of Si and P, respectively. To a 500-mL volumetric flask, add 

0.25 and 0.25 mL of the Si and P primary standard (1000 mg L-1), respectively. 

7.2.4 SIHI is 1.0 and 1.0 mg L-1 of Si and P, respectively. To a 500-mL volumetric flask, add 

0.50 and 0.50 mL of the Si and P primary standard (1000 mg L-1), respectively. 

7.3 Samples are treated with 0.5 mL HCl for each 10 mL water. 

7.4 A 10 mg L-1 Lu internal standard (read at 291.138 nm) is added to the blank, all calibration 

standards, and samples. It is prepared by adding 5.0 mL Lu primary standard (1000 mg L-1) 

and 10 mL conc. HNO3 to a 500 ml volumetric flask, and diluting to volume with RODI water. 

7.5 Use the ICP-AES spectrophotometer in axial mode to analyze elements. Use ultrasonic 

nebulization of sample. Internal standard is added via an external peristaltic pump at 15% 

pump speed using 0.44 mm id. pump tubing. Internal standard and samples or standards are 

mixed via a mixing block and coil prior to entering the ultrasonic nebulizer. Typically, no 

366
initial dilutions of samples because of high concentrations are necessary prior to analysis. 

Perform instrument checks (Hg alignment; BEC and %RSD of 1 mg L-1 Mn solution) prior to 

analysis as discussed in operation manual of instrument. Check instrument alignment and gas 

pressures to obtain optimum readings with maximum signal to noise ratio. 

7.6 Analyses are generally performed at two or more wavelengths for each element. The 

selected wavelengths are as follows: (reported wavelength listed first and in boldface): 

 Element Wavelength 

 ----------- nm --------- 

 Mn 260.570, 257.610, 403.075 

 P 178.221, 213.620, 214.910 

 Al 308.215, 167.022, 396.153 

 Fe 238.203, 239.562, 259.939 

 Si 251.611, 212.412, 288.158

 Lu 291.138 (Internal Standard) 

7.7 Use the blank standard solution to dilute those samples with concentrations greater than the 

high standard. Rerun all elements and use only the data needed from the diluted analysis. 

7.8 Establish detection limits using the blank standard solution. The instrumental detection 

limits are calculated by using 3 times the standard deviation of 10 readings of the blank. These 

values establish the lower detection limits for each element. Analyzed values lower than the 

detection limits are reported as "ND" or non-detected. 

8. Calculations 

With the HCl treatment (0.5 mL per 10 mL water) in the calculations, the 

concentrations are then reported directly, unless additional dilutions are performed because of 

high analyte concentrations. 

9. Report

Data are reported to the nearest 0.01 mg L-1. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

National Research Council. 1993. Soil and Water Quality. An agenda for agriculture. Natl. 

Acad. Press, Washington, DC. 

367
ANALYSIS OF ORGANIC SOILS OR MATERIALS (5) 

Mineral Content (5A) 

1. Application 

The mineral content is the plant ash and soil particles that remain after organic matter 

removal. The percentage of organic matter lost on ignition can be used to define organic soils 

in place of organic matter estimates by the Walkley-Black organic C method (6A1c, method 

obsolete, Soil Survey Staff, 1996). The determination of organic matter by loss on ignition is a 

taxonomic criterion for organic soil materials (Soil Survey Staff, 1999). Organic C data by 

Walkley-Black are generally considered invalid if organic C is >8 %. 

2. Summary of Method 

Dry sample overnight at 110°C in moisture can. Cool and weigh. Place sample in a 

cold muffle furnace and raise the temperature to 400°C. Heat sample overnight (16 h), cool, 

and weigh. The ratio of the weights (400°C/110°C) is the mineral content percentage 

(procedure 5A). 

3. Interferences 

The sample must be placed in a cold muffle furnace to prevent rapid combustion and 

sample splattering. 

4. Safety 

Use caution when the muffle furnace is hot. Wear protective clothing and goggles. 

Handle the heated material with tongs. 

5. Equipment 

5.1 Metal weighing tins 

5.2 Oven, 110°C 

5.3 Muffle furnace, 400°C 

5.4 Electronic Balance, ±0.01-g sensitivity 

6. Reagents 

None. 

7. Procedure 

7.1 Place a 10- to 15-g sample in a tared weighing tin. 

7.2 Dry sample at 110°C overnight. 

7.3 Remove sample from oven, cap, and cool in a desiccator. 

7.4 When cool, record weight to nearest 0.01 g. 

7.5 Place sample and weighing tin in a cold muffle furnace. Raise temperature to 400°C. Heat 

overnight (16 h). 

7.6 Remove sample from oven, cap, and cool in a desiccator. 

7.7 When cool, record sample weight to nearest 0.01 g. 

368
8. Calculations 

8.1 Mineral Content (%) = (RW/ODW) x 100 

where: 

RW = Residue weight after ignition 

ODW = Oven-dry soil weight 

Organic matter percent can then be calculated as follows: 

8.2 Organic Content (%) = 100 - Mineral Content (%) 

9. Report

Report mineral content to the nearest whole percent. 

10. Accuracy and Precision 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Soil Survey Staff. 1996. Soil survey laboratory methods manual. Version No. 3.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, 

DC. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. 

Print. Office, Washington, DC. 

Pyrophosphate Color (5B) 

1. Application 

Decomposed organic materials are soluble in sodium pyrophosphate. The combination 

of organic matter and sodium pyrophosphate form a solution color which correlates with the 

decomposition state of the organic materials. Dark colors are associated with sapric materials 

and light colors with fibric materials (Soil Survey Staff, 1999). 

2. Summary of Method 

Organic material is combined with sodium pyrophosphate. After standing, the color is 

evaluated by moistening a chromatographic strip in the solution and comparing the color with 

standard Munsell color charts (5B). 

3. Interferences 

This test of organic soil material can be used in field offices. Since it is not practical in 

the field to base a determination on a dry sample weight, moist soil is used. The specific 

volume of moist material depends on how it is packed. Therefore, packing of material must be 

standardized in order to obtain comparable results by different soil scientists (Soil Survey Staff, 

1999). 

4. Safety 

Use caution when handling sodium pyrophosphate. 

5. Equipment 

5.1 Polycons, 30 mL, Richards Mfg. Co. 

5.2 Chromatographic paper, Schleicher and Schuell no. 470 A-3. 

5.3 Munsell Color Book, 10YR and 7.5YR pages. 

369
5.4 Half-syringe, 6 mL. Cut plastic syringe longitudinally to form a half-cylinder measuring 

device. 

5.5 Scissors 

5.6 Paper towel 

5.7 Tweezers 

5.8 Metal spatula 

6. Reagents 

6.1 Sodium pyrophosphate (Na4P2O7·10H2O) 

6.2 Reverse osmosis (RO) water 

7. Procedure 

Sample Preparation

7.1 Prepare soil material. If the soil is dry, add water and let stand to saturate. Place 50 to 60 

mL of a representative sample on a paper towel in a linear mound. Roll the towel around the 

sample and express water if necessary. Use additional paper towels as external blotters. 

Remove the sample and place on a fresh paper towel. The sample should be firm but saturated 

with water. 

7.2 Use scissors to cut sample into 5- to 10-mm long segments. 

7.3 Randomly select sample segments for determination of fiber (5C), solubility in 

pyrophosphate (5B), and pH (4C1a1a4). 

Pyrophosphate

7.4 Dissolve 1 g (heaping 1/8 tsp) of sodium pyrophosphate in 4 mL of water in a 30-mL 

polycon container. Allow to equilibrate for 5 min. 

7.5 Use a metal spatula to pack a half-syringe that is adjusted to the 5-mL mark or 2.5-mL (2.5-

cm3

) volume with the moist sample. 

7.6 Transfer soil material cleanly into the container that holds the pyrophosphate solution. 

7.7 Mix thoroughly using a wooden stirrer or metal spatula. Cover and let stand overnight. 

7.8 Mix sample again next morning. 

7.9 Use tweezers to insert a strip of chromatographic paper vertically into the sample to a 1-cm 

depth. Let stand until the paper strip has wetted to a 2-cm height above slurry surface. 

Generally, sample needs to stand ≈ 5 min but may stand longer if cover is closed. Remove the 

paper strip with tweezers. Cut strip and leave in the slurry that portion to which the soil 

adheres. 

7.10 Place the strip on a piece of blotting paper and press gently with tweezers to make even 

contact. 

7.11 Remove paper strip with tweezers and compare color of the strip to Munsell color charts. 

8. Calculations 

No calculations. 

9. Report

Report color using Munsell color notation. 

370
10. Precision and Accuracy 

Precision and accuracy data are not available for this procedure. Experienced analysts 

can usually reproduce results within ± 1 color chip. 

11. References 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. 

Print. Office, Washington, DC. 

Fiber Volume (5C) 

1. Application 

The water-dispersed fiber volume is a method to characterize the physical 

decomposition state of organic materials. The decomposition state of organic matter is used in 

soil taxonomy to define sapric, hemic, and fibric organic materials (Soil Survey Staff, 1999). 

Sapric material passes through a 100-mesh sieve (0.15-mm openings). Fibers are retained on 

the sieve. As defined in soil taxonomy, organic materials that are >2 mm in cross section and 

that are too firm to be readily crushed between thumb and fingers are excluded from fiber. 

2. Summary of Method 

The sample is prepared to a standard water content. The unrubbed fiber content is 

determined in a series of three steps designed to remove the sapric material by increasingly 

vigorous treatments. The rubbed fiber content is determined by rubbing the sample between 

the thumb and fingers. The percent unrubbed fiber after each step and the final unrubbed and 

rubbed fiber are reported (5C). 

3. Interferences 

This test of organic soil material can be used in field offices. Since it is not practical in 

the field to base a determination on a dry sample weight, moist soil is used. The specific 

volume of moist material depends on how it is packed. Therefore, packing of material must be 

standardized in order to obtain comparable results by different soil scientists (Soil Survey Staff, 

1999). 

4. Safety 

Use caution when using electrical equipment. 

5. Equipment 

5.1 Half-syringe, 6 mL. Cut plastic syringe longitudinally to form a half-cylinder measuring 

device. 

5.2 Sieve, 100 mesh, 7.6-cm diameter 

5.3 Eggbeater 

5.4 Microscope or hand lens 

5.5 Electric mixer, Hamilton Beach no. 35 

5.6 Scissors 

5.7 Paper towel 

5.8 Metal spatula 

6. Reagents 

Reverse osmosis (RO) water 

371
7. Procedure 

Sample Preparation

7.1 Prepare soil material. If the soil is dry, add water and allow to stand until saturated. Place 

50 to 60 mL of a representative sample on a paper towel in a linear mound. Roll the towel 

around the sample and gently squeeze to express water if necessary. Use additional paper 

towels as external blotters. Remove the sample and place on a fresh paper towel. The sample 

should be firm but saturated with water. 

7.2 Use scissors to cut sample into 0.5- to 1.0-cm length segments. 

7.3 Randomly select sample segments for determination of fiber (procedure 5C), solubility in 

pyrophosphate (procedure 5B), and pH (procedure 4C1a1a4). 

Unrubbed Fiber: Overview

7.4 The unrubbed fiber procedure involves a series of three steps designed to disperse sapric 

material by increasingly vigorous treatments. All three steps may not be necessary. Following 

each step that is performed, the percentage estimate of sapric material remaining is visually 

determined under a microscope or hand lens. Categories used to estimate the remaining sapric 

component are as follows: 

7.4.1 Clean (<1% sapric) 

7.4.2 Nearly clean (1 to 10% sapric) 

7.4.3 Some sapric (10 to 30% sapric) 

7.4.4 Sapric (>30% sapric) 

Unrubbed Fiber: Part 1

7.5 Use a metal spatula to pack a half-syringe that is adjusted to the 5-mL mark or 2.5-mL (2.5 

cm3

) volume with the moist sample. 

7.6 Transfer all the soil material to a 100-mesh sieve and wash under a stream of tap water, 

adjusted to deliver 200 to 300 mL in 5 s. Wash sample until the water passing through the 

sieve appears clean. To more clearly determine the end point, catch the effluent in a white 

plastic container. Periodically empty the container until the effluent runs nearly clean. 

7.7 Examine the sample under a microscope or hand lens to determine if sample is free of 

sapric material. 

7.8 If sapric material is >10%, proceed to Unrubbed Fiber, Part 2. If sapric material is <10%, 

wash the residue to one side of the screen and blot from underneath with absorbent tissue to 

withdraw water and proceed on as follows with Unrubbed Fiber, Part 1. 

7.9 Repack the residue into a half-syringe and blot again with absorbent tissue. The moisture 

content should be ≈ that of the original sample. 

7.10 Measure the volume by withdrawing the plunger and reading the value on the syringe 

scale. Record as a percentage of the initial 2.5-mL (2.5 cm3

) volume. 

7.11 Proceed with the Rubbed Fiber determination. 

Unrubbed Fiber: Part 2

7.12 Transfer the residue obtained in Unrubbed Fiber, Part 1 to a 500-mL plastic container and 

fill about half full with water. 

372
7.13 Stir vigorously with an eggbeater for 1 min. 

7.14 Transfer to the 100-mesh sieve and repeat procedural steps in Unrubbed Fiber, Part 1 

beginning with Section 7.9. If sapric material is >10%, proceed to Unrubbed Fiber, Part 3. 

Unrubbed Fiber: Part 3 7.15 Transfer residue left from Unrubbed Fiber, Part 2 to an electric mixer container (malt 

mixer or blender) and fill to about two-thirds with water. 

7.16 Mix for 1 min. 

7.17 Transfer to a 100-mesh sieve and repeat Unrubbed Fiber Part beginning with Section 7.6, 

the washing procedure. 

7.18 Examine the residue under a microscope or hand lens and estimate the percentage of 

sapric material, if any. 

7.19 Record the kind of fiber observed. Typical fibers are herbaceous, woody, and 

diatomaceous. 

7.20 Blot the sample and measure the residue volume. 

7.21 Proceed with the Rubbed Fiber determination. 

Rubbed Fiber

7.22 Transfer the residue from the unrubbed fiber treatment to the 100-mesh sieve. 

7.23 Rub sample between thumb and fingers under a stream of tap water, adjusted to deliver 

150 to 200 mL in 5 s, until water passing through the sieve is clean. Clean rubbed fibers roll 

between the thumb and fingers rather than slide or smear. 

7.24 Blot sample and measure volume in half-syringe. 

8. Calculations 

Fiber volume (%) = Reading on half-syringe (mL) x 20 

where: 

Fiber volume = Rubbed + unrubbed fiber 

9. Report

Record the percentage of unrubbed fiber after each completed step. Report the final 

unrubbed and the rubbed fiber to the nearest whole percent and report fiber type. 

10. Precision and Accuracy 

No precision and accuracy data are available for this procedure. 

11. References 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. 

Print. Office, Washington, DC. 

373
Melanic Index (5D) 

1. Application 

Melanic and fulvic Andisols have high contents of humus, related to their soil color 

reflecting pedogenic processes (Honna et al., 1988). Typically, Melanic Andisols are formed 

under grassland ecosystems, with humus dominated by A type humic acid (highest degree of 

humification), whereas Fulvic Andisols are found under forest ecosystems, with humus 

characterized by the high ratio of fulvic acid to humic acid (low degree of humification, e.g., P 

or B type humic acid) (Honna et al., 1988). The organic matter thought to result from large 

amounts of gramineous vegetation can be distinguished from organic matter formed under 

forest vegetation by the melanic index (Soil Survey Staff, 1999). 

2. Summary of Method 

A 0.5-g soil sample is mechanically shaken for 1 h in 25 mL of 0.5% NaOH solution. 

One drop of 0.2% superfloc solution (flocculation aid) is added to sample and then 

mechanically shaken for 10 min. Either a 1 or 0.5 mL extract (<10% or >10% organic C, 

respectively) is pipetted into a test tube, followed by the addition of 20 mL of 0.1% NaOH 

solution and mixing thoroughly. Absorbance of the solution is read using a spectrophotometer 

at 450 and 520 nm, respectively, within 3 h after extraction. Melanic Index is calculated by 

dividing the absorbance at 450 nm by the absorbance at 520 nm (procedure 5D). 

3. Interferences 

No known interferences. 

 4. Safety 

No significant hazards are associated with this procedure. Follow standard laboratory 

safety practices. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity 

5.2 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.3 Centrifuge tubes, 50-mL polypropylene 

5.4 Centrifuge, Centra, GP-8, Thermo IEC, Needham Heights, MA 

5.5 Pipettes, electronic digital, 1000 μL and 10 mL, with tips, 1000 μL and 10 mL 

5.6 Dispenser, 30 mL or 10 mL 

5.7 Cuvettes, plastic, 4.5-mL, 1-cm light path, Daigger Scientific 

5.8 Spectrophotometer, UV-visible, Varian, Cary 50 Conc 

5.9 Computer, Microsoft Windows 98 

5.10 Printer 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 NaOH, 0.5% and 0.1% 

6.3 Superfloc 16, 0.2% (2 g L-1) in RODI water. 

7. Procedure 

7.1 Weigh 0.5 g of <2mm or fine-grind air-dry soil to the nearest 1.0 mg into a 50-mL 

centrifuge tube. If sample is moist, weigh enough soil to achieve ≈ 0.5 of air-dry soil. 

7.2 Dispense 25 mL of 0.5% NaOH solution to the tube. 

374
7.3 Transfer the sample to the shaker. Shake for 1 h at 200 oscillations min-1 at room 

temperature. 

7.4 Remove the sample from the shaker. Add one drop of 0.2% Superfloc 16 solution and 

centrifuge at 4000 rpm for 10 min. 

7.5 Use the pipette to transfer either a 1 or 0.5 mL extract (<10% or >10% organic C, 

respectively) into test tube. 

7.6 Add 20 mL of 0.1% NaOH solution and mix thoroughly. 

7.7 Set the spectrophotometer at 450 nm. Read absorbance. 

7.8 Set the spectrophotometer at 520 nm. Read absorbance. 

8. Calculations 

Melanic Index is calculated as follows: 

Absorbance at 450 nm/Absorbance at 520 nm 

9. Report 

Report Melanic Index. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Honna, T., S. Yamamoto, and K. Matsui. 1988. A simple procedure to determine melanic 

index that is useful for differentiating melanic from fulvic Andisols. Pedologist 32:69-

78. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. 

Print. Office, Washington, DC. 

Ratios and Estimates Related to Organic Matter (5E) 

On the SSL Primary Characterization Data Sheets, there are several ratios and estimates 

associated with organic matter, using either estimated or measured C values. For more detailed 

information on these ratios, their calculations and applications, refer to the SSIR No. 45, Soil 

Survey Information Manual (1995). Additional information on these ratios and estimates can 

also be obtained from the SSL upon request. 

References 

Soil Survey Staff. 1995. Soil survey laboratory information manual. Version No. 1.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, DC. 

SOIL BIOLOGICAL AND PLANT ANALYSIS (6) 

Soil is an ecosystem that contains a broad spectrum of biological components, 

representing many physiological types (Germida, 1996). Soil biota is critical to soil quality, 

affecting nutrient cycling, soil stability and erosion, water quality and quantity, and plant health 

375
(USDA-NRCS, 2004). Many of this biota (e.g., fungi, bacteria, earthworms, protozoa, 

arthropods, and nematodes) and their relationship to soil health are discussed in the USDANRCS Soil Biology Primer (Tugel and Lewandowski, 2001). Also refer to Reeder et al. (2001) 

for information on root biomass and microbial biomass. 

The SSL routinely performs several biological analyses as follows: root and plant 

(above-ground) biomass and nutrient cycling (6C); organic carbon extractions (6A1a1, 6A2a1); 

separation and total analysis of the soil organic matter fraction (6A4); and microbial biomass 

characterization (6B). Additionally, carbonates are determined by acid decomposition and CO2

analysis by gas chromatography (6A3a1a1). This method is more commonly used in soil 

biochemical and biology studies, where organic C in soils with carbonates may be more 

precisely determined by subtracting the total carbonate (inorganic C) from total C. 

References 

Germida, J.J. 1986. Cultural methods for soil microorganisms. p. 263-275. In Martin R. Carter 

(ed.) Soil sampling and methods of analysis. Can. Soc. Soil Sci. Lewis Publ., Boca Raton, 

FL. 

Reeder, J.D., C.D. Franks, and D.G. Milchunas. 2001. Root biomass and microbial biomass. p. 

139-166. In R.F. Follett, J.M. Kimble, and R. Lal (eds.) The potential of U.S. grazing lands 

to sequester carbon and mitigate the greenhouse effect. Lewis Publ., Boca Raton, FL. 

Tugel, A.J., and A.M. Lewandowski (eds.) 2001. Soil biology primer. Soil Quality – Soil 

Biology Technical Note No. 1. Available: 

http://soils.usda.gov/sqi/soil_biology_primer.htm1. 

USDA-NRCS. 2004. Soil biology and land management. Soil Quality – Soil Biology Technical 

Note No. 4. Available: http://soils.usda.gov/sqi/soil_quality/soil_biology_landmgt.html. 

Analyses (6A) 

Sample Preparation (1B3b2b1) 

0.5 M K2SO4 Extraction + Heating with Disodium Bicinchoninic Reagent (6A1) 

UV-Visible Spectrophotometer, Dual Beam (6A1a) 

Hot Water Extractable Organic Carbon (6A1a1) Air-Dry, <2 mm (6A1a1a1) 

1. Application 

Hot water soluble soil carbohydrates are thought to be primarily extra-cellular 

polysaccharides of microbial origin. They help bind soil particles together into stable 

aggregates. Water stable aggregates reduce soil loss through erosion, increase organic matter, 

and nutrient content. They also occur as part of the fast or labile organic carbon pool in soils. 

This labile pool contains the most available carbon for plant, animal and microbial use. The 

hot water soluble organic C makes up from 4 to 10% of the microbial biomass C determined by 

chloroform fumigation. It also makes up about 6 to 8% of the total carbohydrate content in the 

soil. This pool is the most easily depleted of the three organic C pools (Joergensen et al., 1996; 

Haynes and Francis, 1993). 

2. Summary of Method 

Water is added to a 10-g soil sample and autoclaved at 1 h at 121°C. Extractable 

carbohydrates are measured by adding disodium bicinchoninic (BCA) reagent to a 0.5 M

K2SO4 soil extract, heating to 60° C for 2 h, cooling, and reading the absorbance at 562 nm 

using a spectrophotometer. Glucose is used as a standard and results expressed as glucose-C. 

Data are reported as mg glucose equivalent-carbon kg-1 soil by procedure 6A1a1. 

376
3. Interferences 

Carbohydrates from non-microbial sources can be avoided by using the BCA reagent 

that is selective for microbial carbohydrates. 0.5 M K2SO4 extracts of soil are usually 

supersaturated with CaSO4, with the excess CaSO4 precipitating during storage, especially if 

samples are frozen and during heating of the extract with BCA reagent (Joergensen et al., 

1996). Sodium hexmetaphosphate is added to buffer to prevent CaSO4 precipitation 

(Joergensen et al., 1996). Aspartic acid is used to chelate Cu2+, preventing undesirable 

oxidation and so improving precision (Sinner and Puls, 1978). 

4. Safety 

Wear safety glasses when preparing solutions and handling soil extracts. Use oven 

mitts, tongs, and other devices to avoid contact with hot water and instruments used. 

5. Equipment 

5.1 Electronic balance, ±1.0-mg sensitivity

5.2 Steam sterilizer, 121°C-capability 

5.3 Erlenmeyer flasks, 125-mL 

5.4 Filter paper, Whatman 42, 150 mm 

5.5 Pipette, electronic digital, 10000 μL, with tips, 10000 μL 

5.6 Test tubes, 10-mL 

5.7 Hot water bath, 60°C capability 

5.8 Cuvettes, plastic, 4.5-mL, 1-cm light path, Daigger Scientific 

5.9 Spectrophotometer, UV-Visible, Varian, Cary 50 Conc, Varian Australia Pty Ltd. 

5.10 Computer with Cary WinUV software, Varian Australia Pty Ltd., and printer 

6. Reagents 

6.1 Reverse osmosis deionized water (RODI), ASTM Type I grade of reagent water 

6.2 0.5 M K2SO4 solution. In a 1-L volumetric, dissolve 87.135 g K2SO4 (dried for 2 h at 

110°C) in RODI water. Dilute to volume and invert to mix thoroughly. 

6.3 Stock standard glucose solution (SSGS), 20.0 mg glucose L-1. In 1-L of 0.5 M K2SO4

solution, dissolve 0.02 g glucose (dextrose). Dilute to volume and invert to thoroughly 

mix. Store in polyethylene containers. Make fresh weekly. Store in a refrigerator. 

6.4 Solution 1: Add 4 g Na2CO3, 4 g sodium hexametaphosphate [(NaPO3)]6, and 0.2 g DLaspartic acid in 100 mL RODI water. pH solution to 11.25 with NaOH. 

6.5 Solution 2: Dissolve 0.48 g bicinchoninic acid in 12 mL RODI water (0.1 M). 

6.6 Solution 3: Dissolve 1 g CuSO4 in 25 mL RODI water (0.25 M). 6.7 Disodium bicinchoninic (BCA) reagent: Mix 100 mL Solution 1, 12 mL Solution 2, and 

1.8 mL of Solution 3 = BCA reagent. Store in polyethylene containers. Make fresh daily. 

Store in a refrigerator. 

6.8 Standard glucose working solutions (SGWS), 10.0, 5.0, 2.5, 1.25, 0.75, and 0.375 mg 

glucose L-1. In six test tubes, add 5 mL RODI water. Perform six serial dilutions. Begin as 

follows: add 5 mL of SSGS to Tube 1 and shake (10.0 mg glucose L-1) and extract 5 mL 

from Tube 1, add to Tube 2, and shake (5.0 mg glucose L-1). Proceed to make all six 

SGWS. 

6.9 Standard glucose calibration solutions (SGCS). Add 2 mL of each SGWS to a separate test 

tube, followed by 2 mL BCA reagent. Blank = 2 mL RODI water and 2 mL BCA reagent. 

7. Procedure 

7.1 Weigh 10 g of <2-mm (sieved), air-dry soil to the nearest mg and place into a 125-mL 

Erlenmeyer flask If soil is highly organic, weigh 2 g of fine-grind material to the nearest mg. 

7.2 Add RODI water to soil at a 1:4 ratio (10 g to 40 mL water or 2 g soil to 8 mL water). 

377
7.3 Autoclave 1 h at 121°C and 15 psi. Cool and filter. 

7.4 Pipette 2 mL of each sample extract, 0.5 mL K2SO4, and 2 mL disodium BCA reagent into 

test tubes. 

7.5 Place all tubes (SGCS, blank, and samples) in hot water bath for 2 h at 60°C. 

7.6 Allow to cool and transfer sample extract and SGCS to cuvettes. 

7.7 Set the spectrophotometer to read at 562 nm. Autozero with calibration blank. 

7.8 Calibrate the instrument by using the SGCS. The data system will then associate the 

concentrations with the instrument responses for each SGCS. Rejection criteria for SPCS, if R2

<0.99.

7.9 Run samples using calibration curve. Sample concentration is calculated from the 

regression equation. 

7.10 If samples are outside calibration range, dilute sample extracts with extracting solution 

and re-analyze. 

8. Calculations 

Convert extract glucose equivalent (mg L-1) to glucose equivalent-carbon in the soil (mg kg-1)

as follows: 

Soil glucose-C (mg kg-1) = [(A x B x C x R x 0.40 x 1000)/E] 

where: 

A = Sample reading (mg L-1) 

B = Extract volume (L) 

C = Dilution, if performed 

R = Air-dry/oven dry ratio (procedure 3D1) 

0.40 = Mass fraction C in glucose 

1000 = Conversion factor to kg-basis 

E = Sample weight (g) 

9. Report 

Report data as to the nearest 0.1 mg glucose equivalent-carbon kg-1 soil. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Haynes, R.J., and G.S. Francis. 1993. Changes in microbial biomass C, soil carbohydrate 

composition and aggregate stability induced by growth of selected crop and forage 

species under field conditions. J. Soil Sci. 44:665-675. 

Joergensen, R.G., T. Mueller and V.Wolters.1996. Total carbohydrates of the soil 

microbial biomass in 0.5 M K2SO4 soil extracts. Soil Biol. Biochem. 28:9:1147-1153. 

Sinner, M., and J. Puls. 1978. Non-corrosive dye reagent for detection of reducing sugars 

in borate complex ion-exchange chromatography. J.Chrom. 15.

378
Soil Analyses (6A) 

Sample Preparation (1B3b2b1) 

0.02 M KMnO4 Extraction (6A2) UV-Visible Spectrophotometer, Dual Beam (6A2a) 

Active Carbon (6A2a1) 

Air-Dry, <2 mm (6A2a1a1) 

1. Application 

This method, commonly called Weil Carbon (Weil et al., 2003), is designed to be a 

quick and easy field test for the assessment of active soil organic carbon. Following the 

principle of bleaching chemistry, potassium permanganate (KMnO4) is used as an oxidizer of 

organic matter present in soil. The oxidized organic matter is considered to be associated with 

the active carbon pool (Blair et al.,1995). An active soil carbon index can be expressed as the 

quotient of active carbon to soil organic carbon (Blair et al., 2001). The stability of this index 

over time is considered to be a useful measure of soil quality (Islam and Weil, 1997). 

2. Summary of Method 

 A 5-g sample is oxidized with 0.02M potassium permanganate diluted with reverse 

osmosis water. Sample is shaken for 2 min and allowed to stand undisturbed for 5 to10 

minutes. A small aliquot of the supernatant is diluted with reverse osmosis water and the 

absorbance of the solution is read at 550 nm using a spectrophotometer. Extractable carbon by 

0.02 M KMnO4 is reported as mg C kg-1 soil by procedure 6A2a1. 

3. Interferences 

Chemical oxidation methods for the determination of labile soil carbon have a number 

of limitations: different soil samples may have variable amounts of readily oxidizable fractions, 

making standardization of any method a difficult task, with results influenced by the amount of 

C in the sample, MnO4

-

 concentration, and contact time (Blair et al., 1995). 

4. Safety 

Wear protective clothing (coats, aprons, and gloves) and eye protection (safety glasses 

and other devices as appropriate) while preparing reagents and performing procedure. When 

preparing reagents, exercise special care. Use a vented hood. Thoroughly wash hands after 

handling all chemicals. 

Potassium permanganate is a strong oxidizer. Contact with other material may cause 

fire. Avoid contact with eyes, skin, and clothing. In case of fire, soak with water. In case of 

spill, sweep up and remove. Flush spill area with water. Inhalation of KMnO4 dust may be 

severely damaging to respiratory passages and/or lungs. Contact with skin or eyes may cause 

severe irritation or burns. Substance is readily absorbed through the skin. See the Material 

Safety Data Sheet (MSDS) for further information regarding KMnO4. 

 

5. Equipment 

5.1 Centrifuge tubes, 50-mL, graduated, polyethylene, with screw tops 

5.2 Dropper pipette, 1-mL, graduated, disposable 

5.3 Squirt bottle 

5.4 Scoop, 5-g (or electronic balance, ±0.01-g sensitivity) 

5.5 Petri dish, for sun-drying crumbled soil, if necessary 

5.6 Tissues for cleaning cuvettes 

5.7 Stopwatch, timer, or a watch with a second hand 

5.8 Pipette, electronic digital, 10-mL 

5.9 Volumetric flasks, 50, 100, and 200-mL, and 2-L, with stoppers 

5.10 Spectrophotometer, UV-Visible, Varian, Cary 50 Conc, Varian Australia Pty Ltd. 

5.11 Computer with Cary WinUV software, Varian Australia Pty Ltd., and printer 

5.12 Cuvettes, plastic, 4.5-mL, 1-cm light path, Daigger Scientific 

379
6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water

6.2 CaCl2⋅2 H2O, 0.1 M solution. Dissolve 29.40 g of CaCl2⋅2 H2O in a 2-L volumetric flask 

with 1L of RODI. Bring to 2L volume. Store in a polyethylene bottle. 

6.3 KOH, 0.1 M solution. Dissolve 0.561 g of potassium hydroxide with 50-mL of RODI 

water in a 100-mL volumetric flask. Bring to volume with RODI water. Invert to mix 

thoroughly. 

6.4 Stock KMnO4 solution, 0.2 M in 0.1 M CaCl2 solution (pH 7.2). In a 200-mL volumetric, 

dissolve 6.32 g of potassium permanganate crystals in 100-mL of 0.1 M CaCl2. Bring to 

volume with 0.1 M CaCl2. Adjust solution pH to 7.2 with 0.1 M KOH (usually requires 1-2 

drops of KOH). Solution is stable for approximately 3 days. 

6.5 Standard KMnO4 working (SKMnO4WS) solutions, 0.04, 0.02, 0.01 and 0.005 M KMnO4. Prepare fresh weekly. Store in a refrigerator. Allow to equilibrate to room temperature 

before use. In four 50-mL volumetric flasks add as follows: 10, 5, 2.5, and 1.25 mL of 

Reagent 6.4 (0.2 M KMnO4, in 0.1 M CaCl2 solution, pH 7.2). Bring to volume with 

RODI water. Invert to mix thoroughly. 

6.6 Standard KMnO4 calibration (SKMnO4CS) solutions, 0.0004, 0.0002, 0.0001, 0.00005, 

and 0 M KMnO4. To four 50-mL volumetric flasks, add 0.5-mL aliquots of the 

SKMnO4WS. For the blank, add 5 mL 0.1 M CaCl2. Make fresh daily. Bring to volume 

with RODI water. Invert to mix thoroughly. 

7. Procedure 

 

7.1 Add 15-mL RODI water to a clean, labeled centrifuge tube. Add 2 mL of Reagent 6.4 

solution to the centrifuge tube, taking 1 mL twice and washing the pipette with the dilute 

solution in the tube. Add RODI water to make to 20-mL volume. 

 

7.2 Weigh or scoop 5 g of <2-mm (sieved), air-dry soil to the nearest mg and add to the 

centrifuge tube and cap it. Avoid coarse fragments and plant material. 

7.3 Shake vigorously for 2 min and allow to stand for 5 to 10 min to settle the soil. Do not 

disturb during settling period. 

7.4 Add 45 mL of RODI water to a clean, labeled centrifuge tube. Transfer 0.5 mL of the 

supernatant solution into the tubes using a graduated 1-mL dropper pipette. Rinse the pipette 

with the dilute solution from the tube. Add RODI water to make to 50-mL volume. Invert to 

mix thoroughly. Repeat for each sample. Standards (SKMnO4CS) have been treated in the 

same manner as described in Section 6.6. 

7.5 Transfer sample extracts and SKMnO4CS to cuvettes. 

 

7.8 Set the spectrophotometer to read at 550 nm. Autozero with calibration blank. 

 

7.9 Calibrate the instrument by using the calibration solutions. The data system will then 

associate the concentrations with the instrument responses for each calibration solution. 

Rejection criteria for calibration, if R2 <0.99.

7.10 Run samples using calibration curve. Sample concentration is calculated from the 

regression equation. Record results to the nearest 0.01 unit for the sample extract and each 

calibration solution. 

7.11 If some samples have zero absorbance, reweigh at smaller sample size (e.g., 2.5 g) and reanalyze. Samples that have zero absorbance are those that have large amounts of active carbon. 

380
8. Calculations 

The bleaching of the pink KMnO4 color (reduction in absorbance) is proportional to the 

amount of oxidizable C in soil, i.e., the greater the KMnO4 color loss (the lower the absorbance 

reading), the greater the amount of oxidizable C in the soil (Weil et al., 2003). To estimate the 

amount of C oxidized, use the assumption of Blair et al. (1995) that 1 mol MnO4 is consumed 

(reduced from Mn7+ to Mn2+) in the oxidation of 0.75 mol (9000 mg) of C as follows: 

KMnO4 C (mg kg-1) = [0.02 mol L-1 – A] x (9000 mg C mol-1) x (0.02 L solution/0.005 kg) 

where: 

0.02 mol L-1= initial solution concentration 

A = analyte reading (mol L-1) 

9000 = mg C (0.75 mole) oxidized by 1 mole of MnO4 changing from Mn7+ to Mn2+ 0.02 L = volume of KMnO4 solution reacted 

0.005 = kg of soil used 

9. Report 

Report data to the nearest 0.1 mg C kg-1 soil. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Blair, G.J., R.Lefroy, and L. Lise. 1995. Soil carbon fractions based on their degree of 

oxidation, and the development of a carbon management index for agricultural systems. 

Australian J. Agric. Res. 46:1459-1466. 

Blair, G.J., R. Lefroy, A.Whitbread, N. Blair, and A. Conteh. 2001. The development of 

the KMnO4 oxidation technique to determine labile carbon in soil and its use in a 

carbon management index. p. 323-337. In R. Lal. J. Kimble, R. Follet, and B. Stewart 

(eds.) Assessment methods for soil carbon. Lewis Publ. Boca Raton, FL. 

Islam, K.R., and R.R. Weil. 2000. Soil quality indicator properties in mid-Atlantic soils as 

influenced by conservation management. J. Soil and Water Conserv. 55:69-78. 

Weil, R. R., R. I. Kandikar, M.A. Stine, J. B. Gruver, and S. E. Samson-Liebig. 2003. 

Estimating active carbon for soil quality assessment: A simplified method for laboratory 

and field use. Am. J. Alternative Agric. 18(1):3-17. 

Soil Analyses (6A) 

Sample Preparation (1B3b2b1) 

Acid Dissolution (6A3) 

1 N HCl + FeCl2 (6A3a) CO2 Analysis (6A3a1) Gas Chromatography (6A3a1a) 

Carbonates (6A3a1a1) 

Air-Dry, <2 mm (6A3a1a1a1) 

1. Application 

Methods involving determination of CO2 have usually been preferred for measuring soil 

carbonate (Loeppert and Suarez, 1996). CO2 released can be measured gravimetrically 

(Allison, 1960; Alllison and Moodie, 1965), titrimetrically (Bundy and Bremmer, 1972), 

manometrically (Martin and Reeve, 1955; Presley, 1975), volumetrically (Dreimanis, 1962), 

spectrophotometrically by infrared spectroscopy, or by gas chromatography (Loeppert and 

Suarez, 1996). The SSL routinely determines the amount of carbonate in the soil by treating the 

381
CaCO3 with HCl, with the evolved CO2 measured manometrically (procedures 4E1a1a1a1-2 

for <2-mm and 2- to 20-mm bases, respectively). The method herein describes soil carbonate 

by acid decomposition and CO2 analysis by gas chromatography. This method is more 

commonly used in soil biochemical and biology studies, where organic C in soils with 

carbonates may be more precisely determined by subtracting the total carbonates (inorganic C) 

from total C (procedure 4H2a1). 

2. Summary of Method 

Soil carbonate is determined by chromatographic analysis of CO2 evolved upon 

acidification of soil in a closed system of known headspace. Ferrous iron (FeC12) is added to 

the acid as an anti-oxidant, and the dilute acid solution (1N HCl) is chilled before addition to 

soil to minimize the decarboxylation of organic matter by the acid. Data are reported as mg 

CO2-C per g of soil to the nearest 0.1 g (6A3a1a1). These data can be used to estimate soil 

organic carbon by subtracting (CO2-C x 0.2727) from total carbon (4H2a1). 3. Interferences 

It is essential that precautions be taken to ensure that there is no interference from 

organic matter oxidation (Loeppert and Suarez, 1996). This procedure may be more 

appropriate for soils with relatively low amounts of carbonates (<15%). 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when handling acids. Thoroughly wash hands after 

handling acids. Use the fume hood when diluting concentrated HCl. Use the safety showers 

and eyewash stations to dilute spilled acids. Use sodium bicarbonate and water to neutralize 

and dilute spilled acids. 

5. Equipment 

5.1 Canning jars, 1-qt (0.984-L), with lids fitted with gas-sampling septa 

5.2 Syringe, 20-mL, with 18-gauge needle 

5.3 Disposable syringe, 1-mL, for gas sampling 

5.4 Needle, 18 or 20 gauge, for venting jars 

5.5 Electronic balance, ±0.01-g sensitivity 

5.6 Gas chromatograph (GC) with thermal conductivity detector (TCD) 

5.7 Beaker, glass, 600-mL 

5.8 Filter paper, Whatman 42, 150 mm 

5.9 Stirrer 

6. Reagents 

6.1 Reverse osmosis deionized (RODI) water, ASTM Type I grade of reagent water 

6.2 1N HCl with 3.1 g FeCl2 added per 100 mL of solution, chilled to 4 to 5o

C. Prepare 500 

mL of solution of as follows: weigh 15.5 g FeCl2 into 600-mL beaker; add 20-mL RODI 

water; stir (medium speed) until all crystals have dissolved; filter solution to remove 

insoluble ferric iron particulates; transfer to 500-mL volumetric; add 41.7 mL concentrated 

HCl to aqueous FeCl2; bring to volume with RODI water; and chill solution to 4 to 5 °C. 

7. Procedure 

7.1 Determine water content of soil sample so results may be expressed on an oven-dry soil 

basis. Refer to water retention methods (3C). 

7.2 Weigh 5g of <2-mm (sieved), air-dry soil to the nearest 0.01 g into clean 1-qt jar. 

382
7.3 Tightly seal jar with lid fitted with gas sampling septum. Also include one or more jars with 

no soil added to serve as reagent controls and C02 background indicators. 

7.4 Add 20 ml of RODI water (room temperature) to jar through septum with 20-mL syringe, 

venting jar with 18 or 20 gauge needle. 

7.5 Add 20 mL of chilled 1N HCl + FeC12 solution through septum as in Section 7.4 (do not 

vent), let stand 2 h, swirling soil-acid solution occasionally. 

7.6 Take gas sample for gas chromatograph analysis using 1-mL syringe. Purge syringe several 

times before withdrawing final sample for analysis. 

8. Calculations 

Calculation of Soil Carbonate mass from CO2% volumetric concentrations (Kettler and Doran, 

1995). 

8.1 Reaction equation: 

 

CaCO3 + 2HCl (aq) --> CO2 ↑+ H2O + CaC12 (aq) 

mg CO2-C produced = mg CO3-C dissolved by acid in soil 

mg CO2-C produced/OD = mg CO3-C/OD 

where: 

OD = Oven-dry soil (g) 

8.2 Net jar headspace

Volume of Empty 1-qt. jar = 978cm3 (measured by H2O volume displacement). 

Soil Solid Volume (cm3) = [g Moist Soil/(l + %H2O/100)]/(Particle Density) 

= (5.00 g sample/(l + %H2O/100))/(2.65g cm-3) 

where: 

2.65 = assumed particle density (g cm-3) 

Net jar Headspace (cm3

) = Empty Jar - Soil Solid Volume - Soil H2O Volume – Liquid Volume 

= 978 cm3 - (Soil Solid Volume, cm3) - (g Oven-dry Soil/1+ % H2O/100) - (20 cm3 H2O + 20 

cm3 Acid) 

= 978 cm3 - 1.89 cm3 - 40 cm3 

= 936.1 cm3 (936 to 935.4 cm3 for 3 - 30% H2O) 

where: 

5.00 = g soil oven-dry basis, assumed 

8.3 Gaseous CO2-Carbon produced: 

This step is important for soils with >15% carbonates. 

383
mg CO2-Carbon produced by soil carbonate decomposition and detected as CO2 in vapor space 

= 4.594 mg CO2-Carbon / atm x ((Mole % CO2s x Pts, atm) - (Mole % CO2b x Ptb, atm)) 

where: 

Ptb = Total pressure in blank jar by electronic manometer 

Pts = Total pressure in sample jar by electronic manometer 

Mole % CO2b = Mole % CO2 in blank jar by GC 

Mole % CO2s = Mole % CO2 in sample jar by GC 

8.4 CO2-Carbon produced but dissolved in solution: 

mg CO2-Carbon produced by soil carbonate decomposition but dissolved in solution 

= (0.163 mg CO2-C / atm) x ((Mole % CO2s x Pts, atm) - (Mole % CO2b x Ptb, atm)) 

Total mg CO3-Carbon / OD = Total mg CO2-Carbon / OD 

= {[(0.163 mg CO2-C / atm) x ((Mole % CO2s x Pts, atm) - (Mole % CO2b x Ptb, atm))] + [4.594 

mg CO2-Carbon / atm x ((Mole % CO2s x Pts, atm) - (Mole % CO2b x Ptb, 

atm))]}/{FM/FMOD)} 

= {[4.757 mg CO2-C / FM / atm] x [(Mole % CO2s x Pts, atm) - (Mole % CO2b x Ptb, atm)]} x 

(FMOD) 

where: 

OD = Oven-dry soil (g) 

FM = Field-moist soil (g) 

FMOD = Field-moist soil/oven-dry ratio (g/g) (procedure 3D2) 

8.5 Convert mg CO2-C per g of soil to percent CO2-C in soil as follows: 

(mg CO2-C/g soil) (1g / 1000mg) (100g soil) = Percent CO2-C in soil 

9. Report 

Report % CO2-C in soil to the nearest 0.1%. These data can be used to estimate soil 

organic carbon by subtracting (CO2-C x 0.2727) from total carbon (4H2a1). 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Allison, L.E. 1960. Wet combustion apparatus and procedure for organic and inorganic 

carbon in soil. Soil Sci. Soc. Am. Proc. 24:36-40. 

Allison, L.E., and C.D. Moodie. 1965. Carbonate. p. 1379-1400. In C.A. Black, D.D. 

Evans, J.L. White, L.E. Ensminger, and F.E. Clark (eds.) Methods of soil analysis. Part 

2. 2nd ed. Agron. Monogr. 9. ASA, CSSA, and SSSA, Madison, WI. 

Bundy, L.G., and J.M. Bremmer. 1972. A simple titrimetric method for determination of 

inorganic carbon in soils. Soil Sci. Soc. Am. Proc. 36:273-275. 

Dreimanis, A. 1962. Quantitative gasometric determination of calcite and dolomite by 

using Chittick apparatus. J. Sediment. Petrol. 32:520-529. 

Kettler, T., and J. Doran. 1995. Determination of soil carbonate concentration by acid 

decomposition and GC CO2 analysis. USDA-ARS, University of Nebraska, Lincoln 

(unpublished). 

384
Loeppert, R.H., and D.L. Suarez. 1996. Carbonate and gypsum. In D.L. Sparks (ed.) Methods of 

Soil Analysis. Part 3–Chemical methods. ASA and SSSA, Madison, WI 

Martin, S.E., and R. Reeve. 1955. A rapid manometric method for determining soil 

carbonate. Soil Sci. 79:187-197. 

Presley, B.J. 1975. A simple method for determining calcium carbonate in sediment 

samples. J. Sediment. Petrol. 45:745-746. 

Particulate Organic Matter and C-Mineral (6A4) Sample Preparation (1B3b2a1) 

Total Analysis (6A4a) 

Dry Combustion (6A4a1) 

Thermal Conductivity Detector (6A4a1a) 

Carbon, Nitrogen, Sulfur (6A4a1a1-3) 

Air-Dry (6A4a1a1-3a) 

>53 μm, Particulate Organic Matter (6A4a1a1-3a1) <53 μm, C-Mineral (6A4a1a1-3a2) 

1. Application 

Particulate organic matter (POM) is a physical fraction of the soil >53μm in diameter 

(Elliott and Cambardella, 1991; Cambardella and Elliott 1992; Follett and Pruessner, 1997). 

Some researchers combine this fraction with the fast or labile pool. Others have described this 

pool as slow, decomposable, or stabilized organic matter (Cambardella and Elliott, 1992). To 

avoid confusion, this fraction may best described as representing an intermediate pool with 

regards to decomposition. This fraction is similar to various sieved and physical fractions such 

as the resistant plant material (RPM) (Jenkinson and Rayner, 1977), and size fractions 

(Gregorich et al., 1988), and variously determined light fractions of the soil organic matter 

(Strickland and Sollins, 1987; Hassink, 1995). 

Under tillage, the POM fraction becomes depleted (Jenkinson and Rayner, 1977; 

Cambardella and Elliott, 1992). Reductions of more than 50% have been found in long-term 

tillage plots (20 yr.). Measurable reductions are believed to occur in the range of 1 to 5 years 

(Cambardella and Elliott, 1992). 

When paired samples are selected either in time or between two tillage treatments a 

comparison can be made to determine the impact of the tillage practice. POM can be used in 

soil organic matter modeling, as a soil quality indicator and as an indicator of the SOM that can 

move into the active C pool. 

Since the late 1970’s several models have been developed to estimate the dynamics of 

organic matter in the soil. All of these models have at least two phases, slow and rapid. In 

measuring these two phases chemical fractionation (humic and fulvic acids) has been found to 

be less useful than physical fractionation (Hassink, 1995). Examples of some of these models 

can be found in Jenkinson and Rayner (1977), tests of the CENTURY Soil Organic Model, 

(Parton et al., 1987; Metherell et al., 1993; and Montavalli et al., 1994). A minimum data set 

for soil organic carbon is proposed by Gregorich et al (1994) that includes POM as one of the 

primary parameters. 

2. Summary of Method 

The procedural steps described herein encompasses the physical separation (1B3b2a) of 

the soil organic matter (<2 mm) into two fractions: (1) >53-μm, POM and (2) <53 μm, CMineral (C-Min) (Cambardella and Elliot, 1992; Follett and Pruessner, 1997) and the analysis 

of these two fractions for total C, N, and S by procedure 6A4a1a1-3, respectively. Typically, 

this procedure is determined on the A horizons (Soil Survey Staff, 1999) because detectable 

levels of both C and N are most likely to occur in this horizon. 

385
3. Interferences 

In some weathered soils there is approximately the same amount of C in both fractions. 

To date, no research has been done to establish the interpretation of this result. Charcoal in 

native sod that has been historically burned if residence time was to be determined from the 

two fractions, does not affect the POM determination and C and N analysis themselves. 

4. Safety 

Always wear safety glasses when working with glass containers. 

5. Equipment 

5.1 Pressure regulator for water, with stop cock attached to tubing 

5.2 Sieve, 10 mesh, 2 mm 

5.3 Sieve, 270 mesh, 53 μm 

5.4 Mechanical reciprocating shaker, 200 oscillations min-1, 1 1⁄2 strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.5 Glass, Pyrex, pie or round cake pans 

5.6 Evaporating crucibles 

5.7 Drying Oven (110o

C) 

6. Reagents 

6.1 Reverse osmosis deionized water (RODI), ASTM Type I grade of reagent water 

7. Procedure 

Physical Separation of Organic Matter (POM and C-Min) 

7.1 Remove large pieces of organic matter, roots, plant residue, gravel, wood material from an 

air dry soil sample. Do not shake. Save the large fraction and weigh. 

7.2 Weigh 10 g of <2-mm (sieved), air-dry soil to the nearest mg into a 125-mL Erlenmeyer 

flask. Add 30 mL of RODI water to sample. 

7.3 If the soil has carbonates, take a sub-sample and measure the inorganic carbon following 

the gas chromatograph procedure (6A3a1a1). 

7.4 Stopper sample tightly and shake for 15 h (overnight) at 200 oscillations min-1 at room 

temperature (20°C ± 2°C). 

7.5 Sieve the soil through a 53-μm sieve. The POM fraction will remain on top of the sieve and 

the C-min will be a slurry that is collected in a pie pan underneath the sieve. Use the regulator 

that is attached to the RODI water to rinse the POM with a steady gentle stream of water. Keep 

rinsing until the water that comes through the sieve is clear. Capture all the soil slurry and 

water (C-Min fraction) that passes the sieve. 

 

7.6 Label and tare a glass pie pan and an evaporating crucible to the nearest 0.01 g. 

7.7 Transfer the POM into an evaporating crucible by rinsing the sieve, including the sides, 

with a small amount of RODI water. 

7.8 Transfer the C-Min slurry into a glass pie pan for drying. Rinse the contents of the pie pan 

into the labeled glass pie pan. 

7.9 Dry the two fractions (POM, C-Min) in an oven at 110 o

 C oven. The C-Min fraction may 

require 48 h to dry, depending on how much water was used to rinse the sample. 

386
7.10 Once the samples are dry, let them cool briefly and record the weight to the nearest 0.1 

mg. 

7.11 Transfer the entire contents for each fraction to an appropriately labeled scintillating vial. 

Total Carbon, Nitrogen, and Sulfur Analysis 

7.12 Determine total C, N, and S for POM and C-min fractions (6A4a1a1-3), using fine-grind 

samples (≈ 180 μm). Refer to 4H2a1-3 for the remaining procedural steps for 6A4a1a1-3. 

8. Calculations 

Calculate POM-C and C-Min using soil bulk density values determined by procedures 4A or 

ASTM method D-2167 (American Society of Testing and Materials, 2004) and total C values 

determined by procedures 6A4a1a1. 

8.1 (%Total C of POM Fraction/100) x (POM (g)/10) x FMOD = POM-C g/g soil 

where: 

FMOD = Field-moist/oven-dry ratio (procedure 3D2) 

8.2 (%Total C of C-Min Fraction/100) x C-Min (g)/10) x FMOD = C-Min g/g soil 

8.3 (% Total C of POM fraction/100) x [POM (g)/10] x Bulk Density x 100,000 x 

Depth = POM-C kg ha-1 at given depth interval 

8.4 (% Total C of C-Min fraction/100) x [C-Min (g)/10] x Bulk Density x 100,000 x Depth = 

C-Min kg ha-1 at given interval depth. 

Use the above equations for similar computations of N and S (6A4a1a2-3, respectively). 

9. Report 

Report POM-C and C-Min in kg ha-1 at a given depth interval (cm). Report separately 

similarly calculated values for N and S. Report the percent >2-mm fraction. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

American Society for Testing and Materials. 2004. Standard practice for density and unit 

weight of soil in place by the rubber balloon method. D 2167. Annual book of ASTM 

standards. Construction. Section 4. Soil and rock; dimension stone; geosynthesis. Vol. 

04.08. ASTM, Philadelphia, PA. 

Cambardella, C.A., and E.T. Elliott. 1992. Particulate soil organic-matter changes across a 

grassland cultivation sequence. Soil Sci. Soc. Am. J. 56:77-783. 

Elliott, E.T., and C.A. Cambardella. 1991. Physical separation of soil organic matter. 

Agric. Ecosyst. Environ. 34:407-419. 

Follett, R.F and E. Pruessner. 1997. POM procedure. USDA-ARS, Ft. Collins, CO. 

Gregorich, E.G., M.R. Carter, D.A. Angers, C.M. Monreal, and B.H. Ellert. 1994. Towards 

a minimum data set to assess soil organic matter quality in agricultural soil. Can. J. Soil 

Sci. 74:367-385. 

Gregorich, E.G., R.G. Kachanoski, and R.P. Voroney. 1988. Ultrasonic dispersion of 

aggregates: Distribution of organic matter in size fractions. Can. J. Soil. Sci. 68:395-

403. 

387
Hassink, J. 1995. Decomposition rate constants of size and density fractions of soil organic 

matter. Soil Sci. Soc. Am. J. 59:1631-1635. 

Jenkinson, D.S., and J.H. Rayner. 1977. The turnover of soil organic matter in some of the 

Rothamsted classical experiments. Soil Sci. 123:298-305. 

Metherell, A.K., L.A. Harding, C.V. Cove, and W.J. Parton. 1993. CENTURY soil organic 

matter model environment, technical documentation agroecosystem, Version 4.0. Great 

Plains System Res. Unit Tech. Rep. No. 4, USDA-ARS, Ft. Collins, CO. 

Montavalli, P.P., C.Q. Palm, W.J. Parton, E.T. Elliott, and S.D. Frey. 1994. Comparison of 

laboratory and modeling simulation methods for estimating soil carbon pools in tropical 

forest soils. Soil Biol. Biochem. 26:935-944. 

Parton, W.J., D.S. Ojima, C.V. Cole, and D.S. Schimel. 1994. A general model for soil 

organic matter dynamics: sensitivity to litter chemistry, texture and management. p. 

147-167. In Quantitative modeling of soil forming processes, SSSA Spec. Publ. 39. 

SSSA, Madison, WI. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. 

Print. Office, Washington, DC. 

Strickland, T.C., and P. Sollins. 1987. Improved method for separating light- and heavyfraction organic material from soils. Soil Sci. Soc. Am. J. 51:1390-1393 

Fumigation Incubation (6B) 

Sample Preparation (1B3b1a1) 

Gas Chromatography (6B1) 

CO2 Analysis (6B1a) Microbial Biomass (6B1a1) 

Field-Moist, <2 mm (6B1a1a1) 

2 M KCl Extraction (6B2) Automatic Extractor (6B2a) 

Ammonia – Salicylate (6B2a1) 

Flow Injection, Automated Ion Analyzer (6B2a1a) 

N as NH3 (Mineralizable Nitrogen) (6B2a1a1) Field-Moist, <2 mm Fumigated and <2 mm Non-Fumigated (6B2a1a1a1-2) 

1. Application 

Soil microorganisms are an important component of soil organic matter. One of their 

functions is to breakdown non-living organic matter in the soil. A variety of methods exist to 

measure the biomass of living soil microbes. The method described herein by the chloroform 

fumigation incubation (Jenkinson and Powlson, 1976) with modifications, and CO2 evolution 

measurement by gas chromatography. Mineralizable N may also be determined on microbial 

biomass. 

2. Summary of Method 

A freshly collected soil sample is weighed into two separate vials. One sample is 

fumigated using chloroform and the other is used as a control (non-fumigated). After 

fumigation both the fumigated and non-fumigated samples are brought up to 55% water filled 

pore space (WFPS) (Horwath and Paul, 1994). Both samples are placed in a sealed container 

and aerobically incubated for 20 days. During this incubation period it is assumed that normal 

respiration occurs in the control sample container. The fumigated sample having a large carbon 

source for food, supplied from the dead microorganisms, has a higher CO2 production. At the 

end of 10 days respiration readings are taken on both the control and the fumigated sample to 

determine the amount of CO2 evolved by gas chromatography. The CO2 level of the control 

sample is also measured at the end of 20 days. CO2 produced by biomass flush (g CO2-C/g of 

soil) and soil microbial biomass (kg C/ha for a given depth interval) are reported by procedure 

6B1a1. Mineralizable N by 2 M KCl extraction may also be determined on microbial biomass 

388
using a flow injection automated ion analyzer by procedure 6B2a1a. Mineralizable N is 

reported as mg N kg-1 soil as NH3. 

3. Interferences 

The determination of CO2 evolution by gas chromatography gives a rapid and accurate 

measurement and can be used in acidic soils. However, this technique is prone to error in 

neutral and alkaline soils (Martens, 1987), as accumulation of carbonate species in the soil 

solution can lead to lowered CO2 determinations (Horwath and Paul, 1994). 

4. Safety 

All fumigation work needs to be conducted in an adequate fume hood because 

chloroform has carcinogenic-volatile properties. Never determine residual chloroform by sense 

of smell. Make sure the vacuum pump is maintained to ensure proper operations. 

5. Equipment 

5.1 Face Shield 

5.2 Goggles 

5.3 Rubber Apron 

5.4 Rubber Gloves 

5.5 Chloroform spill kit 

5.6 Fume hood, 100-fpm face velocity 

5.7 Vacuum chambers, fiberglass 

5.8 Incubator, 25o

C 

5.9 Vacuum pump, 26 and 14 in Hg, organic/oil free 

5.10 Mason jars, 1-qt, with lids and septa 

5.11 Vials, 60-mL glass, with snap caps, for samples 

5.12 Beakers, 100-mL 

5.13 Refrigerator, for sample and titrate storage 

5.14 Sieve, 10 mesh, 2 mm 

5.15 Electronic balance, ±0.01-g sensitivity 

5.16 Electronic balance, ±1.0-mg sensitivity 

5.17 Oven, 110°C 

5.18 Permanent marker 

5.19 Paper Towels 

5.20 Tongs, 12 in 

5.21 Mechanical vacuum extractor, 24-place, SAMPLETEX, MAVCO Industries, Lincoln, NE 

5.22 Tubes, 60-mL polypropylene, for extraction tubes 

5.23 Rubber tubing, 3.2 ID x 1.6 OD x 6.4 mm (1/8 ID x 1/16 OD x 1 in) for connecting 

syringe barrels 

5.24 Containers, polycon 

5.25 Aluminum weighing pans, 60 mm diameter x 15 mm depth 

5.26 Gas chromatograph (GC) with thermal conductivity detector (TCD) 

5.27 GC syringes, 1-mL 

Reagents 

6.1 Reverse osmosis deionized (RODI), ASTM Type I grade of reagent water 

6.2 Chloroform stabilized in amylene. Use purified chloroform within 3 weeks. 

6.3 Helium, compressed gas 

7. Procedure 

7.1 Until sample preparation and analysis, keep soils moist and refrigerated. 

389
7.2 Weigh soil to the nearest 0.01 g for bulk density determination. Remove a 15 to 20 g 

sample for water content. Sieve moist soil to <2 mm. Sub-sample (10 to 15 g) for post-sieve 

water content. Refrigerate samples until analyses can be performed. Dry post-sieve water 

content samples at 110°C overnight. Weigh samples the following day. 

7.3 Prepare 1 sample for the Fumigated Day 10 (F 10) and 1 for the Non-Fumigated Day 20 

(NF 20). Prepare replicates for each sample. 

7.4 Mark the volume on the glass sample container corresponding to 20 mL (or more if a larger 

quantity of soil is needed). 

 

7.5 Label the non-fumigated container clearly with permanent marker. 

7.6 Use etched containers for the fumigated set, as chloroform can dissolve written labels. 

7.7 Weigh enough moist soil (nearest mg) to achieve approximately 25 g (or 50 g) oven-dry 

soil into 60-mL glass vial. Use soil moisture content conversion. Adjust soil, by gently 

tapping against the counter, so that it is leveled off at the bulk density line. Carefully add 

RODI water with a dropper to bring the moisture up to 55% WFPS, using the moisture content 

conversion. Make the surface as uniformly moist as possible. 

7.8 Cap the vials and refrigerate samples overnight to equilibrate. 

Fumigated Samples 

7.9 Line the vacuum chambers with wet paper towels to prevent desiccation. 

7.10 Place the vacuum chambers in the fume hood. 

7.11 Place beaker with 30 to 40 mL of stabilized chloroform in the chambers. Evacuate at 14” 

Hg to drive off the amylene stabilizer. A volume change will be visible, approximately 5 to 10 

mL. 

7.12 Place the sample vials in the vacuum chambers. 

7.13 Place the pure chloroform into the pan of the vacuum chambers. 

7.14 Fumigate samples for 24 h. 

7.15 Evacuate the fumigated samples 4 times for approximately 15 min at 27” Hg to drive off 

the chloroform. 

Fumigated and Non-fumigated Samples 

7.16 Add 5 to 10 mL of RODI water to the bottom of the mason jar to prevent desiccation. 

7.17 Seal mason jars securely with rings and lids. Lids must be airtight during the incubation.

7.18 Seal mason jars securely with rings and lids. Lids must be airtight during the incubation. 

Incubate samples at 25o

 C for 10 days. 

Day 10 Samples

7.19 Remove mason jars from incubator. Proceed to Section 7.26 for analysis. 

7.20 Remove all F 10 samples from the mason jars. 

390
7.21 Cap F 10 samples and store at 4° C until they can be extracted for mineralizable N (2 M

KCl). If a microbial inhibitor is used, samples can be stored in the refrigerator for up to two 

weeks before analysis. For longer periods they should be frozen. For extraction, proceed to 

Section 7.29. 

7.22 Incubate NF 20 samples at 25o C for 10 days. Make sure the mason jar lids are still 

sealing. If not, replace with new lids 

Day 20 Samples 

7.23 Remove mason jars from incubator. Proceed to Section 7.26 for analysis. 

7.24 Remove all NF 20 samples from the mason jars. 

7.25 Cap samples and store at 4° C until they can be extracted for mineralizable N (procedure 

6B3a1a1). If a microbial inhibitor is used, samples can be stored in the refrigerator for up to 

two weeks before analysis. For longer periods they should be frozen. For extraction, proceed to 

Section 7.29 

Gas Chromatography 

7.26 Measure the CO2 accumulated in the headspace of the mason jars by gas chromatography. 

7.27 Refer to manufacturer’s manual for operation of the gas chromatograph. 

7.28 Calibration curves and retention times for gas under analysis is established by analyzing 

the certified standard gas mixture (1% CO2) by the procedure used for analysis of the sample. 

Flow rate is 30 mL min-1. Monitor the baseline prior to analysis. 

2 M KCl Extraction 

7.29 Mix fumigated replicates together. Mix non-fumigated replicates together. 

7.30 Weigh 5 g of moist soil to the nearest mg into 60-mL polypropylene extraction tubes. 

Tube will need to be tapped and rinsed with 2 M KCl in order to get the moist soil to bottom of 

tube. 

7.31 Set-up vacuum extractors. Add 25 mL of 2 M KCl to extraction tubes. Extract for 1 h. 

7.32 Following extraction, transfer contents of tubes into polycon containers. Proceed with 

determining mineralizable N. Also analyze N in reagent RODI water as blanks. Refer to 

4D10a1a1 for the remaining procedural steps for 6B2a1a1. 

8. Calculations 

8.1 Calculate the bulk density of 25 g of <2-mm, field-moist soil in a 100-mL beaker manually 

compressed to 20 cm3

 volume. 

Db1 (g cm-3) = 25 g /(1 + H2Of)/20 cm3

where: 

Db1 = Bulk density (g cm-3) 

H2Of = Field water content (g g-1) 

H2Of is determined by procedures 4B. 

391
8.2 Calculate the gravimetric water content [Gravimetric H2O0.55 (g/g)] required for soil to be at 

55% water filled pore space (WFPS), using calculated Db1 in Section 8.1 and an assumed 

particle density of 2.65 g cm-3: 

Gravimetric H2O0.55 (g/g) = {0.55 x [1 - (Db1/2.65)]}/Db1 

where: 

Gravimetric H2O0.55 (g/g) = 55% water filled pore space (WFPS) 

2.65 = Assumed particle density (g cm-3) 

8.3 Calculate the additional gravimetric water needed for soil to reach 55% WFPS: 

H2Oadd = {[Gravimetric H2O 0.55 (g/g)] - (H2Of)} x [W / (1 + H2Of)] 

where: 

W= Weight of soil (g) 

H2Oadd = Amount of water to add to reach 55% WFPS (g) 

8.4 Determine the CO2-Carbon produced by biomass flush during 10 day incubation. 

8.4.1 At 10 days, determine the mole % concentration of CO2 in head space of jar by GC 

analysis. 

8.4.2 Calculate the CO2-Carbon produced by biomass flush as follows: 

CO2-Carbon produced by biomass flush, g BioCO2-Carbon / g FM Soil = 

[(mole %CO2, 10 days, fumigated - mole %CO2, 10 days, non-fumigated) x (0.47 g CO2-C)]/W 

where: 

FM = Field-moist soil (g) 

8.5 Determine the difference between fumigated CO2-Carbon produced during the 10 to 20 day 

incubation period and the non-fumigated CO2-Carbon produced during the same period. 

8.5.1 At 20 days, determine the mole % concentration of CO2 in head space of jar by GC 

analysis. 

8.5.2 Calculate the (fumigated - non-fumigated) CO2-Carbon produced during the 10 to 20 day 

incubation period as follows: 

(fumigated - non-fumigated) CO2-Carbon produced during the 10 to 20 day incubation period, 

g BioCO2-Carbon / g FM Soil = 

{[(mole %CO2, 20 days, fumigated - mole %CO2, 10 days, fumigated) - (mole % CO2, 20 days, 

non-fumigated - mole %CO2, 10 days, non-fumigated)] x (0.47 g CO2-C)} / W 

8.6 Calculate the Soil Biomass Flush (kg CO2-C/ha), using the bulk density value (Db2) 

determined by procedure 4A or ASTM method D-2167: 

Soil biomass flush (kg CO2-Carbon / ha) = (g BioCO2-Carbon / g FM Soil) x (g FM Soil / g OD 

soil) x (Db2: g OD soil / cm3 FM Soil) x (1 kg CO2-Carbon / 1000 g CO2-Carbon) x 

(100000000 cm2 / ha) x (layer thickness, cm) 

392
8.7 Calculate Soil Microbial Biomass (kg C/ha for a given depth interval): 

Soil Biomass Flush (kg C/ha) / 0.41 

0.41 = Kc, fraction of biomass C mineralized to CO2 (Anderson and Domsch, 1978) 

8.8 Calculate (fumigated – non-fumigated) mineralizable N (mg kg-1): 

Fumigated N – Non-fumigated N = {[(F1-F2) x A x B x E x 1000] / C} - {[(N1-N2) x D x F x E 

x 1000]} / G} 

where: 

F1 = Analyte reading, fumigated (mg L-1) 

F2 = Blank reading, reagent RODI Water, fumigated (mg L-1) 

A = Extract volume, fumigated (L) 

B = Dilution, fumigated (if performed) 

C = Sample weight, fumigated (g) 

N1 = Analyte reading non-fumigated sample extract (mg L-1) 

N2 = Blank reading, reagent RODI water, non-fumigated (mg L-1) 

D = Extract volume, non-fumigated (L) 

F = Dilution, non-fumigated (if performed) 

G = Sample weight, non-fumigated (g) 

E = Field-moist/oven-dry ratio (procedure 3D2) 

1000 = Conversion factor to kg-basis 

9. Report 

Report CO2 produced by biomass flush (g CO2-C/g of soil) and soil microbial biomass 

(kg C ha-1 for a given depth interval). Report the difference between mineralizable N of 

fumigated and non-fumigated to the nearest mg N kg-1 soil as NH3. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

American Society for Testing and Materials. 2004. Standard practice for density and unit 

weight of soil in place by the rubber balloon method. D 2167. Annual book of ASTM 

standards. Construction. Section 4. Soil and rock; dimension stone; geosynthesis. Vol. 

04.08. ASTM, Philadelphia, PA. 

Anderson, J.P.E., and K.H. Domsch. 1978. Mineralization of bacteria and fungi in 

chloroform fumigated soils. Soil. Biol. Biochem. 10:207-213. 

Horwath, W.R., and E.A. Paul. 1994. Microbial mass. p. 753-771. In R.W. Weaver, J.S. 

Angle, and P.S. Bottomley (eds.) Methods of soil analysis. Part 2. Microbiological and 

biochemical properties. p. 753-771. ASA and SSSA, Madison, WI. 

Jenkinson, D.S., and D.S. Powlson. 1976. The effects of biocidal treatments on metabolism 

in soil – V.A. method for measuring soil biomass. Soil Biol. Biochem. 8:209-213. 

Kettler, T., and J. Doran. 1997. Procedure for determination of soil microbial biomass (gas 

chromatography method). USDA-ARS, University of Nebraska, Lincoln (unpublished). 

Martens, R. 1987. Estimation of microbial biomass in soil by the respiration method: 

Importance of soil pH and flushing methods of the respired CO2. Soil Biol. Biochem. 

19:77-81. 

393
Plant Analyses (6C) 

Sample Preparation (1B3b3a1a1, 1B3b3b1a1) 

Root Biomass (6C1) 

Plant (above-ground) Biomass (6C2) 

Plant Nutrition (6C3) 

Total Analysis (6C3a) 

Dry Combustion (6C3a1) 

Thermal Conductivity Detector (6C3a1a) 

Carbon, Nitrogen, and Sulfur (6C3a1a1-3) 

Dry (50°C), Roots (6C3a1a1-3a1) Dry (50°C), Plant Material (above-ground) (6C3a1a1-3a2) 

1. Application 

Root biomass in the upper 4 inches of the soil is an input value for the Revised 

Universal Soil Loss Equation (RUSLE) (Renard et al., 1997). The mass, size and distribution 

of roots in the near surface is among the most important factors in determining the resistance of 

the topsoil to water and wind erosion. Root biomass is also one of the major Carbon pools 

found in soil. Commonly, root mass and plant residue in the soil form between 3,000 (annual 

crop) and 15,000 (perennial grasses) lbs/ac/yr soil biomass (Harwood, et al, 1998). Aboveground biomass (production) represents annual yield and can be measured following the 

protocols found in the National Range and Pasture Handbook (USDA-NRCS, 1997). Root 

biomass represents biomass from more than one year. 

The development of new roots and ultimately the decomposition of roots within the soil 

is a major contributor to the Soil Organic Carbon (SOC) pool. In this way, plant roots also 

contribute to the fertility of soils by slowly releasing macro- and micro-nutrients back into the 

soil. 

Root biomass and SOC help bind the soil together by forming aggregates and granular 

structure. This improves the tilth as well as the erosion resistance of soil. Depending upon the 

root turnover rate (known for some species), climate, and residue decomposition rate (known 

for some areas, based on climate and soil moisture status) the amount of Carbon stored in the 

soil can be determined from the root biomass, plant residue and SOC. 

Root biomass is frequently used to calculate root/shoot ratios in order to evaluate the 

health and vigor of plants, and determine the success of establishment of seeded plants at the 4-

leaf stage. 

Dried roots can be fine-grind and total C, N, P, and S can be determined. The C/N ratio 

can also be determined, which is typically different from the C/N ratio of the above ground 

plant material. Low levels of N in the soil will promote root growth over top growth (Bedunah 

and Sosebee, 1995). The C/N ratio of roots, plant residue in the soil and SOC each contribute 

to the residue decomposition rate for soils. Low C/N values lead to more rapid decomposition, 

high C/N levels slow decomposition. The C/N ratio required for decomposition of plant 

residue, without a net tie-up of N, is approximately 25:1. Plant residue from young legumes 

commonly has a C/N ratio of 15:1. Plant residue from woody materials commonly is 400:1 

(Harwood et al., 1998). The C/N ratio of soil microbes is quite variable but commonly falls 

between 15:1 and 3:1 (Paul and Clark, 1989). 

Root biomass/horizon can be paired with the description of roots in each soil horizon 

(i.e. few fine, many very fine, etc.) in the pedon description and thus a qualitative estimate can 

be made of the mass in each size fraction of roots. 

This automated method for determining root biomass also includes some plant residue. 

Woody material is removed and weighed separately. 

Because root biomass determined in this manner includes plant residue it can be used to 

estimate the soil plant residue pool in most models (Jenkinson and Rayner, 1977; Metherell et 

al., 1993). 

394
2. Summary of Method 

The procedural steps described herein encompasses the physical separation of roots and 

plant residue from a soil sample using an automated root washer (1B3b3); these weights 

recorded for root (6C1) and plant biomass (6C2); and these fractions analyzed for total C, N, 

and S by procedure 6C3a1a1-3, respectively. 

3. Interferences 

The soil must be dispersed for successful separation of the roots and plant residue from 

the soil sample. Tap water rather than distilled water should be used to help avoid puddling 

and dispersion problems. 

4. Safety 

Do not touch moving parts of the root washer when it is in operation. Avoid electrical 

shock by ensuring that the electrical cord is dry, and prevent the formation of pools of water 

near the cord. 

5. Equipment 

5.1 Automated root washer (after Brown and Thilenius, 1976) 

5.1.1 Root cages, basket sieves, with No. 30 mesh and 0.5 mm-diameter openings. 

5.1.2 Garden hose 

5.1.3 Sediment tank 

5.2 Buckets 

5.3 Analytical balance, ± 0.01 g sensitivity 

5.4 Drying oven (60o

C-capability) 

5.5 Weighing dishes 

5.6 Scintillating vials 

5.7 Tweezers 

5.8 Drying trays 

6. Reagents 

6.1 Tap water 

6.2 Algaecide, Bath Clear 

7. Procedure 

Sample Preparation 

7.1 Weigh approximately 200 g of field-moist soil to the nearest 0.01 g and record the weight. 

7.2 Pour all of the weighed soil into a root cage and cap it. 

7.3 Immerse cage in tap water until soil disperses (overnight if samples are cloddy). 

Root Washing 

7.4 Make sure that machine is level and that the sediment tank is under the drain. 

7.5 Load the root cages containing the soil and root slurry into the rotation bars. Be sure to 

load them evenly. If not using all of the rotation bar slots, load into every other slot. 

7.6 Fill the washing tank with water to the top of the bottom cage. 

7.7 Add 10 drops of algaecide to the washing tank. Attach machine to water source. 

7.8 Turn on the water at the faucet then turn on the machines spray nozzle. Do not start the 

machine with the lid open. Once the rotator has started, turn on spray nozzles. 

395
7.9 Depending upon the number of samples let the machine run from 40 to 90 min. (Ex: 12 

samples usually take about 60 min.) 

Clean Up and Maintenance 

7.10 Upon completion of sample washing, shut down the sprayer first then the rotator. Drain 

the machine first by opening the bottom plug. Make sure the sediment tank is under the drain. 

After the machine is drained, let the water in the sediment tank settle. Replace plug in the 

machine. 

7.11 Drain the sediment tank water off. Collect the sediment out of the machine and the 

sediment tank and properly dispose of it. 

7.12 Flush out all of the sediment in the machine over the sediment tank. Repeat procedure 

until the machine is completely clean. 

7.13 Clean the entire area. Run water down the drain for about 30 min after everything is 

clean. 

Root/Plant Material Separation and Drying 

7.14 Air-dry roots and plant material at room temperature overnight while still in the sieve 

cages. 

7.15 Remove the roots/plant residue in the cage by tapping them. Brush out any roots/plant 

residue that clings to the side of the sieve cages. 

7.16 Add water to a tray of roots/plant material. Float off as much of the organic matter as 

possible by adding water to a tray roots/plant residue. Much of the organic fraction will be less 

dense than the sand particles that are not removed during root washing. Pour floating matter 

into root cage to trap roots/plant residue; avoid introduction of inorganic portion into cage. 

7.17 If roots/plant material remain in the inorganic fraction, use tweezers to remove as much of 

it as possible and return it to the cage. 

7.18 Air dry at room temperature overnight all material in cage. Next day, tap and brush the 

air-dry material into a tray. 

7.19 Remove the woody material, dry at 50° C in an oven overnight, and record weight of 

woody material. 

7.20 Separate plant residue from roots, dry at 50°C in an oven overnight, and record weights of 

plant residue and roots. 

7.21 Place the roots and plant residue into separate scintillation vials. 

Total Carbon, Nitrogen, and Sulfur Analysis 

7.22 Determine total C, N, and S for roots and plant material (6C3a1a1-3), using fine-grind 

samples (≈ 180 μm). Refer to 4H2a1-3 for the remaining procedural steps for 6C3a1a1-3. 

Separating Roots and Organic Matter Residue (picking) 

7.23 Following initial air-drying, use tweezers and separate organic matter residue from roots 

using tweezers. Roots are usually light colored, and organic residue is usually darker colored. 

7.24 Place the organic residue and roots on separate tared watch glasses and re-dry and weigh. 

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7.25 Record each individual weight for plant residue and roots. Subtract the tare weights and 

record the total weight of air-dry roots and the total weight of air-dry plant residue. Report 

separately root biomass and plant residue rather than just roots including some organic residue. 

8. Calculations 

 

Calculate root biomass using soil bulk density values determined by procedures (3B) described 

in this manual or ASTM method D-2167 (American Society for Testing and Materials, 2004). 

Root biomass/ha for soil layer of given thickness (kg ha-1) = 

[Dry Roots (g)/Total sample weight (g) FM soil] x (Bulk density: g OD soil/cm3 FM soil) x (g 

FM soil/g OD soil) x (1 kg/1000 g) x (100000000 cm2/ha) x (Layer thickness, cm). 

where: 

OD = Oven-dry 

FM = Field-moist 

9. Report 

Report root biomass as kg ha-1 at a given depth interval (cm). If plant residue was 

separated from roots, report each separately. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

American Society for Testing and Materials. 2004. Standard practice for density and unit 

weight of soil in place by the rubber balloon method. D 2167. Annual book of ASTM 

standards. Construction. Section 4. Soil and rock; dimension stone; geosynthesis. Vol. 

04.08. ASTM, Philadelphia, PA. 

Bedunah, D.J. and R.E. Sosebee (eds.). 1995. Wildland plants: Physiological ecology and 

developmental morphology. Soc. Range Mgt., Denver, CO. 

Brown, G.R. and J.F. Thilenius. 1976. A low-cost machine for separation of roots from soil 

material. J. Range Mgt. 29:506-507 

Fribourg, H.A. 1953. A rapid method for washing roots. Agron. J. 45:334-335. 

Harwood, R.R., M.A. Cavigelli, S.R. Deming, L.A. Frost and L.K. Probyn (eds.). 1998. 

Michigan field crop ecology: Managing biological processes for productivity and 

environmental quality. Michigan State Univ. Ext. Bull. E-2646, 92 pp. 

Jenkinson, D.S., and J.H. Rayner. 1977. The turnover of soil organic matter in some of the 

Rothamsted classical experiments. Soil Sci. 123:298-305. 

Lauenroth, W.K. and W.C. Whitman. 1971. A rapid method for washing roots. J. Range 

Mgt. 24:308-309. 

Metherell, A.K., L.A. Harding, C.V. Cove and, W.J. Parton. 1993. CENTURY soil organic 

matter model environment, technical documentation agroecosystem, Version 4.0. Great 

Plains System Res. Unit Tech. Rep. No. 4, USDA-ARS, Ft. Collins, CO. 

Paul, E.A., and F.E. Clark. 1989. Soil Microbiology and Biochemistry. Academic Press, 

Inc., Harcourt Brace Jovanovich, Publ., San Diego, CA. 

Renard, K.G., G.R. Foster, G.A. Weesies, D.K. McCool, and D.C. Yoder. 1997. Predicting 

soil erosion by water: A guide to conservation planning with the revised Universal Soil 

Loss Equation (RUSLE). Agric. Handb. 703, USDA-ARS, U.S. Govt. Print Office, 

Washington, DC. . 

Sosebee, R.E. (ed.) 1977. Rangeland plant physiology. Range Sci. Series No. 4. Soc. 

Range Mgt., Denver, CO. 

397
Thornley, J.H.M. 1995. Shoot:root allocation with respect to C, N and P: An investigation 

and comparison of resistance and teleonomic models. An. of Bot. 75:391-405. 

USDA-NRCS, 1997. Inventory and monitoring grazing land resources. p 4i – 4ex21. In

National range and pasture handbook, Chapter 4. U.S. Govt. Print. Office, Washington 

DC. 

Ratios and Estimates Related to Biological Analyses (6E) 

Estimates or calculated values associated with soil biological and plant analyses are 

described within the respective methods. Additional information on the reporting of these 

calculated values can be obtained from the SSL upon request. 

MINERALOGY (7) 

Instrumental Analyses (7A) 

The physical and chemical properties of a soil are controlled to a very large degree by 

the soil minerals, especially by those minerals constituting the clay fraction (McBride, 1989; 

Whittig and Allardice, 1986). Positive identification of mineral species and quantitative 

estimation of their proportions in soils usually require the application of several complementary 

qualitative and quantitative analyses (Whittig and Allardice, 1986). Some of the semiquantitative and quantitative procedures that have been performed by the SSL include X-ray 

diffraction (procedure 7A1a1) and thermal analysis (7A2a, 7A3a, and 7A4a). Other indirect, 

ancillary procedures to infer mineral composition include linear extensibility, elemental 

analysis, and CEC/clay ratios. 

Analysis by x-ray diffraction facilitates identification of crystalline mineral components 

of soil and semi-quantitative estimates of relative amounts. It is commonly applied to the clay 

fraction in soils and to layer silicate (phyllosilicates) minerals in particular. Identification is by 

d-spacings (spatial distance between repeating planes of atoms) characteristic of a mineral, 

according to Bragg’s Law. Because layer silicates structures are very similar from one mineral 

to another, except in the direction perpendicular to the layers, several treatments (cation 

saturation and heating) must be used to correctly identify the several minerals. In x-ray 

analysis of soils or clay samples, there are difficulties in evaluation of and compensation for the 

variations in chemical composition, crystal perfection, amorphous substances, and particle-size 

(Whittig and Allardice, 1986; Hughes et al., 1994). A more reliable and accurate estimation of 

mineral percentages is provided when x-ray diffraction analysis is used in conjunction with 

other methods, e.g., differential-thermal, surface-area, elemental analysis, and other speciesspecific chemical methods (Alexiades and Jackson, 1966; Karathanasis and Hajek, 1982). 

Many soil constituents undergo thermal reactions upon heating that serve as diagnostic 

properties for qualitative and quantitative identification of these substances (Tan et al., 1986; 

Karathanasis and Harris, 1994). Thermogravimetric analysis (TGA) (procedure 7A2a) is a 

technique for determining weight loss of a sample when it is heated at a constant rate. The 

TGA is an outgrowth of dehydration curves that were used in early studies of various 

phyllosilicate clay minerals (Jackson, 1956). However, with TGA the sample weight is 

monitored continuously rather than measured at discrete intervals after periods of heating at a 

constant temperature (Wendlandt, 1986). The TGA measures only reactions that involve 

weight loss of the sample. 

Differential scanning calorimetry (DSC) (procedure 7A4a) is a calorimetric technique 

that theoretically measures the amount of energy required to establish zero temperature 

difference between sample and reference material as the two are heated side by side at a 

controlled rate (Tan et al, 1986; Karathanasis and Harris, 1994). Most common DCS 

instruments have sample and reference pans heated in a single furnace, with the difference in 

temperature measured during various endothermic and exothermic reactions. This difference in 

398
temperature is then converted to a value equivalent to an enthalpy change (expressed in 

calories) using instrumental calibrations (Karathanasis and Harris, 1994). 

The TGA and DSC are complementary methods available to the analyst. Many of the 

same clay mineral reactions, e.g., dehydroxylation, loss of surface adsorbed water, 

decomposition of carbonates, and oxidation, that are studied by DSC can also be studied by 

TGA. However, some transformation reactions, e.g., melting or structural reorganization 

(quartz alpha-beta transition), cannot be measured by TGA because no weight loss is involved 

(Karathanasis and Harris, 1994). The DSC procedures provide information about energy 

relationships in the structures and reactions of the solid phase, whereas TGA provides 

quantitative information about quantities of substances gained or lost by the solid phase during 

certain thermally driven reactions. 

References Alexiades, C.A., and M.L. Jackson. 1965. Quantitative clay mineralogical analysis of soils and 

sediments. Clays and Clay Miner. 14:35-52. 

Jackson, M.L. Soil chemical analysis. Advan. course. M. L. Jackson, Madison, WI. 

Karathanasis, A.D., and B.F. Hajek. 1982. Revised methods for rapid quantitative 

determination of minerals in soil clays. Soil Sci. Soc. Am. J. 46:419-425. 

Karathanasis, A.D., and W.G. Harris. 1994. Quantitative thermal analysis of soil minerals. p. 

360-411. In J.E. Amonette and L.W. Zelazny (eds.) Quantitative methods in soil mineralogy. 

Soil Sci. Soc. Am. Misc. Publ. SSSA, Madison, WI. 

McBride, M.B. 1989. Surface chemistry of soil minerals. p. 35-88. In J.B. Dixon and S.B. 

Weed (eds.) Minerals in soil environments. Soil Sci. Soc. Am. Book Series No. 1. ASA and 

SSSA, Madison, WI. 

Tan, K.H., and B.F. Hajek, and I. Barshad. 1986. Thermal analysis techniques. p. 151-183. In

A. Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical properties. 2nd 

ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Wendlandt, W.W. 1986. Thermal analysis. 3rd ed. John Wiley and Sons, New York. 

Whittig, L.D., and W.R. Allardice. 1986. X-ray diffraction techniques. p. 331-362. In A. Klute 

(ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. 

Monogr. 9. ASA and SSSA, Madison, WI. 

Instrumental Analyses (7A) 

X-Ray Diffractometer (7A1) 

Thin Film on Glass, Resin Pretreatment II (7A1a) Mg Room Temperature, Mg Glycerol Solvated, K 300°, K 500° C (7A1a1) 

1. Application 

Clay fractions of soils are commonly composed of mixtures of one or more 

phyllosilicate minerals together with primary minerals inherited directly from the parent 

material (Olson et al., 1999). Positive identification of mineral species and quantitative 

estimation of their proportions in these polycomponent systems usually require the application 

of several complementary qualitative and quantitative analyses (Whittig and Allardice, 1986; 

Amonette and Zelazny, 1994; Wilson, 1994; Moore and Reynolds, 1997). One of the most 

useful methods to identify and to make semiquantitative estimates of the crystalline mineral 

components of soil is x-ray diffraction analysis (Hughes et al., 1994; Kahle et al., 2002). 

Quantification of a mineral by x-ray diffraction requires attention to many details, including 

sample (slide) size relative to the incident x-ray beam, thickness and particle size uniformity of 

sample, and beam-sample orientation (Moore and Reynolds, 1997). More complex 

quantification procedures include using standard additions, full pattern fitting, and determining 

mineral intensity factors (Kahle et. al., 2002). At best, quantification can approach a precision 

of +5% and an accuracy of +10 to 20% (Moore and Reynolds, 1997). 

The operational strategy at the SSL and the preceding Lincoln SSL has been to base 

mineral quantification on first order peak intensities. Semi-quantitative interpretations have 

399
been held consistent over time (1964 to the present) by adjusting instrumental parameters (e.g., 

scan speed) to maintain a constant peak intensity for a in-house reference clay standard and 

subsequently soil samples. The intent is to keep interpretations consistent from sample to 

sample. 

2. Summary of Method 

Soils are dispersed and separated into fractions of interest. Sands and silts are mounted 

on glass slides as slurries, on a smear of Vaseline, or on double sticky tape for analysis. Clay 

suspensions are placed on glass slides to dry and to preferentially orient clay minerals. Most 

samples of soil clays contain fewer than 7 minerals that require identification. The soil clay 

minerals of greatest interest are phyllosilicates, e.g., kaolinite, mica (illite), smectite, 

vermiculite, hydroxy-interlayered vermiculite, smectite, hydroxy-interlayered smectite and 

chlorite. 

 Diffraction maxima (peaks) develop from the interaction of x-rays with planes of 

elements that repeat at a constant distance (d-spacing) through the crystal structure. Generally, 

no two minerals have exactly the same d-spacings in three dimensions and the angles at which 

diffraction occurs are distinctive for a particular mineral (Whittig and Allardice, 1986; Moore 

and Reynolds, 1997). Phyllosilicates (or layer silicate minerals) have very similar structures 

except in the direction perpendicular to the layers (c-dimension). Several treatments are needed 

to sort out which minerals are present. Glycerol is added to expand smectites. Ionic saturation 

and/or heat treatments are used to collapse some 2:1 layer silicates and dehydroxylate kaolinite, 

gibbsite, and goethite, eliminating characteristic peaks. 

The crystal "d" spacings of minerals, i.e., the interval between repeating planes of 

atoms, can be calculated by Bragg's Law as follows: 

nλ = 2d sin θ

where: 

n = interger that denotes order of diffraction 

λ = x-radiation wavelength (Angstroms, Å) 

d = crystal "d" spacing (Å) 

θ = angle of incidence 

When n = 1, diffraction is of the first order. The wavelength of radiation from an X-ray tube is 

constant and characteristic for the target metal in the tube. Copper radiation (CuKα) with a 

wavelength of 1.54 Å (0.154 nm) is used at the SSL. Because of the similar structure of layer 

silicates commonly present in soil clays, several treatments that characteristically affect the "d" 

spacings are necessary to identify the clay components. At the SSL, four treatments are used, 

i.e., Mg2+ (room temperature); Mg2+-glycerol (room temperature); K+

 (300°C); and K+ (500°C). 

Standard tables to convert θ or 2θ angles to crystal d-spacings are published in the U.S. 

Geological Survey Circular 29 (Switzer et al., 1948) and in other publications (Brown, 1980). 

Through the years hardware has been updated and the recording of data has evolved from a 

strip chart recorder through several kinds of electronic software. X-ray by this procedure 

(7A1a1) is semiquantitative. 

3. Interferences 

Interstratification of phyllosilicate minerals causes problems in identification. These 

interstratified mixtures, differences in crystal size, purity, chemical composition, atomic unit 

cell positions, and background or matrix interferences affect quantification (Moore and 

Reynolds, 1997; Kahle et al., 2002). No pretreatments other than ionic saturation and 

dispersion with sodium hexametaphosphate are used for separation and isolation of the clay 

fraction in the routine procedure. Impurities such as organic matter, carbonates and iron oxides 

may act as matrix interferences causing peak attenuation during X-ray analysis or may interfere 

with clay dispersion and separation. Pretreatments to remove these impurities serve to 

400
concentrate the crystalline clay fraction and may increase accuracy, but also potentially result 

in degradation of certain mineral species (e.g, smectites), as well as loss of precision (Hughes et 

al., 1994). 

The separation (centrifuge) procedure used to isolate the clay fraction from the other 

size fractions of the soil skews the <2-μm clay suspension toward the fine clay, but it 

minimizes the inclusion of fine silt in the fraction. Sedimentation of the clay slurry on a glass 

slide tends to cause differential settling by particle size (i.e., increasing the relative intensity of 

finer clay minerals). 

Dried clay may peel from the XRD slide. One remedy is to rewet the peeled clay on the 

slide with 1 drop of glue-water mixture (1:7). Other remedies are: 

a. Place double sticky tape on the slide prior to re-wetting the dried clay with the glue-water 

mixture. 

b. Dilute the suspension if thick. 

c. Crush with ethanol and dry, and then add water to make a slurry slide. 

d. Roughen the slide surface with a fine-grit sandpaper. 

An optimum amount of glycerol on the slides is required to solvate the clay, i.e., to expand smectites to 18 Å. X-ray analysis should be performed 1 to 2 days after glycerol 

addition. If excess glycerol is applied to the slide and free glycerol remains on the surface, 

XRD peaks are attenuated. Some suggestions to dry the slides and achieve optimum glycerol 

solvation are as follows: 

a. Use a chamber such as a desiccator (with no desiccant) to dry slide, especially when the clay 

is thin. 

b. If the center of slide is whitish and dry, usually with thick clay, brush slide with glycerol or 

add an additional drop of glycerol. 

4. Safety 

Operate the centrifuge with caution. Keep the centrifuge lid closed when in operation. 

Ensure that all rotors and tubes are seated firmly in proper location. Use tongs and appropriate 

thermal protection when operating the muffle furnace. The diffraction unit presents an 

electrical and radiation hazard. Analysts must receive radiation safety training before operating 

the equipment. Employees must wear a radiation film badge while in the room when the 

diffraction unit is in operation. 

5. Equipment 

5.1 Teaspoon (5 g) 

5.2 Dispenser, 5 mL, for sodium hexametaphosphate solution 

5.3 Centrifuge, International No. 2, with No. 240 head and carriers for centrifuge tubes, 

International Equip. Co., Boston, MA 

5.4 Centrifuge tubes, plastic, 100 mL, on which 10-cm solution depth is marked 

5.5 Rubber stoppers, No. 6, for centrifuge tubes 

5.6 Mechanical reciprocating shaker, 100 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.7 Plastic cups, 60 mL (2 fl. oz.) with lids 

5.8 Label printer 

5.9 Hypodermic syringes, plastic, 12 mL, with tip caps 

5.10 Screen, 80 mesh, copper 

5.11 Dropper bottle, plastic, 30 mL (1 fl. oz.), for a 1:7 glycerol:water mixture 

401
5.12 Muffle furnace 

5.13 X-ray diffractometer, Bruker 5000-Dmatic, with X-Y autosampler that accomodates 66 

samples or standards, Bruker AXS Inc., Madison, WI 

5.14 Computer, Diffractplus EVA software, release 2000, Bruker AXS Inc., Madison, WI, and 

printer 

5.15 XRD slides, glass, 2.54 X 2.54 mm (frosted glass slides used for K-treated samples) 

5.16 XRD sample preparation board, wood, with 32 places for glass XRD slides 

5.17 Slide holder. 

5.18 Reference slides: quartz and clay from reference soil 

6. Reagents 

6.1 Reverse Osmosis (RO) water, ASTM Type III grade of reagent water. 

6.2 Sodium hexametaphosphate solution. Dissolve 35.7 g of sodium 

hexametaphosphate (NaPO3)6 and 7.94 g of sodium carbonate (Na2CO3) in 

1 L RO water. 

6.3 Potassium chloride (KCl), 1.0 N. Dissolve 74.60 g KCl in 1 L RO water or 671.40 g KCl 

in 9 L RO water. 

6.4 Magnesium chloride (MgCl2), 1.0 N. Dissolve 47.61 g MgCl2 in 1 L RO water or 428.49 

g MgCl2 in 9 L RO water. 

6.5 Glycerol:water mixture (1:7). Add 4 mL of glycerol to 28 mL RO water plus 2 drops of 

toluene. 

6.6 Exchange resin, Rexyn 101 (H), analytical grade. Pretreatment of resin as follows: 

6.6.1 Divide equally Rexyn 101 (H), approximately 250-g portions, into two 600-mL beakers 

labeled K and Mg and add appropriate salt solution ( 1.0 N KCl or 1.0 N MgCl2). Cover 

resin with salt solution. 

6.6.2 Stir, let settle for 10 min, decant clear solution, and add salt solution. Repeat 3 times. 

Leave resin covered in salt solution for 8 to 12 h. 

6.6.3 Repeat step 6.6.2 on a second day. Resin is ready for syringes. Saturated resin not used 

initially for syringes can be saved for future use. 

6.7 White glue, diluted 1:7 with RO water 

7. Procedure 

Preparation (Recharge) of Resin-Loaded Syringes

7.1 Place a small circle of 80-mesh screen in a 12-mL syringe and add 4 cm3 of exchange resin 

from which salt solution has been drained. The procedure requires 2 Mg and 2 K slides for 

each sample, so two sets of syringes are prepared. 

7.2 Saturate the resin in each of the syringes with 4 mL of the appropriate 1.0 N salt solution 

(MgCl2 or KCl) and expel. Repeat saturation of resin. Individual steps follow. 

7.3 Fill syringe completely with the salt solution and allow to equilibrate for 4 to 20 h. 

7.4 Rinse syringe twice with 4 mL of RO water and rinse tip cap. 

7.5 Completely fill syringe with RO water and allow to equilibrate for 4 to 20 h. 

7.6 Rinse syringe twice with RO water. 

7.7 Expel water, cap syringe, and store. 

Preparation of Clay Suspension

7.8 Print a run sheets using LIMS. Each run consists of 8 samples with 4 treatments for each 

sample. 

402
7.9 Label each 100ml plastic centrifuge tube with a sample number from the run sheet.

7.10 Place ≈ 5 g (1 tsp) of air-dry <2-mm soil in a 100-mL plastic centrifuge tube. If the 

sample appears to be primarily sand, use 10 g (2 tsp) of <2-mm soil to obtain sufficient clay. 

7.11 Add 5 mL of sodium hexametaphosphate dispersion agent. If the soil contains gypsum or 

is primarily calcium carbonate, use 10 mL of sodium hexametaphosphate dispersing agent. 

7.12 Fill tube to 9.5-cm height with RO water and close with a stopper. 

7.13 Place the tubes in a mechanical shaker and shake overnight (at least 4 hours). 

7.14 Remove stopper from tube and rinse stopper and sides of tube with enough water to bring 

the volume to the 10-cm mark. 

7.15 Balance the pairs of tubes and place in centrifuge. Centrifuge at 750 rpm for 3.0 min. 

7.16 If the clay is dispersed, carefully decant 30 mL of suspension into a labeled, 60-mL, 

plastic cup and cover with lid. 

7.17 If the clay did not disperse after being shaken overnight, decant and discard the clear 

supernatant. Then add an additional 10mL sodium hexametaphosphate and sufficient RO water 

to bring the level up to 9.5 cm depth. Repeat Sections 7.13 to 7.16. 

7.18 Clay suspension is used for X-ray diffraction analysis. It can be dried and used for 

elemental or thermal analysis. 

Thin Film on Glass, Resin Pretreatment

7.19 The SSL uses sample boards that hold 32 slides each, i.e., 8 samples x 4 treatments. Place 

run number on the sample board. Prepare the sample board with glass XRD slides to receive 

the following 4 treatments per clay suspension sample. 

Mg2+- room temperature 

Mg2+- glycerol (room temperature) 

K+

- 300°C (heated 2 h) 

K+- 500°C (heated 2 h) 

7.20 Use a hypodermic syringe to place 6 drops of the glycerol:water mixture (1:7) on each 

Mg2+ -glycerol slide 

7.21 Draw 3 to 4 mL of the clay suspension into the Mg syringe and invert back and forth to 

facilitate cation exchange. 

7.22 Dispense 3 drops to clear the tip. 

7.23 Dispense ≈ 0.3 mL (6 to 10 drops) to cover the Mg and mg-glycerol XRD slides. 

Similarly, use the K syringes to apply clay suspension to the frosted glass K-300 and K-500 

slides. Draw RO water into each syringe and expel 3 times to remove all of the clay 

suspension, cap and store syringes. Recharge all syringes after 10 run boards. 

7.24 When the clay suspension has dried, transfer the slides with the K+-saturated clays to the 

muffle furnace. Heat for a minimum of 2 hours at 300°C, remove the K-300 batch of slides. 

403
Set the temperature to 500 °C and heat slides for a minimum of 2 hours at 500°C. After slides 

are cool, return them to the run board. 

X-ray Diffraction Operation

7.25 Complete X-ray analysis of the glycerol slide within 1 to 2 days after the slide dries. If 

this is not possible, add additional glycerol prior to run (e.g., add 6 drops of glycerol:water 

mixture to dry slide 24 h prior to x-ray analysis). 

7.26 Place the tray with filled sample holders in the autosampler and execute the run. Use the 

following parameters: 

CuKα radiation, λ = 1.54 Å (0.154 nm) 

Scan range = 2°to 35°2θ

Generator settings = 40 kv, 30 ma 

Divergence slit = 1° 

Receiving slit = 0.2 mm 

Step-size and scan-speed vary depending on intensity of X-rays generated. Settings should be 

adjusted to maintain the same peak intensities on the standard reference clay and quartz 

standard over the long term regardless of tube intensities. 

7.27 In the laboratory information system (LIMS), create a batch file. Data in file is transferred 

to a job program on the x-ray computer software for data analysis. These data include project 

and sample identification. Include both the quartz and soil standard with each run. 

7.28 Activate job program for analysis. The job stores raw data on the hard disk under the 

subdirectory designated by year, project type, project name. 

7.29 Prepare and print a 4-color graphics chart. The four colors are blue (Mg2+); green (Mg2+-

glycerol); pink (K+ 300°C); and red (K+ 500°C). File hard copies of detected peaks and 

graphics chart in pasteboard binders by state, county, and chronology. 

7.30 Compare quartz and soil standard patterns electronically with previous runs to ensure peak 

intensity and positions have remained constant. 

Interpretation of X-ray Diffraction Data 

7.31 The angle in degrees two theta (2θ) measured in X-ray diffraction analyses is converted to 

angstroms (Å) using tables complied according to Bragg's Law. Refer to summary of method. 

Angstroms convert to nanometers (nm) by a factor of 0.1, e.g., 14 Å = 1.4 nm. 

7.32 Use the following X-ray diffraction criteria to identify some common crystalline minerals. 

The reported "d" values are for 00l basal spacings. The Miller index (hkl)specifies a plane or 

crystal face which has some orientation to the three crystallographic axes of a, b, and c. The 

Miller index (00l) indicates a crystal face that is perpendicular to the a and b axes (Schultz, 

1989). The following X-ray diffraction criteria also have some questions (Q) that may aid the 

analyst in interpreting the diffraction patterns. These questions are a suggested procedural 

approach to help the analyst identify the relative locations of a few peaks and to confirm key 

criteria. For a more complete list of d-spacings for confirmation or identification of a mineral 

consult the Mineral Powder Diffraction File – Data Book (JCPDS 1980). 

404
X-Ray Diffraction Criteria

7.32.1 Kaolinite and Halloysite 

a. Crystal structure missing at 500°C. 

b. 7 Å (7.2 to 7.5 Å) with all other treatments 

Q. Is there a 7 Å peak? Is it destroyed at 500°C? Kaolinite or Halloysite. 

Q. Is the peak sharp and at ~ 7.1 Å (but absent at 500°C)? Kaolinite. 

Q. Is the peak broad and at 7.2 to 7.5 Å (but absent at 500°C)? Halloysite. 

7.32.2 Mica (Illite) a. 10 Å with all treatments. 

b. 10 Å with Mg2+-saturation 

Q. Is there a 10 Å peak with Mg2+-saturation? Mica (Illite). 

7.32.3 Chlorite 

a. Crystal structure of Fe-chlorites destroyed at 650 to 700°C. b. 14 Å with all other treatments. 

c. 14 Å at 500°C. 

d. Generally also has strong 7 Å peak. 

Q. Is there a 14 Å peak when heated to 500°C? Chlorite. 

7.32.4 Vermiculite

a. 14 Å with Mg2+-saturation. 

b. 14 Å with Mg2+-glycerol solvation. c. Nearly 10 Å with K+

saturation. 

d. 10 Å when K+-saturated and heated to 300°C. 

Q. Is there an enhanced 10 Å peak with K+-saturation in comparison to Mg2+saturation that 

cannot be attributed to smectitie? Vermiculite. 

7.32.5 Smectite 

a. 14 Å with Mg2+-saturation 

b. 12 to 12.5 Å with K+- or Na+-saturation. 

c. 17 to 18 Å with Mg2+-glycerol solvation. 

d. 10 Å with K+-saturation and heating to 300°C. 

Q. Is there a 17 to 18 Å peak upon solvation? Smectite. 

7.32.6 Gibbsite

a. Peak at 4.83 to 4.85 Å with Mg2+ and Mg2+-glycerol but destroyed when heated to 300°C. 

7.32.7 Goethite 

a. Peak at 4.16 to 4.18 Å with Mg2+ and Mg2+-glycerol but destroyed when heated to 300°C. 

7.32.8 Hydroxy-interlayed Vermiculite or Smectite 

a. Failure to completely collapse to 10 Å of smectite or vermiculite when K+-saturated and 

heated to 300°C. 

405
7.32.9 Quartz 

a. Peaks at 4.27 Å and 3.34 Å with all treatments (only 3.34 if small amounts). 

7.32.10 Lepidocrocite a. Peak at 6.2 to 6.4 Å with Mg2+ and Mg2+-glycerol but destroyed when heated to 300°C. 

7.32.11 Potassium Feldspar a. Peak at 3.24 Å with all treatments. 

7.32.12 Plagioclase Feldspar 

a. Twin peaks between 3.16 and 3.21 with all treatments. 

7.32.13 Calcite 

a. Peak at 3.035 Å with all treatments. 

7.32.14 Dolomite 

a. Peak at 2.88 to 2.89 Å with all treatments. 

7.32.15 Gypsum a. Peak at 7.56 Å with Mg2+ and Mg2+-glycerol, but destroyed when heated to 300°C. 

7.32.16 Mixed Layer Vermiculite-Mica 

a. Randomly interstratified: Peak between 10 and 14 Å with Mg2+ that does not expand with 

Mg2+-glycerol; peak collapses to 10 Å with K+-saturation and heating to 300°C. b. Regularly interstratified: A 24 Å peak (and higher orders); no change with Mg2+-glycerol 

treatment; K+ saturation and heating collapses vermiculite and a produces a 10 Å peak. 

7.32.17 Mixed Layer Smectite-Mica

a. Randomly interstratified: Peak between 10 and 14 Å with Mg2+ that expands to 14-16 Å with 

Mg2+-glycerol;Peak collapses to 10 Å with K+-saturation and heating to 300°C. b. Regularly interstratified: A small 24 Å peak and large peak at 12 Å with Mg2+-saturation; 

expands to 28 Å with Mg2+-glycerol treatment; K+-saturation and heating collapses smectite, then produces a 10 Å peak. 

7.32.18 Mixed Layer Chlorite-Vermiculite Randomly Interstratified: Peak at 14 Å with Mg2+ and Mg2+-glycerol; Peak collapses incompletely to between 10 and 14 Å with K+

-saturation and heating. b. Regularly interstratified: A 28 Å peak (and higher orders) with Mg-saturation; no expansion 

with Mg2+-glycerol treatment; K+

-saturation and heating to 500°C collapses vermiculite and a 

produces a 24 Å peak. 

7.32.19 Mixed Layer Chlorite-Smectite 

a. Randomly interstratified: Peak at 14 Å with Mg2+-saturation; expands to higher spacings 

(≈16 Å) with Mg2+-glycerol treatment; Peak collapses incompletely to between 10 and 14 Å 

with K+-saturation and heating . 

7.33 Use the X-ray diffraction criteria, i.e., diagnostic basal 00l spacings (Å), in Table 1 for 

identification and ready reference of some common crystalline minerals as affected by 

differentiating sample treatments. 

7.34 Preferential orientation of clay mineral samples enhances diffraction from 

the basal (00l) spacing and tends to minimize the number and intensity of peaks from 

diffraction by other hkl planes. With preferential orientation, second, third, and fourth order 

406
peaks may be recorded in addition to the basal first order peaks. Groups of associated peaks 

that differ by order of diffraction are as follows: 

7.34.1 Smectite (Mg2+-glycerol): a. 17 to 18 Å. 

b. 8.5 to 9 Å (weak). 

7.34.2 Chlorite, vermiculite, and smectite: 

a. 14, 7, 4.7, and 3.5 Å. 

b. 7, 4.7, and 3.5 Å weak for smectite. 

(Note: High Fe substitution in the chlorite structure results in a decrease in the peak intensity of odd numbered orders (e.g., 14 and 4.7 Å) and increase in peak intensity of even number orders (7 and 3.5 Å)). 

7.34.3 Mica: 

a. 10, 5 (weak in biotites and moderate in muscovites), and 3.3 Å. 

7.34.4 Kaolinite: 

a. 7 and 3.5 Å. 

7.35 The differentiation of kaolinite and halloysite in a sample can be aided by the use of 

formamide (Churchman et al., 1984). The intercalation and expansion of halloysite to a dspacing of ≈ 10.4 Å is relatively rapid (20 to 30 min), whereas kaolinite expansion requires ≈ 4 

h upon treatment. The procedure is as follows: 

7.35.1 Lightly spray formamide as an aerosol on the dried Mg2+-saturated slide. 

7.35.2 Wait 15 min but not more than 1 h and X-ray approximately 7.6 to 13.5° 2θ (d = 11.6 to 6.55 Å). 

7.35.3 Halloysite will expand to ≈ 10.4 Å, whereas kaolinite will remain unchanged. 

7.35.4 Heating the sample to 110°C for 15 min will collapse the halloysite to ≈ 7 Å. 

7.35.5 The total amount of kaolinite and halloysite can be determined by thermal analysis. The intensity ratio of the 10.4 to 7.2 Å peaks of the formamide-treated sample can be used to 

determine the relative percentage of halloysite and kaolinite. 

7.35.6 The total amount of kaolinite and halloysite can be determined by thermal analysis. The intensity ratio of the 10.4 to 7.2 Å peaks of the formamide-treated sample can be used to 

determine the relative percentage of halloysite and kaolinite. 

8. Calculations 

X-ray diffraction produces peaks on a chart that corresponds to 2θ angle on a 

goniometer. Standard tables to convert θ or 2θ to crystal "d" spacings are published in the U.S. 

Geological Survey Circular 29 (Switzer et al., 1948) and in other publications (Brown, 1980). 

The crystal "d" spacings of minerals, i.e., the interval between repeating planes of atoms, can 

be calculated by Bragg's Law. Refer to summary of method. 

9. Report

From the "Detected Peaks File" and graphics chart, identify the minerals present 

according to the registered "d" spacings. As a first approximation, use the following peak 

intensities, i.e., peak heights above background in counts s-1, to assign each layer silicate 

mineral to one of the 5 semiquantitative classes. 

407
Peak Height 

Class above Background 

 (counts sec-1) 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

5 (Very Large) >1800 

4 (Large) 1120 to 1800 

3 (Medium) 360 to 1120 

2 (Small) 110 to 360 

1 (Very Small) <110 

Adjust class placement to reflect area under the curve if peak is broad relative to peak 

height or if thermal, elemental, clay activity data, or other evidence warrant class adjustment. 

If there are no peaks or no evidence of crystalline components, place the sample in NX class 

(noncrystalline). If there are only 1 to 3 very small (class1) peaks, also indicate NX to infer a 

major noncrystalline component. 

10. Precision and Accuracy 

X-ray by procedure 7A1a1 is semi-quantitative. Precision and accuracy data are 

available from the SSL upon request. 

11. References 

Amonette, J.E., and L.W. Zelazny. 1994. Quantitative methods in soil mineralogy. Soil 

Sci. Soc. Am. Misc. Publ. SSSA. Madison, WI. 

Brown, G. 1980. Appendix I (Tables for the determination of d in Å from 2θ for the Kα

and Kβ radiations of copper, cobalt, and iron). p. 439-475. In G.W. Brindley and G. 

Brown (eds.) Crystal structures of clay minerals and their x-ray identification. 

Mineralogical Soc. Monograph No. 5. Mineralogical Soc. Great Britain. 

Churchman, G.J., J.S. Whitton, G.G.C. Claridge, and B.K.G. Theng. 1984. Intercalation 

method using formamide for differentiating halloysite from kaolinite. Clays and Clay 

Minerals 32:241-248. 

Hughes, R.E., D.M. Moore, and H.D. Glass. 1994. Qualitative and quantitative analysis 

of clay minerals in soils. p. 330-359. In J.E. Amonette and L.W. Zelazny (eds.) 

Quantitative methods in soil mineralogy. Soil Sci. Soc. Am. Misc. Publ. SSSA. 

Madison, WI. 

JCPDS. 1980. Mineral powder diffraction file – Data book. International Centre for 

Diffraction Data, Swarthmore, PA. 

Kahle, M., M.Kleber, and R. Jahn. 2002. Review of XRD-based quantitative analyses of 

clay minerals in soils: The suitability of mineral intensity factors. Geoderma 109:191-

205. 

Moore, D.M., and R.C. Reynolds, Jr. 1997. X-ray diffraction and the identification and 

analysis of clay minerals. Oxford Univ. Press. NY, York, NY. 

Olson, C.G., M.L. Thompson, and M.A. Wilson. 1999. Section F. Soil Mineralogy, 

Chapter 2. Phyllosilicates. P. F-77 to F-13. In M.E. Sumner (ed.) Handbook of soil 

science. CRC Press, Boca Raton, FL. 

Schulze, D.G. 1989. An introduction to soil mineralogy. p. 1-34. In J.B. Dixon and S.B. 

Weed (eds.) Minerals in soil environments. Soil Sci. Soc. Am. Book Series No. 1. 

SSSA. Madison, WI. 

Switzer, G., J.M. Axelrod, M.L. Lindberg, and E.S. Larsen 3d. 1948. U.S. Dept. Interior. 

Geological Survey. Circular 29. Washington, DC. 

Whittig, L.D., and W.R. Allardice. 1986. X-ray diffraction techniques. In A. Klute (ed.) 

Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. 

Agronomy 9:331-362. 

Wilson, M.J. 1994. Clay mineralogy: Spectroscopic and chemical determinative methods. 

Chapman and Hall, NY. 

408
Table 1. X-ray diffraction parameters of common soil minerals. 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Mineral Treatment 

 Na+ Mg2+ Mg2+ K+ K+ K+ K+

 Gly 300°C 500°C 700°C 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 00l diffraction spacing in angstroms 

Kaolinite 7 7 7 7 7 LD1/ LD 

Halloysite 7B2/ 7B 7B 7B 7B LD LD 

Mica (Illite) 10 10 10 10 10 10 10 

Chlorite 14*3/ 14* 14* 14* 14* 14* T4/

Vermiculite 14 14 14 10 10 10 10 

Smectite 12.5 14 18 12.5 10 10 10 

Gibbsite 4.85 4.85 4.85 4.85 LD LD LD 

Goethite 4.18 4.18 4.18 4.18 LD LD LD 

Lepidocrocite 6.24 6.24 6.24 6.24 LD LD LD 

Interlayer 10-14 10-14 10-18 10-14 10-14 10-14 10-14 

Quartz 3.34 and 4.27 for all treatments 

Calcite 3.035 for all treatments 

Dolomite 2.886 for all treatments 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

1/ LD = Lattice destroyed 

2/ B = Broad peak is common 

3/ * = Sometimes <14 Å 

4/ T = Temperature of decomposition varies with chemical composition, particle-size, and 

heating conditions. 

409
Instrumental Analyses (7A) 

Thermogravimetric Analysis (7A2) 

Thermal Analyzer (7A2a) 

Differential Thermal Analysis (7A3) 

Thermal Analyzer (7A3a) 

1. Application 

Thermal analysis defines a group of analyses that determine some physical parameter, 

e.g., energy, weight, or evolved substances, as a dynamic function of temperature (Tan et al., 

1986; Karathanasis and Harris, 1994). Thermogravimetric analysis (TGA) is a technique for 

determining weight loss of a sample as it is being heated at a controlled rate. The weight 

changes are recorded as a function of temperature, i.e., a thermogravimetric curve, and provide 

quantitative information about substances under investigation, e.g., gibbsite (Al(OH)3), 

kaolinite (Al2Si2O5(OH)4), goethite (FeOOH) and 2:1 expandable minerals (smectite and 

vermiculite). 

2. Summary of Method 

A 5- to 10-mg sample of soil clay or fine earth (finely ground) is placed in a platinum 

sample pan, and the pan is placed in the TGA balance. The instrument records the initial 

sample weight. The sample is then heated from a temperature of 30 to 900°C at a rate of 20°C 

min-1 in a flowing N2 atmosphere. The computer collects weight changes as a function of 

temperature and records a thermogravimetric curve. Gibbsite and kaolinite are quantified by 

calculating the weight loss between approximately 250 to 350°C and 450 to 550°C, 

respectively, and then relating these data to the theoretical weight loss of pure gibbsite or 

kaolinite. The weight loss is due to dehydroxylation, i.e., loss of crystal lattice hydroxyl ions. 

Though not presently performed by the SSL, quantification of the 2:1 expandable minerals 

(smectite + vermiculite) is related to weight loss at <250°C, i.e., loss of adsorbed water 

(Karanthasis and Hajek, 1982a; Karanthasis and Hajek, 1982b; Tan et al., 1986). At this low 

temperature, adsorbed water is proportional to the specific surface area of the sample (Jackson, 

1956; Mackenzie, 1970; Tan and Hajek, 1977; Karathanasis and Hajek, 1982b). In the absence 

of gibbsite, goethite, a Fe oxyhydroxide, can be quantified based on the characteristic weight 

loss of 10.1 to 11.2% between 300 and 400°C (Karathanasis and Harris, 1994). Recent work in 

the SSL has found good agreement between gypsum quantification using dissolution 

procedures and thermal analysis. Gypsum has a weight loss of 20.9% between 100 and 350°C 

(Karathanasis and Harris, 1994). The TGA procedure (7A2a) is especially useful for soils with 

a large percentage (>20%) of gypsum. Burt et al. (2001) had good agreement between total Mg 

analysis and TGA quantification (12.9% weight loss between 600-650°C) of serpentine 

minerals in ultramafic-derived soils in Oregon. 

3. Interferences 

Organic matter is objectionable because it has a weight loss by dehydrogenation and by 

oxidation to CO2 between 300 to 900°C (Tan, et al., 1986). Analysis in an inert N2 atmosphere 

helps to alleviate this problem, but samples with significant organic matter should be pretreated 

with H2O2 (procedure 3A1a1). Mineral salts that contain water of crystallization also may 

interfere. Samples should be washed free of any soluble salts. In some cases, weight loss from 

gibbsite and goethite overlap and prevent quantitative interpretation. These samples can be 

deferrated (procedure 4F1a1) to eliminate goethite. 

A representative soil sample is important as sample size is small (<10 mg). Avoid large 

aggregates in sample, the presence of which may cause thermal interferences, i.e., differential 

kinetics of gas diffusion through the sample and physical movement of sample in a reaction. 

In general, the same reactions that interfere with DSC/DTA also interfere with TGA 

determinations of kaolinite, gibbsite, and 2:1 expandable minerals. However, TGA is more 

sensitive to small water losses at slow rates, whereas DSC/DTA is more sensitive to large water 

losses at rapid rates (Tan, et al., 1986). This sensitivity difference may help to explain why 

410
quantification of kaolinite and gibbsite in TGA vs. DSC/DTA often are not equivalent, i.e., 

TGA estimates tend to be greater than the corresponding DSC/DTA estimates. In TGA, there 

is a greater probability of measuring water losses in specific temperature regimes that are not 

specifically associated with dehydroxylation reactions of interest. This problem is particularly 

apparent with illitic samples, which characteristically contain more "structural" water than ideal 

structural formulae would indicate (Rouston, et al., 1972; Weaver and Pollard, 1973). 

Even though it is well established that various minerals lose the major portion of their 

crystal lattice water in different temperature ranges (Tan et al., 1986), there are overlaps in 

weight loss regions (WLR) of minerals which interfere in the identification and measurement 

of the minerals of interest. The goethite WLR (250 to 400°C) overlaps the gibbsite WLR (250 

to 350°C) (Mackenzie and Berggen, 1970). The illite WLR (550 to 600°C) overlaps the high 

end of the kaolinite WLR (450 to 550°C) (Mackenzie and Caillere, 1975). The WLR of 

hydroxy-Al interlayers in hydroxy-Al interlayered vermiculite (HIV) (400 to 450°C) overlaps 

the low end of the kaolinite WLR (450 to 550°C), especially in the poorly crystalline kaolinites 

(Mackenzie and Caillere, 1976). Similarly, the dehydroxylation of nontronites, Fe-rich 

dioctahedral smectites, (450 to 500°C) may interfere with kaolinite identification and 

measurement (Mackenzie and Caillere, 1975). 

4. Safety 

Secure high pressure N2 tanks and handle with care. When changing the tanks, protect 

valves with covers. Do not program the analyzer for >950°C because it may present a safety 

hazard during sample analysis and cleaning cycles. Always use high quality purge gases with 

the TGA. Minimum purity of 99.9% is recommended. Handle hot furnace with care. 

5. Equipment 

5.1 Thermal analyzer, TGA 51, TA Instruments, New Castle, DE 

5.2 Thermal analyzer operating system software, Thermal Analyst 2100, Version 8.10B, TA 

Instruments, New Castle, DE 

5.3 Computer Data analysis software, TGA Standard Data Analysis Version 5.1, TA 

Instruments, New Castle, DE 

5.4 Computer, IBM-PC 386, TA Instruments Operating System, Version, 8.10B, and printer 

5.5 Thermal analyzer instrument controller (MIM), TA Instruments, New Castle, DE 

5.6 N2 gas, 99.99% purity 

5.7 Two-stage gas regulators, 50 psi maximum outlet pressure 

5.8 Forceps, flat-tipped 

5.9 Weighing spatula 

5.10 Desiccator, glass 

5.11 Mortar and pestle 

5.12 Sieve, 80 mesh 

5.13 Kaolinite, standard, poorly crystalline, Georgia Kaolinite, Clay Minerals Society, Source 

Clay Minerals Project, sample KGa-2. 

5.14 Gibbsite, standard, Surinam Gibbsite, SSL, 67L022. 

6. Reagents 

6.1 Magnesium nitrate saturated solution [Mg(NO3)2·6H2O] 

6.2 Ethanol 

7. Procedure 

Derive <2μm Clay Fractions

7.1 Prepare Na-saturated sample (created during dispersion and separation of clay fraction from 

<2-mm soil). Refer to procedure 7A1a1, sections 7.8 to 7.19. 

411
7.2 Dry the clay suspension and transfer to mortar. Moisten sample with ethanol and grind 

with pestle to make a homogeneous slurry. 

7.3 Air-dry sample using flowing air in hood. Lightly grind sample with pestle to make a 

homogeneous powder. 

7.4 Sieve sample through an 80-mesh screen. Equilibrate sample overnight over a saturated 

magnesium nitrate solution (55% relative humidity) in a glass desiccator. 

TGA Operation

7.5 Turn on power to controller, instrument and computer. 

7.6 Turn on the N2 purge gas and set to 100 cm3 min-1 sample purge. 

7.7 Place the empty platinum sample pan on quartz rod and slide into quartz furnace tube. Use 

the Auto Zero function in the TA 2100 software to zero the balance. 

7.8 Remove the sample pan from the quartz rod. Weigh ≈ 10 mg of sample, i.e., <80-mesh 

fine-earth (<2 mm) soil fraction or derived <2-μm clay fraction, into tared sample pan. Refer 

to section on derived <2-μm clay fractions, Steps 7.1 to 7.4. 

7.9 Use flat-tipped forceps to tap the sample pan against a hard surface several times to 

uniformly distribute the sample. 

7.10 Carefully place sample pan on the quartz rod of the TGA microbalance. 

7.11 The standard sample run heating program is as follows: Equilibrate at 40°C, ramp up at 

20°C min-1 to 110°C, hold at 110°C for 2 minutes (to mark an oven-dry base weight), ramp up 

to an ending temperature of 900°C. 

7.12 Immediately start the "Run" program. 

7.13 At the end of sample run (≈ 45 min), allow the TGA furnace to cool to 350°C. 

7.14 Slide quartz furnace tube out of furnace. Pull furnace from main TGA unit and allow to 

cool on counter top. (Caution: Very Hot!). 

7.15 Place alternate furnace in TGA unit and prepare for next sample run. 

7.16 To analyze data file for weight loss, enter Data Analysis menu of the Thermal Analysis 

2100 System and select the TGA Standard Data Analysis software. 

7.17 Display file and calculate weight loss in specific regions for selected minerals. 

8. Calculations 

The thermogravimetric curve is displayed on the computer monitor. The ordinate (Y) is 

expressed in a relative weight percentage, i.e., the initial sample weight is 100.0%. Use the 

computer to calculate the total change in sample weight (∆ Y), within the predetermined 

temperature range, as a sample weight percent. 

8.1 % Kaolinite = 

{[(∆ sample weight % 450-550°C)]/14} x 100 

412
or (∆ sample weight % 450-550°C) x 7.14 

where: 

∆ sample weight = total change in sample weight expressed as relative percent 

14 = percent weight of hydroxyl water lost from pure kaolinite during dehydoxylation 

8.2 % Gibbsite = 

{[(∆ sample weight % 250-350°C)]/34.6} x 100 

or (∆ sample weight % 250-350°C) x 2.89 

where: 

∆ sample weight = total change in sample weight expressed as relative percent of the 110°C 

base weight. 

34.6 = percent weight of hydroxyl water lost from pure gibbsite during dehydroxylation 

If Fe oxides are removed prior to analysis to prevent the interference with gibbsite 

determination, the calculation is modified to account for weight loss due to deferration as 

follows: 

8.3 % Gibbsite ={[∆ Sample weight % 250-350°C x (Wt2/Wt1)]/34.6} x 100 

where: 

Wt1 = Weight before deferration 

Wt2 = Weight after deferration 

The percent weights of hydroxyl water lost from kaolinite and gibbsite are derived from the 

following assumed dehydroxylation reactions. 

8.4 Si2Al2O5(OH)4 ---> 2SiO2 + Al2O3 + 2H2O 

(kaolinite) 

8.5 2Al(OH)3 ---> Al2O3 + 3H2O 

(gibbsite) 

Using kaolinite as an example, percent weight of hydroxyl water lost is calculated from the 

following formula weights. 

8.6 Si2Al2O5(OH) = 258 g mol-1

4

2H2O = 36 g mol-1

Percent weight of hydroxyl water lost = (36/258) x 100 = 14% 

If serpentine minerals are present in the sample, TGA can be used to quantify these minerals 

(Burt et al., 2001) based on a the onset temperature of 600-650°C (Karathanasis and Harris, 

1994) and a weight loss from 600 to 900°C (12.9%) based on the mineral structure 

[Mg3Si2O5(OH)4]: 

8.7 % Serpentine minerals = 

{[(∆ sample weight % 600-900°C)]/12.9} x 100 

or (∆ sample weight % 600-900°C) x 7.75 

413
Gypsum can be quantified based on a loss of 20.9% (Karathanasis and Harris, 1994) based on 

the weight loss in the region of 100 to 350°C: 

8.8 % Gypsum = 

{[(∆ sample weight % 100-350°C)]/20.9} x 100 

or (∆ sample weight % 100-350°C) x 4.78 

9. Report

Report percent gibbsite, kaolinite, gypsum, or antigorite to nearest whole number. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Burt, R., M. Filmore, M.A. Wilson, E.R. Gross, R.W. Langridge, and D.A. Lammers. 

2001. Soil Properties of selected pedons on ultramafic rocks in Klamath Mountains, 

Oregon. Commun. Soil Sci. Plant Anal. 32:2145-2175. 

Jackson, M.L. 1956. Soil chemical analysis. Adv. course. M. L. Jackson, Madison, WI. 

Karathanasis, A.D., and B.F. Hajek. 1982a. Revised methods for rapid quantitative 

determination of minerals in soil clays. Soil Sci. Soc. Am. J. 46:419-425. 

Karathanasis, A.D., and B.F. Hajek. 1982b. Quantitative evaluation of water adsorption on 

soil clays. Soil Sci. Soc. Am. J. 46:1321-1325. 

Karathanasis, A.D., and W.G. Harris. 1994. Quantitative thermal analysis of soil material. 

P. 260-411. In J.E. Amonette and L.W. Zelazny (eds.). Quantitative methods in soil 

mineralogy. Soil Sci. Soc. Am. Misc. Publ., SSSA, Madison, WI. 

Mackenzie, R.C. 1970. Simple phyllosilicates based on gibbsite- and brucite-like sheets. p. 

498-537. In R.C. Mackenzie (ed.) Differential thermal analysis. Vol. 1. Acad. Press, 

London. 

Mackenzie, R.C., and G. Berggen. 1970. Oxides and hydroxides of higher-valency 

elements. p. 272-302. In R.C. Mackenzie (ed.) Differential thermal analysis. Acad. 

Press, NY. 

Mackenzie, R.C., and S. Caillere. 1975. The thermal characteristics of soil minerals and the 

use of these characteristics in the qualitative and quantitative determination of clay 

minerals in soils. p. 529-571. In J.E. Gieseking (ed.) Soil components. Vol. 2. Inorganic 

components. Springer-Verlag, NY. 

Mackenzie, R.C., and B.D. Mitchell. 1972. Soils. p. 267-297. In R.C. Mackenzie (ed.) 

Differential thermal analysis. Vol. 2. Acad. Press. London. 

Rouston, R.C., J.A. Kittrick, and E.H. Hope. 1972. Interlayer hydration and the broadening 

of the 10A x-ray peak in illite. Soil Sci. 113:167-174. 

Tan, K.H., and B.F. Hajek. 1977. Thermal analysis of soils. p. 865-884. In J.B. Dixon and 

S.B. Weed (eds.) Minerals in soil environments. 2nd ed. Soil Sci. Soc. Am. Book Series 

1. ASA and SSSA, Madison, WI. 

Tan, K.H., and B.F. Hajek, and I. Barshad. 1986. Thermal analysis techniques. p. 151-183. 

In A. Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical properties. 

2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Weaver, C.E., and L.D. Pollard. 1973. The chemistry of clay minerals. Elsevier Sci. Publ. 

Co., Amsterdam. 

414
415

Instrumental Analyses (7A)

Differential Scanning Calorimetry (7A4) Thermal Analyzer (7A4a)

1. Application 

Calorimetry measures specific heat or thermal capacity of a substance. Two separate 

types of differential scanning calorimetry (DSC) instruments have evolved over time. The term 

“DSC” is most appropriate for the power-compensated-type instrument in which the difference 

in the rate of heat flow between a sample and a reference pan is measured as materials are held 

isothermal to one another using separate furnaces (Karathanasis and Harris, 1994). The DSC 

therefore directly measures the magnitude of an energy change (∆H, enthalpy or heat content) 

in a material undergoing an exothermic or endothermic reaction. Heat flow-type DSC 

instruments are more common and are similar in principal to differential thermal analyzers 

(DTA). The heat flow instruments have the sample and reference pans in a single furnace and 

monitor pan temperature from the conducting base. The difference in pan temperatures (∆T) 

results from clay mineral decomposition reactions in the sample as the furnace temperature is 

increased. The configuration of this instrument results in a signal that is independent of the 

thermal properties of the sample and ∆T can be converted to a calorimetric value via instrument 

calibration (Karathanasis and Harris, 1994). DSC is commonly used to quantify gibbsite 

(Al(OH)3) and kaolinite (Al2Si2O5(OH)4) in soils and clays by measuring the magnitude of their 

dehydroxylation endotherms which are between approximately 250 to 350°C and 450 to 550°C, 

respectively (Jackson, 1956; Mackenzie, 1970; Mackenzie and Berggen, 1970; Karathanasis 

and Hajek, 1982). 2. Summary of Method 

An 8-mg sample of soil clay is weighed into an aluminum sample pan and placed in the 

DSC sample holder. The sample and reference pans are heated under flowing N2 atmosphere 

from a temperature of 30 to 600°C at a rate of 10°C min-1. Data are collected by the computer 

and a thermograph is plotted. Gibbsite and kaolinite are quantified by measuring the peak area 

of any endothermic reactions between 250 to 350°C and 450 to 550°C, respectively, and by 

calculating the ∆H of the reaction. These values are related to the measured enthalpies of 

standard mineral specimens (gibbsite and kaolinite). Percent kaolinite and gibbsite are reported 

by procedure 7A4a. 

3. Interferences 

Organic matter is objectionable because it produces irregular exothermic peaks in air or 

O2, commonly between 300 to 500°C, which may obscure important reactions from the 

inorganic components of interest (Schnitzer and Kodama, 1977). Analysis in an inert N2

atmosphere helps to alleviate this problem although thermal decomposition of organic matter is 

still observed. Pretreatment with H2O2 may be necessary for soils with significant amounts of 

organic matter. Mineral salts that contain water of crystallization also may be interferences. 

Samples should be washed free of any soluble salts. 

Use a representative soil sample as sample size is small (<10 mg). Avoid large 

aggregates in sample, the presence of which may cause thermal interferences because of 

differential kinetics of gas diffusion through the sample and physical movement of sample in a 

reaction.

The dehydroxylation of goethite is between 250 to 400°C and may interfere with the 

identification and integration of the gibbsite endotherm (250 to 350°C) (Mackenzie and 

Berggen, 1970). The dehydroxylation of illite is between 550 to 600°C and partially overlaps 

the high end of the kaolinite endotherm (450 to 550°C), resulting in possible peak integrations 

(Mackenzie and Caillere, 1975). The dehydroxylation of hydroxy-Al interlayers in hydroxy-Al 

interlayered vermiculite (HIV) is between 400 to 450°C and may interfere with the low end of 

the kaolinite endotherm (450 to 550°C), especially in the poorly crystalline kaolinites 

(Mackenzie and Caillere, 1976). Similarly, the dehydroxylation of nontronites, Fe-rich 
dioctahedral smectites is between 450 to 500°C and may interfere with kaolinite identification 

and measurement (Mackenzie and Caillere, 1975). 

4. Safety 

Secure high pressure N2 tanks and handle with care. When changing the tanks, valves 

should be protected with covers. Do not heat aluminum sample pans >600°C. Aluminum 

melts at 660°C, and the sample pans alloy with and destroy the DSC cell. Always use high 

quality purge gases with the DSC. Minimum purity of 99.9% is recommended. 

5. Equipment 

5.1 Thermal analyzer, DSC 910S, TA Instruments, New Castle, DE 

5.2 Thermal analyzer operating system software, Thermal Analyst 2100, Version 8.10B, TA 

Instruments, New Castle, DE 

5.3 Data analysis software, TGA Standard Data Analysis Version 4.0, TA Instruments, New 

Castle, DE 

5.4 Computer, IBM-PC 386, TA Instruments Operating System, Version 8.10B 

5.5 Thermal analyzer instrument controller (MIM), TA Instruments, New Castle, DE 

5.6 Autosampler, 920 Auto DSC, TA Instruments, New Castle, DE 

5.7 Printer, Hewlett Packard, HP-7440, 8-pen plotter 

5.8 Two-stage gas regulators, 50 psi maximum outlet pressure 

5.9 Electronic balance, ±0.1-mg sensitivity, Mettler AE160 

5.10 Forceps, flat-tipped 

5.11 Weighing spatula 

5.12 Desiccator 

5.13 Mortar and pestle 

5.14 Sieve, 80 mesh 

5.15 N2 gas, 99.99% purity 

5.16 Kaolinite, standard, poorly crystalline, Georgia Kaolinite, Clay Minerals Society, Source 

Clay Minerals Project, sample KGa-2. 

5.17 Gibbsite, standard, Surinam Gibbsite, SSL 67L022. 

6. Reagents 

6.1 Magnesium nitrate saturated solution [Mg(NO3)2·6H2O] 

6.2 Ethanol 

7. Procedure 

Derive <2μm Clay Fractions

7.1 Prepare Na-saturated clay as in procedure 7A1a1, preparation of clay suspension, sections 

7.8 to 7.19. 

 

7.2 Dry the clay suspension and transfer to mortar. Moisten sample with ethanol and grind 

with pestle to make an homogeneous slurry. 

7.3 Air-dry sample using flowing air in hood. Lightly grind sample with pestle to make a 

homogeneous powder. Transfer to original container for storage until use. 

7.4 Prior to analysis, sieve sample with 80-mesh screen. Equilibrate sample overnight over a 

saturated magnesium nitrate solution (55% relative humidity) in a glass desiccator. 

DSC Operation

7.5 Set-up the instrument and calibrate. Refer to the manufacturer's manual for operation of the 

DSC. Samples can be analyzed singly or with the autosampler for multiple samples. 

416
7.6 Weigh ≈ 8 mg of sample, i.e., <80-mesh fine-earth (<2mm) soil fraction or derived <2-μm 

clay fraction, into tared aluminum sample pan. Refer to section on derived <2-μm clay 

fractions, Steps 7.1 to 7.4. 

7.7 Use flat-tipped forceps to remove aluminum sample pan from balance. Drop sample from a 

4- to 5-mm height to uniformly distribute sample in pan. Return the sample pan with sample to 

the balance and record weight to nearest ±0.1 mg. This weight is entered into computer in 

appropriate menu. 

7.8 Carefully place the aluminum sample pan in the center of DSC platinum sample side (front 

section) of sample holder. 

7.9 Place empty aluminum sample pan in reference side (back section) of sample holder. 

7.10 Cover the DSC cell. 

7.11 The standard sample run heating program has a heating rate of 10°C min-1, a starting 

temperature of 30°C, and an ending temperature of 600°C. 

7.12 Start the "Run" program. 

7.13 When the run is complete, data are analyzed by entering the Data Analysis 2100 System 

and selecting the DSC Standard Data Analysis Program. 

7.14 Display file and calculate joules g-1 for the mineral endotherm. 

8. Calculations 

The area under a curve representing an endothermic dehydroxylation reaction is proportional to 

the enthalpy (∆H) of the reaction. The enthalpy is calculated with the DSC software per g of 

kaolinite or gibbsite (joules g-1) as appropriate. 

Analyze each of the standard clays on the DSC. Calculate the enthalpy per g for the 

endothermic reactions of the standard kaolinite and gibbsite (joules g-1). 

The purity of the standard clays is evaluated via TGA (7A2a). Adjust the DSC results of the 

standards using the purity measurements from TGA. 

Determine the amount of kaolinite and gibbsite in soil samples by dividing the enthalpy of the 

sample (joules g-1) by the enthalpy of the standard (joules g-1). Multiply this result by 100 to 

express as a percentage. 

9. Report 

Report percent kaolinite and/or gibbsite to the nearest whole number. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Karathanasis, A.D., and B.F. Hajek. 1982. Revised methods for rapid quantitative 

determination of minerals in soil clays. Soil Sci. Soc. Am. J. 46:419-425. 

Karathanasis, A.D., and W.G. Harris. 1994. Quantitative thermal analysis of soil 

minerals. p. 360-411. In J.E. Amonette and L.W. Zelazny (eds.) Quantitative methods in 

soil mineralogy. Soil Sci. Soc. Am. Misc. Publ. SSSA. Madison, WI. 

417
Mackenzie, R.C. 1970. Simple phyllosilicates based on gibbsite- and brucite-like sheets. p. 

498-537. In R. C. Mackenzie (ed.) Differential thermal analysis. Vol. 1. Acad. Press, 

London. 

Mackenzie, R.C., and G. Berggen. 1970. Oxides and hydroxides of higher-valency 

elements. p. 272-302. In R.C. Mackenzie (ed.) Differential thermal analysis. Acad. 

Press, NY. 

Mackenzie, R.C., and S. Caillere. 1975. The thermal characteristics of soil minerals and the 

use of these characteristics in the qualitative and quantitative determination of clay 

minerals in soils. p. 529-571. In J.E. Gieseking (ed.) Soil components. Vol. 2. Inorganic 

components. Springer-Verlag, NY. 

Mackenzie, R.C., and B.D. Mitchell. 1972. Soils. p. 267-297. In R.C. Mackenzie (ed.) 

Differential thermal analysis. Vol. 2. Acad. Press., London. 

Rouston, R.C., J.A. Kittrick, and E.H. Hope. 1972. Interlayer hydration and the broadening 

of the 10A x-ray peak in illite. Soil Sci. 113:167-174. 

Schnitzer, M., and H. Kodama. 1977. Reactions of minerals with soil humic substances. p. 

741-770. In J.B. Dixon and S.B. Weed (eds.) Minerals in soil environments. 2nd ed. 

Soil Sci. Am. Book Series No. 1. ASA and SSSA, Madison, WI. 

Tan, K.H., and B.F. Hajek. 1977. Thermal analysis of soils. p. 865-884. In J.B. Dixon and 

S.B. Weed (eds.) Minerals in soil environments. 2nd ed. Soil Sci. Am. Book Series No. 

1. ASA and SSSA, Madison, WI. 

Tan, K.H., and B.F. Hajek, and I. Barshad. 1986. Thermal analysis techniques. p. 151-183. 

In A. Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical properties. 

2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Instrumental Analysis (7A) 

Surface Area (7A5) 

N2 Adsorption (7A5a) Brunauer, Emmett and Teller (BET) Theory (7A5a1) 

Vacuum Degassing (7A5a1a) 

Multi-point (7A5a1a1) 

Air-Dry, <2 mm (7A5a1a1a1) 

Single Point (7A5a1a2) 

Air-Dry, <2-mm (7A5a1a2a1) 

1. Application 

Surface area influences many physical and chemical properties of materials, e.g., 

physical adsorption of molecules and the heat loss or gain that results from this adsorption, 

shrink-swell capacity, water retention and movement, cation exchange capacity, pesticide 

adsorption, and soil aggregation (Carter et al., 1986). In addition, many biological processes 

are closely related to specific surface. Soils vary widely in their relative surface area because 

of differences in mineralogical and organic composition and in their particle-size distribution. 

Specific surface area (SSA) is an operationally defined concept, dependent upon the 

measurement technique and sample preparation (Pennell, 2002). 

The most common approach used to measure SSA is considered indirect, based on 

measurements of the adsorption or retention of probe molecules on a solid surface at monolayer 

coverage (Pennell, 2002). Two common methods of measuring SSA are by ethylene glycol 

monoethyl ether (EGME) and N2-sorption, using the theory of Brunauer, Emmett and Teller 

(N2-BET). N2 as a nonpolar gas does not interact with or have access to interlayer 

crystallographic planes of expandable clay minerals and thus is considered to provide a 

measure of external surface area, whereas polar molecules such as EGME are known to 

penetrate the interlayer surfaces of expandable clay minerals and therefore have been used to 

provide a measure of total surface areas (internal + external surface area) (Pennell, 2002). 

Significant differences between these methods are most apparent in soils containing expandable 

clay minerals and soil organic matter (Chlou and Rutherford, 1993; Pennell et al.1995; de Jong, 

418
1999; Quirk and Murray, 1999). In the past, the SSL determined surface area by glycerol 

retention (7D1, method obsolete, Soil Survey Staff, 1996) or EGME retention (7D2, method 

obsolete, Soil Survey Staff, 1996). The current method described herein is N2 –BET (multipoint). 

2. Summary of Method 

A <2-mm, air-dry soil sample is ground to pass a 0.25 mm (60 mesh) sieve and ovendried (24 h, 110° C). Enough soil (typically 0.5 to 1 g) is added to weighed sample cell to 

achieve 2- to 50- m2 total area. Soil is cleaned of contaminants, e.g., water and oils, by vacuum 

degassing at 10 millitorr for a minimum of 3 h at 110° C and then re-weighed to obtain 

degassed sample weight. The sample is brought to a constant temperature by means of an 

external bath (77° K) and then small amounts of gas (N2) called the absorbate are admitted in 

steps to evacuate sample chamber. Gas molecules that stick to the surface of the solid 

(absorbent) are said to be adsorbed and tend to form a thin layer that covers the entire adsorbate 

surface. The number of molecules required to cover the adsorbent surface with a monolayer of 

adsorbed molecules, Nm, can be estimated based on the BET theory. Multiplying Nm by the 

cross-sectional area of an adsorbate molecule yields the sample’s surface area. Specific surface 

area is reported in m2 

g

-1 by procedure 7A5a1a1 or 7A5a1a2. 

3. Interferences 

Organic material can coat or cover mineral surfaces, generally reducing SSA by N2-

BET. Removal of organic matter prior analysis will typically increase these values. Freezedrying may provide SSA values that are more representative of field conditions, as air-drying 

may result in the collapse and shrinkage of soil humic acid, whereas freeze-drying maintains an 

intricate structural network more characteristic of a natural state (Pennell, 2002). Sample size 

will vary depending on the SSA of the solid. 

4. Safety 

The outer surfaces of the heating mantle may become hot during use. Do not hold hot 

heating mantles without wearing protective gloves. Never insert fingers inside the pocket to 

determine if the mantle is heating up. Do not place a hot heating mantle on a surface that is not 

heat-resistant. Switch off the heating mantle when not in use. Refer to the manufacturer’s 

manual for safe operation of the surface area analyzer. 

5. Equipment 

5.1 Surface area analyzer, with vacuum degassing, Quantachrome, Nova 3000 Series, Boynton 

Beach, FL 

5.2 Computer, with Nova, Enhanced Data Reduction Program, Version 2.13, Quantachrome, 

Boynton Beach, FL. and printer 

5.3 Vacuum pump, capable of achieving 50 millitorr required, 10 millitorr recommended 

5.4 Dewar flask with insulated lid for liquid N2

5.5 Oven, 110° C 

5.6 Sample cells, glass, with outside stem diameters of 6, 9, and 12 mm and internal diameters 

of 4, 7, and 10 mm, respectively 

5.7 Glass filler rods, 6 mm x 268.5 mm and 6mm x 131.5 mm 

5.8 Mortar and pestle 

6. Reagents 

6.1 N2, high purity, 99.9% 

6.2 Liquid N2 (77°K) 

6.3 Standard reference material, 31.16 m2 g-1 SSA, with ±2.03 m2 g-1 reproducibility, 

Quantachrome, Boynton Beach, FL 

419
7. Procedure 

Surface Area Analyzer Set-up and Operation 

7.1 Set N2-regulator at 10 PSIG (70 kPa). 

7.2 Refer to the manufacturer’s manual for the routine operation, manifold calibration, and 

sample cell calibration. 

7.3 The dosing manifold is factory calibrated, and there is no need to repeat this calibration 

before every analysis. However, operator should check this calibration periodically (e.g. once 

every month), or if the operator feels that changes to the system may have altered the manifold 

volume. 

7.4 There needs to be a sample cell calibration for each sample cell + filter rod + station 

combination and for each adsorbate/coolant combination. Once done, there is no need for 

further calibration for that particular combination. For most users, all standard (bulbless) cells 

can be considered equivalent (for each diameter), i.e., one cell/rod/station combination will 

suffice for a different cell (of the same diameter) with the same rode in the same station. 

Sample Preparation and Vacuum Degas 

7.5 Pulverize a <2-mm, air-dry soil sample with a mortar and pestle to break up any aggregates. 

7.6 Weigh sample cell to the nearest 0.1 mg. Weigh enough soil (typically 0.5 to 1.0 g) into 

sample cell to achieve 2- to 50 m2

 total area (sample size will vary depending on the SSA of the 

soil). Oven-dry at 110°C for 24 h. 

7.7 Remove sample cell with soil from oven and seal immediately. Allow to cool to touch. 

7.8 Place the sample cell in the pouch of the heating mantle, set clamp in place, insert cell into 

fitting, tighten fitting, and loop elastic cords over hooks provided. Set the degas temperature at 

110° C for a minimum of 3 h. 

7.9 Upon completion of degassing, switch the mantle off. Allow sample to cool. Unload 

degasser when ready to analyze sample. 

7.10 Remove cell and reweigh to obtain dry, degassed soil sample weight to the nearest 0.1 mg. 

7.11 Use the Preset Analysis option on surface area analyzer allows user to preset and save 

before analysis the following: User ID, stations for analysis, setup files, cell numbers, sample 

ID numbers, and comments. 

Analysis 

7.12 Ensure dewar flask is filled to the red line (approximately 1 in from top) with liquid N2. 

Allow 5 min for liquid N2 to equilibrate for best results. If the liquid N2 is still boiling heavily, 

then the dewar needs to be cleaned before filling it with liquid N2. If boiling continues after a 

dry clean dewar is filled for 5 min, then replace the dewar. Residual boiling will require that the 

dewar be topped-off again. Ensure proper alignment of sample cells with dewar mouth. Foam 

cap is not required for BET analysis only. If however a long isotherm is required, then use the 

foam cap. Ensure that there is no condensed water visible in the stem of the sample cell. 

 

7.13 Follow set-up instructions on the surface area analyzer (e.g., select cell for Stations, enter 

sample ID for Stations, enter dry degassed sample weight by measuring sample volume, etc) 

until prompted to proceed with analysis. Analytical data include Multi Point BET (adsorption), 

slope, intercept, correlation coefficient, BET C, total surface area in cell (m2) and specific 

420
surface area (m2

 g

-1). Set-up and analytical data are automatically recorded by computer and 

printer. 

8. Calculations 

The BET equation for determination of the surface area of solids (Quantachrome Corp., 2000) 

is as follows: 

8.1 1/[W((P0/P)-1)] = [1/(WmC)] + [(C - 1)/WmC] x (P/P0) 

where: 

W = weight of gas adsorbed at a relative pressure of P/P0 Wm = weight of adsorbate constituting a monolayer of surface coverage 

C = BET C constant, related to energy of adsorption in first adsorbed layer and is indicative 

of the magnitude of absorbed/adsorbate interactions (typically, 50 to 250 for most solid 

surfaces) 

The BET equation requires a linear plot of 1/[W((P0/P)-1)] versus P/P0 which for most solids, 

using nitrogen as adsorbate, is restricted to a limited region of the adsorption isotherm, usually 

in the P/P0 range of 0.05 to 0.35 (Quantachrome Corp., 2000). The standard multi-point BET 

procedure requires a minimum of three points in the appropriate relative pressure range. The 

weight of the monolayer of adsorbate Wm can then be obtained from the slope s and intercept i 

of the BET plot. 

8.2 From the BET equation, 

8.2.1 s = (C – 1)/WmC 

8.2.2 i = 1/WmC. 

8.3 Thus, the weight of the monolayer Wm can be obtained by combining these two equations 

as follows: 

Wm = 1/(s+i). 

8.4 Total surface area St of the sample is calculated as follows: 

St = WmNAcs/M 

where: 

N = Avogadro’s number (6.023 x 1023) 

M = Molecular weight of absorbate (28.02 g mol-1) 

Acs = Close-packed nitrogen monolayer at 77 K, the cross-sectional area for nitrogen = 16.2 

Angstroms2 

8.6 Specific surface area S is calculated as follows: 

S = St/w 

where: 

w = Degassed sample weight 

9. Report 

Report specific surface area in m2 g-1 to the nearest 0.01 unit. 

421
10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Carter, D.L., M.M. Mortland, and W.D. Kemper. 1986. Specific surface. In A. Klute (ed.) 

Methods of Soil Analysis. Part 1. Physical and mineralogical methods. 2nd ed. Agron. 

Monogr. 9. Soil Sci. Soc. Am., Madison, WI. 

Chlou, C.T., and D.W. Rutherford. 1993. Sorption of N2 and EGME vapors on some soils, 

clays, and mineral oxides and determination of sample surface areas by use of 

sorption data. Environ. Sci. Technol. 27:1587-1594. 

de Jong, E. 1999. Comparison of three methods of measuring surface area of soils. Can. J. 

Soil Sci. 79:345-351. 

Pennell, K.D. 2002. Specific surface area. In J.H. Dane and G.C. Topp (eds.) Methods of 

Soil Analysis. Part 4. Physical Methods. Soil. Sci. Soc. Am. Book Series No. 5, 

Madison, WI. 

Pennell, K.D., S.A. Boyd, and L.M. Abriola. 1995. Surface area of soil organic matter 

reexamined. Soil Sci. Soc. Am. J. 59:1012-1018. 

Quantachrome Corporation. 2000. Particle characterization technology. Quantachorme 

Corp., Boynton, FL. 

Quirk, J.P., and R.S. Murray. 1999. Appraisal of the ethylene glycol monoethyl ether 

method for measuring hydratable surface area of clays and soils. Soil Sci. Soc. Am. 

J. 63:839-849. 

Soil Survey Staff. 1996. Soil survey laboratory methods manual. Version No. 3.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, 

DC. 

Optical Analyses1

 (7B) Grain Studies (7B1) 

Analysis and Interpretation (7B1a) 

Minerals 

Identification criteria: Important properties in grain identification are listed below in 

approximate order of ease and convenience of determination. Estimates of several of these 

properties often allow identification of a grain so that detailed or extremely accurate 

measurements are seldom necessary. In the finer soil separates, grain identification may be 

impossible because the grains may be too small or not in the right position to permit 

measurement of some properties, e.g., optic angle (2V) or optic sign. A process to help 

practice estimating properties is to crush, sieve, and mount a set of known minerals and to 

compare these known standards to unknowns. 

Refractive index is the ratio of the speed of light in the medium (mineral) to the speed 

of light in a vacuum. It can be estimated by relief or can be accurately determined by using 

calibrated immersion liquids. When relief is used to estimate refractive index, the grain shape, 

color, and surface texture are considered, i.e., thin platy grains may be estimated low, whereas 

colored grains and grains with rough, hackly surface texture may be estimated high. Estimation 

is aided by comparing an unknown with known minerals. 

__________________________________________________________________________ 

1

 The discussion of identification and significance of minerals, microcrystalline aggregates, and 

amorphous substances in optical studies of grain mounts was from material after John G. Cady 

(1965), with permission, and modified by Warren C. Lynn, Research Soil Scientist, NRCS, 

Lincoln, NE. 

422
Relief is an expression of the difference in refractive index between the grain and the 

mounting medium, and the greater the difference, the greater the relief. The analogy is to 

topographic relief. When viewed through the microscope, grains with high relief are distinct, 

whereas grains with low relief tend to fade into the background. The SSL selects a mounting 

medium with an index of refraction close to quartz, i.e., quartz has low relief. Most other 

minerals are identified by comparison. 

Becke line is a bright halo of light that forms near the contact of the grain and the 

mounting medium because of the difference in refractive index between the two. As the plane 

of focus is moved upward through the grain, the Becke line appears to move into the 

component with the higher refractive index. In Petropoxy 154TM, the Becke line moves away 

from potassium feldspar (index of refraction <1.54) but moves into mica (index of refraction 

>1.54). 

Birefringence is the difference between the highest and lowest refractive index of the 

mineral. Accounting for grain thickness and orientation, the birefringence is estimated by 

interference color. Interference color is observed when an anisotropic mineral is viewed 

between crossed-polarized light. Several grains of the same species must be observed because 

the grains may not all lie in positions that show the extremes of refractive index. For example, 

mica has high birefringence but appears low when the platy mineral grain is perpendicular to 

the microscope axis because the refractive indices of the two crystallographic directions in the 

plane are similar. However, a mica grain viewed on edge in a thin section shows a high 

interference color. The carbonate minerals have extremely high birefringence (0.17 to 0.24). 

Most of the ferrogmagnesian minerals are intermediate (0.015 to 0.08). Orthoclase feldspar 

and apatite are low (0.008) and very low (0.005), respectively. 

Color helps to discriminate among the heavy minerals. Pleochroism is the change in 

color or light absorption with stage rotation when the polarizer is inserted. Pleochroism is a 

good diagnostic characteristic for many colored minerals. Tourmaline, green beryl, and 

staurolite are examples of pleochroic minerals. 

Shape, cleavage, and crystal form are characteristic or possibly unique for many 

minerals. Cleavage may be reflected in the external form of the grain or may appear as cracks 

within the grain that show as regularly repeated straight parallel lines or as sets of lines that 

intersect at definite repeated angles. The crystal shape may be different from the shape of the 

cleavage fragment. Plagioclase feldspars, kyanite, and the pyroxenes have strong cleavage. 

Zircon and rutile usually appear in crystal forms. 

Extinction angle and character of extinction observed between crossed-polarized 

light are important criteria for some groups of minerals. To measure extinction angles, the 

grain must show its cleavage or crystal form. These angles may 

be different along different crystallographic axes. Some minerals have sharp, quick total 

extinction, whereas other minerals have more gradual extinction. In some minerals with high 

light dispersion, the interference color dims and changes at the extinction position. 

Optic sign, optic angle, and sign of elongation are useful, if not essential, 

determinations but are often difficult, unless grains are large or in favorable orientation. 

Determination of optic sign requires that the grains show dim, low-order interference colors or 

show no extinction. Grains with bright colors and with sharp, quick extinction rarely provide 

usable interference figures. 

Particular mineral species: The following are the outstanding diagnostic 

characteristics of the most commonly occurring minerals and single-particle grains in the sand 

and silt fractions of soils. The refractive indices that are provided are the intermediate values. 

Quartz has irregular shapes. The refractive index of quartz (1.54) approximates that of 

the epoxy (Petropoxy 154TM) mounting medium. The Becke line may be split into yellow and 

blue components. The interference colors are low order but are bright and warm. There is 

sharp extinction with a small angle of rotation, i.e., "blink extinction". Crystal forms are 

sometimes observed and usually indicate derivation from limestone or other low-temperature 

secondary origin. 

423
Potassium feldspars: Orthoclase may resemble quartz, but the refractive index (1.52) 

and birefringence are lower than that of quartz. In addition, orthoclase may show cleavage. 

Microcline has a refractive index of 1.53. The Becke line moves away from the grain with 

upward focus. A twinning intergrowth produces a plaid or grid effect between crossedpolarized light that is characteristic of microcline. Sanidine has the same refractive index and 

birefringence as other potassium feldspars. Grains are usually clear and twinning is not 

evident. In sanidine, the 2V angle is low (12°) and characteristic. The 2V angle is the acute 

angle between two optic axes, or more simply, the optical axial angle. 

Plagioclase feldspars have refractive indices that increase with an increase in the 

proportion of calcium. The refractive index of the sodium end-member albite (1.53) is lower 

than that of quartz, but the refractive index of the calcium end-member anorthite (1.58) is 

noticeably higher than that of quartz. Some oligoclase has the same refractive index as quartz 

which prevents distinctions by the Becke line. Plagioclase feldspars often show a type of 

twinning (defined as albite twinning) that appears as multiple alternating dark and light bands 

in crossed-polarized light. Cleavage is good in two directions parallel to (001) and (010), often 

producing lathlike or prismatic shapes. 

Micas occur as platy grains that are often very thin. The plate view shows very low 

birefringence, whereas the edge view shows a very high birefringence. Plates are commonly 

equidimensional and may appear as hexagons or may have some 60° angles. Biotite is green to 

dark brown. Green grains may be confused with chlorite. Paler colors, a lowering of refractive 

index, and a distortion of the extinction and interference figure indicate weathering to 

hydrobiotite, kaolinite, or vermiculite. Muscovite is colorless. Muscovite has a moderate 

refractive index (1.59) in the plate view and an interference figure that shows a characteristic 

2V angle of 30 to 40° which can be used as a standard for comparing 2V angles of other 

minerals. 

Amphiboles are fibrous to platy or prismatic minerals with slightly inclined extinction, 

or occasionally with parallel extinction. Color and refractive index increase as the Fe content 

increases. Amphiboles have good cleavage at angles of ~ 56 and 124°. Refractive index of the 

group ranges from 1.61 to 1.73. Hornblende is the most common member of the amphiboles. 

Hornblende is slightly pleochroic; usually has a distinctive color close to olive-green; has 

inclined extinction; and is often used as an indicator of weathering. 

Pyroxenes: Enstatite and aegerine-augite are prismatic and have parallel extinction. 

Aegerine-augite has unique and striking green-pink pleochroism. Augite and diopside have 

good cleavage at angles close to 90° and large extinction angles. Colors usually are shades of 

green, with interference colors of reds and blues. Refractive indices in the pyroxenes (1.65 to 

1.79) are higher than for amphiboles. 

Olivine is colorless to very pale green and usually irregular in shape (weak cleavage). 

Olivine has vivid, warm interference colors. Olivine is an easily weathered mineral and may 

have cracks or seams filled with serpentine or goethite. It is seldom identified in soils, but has 

been observed in certain soils from Hawaii. 

Staurolite is pleochroic yellow to pale brown and sometimes contains holes, i.e., the 

"Swiss cheese" effect. The refractive index is ~ 1.74. Grains may have a foggy or milky 

appearance which may be caused by colloidal inclusions. 

Epidote is a common heavy mineral, but the forms that occur in soils may be difficult to 

identify positively. Typical epidote is unmistakable with its high refractive index (1.72 to 

1.76), strong birefringence, and a pleochroism that includes the pistachio-green color. It has 

typical interference colors of reds and yellows. Commonly, grains show an optic axis 

interference figure with a 2V angle that is nearly 90°. However, epidote is modified by 

weathering or metamorphism to colorless forms with lower birefringence and refractive index. 

Zoisite and clinozoisite in the epidote group are more common than some of the literature 

indicates. These minerals of the epidote group commonly appear as colorless, pale-green, or 

bluish-green, irregularly shaped or roughly platy grains with high refractive index (1.70 to 

1.73). Most of these minerals show anomalous interference colors (bright pale blue) and no 

424
complete extinction and can be confused with several other minerals, e.g., kyanite and diopside. 

Zoisite has a distinctive deep blue interference color. Identification usually depends on 

determination of properties for many grains. 

Kyanite is a common mineral but is seldom abundant. The pale blue color, the platy, 

angular cleavage flakes, the large cleavage angles, and the large extinction angles (30° extinction) usually can be observed and make identification easy. 

Sillimanite and andalusite resemble each other. These minerals are fibrous to prismatic 

with parallel extinction. However, their signs of elongation are different. In addition, 

sillimanite is colorless, and andalusite commonly has a pink color. 

Garnet is found in irregularly shaped, equidimensional grains that are isotropic and 

have high refractive index (>1.77). Garnet of the fine sand and silt size is often colorless. Pale 

pink or green colors are diagnostic in the larger grains. 

Tourmaline has a refractive index of 1.62 to 1.66. Prismatic shape, strong pleochroism, 

and parallel extinction are characteristic. Some tourmaline is almost opaque when at right 

angles to the vibration plate of the polarizer. 

Zircon occurs as tetragonal prisms with pyramidal ends. Zircon has very high refractive 

index (>1.9), parallel extinction, and bright, strong interference colors. Broken and rounded 

crystals frequently are found. Zircon crystals and grains are almost always clear and fresh 

appearing. 

Sphene, in some forms, resembles zircon, but the crystal forms have oblique extinction. 

The common form of sphene, a rounded or subrounded grain, has a color change through 

ultrablue with crossed polarizers instead of extinction because of its high dispersion. Sphene is 

the only pale-colored or colorless high-index mineral that provides this effect. It is amber 

colored in reflected light. The refractive index of sphene is slightly lower than that of zircon, 

and the grains are often cloudy or rough-surfaced. 

Rutile grains have prismatic shape. The refractive index and birefringence are 

extremely high (2.6 to 2.9). The interference colors usually are obscured by the brown, 

reddish-brown, or yellow colors of the mineral. Other TiO2 minerals, anatase and brookite, also have very high refractive indices and brown colors and may be difficult to distinguish in 

small grains. The anatase and brookite usually occur as tabular or equidimensional grains. 

Apatite is common in youthful soil materials. Apatite has a refractive index slightly 

<1.63 and a very low birefringence. Crystal shapes are common and may appear as prisms, and 

is often bullet shaped. Rounding by solution produces ovoid forms. Apatite is easily attacked 

by acid and may be lost in pretreatments. 

Carbonates: Calcite, dolomite, and siderite, in their typical rhombohedral cleavage 

forms, are easily identified by their extremely high birefringence. In soils, these minerals have 

other forms, e.g., scales and chips; cements in aggregates; microcrystalline coatings or 

aggregates; and other fine-grained masses that are often mixed with clay and other minerals. 

The extreme birefringence is always the identification clue and is shown by the bright colors 

between crossed-polarized light and by the marked change in relief when the stage is rotated 

with one polarizer in. The microcrystalline aggregates produce a twinking effect when rotated 

between crossed-polarized light. These three minerals have differences in their refractive 

indices which may be used to distinguish them. Siderite is the only one with both indices 

>Petropoxy 154TM. It is more difficult to distinguish calcite from dolomite, and additional 

techniques such as staining or x-ray diffraction may be used. 

Gypsum occurs in platy or prismatic flat grains with refractive index approximately 

equal to orthoclase. It usually has a brushed or “dirty” surface. 

Opaque minerals, of which magnetite and ilmenite are the most common, are difficult to 

identify, especially when they are worn by transportation or otherwise affected by weathering. 

Observations of color and luster by reflected light, aided by crystal form if visible, are the best 

procedures. Magnetic separations help to confirm the presence of magnetite and ilmenite. 

Many grains that appear opaque by plain light can appear translucent if viewed between strong 

crossed-polarized light. Most grains that behave in this way are altered grains or aggregates 

and are not opaque minerals. 

425
Microcrystalline Aggregates and Amorphous Substances 

Identification criteria: Most microcrystalline aggregates have one striking 

characteristic feature, i.e., they show birefringence but do not have definite, sharp, complete 

extinction in crossed-polarized light. Extinction may occur as dark bands that sweep through 

the grain or parts of the grain when the stage is turned or may occur in patches of irregular size 

and shape. With a few exceptions, e.g., well-oriented mineral pseudomorphs and certain clayskin fragments, some part of the grain is bright in all positions. Aggregates and altered grains 

should be examined with a variety of combinations of illumination and magnification in both 

plain and polarized lights. The principal properties that can be used to identify or at least 

characterize aggregates are discussed below. 

Color, if brown to bright red, is usually related to Fe content and oxidation. Organic 

matter and Mn may contribute black and grayish-brown colors. 

Refractive index is influenced by a number of factors, including elemental 

composition, atom packing, water content, porosity, and crystallinity. Amorphous 

(noncrystalline) substances have a single index of refraction, which may vary depending on 

chemical composition. For example, allophane has a refractive index of 1.47 to 1.49, but the 

apparent refractive index increases with increasing inclusion of ferrihydrite (noncrystalline Fe 

oxide) in the mineral. 

Strength of birefringence is a clue to the identity of the minerals. Even though the 

individual units of the aggregate are small, birefringence can be estimated by interference color 

and brightness. Amorphous substances, having only a single index of refraction, exhibit no 

birefringence and are isotropic between crossed-polarized light. 

Morphology may provide clues to the composition or origin of the aggregate. Some 

aggregates are pseudomorphs of primary mineral grains. Characteristics of the original 

minerals, i.e., cleavage traces, twining, or crystal form can still be observed. Morphology can 

sometimes be observed in completely altered grains, even in volcanic ash shards and basalt 

fragments. Other morphological characteristics may be observed in the individual units or in 

the overall structure, e.g., the units may be plates or needles, or there may be banding. 

Particular species of microcrystalline aggregates and amorphous substances: For 

purposes of soil genesis studies, the aggregates that are present in sand or silt fractions are not 

of equal significance. Some are nuisances but must be accounted for, and others are particles 

with important diagnostic value. Useful differentiating criteria for some of the commonly 

occurring aggregate types are discussed below. 

Rock fragments include chips of shale, schist, and fine-gained igneous rocks, e.g., 

rhyolite. Identification depends on the recognition of structure and individual components and 

the consideration of possible sources. Rock fragments are common in mountainous regions and 

are often hydrothermally-altered in the western U.S. 

Clay aggregates may be present in a wide variety of forms. Silt and sand that are bound 

together into larger grains by a nearly isotropic brownish material usually indicate incomplete 

dispersion. Clay skins may resist dispersion and consequently may appear as fragments in 

grain mounts. Such fragments are usually brown or red and translucent with wavy extinction 

bands. Care is required to distinguish these fragments from weathered biotite. Clay aggregates 

may be mineral pseudomorphs. Kaolin pseudomorphs of feldspar commonly are found. 

Montmorillonite aggregates, pseudomorphic of basic rock minerals, have been observed. In 

this form, montmorillonite shows high birefringence and an extinction that is mottled or patchy 

on a small scale. Coarse kaolinite flakes, books, and vermicular aggregates resist dispersion 

and may be abundant in sand and silt. These particles may resemble muscovite, but they are 

cloudy; show no definite extinction; and have very low birefringence. Many cases of 

anomalously high cation exchange capacity (CEC) of sand and silt fractions that are calculated 

from whole soil CEC and from clay CEC and percent content, can be accounted for by the 

occurrence of these aggregates in the sand and silt fractions. 

Volcanic glass is isotropic and has a low refractive index, lower than most of the silicate 

minerals. The refractive index ranges from 1.48 in the colorless siliceous glasses to as high as 

426
1.56 in the green or brown glasses of basalt composition. Shapes vary, but the elongated, 

curved shard forms, often with bubbles, are common. This glassy material may adhere to or 

envelop other minerals. Particles may contain small crystals of feldspar or incipient crystals 

with needles and dendritic forms. The colorless siliceous types (acidic, pumiceous) are more 

common in soils, as the basic glasses weather easily. Acidic glasses are more commonly part 

of "ash falls", as the magma usually is gaseous and explosive when pressure is released. Basic 

glasses are more commonly associated with volcanic flow rocks which are usually not gaseous. 

Allophane is present in many soils that are derived from volcanic ash. Allophane 

seldom can be identified directly, but its presence can be inferred when sand and silt are 

cemented into aggregates by isotropic material with low refractive index, especially if volcanic 

ash shards are also present. 

Opal, an isotropic material, occurs as a cementing material and in separate grains, some 

of which are of organic origin, i.e., plant opal, sponge spicules, and diatoms. The refractive 

index is very low (<1.45), which is lower than the value for volcanic ash. Identification may 

depend in part on form and occurrence. 

Iron oxides may occur as separate grains or as coatings, cementing agents, and mixtures 

with other minerals. Iron oxides impart brown and red colors and raise the refractive index in 

the mixtures. Goethite is yellow to brown. Associated red areas may be hematite. These red 

varieties have a refractive index and birefringence that are higher and seem to be better 

crystallized, often having a prismatic or fibrous habit. Aggregates have parallel extinction. In 

oriented aggregates, the interference colors often have a greenish cast. Hematite has higher 

refractive index than goethite and is granular rather than prismatic. Large grains of hematite 

are nearly opaque. 

Gibbsite often occurs as separate, pure, crystal aggregates, either alone or inside altered 

mineral grains. The grains may appear to be well-crystallized single crystals, but close 

inspection in crossed-polarized light shows patchy, banded extinction, indicating intergrown 

aggregates. Gibbsite is colorless. The refractive index (1.56 to 1.58) and the birefringence are 

higher for gibbsite than the corresponding values for quartz. The bright interference colors and 

aggregate extinction are characteristic of gibbsite. 

Chalcedony is a microcrystalline form of quartz that was formerly considered a distinct 

species. Chalcedony occurs as minute quartz crystals and exhibits aggregate structure with 

patchy extinction between crossed-polarized light. It may occur in nodules of limestone 

deposits and may be a pseudomorphic replacement in calcareous fossils. The refractive index 

is slightly lower than that of quartz, and the birefringence is lower than that of gibbsite. Chert

is a massive form of chalcedony. 

Glauconite occurs in aggregates of small micaceous grains with high birefringence. 

When fresh, glauconite is dark green and almost opaque, but it weathers to brown and more 

translucent forms. Glauconite is difficult to identify on optical evidence alone. Knowledge of 

source area or history are helpful in identification. 

Titanium oxide aggregates have been tentatively identified in the heavy mineral 

separates of many soils. These bodies have an extremely high refractive index and high 

birefringence similar to rutile. The yellow to gray colors are similar to those of anatase. The 

TiO2 aggregates are granular and rough-surfaced. This growth habit with the little spurs and 

projections suggests that TiO2 aggregates may be secondary. 

References 

Cady, J.G. 1965. Petrographic microscope techniques. p. 604-631. In D.D. Evans, L.E. 

Ensminger, J.L. White, and F.E. Clark (eds.) Methods of soil analysis. Part 1. Physical and 

mineralogical properties, including statistics of measurement and sampling. 1st ed. Agron. 

Monogr. 9. ASA and SSSA, Madison, WI. 

427
Optical Analyses (7B) 

Grain Studies (7B1) 

Separation by Heavy Liquids (7B1a1) 

1. Application 

The sand and silt fractions of most soils are dominated by quartz or by quartz and 

feldspars (Cady, 1965). These minerals have a relatively low specific gravity (2.57 to 2.76). 

The large numbers of "heavy" mineral grains (specific gravity >2.8 or 2.9) with a wide range of 

weatherability and diagnostic significance may be only a small percentage of the grains (Cady, 

1965). However, these "heavy" minerals are often indicative of provenance, weathering 

intensities, and parent material uniformity (Cady, Wilding, and Drees, 1986). 

2. Procedure 

To study "heavy" minerals, a common practice is to concentrate these grains by 

specific-gravity separations in a heavy liquid. This procedure (7B1a1) is rarely used at the SSL 

but is done on occasion for special studies. 

Micas are difficult to separate because of their shape and because a little weathering, 

especially in biotite, significantly decreases the specific gravity. These differences in density in 

biotite may be used to concentrate weathered biotite in its various stages of alteration . 

Separation of grains by heavy liquids is most effective when grains are clean. Organic 

matter may prevent wetting and cause grains to clump or raft together. Light coatings may 

cause heavy grains to float, and iron-oxide coatings may increase specific gravity. In some 

kinds of materials, an additional technique is to separate and weigh the magnetic fraction, either 

before or after the heavy-liquid separation. 

Concentrate the "heavy" minerals, i.e., specific gravity >2.8 or 2.9, by specific-gravity 

separations in a heavy liquid. The reagent of choice is sodium polytungstate (density 2.8 g-1

mL). Dilute the sodium polytungstate with distilled water to obtain required densities <2.8 g-1

mL. Use a specific gravity ≈ 2.5, to concentrate volcanic glass, plant opal, or sponge spicules. 

When using this liquid, avoid contact with skin and work in a well-ventilated area. 

Separation by specific gravity alone in separatory funnels, cylinders or various kinds of 

tubes is usually adequate for grains >0.10 mm. Separation by centrifuging is required for 

grains <0.10 mm. Use pointed, 15-ml centrifuge tubes for these separations. 

Decant the light minerals after inserting a smooth bulb glass rod to stop off the tapered 

end of centrifuge tube. Alternatively, remove the heavy minerals by gravity flow using a lower 

stopcock or maintain the heavy minerals in place by freezing the lower part of tube. 

3. References

Cady, J.G. 1965. Petrographic microscope techniques. p. 604-631. In D.D. Evans, L.E. 

Ensminger, J.L. White, and F.E. Clark (eds.) Methods of soil analysis. Part 1. Physical 

and mineralogical properties, including statistics of measurement and sampling. 1st ed. 

Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Cady, J.G., L.P. Wilding, and L.R. Drees. 1986. Petrographic microscope techniques. p. 

198-204. In A. Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical 

methods. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Optical Analysis (7B) 

Grain Mounts, Epoxy (7B1a2) 

1. Application 

Grain counts are used to identify and quantify minerals in the coarse silt and sand 

fractions of soils. Results are used to classify soil pedons in mineralogy families of soil 

taxonomy (Soil Survey Division Staff, 1999), to help determine substrate provenance of source 

materials, and to support or identify lithologic discontinuities. 

428
2. Summary of Method 

In particle-size analysis, soils are dispersed so that material <20 μm in diameter is 

separated by settling and decanting, and the sand and coarse silt fractions are separated by 

sieving. Refer to procedure for the separation by heavy liquids of the less abundant minerals 

with a specific gravity >2.8 or 2.9 (7B1a1). 

Following sample selection, permanent mounts are prepared for the two most abundant 

particle-size fractions among the fine sand, very fine sand and coarse silt. The grains are 

mounted in a thermo-setting epoxy cement with a refractive index of 1.54. The grains are then 

identified and counted under a petrographic microscope. 

A mineralogical analysis of a sand or silt fraction may be entirely qualitative, or it may 

be quantitative to different degrees (Cady, 1965). The SSL performs a quantitative analysis 

(7B1a2). Data are reported as a list of minerals and an estimated quantity of each mineral as a 

percentage of the grains counted in the designated fraction. The percentages of minerals are 

obtained by identifying and counting a minimum of 300 grains on regularly spaced line 

traverses that are 2 mm apart. 

The identification procedures and reference data on minerals are described in references 

on sedimentary petrography (Krumbein and Pettijohn, 1938; Durell, 1948; Milner, 1962; Kerr, 

1977; Deer et al., 1992) and optical crystallography (Bloss, 1961; Stoiber and Morse, 1972; 

Shelley, 1978; Klein and Hurlbut, 1985; and Drees and Ransom, 1994). 

3. Interferences 

The sample must be thoroughly mixed because the sub-sample on the slide is small. If 

grains are coated with clay or if aggregates of finer material remain in the fraction that is 

counted, results may be skewed. Variations in the time or temperature of heating the epoxy 

may result in either matrix stress or variation the refractive index of the epoxy. Do not use 

steel needles or spatulas because magnetic minerals may adhere to steel resulting in uneven 

distribution of grains on the slide. 

4. Safety 

Heat the epoxy in a fume hood. Use caution in handling hot glass slides. Use heat 

resistant gloves as needed. Immediately wash or remove any epoxy that comes in contact with 

the skin. Carefully handle slides and cover slips to avoid cuts. 

5. Equipment 

5.1 Petrographic microscope slides, precleaned, 27 x 46 mm 

5.2 Cover slips, glass, 25 x 25 mm 

5.3 Hot plate 

5.4 Micro-spatula 

5.5 Dissecting needle 

5.6 Plywood covered with formica (6 x 8 x 1.25 cm) 

5.7 Timer 

5.8 Polarizing petrographic microscope 

5.9 Tally counter 

5.10 Set of 76-mm (3 in) sieves, square weave phosphor bronze wire cloth except 300 mesh 

which is twilled weave. U.S. series and Tyler Screen Scale equivalent designations are as 

follows: 

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Sand 

Size 

Opening 

(mm) 

U.S. No. Tyler 

Mesh 

Size 

VCS 1.0 18 16 

CS 0.5 35 32 

MS 0.25 60 60 

FS 0.105 140 150 

VFS 0.047 300 300 

5.11 Oven, 110 C 

6. Reagents 

6.1 Petropoxy 154TM Resin and Curing Agent, Palouse Petro Products, 425 Sand Rd., 

Palouse, WA 99163 

6.2 Index immersion oils 

6.3 Reverse Osmosis (RO) water, ASTM Type III grade of reagent water 

7. Procedure 

Sample Selection and Grain Mount Preparation

7.1 Refer to the analysis request sheets. Record optical mineralogy requests in the LIMS 

Report “Optical Priority List.” Note any special instructions by soil scientists. Sample 

selection depends on the purpose of analysis. In most work, e.g., checks on discontinuities or 

estimation of degree of weathering in different soil horizons, the study of those fractions that 

comprise a significant quantitative part of the soil is important. The SSL convention is to 

count the most abundant fraction, i.e., coarse silt (CSI), very fine sand (VFS) or fine sand (FS), 

especially if the fraction is clearly larger. This procedure works well in the establishment of 

mineralogy families for soil taxonomy (Soil Survey Staff, 1999). This procedure may result in 

different size fractions being counted for different horizons within a single pedon. If fractions 

are rather equal in abundance, the VFS is selected as it provides the widest range of 

information. The SSL does not count multiple fractions for a single sample, or count combined 

fractions, or present the data as weighted averages. If it is appropriate to count the same size 

fraction for each horizon within a pedon or project such as for a study of soil lithology, this 

request must be specified by the project coordinator. 

7.2 Refer to the laboratory information system (LIMS) report “Optical Priority List” for daily 

work or check the sand box lids to determine which sands have been fractionated. Sands are 

fractionated during particle-size distribution analysis (PSDA) (procedure 3A1a). Fine sand, and 

very fine sand, fractions placed in gelatin capsules and stored in a labeled vial. Coarse silts are 

stored in aluminum pans. For projects, the LIMS report provides the following: 

a. Sample numbers by project 

b. Type of count requested (full grain count or glass count) 

c. Percent of <2-mm fraction for CSI, VFS, or FS as determined by SSL PSDA. 

7.3 If the particle-size section does not provide a sand and coarse silt separate, derive these 

fractions by repeated gravity sedimentation at 20 μm and sieving the 20-μm to 2.0-mm material 

as follows: 

7.3.1 Disperse the sample in sodium hexametaphosphate as described in procedure 7A1a1. 

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7.3.2 Pour the soil suspension into a 200-mL beaker that has a line marked 5 cm above the 

bottom. 

7.3.3 Add RO water to the beaker up to the 5-cm mark. 

7.3.4 Stir the suspension and allow to settle 2.0 min. Use a stopwatch. 

7.3.5 Decant and discard the suspension containing the clay and fine silt. 

7.3.6 Repeat Steps 7.3.3 to 7.3.5 until the supernatant is clear or reasonably so. 

7.3.7 Transfer the sediment to a drying dish and dry at 105-110°C. 

7.3.8 Sieve the dried sample to isolate the individual fractions. 

7.4 Review the PSDA data and select samples. Make grain mounts from the one or two most 

abundant fractions, preferably from the CSI, VFS, or FS. Record sample numbers and 

respective PSDA data. 

7.5 Mix a small amount of Petropoxy 154TM resin and curing agent (1:10 ratio resin to curing 

agent) in a clean graduated plastic beaker that is provided with the reagents. 

 

7.6 Prepare epoxy at least one day prior to use and refrigerate until needed. 

7.7 Turn on hot plate and allow to equilibrate at 125°C for ≈ 1 h. 

7.8 Remove mixture from refrigerator at least 40 min prior to use. If the petropoxy 

crystallizes, gently warm mixture until crystals dissolve. 

7.9 At the base of the glass slides, record the grain size fraction (CSI, VFS, FS, etc.) and SSL 

LIMS sample number. An example is as follows:VFS 35126 

7.10 Obtain sand vials and/or silt dishes. Arrange in an orderly manner. Work with 4-6 slides 

and samples at a time. 

7.11 Remove lids from sand vials and place upside down in front of respective vials. Remove 

gelatin capsules (VFS or FS) from vial. Rotate capsule to mix contents and place in lid. Stir 

with a micro-spatula to mix coarse silts. 

7.12 Use a small, rounded glass or plastic rod to drop petropoxy mixture on the upper middle of 

each slide. Use one drop of petropoxy for CSI or VFS and two drops for FS. 

7.13 Use a micro-spatula to add the mixed grains to petropoxy. Use larger amounts for smaller 

fractions. The analyst's technique of adding the appropriate amount of petropoxy and of 

making grain counts on prepared slides develops with experience. Use a dissecting needle to 

slowly and carefully stir the grains into the petropoxy. Avoid introduction of air bubbles. 

Obvious air bubbles can be popped with the dissecting needle. 

7.14 Gently place one cover slip (check to be certain) on the petropoxy. Avoid fingerprints. 

Allow the petropoxy to spread under the cover slip. Center the cover slip at top center of glass 

microscope slide so that there is a parallel, equidimensional border around the top and sides of 

slide. 

431
7.15 To ensure the uniform distribution of grains and the removal of air bubbles, use a 

dissecting needle to gently tap or press down cover slip. If necessary, the analyst may need to 

recenter the cover slip. Be careful not to crack cover slip. 

7.16 Align a batch of 4-6 slides in two rows on center of hot plate. 

7.17 Set timer and heat slides at 125°C for 8 min. Time can be adjusted by experience. As a 

rule, when epoxy is set, it has cured to yield a refractive index of 1.540. Longer heating may 

result in a distortion of the optical characteristics of the petropoxy and a refractive index 

differing from 1.540. 

7.18 As one batch of slides heats, prepare the next batch. After heating for 8 min, slide the 

glass slides off the hot plate onto the formica block. Allow to cool. 

7.19 Examine the grain mount for quality. The epoxy medium should be isotropic. The 

presence of anisotropic stress lines around grains under X-Nicols may interfere with 

observation of optical properties. Remake any unsatisfactory grain mounts. Place satisfactory 

mounts in a microscope slide file box. Neatly record project number and grain mount positions 

on interior of box lid, and record box number(s) in the LIMS Sample Disposition files. 

7.20 Return the petropoxy mixture to the refrigerator in order to extend shelf life of the 

mixture. 

Observations of Grain Mount 

7.21 Record raw grain count data in a logbook. Most grain counts are made with a 10X 

magnification ocular and either a 10X (for very fine or fine sand) or 25X (for coarse silt) 

magnification objective lens. 

7.22 The first step is to seat the grain mount in the mechanical stage of the microscope and to 

survey the slide with a low-power magnification power (10X) to become familiar with the grain 

assemblage and to make a rough estimate of the relative abundance of minerals and other 

grains. 

7.23 Initially, identify the most abundant minerals as they are probably the easiest to identify, 

and their elimination decreases the number of possibilities to consider in identifying the less 

common minerals. Furthermore, there are certain likely and unlikely assemblages of minerals, 

and an awareness of the overall types that are present gives clues to the minor species that may 

be expected. 

7.24 Note the observed minerals by a two-letter code, e.g., QZ for quartz. Refer to the list of 

mineralogy codes, provided at the end of the mineralogy section (7). 

7.25 Make grain counts in horizontal traverses across the grain mount. A 10X magnification 

objective is appropriate for FS and VFS. A 25X objective is appropriate for CSI. 

7.26 To make a grain count, move the slide via the mechanical stage so that the left border of 

cover slip is in view and in the proximity of but not in the upper left corner. Place vertical 

scale on mechanical stage on an even number, e.g., 72 or 74 mm. 

7.27 Set the rotating stage so that the horizontal movement of a grain, via the mechanical stage, 

parallels the horizontal cross-hair in the ocular. 

432
7.28 List the most abundant grains and associated counter number in logbook. Mineral 

identification is facilitated by the familiarity with a few striking features and by the process of 

elimination. 

7.29 Set counters to zero. Move the slide laterally one field width at a time. Identify and tally 

each grain that touches the horizontal cross-hair in each field of view until the right margin of 

cover slip is in view. 

7.30 Translate the slide vertically a distance of 2 mm and run another traverse in the reverse 

direction. 

7.31 Repeat process until the end of traverse in which 300 grains have been tallied. If there are 

only a few species, a counting of 300 grains provides a good indication of composition. As the 

number of species increases, the count should increase within limits of practicability. To count 

more than 1000 grains is seldom necessary. 

7.32 The counting of complete traverses minimizes the effects of non-random distribution of 

grains on the slide. This non-random distribution of grains is usually most pronounced near the 

edges of the cover slip. If the entire slide has been traversed, and the total grain count is <300, 

reverse the direction of vertical translation and count traverses on odd-numbered settings, e.g., 

81 or 79 mm. 

7.33 Counting isotropic grains only (e.g., volcanic glass) can be done more rapidly using either 

of the following microscope configurations: 

7.33.1 Positioning the polarizer slightly off the extinction or "blackout" position. 

OR 

7.33.2 With crossed Nicols and a gypsum plate, the outline of the grains is visible with the 

color of the grain being the same as the epoxy background. 

7.34 When the count is complete, enter the raw data (project, sample number, fraction(s), 

minerals, and counts) into the SSL LIMS data base. 

8. Calculations 

Calculations are made by a computer program written to facilitate data entry and manipulation. 

Required inputs are as follows: project number; sample number; grain-size fractions; mineral 

identification; and number of grains counted per mineral. 

Percentage of minerals (frequency per 100 grains) is calculated by the formula as follows: 

8.1 Mineral frequency (%) = (Number of grains for a mineral x 100)/Total number of grains 

counted 

9. Report

Report mineral contents to the nearest whole percentage of grains counted. These data 

are accurate number percentages for the size-fraction analyzed but may need to be recomputed 

to convert to weight percentages (Harris and Zelazny, 1985). Grain counts can deviate 

significantly from weight percentage due to platy grains and density variations. These data are 

reported on the mineralogy data page of the primary characterization data set. For each grain 

size counted, the mineral type and amount are recorded, i.e., quartz, 87% of fraction, is 

433
recorded as QZ87. The percentage of resistant minerals in each fraction is reported on the SSL 

datasheet. Refer to 7C1 for more information on resistant minerals. 

10. Precision and Accuracy 

Precision and accuracy data are available from the SSL upon request. 

11. References 

Bloss, D.F. 1961. An introduction to the methods of optical crystallography. Holt, 

Rinehart, and Winston, NY. 

Cady, J.G. 1965. Petrographic microscope techniques. p. 604-631. In D.D. Evans, L.E. 

Ensminger, J.L. White, and F.E. Clark (eds.) Methods of soil analysis. Part 1. Physical 

and mineralogical properties, including statistics of measurement and sampling. 1st ed. 

Agron. Monogr. 9. ASA and SSSA, Madison, WI. 

Deer, W.A., R.A. Howie, and J. Zussman. 1992. An introduction to the rock-forming 

minerals. 2nd ed. Longman Scientific and Technical, Essex, England. 

Drees, L.R., and M.D. Ransom. 1994. Light microscope techniques in quantitative 

mineralogy. p.137-176. In J.E.Amonette and L.W. Zelazny (eds.) Quantitative methods 

in soil mineralogy. SSSA Misc. Publ. Soil Sci. Soc. Am., Madison, WI. 

Durrell, Cordell. 1948. A key to common rock-forming minerals in thin section. W.H. 

Freeman and Co., Publ., San Francisco, CA. 

Harris, W.G., and L.W. Zelazny. 1985. Criteria assessment for micaceous and illitic classes 

in Soil Taxonomy. p. 147-160. In J.A. Kittrick (ed.) Mineral classification of soils. 

SSSA Spec. Publ. No. 16. Madison, WI. 

Kerr, P.F. 1977. Optical mineralogy. McGraw-Hill Book Co., Inc., NY. 

Klein, Cornelis, and C.S. Hurlbut, Jr. 1985. Manual of mineralogy. John Wiley and Sons, 

NY. 

Krumbein, W.C. and F.J. Pettijohn. 1938. Manual of sedimentary petrography. AppletonCentury-Crofts, NY. 

Milner, H.B. 1962. Sedimentary petrography, 4th ed. The Macmillan Co., NY. 

Shelley, David. 1978. Manual of optical mineralogy. Elsevier. North-Holland, Inc., NY. 

Stoiber, R.E., and S.A. Morse. 1972. Microscopic identification of crystals. Ronald Press 

Company, NY. 

Soil Survey Staff. 1999. Soil Taxonomy: A Basic System of Soil Classification for 

Making and interpreting Soil Surveys. 2nd ed. USDA-NRCS Agric. Handb. 436. U.S. 

Gov. Print. Office, Washington, DC. 

Platy Grains (7B2) 

Magnetic Separation (7B2a) 

 

1. Application 

A magnetic separator is used to separate magnetic or paramagnetic minerals from nonmagnetic mineral grains from the fine earth fractions that range from 0.02 to 0.5 mm in size. In 

the SSL, the common application is to quantify the amount of platy grains (phyllosilicates) in 

micaceous or paramiceous soils. Ferrimagnetic magnetic grains such as magnetite and ilmenite 

typically are separated first with a hand magnet. The separator then concentrates grains of 

paramagnetic minerals such as biotite and muscovite from non-magnetic minerals such quartz 

and feldspar. This procedure (7B2a) is often used in combination with static tube separation 

(7B2b) or froth flotation (7B2c). Grains in each separate can be further analyzed by optical 

microscopy or x-ray diffraction. 

2. Summary of Method 

A magnetic separator applies a strong magnetic field along a shallow trough that slopes 

down from an entry point to an exit point. Grains travel the path under the force of gravity. 

434
The trough is also tilted perpendicular to the travel path. The magnetic field draws 

paramagnetic grains up the tilt slope. A divider at midslope along the path separates the 

paramagnetic from non-magnetic grains. Grains exit the path into separate containers and the 

two components are weighed to obtain a relative percentage. Percent platy minerals of specific 

analyzed fraction are reported (7B2a). 

3. Inerferences 

Some mafic minerals are paramagnetic, and exit with the platy grains. The two groups 

may be separated by the static tube procedure (7B2b). Mafic minerals commonly are heavy 

minerals and may be separated from platy grains by density separation (7B1a2). 

4. Safety 

The magnetic field is not a direct biological health hazard. Keep mechanical watches 

away from the magnetic field. Keep iron/steel objects away from the magnetic field because of 

the strength of field. The separator will need to be turned off to retrieve them. 

5. Equipment 

5.1 300-mL fleaker, with a fill line marked at 5cm above bottom 

5.2 Glass stirring rod, with a rubber policeman 

5.3 Stop watch 

5.4 Sonic probe, Vibra Cell Model V1A, Sonics and Materials, Inc., Danbury, CT 

5.5 Magnetic separator; Frantz Isodynamic Magnetic Separator, Model L-1, S.G. Frantz, Inc, 

Trenton, NJ (Fig. 1) 

5.6 Centrifuge tube, plastic, 100-mL 

5.7 Beaker, pyrex, 150-200 mL, marked with a line 5-cm above bottom 

5.8 Sieves: 

5.8.1 0.5 - 2.0 mm = US 35 mesh sieve or Tyler 32 mesh sieve 

5.8.2 0.1 - 0.5mm = US 140 mesh sieve or Tyler 150 mesh sieve 

5.8.3 0.05 - 0.1mm = US 300 mesh sieve or Tyler 300 mesh sieve 

5.8.4 0.02 - 0.05mm = Material that passes through the 300 mesh sieve 

5.9 Mechanical reciprocating shaker, 100 oscillations min-1, 1 1⁄2 in strokes, Eberbach 6000, 

Eberbach Corp., Ann Arbor, MI 

5.10 Oven, 110 C 

6. Reagents 

6.1 Reverse Osmosis (RO) water (ASTM type III grade)

6.2 Sodium hexametaphosphate solution. Dissolve 35.7 g of sodium 

hexametaphosphate (NaPO3)6 and 7.94 g sodium carbonate (Na2CO3) L-1 

7. Procedure 

Separation of Target Fraction (0.02 to 2.0 mm) 

(for magnetic separation, static tube separation, and/or froth flotation) 

7.1 For magnetic separation alone or in combination with static tube separation, 5 grams of 

<2-mm soil is sufficient. If froth floatation is used in combination with magnetic separation, 

use 20 to 30 g of <2.0-mm sample. 

7.2 Place sample into a 100-mL centrifuge tube for magnetic or tube methods, or in a 300-mL 

fleaker for froth flotation is intended. Add 10 to 60 mL of dispersing agent, as appropriate 

for sample weight. 

7.3 Fill the centrifuge tube half full, or fleaker to the 5-cm mark with distilled water. Stopper 

and shake the solution overnight at 100 oscillations min-1. 

435
7.4 Transfer contents of the centrifuge tube to a 150-200 mL beaker. Add RO to the fleaker to 

the 5-cm mark, if needed. 

7.5 With the stirring rod, stir the sample for 15 seconds and allow to stand for 2 minutes. 

Decant and discard the dispersant. 

7.6 Repeat the settling process, usually 4 to 5 times, until the dispersant is clear. Sediment is 

the 0.02-2 mm fraction. 

Sonic Cleaning of Sample 

7.8 Add approximately 50 mL of RO water to the fleaker or beaker containing the 0.02-2.0 

mm sample. 

7.9 Turn on and tune the sonic cleaner for optimal performance. Set the % Duty cycle knob to 

50; output control knob to 10; run time to 360 s; and turn on the pulser switch. 

7.10 Lower the sonic probe horn 0.5 to 1.0 cm below the water level of the fleaker containing 

the washed sample and turn on the sonic probe. 

7.11 Repeat the decanting process (see separation of working fraction) to remove fines (<0.02 

mm) produced by the sonic probe treatment. 

7.12 Oven-dry the sample at 110°C. 

Particle-Size Separation 

7.13 Dry sieve the .02-2mm fraction cleaned by sonication into the following subfractions: 0.5-

2.0, 0.1-0.5, 0.05-0.1, and 0.02-0.05 mm. 

7.14 Weigh and record dry weigh of each of the separates. 

Procedure Options for Each Size Fraction 

7.15 0.5-2mm fraction: Separate platy grains via magnetic separator only (Fig. 1). This fraction 

seems unsuited for static tube or froth floatation separation. 

Fig. 1. Apparatus for Magnetic Separation 

436
7.16 0.1-0.5, 0.05-0.1, and 0.02-0.05mm fractions: Separate by the following methods: 

7.16.1 Magnetic separation (procedure 7B3a), or 

7.16.2 Static tube separation (procedure 7B3b) followed by magnetic separation (procedure 

7B3a) of residual fraction, or 

7.16.3 Froth flotation separation (procedure 7B3c) followed by magnetic separation (procedure 

7B3a) of residual fraction. 

Magnetic Separation 

7.17 Turn on the magnetic separator and adjust the machine to the high-high, positive position, 

and set the amp meter to 1.25 amperes. 

7.18 Set the slope to about 20 degrees and the tilt to 15 degrees. 

7.19 Introduce sample into the funnel and set the vibrator adjustment knob between 5 and 8. 

Observe the flow of the grains down the separator trough and adjust the vibrator setting 

accordingly. 

7.20 Repeat the process using the non-magnetic portion 2-4 times or until the non-magnetic 

fraction is free of platy minerals. 

7.21 Weigh and record the weight of the magnetic fraction as platy grains, and the nonmagnetic fraction as residual grains. Calculate amount of platy grains as percent by weight of 

analyzed fraction. 

8. Calculations 

8.1 Percent platy grains = [100 x (weight of platy grains)]/sample weight) 

8.2 Percent residual grains = [100 x (weight of residual grains)]/(sample weight) 

8.3 Recovery = (weight of platy and residual grains)/(sample weight) 

9. Report 

Report platy grains as a percent of the specific particle size fraction analyzed, ovendried soil weight. 

10. Precision and Accuracy 

Precision and accuracy data are not available for this method. 

Platy Grains (7B2) 

Static Tube Separation (7B2b) 

1. Application 

Static charge of mineral grains to glass and a magnetic separator are used to separate 

platy grains from non-platy grains in the 0.02 -2 mm fraction of soil. The separates are 

weighed to determine the quantity of platy minerals. The platy separates are examined by 

optical microscope and analyzed by X-ray diffraction to determine the kinds of minerals 

present. 

437
2. Summary of Method 

A sample of <2-mm soil is prepared according to the procedure described in 7B2a. A 

small portion of sample is introduced into the top of an inclined glass tube mounted on a 

vibrator. As the tube is rotated and vibrated, the platy grains adhere to the tube and the nonplaty grains (residue) roll or slide through. The residue is run through a magnetic separator to 

separate the coarser platy grains that did not adhere to the glass tube. Percent platy minerals 

of specific analyzed fraction are reported (7B2b). 

3. Interferences 

Large platy grains tend to slide through the tube into the residue, especially if the 

plates are stacked into a book. 

4. Safety

No known hazards exist. 

5. Equipment 

5.1 Glass tube, 1.5 cm inside diameter, 30 cm long vibrating mechanism 

5.2 Receptacles to hold grains 

5.3 Funnel or glassine paper or aluminum weighing dish 

5.4 Camel's hair brush 

5.5 Gelatin capsules. 

5.6 Mechanical Vibrator 

6. Reagents 

None. 

7. Procedure 

7.1 Prepare sample (disperse, fractionate, and dry sample as described in Method 7B2a) 

Static Charge Separation by Glass Tube 

7.2 Set up vibrator as shown in Fig. 1. 

Fig. 1. Apparatus for Static Tube Separation 

7.3 Weigh 0.1500 g of 0.02-2 mm material or particle-size separate onto a square of 

glassine paper and introduce into the upper end of the glass tube. 

438
7.4 Turn on the vibrator until the material begins to flow. Rotate the tube slowly so the 

platy grains adhere to the tube wall. Adjust vibrator intensity and rotation to achieve a 

slow smooth flow rate. 

7.5 When rounded grains have passed through the tube, remove the tube and hold it 

vertically over a tared weighing dish. Tap the tube to remove the platy grains. If grains 

remain, wash them out with RO water, dry, and weigh. 

Note: The glass tube separation can be done by hand, without mechanical vibration in 

the field office to obtain a fair approximation of the platy grain component. 

8. Calculations 

8.1 Percent platy grains = [100 x (weight of platy grains)]/sample weight) 

8.2 Percent residual grains = [100 x (weight of residual grains)]/(sample weight) 

8.3 Recovery = (weight of platy and residual grains)/(sample weight) 

9. Report 

Report platy grains as a percent of the specific particle size fraction analyzed, ovendried soil weight. 

11. Precision and Accuracy 

Precision and accuracy data are not available for this method. 

Platy Grains (7B2) 

Froth Flotation (7B2c) 

1. Application 

This method used with coarse silt, very fine, fine, and medium sand fractions of soils 

with significant amounts of platy minerals (mica, vermiculite, chlorite, and their 

pseudomorphically altered weathering products). It provides weight percent data on each of the 

fractions. Combined use of froth flotation and magnetic separation improve separation of platy 

and non-platy grains to better estimate weight percentages of components. 

2. Summary of Method 

Platy minerals (muscovite, biotite, vermiculite, and kaolinite) are floated off over the 

top of a container in an agitated aqueous suspension by action of a complexer and frother, 

adapted from procedure provided by Louis Schlesinger of the Minerals Research Laboratory 

School of engineering, North Carolina State University, in Asheville, NC. Percent platy 

minerals of specific analyzed fraction are reported (7B2c). 

3. Interferences 

There are no known interferences. 

4. Safety 

There are no known safety hazards. 

439
5. Equipment 

5.1 Modified 800 mL glass beaker for mixing container 

5.2 Plastic bucket, 5 qt, for catch container 

5.3 Mechanical mixer - 1 laboratory reagent mixer or a magnetic bar stirrer 

5.4 Manual mixer - 1 glass rod pH meter 

5.5 Oven, 110 °C 

5.6 Wood tongue depressors or a similar spatula-like device 

5.7 Syringe - 1 mL 

5.8 Beaker - 800 mL aerator 

5.9 Ring stand (to hold Aerator assembly) 

5.10 Funnel and stand to hold funnel 300-mesh sieve 

5.11 Glass rod with rubber policeman 

6. Reagents 

6.1 Reverse osmosis (RO) water, ASTM Type III grade of reagent water 

6.2 Frother: Econofroth 910 frother, 100% solution (Mfg: Nottingham Company; P.O. Box 

250049; Station N; 1303 Boyd Ave. NW; Atlanta, GA 303025; phone: 404-351-3501) 

6.3 Promoter: Econofloat A-50 promoter, 5% solution (1mL/20mL or 50mL/1000mL); (Mfg: 

Nottingham Company) 

6.4 NaOH (2.5% solution or 12.5 g per 500 g) 25 g/liter 

6.5 H2SO4 , 0.9 N (2.5% solution or 12.5 g conc. H2SO4 per 500 g water) 

6.6 Ethyl alcohol in wash bottle 

7. Procedure 

7.1 Prepare sample (disperse, fractionate, and dry sample as described in procedure 7B2a. 

7.2 Set up apparatus as shown in Fig. 1. 

Fig. 1. Apparatus for Froth Flotation 

7.3 Prepare 700 mL RO water, pH 2.5: Put 800-mL glass beaker on mechanical mixer and fill 

to 700 mL level. Adjust to pH 2.5 (not over 3.0) with 0.9 N H2SO4 solution and set the full 

beaker aside for use later. 

440
7.4 Place 800 mL mixing container on mechanical mixer, and fill 3/4 full with RO water. 

7.5 Add 5 g of sample to water and start a strong mixing action. 

7.6 Adjust pH of sample and water to 2.5 with 0.9 N H2SO4 solution. 

7.7 Add 0.25ml of Promoter. 

7.8 Add 0.2ml of frother. 

7.9 Continue to mix the sample solution for 2-5 minutes. 

7.10 Check and readjust the pH level as necessary. 

7.11 Place mixing container in plastic 5-qt catch bucket, lower aerator into solution, fill mixing 

container almost to top, using the water from section 7.3. 

7.12 Turn off the mechanical mixer and turn on the air to the aerator to start the frothing action. 

The frothing foam should build to a point where the foam pours out of the modified mixing 

container. Add water from section 7.3 as needed to maintain foam overflow from the mixing 

container. 

7.13 Use a glass stirring rod with a rubber policeman to mix the sample on the bottom of the 

mixing chamber in a grid like motion. As the platy minerals froth to the surface use the wood 

tongue depressor to rake them over the side of the mixing chamber. 

7.14 After 1-5 minutes the amount of platy minerals floating to the surface should diminish. 

At this time turn off the air, thoroughly remix the sample with the glass stirring rod, and 

repeat the procedure starting at section 7.12. 

7.15 After 2-5 minutes during the second run through section 7.12, carefully inspect the foam 

to see if platy minerals are still frothing to the surface. Continue until little or no platy 

minerals are frothing to the surface. 

7.16 Transfer contents of the catch bucket with ethyl alcohol to the 300-mesh sieve and rinse 

the sample. 

7.17 Transfer the rinsed grains to an aluminum dish, dry in an oven at 110°C, weigh and 

record the weight as platy grains. 

7.18 Repeat steps 7.16 and 7.17 for the contents in the mixing container and record the weight 

as residual grains. NOTE: Delay weighing samples if magnetic separation (procedure 7B2a) 

will be done next. 

8. Calculations 

8.1 Percent platy grains = [100 x (weight of platy grains)]/sample weight) 

8.2 Percent residual grains = [100 x (weight of residual grains)]/(sample weight) 

8.3 Recovery = (weight of platy and residual grains)/(sample weight) 

441
9. Report 

Report platy grains as a percent of the specific particle size fraction analyzed, ovendried soil weight. 

10. Precision and Accuracy 

Precision and accuracy data are not available for this method. 

Ratios and Estimates Related to Optical Analysis (7C) 

Total Resistant Minerals (7C1) 

The sum of the grain-count percentages of resistant minerals are reported (7C1). For 

more detailed information on total resistant minerals, refer to the Soil Survey Staff (1995, 

1999). Also refer to the list of mineralogy codes for resistant and weatherable minerals, 

following procedure 7C1. 

References 

Soil Survey Staff. 1995. Soil survey laboratory information manual. Version No. 1.0. USDANRCS. Soil Survey Investigations Report No. 42. U.S. Govt. Print. Office, Washington, DC. 

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and 

interpreting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. Print. Office, 

Washington, DC. 

442
MINERALOGY CODES 

Resistant Minerals 

AE = Anatase 

AG = Antigorite 

AN = Andalusite 

BY = Beryl 

CD = Chalcedony (Chert, Flint, 

 Jasper, Agate, Onyx) 

CE = Cobalite 

CH = Cliachite (Bauxite) 

CN = Corundum 

CR = Cristobalite 

CT = Cassiterite 

FE = Iron Oxides (Goethite, 

 Magnetite, Hematite, Limonite) 

GD = Gold 

GE = Goethite 

GI = Gibbsite 

GN = Garnet 

HE = Hematite 

KK = Kaolinite 

KY = Kyanite 

LE = Lepidocrocite 

LM = Limonite 

LU = Leucoxene 

MD = Resistant Mineraloids 

MG = Magnetite 

MH = Maghemite 

MZ = Monazite 

OP = Opaques 

OR = Other Resistant Minerals 

PN = Pollen 

PY = Pyrophyllite 

QC = Clay-Coated Quartz 

QI = Iron-Coated Quartz 

QZ = Quartz 

RA = Resistant Aggregates 

RE = Resistant Minerals 

RU = Rutile 

SA = Siliceous Aggregates 

SL = Sillimanite 

SN = Spinel 

SO = Staurolite 

SP = Sphene 

TD = Tridymite 

TM = Tourmaline 

TP = Topaz 

ZR = Zircon 

Weatherable Minerals 

AC = Actinolite 

AF = Arfvedsonite 

AH = Anthophyllite 

AI = Aegerine-Augite 

AL = Allophane 

AM = Amphibole 

AO = Aragonite 

AP = Apatite 

AR = Weatherable Aggregates 

AU = Augite 

AY = Anhydrite* 

BA = Barite 

BC = Biotite-Chlorite 

BE = Boehmite 

BK = Brookite 

BR = Brucite 

BT = Biotite 

BZ = Bronzite 

CA = Calcite* 

CB = Carbonate Aggregates*

CC = Coal 

CL = Chlorite 

CM = Chlorite-Mica 

CO = Collophane 

CY = Chrysotile 

CZ = Clinozoisite 

DL = Dolomite 

DP = Diopside 

DU = Dumortierite 

EN = Enstatite 

EP = Epidote 

FA = Andesite 

FB = Albite 

FC = Microcline 

FD = Feldspar 

FF = Foraminifera 

FH = Anorthoclase 

FK = Potassium Feldspar 

FL = Labradorite 

FM = Ferromagnesium Mineral 

FN = Anorthite 

FO = Oligoclase 

FP = Plagioclase Feldspar 

FR = Orthoclase 

FS = Sanidine 

FU = Fluorite 

FZ = Feldspathoids 

GG = Galena 

443
GL = Glauconite 

GO = Glaucophane 

GY = Gypsum* 

HA = Halite 

HB = Hydrobiotite 

HN = Hornblende 

HS = Hydroxy-Interlayerd Smectite 

HV = Hydroxy-Interlayered Vermiculite 

ID = Iddingsite 

IL = Illite (Hydromuscovite) 

JO = Jarosite 

KH = Halloysite 

LA = Lamprobolite 

LC = Analcime*

LI = Leucite 

LO = Lepidomelane 

LP = Lepidolite 

LT = Lithiophorite 

MC = Montmorillonite-Chlorite 

ME = Magnesite 

MI = Mica 

ML = Melilite 

MM = Montmorillonite-Mica 

MR = Marcasite 

MS = Muscovite 

MT = Montmorillonite 

MV = Montmorillonite-Vermiculite 

NE = Nepheline 

NJ = Natrojarosite 

NX = Non-Crystalline 

OV = Olivine 

OW = Other Weatherable Minerals 

PD = Piemontite 

PG = Palygorskite 

PI = Pyrite 

PJ = Plumbjarosite 

PK = Perovskite 

PL = Phlogopite 

PR = Pyroxene 

PU = Pyrolusite 

RB = Riebeckite (Blue Amphibole) 

RO = Rhodocrosite 

SC = Scapolite 

SE = Sepiolite 

SG = Sphalerite 

SI = Siderite 

SM = Smectite 

SR = Sericite 

ST = Stilbite 

SU = Sulphur 

TA = Talc 

TE = Tremolite 

TH = Thenardite*

VC = Vermiculite-Chlorite 

VH = Vermiculite-Hydrobiotite 

VI = Vivianite 

VM = Vermiculite-Mica 

VR = Vermiculite 

WE = Weatherable Mineral 

WV = Wavelite 

ZE = Zeolite 

ZO = Zoisite 

Glass Count Minerals and Mineraloids 

BG = Basic Glass GM = Glassy Materials 

DI = Diatoms OT = Other 

GS = Glass PA = Palagonite 

GA = Glass Aggregates PO = Plant Opal 

FG = Glass-Coated Feldspar SS = Sponge Spicule 

GC = Glass-Coated Grain 

HG = Glass-Coated Hornblende 

OG = Glass-Coated Opaque 

QG = Glass-Coated Quartz 

*

Minerals not included as “weatherable minerals” as defined by Soil Taxonomy (1999) - “the intent is to 

include only those weatherable minerals that are unstable in a humid climate compared to other minerals 

such as quartz and 1:1 lattice clays, but are more resistant to weathering than calcite”. This group of 

minerals is not part of the calculation for percent resistant minerals used in the siliceous family mineralogy 

class or percent weatherable minerals used as criteria for oxic horizon but are included in the calculation of 

“total resistant minerals” on the Soil Survey Laboratory mineralogy data sheet. Therefore, the value on the 

data sheet should be recalculated for strict use in Soil Taxonomy criteria if these minerals (e.g., calcite) are 

present in the grain count of a selected horizon. 

444
SOIL SURVEY LABORATORY METHODS 

(obsolete methods with old method codes) 

This section of the Soil Survey Laboratory (SSL) Methods Manual describes the 

procedures that are no longer used at the SSL. These metods were described in earlier versions 

of Soil Survey Investigations Report (SSIR) No. 42 (1989, 1992, and 1996) and the SSIR No. 

1, Procedures for Collecting Soil Samples and Methods of Analysis for Soil Survey (1972, 

1982, and 1984). Some of these procedures are in the old format. Information is not available 

to describe some of these obsolete procedures in the same detail as used to describe the current 

methods in the laboratory. Also included in this section are examples of earlier versions of the 

Soil Survey Laboratory data sheet (Fig.1) and pedon description (Fig. 2). Figure 1 and 2 are 

located at the back of this section on obsolete methods. 

Since the publication of the SSIR No. 42 (1996), there has been a significant increase in 

the number and kinds of methods performed at the SSL, resulting in a re-structuring of the 

method codes. All the methods described in this section of the manual carry the the old method 

codes. These old method codes have a maximum of four characters, e.g., 6A2b. These older 

codes are cross-referenced in a table preceding the descriptions of the obsolete SSL methods. 

This linkage between the method code systems is important to maintain as many older SSL 

data sheets and scientific publications report these older codes. While there may be slight 

differences between these cross-referenced methods, the intent here is to provide an historical 

linkage for the core SSL methods. 

This section of the manual is divided into three parts as follows: 

Part I, SSIR No. 42, Soil Survey Laboratory Methods Manual, Version 3.0 (1996) 

Part II, SSIR No. 42, Soil Survey Laboratory Methods Manual, Versions 1.0 and 2.0 (1989, 

1992, respectively) 

Part III: SSIR No. 1, Procedures for Collecting Soil samples and Methods of Analysis for Soil 

Survey (1972, 1982, 1984) 

445
METHODS OF ANALYSIS FOR SOILS, WATER, 

AND BIOLOGICAL MATERIALS 

CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS 

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

SAMPLE COLLECTION AND PREPARATION 1 1 

Field Sample Collection and Preparation 1A 1A 

Site Selection 1A1 1A1 

Geomorphic 1A1a 

Pedon 1A1b 1A2 

Water 1A1c 

Biological 1A1d 

Laboratory Sample Collection and Preparation 1B 

Soils 1B1 

Samples 1B1a 

Bulk 1B1a1 

Natural Fabrics 1B1a2 

Clods 1B1a3 

Cores 1B1a4 

Preparation 1B1b 1B 

Field-Moist Preparation 1B1b1 1B2 

Whole Soil 1B1b1a 

Histosol Analysis 1B1b1a1 1B7 

Biological Analysis 1B1b1a2 

<2-mm Fraction 1B1b1b 

Chemical and Selected Physical Analysis 1B1b1b1 

1500-kPa Water Content 1B1b1b2 

Field-Field-Moist/Air-dry Ratio 1B1b1b3 

<2-mm Fraction Sieved to < 0.425 mm 1B1b1c 

Atterberg Limits 1B1b1c1 

Air-Dry Preparation 1B1b2 1B1 

Whole Soil 1B1b2a 

Aggregate Stability 1B1b2a1 

Repository Samples 1B1b2a2 

<2-mm Fraction 1B1b2b 

Standard Chemical, Physical, Mineralogical Analysis 1B1b2b1 

Salt Analysis 1B1b2b2 

1500-kPa Water Content 1B1b2b3 

Air-Dry/Oven-Dry Ratio 1B1b2b4 

Presence of Carbonates 1B1b2b5 

<2-mm Fraction Sieved to <0.425 mm 1B1b2c 

Atterberg Limits 1B1b2c1 

<2-mm Fraction Processed to ≈ 180 μm 1B1b2d

446
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

Total Carbon, Nitrogen, and Sulfur 1B1b2d1 

Carbonates and/or Gypsum 1B1b2d2 

Chemical Analysis of Organic Materials 1B1b2d3 

<2-mm Fraction Sieved to 75 μm 1B1b2e 

Major and/or Trace Elements 1B1b2e1 

Particles >2 mm 1B1b2f 

Particle-Size Analysis 1B1b2f1 

Particle-Size Analysis, Recorded 1B1b2f1a 1B1 

2- to 20-mm Fraction Processed to <2-mm 1B1b2f1a1 1B5 

Chemical, Physical, and Mineralogical Analysis 1B1b2f1a1a 

2- to 20-mm Fraction Processed to <2-mm and Recombined 1B1b2f1a2 

 with <2-mm Fraction 

Chemical, Physical, and Mineralogical Analysis 1B1b2f1a2a 

Proportion and Particle-Size of Air-Dry Rock Fragments that 1B1b2f1a3 

 Resist Abrupt Immersion in Tap Water 

Particle-Size Analysis, Not Recorded 1B1b2f1b 

Whole-Soil Processed to <2-mm 1B1b2f1b1 1B6 

Chemical, Physical, and Mineralogical Analysis 1B1b2f1b1a 

Water 1B2 

Samples 1B2a 

Preparation 1B2b 

Biological Materials 1B3 

Samples 1B3a 

Biology Bulk Sample 1B3a1 

Microbial Biomass Sample 1B3a2 

Preparation 1B3b 

Field-Moist Preparation 1B3b1 

<2-mm Fractin 1B3b1a 

Microbial Biomass 1B3b1a1 

Air-Dry Preparation 1B3b2 

<2-mm Fraction Sieved <53 μm, with <53 μm (C-Mineral) and 1B3b2a 

> 53 μm (Particulate Organic Matter) Processed to ≈ 180 μm 

Total Carbon, Nitrogen, and Sulfur Analysis 1B3b2a1 

<2-mm Fraction 1B3b2b 

Other Biological Analyses 1B3b2b1 

Dry (50 ̊C) Preparation 1B3b3 

Roots 1B3b3a 

Root Biomass 1B3B3a1 

Roots Processed to ≈ 180 μm 1B3b3a1a 

Total Carbon, Nitrogen, and Sulfur Analysis 1B3b3a1a1 

Plants 1B3b3b 

Plant Biomass 1B3b3b1 

Plants Processed to ≈ 180 μm 1B3b3b1a 

Total Carbon, Nitrogen, and Sulfur Analysis 1B3b3b1a1 

447
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

CONVENTIONS 2 2 

Methods and Codes 2A 

Data Types 2B 

Particle-Size Fraction Base for Reporting Data 2C 2A 

Particles <2 mm 2C1 2A1 

Particles >2 mm 2C2 2A2 

Sample Weight Base for Reporting Data 2D 

Air-Dry/Oven-Dry 2D1 

Field-Field-Moist/Oven-Dry 2D2 

Correction for Crystal Water 2D3 

Significant Figures and Rounding 2E 

Data Sheet Symbols 2F 2B 

SOIL PHYSICAL AND FABRIC-RELATED 3 3 

ANALYSES 

Particle-Size Distribution Analysis 3A 3A 

Particles <2 mm 3A1 3A1 

Pipet Analysis for routinely reported size fractions 3A1a 3A1, 3A1b, 3A1d 

(1, 0.5, 0.25, 0.1, 0.047 mm, <20 μm, and <2 μm), with or 3A2, 3A2b, 3A2d 

 without <0.2-μm fraction, with or without <2-μm carbonate clay 

Pipet Analysis with Standard Pretreatments and Dispersion 3A1a1 

Air-Dry 3A1a1a 

Field-Moist 3A1a1b 

Pipet Analysis with Carbonate Removal 3A1a2 

Air-Dry 3A1a2a 3A1e 

Field-Moist 3A1a2b 3A2e 

Pipet Analysis with Iron Removal 3A1a3 

Air-Dry 3A1a3a 3A1f 

Field-Moist 3A1a3b 3A2f 

Pipet Analysis with Silica Removal 3A1a4 

Air-Dry 3A1a4a 3A1g 

Field-Moist 3A1a4b 3A2g 

Pipet Analysis with Ultrasonic Dispersion 3A1a5 

Air-Dry 3A1a5a 3A1h 

Field-Moist 3A1a5b 3A2h

448
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE

Pipet Analysis with Water Dispersion 3A1a6 

Air-Dry 3A1a6a 3A1c 

Field-Moist 3A1a6b 3A2c 

Particles > 2mm 3A2 3B 

Weight Estimates 3A2a 3B1 

By Field and Laboratory Weighing 3A2a1 3B1a 

From Volume and Weight Estimates 3A2a2 3B1b 

Volume Estimates 3A2b 3B2 

 Bulk Density 3B 4A 

Saran-Coated Natural Clods 3B1 4A1 

Field State 3B1a 4A1a 

33 kPa 3B1b 4A1d 

Oven-dry 3B1c 4A1h 

Rewet 3B1d 4A1i 

Reconstituted 3B2 

33 kPa 3B2a 

Oven-Dry 3B2b 

Compliant Cavity 3B3 4A 

Field State 3B3a 4A5 

Ring Excavation 3B4 

Field State 3B4a 

Frame Excavation 3B5 

Field State 3B5a 

Soil Cores 3B6 4A3

Field State 3B6a 4A3a 

Water Retention 3C 4B 

Pressure-Plate Extraction 3C1 4B1 

6 10, 33, 100, or 200 kPa Water Retention 3C1a-e 

<2 mm Sieved, Air-Dry 3C1a-e1a 4B1a 

Natural Clods 3C1a-d2 4B1c 

Soil Cores 3C1a-d3 4B1d 

Rewet 3C1c4 4B1e 

Reconstituted 3C1c5 

Pressure-Membrane Extraction 3C2 4B2 

1500 kPa Water Retention 3C2a 

<2 mm Sieved, Air-Dry 3C2a1a 4B2a 

<2 mm Sieved, Field-Moist 3C2a1b 4B2b

449
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE

Water Retention at Field State 3C3 4B4 

Ratios and Estimates Related to Particle Size 3D 

Analysis, Bulk Density, and Water Retention 

Air-Dry/Oven-Dry Ratio 3D1 4B5 

Field-Moist/Oven-Dry Ratio 3D2 

Correction for Crystal Water 3D3 6S3 

Coefficient of Linear Extensibility 3D4 4D 

Air-Dry or Oven-Dry to 33-kPa Tension 3D4a 4D1 

Water Retention Difference, Whole Soil 3D5 4C 

Between 33-kPa and 1500-kPa Tension 3D5a 4C1 

Between 10-kPa and 1500-kPa Tension 3D5b 4C2 

Between 33-kPa and 1500-kPa (Air-Dry) Tension 3D5c 4C3 

1500 kPa Water/Clay Ratio 3D6 8D1 

Total Silt Fraction 3D7 

Total Sand Fraction 3D8 

2- to 5-mm Fraction 3D9 

5- to 20-mm Fraction 3D10 

20- to 75-mm Fraction 3D11 

0.1- to 75-mm Fraction 3D12 

>2-mm Fraction 3D13 

 

Micromorphology 3E 4E 

Thin sections 3E1 4E1 

Preparation 3E1a 4E1a 

Interpretation 3E1b 4E1b 

Wet Aggregate Stability 3F 4G 

Wet Sieving 3F1 

Air-dry 3F1a 

2 to 1 mm 3F1a1 

2- to 0.5-mm Aggregates Retained 3F1a1a 4G1

Particle Density 3G 

Pycnometer Gas Displacement 3G1 

Oven-dry 3G1a 

<2 mm 3G1a1 

>2 mm 3G1a2 

 

Atterberg Limits 3H 4F 

Liquid Limit 3H1 4F1 

Air-Dry, <0.4 mm 3H1a1 

Field-Moist, <0.4 mm 3H1b1 

Plasticity Index 3H2 4F2 

Air-Dry, <0.4 mm 3H2a1 

Field-Moist, <0.4 mm 3H2b1 

450
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

SOIL AND WATER CHEMICAL EXTRACTIONS 4 

AND ANALYSES 

Acid Standardization 4A Ion Exchange and Extractable Cations 4B 5A 

Displacement after Washing 4B1 

NH4OAc, pH 7 4B1a 

Automatic Extractor 4B1a1 

2 M KCl Rinse 4B1a1a 

Steam Distillation 4B1a1a1 

HCl Titration 4B1a1a1a 

Cation Exchange Capacity (CEC-7) 4B1a1a1a1 5A8c 

Air-Dry, <2 mm 4B1a1a1a1a1 

Field-Moist, <2 mm 4B1a1a1a1b1 

Atomic Absorption Spectrophotometer 4B1a1b 

Calcium, Magnesium, Potassium, and Sodium 4B1a1b1-4 6N2e, 6O2d, 

 6Q2b, 6P2b 

Air-Dry, <2 mm 4B1a1b1-4a1 

Field-Moist, <2 mm 4B1a1b1-4b1 

 

NH4Cl, Neutral Unbuffered 4B1b 

Automatic Extractor 4B1b1 

2M KCl Rinse 4B1b1a 

Steam Distillation 4B1b1a1 

HCl Titration 4B1b1a1a 

Cation Exchange Capacity 4B1b1a1a1 5A9c 

Air-Dry, <2 mm 4B1b1a1a1a1 

Field-Moist, <2 mm 4B1b1a1a1b1 

Atomic Absorption Spectrophotometer 4B1a1b 

Calcium, Magnesium, Potassium, and Sodium 4B1b1b1-4 

Air-Dry, <2 mm 4B1b1b1-4a1 

Field-Moist, <2 mm 4B1b1b1-4b1 

 

BaCl2-Triethanolamine, pH 8.2 Extraction 4B2 

Automatic Extractor 4B2a 

Automatic Titrator 4B2a1 

Back Titration with HCl 4B2a1a 

Extractable Acidity 4B2a1a1 6H5a 

Air-Dry, <2 mm 4B2a1a1a1 

Field-Moist, <2 mm 4B2a1a1b1

451
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

Centrifuge 4B2b 

Automatic Titrator 4B2b1 

Back Titration with HCl 4B2b1a 

Extractable Acidity 4B2b1a1 

Air-Dry, <2 mm 4B2b1a1a1 

Field-Moist, <2 mm 4B2b1a1b1 

1 N KCl Extraction 4B3 

Automatic Extractor 4B3a 

Inductively Coupled Plasma Spectrophotometer 4B3a1 

Radial Mode 4B3a1a 

Al, Mn 4B3a1a1-2 6G9c, 6D3b 

Air-Dry, <2 mm 4B3a1a1-2a1 

Field-Moist, <2 mm 4B3a1a1-2b1 

Ratios and Estimates Related to Ion Exchange and 4B4 

Extractable Cations 

Sum of Extractable Bases 4B4a 

Sum of Extractable Bases by NH4OAc, pH 7 4B4a1 5B5a 

Sum of Extractable Bases by NH4OAc, pH 7, Calculated 4B4a1a 

Sum of Extractable Bases by NH4Cl 4B4a2 

Sum of Extractable Bases by NH4Cl, Calculated 4B4a2a 

Cation Exchange Capacity (CEC) 4B4b 

CEC-8.2 (Sum of Cations) 4B4b1 5A3a 

CEC-8.2, Calculated 4B4b1a 

CEC-8.2, Not Calculated 4B4b1b 

Effective Cation Exchange Capacity (ECEC) 4B4b2 

Sum of NH4OAc Extractable Bases + 1 N KCl Extractable 4B4b2a 5A3b 

Aluminum, Calculated 

 Sum of NH4OAc Extractable Bases + 1 N KCl Extractable 4B4b2b 

Aluminum, Not Calculated 

Base Saturation 4B4c 

Base Saturation by NH4OAc, pH 7 (CEC-7) 4B4c1 5C1 

Base Saturation by CEC-7, Calculated 4B4c1a 

Base Saturation by CEC-7, Set to 100% 4B4c1b

Base Saturation by NH4Cl 4B4c2 

Base Saturation by NH4Cl, Calculated 4B4c2a 

Base Saturation by NH4Cl, Set to 100% 4B4c2b 

Base Saturation by CEC-8.2 4B4c3 5C3 

Base Saturation by CEC-8.2, Calculated 4B4c3a 

Base Saturation by CEC-8.2, Not Calculated 4B4c3b 

Base Saturation by ECEC 4B4c4 

Base Saturation by Sum of NH4OAc Extractable Bases 4B4c4a 

+ 1 N KCl Extractable Aluminum, Calculated 

Base Saturation by Sum of NH4OAc Extractable Bases 4B4c4b 

+ 1 N KCl Extractable Aluminum, Not Calculated 

452
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

Aluminum Saturation 4B4d 

Aluminum Saturation by ECEC 4B4d1 

Aluminum Saturation by Sum of NH4OAc Extractable Bases 4B4d1a 

+ 1 N KCl Extractable Aluminum, Calculated 

 Aluminum Saturation by Sum of NH4OAc Extractable Bases 4B4d1b 

+ 1 N KCl Extractable Aluminum, Not Calculated 

Activity 4B4e 

1500 kPa water/CEC-7 4B4e1 8D1 

Reaction 4C 

Soil Suspensions 4C1 

Electrode 4C1a 

Standard Glass Body Combination 4C1a1 

Digital pH/Ion Meter 4C1a1a 

1 N NaF, pH 7.5 – 7.8 4C1a1a1 8C1d 

Air-Dry, <2 mm 4C1a1a1a1 

Field-Moist, <2 mm 4C1a1a1b1 

Saturated Paste pH 4C1a1a2 8C1b 

Air-Dry, <2 mm 4C1a1a2a1 

Oxidized pH 4C1a1a3 8C1h 

Organic Materials pH, Final Solution ≈ 0.01 M CaCl2 pH 4C1a1a4 8C2a 

Combination pH-reference electrode 4C1a2 

Automatic Titrator 4C1a2a 

1:1 water pH 4C1a2a1 8C1f 

Air-Dry, <2 mm 4C1a2a1a1 

Field-Moist, <2 mm 4C1a2a1b1 

1:2 0.01 M CaCl2 pH 4C1a2a2 8C1f 

Air-Dry, <2 mm 4C1a2a2a1 

Field-Moist, <2 mm 4C1a2a2b1 

1 M KCl pH 4C1a2a3 8C1g 

Air-Dry, <2 mm 4C1a2a3a1 

Field-Moist, <2 mm 4C1a2a3b1 

Soil Test Analyses 4D 

Anion Resin Extraction 4D1 

Two-Point Extraction 4D1a 

1 h, 24h, 1 M KCl 4D1a1a1 

UV-Visible Spectrophotometer, Dual-Beam 4D1a1a1a 

Phosphorus (2 points) 4D1a1a1a1-2 

Air-Dry, <2 mm 4D1a1a1a1-2a-b1 

Field-Moist, <2 mm 4D1a1a1a1-2b1 

453
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

Aqueous Extraction 4D2 

Single-Point Extraction 4D2a 

1:10, 30 min 4D2a1 

UV-Visible Spectrophotometer, Dual Beam 4D2a1a 

Phosphorus 4D2a1a1 

Air-Dry, <2 mm 4D2a1a1a1 

Field-Moist, <2 mm 4D2a1a1b1 

Flow Injection, Automated Ion Analyzer 4D2a1b 

Phosphorus 4D2a1b1 6S7a 

Air-Dry, <2 mm 4D2a1b1a1 

Field-Moist, <2 mm 4D2a1b1b1 

Bray P-1 Extraction 4D3 

UV-Visible Spectrophotometer, Dual Beam 4D3a 

Phosphorus 4D3a1 6S3 

Air-Dry, <2 mm 4D3a1a1 

Field-Moist, <2 mm 4D3a1b1 

Flow Injection, Automated Ion Analyzer 4D3b 

Phosphorus 4D3b1 6S3b 

Air-Dry, <2 mm 4D3b1a1 

Field-Moist, <2 mm 4D3b1b1 

Bray P-2 Extraction 4D4 

UV-Visible Spectrophotometer, Dual-Beam 4D4a 

Phosphorus 4D4a1 

Air-Dry, <2 mm 4D4a1a1 

Field-Moist, <2 mm 4D4a1b1 

Olsen Sodium-Bicarbonate Extraction 4D5 

UV-Visible Spectrophotometer, Dual Beam 4D5a 

Phosphorus 4D5a1 

Air-Dry, <2 mm 4D5a1a1 

Field-Moist, <2 mm 4D5a1b1 

Mehlich No. 3 Extraction 4D6 

UV-Visible Spectrophotometer, Dual Beam 4D6a 

Phosphorus 4D6a1 

Inductively Coupled Plasma Atomic Emission 4D6b 

Spectrophotometer 

Axial Mode 4D6b1 

Ultrasonic Nebulizer 4D6b1a 

Aluminum, Arsenic, Barium, Calcium, Cadmium, Cobalt, 4D6b1a1-18 

Chromium, Copper, Iron, Potassium, Magnesium, Manganese, 

Sodium, Nickel, Phosphorus, Lead, Selenium, and Zinc 

Air-Dry, <2 mm 4D6b1a1-18a1 

Field-Moist, <2 mm 4D6b1a1-18b1 

454
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

Citric Acid Soluble 4D7 

UV-Visible Spectrophotometer, Dual Beam 4D7a 

Phosphorus 4D7a1 6S5 

Air-Dry, <2 mm 4D7a1a1 

Field-Moist, < 2 mm 4D7a1b1 

New Zealand P Retention 4D8 

UV-Visible Spectrophotometer, Dual Beam 4D8a 

Phosphorus 4D8a1 6S4b 

Air-Dry, <2 mm 4D8a1a1 

Field-Moist, <2 mm 4D8a1b1 

1 M KCl Extraction 4D9 

Cadmium-Copper Reduction 4D9a 

Sulfanilamide N-1-Naphthylethylenediamine Dihydrochloride 4D9a1 

Flow-Injection, Automated Ion Analyzer 4D9a1a 

Nitrate-Nitrite 4D9a1a1-2 6M2a 

Air-Dry, <2 mm 4D9a1a1-2a1 

Field-Moist, <2 mm 4D9a1a1-2b1 

Field-Moist, <2 mm, Fumgiated and Non-fumigated 4D9a1a1-2b2-3 

Anaerobic Incubation 4D10 

2 M KCl Extraction 4D10a 

Ammonia – Salicylate 4D10a1 

Flow Injection, Automated Ion Analyzer 4D10a1a 

N as NH3 – Mineralizable N 4D10a1a1 6B5a 

Air-Dry, <2 mm 4D10a1a1a1 

Field-Moist, <2 mm 4D10a1a1b1 

Carbonate and Gypsum 4E 

3 N HCl Treatment 4E1 

CO2 Analysis 4E1a 

Manometer, Electronic 4E1a1 

Carbonates 4E1a1a 

Calcium Carbonate 4E1a1a1 

Air-Dry, <2 mm 4E1a1a1a1 6E1g 

Air-Dry, 2 to 20 mm 4E1a1a1a2 6E4 

Aqueous Extraction 4E2a 

Conductivity Bridge 4E2a1 

Electrical Conductivity 4E2a1a 

Gypsum, qualitative and quantitative 4E2a1a 6F1a 

Air-Dry, <2 mm 4E2a1a1a1 

Air-Dry, 2 to 20 mm 4E2a1a1a2 

455
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

Electrical Conductivity and Soluble Salts 4F 

Aqueous Extraction 4F1 

1:2 Aqueous Extraction 4F1a 

Conductivity Bridge 4F1a1 

Electrical Conductivity 4F1a1a 

Salt Prediction 4F1a1a1 8I 

Air-Dry, <2 mm 4F1a1a1a1 

Saturated Paste 4F2 8A 

Gravimetric 4F2a 

Water Percentage 4F2a1 8A 

Air-Dry, <2 mm 4F2a1a1 

Conductivity Bridge 4F2b 

Electrical Conductivity 4F2b1 8A3a 

Air-Dry, <2 mm 4F2b1a1 

Resistivity 4F2b2 8E1 

Air-Dry, <2 mm 4F2b2a1 

Saturated Paste Extraction 4F2c 8A3 

Automatic Extractor 4F2c1 

Atomic Absorption Spectrophotometer 4F2c1a 

Calcium, Magnesium, Potassium, and Sodium 4F2c1a1-4 6N1b, 6O1b, 

6Q1b, 6P1b 

Air-Dry, <2 mm 4F2c1a1-4a1 

Ion Chromatograph 4F2c1b 

Conductivity Detector 4F2c1b1 

Self-Regeneration Suppressor, 4F2c1b1a 

*Bromide, Acetate, Chloride, Fluoride, Nitrate, Nitrite, 4F2c1b1a1-8 6K1d, 6U1b, 

Phosphate, and Sulfate 6M1d, 6W1d, 

6L1d 

Air-Dry, <2 mm 4F2c1b1a1-8a1 

Automatic Titrator 4F2c1c 

Combination pH-Reference Electrode 4F2c1c1 

Acid Titration, H2SO4 4F2c1c1a 

Carbonate and Bicarbonate 4F2c1c1a1-2 6I1b, 6J1b 

Air-Dry, <2 mm 4F2c1c1a1-2a1 

Ratios and Estimates Related to Soluble Salts 4F3 

Exchangeable Sodium Percentage (ESP) 4F3a 

ESP, Calculated without Saturated Paste Extraction 4F3a1 5D2 

ESP, Calculated with Saturated Paste Extraction 4F3a2 5D2 

Sodium Adsorption Ratio (SAR) 4F3b 5E 

Estimated Total Salt 4F3c 8D5 

* Bromide, Acetate, and Phosphate – No previous obsolete method as cited in the SSIR No. 42 

(1996). 

456
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

Selective Dissolutions 4G

Dithionite-Citrate Extraction 4G1 

Atomic Absorption Spectrophotometer 4G1a 

Aluminum, Iron, and Manganese 4G1a1-3 6G7a, 6C2b, 

6D2a 

Air-Dry, <2 mm 4G1a1-3a1 

Field-Moist, <2 mm 4G1a1-3b1 

Ammonium Oxalate Extraction 4G2 

Automatic Extractor 4G2a 

Inductively Coupled Plasma Atomic Emission 4G2a1 

Spectrophotometer 

Radial Mode 4G2a1a 

Aluminum, Iron, Manganese, *Phosphorus, and Silicon 4G2a1a1-5 6G12b, 6C9b, 

6D5b, 6V2b 

Air-Dry, <2 mm 4G2a1a1-5a1 

Field-Moist, <2 mm 4G2a1a1-5b1 

UV-Visible Spectrophotometer, Dual Beam 4G2a2 

Transmittance 4G2a2a 

Optical Density 4G2a2a1 8J 

Air-Dry, <2 mm 4G2a2a1a1 

Field-Moist, <2 mm 4G2a2a1b1 

Ratios and Estimates Related to Ammonium Oxalate Extraction 4G2b 

Al + 1⁄2 Fe 4G2b1 

Sodium Pyrophosphate Extraction 4G3 

Atomic Absorption Spectrophotometer 4G3a 

Aluminum, Iron, and Manganese 4G3a1-3 6G10a, 6C8a, 

6D4a 

Air-Dry, <2 mm 4G3a1-3a1 

Field-Moist, <2 mm 4G3a1-3b1 

Acid Digestion 4G3b 

K2Cr2O7 + (H2SO4 + H3PO4 Digestion) 4G3b1 

Nesbitt Bulb 4G3b1 

CO2 Evolution, Gravimetric 4G3b1a 

Organic Carbon 4G3b1a1 6A4a 

Air-Dry, <2 mm 4G3b1a1a1 

Field-Moist, <2 mm 4G3b1a1b1 

*Phosphate – No previous obsolete method as cited in the SSIR No. 42 (1996). 

457
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

Total Analysis 4H 

Acid Digestion 4H1 

HNO3 + HCl Digestion 4H1a 

Microwave 4H1a1 

Inductively Coupled Plasma Atomic Emission 4H1a1a 

Spectrophotometer 

Axial Mode 4H1a1a1 

Ultrasonic Nebulizer 4H1a1a1a 

Silver, Arsenic, Barium, Beryllium, Cadmium, Cobalt, 4H1a1a1a1-20 

Chromium, Copper, Manganese, Molybdenum, Nickel, 

Phosphorus, Lead, Antimony, Tin, Strontium, Thallium, 

Vanadium, Tungsten, Zinc 

Air-Dry, <2 mm 4H1a1a1-20a1 

HCl Digestion 4H1a1b 

Water Bath 4H1a1b1 

Flow through Hydride-Generation and Atomic 4H1a1b1 

Absorption Spectrophotometer 

Arsenic and Selenium 4H1a1b1a1-2 

Air-Dry, <2 mm 4H1a1b1a1-2a1 

Cold Vapor Atomic Absorption Spectrophotometer 4H1a1c 

Mercury 4H1a1c1 

Air-Dry, <2 mm 4H1a1c1a1 

HF + HNO3 + HCl Digestion 4H1b 7C4a 

Microwave 4H1b1 

Boric Acid 4H1b1a 

Inductively Coupled Plasma Atomic Emission 4H1b1a1 

Spectrophotometer 

Radial Mode 4H1b1a1a 

Aluminum, Calcium, Iron, Potassium, Magnesium, Manganese, 4H1b1a1a1-11 6G11b, 6N5b, 

Sodium, Phosphorus, Silicon, Zirconium, Titanium 6C7b, 6Q3b, 

6O5b, 6D6a, 

6P3b, 6S6a, 

6V1b, 8K1a, 

8O1a 

Air-Dry, <2 mm 4H1b1a1a1-11a1 

Oven-Dry, <2 μm 4H1b1a1a1-11b2 

458
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

Dry Combustion 4H2 

Thermal Conductivity Detector 4H2a 

Carbon, Nitrogen, and Sulfur 4H2a1-3 

Air-Dry, <2 mm 4H2a1-3a1 

 

Ground and Surface Water Analyses 4I 

Reaction 4I1 

Electrode 4I1a 

Standard Glass Body Combination 4I1a1 

Digital pH/Ion Meter 4I1a1a 

pH 4I1a1a1 

Electrical Conductivity and Salts 4I2 

Conductivity Bridge and Cup 4I2a 

Electrical Conductivity 4I2a1 

Atomic Absorption Spectrophotometer 4I2b 

Calcium, Magnesium, Potassium, and Sodium 4I2b1-4 

Ion Chromatograph 4I2c 

Conductivity Detector 4I2c1 

Self-Regeneration Suppressor 4I2c1a 

Bromide, Acetate, Chloride, Fluoride, Nitrate, Nitrite, 4I2c1a1-8 

Phosphate, and Sulfate 

Automatic Titrator 4I2d 

Combination pH-reference Electrode 4I2d1 

Acid Titration, H2SO4 4I2d1a 

Carbonate and Bicarbonate 4I2d1a1-2 

Total Analysis 4I3 

Inductively Coupled Plasma Atomic Emission 4I3a 

Spectrophotometer 

Radial Mode 4I3a1 

Ultrasonic Nebulizer 4I3a1a 

Aluminum, Iron, Manganese, Phosphorus, and Silicon 4I3a1a1-5

ANALYSIS OF ORGANIC SOILS OR MATERIALS 5 

Mineral Content 5A 8F1 

Pyrophosphate Color 5B 8H 

Fiber Volume 5C 8G1 

459
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

Melanic Index 5D 

Ratios and Estimates Related to Organic Matter 5E

SOIL BIOLOGICAL AND PLANT ANALYSES 6 

Soil Analyses 6A 

0.5 M K2SO4 Extraction + Heating with Disodium 6A1 

Bicinchoninic Reagent 

UV-Visible Spectrophotometer, Dual Beam 6A1a 

Hot Water Extractable Organic Carbon 6A1a1 

Air-Dry, <2 mm 6A1a1a1 

0.02 M KMnO4 Extraction 6A2 

UV-Visible Spectrophotometer, Dual Beam 6A2a 

Active Carbon 6A2a1 

Air-Dry, <2 mm 6A2a1a1

Acid Dissolution 6A3 

1 N HCl Dissolution + FeCl2 6A3a 

Gas Chromatography 6A3a1 

CO2 Analysis 6A3a1a 

Carbonates 6A3a1a1 

Air-Dry, <2 mm 6A3a1a1a1

Particulate Organic Matter and Carbon-Mineral 6A4 

Total Analysis 6A4a 

Dry Combustion 6A4a1 

Thermal Conductivity Detector 6A4a1a 

Carbon, Nitrogen, and Sulfur 6A4a1a1-3 

Air-Dry, >53 μm (POM) 6A4a1a1-3a1 

Air-Dry, <53 μm (C-Min) 6A4a1a1-3a2 

Fumigation Incubation 6B 

Gas Chromatography 6B1 

CO2 Analysis 6B1a 

Soil Microbial Biomass 6B1a1 

Field-Moist, Whole-Soil 6B1a1a1 

460
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

2 M KCl Extraction 6B2 

Automatic Extractor 6B2a 

Ammonia – Salicylate 6B2a1 

Flow Injection, Automated Ion Analyzer 6B2a1a 

N as NH3 – Mineralizable N 6B2a1a1 

Field-Moist, Whole-Soil Fumigated, Whole-Soil 6B2a1a1a1-2 

 Non-Fumigated 

 

Plant Analyses 6C 

Root Biomass 6C1 

Plant (above-ground) Biomass 6C2 

Plant Nutrition 6C3 

Total Analysis 6C3a 

Dry Combustion 6C3a1 

Thermal Conductivity Detector 6C3a1a 

Carbon, Nitrogen, and Sulfur 6C3a1a1-3 

Dry (50 ̊C), Roots 6C3a1a1-3a1 

Dry (50 ̊C), Plants (above-ground) 6C3a1a1-3a2

Ratios and Estimates Related to Biological Analyses 6E 

MINERALOGY 7 

Instrumental Analyses 7A 7A 

X-Ray Diffraction 7A1 

Thin Film on Glass, Resin Pretreatment II 7A1a 

Mg Room Temperature, Mg Glycerol Solvated, K 300°C, 7A1a1 7A2i 

K 500°C 

 

Thermogravimetric Analysis 7A2 7A4 

Thermal Analyzer 7A2a 7A4c 

Differential Scanning Colorimetry 7A3 7A6 

Thermal Analyzer 7A3a 7A6b 

Differential Thermal Analysis 7A4 7A3 

Thermal Analyzer 7A4a 7A3c 

Surface Area 7A5 

N2 Adsorption 7A5a 

Brunauer, Emmett and Teller Theory 7A5a1 

Vacuum Degassing 7A5a1a 

Multi-Point 7A5a1a1 

Air-Dry, <2 mm 7A5a1a1a1 

Single Point 7A5a1a2 

Air-Dry, <2 mm 7A4a1a2a1 

461
CROSS-REFERENCE BETWEEN CURRENT AND OBSOLETE METHODS

METHOD TITLE CURRENT OBSOLETE 

METHOD METHOD 

CODE CODE 

Optical Analyses 7B 7B 

Grain Studies 7B1 7B1 

Analysis and Interpretation 7B1a 7B1 

Separation by Heavy Liquids 7B1a1 7B1 

Grain Mounts, Epoxy 7B1a2 7B1a 

Platy Grains 7B2 

Magnetic Separation 7B2a 

Static Tube Separation 7B2b 

Froth Flotation 

 7B2c 

Ratios and Estimates Related to Optical Analysis 7C 

Total Resistant Minerals 7C1 

462
PART I: 

SSIR NO. 42, SOIL SURVEY LABORATORY METHODS 

MANUAL, VERSION 3.0 (1996) 

ION ANALYSES (5) 

Cation Exchange Capacity (5A) 

NH4OAc, pH 7.0 (5A8) Automatic Extractor (CEC-7) 

Steam Distillation 

Kjeltec Auto 1035 Analyzer (5A8c)

1. Application

The CEC determined with 1 N NH4OAc buffered at pH 7.0, is a commonly used 

method and has become a standard reference to which other methods are compared (Peech et 

al., 1947). The advantages of using this method are that the extractant is highly buffered so that 

the extraction is performed at a constant, known pH (7.0) and that the NH4+ on the exchange 

complex is easily determined. 

2. Summary of Method 

Displacement after washing is the basis for this procedure. The CEC is determined by 

saturating the exchange sites with an index cation (NH4+); washing the soil free of excess 

saturated salt; displacing the index cation (NH4+) adsorbed by the soil; and measuring the 

amount of the index cation (NH4+). A sample is leached using 1 N NH4OAc and a mechanical 

vacuum extractor (Holmgren et al., 1977). The extract is weighed and saved for analyses of the 

cations. The NH4

+

 saturated soil is rinsed with ethanol to remove the NH4

+

 that was not 

adsorbed. Steam distillation and titration are used to determine the NH4

+

 adsorbed on the soil 

exchange complex. The CEC by NH4OAc, pH 7 is reported in meq 100 g-1 oven-dry soil in 

procedure 5A8c. 

3. Interferenes 

Incomplete saturation of the soil with NH4

+

 and insufficient removal of NH4

+

 are the 

greatest interferences to this method. Ethanol removes some adsorbed NH4

+

 from the exchange 

sites of some soils. Isopropanol rinses has been used for some soils in which ethanol removes 

adsorbed NH4

+

. Soils that contain large amounts of vermiculite can irreversibly "fix" NH4

+

. 

Soils that contain large amounts of soluble carbonates can change the extractant pH and/or can 

contribute to erroneously high cation levels in the extract. 

4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

and bases. Dispense concentrated acids and bases in a fume hood. Thoroughly wash hands 

after handling reagents. Use the safety showers and eyewash stations to dilute spilled acids and 

bases. Use sodium bicarbonate and water to neutralize and dilute spilled acids. Nessler's 

reagent contains mercury which is toxic. Proper disposal of the Nessler's reagent and clean-up 

of equipment in contact with the reagent is necessary. 

463
Ethanol is flammable. Avoid open flames and sparks. Standard laboratory equipment 

includes fire blankets and extinguishers for use when necessary. Follow the manufacturer's 

safety precautions when using the vacuum extractor and the Kjeltec Auto 1035 Analyzer. 

5. Equipment 

5.1 Mechanical vacuum extractor, 24 place, Centurion International, Inc., Lincoln, NE 

5.2 Mechanical vacuum extractor, Mavco Sampletex, 5300 N. 57th St., Lincoln, NE 

5.3 Syringes, polypropylene, disposable, 60 mL, for extraction vessel, extractant reservoir 

and tared extraction syringe 

5.4 Rubber tubing, 3.2 ID x 6.4 OD x 25.4 mm (1/8 ID x 1/4 OD x 1 in) for connecting 

syringe barrels. 

5.5 Polycons, Richards Mfg. Co. 

5.6 Kjeltec Auto 1035/1038 Sampler System, Tecator, Perstorp Analytical Inc. 

5.7 Digestion tubes, straight neck, 250 mL 

5.8 Analytical filter pulp, ash-free, Schleicher and Schuell, No. 289 

5.9 Plunger, modified. Remove rubber and cut plastic protrusion from plunger end. 

5.10 Electronic balance, ±1-mg sensitivity 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Ammonium acetate solution (NH4OAc), 1 N, pH 7.0. Add 1026 mL of glacial acetic acid 

(CH3COOH) to 15 L DDI water. Add 1224 mL of concentrated ammonium hydroxide 

(NH4OH). Mix and cool. Dilute with DDI water to 18 L and adjust to pH 7.0 with 

CH3COOH or NH4OH. 

6.3 Ethanol (CH3CH2OH), 95%, U.S.P. 

6.4 Nessler's reagent. Add 4.56 g of potassium iodide (KI) to 30 mL DDI water. Add 5.68 g 

of mercuric iodide (HgI2). Stir until dissolved. Dissolve 10 g of sodium hydroxide 

(NaOH) in 200 mL of DDI water. Transfer NaOH solution to a 250-mL volumetric flask 

and slowly add K-Hg-I solution. Dilute to volume with DDI water and thoroughly mix. 

Solution should not contain a precipitate. Solution can be used immediately. Store in 

brown bottle to protect from light. 

6.5 Sodium chloride (NaCl), reagent, crystal. 

6.6 Antifoam agent, slipicone release spray, Dow Chemical Corp. Alternatively, use n-octyl 

alcohol. 

6.7 Boric acid, 4% (w:v), with bromcresol green-methyl red indicator (0.075 % bromcresol 

green and 0.05% methyl red), Chempure Brand 

6.8 Hydrochloric acid (HCl), 0.05 N, standardized. Dilute 83 mL of concentrated HCl in 20 L 

of DDI water. 

6.9 NaOH, 1 M. Add 500 mL of 50% NaOH solution to 8 L of DDI water. Dilute to 9 L 

with DDI water. 

7. Procedure 

Extraction of Bases 

7.1 Prepare extraction vessel by tightly compressing a 1-g ball of filter pulp into the bottom of 

a syringe barrel with a modified plunger. 

7.2 Weigh 2.50 g of <2-mm, air-dry soil and place in an extraction vessel. Weigh a smaller 

amount of sample, if the soil is highly organic. Prepare one quality control check sample per 

48 samples. 

7.3 Place extraction vessel on upper disk of the extractor and connect a tared extraction syringe. 

Use a 25.4-mm (1 in) length rubber tubing and insert the plunger in the slot of the stationary 

disk of the extractor. 

464
7.4 Use a squeeze bottle to fill extraction vessel to the 20-mL mark with NH4OAc solution (≈

10 mL). Thoroughly wet the sample. Let stand for at least 20 min. 

7.5 Put reservoir tube on top of the extraction vessel. Rapidly extract the NH4OAc solution to a 

0.5- to 1.0-cm height above sample. Turn off extractor. Add ≈ 45 mL of NH4OAc solution to 

the reservoir tube. Set extractor for an overnight (12 to 16 h) extraction. 

7.6 Next morning turn off the extractor. Pull the plunger of the syringe down. Do not pull 

plunger from the barrel of the syringe. Carefully remove the syringe containing the extract. 

Leave the rubber tubing on the extraction vessel. Weigh each syringe containing the NH4OAc 

extract to the nearest 0.01 g. 

7.7 Mix the extract in each syringe by manually shaking. Fill a polycon with extract solution 

and discard the excess. The solution in the polycon is reserved for analyses of extracted cations 

(procedures 6N2, 6O2, 6P2, and 6Q2). 

Removal of Excess Ammonium Acetate 7.8 Return the extractor to starting position. Attach syringe to the extraction vessel and rinse 

the sides of the extraction vessel with ethanol from a wash bottle. Fill the extraction vessel to 

the 20-mL mark with ethanol and let stand for 15 to 20 min. 

7.9 Place reservoir tube on the extraction vessel. Rapidly extract the ethanol level to a 0.5- to 

1.0-cm height above the sample. Turn off the extractor and add 55 to 60 mL of ethanol to the 

reservoir. Extract at a 45-min rate. 

7.10 After the extractor has stopped, turn off the switch. Pull the plunger of the syringe down. 

Do not pull the plunger from the syringe barrel. Remove the syringe and discard the ethanol. 

7.11 Repeat the ethanol wash. 

7.12 After the second wash, collect a few drops of ethanol extract from the extraction vessel on 

a spot plate. Test for NH4

+

 by using Nessler's reagent. A yellow, red to reddish brown 

precipitate is a positive test. If the test is positive, repeat the ethanol wash and retest with 

Nessler's reagent. Repeat until a negative test is obtained. 

Steam Distillation: Samples and Reagent Blanks 

7.13 Remove the extraction vessel and transfer the sample to a 250-mL digestion tube. Add 6 

to 7 g of NaCl to the digestion tube. 

7.14 Perform the same transfer and addition of reagents for blanks as for samples. 

7.15 Spray silicone antifoam agent (or 2 drops of n-octyl alcohol solution) into the digestion 

tubes for each of the samples and reagent blanks. 

7.16 When using new reagents, e.g., boric acid, reagent blanks are distilled in 2 sets of 6, one 

set per Kjeltec machine. Each set of 6 is averaged and recorded on bench worksheet and 

manually set on each machine. During the steam distillation, the mean reagent blank titer is 

automatically subtracted from the sample titer. 

7.17 On bench worksheet, record the normality of standardized acid, i.e., ≈ 0.05 N HCl. 

465
7.18 Connect the tube to the distillation unit. Close the safety door. Distillation and titration 

are performed automatically. Record the titer in mL of titrant. 

8. Calculations 

CEC = [Titer x N x 100 x AD/OD]/[Sample Weight (g)] 

where: 

CEC = Cation Exchange Capacity (meq 100 g-1) 

Titer = Titer of sample (mL) 

N = Normality of HCl titrant 

100 = Conversion factor to 100-g basis 

AD/OD= Air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report CEC-7 in units of meq 100 g-1 of oven-dry soil to the nearest 0.1 meq 100 g-1. 

10. Precision 

Precision data are not available for this procedure. 

11. References 

Holmgren, G.G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically controlled 

variable rate leaching device. Soil Sci. Amer. J. 41:1207-1208. 

Peech, M., L.T. Alexander, L.A. Dean, and J.F. Reed. 1947. Methods of soil analysis for 

soil fertility investigations. U.S. Dept. Agr. Circ. 757, 25 pp. 

Cation Exchange Capacity (5A) 

NH4Cl (5A9) Automatic Extractor 

Steam Distillation (5A9c) 

Kjeltec Auto 1035 Analyzer (5A9c) 

1. Application 

The CEC determined with a neutral unbuffered salt, e.g., 1 N NH4Cl, is an estimate of 

the "effective" CEC (ECEC) of the soil (Peech et al., 1947). For a soil with a pH of <7.0, the 

ECEC value should be < CEC measured with a buffered solution at pH 7.0. The NH4Cl CEC is ≈ equal to the NH4OAc extractable bases plus the KCl extractable Al for noncalcareous soils. 

2. Summary of Method 

Displace 

ment after washing is the basis for this procedure. The CEC is determined by saturating 

the exchange sites with an index cation (NH4+

); washing the soil free of excess saturated salt; 

displacing the index cation (NH4+) adsorbed by the soil; and measuring the amount of the index 

cation (NH4+). A sample is leached using 1 N NH4Cl and a mechanical vacuum extractor 

(Holmgren et al., 1977). The extract is weighed and saved for analyses of the cations. The 

NH4

+

 saturated soil is rinsed with ethanol to remove the NH4

+

 that was not adsorbed. Steam 

distillation and titration are used to determine the NH4

+

 adsorbed on the soil exchange complex. 

The CEC by NH4Cl is reported in meq 100 g-1 oven-dry soil in procedure 5A9c. 

3. Interferences 

Incomplete saturation of the soil with NH4

+

 and insufficient removal of NH4

+

 are the 

greatest interferences to this method. Ethanol removes some adsorbed NH4

+

 from the exchange 

sites of some soils. Isopropanol rinses have been used for some soils in which ethanol removes 

adsorbed NH4

+

. Soils that contain large amounts of vermiculite can irreversibly "fix" NH4

+

. 

466
Soils that contain large amounts of soluble carbonates can change the extractant pH and/or can 

contribute to erroneously high cation levels in the extract. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

and bases. Dispense concentrated acids and bases in a fume hood. Nessler's reagent contains 

mercury which is toxic. Proper disposal of the Nessler's reagent and clean-up of equipment in 

contact with the reagent is necessary. Thoroughly wash hands after handling reagents. Use the 

safety showers and eyewash stations to dilute spilled acids and bases. Use sodium bicarbonate 

and water to neutralize and dilute spilled acids. 

Ethanol is flammable. Avoid open flames and sparks. Standard laboratory equipment 

includes fire blankets and extinguishers for use when necessary. Follow the manufacturer's 

safety precautions when using the vacuum extractor and the Kjeltec Auto 1030 Analyzer. 

5. Equipment 

5.1 Mechanical vacuum extractor, 24 place, Centurion International, Inc., Lincoln, NE 

5.2 Mechanical vacuum extractor, Mavco Sampletex, 5300 N. 57th St., Lincoln, NE 

5.3 Syringes, polypropylene, disposable, 60 mL, for extraction vessel, extractant reservoir, 

and tared extraction syringe 

5.4 Rubber tubing, 3.2 ID x 6.4 OD x 25.4 mm (1/8 ID x 1/4 OD x 1 in), for connecting 

syringe barrels. 

5.5 Polycons, Richards Mfg. Co. 

5.6 Kjeltec Auto 1035/1038 Sampler System, Tecator, Perstorp Analytical Inc. 

5.7 Digestion tubes, straight neck, 250 mL 

5.8 Analytical filter pulp, ash-free, Schleicher and Schuell, No. 289 

5.9 Plunger, modified. Remove rubber and cut plastic protrusion from plunger end. 

5.10 Electronic balance, ±1-mg sensitivity 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Ammonium chloride solution (NH4Cl), 1 N. Dissolve 535 g of NH4Cl reagent in DDI 

water and dilute to 10 L. 

6.3 Ethanol (CH3CH2OH), 95%, U.S.P. 

6.4 Nessler's reagent. Add 4.56 g of potassium iodide (KI) to 30 mL DDI water. Add 5.68 g 

of mercuric iodide (HgI2). Stir until dissolved. Dissolve 10 g of sodium hydroxide 

(NaOH) in 200 mL DDI water. Transfer NaOH solution to a 250-mL volumetric flask 

and slowly add K-Hg-I solution. Dilute to volume with DDI water and thoroughly mix. 

Solution should not contain a precipitate. Solution can be used immediately. Store the 

reagent in a brown bottle to protect from light. 

6.5 Sodium chloride (NaCl), reagent, crystal. 

6.6 Antifoam agent, slipicone release spray, Dow Chemical Corp. Alternatively, use n-octyl 

alcohol 

6.7 Boric acid, 4% (w:v), with bromcresol green-methyl red indicator (0.075 % bromcresol 

green and 0.05% methyl red), Chempure Brand 

6.8 Hydrochloric acid (HCl), 0.05 N, standardized. Dilute 83 mL of concentrated HCl in 16 L 

of DDI water. 

6.9 NaOH, 1 M. Add 500 mL of 50% NaOH solution to 8 L of DDI water. Dilute to 9 L 

with DDI water. 

467
7. Procedure 

Extraction of Bases

7.1 Prepare extraction vessel by tightly compressing a 1-g ball of filter pulp into the bottom of a 

syringe barrel with a modified plunger. 

7.2 Weigh 2.50 g of <2-mm, air-dry soil and place in an extraction vessel. Weigh a smaller 

amount of sample, if the soil is highly organic. Prepare one quality control check sample per 

48 samples. 

7.3 Place extraction vessel on upper disk of the extractor and connect a tared extraction syringe. 

Use 25.4-mm (1 in) length rubber tubing and insert the plunger in the slot of the stationary disk 

of the extractor. 

7.4 Use a squeeze bottle to fill extraction vessel to the 20-mL mark with NH4Cl solution (≈ 10 

mL). Thoroughly wet the sample. Let stand for at least 20 min. 

7.5 Put reservoir tube on top of the extraction vessel. Rapidly extract the NH4Cl solution to a 

0.5- to 1.0-cm height above sample. Turn off extractor. Add ≈ 45 mL of NH4Cl solution to the 

reservoir tube. Set extractor for an overnight (12 to 16 h) extraction. \ 

7.6 Next morning turn off the extractor. Pull the plunger of the syringe down. Do not pull 

plunger from the barrel of the syringe. Carefully remove the syringe containing the extract. 

Leave the rubber tubing on the extraction vessel. Weigh each syringe containing the NH4Cl 

extract to the nearest 0.01 g. 

7.7 Mix the extract in each syringe by manually shaking. Fill a polycon with extract solution 

and discard the excess. The solution in the polycon is reserved for analyses of extracted cations 

(procedures 6N2, 6O2, 6P2, and 6Q2). 

Removal of Excess Ammonium Chloride 

7.8 Return the extractor to starting position. Attach syringe to the extraction vessel and rinse 

the sides of the extraction vessel with ethanol from a wash bottle. Fill the extraction vessel to 

the 20-mL mark with ethanol and let stand for 15 to 20 min. 

7.9 Place reservoir tube on the extraction vessel. Rapidly extract the ethanol level to a 0.5- to 

1.0-cm height above the sample. Turn off the extractor and add 55 to 60 mL of ethanol to the 

reservoir. Extract at a 45-min rate. 

7.10 After the extractor has stopped, turn off the switch. Pull the plunger of the syringe down. 

Do not pull the plunger from the syringe barrel. Remove the syringe and discard the ethanol. 

7.11 Repeat the ethanol wash. 

7.12 After the second wash, collect a few drops of ethanol extract from the extraction vessel on 

a spot plate. Test for NH4

+

 by using Nessler's reagent. A yellow, red to reddish brown 

precipitate is a positive test. If the test is positive, repeat the ethanol wash and retest with 

Nessler's reagent. Repeat until a negative test is obtained. 

Steam Distillation: Samples and Reagent Blanks 

7.13 Remove the extraction vessel and transfer the sample to a 250-mL digestion tube. Add 6 

to 7 g of NaCl to the sample. 

7.14 Perform the same transfer and addition of reagents for blanks as for samples. 

468
7.15 Spray silicone antifoam agent (or 2 drops of n-octyl alcohol solution) into the digestion 

tubes for each of the samples and reagent blanks. 

7.16 When using new reagents, e.g., boric acid, reagent blanks are distilled in 2 sets of 6, one 

set per Kjeltec machine. Each set of 6 is averaged and recorded on bench worksheet and 

manually set on each machine. During the steam distillation, the mean reagent blank titer is 

automatically subtracted from the sample titer. 

7.17 On bench worksheet, record the normality of standardized acid, i.e., ≈ 0.05 N HCl. 

7.18 Connect the tube to the distillation unit. Close the safety door. Distillation and titration 

are performed automatically. Record the titer in mL of titrant. 

8. Calculations 

CEC = [Titer x N x 100 x AD/OD]/[SampleWeight (g)] 

where: 

CEC = Cation Exchange Capacity (meq 100 g-1) 

Titer = Titer of sample (mL) 

N = Normality of HCl titrant 

100 = Conversion factor to 100-g basis 

AD/OD= Air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report neutral salts CEC in units of meq 100 g-1 of oven-dry soil to the nearest 0.1 meq 

100 g-1. 

10. Precision 

Precision data are not available for this procedure. 

11. References 

Holmgren, G.G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically controlled 

variable rate leaching device. Soil Sci. Amer. J. 41:1207-1208. 

Peech, M., L.T. Alexander, L.A. Dean, and J.F. Reed. 1947. Methods of soil analysis for 

soil fertility investigations. U.S. Dept. Agr. Circ. 757, 25 pp. 

CHEMICAL ANALYSES (6) 

Organic Carbon (6A) 

Walkley-Black Modified Acid-Dichromate Organic Carbon (6A1) FeSO4 Titration, Automatic Titrator 

Metrohm 686 Titroprocessor (6A1C) 

1. Application 

Organic C by the Walkley-Black method is a wet combustion technique to estimate 

organic C. A correction factor is used to convert the Walkley-Black value to an organic matter 

content. A common value for the factor is 1.724 based upon the assumption that soil organic 

matter contains 58% organic C. A review of the literature reveals that the factor is highly 

variable, not only among soils but also between horizons in the same soil (Broadbent, 1953). 

In addition, a recovery factor is used because the Walkley-Black method does not completely 

oxidize all the organic C. 

469
2. Summary of Method 

The SSL uses the Walkley-Black modified acid-dichromate FeSO4 titration organic 

carbon procedure. A sample is oxidized with 1 N potassium dichromate and concentrated 

sulfuric acid (1:2 volume ratio). After 30 min, the reaction is halted by dilution with water. 

The excess dichromate is potentiometrically back-titrated with ferrous sulfate. A blank is 

carried throughout the procedure to standardize the ferrous sulfate. Percent organic C is 

reported on an oven-dry soil basis. 

3. Interferences 

Dichromate methods that do not use additional heating do not give complete oxidation 

of organic matter. Even with heating, the recovery may not be complete. Walkley and Black 

(1934) determined an average recovery factor of 76%. Other studies have found recovery 

factors ranging from 60% to 86%. Thus, an average correction factor yields erroneous values 

for many soils. The Walkley-Black method is only an approximate or semiquantitative 

estimate of organic C. 

Maintain the ratio of dichromate solution to concentrated H2SO4 at 1:2 to help maintain 

uniform heating of the mixture. 

The presence of significant amounts of chloride in the soil results in a positive error. If 

the chloride in the soil is known, use the following correction factor (Walkley, 1947) for the 

organic C. 

Organic C (%) = Apparent soil C % - (Soil Cl-

 %)/12 

The presence of significant amounts of ferrous ions results in a positive error (Walkley, 

1947). The dichromate oxidizes ferrous to ferric iron. 

Cr207

2- + 6 Fe2+ + 14 H+

 = 2 Cr3+ + 6 Fe3+ + 7 H2O 

The presence of manganese dioxide results in a negative error (Walkley, 1947). When 

heated in an acidic medium, the higher oxides of manganese, e.g., MnO2, compete with 

dichromate for oxidizable substances. 

2 MnO2 + Co + 4 H+ = CO2 + 2 Mn2+ + 2 H2O 

All dichromate methods assume that the organic C in the soil has an average oxidation 

state of zero and an equivalent weight of 3 g per equivalent when reacting with dichromate. 

When the soil has carbonized material, e.g., charcoal, graphite, coal and soot, the WalkleyBlack method gives low recovery of this material, i.e., recovery range is from 2 to 36%. 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing acids and dichromate. Toxic chromyl 

chloride may be released from the sample, if high concentrations of chloride are present. Use 

the fume hood to contain the gases released by this procedure. Use the safety showers and 

eyewash stations to dilute spilled acids. Use sodium bicarbonate and water to neutralize and 

dilute spilled acids and dichromate. Follow the manufacturer's safety precautions when using 

the automatic titrator. 

5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Titration beakers, borosilicate glass, 250 mL 

5.3 Automatic dispenser, 5 to 20 mL, Oxford no. 470 or equivalent, for K2Cr2O7, capable of 

volume adjustment to 10.00 ± 0.01 mL, 0.5% reproducibility. 

470
5.4 Dispenser, Zippette 30 mL or equivalent, for concentrated H2SO4, Brinkmann Instruments, 

Inc. 

5.5 Shaker, Eberbach 6000 power unit, fitted with spring holders for titration beakers, 

reciprocating speed of 60 to 260 epm, with 6040 utility box carrier and 6110 floor stand, 

Eberbach Corp., Ann Arbor, MI. 

5.6 Automatic titrator, Metrohm 686 Titroprocessor Series 04, 664 Control Unit, 674 Sample 

Changer Series 5, and 665 Dosimat Series 14, Metrohm Ltd., Brinkmann Instruments, Inc. 

5.7 Platinum electrode, Metrohm part no. 6.0412.000 

6. Reagents 

6.1 Distilled deionized (DDI) water

6.2 Potassium dichromate, 1.000 N, primary standard. Dissolve 49.035 g of K2Cr2O7 reagent, 

dried @ 105°C, in 1-L volumetric flask with DDI water. 

6.3 Sulfuric acid (H2SO4), concentrated, reagent 

6.4 Ferrous sulfate, 1 N, acidic. Dissolve 1 kg of FeSO4·7H2O in 6 L of DDI water. Carefully 

add 640 mL of concentrated H2SO4 with stirring. Cool and dilute to 8 L with DDI water. 

7. Procedure 

Digestion of Organic C 

7.1 Weigh 1.000 g air-dry soil and place in a titration beaker. If the sample contains >3% of 

organic C, use a smaller sample size. Refer to Table 1 for sample weight guide. If sample size 

is <0.5 g, use <80-mesh soil. If sample size is >0.5 g, use <2-mm soil. 

7.2 With automatic dispenser, add 10.00 mL of K2Cr2O7 solution to the titration beaker. Mix 

by swirling the sample. 

7.3 Use the dispenser to carefully add 20 mL of concentrated H2SO4 to the beaker. Mix by 

swirling solution. Adjustment in the amount of K2Cr2O7 added to sample requires appropriate 

adjustment in the amount of H2SO4 so that a 1:2 volume is maintained. 

7.4 Place titration beaker on the reciprocating shaker and shake 1 min. If the dichromate-acid 

mixture turns a blue-green color, all the dichromate has been reduced. Add more dichromate 

and acid to maintain a 1:2 volume. Refer to Table 1 for dichromate:acid volumes. 

Table 1. Digestion of organic C. Guide for sample weight and dichromate:acid volumes. 

OC Sample K2Cr2O7 H2SO4

(%) (g) (mL) (mL) 

0-3 1.000 10.00 20 

3-6 0.500 10.00 20 

3-6 1.000 20.00 40 

6-12 0.500 20.00 40 

12-24 0.250 20.00 40 

24-50 0.100 30.00 60 

 

7.5 Place the beaker on a heat resistant surface for 30 min. 

7.6 Add≈ 180 mL DDI water to the beaker to stop the reaction. 

471
Titration of Excess Dichromate 

7.7 Titrate eight reagent blanks at the start of each batch to determine the normality of the 

ferrous sulfate. A blank is 10.00 mL K2Cr2O7 plus H2SO4 without soil. The average titer is 

used for the blank titer value. 

7.8 Place the appropriate blanks and samples in the sample holder magazines and place on the 

sample changer. 

7.9 Refer to the manufacturer's instruction manual for operation of automatic titrator. 

7.10 Set the endpoint to 700 mV. Set the controls of the 664 Control Unit to the appropriate 

settings. 

7.11 Prime the buret with 50 mL of ferrous sulfate solution before starting the titrations. 

7.12 When a long series of samples are being titrated, intersperse blank samples throughout the 

titrations. The blank titer drifts over time, mainly because of the temperature change of the 

solution. Any sample with a titer of less one milliter and/or endpoint of less than 620 millivolts 

should be reanalyzed. 

7.13 Press "Start" on the titrator. 

8. Calculations

OC (%) = [(Blank x Volume) - (10 x Titer) x 3 x 100 x AD/OD]/ 

[Blank x Sample Weight (g) x 0.77 x 1000]

where: 

OC (%) = Organic C (%) 

Blank = Average titer of reagent blanks (mL) 

Volume = Volume of 1 N K2Cr2O4 (mL) 

Titer = Titer of FeSO4 (mL) 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

3 = Equivalents per C (assumed) 

1000 = Meq eq-1

100 = Convert to 100-g basis 

0.77 = Assumed C oxidation factor. 

9. Report 

Report organic C percentage to two decimal places, e.g., 0.95% OC, on an oven-dry 

basis. 

10. Precision 

Precision data are not available for this procedure. A quality control check sample is 

run in every batch of 20 samples. With 251 observations of the quality control check sample, 

the mean, standard deviation, and C.V. for organic carbon are 1.47, 0.025, and 1.7%, 

respectively. 

11. References 

Broadbent, F.E. 1953. The soil organic fraction. Adv. Agron. 5:153-183. 

Walkley, A. 1946. A critical examination of a rapid method for determining organic carbon 

in soils: Effect of variations in digestion conditions and of inorganic soil constituents. 

Soil Sci. 63:251-263. 

472
Walkley, A., and Black, I.A. 1934. An examination of the Degtjareff method for 

determining soil organic matter and a proposed modification of the chromic acid 

titration method. Soil Sci. 37:29-38. 

Total Carbon (6A) 

Dry Combustion (6A2) 

LECO SC-444 Carbon Analyzer (6A2e)

1. Application

Total C in soils is the sum of organic and inorganic C. Most of the organic C is 

associated with the organic matter fraction, and the inorganic C is generally found with 

carbonate minerals. The organic C in mineral soils generally ranges from 0 to 12 percent. 

Total C is quantified by two basic methods, i.e., wet or dry combustion. The SSL uses 

dry combustion. In total C determinations, all forms of C in a soil are converted to CO2

followed by a quantification of the evolved CO2. Total C can be used to estimate the organic C 

content of a soil. The difference between total and inorganic C is an estimate of the organic C. 

Organic C also can be determined directly (procedure 6A1c). The inorganic C should be 

equivalent to carbonate values measured by CO2 evolution with strong acid (Nelson and 

Sommers, 1982). 

Organic C defines mineral and organic soils. In Soil Taxonomy, organic C is also used 

at lower taxonomic levels, e.g., ustollic and fluventic subgroups (Soil Survey Staff, 1975). 

2. Summary of Method

A fine-ground (<80-mesh) soil sample is oxidized at high temperatures. The released 

gases are scrubbed, and the CO2 in the combustion gases is measured by using an infrared 

detector. The microprocessor formulates the analytical results (Ci) by combining the outputs of 

the infrared detector and the system ambient sensors with pre-programmed calibration, 

linearization and weight compensation factors. Percent total C is reported on an oven-dry soil 

basis. 

3. Interferences 

This procedure simultaneously measures inorganic and organic C. A high rate of 

combustion can oversaturate the carbon detection cell. The rate of combustion can be retarded 

by adding a solid/powder combustion controller. 

4. Safety 

Wear protective clothing and safety glasses. Magnesium perchlorate may form 

explosive mixtures. Magnesium perchlorate may contain traces of perchloric acid, which 

remain from manufacturer's operations. This acid is anhydrous because of the strong 

desiccating capability of the salt. Avoid prolonged contact with oxidizable material or material 

capable of forming unstable perchlorate esters or salts. Remove magnesium perchlorate by 

using an excess of water to thoroughly dilute the material. 

The use of high temperatures in the oxidation of samples requires that extreme caution 

be used to prevent burns and fires. Follow standard laboratory procedures when handling 

compressed gases. Oxygen is highly flammable. Avoid open flames and sparks. Standard 

laboratory equipment includes fire blankets and extinguishers for use when necessary. Follow 

the manufacturer's safety precautions when using the carbon analyzer. 

5. Equipment

5.1 Carbon analyzer, Leco Model SC-444, Sulfur and Carbon Analyzers, Leco Corp., St. 

Joseph, MI 

5.2 Combustion boats, part no. 529-203, Leco Corp., St. Joseph, MI 

5.3 Single-stage regulator, oxygen service, part no. E11-W-N115Box, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 18105 

473
5.4 Electronic balance, ±1-mg sensitivity 

6. Reagents 

6.1 Anhydrous magnesium perchlorate, granular 

6.2 Glass wool 

6.3 Compressed oxygen, >99.5% @ 30 psi 

6.4 Calcium carbonate, CaCO3, reagent grade. 

6.5 Solid/Powder Combustion Controller, part no. 501-426, Leco Corp., St. Joseph, MI 

6.6 Soil Calibration Sample, part no. 502-062, Leco Corp., St. Joseph, MI 

7. Procedure

7.1 Use a fine-ground 80-mesh, air-dry soil 

7.2 Prepare instrument as outlined in the operator's instruction manual (Leco, 1994; Leco, 

1993). 

7.3 Methods are created with the method menu and stored in the instrument memory. System 

parameters are set as follows: 

Furnace operating temperature: 1450°C 

Lance delay: 20 s 

Analysis time settings: 70 to 180 s 

Comparator level settings: 0.1% 

7.3 Condition instrument by analyzing a few soil samples, until readings are stable. 

7.4 Calibrate instrument by analyzing at least three replicates of each calibration standard. Use 

the soil calibration standard for samples with less than three to four percent total carbon and 

calcium carbonate for samples with more than four percent total carbon. Weigh standards in a 

range from 0.2 to 0.7 g. 

7.5 Load samples on autoload rack, place in the analyzer, and press analyze key. 

7.6 Weigh 0.2 to 0.5 g sample in a tared combustion boat. 

7.7 Load samples on autoload rack, place in the analyzer, and press analyze key. 

7.8 If results exceed calibration range, reduced weight of sample. If carbon detection cell is 

saturated, add approximately 1 g of solid/powder combustion controller to sample. 

7.9 Repack the reagent (anhydrous magnesium perchlorate) tubes whenever the reagent 

becomes caked or moist or the warning alarm displays. 

8. Calculations

C (%) = Ci x AD/OD 

where: 

C (%) = C (%), oven-dry basis 

Ci = C (%) instrument 

AD/OD = air-dry/oven-dry ratio (procedure 4B5) 

474
9. Report

Report total C percentage on an oven-dry basis to the nearest 0.1%. 

10. Precision

A quality control check sample is included in every batch of ten samples. For 191 

observations of calcium carbonate (actual total C = 12%), the mean, standard deviation, and 

C.V. for total carbon are 12.04, 0.31, and 2.5%, respectively. For 86 observations of soil 

calibration standard (reported total C = 0.77%), the mean, standard deviation, and C.V. for total 

carbon are 0.79, 0.02, and 2.2%, respectively. 

11. References 

Leco Corp. 1993. Sulfur and carbon in cements, soils, rock, ceramic and similar materials. 

Application Bulletin. Leco Corp., 3000 Lakeview Ave., St. Joseph, MI. 

Leco Corp. 1994. Instruction Manual. SC-444 Sulfur and Carbon Analyzers. Leco Corp. , 

3000 Lakeview Ave., St. Joseph, MI. 

Nelson, D.W., and L.E. Sommers. 1982. Total carbon, organic carbon, and organic matter. 

In A.L. Page, R.H. Miller, and D.R. Keeney (eds.) Methods of soil analysis. Part 2. 

Chemical and microbiological properties. 2nd ed. Agronomy 9:539-579. 

Soil Survey Staff. 1975. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. USDA-SCS Agric. Handb. 436. U.S. Govt. Print. Office, 

Washington, DC. 

Total Nitrogen (6B) 

Dry Combustion (6B4) 

LECO FP-428 Analyzer (6B4a) 

1. Application

The total N content of the soil may range from <0.02% in subsoils, 2.5% in peats, and 

0.06 to 0.5% in surface layers of many cultivated soils (Bremmer and Mulvaney, 1982). The 

total N data may be used to determine the soil C:N ratio, the soil potential to supply N for plant 

growth, and the N distribution in the soil profile. The C:N ratio generally ranges between 10 to 

12. Variations in the C:N ratio may serve as an indicator of the amount of soil inorganic N. 

Uncultivated soils usually have higher C:N ratios than do cultivated soils. 

Soils with large amounts of illites or vermiculites can "fix" significant amounts of N 

compared to those soils dominated by smectites or kaolinites (Young and Aldag, 1982; 

Nommik and Vahtras, 1982). Since the organic C of many soils diminishes with depth while 

the level of "fixed" N remains constant or increases, the C:N ratio narrows (Young and Aldag, 

1982). The potential to "fix" N has important fertility implications as the "fixed" N is slowly 

available for plant growth. 

2. Summary of Method

A soil sample is combusted at high temperature with oxygen to release NOx. The gases 

released are scrubbed to remove interferences (e.g., CO2 and H2O), and the NOx is reduced to 

N2. The N2 is measured by thermal conductivity detection and reported as percent N. 

3. Interferences

The total N that is measured by the combustion method does not distinguish among the 

types of N that are present in the soil. The purity of the helium and oxygen gases used in the 

instrument may affect the results of the analysis. The highest purity gases available are 

required to assure low detection limits and consistent results. 

475
4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(goggles or safety glasses) when handling hot crucibles. Standard laboratory equipment 

includes fire blankets and extinguishers for use when necessary. 

5. Equipment

5.1 Electronic balance, ±0.001-g sensitivity 

6. Reagents

None 

7. Procedure

7.1 Weigh 0.200 g of 80-mesh, air-dry soil into a tin foil cup. 

7.2 Close the tin foil cup by twisting the top closed as to fit the sample holder. 

7.3 Place the enclosed sample in the sample holder. 

7.4 When all the samples are in the sample holder, place the sample holder on the instrument. 

7.5 Refer to manufacturer’s manual for operation and calibration of the LECO FP-438 

Analyzer. 

7.6 On the bench worksheet, record the percent N for the samples. 

8. Calculations

N (%) = Instrument Reading x AD/OD 

where: 

AD/OD = Air-dry/Ovendry ratio (procedure 4B5) 

9. Report

Report total N as a dimensionless value to the nearest 0.001 unit on an ovendry basis. 

10. Precision

Precision data are not available for this procedure. For 105 observations of the quality 

control check sample for total N, the mean, standard deviation, and C.V. are 0.143, 0.004, and 

2.7 percent, respectively. 

11. References

Bremmer, J.M., and C.S. Mulvaney. 1982. Nitrogen - Total. In A.L. Page, R.H. Miller, and 

D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agronomy 9:595-624. 

Nommik, H., and K. Vahtras. 1982. Retention and fixation of ammonium and ammonia in 

soils. In F.J. Stevenson (ed.) Nitrogen in agricultural soils. Agronomy 22:123-171. 

Young, J.L., and R.W. Aldag. 1982. Inorganic forms of nitrogen in soil. In F.J. Stevenson 

(ed.) Nitrogen in agricultural soils. Agronomy 22:43-66. 

476
Mineralizable Nitrogen (6B) 

Steam Distillation (6B5) 

Kjeltec Auto 1035 Sampler (6B5A)

1. Application

The most satisfactory methods currently available for obtaining an index for the 

availability of soil N are those involving the estimation of the N formed when soil is incubated 

under conditions which promote mineralization of organic N by soil microorganisms 

(Environmental Protection Agency, 1992). The method described herein for estimating 

mineralizable N is one of anaerobic incubation and is suitable for routine analysis of soils. This 

method involves estimation of the ammonium produced by a 1-week period of incubation of 

soil at 40°C (Keeney and Bremner, 1966) under anaerobic conditions to provide an index of N 

availability. 

2. Method Summary 

An aliquot of air-dry homogenized soil is placed in a test tube with water, stoppered, 

and incubated at 40°C for 1 week. The contents are transferred to a steam distillation, rinsed 

with 4 N KCl. The amount of ammonium-N is determined by steam distillation and titration 

for the KCl:soil mixture. 

3. Interferences 

There are no known interferences. The temperature and incubation period must remain 

constant for all samples. The test can be performed on field-moist or air-dry soil samples. 

4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

and bases. Dispense concentrated acids and bases in a fume hood. Thoroughly wash hands 

after handling reagents. Use the safety showers and eyewash stations to dilute spilled acids and 

bases. Use sodium bicarbonate and water to neutralize and dilute spilled acids. Follow the 

manufacturer's safety precautions when using the incubator and Kjeltec Auto 1035 Analyzer. 

5. Equipment

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Test tubes, 16-mm x 150-mm 

5.3 PVC stoppers 

5.4 Incubator, Model 10-140, Quality Lab Inc., Chicago, IL 

5.5 Digestion tubes, straight neck, 250 mL 

5.6 Kjeltec Auto 1035/1038 Sampler System, Tecator, Perstorp Analytical Inc. 

6. Reagents

6.1 Distilled deionized (DDI) water 

6.2 Potassium chloride (KCl), 4 N. Dissolve 298.24 g KCl in DDI water and dilute to 1-L 

volume. 

6.3 Hydrochloric acid (HCl), 0.05 N, standardized. Dilute 83 mL of concentrated HCl in 20 L 

of DDI water. 

6.4 Antifoam agent, slipicone release spray, Dow Chemical Corp. Alternatively, use n-octyl 

alcohol. 

6.5 Boric acid, 4% (w:v), with bromcresol green-methyl red indicator (0.075 % bromcresol 

green and 0.05% methyl red), Chempure Brand 

477
7. Procedure

Anaerobic Incubation of Soil Sample

7.1 Place 5.00 g of mineral soil (or 1.25 g of organic soil) into a 16-mm x 150-mm test tube. 

Record the soil sample weight to the nearest 0.00 g. 

7.2 Add 12.5 ±1 mL of DDI water. Do not add ethanol to overcome any wetting difficulties as 

ethanol may act as an interference with microbial activity. Stopper the tube, shake, and place 

in a 40°C constant-temperature incubator for 7 days. Refer to the manufacturer's instructions 

for set-up and operation of the incubator. 

7.3 At the end of 7 days, remove the tube and shake for 15 s. 

7.4 Transfer the contents of the test tube to a 250-mL digestion tube. Complete the transfer by 

rinsing the tube with 3 times with 4 ml of 4 N KCl, using a total of 12.5 ±1 mL of the KCl. 

Steam Distillation: Samples and Reagent Blanks 

7.5 Remove the extraction vessel and transfer the sample to a 250-mL digestion tube. 

7.6 Perform the same transfer and addition of reagents for blanks as for samples. 

7.7 Spray silicone antifoam agent (or 2 drops of n-octyl alcohol solution) into the digestion 

tubes for each of the samples and reagent blanks. 

7.8 When using new reagents, e.g., boric acid, reagent blanks are distilled in 2 sets of 6, one set 

per Kjeltec machine. Each set of 6 is averaged and recorded on bench worksheet and manually 

set on each machine. During the steam distillation, the mean reagent blank titer is 

automatically subtracted from the sample titer. 

7.9 On bench worksheet, record the normality of standardized acid, i.e., ≈ 0.0500 N HCl. 

7.10 Load samples in racks of 20. Distillation and titration are performed automatically. 

Record the titer in mL of titrant. 

8. Calculations

N= (Titer x N x 100 x AD/OD)/ Sample Weight (g) 

where: 

N = Mineralizable N (meq 100 g-1) 

Titer = Titer of sample (mL) 

N = Normality of HCl titrant 

100 = Conversion factor to 100-g basis 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

9. Report

Report mineralizable N in units of meq 100 g-1 of oven-dry soil to the nearest 0.001 

meq 100 g-1. 

10. Precision

No precision data are available for this procedure. 

478
11. References

Environmental Protection Agency. 1992. Handbook of laboratory methods for forest 

health monitoring. G.E. Byers, R.D. Van Remortel, T.E. Lewis, and M. Baldwin (eds.). 

Part III. Soil analytical laboratory. Section 10. Mineralizable N. U.S. Environmental 

Protection Agency, Office of Research and Development, Environmental Monitoring 

Systems Laboratory, Las Vegas, NV. 

Keeney, D.R. and J.M. Bremner. 1966. Comparison and evaluation of laboratory methods 

of obtaining an index of soil nitrogen availability. Agron. J. 58:498-503. 

Iron, Manganese, and Aluminum (6C, 6D, and 6G) 

Dithionite-Citrate Extraction (6C2, 6D2, and 6G7) 

Atomic Absorption Perkin-Elmer AA 5000 

(6C2b, 6D2a, and 6G7a)

1. Application

Dithionite-citrate (CD) is used as a selective dissolution extractant for organically 

complexed Fe and Al, noncrystalline hydrous oxides of Fe and Al, and amorphous 

aluminosilicates (Wada, 1989). The CD solution is a poor extractant of crystalline hydrous 

oxides of Al, allophane, and imogolite. The CD solution does not extract opal, Si, or other 

constituents of crystalline silicate minerals (Wada, 1989). In Soil Taxonomy, the CD 

extractable Fe and Al are criteria for spodic placement (Soil Survey Staff, 1975). 

2. Summary of Method

A soil sample is mixed with sodium dithionite, sodium citrate, and distilled deionized 

water, and shaken overnight. Superfloc 16 is added, and the mixture is made to volume. 

Solution is allowed to settle, and a clear extract is obtained. The CD extract is diluted with 

distilled deionized (DDI) water. The analytes are by an atomic absorption spectrophotometer 

(AA). The data are automatically recorded by a microcomputer and printer. The percent CD 

extractable Fe, Mn, and Al are reported in procedures 6C2b, 6D2a, and 6G7a, respectively. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

AA analyses of these elements. These interferences vary in importance, depending upon the 

particular analyze selected. 

The redo potential of the extractant is dependent upon the pH of the extracting solution 

and the soil system. Sodium citrate complexes the reduced Fe and usually buffers the system to 

a pH of 6.5 to 7.3. Some soils may lower the pH, resulting in the precipitation of Fe sulfides. 

The SSL has not had significant problems with this interference. 

Filtered extracts can yield different recoveries of Fe, Mn, and Al, relative to unfiltered 

extracts. 

4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves); eye protection (face 

shields, goggles, or safety glasses); and a breathing filter when handling dry sodium dithionite. 

Sodium dithionite may spontaneously ignite if allowed to become moist, even by atmospheric 

moisture. Keep dithionite in a fume hood. 

Follow standard laboratory practices when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene gas is highly flammable. Avoid 

open flames and sparks. Standard laboratory equipment includes fire blankets and 

extinguishers for use when necessary. Follow the manufacturer's safety precautions when 

using the AA. 

479
5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Filter paper, pre-pleated, 185-mm diameter, Schleicher and Schuell 

5.3 Atomic absorption spectrophotometer (AA), model 5000, Perkin-Elmer Corp., Norwalk, 

CT 

5.4 Automatic burner control, model 5000, Perkin-Elmer Corp., Norwalk, CT 

5.5 Autosampler, AS-50, Perkin-Elmer Corp., Norwalk, CT 

5.6 Dot matrix printer, P-132, Interdigital Data Systems,Inc. 

5.7 Single-stage regulator, acetylene service, part number E11-0-N511A, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 

5.8 Digital diluter/dispenser, MicroLab 500, Hamilton Co., P.O. Box 10030, Reno, NV 

5.9 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV 

5.10 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer, Curtin 

Matheson Scientific, Inc., Houston, TX 

5.11 Containers, polypropylene 

6. Reagents

6.1 Distilled deionized (DDI) water 

6.2 Sodium dithionite (Na2S2O4), purified powder 

6.3 Sodium citrate dihydrate (Na3C6H507·2H2O), crystal, reagent 

6.4 Hydrochloric acid (HCl), concentrated 12 N

6.5 HCl, 1:1 HCl:DDI, 6 N. Carefully mix 1 part of concentrated HCl to 1 part DDI water. 

6.6 HCl, 1% wt. Carefully dilute 25 mL of concentrated HCl to 1 L with DDI water. 

6.7 Superfloc 16, 0.2% solution (w:v). Dissolve 2 g of Superfloc 16 in 1 liter of DDI water. 

Do not shake the mixture as this breaks the polymer chains of the Superfloc. Gently 

swirl the mixture occasionally over the several days that the solution requires to 

completely dissolve the Superfloc. Suggested source is American Cyanamid Co., P.O. 

Box 32787, Charlotte, NC. 

6.8 Primary mixed standard, 4000 mg L-1 (4000 ppm) Fe, 600 mg L-1 (600 ppm) Mn, and 

3000 mg L-1 (3000 ppm) Al. Dissolve 4.000 g of Fe wire, 0.6000 g of Mn metal powder, 

and 3.000 g of Al wire with 1:1 HCl in a glass beaker. When dissolved transfer to a 1-L 

volumetric flask and make to volume with 1% HCl solution. Store in a polypropylene 

bottle. 

6.9 High calibration standard, 240 mg/8 oz (1012 ppm) Fe; 36 mg/8 oz (152 ppm) Mn; and 

180 mg/8 oz (759 ppm) Al. Pipet 60 mL of primary mixed standard into 8 oz bottle. 

Add 20 g of sodium citrate dihydrate, 1.24 mL of concentrated H2SO4, and 2 mL of 

Superfloc 16 solution. In standards, the H2SO4 substitutes for the dithionite. Fill to 8-oz 

volume with DDI water and mix thoroughly. After dissolution, transfer solution to a 

plastic bottle. 

6.10 Low calibration standard, 120 mg/8 oz (506 ppm) Fe; 18 mg/8 oz (76 ppm) Mn; and 90 

mg/8 oz (380 ppm) Al. Pipet 30 mL of primary mixed standard into 8 oz bottle. Add 20 

g of sodium citrate dihydrate, 1.24 mL of concentrated H2SO4, and 2 mL of Superfloc 16 

solution. In standards and reagent blanks, the H2SO4 substitutes for the dithionite. Fill to 

8-oz volume with DDI water and mix thoroughly. After dissolution, transfer solution to a 

plastic bottle. 

6.11 Calibration reagent blank solution. Add 20 g of sodium citrate dihydrate, 1.24 mL of 

concentrated H2SO4, and 2 mL of Superfloc 16 solution. In standards and reagent blanks, 

the H2SO4 substitutes for the dithionite. Fill to 8-oz volume with DDI water and mix 

thoroughly. After dissolution, transfer solution to a plastic bottle. 

6.12 Acetylene gas, purity 99.6% 

6.13 Compressed air with water and oil traps 

480
7. Procedure

Extraction of Fe, Mn, and Al 

7.1 Weigh 4.00 g of <2-mm, air-dry soil sample and place in an 8-oz nursing bottle. 

7.2 Add 2 g of sodium dithionite and 20 to 25 g of sodium citrate dihydrate. 

7.3 Add DDI water to 4-oz level on bottle and securely stopper bottle. 

7.4 Shake overnight (12 to 16 h) in a reciprocating shaker. After shaking, use a dispenser to 

add 2 ml of Superfloc 16 solution. 

7.5 Fill bottle to 8-oz volume with DDI water. Stopper and shake thoroughly for ~ 15 s. 

7.6 Allow to settle for at least 3 day (3 to 5 days typical). The Fe, Mn, and Al are determined 

from a clear aliquot of solution. 

Dilution of Sample Extracts and Standards

7.7 No ionization suppressant is required as the Na in the extractant is present in sufficient 

quantity. Set the digital diluter at 66 for diluent and 35 for CD extracts, calibration reagent 

blanks, and calibration standards for a 1:20 dilution as follows: 

7.8 Dilute 1 part CD sample extract with 19 parts of DDI water (1:20 dilution). 

7.9 Dilute 1 part calibration reagent blank with 19 parts of DDI water (1:20 dilution). 

7.10 Dilute 1 part low calibration standard with 19 parts of DDI water (1:20 dilution). 

7.11 Dilute 1 part high calibration standard with 19 parts of DDI water (1:20 dilution). 

7.12 Dispense the reagent blanks and calibration standards in polycons from which the 

solutions are transferred to test tubes. Dispense the diluted sample solutions into test tubes 

which have been placed in the sample holders of the sample changer. 

AA Calibration

7.13 Use the calibration reagent blank and high calibration standard to calibrate the AA. The 

AA program requires a blank and a standard, in that order, to establish a single point calibration 

curve for element determination. Perform one calibration, i.e., blank plus standard, for every 

12 samples. 

7.14 Use the low calibration standard (120 mg/8 oz Fe; 18 mg/8 oz Mn; and 90 mg/8 oz Al) as 

a check sample. Use high calibration standard for Fe check sample and low calibration 

standard for Mn and Al check sample. 

AA Set-up and Operation

7.15 Refer to the manufacturer's manual for operation of the AA. The following are only very 

general guidelines for instrument conditions for the various analytes. 

481
Element Wavelength 

Burner head 

& Angle 

Fuel/ 

Oxidant 

(nm) 

Fe 248.5 5-cm 

parallel 

10 C2H2/ 

25 Air 

Al 309.35 5-cm 

parallel 

30 C2H2/ 

17 N2O 

Mn 280.15 5-cm 

parallel 

10 C2H2/ 

25 Air 

Typical read delay is 6 s, and integration time is 8 s. 

7.16 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.17 If sample exceeds calibration standard, dilute the sample (dilution ratio in calculation) 

with appropriate matrix and record dilution. Remember to keep the matrix the same after 

dilution by diluting with DDI water (1:20 dilution). 

7.18 The instrument readings are usually programmed to display analyte concentration in mg/8 

oz. 

8. Calculations

Fe (%) = (Fe x DR x 100 x AD/OD)/(Sample x 1000) 

Fe2O3 (%) = (Fe X DR x 1.43 x 100 x AD/OD)/(Sample x 1000) 

Mn (%) = (Mn x DR x 100 x AD/OD)/(Sample x 1000) 

Al (%) = (Al x DR x 100 x AD/OD)/(Sample x 1000) 

where: 

Fe = mg/8 oz 

Mn = mg/8 oz 

Al = mg/8 oz 

DR = Dilution Ratio 

Sample = Sample weight (g) 

1.43 = Conversion factor from Fe to Fe2O3 

100 = Conversion factor to percent 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

1000 = Conversion factor (mg g-1) 

9. Report

Report percent CD extractable Fe, Mn, and Al on oven-dry soil basis to the nearest 

whole number. 

10. Precision

Precision data are not available for this procedure. A quality control check sample is 

run with every batch of samples. For the quality control check sample, the mean, standard 

deviation, and CV for Fe, Mn, and Al are as follows: 

482
Element Mean n Std. 

Dev. 

C.V. 

Fe 2.5 35 0.05 2.2% 

Mn 0.01 19 0.00 0.0% 

Al 0.26 33 0.01 5.4% 

11. References 

Wada, K. 1989. Allophane and imogolite. In J.B. Dixon and S.B. Weed (eds.). Minerals in 

soil environment. 2nd ed. Soil Sci. Soc. Amer. No. 1. p. 1051-1087. 

Soil Survey Staff. 1975. Soil Taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. USDA-SCS Agric. Handb. 436. U.S. Govt. Print. Office, 

Washington, DC. 

Iron, Manganese, and Aluminum (6C, 6D, and 6G) 

Dithionite-Citrate Extraction (6C2, 6D2, and 6G7) 

Atomic Absorption 

Thermo Jarrell Ash, Smith-Hietje 4000 

(6C2c, 6D2b, and 6G7b) 

1. Application

Dithionite-citrate (CD) is used as a selective dissolution extractant for organically 

complexed Fe and Al, noncrystalline hydrous oxides of Fe and Al, and amorphous 

aluminosilicates (Wada, 1989). The CD solution is a poor extractant of crystalline hydrous 

oxides of Al, allophane, and imogolite. The CD solution does not extract opal, Si, or other 

constituents of crystalline silicate minerals (Wada, 1989). In Soil Taxonomy, the CD 

extractable Fe and Al are criteria for spodic placement (Soil Survey Staff, 1975). 

2. Summary of Method

A soil sample is mixed with sodium dithionite, sodium citrate, and distilled deionized 

water, and shaken overnight. Superfloc 16 is added, and the mixture is made to volume. 

Solution is allowed to settle, and a clear extract is obtained. The CD extract is diluted with 

distilled deionized (DDI) water. The analytes are measured by an atomic absorption 

spectrophotometer (AA). The data are automatically recorded by a microcomputer and printer. 

The percent CD extractable Fe, Mn, and Al are reported in procedures 6C2c, 6D2b, and 6G7b, 

respectively. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

AA analyses of these elements. These interferences vary in importance, depending upon the 

particular analyte selected. 

The redox potential of the extractant is dependent upon the pH of the extracting solution 

and the soil system. Sodium citrate complexes the reduced Fe and usually buffers the system to 

a pH of 6.5 to 7.3. Some soils may lower the pH, resulting in the precipitation of Fe sulfides. 

The SSL has not had significant problems with this interference. 

Filtered extracts can yield different recoveries of Fe, Mn, and Al, relative to unfiltered 

extracts. 

4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves); eye protection (face 

shields, goggles, or safety glasses); and a breathing filter when handling dry sodium dithionite. 

483
Sodium dithionite may spontaneously ignite if allowed to become moist, even by atmospheric 

moisture. Keep dithionite in a fume hood. 

Follow standard laboratory practices when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene gas is highly flammable. Avoid 

open flames and sparks. Standard laboratory equipment includes fire blankets and 

extinguishers for use when necessary. Follow the manufacturer's safety precautions when 

using the AA. 

5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Filter paper, pre-pleated, 185-mm diameter, Schleicher and Schuell 

5.3 Atomic absorption spectrophotometer (AA), Smith-Hieftje Model 4000, Thermo Jarrell 

Ash Corp., Franklin, MA 

5.4 Autosampler, Model 150, Thermo Jarrell Ash Corp., Franklin, MA 

5.5 ThermoSpec software, Version 3.01, Enable 4.0, DOS 5.0, Thermo Jarrell Ash Corp., 

Franklin, MA 

5.6 Computer, CUi Advantage 486, Thermo Jarrell Ash Corp., Franklin, MA 

5.7 Printer, NEC Pinwriter P3200 

5.8 Single-stage regulator, acetylene service, part number E11-0-N511A, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 

5.9 Digital diluter/dispenser, MicroLab 500, Hamilton Co., P.O. Box 10030, Reno, NV 

5.10 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV 

5.11 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer, Curtin 

Matheson Scientific, Inc., Houston, TX 

5.12 Containers, polypropylene 

6. Reagents

6.1 Distilled deionized (DDI) water 

6.2 Sodium dithionite (Na2S2O4), purified powder 

6.3 Sodium citrate dihydrate (Na3C6H507·2H2O), crystal, reagent 

6.4 Hydrochloric acid (HCl), concentrated 12 N

6.5 HCl, 1:1 HCl:DDI, 6 N. Carefully mix 1 part of concentrated HCl to 1 part DDI water. 

6.6 HCl, 1% wt. Carefully dilute 25 mL of concentrated HCl to 1 L with DDI water. 

6.7 Superfloc 16, 0.2% solution (w:v). Dissolve 2 g of Superfloc 16 in 1 liter of DDI water. 

Do not shake the mixture as this breaks the polymer chains of the Superfloc. Gently 

swirl the mixture occasionally over the several days that the solution requires to 

completely dissolve the Superfloc. Suggested source is American Cyanamid Co., P.O. 

Box 32787, Charlotte, NC. 

6.8 Primary mixed standard, 4000 mg L-1 (4000 ppm) Fe, 600 mg L-1 (600 ppm) Mn, and 

3000 mg L-1 (3000 ppm) Al. Dissolve 4.000 g of Fe wire, 0.6000 g of Mn metal powder, 

and 3.000 g of Al wire with 1:1 HCl in a glass beaker. When dissolved transfer to a 1-L 

volumetric flask and make to volume with 1% HCl solution. Store in a polypropylene 

bottle. 

6.9 High calibration standard, 240 mg/8 oz (1012 ppm) Fe; 36 mg/8 oz (152 ppm) Mn; and 

180 mg/8 oz (759 ppm) Al. Pipet 60 mL of primary mixed standard into 8 oz bottle. 

Add 20 g of sodium citrate dihydrate, 1.24 mL of concentrated H2SO4, and 2 mL of 

Superfloc 16 solution. In standards, the H2SO4 substitutes for the dithionite. Fill to 8-oz 

volume with DDI water and mix thoroughly. After dissolution, transfer solution to a 

plastic bottle. 

6.10 Low calibration standard, 120 mg/8 oz (506 ppm) Fe; 18 mg/8 oz (76 ppm) Mn; and 90 

mg/8 oz (380 ppm) Al. Pipet 30 mL of primary mixed standard into 8 oz bottle. Add 20 

g of sodium citrate dihydrate, 1.24 mL of concentrated H2SO4, and 2 mL of Superfloc 16 

solution. In standards and reagent blanks, the H2SO4 substitutes for the dithionite. Fill to 

484
8-oz volume with DDI water and mix thoroughly. After dissolution, transfer solution to a 

plastic bottle. 

6.11 Calibration reagent blank solution. Add 20 g of sodium citrate dihydrate, 1.24 mL of 

concentrated H2SO4, and 2 mL of Superfloc 16 solution. In standards and reagent blanks, 

the H2SO4 substitutes for the dithionite. Fill to 8-oz volume with DDI water and mix 

thoroughly. After dissolution, transfer solution to a plastic bottle. 

6.12 Acetylene gas, purity 99.6% 

6.13 Compressed air with water and oil traps 

7. Procedure

Extraction of Fe, Mn, and Al 

7.1 Weigh 4.00 g of <2-mm, air-dry soil sample and place in an 8-oz nursing bottle. 

7.2 Add 2 g of sodium dithionite and 20 to 25 g of sodium citrate dihydrate. 

7.3 Add DDI water to 4-oz level on bottle and securely stopper bottle. 

7.4 Shake overnight (12 to 16 h) in a reciprocating shaker. After shaking, use a dispenser to 

add 2 ml of Superfloc 16 solution. 

7.5 Fill bottle to 8-oz volume with DDI water. Stopper and shake thoroughly for ~ 15 s. 

7.6 Allow to settle for at least 3 day (3 to 5 days typical). The Fe, Mn, and Al are determined 

from a clear aliquot of solution. 

Dilution of Sample Extracts and Standards

7.7 No ionization suppressant is required as the Na in the extractant is present in sufficient 

quantity. Set the digital diluter at 66 for diluent and 35 for CD extracts, calibration reagent 

blanks, and calibration standards for a 1:20 dilution as follows: 

7.8 Dilute 1 part CD sample extract with 19 parts of DDI water (1:20 dilution). 

7.9 Dilute 1 part calibration reagent blank with 19 parts of DDI water (1:20 dilution). 

7.10 Dilute 1 part low calibration standard with 19 parts of DDI water (1:20 dilution). 

7.11 Dilute 1 part high calibration standard with 19 parts of DDI water (1:20 dilution). 

7.12 Dispense the reagent blanks and calibration standards in polycons from which the 

solutions are transferred to test tubes. Dispense the diluted sample solutions into test tubes 

which have been placed in the sample holders of the sample changer. 

AA Calibration

7.13 Use the calibration reagent blank and high calibration standard to calibrate the AA. The 

AA program requires a blank and a standard, in that order, to establish a single point calibration 

curve for element determination. Perform one calibration, i.e., blank plus standard, for every 

12 samples. 

7.14 Use the low calibration standard (120 mg/8 oz Fe; 18 mg/8 oz Mn; and 90 mg/8 oz Al) as 

a check sample. Use high calibration standard for Fe check sample and low calibration 

standard for Mn and Al check sample. 

485
AA Set-up and Operation

7.15 Refer to manufacturer's manual for operation of the AA. The following are only very 

general guidelines for instrument conditions for the various analytes. 

Element Wavelength Burner head 

& Angle 

Fuel/ 

Oxidant 

(nm) 

Fe 248.5 5-cm 

parallel 

4 C2H2/ 

16 Air 

Al 309.35 5-cm 

parallel 

20 C2H2/ 

10 N2O 

Mn 280.15 5-cm 

parallel 

4 C2H2/ 

10 Air 

Typical read delay is 6 s, and integration time is 8 s. 

7.16 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.17 If sample exceeds calibration standard, dilute the sample (dilution ratio in calculation) 

with appropriate matrix and record dilution. Remember to keep the matrix the same after 

dilution by diluting with DDI water (1:20 dilution). 

7.18 The instrument readings are usually programmed to display analyte concentration in mg/8 

oz. 

8. Calculations

Fe (%) = (Fe x DR x 100 x AD/OD)/ (Sample x 1000) 

Fe2O3 (%) = (Fe X DR x 1.43 x 100 x AD/OD)/(Sample x 1000) 

Mn (%)= (Mn x DR x 100 x AD/OD)/(Sample x 1000) 

Al (%) = (Al x DR x 100 x AD/OD)/(Sample x 1000) 

where: 

Fe = mg/8 oz 

Mn = mg/8 oz 

Al = mg/8 oz 

DR = Dilution Ratio 

Sample = Sample weight (g) 

1.43 = Conversion factor from Fe to Fe2O3 

100 = Conversion factor to percent 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

1000 = Conversion factor (mg g-1) 

9. Report

Report percent CD extractable Fe, Mn, and Al on oven-dry soil basis to the nearest 

whole number. 

486
10. Precision

Precision data are not available for this procedure. A quality control check sample is 

run with every batch of samples. 

11. References 

Wada, K. 1989. Allophane and imogolite. In J.B. Dixon and S.B. Weed (eds.). Minerals in 

soil environment. 2nd ed. Soil Sci. Soc. Amer. No. 1. p. 1051-1087. 

Soil Survey Staff. 1975. Soil Taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. USDA-SCS Agric. Handb. 436. U.S. Govt. Print. Office, 

Washington, DC. 

Iron, Manganese, Aluminum, Calcium, Magnesium, Sodium, Potassium, Phosphorus, Silicon, Zirconium, Copper, Zinc, Titanium, Cadmium, Lead, Nickel, Chromium, and Cobalt 

HF Plus Aqua Regia (HF + HNO3 + HCl) Dissolution Inductively Coupled Plasma Spectrometry 

Thermo Jarrell Ash ICAP 61E Optima 3300 DV 

(6C7b, 6D6a, 6G11b, 6N5b, 6O5b, 6P3b, 6Q3b, 6S6a, 6V1b, 8K1a, 8L1a, 8M1a, 8N1a, 8O1a, 8P1a, 8Q1a, and 8R1a) 

1. Application 

This procedure is an integral part of total analysis (7C4a) and represents the 

spectroscopic analysis of elements in the digestate. 

2. Summary of Method 

High and low calibration standards are prepared for Ca, K, Mg, Mn, Cu, Zn, Cd, Pb, Co 

(mixed standards CALO and CAHI); Al, Fe, Ti, Zr, Na, (mixed standards ALLO and ALHI); 

and Si, P, Se, As (mixed standards SILO and SIHI). A blank of HF, HNO3, HCl, and H3BO3 is 

prepared. A Thermo Jarrell Ash ICAP 61E spectrometer is used for analysis. The 

concentration of Fe, Mn, Al, Ca, Mg, Na, K, P, Si, Zr, Cu, Zn, Ti, Cd, Pb, Cr, and Co are 

determined by ICP analysis by procedures 6C7b, 6D6a, 6G11b, 6N5b, 6O5b, 6P3b, 6Q3b, 

6S6a, 6V1b, 8K1a, 8L1a, 8M1a, 8N1a, 8O1a, 8P1a, 8Q1a, and 8R1a. 

3. Interferences 

None. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated acids to the fume hood. Keep HF acid refrigerated and 

avoid contact with skin of all acids. Wash hands thoroughly after handling reagents. 

5. Equipment 

5.1 Volumetrics, 500-mL, polypropylene 

5.2 Containers, 500-mL, polypropylene, with screw caps 

5.3 Pipettors, electronic digital, Rainin Instrument Co., Woburn, MA, 2500 μL and 10 mL 

5.4 Inductively coupled plasma spectrometer, ICAP-61E, Thermo Jarrell Ash Corp. , 

Franklin, MA. 

5.5 RF generator, floor mounted power unit, 45 MHz free running, Perkin-Elmer Corp., 

Norwalk, CT. 

5.6 Computer, AT&T 386 Starstation, Model CPU-G72, and printer, NEC Pinwriter, 

P2200XE, Dot Matrix 

5.7 ThermoSpec software, Thermo Jarrell Ash Corp., Franklin, MA 

5.8 Line conditioner, Unity/1, Model UT8K, Best Power Technology, Inc., Necedah, WI 

5.9 Compressed argon gas 

487
5.10 Autosampler, Thermo Jarrell Ash Corp., Franklin, MA. 

5.11 High flow torch, Part No. 126440-01; Saffire (HF-resistant) tip, Part No. 127190-00; 

Polypropylene spray chamber, Part 131129-00, Thermo Jarrell Ash Corp., Franklin, MA 

6. Reagents 

6.1 Deionized distilled (DDI) water 

6.2 Hydrofluoric acid (HF), 48%, low trace metal content 

6.3 Concentrated hydrochloric acid (HCl), 12 N. Use instrumental grade which contains low 

levels of impurities. 

6.4 Concentrated nitric acid (HNO3), 16 N. Use instrumental grade which contains low levels 

of impurities. 

6.5 Boric acid solution. Dissolve 25.0 g low trace metal, granular boric acid (H3BO3) in 1000 

mL DDI water. 

6.6 Standards, 1000 ppm, suitable for atomic absorption spectroscopy for all elements. 

7. Procedure 

7.1 Instrument calibration standards for analysis are limited to specific combinations of 

elements because of chemical incompatibilities of certain elements. Specific combinations of 

elements in calibration standards are based on suggestion by Thermo Jarrell Ash (TJA), Inc. 

Each working standard is used in two concentrations, high and low. The concentrations of 

elements in the low standards (CALO, ALLO, and SILO) are 50 percent of the concentrations 

of elements in the low standards (CALO, ALLO, and SILO). Refer to Tables 1-3 for the 

amounts of primary standards (1000 ppm) to make 500-mL volume of the low and high 

calibration standards, at the specified concentrations, for ICP analysis. 

Table 1. Calilbration standards for CALO and CAHI1

 

Element Concentration Concentration

Primary Std. 

Required 

For 

Primary Std. 

Required 

For 

CALO CAHI CALO CAHI 

ppm ppm mL mL 

Ca 75 150 37.5 75.0 

K 25 50 12.5 25.0 

Mg 20 40 10.0 20.0 

Mn 10 20 5.0 10.0 

Cu 5 10 2.5 5.0 

Zn 5 10 2.5 5.0 

Cd 5 10 2.5 5.0 

Pb 5 10 2.5 5.0 

1

All calibration standards based on 500-ml final volume

488
Table 2. Calibration standards for ALLO and ALHI1

Element Concentration Concentration 

Primary Std. 

Required 

For 

Primary Std. 

Required 

For 

ALLO AlHI ALLO AlHI 

ppm ppm mL ML 

Al 100 200 50.0 100.0 

Fe 75 150 37.5 75.0 

Ti 5 10 2.5 5.0 

Zr 5 10 2.5 5.0 

Na 25 50 12.5 25.0 

1

All calibration standards based on 500-ml final volume

Table 3. Calibration standards for SILO and SIHI1

Element Concentration Concentration

Primry Std. 

Required 

For 

Primary Std. 

Required 

For 

SILO SIHI SILO SIHI 

ppm Ppm mL Ml 

Si 225 450 112.5 225.0 

P 5 10 2.5 5.0 

Ti 5 10 2.5 5.0 

Se 5 10 2.5 5.0 

As 5 10 2.5 5.0 

1

All calibration standards based on 500-ml final volume

7.2 To the calibration standards and a blank, also add the following chemicals: 25.0 mL HF; 

3.75 mL HNO3; 1.25 mL HCl; and 12.5 g granular Boric Acid. Make all standards and the 

blank to a final 500-mL volume with DDI water. 

7.3 Use the TJA ICAP 61E spectrophotometer and analyze for the following elements: Fe, 

Mn, Al, Ca, Mg, Na, K, P, Si, Zr, Cu, Zn, As, Ti, Se, Cd, and Pb. No initial dilutions of 

samples are necessary prior to analysis. Use polypropylene spray chamber and HF resistant 

torch on ICP. Check instrument alignment and gas pressures to obtain optimum readings with 

maximum signal to noise ratio. The torch tip used for HF digestions should not be run dry or 

used with RF powers exceeding 1350. The HF torch tip should only be used with high flow 

torch. 

 

7.4 Use the HF blank standard solution to dilute those samples with concentrations greater than 

the high standard. Rerun all elements and use only the data needed from the diluted analysis. 

489
7.5 Run the detection limits using the blank standard solution. These values establish the 

lower detection limits for each element. Analyzed values lower than the detection limits are set 

equal to zero. 

7.6 When ICP analyses are completed, transfer data from the hard drive storage to a 3.5 inch 

floppy disk as an ASCII file via the “Report Writer” in the TJA software Thermospec, Version 

5.06. These data are imported into a LOTUS 123, Version 3.1 spreadsheet for data analysis. 

Refer to procedure 7C4a. 

 

8. Calculations

Refer to procedure 7C4a. 

9. Report

Refer to procedure 7C4a. 

10. Precision

No precision data are yet available for this procedure. 

11. References 

 Refer to digestion procedure. 

Organic Carbon, Iron, Manganese, and Aluminum (6A, 6C, 6D, and 6G) Sodium Pyrophosphate Extraction (6A4) 

CO2 Evolution Gravimetric (6A4a) Sodium Pyrophosphate Extraction (6C8, 6D4, and 6G10) Atomic Absorption 

Perkin-Elmer 5000 AA (6C8a, 6D4a, and 6G10a)

1. Application

Sodium pyrophosphate (0.1 M Na4P2O7) is used as a selective dissolution extractant for 

organically complexed Fe and Al (Wada, 1989). The Na4P2O7 solution is a poor extractant for 

allophane, imogolite, amorphous aluminosilicates, and noncrystalline hydrous oxides of Fe and 

Al. The Na4P2O7 solution does not extract opal, crystalline silicates, layer silicates, and 

crystalline hydrous oxides of Fe and Al (Wada, 1989). In Soil Taxonomy, sodium 

pyrophosphate extractable organic C, Fe, and Al are criteria for spodic placement (Soil Survey 

Staff, 1975). 

2. Summary of Method

The soil sample is mixed with 0.1 M Na4P2O7 and shaken overnight. Superfloc 16 is 

added, and the mixture is made to volume. The solution is allowed to settle and a clear extract 

is obtained. The Na4P2O7 extracted solution is diluted with distilled deionized (DDI) water. 

The diluted extract is aspirated into an atomic absorption spectrophotometer (AA). The analyte 

is measured by absorption of the light from a hollow cathode lamp. An automatic sample 

changer is used to aspirate a series of samples. The AA converts absorption to analyte 

concentration. Percent sodium pyrophosphate extractable Fe, Mn, and Al are reported in 

procedures 6C8a, 6D4a, and 6G10a, respectively. The organic C in the sodium pyrophosphate 

extract is wet oxidized and gravimetrically measured in procedure 6A4a. 

3. Interferences

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

AA analyses of these elements. These interferences vary in importance, depending upon the 

particular analyte selected. 

The concentration of Na4P2O7 solution must be close to 0.1 M. Variable amounts of Fe, 

Al, Mn, and organic C may be extracted by varying the pyrophosphate concentration. 

490
4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Thoroughly wash hands after handling these metal salts. 

Follow standard laboratory procedures when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene is highly flammable. Avoid open 

flames and sparks. Standard laboratory equipment includes fire blankets and extinguishers for 

use when necessary. Follow the manufacturer's safety precautions when using the AA. 

5. Equipment

5.1 Electronic balance, ±0.0001 g 

5.2 Shaker, Eberbach 6000 power unit, reciprocating speed of 60 to 260 epm, with 6040 

utility box carrier and 6110 floor stand, Eberbach Corp., Ann Arbor, MI 

5.3 Nursing bottle, 240 mL (8 fl. oz.), graduated 

5.4 Rubber stoppers, No. 2, to fit nursing bottles 

5.5 Dispenser/diluters, Repipet, 0 to 10 mL, Labindustries, 1802 2nd St., Berkeley, CA 

5.6 Atomic absorption spectrophotometer (AA), model 5000, Perkin-Elmer Corp., Norwalk, 

CT 

5.7 Automatic burner control, model 5000, Perkin-Elmer Corp., Norwalk, CT 

5.8 Autosampler, AS-50, Perkin-Elmer Corp., Norwalk, CT 

5.9 Single-stage regulator, acetylene service, part number E11-0-N511A, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 

5.10 Heated regulator, single-stage, nitrous oxide, stock number 808 8039, Airco Welding 

Products, P.O. Box 486, Union, NJ 

5.11 Diluter/dispenser, Microlab 500, Catalogue No. 69052, Hamilton Co., Bonaduz, GR, 

Switzerland 

5.12 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV, 89510 

5.13 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer, Curtin 

Matheson Scientific, Inc., Houston, TX 

5.14 Absorption bulb, Nesbitt with stopper 

5.15 Absorption bulb, Stetser-Norton 

5.16 Flask, boiling, round bottom, short neck 

5.17 Condenser, Allihn 

5.18 Funnel, separatory, cylindrical, open top, with stopcock 

5.19 Tube, drying, Schwartz 

5.20 Containers, polypropylene 

5.21 Dot matrix printer, P-132, Interdigital Data Systems, Inc. 

6. Reagents

6.1 Distilled deionized (DDI) water 

6.2 Hydrochloric acid (HCl), concentrated, 12 N

6.3 HCl, 1:1 HCl:DDI, 6 N. Carefully mix 1 part of concentrated HCl to 1 part DDI H2O. 

6.4 HCl, 1% wt. Carefully dilute 25 mL of concentrated HCl to 1 L with DDI H2O. 

6.5 Superfloc 16, 0.2% solution (w:v). Dissolve 2 g of Superfloc 16 in 1 liter of DDI H2O. 

Do not shake the mixture as this breaks the polymer chains of the Superfloc. Gently 

swirl the mixture occasionally over the several days that the solution requires to 

completely dissolve the Superfloc. Suggested source is American Cyanamid Co., P.O. 

Box 32787, Charlotte, NC 

6.6 Sodium pyrophosphate solution, 0.1 M. Dissolve 800 g of Na4P2O7·H2O in 16 L of DDI 

H2O. Dilute to 18 L with DDI H2O. 

6.7 Primary mixed standard, 4000 mg L-1 (4000 ppm) Fe; 2000 mg L-1 (3000 ppm) Al; and 

600 mg L-1 (600 ppm) Mn. Dissolve 4.000 g of Fe wire, 3.000 g of Al wire, and 0.600 g 

491
of Mn metal powder in 1:1 HCl:DDI in a glass beaker. When dissolved transfer to a 1-L 

volumetric flask and fill with 1% HCl solution. Store in a polypropylene bottle. 

6.8 High calibration mixed standards solution (HCMSS), 80 mg/8 oz (80 ppm) Fe; 12 mg/8 

oz (12 ppm) Mn; and 60 mg/8 oz (60 ppm) Al. Pipet 20 mL of primary mixed standard 

into an 8-oz bottle. Add 10.55 g of Na4P2O7·H2O and 3.5 mL of concentrated H3PO4. Dilute to 8 oz with DDI H2O. Store in a polypropylene bottle. 

6.9 Low calibration mixed standards solution (LCMSS), 40 mg/8 oz (40 ppm) Fe; 6 mg/8 oz 

(6 ppm) Mn; and 30 mg/8 oz (30 ppm) Al. Pipet 10 mL of primary mixed standard into 

an 8-oz bottle. Add 10.55 g of Na4P2O7·H2O and 3.5 mL of concentrated H3PO4. Dilute 

to 8 oz with DDI H2O. Store in a polypropylene bottle. 

6.10 Calibration reagent blank solution (CRBS). Add 10.55 g of Na4P2O7·H2O and 3.5 mL of 

concentrated H3PO4. Dilute to 8 oz with DDI H2O. Store in a polypropylene bottle. 

6.11 Potassium dichromate (K2Cr2O7), reagent 

6.12 Potassium iodide solution. Dissolve 100 g of KI in 100 mL of DDI H2O. 

6.13 Silver sulfate, saturated aqueous solution. 

6.14 Digestion acid mixture. Mix 600 mL of concentrated H2SO4 and 400 mL of 85% H3PO4. 6.15 Indicarb or Mikohlbite 

6.16 Soda lime 

6.17 Zinc granules, 300 mesh 

6.18 Anhydrone 

6.19 Acetylene gas, purity 99.6% 

6.20 Nitrous oxide gas, compressed 

6.21 Compressed air with water and oil traps 

7. Procedure

Extraction of Fe, Mn, and Al

7.1 Weigh 2.00 g of <2-mm, air-dry soil sample and place in an 8-oz nursing bottle. 

7.2 Add 0.1 M Na4P2O7 solution to 7-oz level on bottle and securely stopper bottle. 

7.3 Shake overnight (12 to 16 h) in a reciprocating shaker. After shaking, use a dispenser to 

add 4 mL of Superfloc 16 solution. 

7.4 Fill bottle to 8-oz volume with Na4P2O7 solution. 

7.5 Stopper and shake vigorously for ≈ 15 s. 

7.6 Allow to settle for at least 3 days (4 to 6 days typical). The Fe, Mn, and Al are determined 

from a clear aliquot of solution. 

Dilution of Sample Extracts and Standards

7.7 No ionization suppressant is required as the Na in the extractant is present in sufficient 

quantity. Set the digital diluter on Hamilton diluter to 66 for diluent and 35 for sodium 

pyrophosphate sample extracts, calibration reagent blanks, and calibration standards for a 1:20 

dilution as follows: 

7.8 Dilute 1 part sample sodium pyrophosphate sample extract with 19 parts of DDI H2O (1:20 

dilution). 

7.9 Dilute 1 part CRBS with 19 parts of DDI H2O (1:20 dilution). 

7.10 Dilute 1 part LCMSS with 19 parts of DDI H2O (1:20 dilution). 

492
7.11 Dilute 1 part HCMSS with 19 parts of DDI H2O (1:20 dilution). 

7.12 Dispense the diluted solutions into test tubes which have been placed in the sample holder 

of the sample changer. 

AA Calibration

7.13 Use the calibration reagent blank and high calibration standard to calibrate the AA. The 

AA requires a blank and a standard, in that order, to establish a single point calibration curve 

for element determination. Perform one calibration, i.e., blank plus standard, for every 12 

samples. 

7.14 Use the low calibration standard as a check sample. 

AA Set-up and Operation

7.15 Refer to the manufacturer's manual for operation of the Perkin-Elmer 5000 AA. The 

following are only very general guidelines for instrument conditions for the various analytes. 

Analyte Wavelength 

 nm 

Fe 248.8 

Mn 280.1 

Al 309.3 

Analyte Burner Head 

Fe 5-cm parallel 

Mn 5-cm parallel 

Al 5-cm parallel 

Analyte Fuel/Oxidant 

 

Fe 10 C2H2/25 Air 

Mn 10 C2H2/25 Air 

Al 30 C2H2/17 Air 

Typical read delay is 6 s, and the integration by peak area is 8 s. 

7.16 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.17 If sample exceeds calibration standard, dilute the sample (dilution ratio in calculation) 

with appropriate matrix and record dilution. Remember to keep matrix the same after dilution 

by diluting with DDI H2O (1:20 dilution). 

Organic C Determination

7.18 Pipet 100 mL of the extract into a 100-ml flask. 

7.19 Evaporate the extract to near dryness using a 50°C waterbath and a gentle stream of clean, 

filtered air. 

493
7.20 Construct the wet combustion apparatus. Refer to Fig. 3 of the apparatus for gravimetric 

organic C determination. 

7.21 Add 1 to 2 g of potassium dichromate. 

.22 Wash the neck of the flask with 3 mL of DDI H O and connect to condenser. 

.23 Attach a weighed Nesbitt bulb to the system and open the valve at the top. 

id mixture into the funnel. Add the mixture to the flask and 

ediate acid mixture to lubricate the stopcock. 

ould be ≈ 0.5 cm below the digestion-acid mixture. 

intain 1 to 2 bubble s-1 rate throughout the 

of the Nesbitt bulb. Gentle air pressure and needle 

t adjustment. 

ixture boils (≈ 3 to 4 min). Continue a gentle boiling for 10 min. Heating is too rapid if 

mes of SO are visible above the second bulb of the reflux condenser. 

mov nal min at a rate of 6 to 8 bubbles s-1. 

t the bulb from the system, and weigh to 

. Calculations

Analyte (%) = (AA x DR x AD/OD x 100)/(Sample Weight (g) x 1000) 

7 2

7

7.24 Pour 25 mL of digestion-ac

imm ly close the stopcock. Use the digestion7.25 The tip of the air-delivery tube sh

Adjust the flow of the "carrier stream" to ma

digestion. Apply suction on the outlet side 

valve on he air pressure line aids flow 

7.26 With a gas flame or a variable power heating mantle, gently heat the flask until the 

m

white fu 2

7.27 Re e the heat and allow to aerate for 10 additio

7.28 Close the stopcock on the Nesbitt bulb, disconnec

the nearest 0.0001 g. 

8

494
nalyte = Fe, Mn, and Al 

Analyte concentration AA reading 

DR 

ample = Sample weight (g) 

ctor to convert to percent 

1000

AD/OD

Org

dure 4B5) 

L) 

. Report

rcent sodium pyrophosphate extractable Fe, Mn, and Al on oven-dry soil basis 

to the n

g 

Wada, K. 1989. Allophane and imogolite. In J.B. Dixon and S.B. Weed (eds.). Minerals in 

soil environment. 2nd ed. Soil Sci. Soc. Amer. No. 1. p. 1051-1087. 

Iron, Manganese, Aluminum, Silicon, and Phosphate (6C, 6D, 6G,6V, 6S) Ammonium Oxalate Extraction (6C9, 6D6, 6G12, 6V2, 6S8) Inductively Coupled Plasma Spectrometry 

Thermo Jarrell Ash, ICAP 61E 

(6C9b, 6D5b, 6G12b, 6V2b, 6S8a) 

Optical Density (8J) 

(of ammonium oxalate extract) 

1. Application 

Oxalic acid-ammonium oxalate (acid oxalate) is used as a selective dissolution 

extractant for organically complexed Fe and Al, noncrystalline hydrous oxides of Fe and Al, 

allophane, and amorphous aluminosilicates (Wada, 1989). Acid oxalate is a poor extractant of 

imogolite and layer silicates and does not extract crystalline hydrous oxides of Fe and Al, opal, 

or crystalline silicate (Wada, 1989). A more reliable and accurate estimation of soil properties 

and a better understanding of soil exchange complex is provided when acid oxalate extraction 

is used in conjunction with other selective dissolution procedures, thermal techniques, and 

chemical tests. In Soil Taxonomy, acid oxalate extractable Fe and Al are criteria for andic soil 

properties (Soil Survey Staff, 1990). 

where: 

A

AA = 

 = Dilution ratio of 1 if no additional dilution 

S

100 = Fa

 = Conversion factor (mg g-1) 

 = Air-dry/oven-dry ratio 

anic C (%) = [(WtF - WtI) x 27.3 x Volume x AD/OD]/(Sample Weight (g) x 236.6) 

where: 

WtF = Nesbitt bulb weight after digestion (g) 

WtI = Nesbitt bulb weight before digestion (g) 

Volume = Volume of extract digested (mL) 

AD/OD = Air-dry/oven-dry ratio (proce

27.3 = Conversion factor 

236.6 = Total volume of extract (m

9

Report pe

earest whole number. 

10. Precision

Precision data are not available for this procedure. 

11. References 

Soil Survey Staff. 1975. Soil Taxonomy: A basic system of soil classification for makin

and interpreting soil surveys. USDA-SCS Agric. Handb. 436. U.S.Govt. Print. Office, 

Washington, DC. 

495
2. Summary of Method

A soil sample is extracted with a mechanical vacuum extractor (Holmgren et al., 1977) 

in a 0.2 M acid oxalate solution buffered at pH 3.0 under darkness. The acid oxalate extract is 

weighed. The acid oxalate extract is diluted with 0.002 M DDBSA. The analytes are measured 

by a inductively coupled plasma emission spectrophotometer (ICP). Data are automatically 

recorded by a microcomputer and printer. The percent acid oxalate extractable Fe, Mn, Al, Si, 

and P are reported in procedures 6C9b, 6D5b, 6G12b, 6V2b, and 6S8a respectively. In 

procedure 8J, the optical density of the extract is measured with a UV spectrophotometer at 430 

nm. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

ICP analyses of these elements. These interferences vary in importance, depending upon the 

particular analyte chosen. 

The acid oxalate buffer extraction is sensitive to light, especially UV light. The 

exclusion of light reduces the dissolution effect of crystalline oxides and clay minerals. If the 

sample contains large amounts of amorphous material (>2% Al), an alternate method should be 

used, i.e., shaking with 0.275 M acid oxalate, pH 3.25, 1:100 soil:extractant. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Follow standard laboratory practices when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Follow the manufacturer's safety 

precautions when using the UV spectrophotometer and ICP. 

5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Mechanical vacuum extractor, 24 place, Centurion International, Inc., Lincoln, NE 

5.3 Mechanical vacuum extractor, Mavco Sampletex, 5300 N. 57th St., Lincoln, NE 

5.4 Syringes, polypropylene, disposable, 60 mL, for extractant reservoir, extraction 

vessel, and tared extraction syringe 

5.5 Rubber tubing, 3.2 ID x 6.4 OD x 25.4 mm, (1/8 ID x 1/4 OD x 1 in) for connecting 

syringe barrels 

5.6 Pre-pulped tubes 

5.7 Extraction vessel, 60-mL, 10u polypropylene, part no. 6986-6010, Whatman Inc., 9 

Bridewell Place, Clifton, NJ 

5.8 Disposable glass tubes 

5.9 UV-visible spectrophotometer, Carey-50, Varian Instruments 

5.10 Cuvettes, disposable, polystrene, 1-cm light path 

5.11 Inductively coupled plasma spectrometer, ICAP 61E, Thermo Jarrell Ash Corp., 

Franklin, MA 

5.12 Nebulizers, High-Solids, 41 psgi, Thermo Jarrell Ash Corp., Franklin, MA. 

5.13 RF generator, floor mounted power unit, Model 7/90, Thermo Jarrell Ash Corp., 

Franklin, MA 

5.14 Computer, AT&T 386 Starstation, Model CPU-G72, and printer, NEC Pinwriter, 

P2200XE, Dot Matrix 

5.15 ThermoSpec software, Thermo Jarrell Ash Corp., Franklin, MA 

5.16 Line conditioner, Unity/I, Model UT8K, Best Power Technology, Inc., Necedah, WI 

5.17 Single-stage regulator, high-purity, high-flow, argon, product no. E11-X-N145DHF, Air 

Products and Chemicals, Inc., Box 538, Allentown, PA 

5.18 Autosampler, Thermo Jarrell Ash Corp., Franklin, MA

5.19 Digital diluter/dispenser, MicroLab 500, Hamilton Co., P.O. Box 10030, Reno, NV 

5.20 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gastight, Hamilton Co., P.O. 

Box 10030, Reno, NV 

496
5.21 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer, Curtin 

Matheson Scientific, Inc., Houston, TX 

5.22 Containers, polyproylene 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Acid oxalate buffer solution, 0.2 M, pH 3.0. Solution A (base): Dissolve 284 g of 

(NH4)2C2O4·2H2O in 10 L of DDI water. Solution B (acid): Dissolve 252 g of 

H2C2O4·H2O in 10 L of DDI water. Mix 4 parts solution A with 3 parts solution B. 

Adjust acid oxalate solution pH by adding either acid or base solution. Store in a 

polypropylene bottle. 

6.3 pH buffers, pH 4.00 and 7.00, for electrode calibration 

6.4 Primary Fe standard, 1000 ppm. Certified Reference Solution, Fisher Chemical Scientific 

Co., Fairlawn, N.J. 

6.5 Primary Al standard, 1000 ppm. Certified Reference Solution, Fisher Chemical Scientific 

Co., Fairlawn, N.J. 

6.6 Primary Si standard, 1000 ppm. Certified Reference Solution, Fisher Chemical Scientific 

Co., Fairlawn, N.J. 

6.7 Primary Mn standard, 1000 ppm. Certified Reference Solution, Fisher Chemical 

Scientific Co., Fairlawn, N.J. 

6.8 Primary P standard, 1000 ppm. Certified Reference Solution, Fisher Chemical Scientific 

Co., Fairlwan, N.J. 

6.9 Dodecylbenzenesulfonic acid (DDBSA), Tech 97%, 0.1 M. Dissolve 32.2 g DDBSA in 

1-L DDI water. 

6.10 DDBSA solution. Dilution solution for acid oxalate extracts. Add 40.0 mL of 0.1 M

DDBSA and make to 2-L volume with DDI water (0.002 M DDBSA solution). 

6.11 High calibration standard. Mix 60 mL of each primary standard (Si, Fe, and Al) with 10 

mL of primary Mn standard and 20 mL of primary P standard in 1 L volumetric flask. 

Add 50 mL of 0.4 M acid oxalate solution and 16.0 mL of 0.1 M DDBSA and make to 1-

L volume with DDI water. The elements are added in the order (Si, Fe, Al, Mn, P) to 

avoid element precipitation. Resulting solution contains 60 ppm each of Si, Fe, and Al, 

10 ppm Mn, and 20 ppm P. Store in a polypropylene bottle. 

6.12 Medium calibration standard. Mix 30 mL of each primary standard (Si, Fe, and Al) with 

5 mL of primary Mn standard and 10 mL of primary P standard in 1 L volumetric flask. 

Add 50 mL of 0.4 M acid oxalate solution and 16.0 mL of 0.1 M DDBSA and make to 

1-L volume with DDI water. Resulting solution contains 30 ppm each of Si, Fe, and Al, 

5 ppm Mn, and 10 ppm P. Store in a polypropylene bottle. 

6.13 Low calibration standard. Mix 10 mL of each primary standard (Si, Fe, and Al) with 2 

mL of primary Mn standard, and 3 mL primary P standard in 1 L volumetric flask. Add 

30 mL of 0.4 M acid oxalate solution and 16.0 mL of 0.1 M DDBSA and make to 1-L 

volume with DDI water. Resulting solution contains 10 ppm each of Si, Fe, and Al, 2 

ppm Mn, and 3 ppm P. Store in a polypropylene bottle. 

6.14 Calibration reagent blank solution. Add 50 mL of 0.4 M acid oxalate solution and 16.0 

mL of 0.1 M DDBSA and make to 1-L volume with DDI water. 

6.15 Argon gas, purity 99.9% 

7. Procedure 

Extraction of Fe, Mn, Al, Si, and P 

7.1 Prepare disposable sample tubes. 

7.2 Weigh 0.500 g of <2-mm, air-dry soil and place in sample tube. Prepare two reagent blanks 

(no sample in tube) per set of 48 samples. 

497
7.3 Place the sample tube on the upper disk of the extractor and connect a tared extraction 

syringe. Use 25.4-mm (1-in) length rubber tubing to insert the handle of the plunger in the slot 

of the stationary extractor disk. 

7.4 Use a dispenser to add 15.00 mL of acid oxalate buffer to the sample tube. Make sure that 

the sample is thoroughly wetted. During the addition, wash sides of the tube and wet the 

sample. Shaking, swirling, or stirring may be required to wet organic samples. Allow sample 

to stand for at least 30 min. 

7.5 Set extractor for 30-min extraction rate and extract until the acid oxalate buffer solution is 

at a 0.5 to 1.0-cm height above sample. Turn off extractor. 

7.6 Put reservoir tube on top of the sample tube. 

7.7 Add 35 mL of acid oxalate buffer to the reservoir tube. 

7.8 Cover the extractor with a black plastic bag to exclude light. Adjust the extraction rate for a 

12-h extraction. 

7.9 After the extraction, shut off the extractor and pull plunger of syringe down. Do not 

remove the plunger from syringe barrel. Carefully remove the syringe with extract leaving the 

rubber tubing on the extraction vessel. 

7.10 Weigh each syringe containing acid oxalate extract to the nearest 0.01 g. 

7.11 Mix extract in each syringe by manually shaking. Fill a disposable tube with extract 

solution. This solution is reserved for determinations of Fe, Mn, Al, Si, and P. If optical 

density is to be measured, fill a disposable cuvette with extract solution. Discard excess 

solution. 

Determination of Optical Density of Extract

7.12 Place 4 mL of acid oxalate extract in disposable cuvette. 

7.13 Place 4 mL of acid oxalate reagent blank in disposable cuvette. 

7.14 On Varian spectrophotometer, select a 430-nm wavelength. Select normal slit width and 

height. Refer to the manufacturer's manual for operation of the spectrophotometer. 

7.15 Use the acid oxalate extract reagent blank to set spectrophotometer. 

7.16 Record optical density of acid oxalate extract to nearest 0.000. 

Dilution of Sample Extracts and Standards

7.17 Dilute acid oxalate extracts (1:10) with 0.002 M DDBSA solution. Add 1 part acid 

oxalate sample extract with 10 parts dilution solution. 

7.18 Set the digital settings of the Hamilton diluter for a 1:10 dilution. Calibration reagent 

blanks and calibration standards are not diluted. 

7.19 Dispense the diluted solutions into test tubes which have been placed in the sample holder 

of the sample changer. 

498
ICP Calibration

7.20 Use a multipoint calibration for ICP analysis of acid oxalate extracts. The ICP calibrates 

the blank first, low standard, medium standard, followed by the high standard. Prepare a 

quality control (QC) standard with analyte concentration between the high and low calibration 

standards. The ICP reads the QC after the high standard. If the QC falls within the range set 

by operator, the instrument proceeds to analyze the unknowns. If the QC is outside the range, 

the instrument restandardizes. The QC is analyzed approximately every 12 samples. 

ICP Set-up and Operation

7.21 Refer to the manufacturer's manual for operation of the ICP. The following parameters 

are only very general guidelines for instrument conditions for the various analytes. 

Parameter Value 

Gas Flow 

 Torch Gas High Flow 

 Auxiliary Gas Flow Medium 1.0 LPM 

 Nebulizer Pressure 41 psi 

Power 

 Approximate RF 1150 

 Power 

Peristaltic Pump 

 Analysis Pump Rate 150 RPM 

 Flush Pump Rate 200 RPM 

 Relaxation Time 10 s 

 Pumping Tube Type Silicone-Orange-3stop 

Argon Flow Rate 2.0 LPM 

 Purged Optical 2.0 SLPM Air 

 Pathway Enclosure Purge 

Nebulizer pressure depends on the type of nebulizer that is being used, i.e., low flow nebulizer 

requires a higher nebulizer pressure whereas a higher flow nebulizer requires a lower nebulizer 

pressure. To check for correct nebulizer pressure, aspirate with 1000.0 ppm yttrium. Adjust 

pressure to correct yttrium bullet. 

7.22 Analyte data are reported at the following wavelengths. 

Analyte Wavelength 

 (nm) 

 

Fe 259.940 

Al 167.081 

Si 251.611 

Mn 257.610 

P 178.28 

7.23 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. The instrument readings are usually programmed in ppm. 

7.24 If sample exceeds calibration standard, dilute the sample (1:5) with 0,4 M acid oxalate 

solution (matrix) and then dilute (1:10) with the DDBSA solution. 

499
8a. Calculations (Fe, Al, Si,)

 

Analyte (%) = [ICP x (Syrfin -Syrinit) x D.R. x AD/OD]/[Sample Weight (g) x 10000 x Density]

where: 

ICP = ICP analyte concentration (ppm) 

Syrfin = Weight of syringe + extract (g) 

Syrinit = Tare weight of syringe (g) 

D.R. = Dilution ratio of samples over calibration range 

Density = Density of acid oxalate solution (1.007) 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

8b. Calculations (Mn, P) 

Analyte (ppm) = [ICP x (Syrfin -Syrinit) x D.R. x AD/OD]/[Sample Weight (g) x Density]

where: 

ICP = ICP analyte concentration (ppm) 

Syrfin = Weight of syringe + extract (g) 

Syrinit = Tare weight of syringe (g) 

D.R. = Dilution ratio of samples over calibration range 

Density = Density of acid oxalate solution (1.007) 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report the percent acid oxalate extractable Fe, Al, and Si to the nearest 0.01%. Report 

the concentration of acid oxalate extractable Mn and P in ppm. Report the optical density of 

the acid oxalate extract to the nearest 0.001 unit. 

10. Precision 

Precision data are not available for this procedure. 

11. References 

Holmgren, G.G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically controlled 

variable rate leaching device. Soil Sci. Amer. J. 41:1207-1208. 

Soil Survey Staff. 1999. Soil Taxonomy. A Basic System of Soil Classification for Making 

and Interpreting Soil Surveys. 2nd ed. USDA-NRCS. Govt. Print.Office, Washington 

DC. 

Wada, K. 1989. Allophane and imogolite. In J.B. Dixon and S.B. Weed (eds.). Minerals in 

soil environment. 2nd ed. Soil Sci. Soc. Amer. No. 1. p 

Manganese and Aluminum (6D and 6G) 

KCl, Automatic Extractor (6D3 and 6G9) 

Inductively Coupled Plasma Spectrometry, Thermo Jarrell Ash, ICAP 61E (6D3b and 6G9c)

1. Application 

The Al extracted by 1 N KCl approximates exchangeable Al and is a measure of the 

"active" acidity present in soils with a 1:1 water pH <5.5. Above pH 5.5, precipitation of Al 

occurs during analysis. This method does not measure the acidity component of hydronium 

ions (H3O+). If Al is present in measurable amounts, the hydronium is a minor component of 

the active acidity. Because the 1 N KCl extractant is an unbuffered salt and usually affects the 

soil pH one unit or less, the extraction is determined at or near the soil pH. The KCl 

500
extractable Al is related to the immediate lime requirement and existing CEC of the soil. The 

"potential" acidity is better measured by the BaCl2-TEA method (procedure 6H5a) (Thomas, 

1982). 

2. Summary of Method 

A soil sample is leached with 1 N KCl using the mechanical vacuum extractor 

(Holmgren et al., 1977). The extract is weighed. The KCl extracted solution is diluted with 

distilled deionized water. The anlaytes are measured by inductively coupled plasma emission 

spectrophotometer (ICP). Data are automatically recorded by a microcomputer and printer. 

The Mn and Al are reported in mg kg-1 (ppm) and meq 100 g-1 ovendry soil in procedures 6D3b 

and 6G9c, respectively. 

3. Interferences

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

ICP analyses of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. 

The soil:extractant ratio must remain constant. A soil:extractant ratio of 1:10 (w:v) for 

batch procedures is most commonly used. Using a leaching technique, a 1:20 (w:v) ratio gives 

comparable results. If the sample size is changed, the amount of extractable Al is changed. No 

other significant interferences have been identified for this procedure. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Follow standard laboratory practices when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Follow the manufacturer's safety 

precautions when using the ICP. 

5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Mechanical vacuum extractor, 24 place, Centurion International, Inc., Lincoln, NE 

5.3 Mechanical vacuum extractor, Mavco Sampletex, 5300 N. 57th St., Lincoln, NE 

5.4 Syringes, polypropylene, disposable, 60 mL, for extraction vessel, extractant reservoir 

and tared extraction syringe 

5.5 Rubber tubing, 3.2 ID x 6.4 OD x 25.4 mm, (1/8 ID x 1/4 OD x 1 in) for connecting 

syringe barrels 

5.6 Analytical filter pulp, ash-free, Schleicher and Schuell, No. 289 

5.7 Plunger, modified. Remove rubber and cut plastic protrusion from plunger end. 

5.8 Wash bottle, 20 mL, to dispense KCl. 

5.9 Polycons, Richards Mfg. Co. 

5.10 Inductively coupled plasma spectrometer, ICAP 61E, Thermo Jarrell Ash Corp., 

Franklin, MA 

5.11 RF generator, floor mounted power unit, Model 7/90, Thermo Jarrell Ash Corp., Franklin, 

MA 

5.12 Computer, AT&T 386 Starstation, Model CPU-G72, and printer, NEC Pinwriter, 

P2200XE, Dot Matrix 

5.13 ThermoSpec software, Thermo Jarrell Ash Corp., Franklin, MA 

5.14 Line conditioner, Unity/I, Model UT8K, Best Power Technology, Inc., Necedah, WI 

5.15 Single-stage regulator, high-purity, high-flow, argon, product no. E11-X-N145DHF, Air 

Products and Chemicals, Inc., Box 538, Allentown, PA 

5.16 Autosampler, Thermo Jarrell Ash Corp., Franklin, MA 

5.17 Nebulizers, Precision Glass, Type A, 2.3 mlpm, 35 psig, Precision Glass Co., 14775 

Hinsdale Ave., Englewood, CO. 

5.18 Digital diluter/dispenser, MicroLab 500, Hamilton Co., P.O. Box 10030, Reno, NV \ 

501
5.19 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gastight, Hamilton Co., P.O. 

Box 10030, Reno, NV 

5.20 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer, Curtin 

Matheson Scientific, Inc., Houston, TX 

5.21 Containers, polyproylene 

6. Reagents

6.1 Distilled deionized (DDI) water 

6.2 Potassium chloride solution (KCl), 1.0 N. Dissolve 1342 g of KCl reagent in 16 L DDI 

water. Allow solution to equilibrate to room temperature. Dilute to 18 L with DDI 

water. Use 1.0 N KCl for Al and Mn extraction. 

6.3 Potassium chloride solution (KCl), 2.0 N. Dissolve 298.24 g of KCl reagent in 1.5 L DDI 

water. Allow solution to equilibrate to room temperature. Dilute to 2 L with DDI water. 

Use 2.0 N KCl for standards. 

6.4 Primary Al standard, 1000 ppm (111 meq L-1). Certified Reference Solution, Fisher 

Chemical Scientific Co., Fairlawn, N.J. 

6.5 Primary Mn standard, 1000 ppm (250 meq L-1). Certified Reference Solution, Fisher 

Chemical Scientific Co., Fairlawn, N.J. 

6.6 High calibration Al and Mn standard, 10 meq L-1 and 8 ppm, respectively. Pipet 22.476 

mL of primary Al standard into a 250-mL volumetric flask. Add 125.0 mL 2 N KCl 

solution to the flask and mix. Pipet 2.0 mL of primary Mn standard into flask and mix. 

Dilute to volume with DDI water. 

6.7 Calibration reagent blank solution, 1.0 N KCl. Add 125 mL of 2.0 N KCl to a volumetric 

flask and make to 250-mL volume with DDI water. Store in polypropylene container. 

6.8 Calibration Al and Mn check standard, 5 meq L-1 and 3.0 ppm, respectively. Pipet 11.24 

mL of primary Al standard into a 250-mL volumetric flask. Add 125.0 mL 2 N KCl 

solution to the flask and mix. Pipet 0.75 mL of primary Mn standard into flask and mix. 

Dilute to volume with DDI water. 

6.9 Dodecylbenzenesulfonic acid (DDBSA), tech 97%., 0.1 M. Dissolve 32.2 g DDBSA in 

1-L DDI water. 

6.10 DDBSA rinse solution. Dilute 40.0 mL 0.1 M DDBSA to 2-L volume with DDI water. 

6.11 Argon gas, purity 99.9% 

7. Procedure 

Extraction of Al and Mn

7.1 Prepare extraction vessel by tightly compressing a 1-g ball of filter pulp into the bottom of a 

syringe barrel with a modified plunger. 

7.2 Weigh exactly 2.50 g of <2-mm, air-dry soil and place in an extraction vessel. Prepare one 

quality control check sample per 48 samples. 

7.3 Place the extraction vessel on the upper disk of the extractor and connect a tared extraction 

syringe. Use 25.4-mm (1-in) length rubber tubing to insert the handle of the plunger in the slot 

of the stationary extractor disk. 

7.4 Use a squeeze bottle and fill extraction vessel to the 20-mL mark with 1.0 N KCl solution 

(≈ 10 mL). Make sure that the sample is thoroughly wetted. During the addition, wash sides of 

the tube and wet the sample. Shaking, swirling, or stirring may be required to wet organic 

samples. Allow sample to stand for at least 30 min. 

7.5 Put reservoir tube on top of the extraction vessel. Set extractor for fast extraction rate and 

extract until the KCl solution is at a 0.5- to 1.0-cm height above sample. Turn off extractor. 

502
7.6 Add 45 mL KCl solution to reservoir tube. Set extractor for 45-min extraction. 

7.7 After the extraction, shut off extractor and pull plunger of syringe down. Do not remove 

the plunger from syringe barrel. Carefully remove the syringe with extract leaving the rubber 

tubing on the extraction vessel. 

7.8 Weigh each syringe containing KCl extract to the nearest 0.01 g. 

7.9 Mix extract in each syringe by manually shaking. Fill a polycon with extract solution and 

discard the excess. This solution is reserved for extractable Al and Mn analyses. Dilution of Extracts and Standards

7.10 Set the digital settings at a 1:5 dilution for the KCl sample extracts, calibration reagent 

blanks, calibration standards, and calibration check standards as follows: 

7.11 Dilute 1 part KCl sample extract with 4 parts of DDI water (1:5 dilution). 

7.12 Dilute 1 part calibration reagent blank with 4 parts of DDI water (1:5 dilution). 

7.13 Dilute 1 part calibration standard with 4 parts of DDI water (1:5 dilution). 

7.14 Dilute 1 part calibration check standard with 4 parts of DDI water (1:5 dilution). 

7.15 Dispense the diluted solutions into test tubes and place in the sample holder of the sample 

changer. 

ICP Calibration

7.16 Use the calibration reagent blank (1.0 N KCl), high standard (10 meq L-1 Al and 8 ppm 

Mn), and the blank to calibrate the ICP. 

7.17 Use the calibration check standard (5 meq L-1 Al and 3 ppm Mn) as a check sample. 

Perform a calibration check every 12 samples. 

ICP Set-up and Operation 7.18 Refer to the manufacturer's manual for operation of the ICP. The following parameters 

are only very general guidelines for instrument conditions for the analytes. 

Parameter Value

Gas Flow 

 Torch Gas High Flow 

 Auxiliary Gas Flow Medium 1.0 LPM 

 Nebulizer Pressure 32 PSI 

RF Power 1150 

Analyte Wavelength High/Low Peak 

 (nm) Offset Offset 

Al 167.081 0/-21 -2 

Mn 257.610 0/-18 0 

7.19 Determine a set of 24 unknown samples for each successful calibration check. 

503
7.20 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.21 If a sample exceeds the calibration standard, dilute the sample (1:5) as follows. 

7.22 Analyze 4 quality control check sample for every 48 samples. 

8. Calculations 

8.1 The instrument readings are the analyte concentration (meq L-1 Al and ppm Mn) in 

undiluted extract. Use these values to calculate the analyte concentration on an oven-dry soil 

basis (meq 100 g-1). 

Analyte (meq 100 g-1) = [ICP x (Wtsyr+ext - Wtsyr) x D.R. x 100 x AD/OD]/[Sample Weight x 

1.0412 x 1000]

where: 

ICP = ICP analyte reading 

Wtsyr+ext = Weight of extraction syringe & extract (g) 

Wtsyr = Weight of tared extraction syringe (g) 

D.R. = Dilution ratio of samples over calibration range 

1.0412 = Density of 1 N KCl @ 20°C 

1000 = g L-1

100 = Conversion factor (100-g basis) 

AD/OD= Air-dry/oven-dry ratio (procedure 4B5) 

9. Report

Report KCl extractable Al and Mn in units of meq 100 g-1 of oven-dry soil to the 

nearest 0.01 meq 100 g-1. 

10. Precision

Precision data are not available for this procedure. 

11. References

Holmgren, George G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically 

controlled variable rate leaching device. Soil Sci. Amer. J. 41:1207-1208. 

Thomas, G.W. 1982. Exchangeable cations. In A. Klute (ed.) Methods of soil analysis. Part 

2. Chemical and microbiological properties. 2nd ed. Agronomy 9:159-165. 

Manganese and Aluminum (6G) 

KCl, Automatic Extractor (6G9) 

Atomic Absorption 

Thermo Jarrell Ash, Smith Hieftje 4000 

(6D3c and 6G9d)

1. Application 

The Al extracted by 1 N KCl approximates exchangeable Al and is a measure of the 

"active" acidity present in soils with a 1:1 water pH <5.5. Above pH 5.5, precipitation of Al 

occurs during analysis. This method does not measure the acidity component of hydronium 

ions (H3O+

). If Al is present in measurable amounts, the hydronium is a minor component of 

the active acidity. Because the 1 N KCl extractant is an unbuffered salt and usually affects the 

soil pH one unit or less, the extraction is determined at or near the soil pH. The KCl 

504
extractable Al is related to the immediate lime requirement and existing CEC of the soil. The 

"potential" acidity is better measured by the BaCl2-TEA method (procedure 6H5a) (Thomas, 

1982). 

2. Summary of Method 

A soil sample is leached with 1 N KCl using the mechanical vacuum extractor 

(Holmgren et al., 1977). The extract is weighed. The KCl extract is diluted with distilled 

deionized (DDI) water. The analytes are measured by an atomic absorption spectrophotometer. 

The data are automatically recorded by a microcomputer and printer. The Al and Mn are 

reported in meq 100 g-1 and mg kg-1 (ppm) ovendry soil in procedure 6D3c and 6G9d. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

AA analyses of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. 

The soil:extractant ratio must remain constant. A soil:extractant ratio of 1:10 (w:v) for 

batch procedures is most commonly used. Using a leaching technique, a 1:20 (w:v) ratio gives 

comparable results. If the sample is changed, the amount of extractable Al is changed. No 

other significant interferences have been identified for this procedure. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Follow standard laboratory practices when handling 

compressed gases. Gas cylinders should be chained or bolted in an upright position. Acetylene 

gas is highly flammable. Avoid open flames and sparks. Standard laboratory equipment 

includes fire blankets and extinguishers for use when necessary. Follow the manufacturer's 

safety precautions when using the AA. 

5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Mechanical vacuum extractor, 24 place, Centurion International, Inc., Lincoln, NE 

5.3 Mechanical vacuum extractor, Mavco Sampletex, 5300 N. 57th St., Lincoln, NE 

5.4 Syringes, polypropylene, disposable, 60 mL, for extraction vessel, extractant 

reservoir, and tared extraction syringe 

5.5 Rubber tubing, 3.2 ID x 6.4 OD x 25.4 mm, (1/8 ID x 1/4 OD x 1 in) for connecting 

syringe barrels 

5.6 Analytical filter pulp, ash-free, Schleicher and Schuell, No. 289 

5.7 Wash bottle, 20 mL, to dispense KCl. 

5.8 Polycons, Richards Mfg. Co. 

5.9 Atomic absorption spectrophotometer (AA), Smith-Hieftje Model 4000, Thermo Jarrell 

Ash Corp., Franklin, MA 

5.10 Autosampler, Model 150, Thermo Jarrell Ash Corp., Franklin, MA 

5.11 ThermoSpec software, Version 3.01, Enable 4.0, DOS 5.0, Thermo Jarrell Ash Corp., 

Franklin, MA 

5.12 Computer, CUi Advantage 486, Thermo Jarrell Ash Corp., Franklin, MA 

5.13 Printer, NEC Pinwriter P3200 

5.14 Single-stage regulator, acetylene service, part number E11-0-N511A, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 

5.15 Digital diluter/dispenser, MicroLab 500, Hamilton Co., P.O. Box 10030, Reno, NV 

5.16 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV 

5.17 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer, Curtin 

Matheson Scientific, Inc., Houston, TX 

505
5.18 Containers, polypropylene 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Potassium chloride solution (KCl), 1.0 N. Dissolve 1342 g of KCl reagent in 16 L DDI 

water. Allow solution to equilibrate to room temperature. Dilute to 18 L with DDI 

water. Use 1.0 N KCl solution for Al extraction. 

6.3 Potassium chloride solution (KCl), 2.0 N. Dissolve 298.24 g of KCl reagent in 1.5 L DDI 

water. Allow solution to equilibrate to room temperature. Dilute to 2 L with DDI water. 

Use 2.0 N KCl solution for standards. 

6.4 Primary Al standard, 1000 ppm. Certified Reference Solution, Fisher Chemical Scientific 

Co., Fairlawn, N.J. 

6.5 Primary Mn standard, 1000 ppm. Certified Reference Solution, Fisher Chemical 

Scientific Co., Fairlawn, N.J. 

6.6 High calibration Al (4 meq L-1) and Mn (3 ppm) standard. Mix 9 mL of primary Al 

standard with 125 mL 2 N KCl. Add 0.75 mL of primary Mn standard and make to 250-

mL volume with DDI water. 

6.7 Low calibration Al (0.2 meq L-1) and Mn (0.2 ppm) standard. Mix 1.8 mL of primary Al 

standard with 125 mL 2 N KCl. Add 0.05 mL of primary Mn standard and make to 250-

mL volume with DDI water. 

6.8 Calibration Al (2 meq L-1) and Mn (1.5 ppm) check standard. Mix 4.5 mL of primary Al 

standard with 125 mL 2 N KCl. Add 0.375 mL of primary Mn standard and make to 250-

mL volume with DDI water. 

6.9 Calibration reagent blank solution, 1.0 N KCl. Add 125 mL of 2.0 N KCl to a volumetric 

flask and make to 250-mL volume with DDI water. 

6.10 Nitrous oxide gas, compressed 

6.11 Acetylene gas, compressed, purity 99.6% 

6.12 Compressed air with water and oil traps 

7. Procedure

Extraction of Al 

7.1 Prepare extraction vessel by tightly compressing a 1-g ball of filter pulp into the bottom of a 

syringe barrel with a modified plunger. 

7.2 Weigh exactly 2.50 g of <2-mm, air-dry soil and place in an extraction vessel. Prepare one 

quality control check sample per 48 samples. 

7.3 Place the extraction vessel on the upper disk of the extractor and connect a tared extraction 

syringe. Use 25.4-mm (1-in) length rubber tubing to insert the handle of the plunger in the slot 

of the stationary extractor disk. 

7.4 Use a squeeze bottle and fill extraction vessel to the 20-mL mark with 1.0 N KCl solution 

(≈10 mL). Make sure that the sample is thoroughly wetted. During the addition, wash sides of 

the tube and wet the sample. Shaking, swirling, or stirring may be required to wet organic 

samples. Allow sample to stand for at least 30 min. 

7.5 Put reservoir tube on top of the extraction vessel. Set extractor for fast extraction rate and 

extract until the KCl solution is at a 0.5- to 1.0-cm height above sample. Turn off extractor. 

7.6 Add 45 mL KCl solution to reservoir tube. Set extractor for 45-min extraction. 

506
7.7 After the extraction, shut off extractor and pull plunger of syringe down. Do not remove 

the plunger from syringe barrel. Carefully remove the syringe with extract leaving the rubber 

tubing on the extraction vessel. 

7.8 Weigh each syringe containing KCl extract to the nearest 0.01 g. 

7.9 Mix extract in each syringe by manually shaking. Fill a polycon with extract solution and 

discard the excess. This solution is reserved for extractable Al and Mn analyses. 

Dilution of Sample Extracts and Standards

7.10 No ionization suppressant is required as the K in the extractant is present in sufficient 

quantity. Set the digital settings at a 1:2 dilution for the KCl sample extracts, calibration 

reagent blanks, calibration standards, and calibration check standards as follows: 

7.11 Dilute 1 part KCl sample extract with 1 part of DDI water (1:2 dilution). 

7.12 Dilute 1 part calibration reagent blank with 1 part of DDI water (1:2 dilution). 

7.13 Dilute 1 part calibration standard with 1 part of DDI water (1:2 dilution). 

7.14 Dilute 1 part calibration check standard with 1 part of DDI water (1:2 dilution). 

7.15 Dispense the diluted solutions into test tubes and place in the sample holder of the sample 

changer. 

AA Calibration

7.16 Use the calibration reagent blank (1.0 N KCl), high standard (4 meq L-1 Al and 3 ppm 

Mn), and the low standard (2 meq L-1 Al and 1.5 ppm Mn) to calibrate the AA. 

7.17 Use the calibration check standard (2 meq L-1 Al and 1.5 ppm Mn) as a check sample. 

Perform a calibration check every 12 samples. 

AA Set-up and Operation 

7.18 Refer to the manufacturer's manual for operation of the AA. The following parameters are 

only very general guidelines for instrument conditions for the analyte. 

Element Wavelength Burner head 

& Angle 

Fuel/ 

Oxidant 

(nm) 

Al 309.3 5-cm 

parallel 

20 C2H2/ 

10 N2O 

Mn 280.1 5-cm 

parallel 

4 C2H2/ 

16 Air 

Typical read delay is 6 s, and integration by peak area is 8 s. 

7.19 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.20 If a sample exceeds the calibration standard, dilute the sample (dilution ratio in 

calculation) with appropriate matrix and record dilution. Remember to keep the matrix the 

same after dilution by diluting with DDI water (1:2 dilution). 

507
7.21 Analyze one quality control check sample for every 48 samples. 

8. Calculations

8.1 The instrument readings are the analyte concentration (meq L-1 Al) in undiluted extract. 

Use these values to calculate the analyte concentration on an oven-dry soil basis (meq 100 g-1). 

Al (meq 100 g-1) = [AAAl x (Wtsyr+ext - Wtsyr) x D.R. x 100 x AD/OD]/[Sample Weight (g) x 

1.0412 x 1000]

where: 

AAAl = AA Al reading (meq L-1) 

Wtsyr+ext= Weight of extraction syringe and extract (g) 

Wtsyr = Weight of tared extraction syringe (g) 

D.R. = Dilution ratio for samples over calibration range 

1.0412 = Density of 1 N KCl @ 20°C 

1000 = g L-1

100 = Conversion factor (100-g basis) 

AD/OD= Air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report KCl extractable Al in units of meq 100 g-1 of oven-dry soil to the nearest 0.1 

meq 100 g-1. 

10. Precision 

Precision data are not available for this procedure. A quality control check sample is 

run with every batch of 48 samples. 

11. References 

Holmgren, George G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically 

controlled variable rate leaching device. Soil Sci. Amer. J. 41:1207-1208. 

Thomas, G.W. 1982. Exchangeable cations. In A. Klute (ed.) Methods of soil analysis. Part 

2. Chemical and microbiological properties. 2nd ed. Agronomy 9:159-165. 

Chloride, Sulfate, Nitrate, Fluoride, and Nitrite (6K, 6L, 6M, 6U, and 6W) Saturation Extract (6K1, 6L1, 6M1, 6U1, and 6W1) Chromatograph, Anion Suppressor 

Dionex 2110i Ion Chromatograph (6K1d, 6L1d, 6M1d, 6U1b, and 6W1b) 

1. Application 

The soluble anions that are commonly determined in saline and alkali soils are 

carbonate, bicarbonate, sulfate, chloride, nitrate, nitrite, fluoride, phosphate, silicate, and borate 

(Khym, 1974; U.S. Salinity Laboratory Staff, 1954). Carbonate and bicarbonate are 

determined by titration. Phosphate, silicate, and borate usually are not determined because they 

are found only occasionally in measurable amounts in soils. Chloride, sulfate, nitrate, fluoride, 

and nitrite are measured in solution by chromatography. In saline and alkali soils, carbonate, 

bicarbonate, sulfate, and chloride are the anions that are found in the greatest abundance. In 

general, soluble sulfate is usually more abundant than soluble chloride. 

508
2. Summary of Method 

The saturation extract is diluted according to its electrical conductivity (ECs). The 

diluted sample is injected into the ion chromatograph, and the anions are separated. A 

conductivity detector is used to measure the anion. A chart recording is made of the 

chromatograph. Standard anions are used to calibrate the system. A calibration curve is 

determined, and the anion concentrations are calculated. A computer program automates these 

actions. The saturated extract anions, Cl-, SO4

2-, NO3-

, F-, and NO2

-

 are reported in meq L-1 in 

procedures 6K1d, 6L1d, 6M1d, 6U1b, and 6W1b, respectively. 

3. Interferences 

Some saturation extracts contain suspended solids. Filtering after dilution removes the 

particles. Saturation extracts of acid soils that contain Fe and/or Al may precipitate and clog 

the separator column. Saturation extracts of very high pH may contain organic material which 

may clog or poison the column. Low molecular weight organic anions will co-elute with 

inorganic anions from the column. 

4. Safety 

Wear protective clothing and safety glasses. When preparing reagents, exercise special 

care. Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash 

hands after handling these metal salts. Follow the manufacturer's safety precautions when 

using the chromatograph. 

5. Equipment 

5.1 Ion chromatograph, Series 2110i, dual-channel system 

5.2 Analytical column, AS4A 4mm P/N 37041, Dionex Corp., 1228 Titan Way, Sunnyvale, 

CA 

5.3 Guard column, AG4A 4mm P/N 37042, Dionex Corp., 1228 Titan Way, Sunnyvale, CA 

5.4 Analytical pumps, Dionex Corp., 1228 Titan Way, Sunnyvale, CA 

5.5 Automated sampler, Dionex Corp., 1228 Titan Way, Sunnyvale, CA 

5.6 Conductivity detectors, Dionex Corp., 1228 Titan Way, Sunnyvale, CA 

5.7 Anion self-regenerating suppressor (ASRS-1) with controller (SRC-1), Dionex Corp., 

1228 Titan Way, Sunnyvale, CA 

5.8 Computer interfaces, Dionex Corp., 1228 Titan Way, Sunnyvale, CA 

5.9 Computer software, A1-450 Chromatography Software Program Release 3.32, Microsoft 

Windows Operating Environment; Dionex Corp., 1228 Titan Way, Sunnyvale, CA 

5.10 Computer, DFI. 

5.11 Printer, Epson, Fx-850 

5.12 Poly-vials, 5 mL, P/N 038008, Dionex Corp., 1228 Titan Way, Sunnyvale, CA 

5.13 Poly-vials, filtercaps, 5 mL, P/N 038009, Dionex Corp., 1228 Titan Way, Sunnyvale, CA 

5.14 Digital diluter/dispenser, MicroLab 500, Hamilton C., P.O. Box 10030, Reno, NV 

5.15 Syringes, gas tight, Hamilton 1001 DX and 1010-TEF LL, Hamilton Co., P.O. Box 

10030, Reno, NV 

5.16 Disposable 0.2-μm pore size, 25-mm filter assembly, Gelman Sciences, Inc., 674 South 

Wagner Road, Ann Arbor, MI 48106. Use for saturation extracts and standards. 

5.17 Disposable 0.2-μm pore size, Ultipor N66 DFA3001NAEY, Pall Trinity Micro Corp., 

Cortland, NY. Use for filtering distilled deionized (DDI) water. 

6. Reagents 

6.1 Distilled deionized (DDI) filtered water 

6.2 Sulfuric acid (H2SO4), concentrated, reagent 

6.3 Toluene 

6.4 Isopropanol to de-gas column 

6.5 Stock NaHCO3 solution, 0.480 M. Mix 40.34 g of dried NaHCO3 with filtered DDI water 

and dilute to 1-L volume. 

509
6.6 Stock Na2CO3 solution, 0.5040 M. Mix 53.42 g of dried Na2CO3 with filtered DDI water 

and dilute to 1-L volume. 

6.7 Working eluent solution. Mix 100 mL of 0.5040 M NaHCO3 and 100 mL of 0.4800 M

Na2CO3 with filtered DDI water and dilute to 20-L volume. Add 8 drops of toluene to 

retard microbial growth. 

6.8 Primary SO4

2- standard, 0.5 M (1.0 N). Mix 17.7560 g of Na2SO4 with filtered DDI water 

and dilute to 250-mL volume. 

6.9 Primary Cl- standard, 1.0 M (1.0 N). Add 18.6392 g of KCl with filtered DDI water and 

dilute to 250-mL volume. 

6.10 Primary F- standard, 0.125 M (0.125 N). Add 1.3122 g of NaF with filtered DDI water 

and dilute to 250-mL volume. 

6.11 Primary NO3

-

 standard, 1.0 M (1.0 N). Add 25.2770 g of KNO3 with filtered DDI water 

and dilute to 250-mL volume. 

6.12 Primary mixed standard. Prepare 1 primary mixed standard by taking aliquots of each of 

the proceeding primary standards and diluting the combined aliquots to a 1-L volume 

with working eluent as follows: 

Primary Aliquot Final Concentration 

Standards Volume 

 w/Eluent 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 mL mL meq L-1

Na2SO4 50 1000 50 

KCl 10 1000 10 

NaF 100 1000 12.5 

KNO3 30 1000 30 

Add eight drops of toluene to primary mixed standard to retard microbial growth and store in a 

glass container. 

6.13 Mixed calibration standards. Prepare 4 mixed calibration standards (0.5, 1.0, 3.0, and 7.0 

readings) by taking aliquots of primary mixed standard and diluting each aliquot to 100-

mL volume with working eluent as follows: 

Primary Final Concentration 

Mixed Volume 

Standards w/Eluent SO4

2- Cl-

 F- NO3

-

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ 

 mL mL meq L-1

0.5 100 0.25 0.05 0.0625 0.15 

1.0 100 0.50 0.10 0.125 0.30 

3.0 100 1.5 0.30 0.375 0.90 

7.0 100 3.5 0.70 0.875 2.1 

6.14 NaNO2, Baker reagent grade, 99.5% purity 

6.15 Primary NO2

-

 standard, 1 N (1000 meq L-1). Mix 69.3568 g of reagent grade NaNO2 with 

filtered DDI water and dilute to 1-L volume. Take 5 mL aliquot of primary NO2

-

standard and dilute with 500 mL of filtered DDI water (10 meq L -1). Add eight drops of 

toluene to primary NO2

-

 standard to retard microbial growth and store in a glass 

container. 

510
6.16 NO2

-

 calibration standards. Prepare 4 NO2

-

 calibration standards (0.5, 1.0, 3.0, and 7.0 

readings) by taking aliquots of primary NO2

-

 standard (10 meq L-1) and diluting each 

aliquot to 100-mL volume with working eluent as follows: 

Primary Final NO2- Concentration 

Standard Volume 

meq L-1 w/Eluent ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 mL mL meq L-1

0.5 100 0.5 

1.0 100 1.0 

3.0 100 3.0 

7. Procedure 

Dilution of extracts 

7.1 To estimate the total soluble anion concentration (meq L-1), multiply the ECs (procedure 

8A3a) by 10. Subtract the CO3

2- and HCO3-

 concentrations (procedures 6I1b and 6J1b) from 

the total anion concentration. The remainder is the ≈ concentration (meq L-1) of anions to be 

separated by ion chromatography. 

Anion concentration (meq L-1) = ECs x 10 - (HCO3

-

 + CO3

2-) 

7.2 Refer to Table 1 for dilution of saturation extract with the working eluent. 

7.3 Place the diluted samples in the Poly-vials and cap with filtercaps. 

7.4 Place the mixed calibration standards in the Poly-vials. 

Set-up and Operation of Ion Chromatograph (IC) 

7.5 Because any number of factors may cause a change in IC operating conditions, only a 

general set-up of the Dionex 2110i ion chromatograph is presented. Individual analysts may 

modify some or all of the operating conditions to achieve satisfactory results. Typical 

operation parameters are as follows: 

 Parameter Range 

Conductivity cell range 3 uS cm-1 full scale to 

100 uS cm-1

Auto offset "On" 

Analytical pump flow rate 2.0 to 2.5 mL min-1

Low pressure limit 100 psi 

High pressure limit 1200 psi 

Regenerant flow rate 3 to 4 mL min-1

Injector loop 0.50 mL 

Air pressure 3 to 8 psi 

7.6 Load the sample holder cassettes with the capped samples, standards, and check samples. 

7.7 Refer to the manufacturer's manual for the operation of chromatograph. 

511
8. Calculations 

Calibration Calculations

8.1 Use the peak height of each anion standard to either construct a calibrated curve to plot 

anion concentration or use a least squares analysis to calculate anion concentration. The 

analytes are reported in meq L-1. 

8.2 Calibration Curve: Plot the peak height against the meq L-1 of each anion standard on graph 

paper. Construct the calibration curve by finding the "best" line that fits the plotted standards. 

8.3 Linear Squares Analysis: Use a least squares criterion, i.e. best moving average. Refer to a 

statistical analysis book for additional information on least squares analysis. An example for 

the anion Cl- is as follows: 

Cl- concentration (meq L-1) = Y = 0.1 1.5 4.0 

Peak height = X = 8.43 170.0 441.5 

Number of standards = n = 3 

∑Yi = 5.6 ∑Xi = 619.93 

∑Yi/n = Y = 1.866 ∑Xi/n = X = 206.6433 

∑XiYi = 2021.843 ∑Xi

2

 = 223893.31 

∑Xi∑Yi = 3471.608 

b = ∑XiYi - ∑Xi∑Yi/n 2021.843 - 1157.2027 ⎯⎯⎯⎯⎯⎯⎯ = ⎯⎯⎯⎯⎯⎯⎯⎯⎯ = 0.0090265 

∑Xi

2

 - (∑Xi)

2

/n 223893.31 - 128104.4 

b = slope of the line, i.e., the amount that Y changes when X changes by 1 unit. 

The equation is as follows: 

Y = Y + b (X - X) 

Y = 1.866 + 0.0090265 (X) - 1.8653 

Analyte Calculation

8.4 Calibration curve: Read the analyte concentration (meq L-1) directly from the calibration 

curve. 

512
Table 1. Dilution factor for saturated paste soil extracts based on EC readings.

ECs (mmhos cm-1) Dilution Factor 

 

 0.00 to 0.55 4 

 0.56 to 0.65 5 

 0.66 to 0.75 6 

 0.76 to 0.85 7 

 0.86 to 0.95 8 

 0.96 to 1.05 9 

 1.06 to 1.20 10 

 1.21 to 1.40 15 

 1.41 to 1.50 25 

 1.51 to 1.60 30 

 1.61 to 1.80 40 

 1.81 to 2.00 50 

 2.01 to 2.30 60 

 2.31 to 2.60 70 

 2.61 to 3.10 80 

 3.11 to 3.55 90 

 3.56 to 4.05 100 

 4.06 to 4.60 120 

 4.61 to 5.20 140 

 5.21 to 5.85 150 

 5.86 to 6.55 160 

 6.56 to 7.30 180 

 7.31 to 8.00 200 

 8.01 to 9.00 225 

 9.01 to 10.00 240 

 10.01 to 11.50 270 

 11.51 to 13.00 280 

 13.01 to 14.50 300 

 14.51 to 16.00 320 

 16.01 to 17.00 360 

 17.01 to 18.00 400 

 18.01 to 20.00 450 

 20.01 to 21.00 480 

 21.01 to 23.00 500 

 23.01 to 24.00 540 

 24.01 to 25.00 560 

 25.01 to 27.00 600 

 27.01 to 28.00 640 

 28.01 to 30.00 680 

 30.01 to 32.00 700 

 32.01 to 33.00 720 

 33.01 to 36.00 800 

 36.01 to 40.00 900 

 40.01 to 44.00 1000 

513
8.5 Linear regression: Put the peak height in the preceding equation and solve for analyte 

concentration (meq L-1). Thus, if sample extract has 204 peak height, the preceding equation is 

as follows: 

Y = 1.866 + 0.0090265 (204) - 1.8653 = 1.84 meq L-1 

8.6 Repeat the calibration set and analyte calculation for each anion. 

8.7 The chromatograph software automatically calculates the analyte concentrations and prints 

a report of the results. 

9. Report

Report the saturation extract anions in units of meq L-1 to the nearest 0.1 meq L-1. 

10. Precision 

Precision data are not available for this procedure. 

11. References

Khym, J.X. 1974. Analytical ion-exchange procedures in chemistry and biology: theory, 

equipment, techniques. Prentice-Hall, Inc., Englewood Cliffs, NJ. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. U.S. Dept. of Agric. Handb. 60. U.S. Govt. Print. Office, 

Washington, DC. 

Calcium, Magnesium, Sodium, and Potassium 

(6N, 6O, 6P, and 6Q) 

Saturation Extraction 

(6N1, 6O1, 6P1, and 6Q1) 

Atomic Absorption 

Perkin-Elmer AA 5000 

(6N1b, 6O1b, 6P1b, and 6Q1b)

1. Application

The commonly determined soluble cations are Ca2+, Mg2+, Na+, and K+. In soils with a 

low saturation pH, measurable amounts of Fe and Al may be present. Determination of soluble 

cations is used to obtain the relations between total cation concentration and other properties of 

saline solutions such as electrical conductivity and osmotic pressure (U.S. Salinity Laboratory 

Staff, 1954). The relative concentrations of the various cations in the soil-water extracts also 

provide information on the composition of the exchangeable cations in the soil. Complete 

analyses of the soluble ions provide a means to determine total salt content of the soils and salt 

content at field-moisture conditions. 

2. Summary of Method

The saturation extract from procedure 8A3a is diluted with an ionization suppressant 

(LaC13). The analytes are measured by an atomic absorption spectrophotometer (AA). The 

data are automatically recorded by a microcomputer and printer. The saturation extracted 

cations, Ca2+, Mg2+, Na+, and K+, are reported in meq L-1 in procedures 6N1b, 6O1b, 6P1b, and 

6Q1b, respectively. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

analysis of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. 

514
4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Thoroughly wash hands after handling these metal salts. 

Follow standard laboratory procedures when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene is highly flammable. Avoid open 

flames and sparks. Standard laboratory equipment includes fire blankets and extinguishers for 

use when necessary. Follow the manufacturer's safety precautions when using the AA. 

5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Filter paper, pre-pleated, 185-mm diameter, Schleicher and Schuell 

5.3 Atomic absorption spectrophotometer (AA), model 5000, Perkin-Elmer Corp., Norwalk, 

CT 

5.4 Automatic burner control, model 5000, Perkin-Elmer Corp., Norwalk, CT 

5.5 Autosampler, AS-50, Perkin-Elmer Corp., Norwalk, CT 

5.6 Dot matrix printer, P-132, Interdigital Data Systems,Inc. 

5.7 Single-stage regulator, acetylene service, part number E11-0-N511A, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 

5.8 Digital diluter/dispenser, MicroLab 500, Hamilton Co., P.O. Box 10030, Reno, NV 

5.9 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV 

5.10 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer, Curtin 

Matheson Scientific, Inc., Houston, TX 

5.11 Containers, polypropylene 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Hydrochloric acid (HCl), concentrated 12 N

6.3 HCl, 1:1 HCl:DDI, 6 N. Carefully mix 1 part of concentrated HCl to 1 part DDI water. 

6.4 HCl, 1% wt. Carefully dilute 25 mL of concentrated HCl to 1 L with DDI water. 

6.5 NH4OH, reagent grade, sp gr 0.90 

6.6 Glacial acetic acid, 99.5% 

6.7 Primary stock mixed standards solution (PSMSS). Dissolve 0.8759 g of oven-dry reagent 

grade calcium carbonate (CaCO3) in a minimum of volume of 1:1 HCl:DDI. Add 0.2127 

g of clean Mg ribbon dissolved in 1:1 HCl. Add 1.0956 g of dry reagent grade sodium 

chloride (NaCl) and 0.1864 g of dry reagent grade KCl. Transfer to a 250-mL volumetric 

and bring to volume with 1% HCl solution. Resulting solution contains 70 meq L-1 (1403 

ppm) Ca; 70 meq L-1 (851 ppm) Mg; 75 meq L-1 (1724 ppm) Na; 10 meq L-1 (391 ppm) 

K. Store in a polypropylene container. 

6.8 NH4OAc solution, 1.0 N, pH 7.0, reagent blank. Mix 57 mL of glacial acetic acid in 600 

mL DDI water. While stirring, carefully add 68 mL concentrated of NH4OH. Cool and 

adjust pH to 7.0 using NH4OH or acetic acid. Dilute to 1 L with DDI water. The 

NH4OAc solution is used for extraction of cations (procedure 5A8c). 

6.9 Working stock mixed standards solution (WSMSS). Dilute 20 mL of the PSMSS with 

80 mL DDI water (1:5). Resulting solution contains 14 meq L-1 (281 ppm) Ca; 14 meq L1

 (170 ppm) Mg; 15 meq L-1 (345 ppm Na); 2 meq L-1 (78 ppm) K. Store in a 

polypropylene container. 

6.10 Stock lanthanum ionization suppressant solution, 65,000 ppm. Wet 152.4 g of lanthanum 

oxide (La2O3) with 100 mL DDI water. Slowly and cautiously add 500 mL of 6 N HCl to 

dissolve the La2O3. Cooling the solution is necessary. Dilute to 2 L with DDI water. 

Filter solution. Store in polypropylene container. 

515
6.11 Lanthanum ionization suppressant solution, 6500 ppm. Dilute 200 mL of stock 

lanthanum ionization suppressant solution with 1800 mL of DDI water (1:10). Store in 

polypropylene container. 

6.12 Dilute calibration mixed standards solution (DCMSS). Dilute 1 part of the WSMSS with 

39 parts of the lanthanum solution (1:40). Resulting solution contains 0.35 meq L-1 (7 

ppm) Ca; 0.35 meq L-1 (4 ppm) Mg; 0.375 meq L-1 (9 ppm) Na; 0.05 meq L-1 (2 ppm) K. 

Store in polypropylene container. 

6.13 Dilute calibration reagent blank solution (DCRBS). Dilute 1 part of DDI water with 39 

parts of the lanthanum solution (1:40). Store in polypropylene container. 

6.14 Compressed air with water and oil traps. 

6.15 Acetylene gas, purity 99.6%. 

7. Procedure 

Dilution of Sample Extracts and Standards 

7.1 The 10-mL syringe is for diluent (lanthanum ionization suppressant solution). The 1-mL 

syringe is for saturation sample extracts (procedure 8A3a), calibration reagent blanks, and 

calibration standards. Set the digital diluter at 1:40 dilution for saturation sample extracts, 

reagent blanks, and calibration standards as follows: 

7.2 Dilute 1 part saturation sample extract with 39 parts of lanthanum ionization suppressant 

solution (1:40 dilution). 

7.3 Dilute 1 part WSMSS with 39 parts of lanthanum ionization suppressant solution (1:40 

dilution). This dilution is the DCMSS. Refer to reagents section. 

7.4 Dilute 1 part DDI water with 39 parts of lanthanum ionization suppressant solution (1:40 

dilution). This dilution is the DCRBS. Refer to reagents section. 

7.5 Dispense the diluted solutions into test tubes which have been placed in the sample holders 

of the sample changer. 

AA Calibration 

7.6 Use the DCRBS and the DCMSS to calibrate the AA. The AA program requires a blank 

and a standard, in that order, to establish a single point calibration curve for element 

determination. Perform one calibration, i.e., blank plus standard, for every 12 samples. 

AA Set-up and Operation 

7.7 Refer to the manufacturer's manual for operation of the AA. The following are only very 

general guidelines for instrument conditions for the various analytes. 

Analyte Conc. 

meq/L 

Burner & 

Angle 

Wavelength Slit Fuel/ 

Oxidant 

C2H2/ Air 

Ca 14.00 50cm 

@ 0°

422.7 0.7 10/25 

Mg 14.00 50 cm 

@ 30°

285.2 0.7 10/25 

K 2.00 50 cm 

@ 0°

766.5 1.4 10/25 

Na 15.00 50 cm 

@ 30°

589.0 0.4 10/25 

516
7.8 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.9 If sample exceeds calibration standard, dilute the sample (dilution ratio in calculation) with 

appropriate matrix and record dilution. Remember to keep the matrix the same after dilution by 

diluting with the lanthanum ionization suppressant solution (1:40 dilution). 

7.10 Analyze one quality control check sample for every 48 samples. 

7.11 The instrument readings are usually programmed in meq L-1. Record analyte readings to 

0.01 meq L-1. 

8. Calculations

8.1 The instrument readings are the analyte concentration (meq L-1 cation) in undiluted extract. 

Use these values and dilution ratio (if any) and calculate the analyte concentration in meq L-1

cation. 

Analyte Concentration in Soil (meq L-1) = Analyte AA reading (meq L-1) x Dilution ratio (if 

any) 

9. Report 

Report the saturation extraction cations of Ca2+, Mg2+, Na+

, and K+ in units of meq L-1

to the nearest 0.1 meq L-1. 

10. Precision

Precision data are not available for this procedure. 

11. References

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. U.S. Dept. of Agric. Handb. 60. U.S. Govt. Print. Office, 

Washington, DC. 

Calcium, Magnesium, Sodium, and Potassium 

(6N, 6O, 6P, and 6Q) 

Saturation Extraction 

(6N1, 6O1, 6P1, and 6Q1) 

Atomic Absorption 

Thermo Jarrell Ash, Smith-Hieftje AA 4000 (6N1c, 6O1c, 6P1c, and 6Q1c)

1. Application

The commonly determined soluble cations are Ca2+, Mg2+, Na+, and K+. In soils with a 

low saturation pH, measurable amounts of Fe and Al may be present. Determination of soluble 

cations is used to obtain the relations between total cation concentration and other properties of 

saline solutions such as electrical conductivity and osmotic pressure (U.S. Salinity Laboratory 

Staff, 1954). The relative concentrations of the various cations in the soil-water extracts also 

provide information on the composition of the exchangeable cations in the soil. Complete 

analyses of the soluble ions provide a means to determine total salt content of the soils and salt 

content at field-moisture conditions. 

2. Summary of Method

The saturation extract from procedure 8A3a is diluted with an ionization suppressant 

(LaC13). The analytes are measured by an atomic absorption spectrophotometer (AA). The 

517
data are automatically recorded by a microcomputer and printer. The saturation extracted 

cations, Ca2+, Mg2+, Na+, and K+, are reported in meq L-1 in procedures 6N1c, 6O1c, 6P1c, and 

6Q1c, respectively. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

analysis of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Thoroughly wash hands after handling these metal salts. 

Follow standard laboratory procedures when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene is highly flammable. Avoid open 

flames and sparks. Standard laboratory equipment includes fire blankets and extinguishers for 

use when necessary. Follow the manufacturer's safety precautions when using the AA. 

5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Filter paper, pre-pleated, 185-mm diameter, Schleicher and Schuell 

5.3 Atomic absorption spectrophotometer (AA), Smith-Hieftje Model 4000, Thermo Jarrell 

Ash Corp., Franklin, MA 

5.4 Autosampler, Model 150, Thermo Jarrell Ash Corp., Franklin, MA 

5.5 ThermoSpec software, Version 3.01, Enable 4.0, DOS 5.0, Thermo Jarrell Ash Corp., 

Franklin, MA 

5.6 Computer, CUi Advantage 486, Thermo Jarrell Ash Corp., Franklin, MA 

5.7 Printer, NEC Pinwriter P3200 

5.8 Single-stage regulator, acetylene service, part number E11-0-N511A, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 

5.9 Digital diluter/dispenser, MicroLab 500, Hamilton Co., P.O. Box 10030, Reno, NV 

5.10 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV 

5.11 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer, Curtin 

Matheson Scientific, Inc., Houston, TX 

5.12 Containers, polypropylene 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Hydrochloric acid (HCl), concentrated 12 N

6.3 HCl, 1:1 HCl:DDI, 6 N. Carefully mix 1 part of concentrated HCl to 1 part DDI water. 

6.4 HCl, 1% wt. Carefully dilute 25 mL of concentrated HCl to 1 L with DDI water. 

6.5 NH4OH, reagent grade, sp gr 0.90 

6.6 Glacial acetic acid, 99.5% 

6.7 Primary stock mixed standards solution (PSMSS). Dissolve 0.8759 g of oven-dry reagent 

grade calcium carbonate (CaCO3) in a minimum of volume of 1:1 HCl:DDI. Add 0.2127 

g of clean Mg ribbon dissolved in 1:1 HCl. Add 1.0956 g of dry reagent grade sodium 

chloride (NaCl) and 0.1864 g of dry reagent grade KCl. Transfer to a 250-mL volumetric 

and bring to volume with 1% HCl solution. Resulting solution contains 70 meq L-1 (1403 

ppm) Ca; 70 meq L-1 (851 ppm) Mg; 75 meq L-1 (1724 ppm) Na; 10 meq L-1 (391 ppm) 

K. Store in a polypropylene container. 

6.8 NH4OAc solution, 1.0 N, pH 7.0, reagent blank. Mix 57 mL of glacial acetic acid in 600 

mL DDI water. While stirring, carefully add 68 mL concentrated of NH4OH. Cool and 

518
adjust pH to 7.0 using NH4OH or acetic acid. Dilute to 1 L with DDI water. The 

NH4OAc solution is used for extraction of cations (procedure 5A8c). 

6.9 Working stock mixed standards solution (WSMSS). Dilute 20 mL of the PSMSS with 

80 mL DDI water (1:5). Resulting solution contains 14 meq L-1 (281 ppm) Ca; 14 meq L1

 (170 ppm) Mg; 15 meq L-1 (345 ppm Na); 2 meq L-1 (78 ppm) K. Store in a 

polypropylene container. 

6.10 Stock lanthanum ionization suppressant solution, 65,000 ppm. Wet 152.4 g of lanthanum 

oxide (La2O3) with 100 mL DDI water. Slowly and cautiously add 500 mL of 6 N HCl to 

dissolve the La2O3. Cooling the solution is necessary. Dilute to 2 L with DDI water. 

Filter solution. Store in polypropylene container. 

6.11 Lanthanum ionization suppressant solution, 6500 ppm. Dilute 200 mL of stock 

lanthanum ionization suppressant solution with 1800 mL of DDI water (1:10). Store in 

polypropylene container. 

6.12 Dilute calibration mixed standards solution (DCMSS). Dilute 1 part of the WSMSS with 

39 parts of the lanthanum solution (1:40). Resulting solution contains 0.35 meq L-1 (7 

ppm) Ca; 0.35 meq L-1 (4 ppm) Mg; 0.375 meq L-1 (9 ppm) Na; 0.05 meq L-1 (2 ppm) K. 

Store in polypropylene container. 

6.13 Dilute calibration reagent blank solution (DCRBS). Dilute 1 part of DDI water with 39 

parts of the lanthanum solution (1:40). Store in polypropylene container. 

6.14 Compressed air with water and oil traps. 

6.15 Acetylene gas, purity 99.6%. 

7. Procedure 

Dilution of Sample Extracts and Standards 

7.1 The 10-mL syringe is for diluent (lanthanum ionization suppressant solution). The 1-mL 

syringe is for saturation sample extracts (procedure 8A3a), calibration reagent blanks, and 

calibration standards. Set the digital diluter at 1:40 dilution for saturation sample extracts, 

reagent blanks, and calibration standards as follows: 

7.2 Dilute 1 part saturation sample extract with 39 parts of lanthanum ionization suppressant 

solution (1:40 dilution). 

7.3 Dilute 1 part WSMSS with 39 parts of lanthanum ionization suppressant solution (1:40 

dilution). This dilution is the DCMSS. Refer to reagents section. 

7.4 Dilute 1 part DDI water with 39 parts of lanthanum ionization suppressant solution (1:40 

dilution). This dilution is the DCRBS. Refer to reagents section. 

7.5 Dispense the diluted solutions into test tubes which have been placed in the sample holders 

of the sample changer. 

AA Calibration 

7.6 Use the DCRBS and the DCMSS to calibrate the AA. The AA program requires a blank 

and a standard, in that order, to establish a single point calibration curve for element 

determination. Perform one calibration, i.e., blank plus standard, for every 12 samples. 

AA Set-up and Operation 

7.7 Refer to the manufacturer's manual for operation of the AA. The following are only very 

general guidelines for instrument conditions for the various analytes. 

519
Analyte Conc. 

meq/L 

Burner & 

Angle 

Wavelength Slit Fuel/ 

Oxidant 

C2H2/ 

Air 

Ca 14.00 50cm 

@ 0°

422.7 0.7 10/25 

Mg 14.00 50 cm 

@ 30°

285.2 0.7 10/25 

K 2.00 50 cm 

@ 0°

766.5 1.4 10/25 

Na 15.00 50 cm 

@ 30°

589.0 0.4 10/25 

7.8 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.9 If sample exceeds calibration standard, dilute the sample (dilution ratio in calculation) with 

appropriate matrix and record dilution. Remember to keep the matrix the same after dilution by 

diluting with the lanthanum ionization suppressant solution (1:40 dilution). 

7.10 Analyze one quality control check sample for every 48 samples. 

7.11 The instrument readings are usually programmed in meq L-1. Record analyte readings to 

0.01 meq L-1. 

8. Calculations

8.1 The instrument readings are the analyte concentration (meq L-1 cation) in undiluted extract. 

Use these values and dilution ratio (if any) and calculate the analyte concentration in meq L-1

cation. 

Analyte Concentration in Soil (meq L-1) = Analyte AA reading (meq L-1) x Dilution ratio (if 

any) 

9. Report 

Report the saturation extraction cations of Ca2+, Mg2+, Na+

, and K+ in units of meq L-1

to the nearest 0.1 meq L-1. 

10. Precision

Precision data are not available for this procedure. 

11. References

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. U.S. Dept. of Agric. Handb. 60. U.S. Govt. Print. Office, 

Washington, DC. 

520
Calcium, Magnesium, Sodium, and Potassium 

(6N, 6O, 6P, and 6Q) 

NH4OAC Extraction 

(6N2, 6O2, 6P2, and 6Q2) 

Atomic Absorption 

Perkin-Elmer AA 5000 

(6N2e, 6O2d, 6P2b, and 6Q2b) 

1. Application 

The extractable bases (Ca2+, Mg2+, Na+, and K+) from the NH4OAC extraction 

(procedure 5A8c) are generally assumed to be those exchangeable bases on the cation exchange 

sites of the soil. The abundance of these cations usually occurs in the sequence of Ca2+ > Mg2+

> K+ > Na+. Deviation from this usual order signals that some factor or factors, e.g., free 

CaCO3 or gypsum, serpentine (high Mg2+), or natric material (high Na+), have altered the soil 

chemistry. The most doubtful cation extractions with this method are Ca2+ in the presence of 

free CaCO3 or gypsum and K+ in soils that are dominated by mica or vermiculite (Thomas, 

1982). 

2. Summary of Method 

The NH4OAc extract from procedure 5A8c is diluted with an ionization suppressant 

(LaC13). The analytes are measured by an atomic absorption spectrophotometer (AA). The 

analyte is measured by absorption of the light from a hollow cathode lamp. An automatic 

sample changer is used to aspirate a series of samples. The AA converts absorption to analyte 

concentration. The data are automatically recorded by a microcomputer and printer. The 

NH4OAc extracted cations, Ca2+, Mg2+, Na+

, and K+, are reported in meq 100 g-1 oven-dry soil 

in procedures 6N2e, 6O2d, 6P2b, and 6Q2b, respectively. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

analyses of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. 

4. Safety 

Wear protective clothing and safety glasses. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Thoroughly wash hands after handling these metal salts. 

Follow standard laboratory procedures when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene gas is highly flammable. Avoid 

open flames and sparks. Standard laboratory equipment includes fire blankets and 

extinguishers for use when necessary. Follow the manufacturer's safety precautions when 

using the AA. 

5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Filter paper, pre-pleated, 185-mm diameter, Schleicher and Schuell 

5.3 Atomic absorption spectrophotometer (AA), model 5000, Perkin-Elmer Corp., Norwalk, 

CT 

5.4 Automatic burner control, model 5000, Perkin-Elmer Corp., Norwalk, CT 

5.5 Autosampler, AS-50, Perkin-Elmer Corp., Norwalk, CT 

5.6 Dot matrix printer, P-132, Interdigital Data Systems,Inc. 

5.7 Single-stage regulator, acetylene service, part number E11-0-N511A, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 

5.8 Digital diluter/dispenser, MicroLab 500, Hamilton Co., P.O. Box 10030, Reno, NV 

521
5.9 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV 

5.10 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer, Curtin 

Matheson Scientific, Inc., Houston, TX 

5.11 Containers, polypropylene 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Hydrochloric acid (HCl), concentrated 12 N

6.3 HCl, 1:1 HCl:DDI, 6 N. Carefully mix 1 part of concentrated HCl to 1 part DDI water. 

6.4 HCl, 1% wt. Carefully dilute 25 mL of concentrated HCl to 1 L with DDI water. 

6.5 NH4OH, reagent-grade, sp gr 0.90 

6.6 Glacial acetic acid, 99.5% 

6.7 Primary stock mixed standards solution (PSMSS). Dissolve 0.8759 g of ovendry reagent 

grade calcium carbonate (CaCO3) in a minimum of volume of 1:1 concentrated HCl:DDI 

water. Add 0.2127 g of clean Mg ribbon dissolved in 1:1 HCl. Add 1.0956 g of dry 

reagent grade sodium chloride (NaCl) and 0.1864 g of dry reagent grade KCl. Transfer 

to a 250-mL volumetric and bring to volume with 1% HCl solution. Resulting solution 

contains 70 meq L-1 (1403 ppm) Ca; 70 meq L-1 (851 ppm) Mg; 75 meq L-1 (1724 ppm) 

Na; 10 meq L-1 (391 ppm) K. Store in a polypropylene container. 

6.8 NH4OAc solution, 1.0 N, pH 7.0, reagent blank. Mix 57 mL of glacial acetic acid in 600 

mL of DDI water. While stirring, carefully add 68 mL of concentrated NH4OH. Cool 

and adjust pH to 7.0 using NH4OH or acetic acid. Dilute to 1 L with DDI water. The 

NH4OAc solution is used for extraction of cations (procedure 5A8c). 

6.9 Working stock mixed standards solution (WSMSS). Dilute 20 mL of the PSMSS with 80 

mL DDI water (1:5). Resulting solution contains 14 meq L-1 (281 ppm) Ca; 14 meq L-1

(170 ppm) Mg; 15 meq L-1 (345 ppm Na); 2 meq L-1 (78 ppm) K. Store in a 

polypropylene container. 

6.10 Stock lanthanum ionization suppressant solution, 65,000 ppm. Wet 152.4 g lanthanum 

oxide (La2O3) with 100 mL DDI water. Slowly and cautiously add 500 mL of 6 N HCl to 

dissolve the La2O3. Cooling the solution is necessary. Dilute to 2 L with DDI water. 

Filter solution. Store in polypropylene container. 

6.11 Lanthanum ionization suppressant solution, 6500 ppm. Dilute 200 mL of stock 

lanthanum ionization suppressant solution with 1800 mL of DDI water (1:10). Store in 

polypropylene container. 

6.12 Dilute calibration mixed standards solution (DCMSS). Dilute 1 part of the WSMSS with 

39 parts of the lanthanum solution (1:40). Resulting solution contains 0.35 meq L-1 (7 

ppm) Ca; 0.35 meq L-1 (4 ppm) Mg; 0.375 meq L-1 (9 ppm) Na; 0.05 meq L-1 (2 ppm) K. 

Store in polypropylene container. 

6.13 Dilute calibration reagent blank solution (DCRBS). Dilute 1 part of DDI water with 39 

parts of the lanthanum solution (1:40). Store in polypropylene container. 

6.14 Compressed air with water and oil traps. 

6.15 Acetylene gas, purity 99.6%. 

7. Procedure 

Dilution of Sample Extracts and Standards 

7.1 The 10-mL syringe is for diluent (lanthanum ionization suppressant solution). The 1-mL 

syringe is for NH4OAc sample extracts (procedure 5A8c), calibration reagent blanks, and 

calibration standards. Set the digital diluter at a 1:40 dilution for the NH4OAc sample extracts, 

reagent blanks, and calibration standards as follows: 

7.2 Dilute 1 part NH4OAc sample extract with 39 parts of lanthanum ionization suppressant 

solution (1:40 dilution). 

522
7.3 Dilute 1 part WSMSS with 39 parts of lanthanum ionization suppressant solution (1:40 

dilution). This is the DCMSS. Refer to reagents section. 

7.4 Dilute 1 part DDI water with 39 parts of lanthanum ionization suppressant solution (1:40 

dilution). This is the DCRBS. Refer to reagents section. 

7.5 Dispense the diluted solutions into test tubes which have been placed in the sample holders 

of the sample changer. 

AA Calibration 

7.6 Use the DCRBS and the DCMSS to calibrate the AA. The AA program requires a blank 

and a standard, in that order, to establish a single point calibration curve for element 

determination. Perform one calibration, i.e., blank plus standard, for every 12 samples. 

AA Set-up and Operation 

7.7 Refer to the manufacturer's manual for operation of the AA. The following are only very 

general guidelines for instrument conditions for the various analytes. 

Analyte Conc. 

meq/L 

Burner & 

Angle 

Wavelength Slit Fuel/ 

Oxidant 

C2H2/Air 

Ca 14.00 50cm 

@ 0°

422.7 0.7 10/25 

Mg 14.00 50 cm 

@ 30°

285.2 0.7 10/25 

K 2.00 50 cm 

@ 0°

766.5 1.4 10/25 

Na 15.00 50 cm 

@ 30°

589.0 0.4 10/25 

7.8 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.9 If sample exceeds calibration standard, dilute the sample (dilution ratio in calculation) with 

appropriate matrix and record dilution. Remember to keep the matrix the same after dilution by 

diluting with the lanthanum ionization suppressant solution (1:40 dilution). 

7.10 Analyze one quality control check sample for every 48 samples. 

7.11 The instrument readings are usually programmed in meq L-1. Record analyte readings to 

0.01 meq L-1. 

8. Calculations 

8.1 The instrument readings are the analyte concentration (meq L-1 cation) in undiluted extract. 

Use these values and calculate the analyte concentration on an ovendry soil basis (meq 100 g-1). 

Analyte Concentration in Soil (meq 100 g-1) = (A x B x C x E)/(10 x D) 

where: 

A = Analyte concentration in extract (meq L-1) 

523
B = Extract volume (mL). Refer to procedure 5A8c.

= Weight of extract in syringe (g)/Density of 1 N NH4OAc (1.0124 g cm-3) 

C = Dilution ratio, if needed 

D = Soil sample weight (g) 

E = AD/OD ratio (procedure 4B5) 

9. Report 

Report the extractable Ca2+, Mg2+, Na+, and K+ in units of meq 100 g-1 of oven-dry soil 

to the nearest 0.1 meq 100 g-1. 

10. Precision 

Precision data are not available for this procedure. A quality control check sample is 

run with every batch of 48 samples. The number of observations, mean, standard deviation, 

and C.V. for the quality control check sample are as follows: 

Cation n Mean Std. Dev. C.V. 

Ca 85 18.4 0.95 5.1% 

Mg 84 7.5 0.23 3.1% 

K 81 2.04 0.10 

11. References 

Thomas, G.W. 1982. Exchangeable cations. In A.L. Page, R.H. Miller, and D.R. Keeney 

(eds.) Methods of soil analysis. Part 2. Chemical and microbiological properties. 2nd 

ed. Agronomy 9:159-165. 

Calcium, Magnesium, Sodium, and Potassium (6N, 6O, 6P, and 6Q) NH4OAC Extraction 

(6N2, 6O2, 6P2, and 6Q2) 

Atomic Absorption 

Thermo Jarrell Ash, Smith-Hieftje 4000 

(6N2f, 6O2e, 6P2c, and 6Q2c) 

1. Application 

The extractable bases (Ca2+, Mg2+, Na+, and K+) from the NH4OAC extraction 

(procedure 5A8c) are generally assumed to be those exchangeable bases on the cation exchange 

sites of the soil. The abundance of these cations usually occurs in the sequence of Ca2+ > Mg2+

> K+ > Na+. Deviation from this usual order signals that some factor or factors, e.g., free 

CaCO3 or gypsum, serpentine (high Mg2+), or natric material (high Na+), have altered the soil 

chemistry. The most doubtful cation extractions with this method are Ca2+ in the presence of 

free CaCO3 or gypsum and K+ in soils that are dominated by mica or vermiculite (Thomas, 

1982). 

2. Summary of Method 

The NH4OAc extract from procedure 5A8c is diluted with an ionization suppressant 

(LaC13). The analytes are measured by an atomic absorption spectrophotometer (AA). The 

data are automatically recorded by a microcomputer and printer. The NH4OAc extracted 

cations, Ca2+, Mg2+, Na+, and K+, are reported in meq 100 g-1 oven-dry soil in procedures 6N2f, 

6O2e, 6P2c, and 6Q2c, respectively. 

524
3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

analyses of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. 

4. Safety 

Wear protective clothing and safety glasses. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Thoroughly wash hands after handling these metal salts. 

Follow standard laboratory procedures when handling compressed gases. Gas cylinders 

should be chained or bolted in an upright position. Acetylene gas is highly flammable. Avoid 

open flames and sparks. Standard laboratory equipment includes fire blankets and 

extinguishers for use when necessary. Follow the manufacturer's safety precautions when 

using the AA. 

5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Filter paper, pre-pleated, 185-mm diameter, Schleicher and Schuell 

5.3 Atomic absorption spectrophotometer (AA), Smith-Hieftje Model 4000, Thermo Jarrell 

Ash Corp., Franklin, MA 

5.4 Autosampler, Model 150, Thermo Jarrell Ash Corp., Franklin, MA 

5.5 ThermoSpec software, Version 3.01, Enable 4.0, DOS 5.0, Thermo Jarrell Ash Corp., 

Franklin, MA 

5.6 Computer, CUi Advantage 486, Thermo Jarrell Ash Corp., Franklin, MA 

5.7 Printer, NEC Pinwriter P3200 

5.8 Single-stage regulator, acetylene service, part number E11-0-N511A, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 

5.9 Digital diluter/dispenser, MicroLab 500, Hamilton Co., P.O. Box 10030, Reno, NV 

5.10 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV 

5.11 Test tubes, 15-mL, 16 mm x 100, for sample dilution and sample changer, Curtin 

Matheson Scientific, Inc., Houston, TX 

5.12 Containers, polypropylene 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Hydrochloric acid (HCl), concentrated 12 N

6.3 HCl, 1:1 HCl:DDI, 6 N. Carefully mix 1 part of concentrated HCl to 1 part DDI water. 

6.4 HCl, 1% wt. Carefully dilute 25 mL of concentrated HCl to 1 L with DDI water. 

6.5 NH4OH, reagent-grade, sp gr 0.90 

6.6 Glacial acetic acid, 99.5% 

6.7 Primary stock mixed standards solution (PSMSS). Dissolve 0.8759 g of ovendry reagent 

grade calcium carbonate (CaCO3) in a minimum of volume of 1:1 concentrated HCl:DDI 

water. Add 0.2127 g of clean Mg ribbon dissolved in 1:1 HCl. Add 1.0956 g of dry 

reagent grade sodium chloride (NaCl) and 0.1864 g of dry reagent grade KCl. Transfer 

to a 250-mL volumetric and bring to volume with 1% HCl solution. Resulting solution 

contains 70 meq L-1 (1403 ppm) Ca; 70 meq L-1 (851 ppm) Mg; 75 meq L-1 (1724 ppm) 

Na; 10 meq L-1 (391 ppm) K. Store in a polypropylene container. 

6.8 NH4OAc solution, 1.0 N, pH 7.0, reagent blank. Mix 57 mL of glacial acetic acid in 600 

mL of DDI water. While stirring, carefully add 68 mL of concentrated NH4OH. Cool 

and adjust pH to 7.0 using NH4OH or acetic acid. Dilute to 1 L with DDI water. The 

NH4OAc solution is used for extraction of cations (procedure 5A8c). 

525
6.9 Working stock mixed standards solution (WSMSS). Dilute 20 mL of the PSMSS with 80 

mL DDI water (1:5). Resulting solution contains 14 meq L-1 (281 ppm) Ca; 14 meq L-1

(170 ppm) Mg; 15 meq L-1 (345 ppm Na); 2 meq L-1 (78 ppm) K. Store in a 

polypropylene container. 

6.10 Stock lanthanum ionization suppressant solution, 65,000 ppm. Wet 152.4 g lanthanum 

oxide (La2O3) with 100 mL DDI water. Slowly and cautiously add 500 mL of 6 N HCl to 

dissolve the La2O3. Cooling the solution is necessary. Dilute to 2 L with DDI water. 

Filter solution. Store in polypropylene container. 

6.11 Lanthanum ionization suppressant solution, 6500 ppm. Dilute 200 mL of stock 

lanthanum ionization suppressant solution with 1800 mL of DDI water (1:10). Store in 

polypropylene container. 

6.12 Dilute calibration mixed standards solution (DCMSS). Dilute 1 part of the WSMSS with 

39 parts of the lanthanum solution (1:40). Resulting solution contains 0.35 meq L-1 (7 

ppm) Ca; 0.35 meq L-1 (4 ppm) Mg; 0.375 meq L-1 (9 ppm) Na; 0.05 meq L-1 (2 ppm) K. 

Store in polypropylene container. 

6.13 Dilute calibration reagent blank solution (DCRBS). Dilute 1 part of DDI water with 39 

parts of the lanthanum solution (1:40). Store in polypropylene container. 

6.14 Compressed air with water and oil traps. 

6.15 Acetylene gas, purity 99.6%. 

7. Procedure 

Dilution of Sample Extracts and Standards 

7.1 The 10-mL syringe is for diluent (lanthanum ionization suppressant solution). The 1-mL 

syringe is for NH4OAc sample extracts (procedure 5A8c), calibration reagent blanks, and 

calibration standards. Set the digital diluter at a 1:40 dilution for the NH4OAc sample extracts, 

reagent blanks, and calibration standards as follows: 

7.2 Dilute 1 part NH4OAc sample extract with 39 parts of lanthanum ionization suppressant 

solution (1:40 dilution). 

7.3 Dilute 1 part WSMSS with 39 parts of lanthanum ionization suppressant solution (1:40 

dilution). This is the DCMSS. Refer to reagents section. 

7.4 Dilute 1 part DDI water with 39 parts of lanthanum ionization suppressant solution (1:40 

dilution). This is the DCRBS. Refer to reagents section. 

7.5 Dispense the diluted solutions into test tubes which have been placed in the sample holders 

of the sample changer. 

AA Calibration 

7.6 Use the DCRBS and the DCMSS to calibrate the AA. The AA program requires a blank 

and a standard, in that order, to establish a single point calibration curve for element 

determination. Perform one calibration, i.e., blank plus standard, for every 12 samples. 

AA Set-up and Operation 

7.7 Refer to the manufacturer's manual for operation of the AA. The following are only very 

general guidelines for instrument conditions for the various analytes. 

526
Analyte Conc. 

meq/L 

Burner & 

Angle 

Wavelength Slit Fuel/ 

Oxidant 

C2H2/Air 

Ca 14.00 50cm 

@ 0°

422.7 0.7 10/25 

Mg 14.00 50 cm 

@ 30°

285.2 0.7 10/25 

K 2.00 50 cm 

@ 0°

766.5 1.4 10/25 

Na 15.00 50 cm 

@ 30°

589.0 0.4 10/25 

7.8 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.9 If sample exceeds calibration standard, dilute the sample (dilution ratio in calculation) with 

appropriate matrix and record dilution. Remember to keep the matrix the same after dilution by 

diluting with the lanthanum ionization suppressant solution (1:40 dilution). 

7.10 Analyze one quality control check sample for every 48 samples. 

7.11 The instrument readings are usually programmed in meq L-1. Record analyte readings to 

0.01 meq L-1. 

8. Calculations 

8.1 The instrument readings are the analyte concentration (meq L-1 cation) in undiluted extract. 

Use these values and calculate the analyte concentration on an ovendry soil basis (meq 100 g-1). 

Analyte Concentration in Soil (meq 100 g-1) = (A x B x C x E)/(10 x D) 

where: 

A = Analyte concentration in extract (meq L-1) 

B = Extract volume (mL). Refer to procedure 5A8c. 

= Weight of extract in syringe (g)/Density of 1 N NH4OAc (1.0124 g cm-3) 

C = Dilution ratio, if needed 

D = Soil sample weight (g) 

E = AD/OD ratio (procedure 4B5) 

9. Report 

Report the extractable Ca2+, Mg2+, Na+, and K+ in units of meq 100 g-1 of oven-dry soil 

to the nearest 0.1 meq 100 g-1. 

10. Precision 

Precision data are not available for this procedure. A quality control check sample is 

run with every batch of 48 samples. 

527
11. References 

Thomas, G.W. 1982. Exchangeable cations. In A.L. Page, R.H. Miller, and D.R. Keeney 

(eds.) Methods of soil analysis. Part 2. Chemical and microbiological properties. 2nd 

ed. Agronomy 9:159-165. 

Total Sulfur (6R) 

SO2 Evolution, Infrared (6R3) 

LECO SC-444 Sulfur Analyzer (6R3c) 

1. Application 

Organic and inorganic S forms are found in soils, with the organic S fraction accounting 

for >95% of the total S in most soils from humid and semi-humid (Tabatabai, 1982). 

Mineralization of organic S and its conversion to sulfate by chemical and biological activity 

may serve as a source of plant available S. Total S typically ranges from 0.01 to 0.05% in most 

mineral soils. In organic soils, total S may be >0.05%. 

In well-drained, well-aerated soils, most of the inorganic S normally occurs as sulfate. 

In marine tidal flats, other anaerobic marine sediments, and mine spoils, there are usually large 

amounts of reduced S compounds which oxidize to sulfuric acid upon exposure to the air. In 

arid regions, significant amounts of inorganic S are found as sulfates such gypsum and barite. 

The typical use of total S is as an index of the total reserves of this element, which may 

be converted to plant available S. The SSL uses the combustion technique (LECO sulfur 

analyzer) for analysis of total S (procedure 6R3b). Extractable sulfate S (SO4

2

-S) is an index of 

readily plant-available S. Reagents that have been used for measuring SO4

2

-S include water, 

hot water, ammonium acetate, sodium carbonate and other carbonates, ammonium chloride and 

other chlorides, potassium phosphate and other phosphates, and ammonium fluoride (Bray-1). 

Extractable SO4

2

-S does not include the labile fraction of soil organic S that is mineralized 

during the growing season (Tabatabai, 1982). Extraction reagents for organic S include 

hydrogen peroxide, sodium bicarbonate, sodium hydroxide, sodium oxalate, sodium peroxide, 

and sodium pyrophosphate. There other methods available for determination of soil S, 

especially for total S and SO4

2

-S. The investigator may refer to the review by Beaton et al. 

(1968). 

2. Summary of Method 

A fine-ground (<80-mesh) soil sample is oxidized at high temperature. The gases 

released are scrubbed, and the SO2 in the combustion gases are measured using an infrared 

detector. Percent S is reported on an oven-dry soil basis. 

3. Interferences 

No significant interferences are known to affect the oxidizable S measurement. 

4. Safety 

Wear protective clothing and safety glasses. Magnesium perchlorate may form 

explosive mixtures. Magnesium perchlorate may contain traces of perchloric acid, which 

remain from manufacturer's operations. This acid is anhydrous because of the strong 

desiccating capability of the salt. Avoid prolonged contact with oxidizable material or material 

capable of forming unstable perchlorate esters or salts. Remove magnesium perchlorate by 

using an excess of water to thoroughly dilute the material. 

The use of high temperatures in the oxidation of samples requires that extreme caution 

be used to prevent burns and fires. Follow standard laboratory procedures when handling 

compressed gases. Oxygen is highly flammable. Avoid open flames and sparks. Standard 

laboratory equipment includes fire blankets and extinguishers for use when necessary. Follow 

the manufacturer's safety precautions when using the sulfur analyzer. 

528
5. Equipment 

5.1 Sulfur analyzer, Leco Model SC-444, Sulfur and Carbon Analyzers, Leco Corp., St. 

Joseph, MI 

5.2 Combustion boats, part no. 529-203, Leco Corp., St. Joseph, MI 

5.3 Single-stage regulator, Oxygen Service, Part No. E11-W-N115BOX, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 18105 

5.4 Electronic balance, ±1-mg sensitivity 

6. Reagents 

6.1 Anhydrone, anhydrous magnesium perchlorate, granular 

6.2 Glass wool 

6.3 Compressed oxygen, >99.5% @ 30 psi 

6.4 Calcium carbonate, CaCO3, reagent grade. 

6.5 Solid/Powder Combustion Controller, part no. 501-426, Leco Corp., St. Joseph, MI 

6.6 Soil Calibration Sample, part no. 502-062, Leco Corp., St. Joseph, MI 

6.7 Sulfur Calibration Sample, part no. 502-648, Leco Corp., St. Joseph, MI 

7. Procedure 

7.1 Use a fine-ground 80-mesh, air-dry soil 

7.2 Prepare instrument as outlined in the operator's instruction manual (Leco, 1994; Leco, 

1993). 

7.3 Methods are created with the method menu and stored in the instrument memory. System 

parameters are set as follows: 

Furnace operating temperature: 1450°C 

Lance delay: 20 s 

Analysis time settings: 120 to 300 s 

Comparator level settings: 0.3% 

7.3 Condition instrument by analyzing a few soil samples, until readings are stable. 

7.4 Calibrate instrument by analyzing at least three replicates of each calibration standard. Use 

the soil calibration standard for samples with less than 0.01 percent TS and the sulfur standard 

for samples with more than 0.01 percent TS. Weigh standards in a range from 0.2 to 0.5 g. 

7.5 Load samples on autoload rack, place in the analyzer, and press analyze key. 

7.6 Weigh 0.2 to 0.5 g sample in a tared combustion boat. Add approximately 1 g of 

solid/powder combustion controller to sample. 

7.7 Load samples on autoload rack, place in the analyzer, and press analyze key. 

7.9 Repack the reagent (anhydrous magnesium perchlorate) tubes whenever the reagent 

becomes caked or moist or the warning alarm displays. 

8. Calculations

S (%) = Si x AD/OD 

where: 

S (%) = S (%) on oven-dry basis 

Si = S (%) instrument 

529
AD/OD = air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report total S as a percentage of oven-dry weight to the nearest 0.1%. 

10. Precision

Precision data are not available for this procedure. A quality control check sample is 

run in every batch of 12 samples. A blank (crucible only) and a rerun of one of the 12 samples 

(unknowns) also are run in every batch. For 27 observations of the quality control check 

sample, the mean, standard deviation, and C.V. for total S are 0.57, 0.02, and 4.3%, 

respectively. 

11. References 

Beaton, James D., G.R. Burns, and J. Platou. 1968. Determination of sulfur in soils and 

plant material. Tech. Bull. No. 14. The Sulfur Inst., 1725 K Street, N.W., Washington, 

D.C. 20006 

Leco Corp. 1993. Sulfur and carbon in cements, soils, rock, ceramic and similar materials. 

Application Bulletin. Leco Corp., 3000 Lakeview Ave., St. Joseph, MI. 

Leco Corp. 1994. Instruction Manual. SC-444 Sulfur and Carbon Analyzers. Leco Corp. , 

3000 Lakeview Ave., St. Joseph, MI. 

Tabatabai, M.A. 1982. Sulfur. In A.L. Page, R.H. Miller, and D.R. Keeney (eds.) Methods 

of soil analysis. Part 2. Chemical and microbiological properties. 2nd ed. Agronomy 

9:501-538. 

Bray P-1 Absorbed Phosphorus (6S) 

Baush and Laumb, Spectrophotometer 20 (6S3) 

1. Application

The Bray P-1 procedure is widely used as an index of available P in the soil. The 

selectivity of the Bray extractant is designed to remove the easily acid-soluble P, largely 

calcium phosphates, and a portion of the phosphates of Al and Fe (Bray and Kurtz, 1945; Olsen 

and Sommers, 1982). In general, this method has been most successful on acid soils (Bray and 

Kurtz, 1945; Olsen and Sommers, 1982). 

2. Summary of Method A 1-g soil sample is shaken with 10 mL of extracting solution for 15 min at 100 

oscillations per min-1. The solution is filtered. A 2-mL aliquot is transferred to a colorimetric 

tube to which 8-mL of ascorbic acid molybdate solution are added. The percent transmittance 

of the solution is read using a spectrophotometer. The Bray P-1 is reported in mg kg-1 (ppm) P. 

3. Interferences

Many procedures may be used to determine P. Studies have shown that incomplete or 

excessive extraction of P to be the most significant contributor to interlaboratory variation. The 

Bray P-1 procedure is sensitive to the soil/extractant ratio, shaking rate, and time. This 

extraction uses the ascorbic acid-potassium antimonyl-tartrate-molybdate method. The FiskeSubbarrow method is less sensitive but has a wider range before dilution is required (North 

Central Regional Publication No. 221, 1988). For calcareous soils, the Olsen method is 

preferred. An alternative procedure for calcareous soils is to use the Bray P-1 extracting 

solution at a 1:50 soil:solution ratio. This procedure has been shown to be satisfactory for 

some calcareous soils (North Central Regional Publication No. 221, 1988; Smith et al., 1957). 

530
4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated H2SO4 and HCl to a fume 

hood. Use safety showers and eyewash stations to dilute spilled acids and bases. Use sodium 

bicarbonate and water to neutralize and dilute spilled acids. 

5. Equipment

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Shaker, Eberbach 6000 power unit, reciprocating speed of 60 to 260 oscillations min-1, with 6040 utility box carrier and 6110 floor stand, Eberbach Corp., Ann Arbor, MI 

5.3 Spectrophotometer 20, Baush and Laumb 

5.4 Pipettors, electronic digital, Rainin Instrument Co., Woburn, MA, 2500 μL and 10 mL 

5.5 Cuvettes, glass, 10 mL, 1-cm light path 

5.5 Funnel, 60° angle, long stem, 50-mm diameter 

5.7 Filter paper, quantitative, Whatman grade 2, 9-cm diameter 

5.8 Erlenmeyer flasks, 50 mL 

5.9 Centrifuge, high-speed, International Equipment Co., IECB-22M 

6. Reagents

6.1 Distilled deionized (DDI) water 

6.2 Hydrochloric acid (HCl), concentrated, 12 N 6.3 HCl, 1 N. Carefully add 83.33 mL of concentrated HCl to DDI water and dilute to 1-L 

volume. 

6.4 Sulfuric acid (H2SO4), concentrated, 36 N

6.5 Bray No. 1 Extracting solution, 0.025 N HCl and 0.03 N NH4F. Dissolve 8.88 g of NH4F 

in 4 L DDI H2O. Add 200 mL of 1.0 N HCl and dilute to 8 L with DDI water. The 

solution pH should be 2.6 ± 0.5. Store in a polyethylene bottle. 

6.6 Stock standard P solution (SSPS), 100 ppm P. Add 0.2197 g of KH2PO4 in 25 mL of DDI 

water. Dilute to a final volume of 500 mL with extracting solution. Store in a 

refrigerator. Solution is stable to 1 yr. 

6.7 Sulfuric-tartrate-molybdate solution (STMS). Dissolve 60 g of ammonium molybdate 

tetrahydrate [(NH4)6Mo7O24·4H2O] in 200 mL of boiling DDI water. Allow to cool to 

room temperature. Dissolve 1.455 g of antimony potassium tartrate (potassium 

antimonyl tartrate hemihydrate K(SbO)C4H4O6·1/2H2O) in the ammonium molybdate 

solution. Slowly and carefully add 700 mL of concentrated H2SO4. Cool and dilute to 1 

L with DDI water. Store in the dark in the refrigerator. 

6.8 Ascorbic acid solution. Dissolve 33.0 g of ascorbic acid in DDI water and dilute to 250 

mL with DDI water. Store in the dark in the refrigerator. 

6.9 Working ascorbic acid molybdate solution (WAMS). Prepare fresh each day. Mix 25 

mL of STMS solution with 800 mL of DDI water. Add 10 mL of ascorbic acid solution 

and dilute to 1 L with DDI water. 

6.10 Standard P calibration solutions (SPCS), 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, and 6.0, 7.0, and 

8.0 ppm. Dilute the SSPS with the extracting solution as follows: 0.2 ppm = 0.5:250; 0.5 

ppm = 0.5:100; 1.0 ppm = 1:100; 2.0 ppm = 2:100; 3.0 ppm = 3:100; 4.0 ppm = 4:100; 

5.0 ppm = 5:100; 6.0 ppm = 6:100; 7:0 ppm = 7:100; 8.0 ppm = 8:100. 

7. Procedure

7.1 Weigh 1.00 g of air-dry soil into a 50-mL Erlenmeyer flask. 

7.2 Dispense 10.0 mL of extracting solution to flask. 

531
7.3 Securely place the flask in the shaker. Shake for 15 min at 100 oscillations min-1 at room 

temperature (20°C). 

7.4 Remove the sample from the shaker. Decant, filter, and collect extract. 

7.5 Centrifuging or repeated filtering may be necessary to obtain clear extracts. Decant into 

13-mL centrifuge tube and centrifuge at 10000 RPM for 10 min. 

7.6 Use the pipettor to transfer a 2-mL aliquot of the sample to a cuvette. Also transfer a 2-mL 

aliquot of each SPCS to a cuvette. Use a clean pipette tip for each sample and SPCS. 

7.7 Dispense 8 mL of the WAMS to sample aliquot and to each SPCS (1:5 dilution). 

7.8 The color reaction requires a minimum of 20 min before analyst records readings. 

7.9 Set the spectrophotometer (red bulb) to read at 882 nm. 

7.10 Set the 100% transmittance against the blank which has 8 mL of the WAMS solution and 

2 mL of extracting solution. 

8. Calculations

8.1 Transmittance of a solution is the fraction of incident radiation transmitted by the solution, 

i.e., T = P/Po and is often expressed as a percentage, i.e., %T = P/Po x 100. The absorbance of a 

solution is directly proportional to concentration and is defined by the equation, A = -log10 T. 

These relationships are derived from Beer's law. 

Calibration Calculations

8.2 Use transmission of each SPCS to either construct a calibrated curve to plot P or use a least 

squares analysis to calculate P. The P is reported in ppm. 

8.3 Calibration Curve: Plot the transmittance against the ppm P of each SPCS on semilog 

graph paper or convert to absorbances and plot on linear graph paper. Construct the calibration 

curve by finding the "best" line that fits the plotted SPCS. 

8.4 Linear Squares Analysis: Use a least squares criterion, i.e. best moving average. Refer to a 

statistical analysis book for additional information on least squares analysis. To facilitate data 

manipulation in a least squares analysis, the following standard curve is developed using the 

concentration of SPCS as a f[ln(%T]. Final calculated analyte concentration with either log10

or ln base would be the same. Using the following example, calculate analyte concentration 

with P (ppm) in extract = Y variable and percent transmittance (% T) = the X variable. The X 

variable is the natural logarithm of T. 

 P T 

(ppm) (%) 

 0 100 

 2 77 

 4 59 

 6 45 

 8 33 

10 24 

Number of standards = n = 6 

532
∑Yi = 30 ∑Xi = 23.5077 

∑Yi/n = Y = 5 ∑Xi/n = X = 3.9180 

∑XiYi = 107.5902 ∑Xi

2

 = 93.5185 

∑Xi∑Yi = 705.231 

∑XiYi - ∑Xi∑Yi/n 107.5902 - 117.5385 

b = ⎯⎯⎯⎯⎯⎯⎯⎯⎯ = ⎯⎯⎯⎯⎯⎯⎯⎯⎯ -7.023 

∑Xi

2

 - (∑Xi)

2

/n 93.5185 - 92.102 

b = slope of the line, i.e., the amount that Y changes when X changes by 1 unit. 

The equation is as follows: 

Y = Y + b (X - X) 

Y = 5 -7.023 (ln(X) - 3.9180) 

Analyte Calculation 

8.5 Calibration Curve: Read the P (ppm) directly from the calibration curve. 

8.6 Least Squares Analysis: Put the ln(%T) in the preceding equation and solve for ppm P. 

Thus, if sample extract has 84% transmission, the preceding equation is as follows: 

Y = 5 -7.023 ln(84) + 27.516 = 1.40 ppm 

8.7 Convert the extract P (ppm) to soil P (ppm or lbs/A) as follows: 

Soil P (ppm) = Extract P (ppm) x 10 

Soil P (lbs/A) = Extract P (ppm) x 20 

9. Report 

Report the soil Bray P-1 mg kg-1 (ppm) to the nearest whole number. 

10. Precision

Precision data are not available for this procedure. 

11. References

Bray, R.H., and L.T. Kurtz. 1945. Determination of total, organic, and available forms of 

phosphorus in soils. Soil Sci. 59:39-45. 

North Central Regional Publication No. 221. 1988. Recommended chemical soil test 

procedures for the North Central region. Agric. Exp. Stn. of IL, IN, IA, KS, MI, MN, 

MS, NE, ND, OH, SD, WI, and USDA cooperating. 

Olsen, S.R., and L.E. Sommers. 1982. In A.L. Page, R.H. Miller, and D.R. Keeney (eds.) 

Methods of soil analysis. Part 2. Chemical and microbiological properties. 2nd ed. 

Agronomy 9:403-430. 

Smith, F.W., B.G. Ellis, and J. Grava. 1957. Use of acid-fluoride solutions for the 

extraction of available phosphorus in calcareous soils and in soils to which rock 

phosphate has been added. Soil Sci. Soc. Am. Proc. 21:400-404. 

533
New Zealand P Retention (6S)

UV-Visible Spectrophotometer (6S4) 

Beckmann DU-7 (6S4b)

1. Application 

In Soil Taxonomy, the P retention of soil material is a criterion for andic soil properties 

(Soil Survey Staff, 1990). Andisols and other soils that contain large amounts of allophane and 

other amorphous minerals have capacities for binding P (Gebhardt and Coleman, 1984). The 

factors that affect soil P retention are not well understood. However, allophane and imogolite 

have been considered as major materials that contribute to P retention in Andisols (Wada, 

1985). Phosphate retention is also called P absorption, sorption, or fixation. 

2. Summary of Method

A 5-g soil sample is shaken in a 1000-ppm P solution for 24 h. The mixture is 

centrifuged at 2000 rpm for 15 min. An aliquot of the supernatant is transferred to a 

colorimetric tube to which nitric vanadomolybdate acid reagent (NVAR) is added. The percent 

transmittance of the solution is read using a spectrophotometer. The New Zealand P retention 

is reported as percent P retained. 

3. Interferences 

No significant problems are known to affect the P retention measurement. 

4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated HNO3 to a fume hood. Use 

safety showers and eyewash stations to dilute spilled acids and bases. Use sodium bicarbonate 

and water to neutralize and dilute spilled acids. 

5. Equipment

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Shaker, Eberbach 6000 power unit, reciprocating speed of 60 to 260 epm, with 6040 

utility box carrier and 6110 floor stand, Eberbach Corp., Ann Arbor, MI 

5.3 Digital diluter/dispenser, Microlab 500, Hamilton Co., P.O. Box 10030, Reno, NV 

5.4 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV 

5.5 Diluter/dispenser, 25 mL 

5.6 UV-Visible Spectrophotometer, DU-7, Beckmann Instruments Inc. 

5.7 Cuvettes, Labcraft Brand, disposable, polystyrene, square-bottom, 4.5 mL, 12.5 mm x 

12.5 mm x 46 mm, Curtin Matheson Scientific, Inc., Houston, TX 

5.8 Centrifuge, International No. 2, Model V, with no. 250 A head, International Equip. Co., 

Boston, MA 

5.9 Trunions, International no. 320, International Equip. Co., Boston, MA 

5.10 Centrifuge tubes, 50 mL, Oak-Ridge, polyallomer, Nalgene 3119, Nalge Co., Box 20365, 

Rochester, NY 

5.11 Plastic cups, 2 fl. oz. 

5.12 Pipets, volumetric, class A, glass, various sizes of 1 to 20 mL 

6. Reagents

6.1 Distilled deionized (DDI) water 

6.2 Nitric acid (HNO3), concentrated, 16 N

6.3 P retention solution, 1000 ppm P. Dissolve 35.2 g of KH2PO4 and 217.6 g of sodium 

acetate (Na2C2H3O2·3H2O) in DDI water. Add 92 mL of glacial acetic acid. Dilute to 8 L 

534
with DDI water in a volumetric flask. The solution pH should range between 4.55 and 

4.65. 

6.4 Molybdate solution. Dissolve 16 g of ammonium molybdate (VI) [(NH4)6Mo7O24·4H2O] 

in 50°C DDI water. Allow the solution to cool to room temperature and dilute to 1 L with 

DDI water. 

6.5 Nitric acid solution. Carefully and slowly dilute 100 mL of concentrated HNO3 to 1 L of 

DDI water. Add the acid to the water. 

6.6 Nitric vanadomolybdate acid reagent (NVAR), vanadate solution. Dissolve 0.8 g of 

NH4VO3 in 500 mL of boiling DDI water. Allow the solution to cool to room temperature. 

Carefully and slowly add 6 mL of concentrated HNO3. Dilute to 1 L with DDI water. Mix 

the nitric acid solution with the vanadate solution and then add the molybdate solution. 

Mix well. 

6.7 Stock P standard solution (SPSS), 4000 ppm P. Dissolve 17.6 g KH2PO4 in DDI water. 

Dilute to 1 L with DDI water. 

6.8 Standard P calibration P solutions (SPCS), 100, 80, 60, 40, 20, and 0% P retained. Dilute 

the SPSS with a solution that contains 32.8 g of sodium acetate (CH3COONa) and 23 mL 

of glacial acetic acid diluted to 2 L with DDI water as follows: 100% = DDI water (0 

ppm); 80% = 1:20 (200 ppm); 60% = 1:10 (400 ppm); 40% = 3:20 (600 ppm); 20% = 1:5 

(800 ppm); and 0% = 1:4 (1000 ppm). The percent amount refers to percent P retention. 

7. Procedure

7.1 Weigh 5.00 g of air-dry soil into a 50-mL centrifuge tube. 

7.2 Use the dispenser to add 25.0 mL of P-retention solution to centrifuge tube. 

7.3 Cap centrifuge tube and place in shaker and shake for 24 h at room temperature (20°C). 

7.4 Add 2 to 3 drops of Superfloc, 0.02% w/v to each tube. 

7.5 Centrifuge sample at 2000 rpm for 15 min. Filter using a Milipore filter, if necessary. 

7.6 Pour sample supernatant into plastic cup. 

7.7 Use the digital diluter to add the nitric vanadomolybdate acid reagent (NVAR) to each 

sample supernatant and to each SPCS. To fill a 4.5-mL cuvette, use a dilution of 1:20 sample 

dilution. 

7.8 The color reaction requires a minimum of 30 min before the analyst records readings. 

7.9 Set the spectrophotometer to read at 466 nm. Auto zero using the DDI water (blank). A 

blank has all reagents contained in the sample extract except the soil. 

7.10 Record the percent transmittance to the nearest 0.01 unit for the sample extract and each 

SPCS. 

8. Calculations

8.1 Transmittance of a solution is the fraction of incident radiation transmitted by the solution, 

i.e., T = P/Po and is often expressed as a percentage, i.e., T = P/Po x 100. The absorbance of a 

solution is directly proportional to concentration and is defined by the equation, A = -log10 T. 

These relationships are derived from Beer's law. 

535
Calibration Calculations

8.2 Use the transmittance of each SPCS to either construct a calibrated curve to plot P or use a 

least squares analysis to calculate P. The P is reported in percent retained. 

8.3 Calibration Curve: Plot the transmittances against the ppm P of each SPCS on semilog 

graph paper or convert to absorbances and plot on linear graph paper. Construct the calibration 

curve by finding the "best" line that fits the plotted SPCS. 

8.4 Least Squares Analysis: Use a least squares criterion, i.e. best moving average. Refer to a 

statistical analysis book for additional information on least squares analysis. To facilitate data 

manipulation in a least squares analysis, the following standard curve is developed using the 

concentration of SPCS as a f[ln(%T]. Final calculated analyte concentration with either log10

or ln base would be the same. Refer to procedure 6S3b for an example of least squares 

analysis. 

Analyte Calculation 

8.5 Calibration Curve: Read the percent P directly from the calibration curve. 

8.6 Least Squares Analysis: Refer to procedure 6S3 for an example of least squares analysis. 

9. Report

Report the percent New Zealand P retention to the nearest whole number. 

10. Precision

Precision data are not available for this procedure. 

11. References

Gebhardt, H., and N.T. Coleman. 1984. Anion adsorption of allophanic tropical soils: III. 

Phosphate adsorption. p. 237-248. In K.H. Tan (ed.) Anodosols. Benchmark papers in 

soil science series. Van Nostrand Reinhold, Co., Melbourne, Canada. 

Soil Survey Staff. 1990. Keys to soil taxonomy. 4th ed. SMSS technical monograph no. 6. 

Blacksburg, VA. 

Wada, K. 1985. The distinctive properties of Andosols. p. 173-229. In B.A. Stewart (ed.) 

Adv. Soil Sci. Springer-Verlag, NY. 

Citric Acid Extractable Phosphorus (6S) 

Beckmann DU-7, UV-Visible Spectrophotmeter (6S5) 

1. Application

In Soil Taxonomy, citric acid soluble P2O5 is a criterion for distinguishing between 

mollic (<250 ppm P2O5) and anthropic epipedons (>250 ppm P2O5) (Soil Survey Staff, 1975). 

Additional data on anthropic epipedons from several parts of the world may permit 

improvements in this definition (Soil Survey Staff, 1994). The procedure 6S5 is used by 

N.A.A.S. (England and Wales) and is based on the method developed by Dyer (1894). 

2. Summary of Method

A sample is checked for CaCO3 equivalent. Sufficient citric acid is added to sample to 

neutralize the CaCO3 plus bring the solution concentration of citric acid to 1%. A 1:10 

soil:solution is maintained for all samples. The sample is shaken for 16 h and filtered. 

Ammonium molybdate and stannous chloride are added. The percent transmittance of the 

solution is read using a spectrophotometer. The 1% citric acid extractable P2O5 is reported in 

mg kg-1 (ppm). 

536
3. Interferences

Unreacted carbonates interfere with the extraction of P2O5. Sufficient citric acid is 

added to sample to neutralize the CaCO3. However, a high citrate level in sample may interfere 

with the molybdate blue test. If this occurs, the method can be modified by evaporating the 

extract and ashing in a muffle furnace to destroy the citric acid. 

Positive interferences in the analytical determination of P2O5 are silica and arsenic, if 

the sample is heated. Negative interferences in the P2O5 determination are arsenate, fluoride, 

thorium, bismuth, sulfide, thiosulfate, thiocyanate, or excess molybdate. A concentration of Fe 

>1000 ppm interferes with P2O5 determination. Refer to Snell and Snell (1949) and Metson 

(1956) for additional information on interferences in the citric acid extraction of P2O5. 

4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

and bases. Dispense concentrated acids and bases in fume hood. Use the safety showers and 

eyewash stations to dilute spilled acids and bases. Use sodium bicarbonate and water to 

neutralize and dilute spilled acids. Follow standard laboratory procedures. 

5. Equipment

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Shaker, Eberbach 6000 power unit, reciprocating speed of 60 to 260 oscillations min-1, 

with 6040 utility box carrier and 6110 floor stand, Eberbach Corp., Ann Arbor, MI 

5.3 Digital diluter/dispenser, product no. 100004, with hand probe and actuator, product no. 

230700, Hamilton Co., P.O. Box 10030, Reno, NV 

5.4 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV, 

5.5 Centrifuge tubes, 50 mL, Oak-Ridge, polyallomer, Nalgene 3119, Nalge Co., Box 20365, 

Rochester, NY 

5.6 Filter paper, quantitative, Whatman grade 2, 9-cm diameter 

5.7 Funnel, 60° angle, long stem, 50-mm diameter 

5.8 Erlenmeyer flasks, 50 ml 

5.9 Bottles with gas release caps 

5.10 Pipettors, electronic digital, Rainin Instrument Co., Woburn, MA, 2500 μL and 10 mL 

Digital Pipet, 10-ml 

5.11 UV-visible spectrophotometer, DU-7, Beckmann Instruments, Inc. 

5.12 Cuvettes, Labcraft Brand, disposable, polystyrene, square-bottom, 4.5 mL, 12.5 mm x 

12.5 mm x 46 mm, Curtin Matheson Scientific, Inc., Houston, TX 

6. Reagents

6.1 Distilled, dionized (DDI) water 

6.2 Hydrochloric acid (HCl), concentrated, 12 N

6.3 Citric acid solution, 10%. Dissolve 100 g of anhydrous citric acid (C6H8O7) in 1-L 

volumetric flask. 

6.4 Citric acid solution, 1%. Dilute 100.0 ml of 10% citric acid solution to 1-L with DDI 

water 

6.5 Ammonium molybdate solution, 1.5%. Dissolve 15.0 g of ammonium molybdate 

[(NH4)6MO7O24·4H2O] in 300 mL of distilled water. Transfer to a 1-L volumetric flask 

and carefully add 310 mL of concentrated HCl. Allow to cool. Make to 1-L volume with 

DDI water. Store in brown bottle in the dark. Solution is stable for ~ 3 months. 

6.6 Stock stannous chloride solution (SSCS). Dissolve 10 g of stannous chloride 

(SnCl2·2H2O) in 100 mL of concentrated HCl. 

6.7 Working stannous chloride solution (WSCS). Dilute 2 mL of SSCS with 100 mL of DDI 

water. Use immediately as solution is only stable for ~ 4 h. 

537
6.8 Stock standard P2O5 solution (SSPS), 250 ppm P. Dissolve 1.099 g of potassium 

dihydrogen orthophosphate (KH2PO4) with DDI water in 1-L volumetric flask. Add 5 ml 

of 2 N HCL. Make to 1-L volume with DDI water. 

6.9 Working stock standard P2O5 solution (WSSPS), 2.5 ppm P. Pipet 10.0 mL of SSPS and 

dilute to 1-L in a volumetric flask with DDI water. 

6.10 Standard P2O5 calibration solutions (SPCS). Pipet 0, 1, 2, 3, 4, and 5 mL of WSSPS into 

50-mL oakridge tubes. Add 1 ml of 1% citric acid solution. Continue color development 

as for samples. Distilled water may be used as a blank. 

7. Procedure 

7.1 Weigh 3.00 g of <2-mm, air-dry soil into a bottle gas release tops. If the soil does not 

contain free carbonates, proceed to step 7.3. 

7.2 If the soil contains free CaCO3, refer to Table 1 to determine the amount of 10% citric acid 

solution required to neutralize the CaCO3. Add required mls of 10% citric acid into a 

graduated cylinder and bring to a volume of 30-ml with DDI water. Add this solution to the 

soil. Swirl the bottle over a period of 6 h at 100 oscillations min-1 dissolve and neutralize the 

CaCO3. Proceed to step 7.4. 

Table 1. Volume of 10% citric acid (mL) required to decompose CaCO3 (%) and to bring 

to solution concentration to 1% in a final volume of 30 mL for 3-g sample. 

____________________________________________________________________________________________________________

%CC1 mL CA2 % CC mL CA % CC mL CA %CC mL CA 

0 3.0 16 9.7 32 16.4 48 23.2 

1 3.4 17 10.2 33 49 23.6 

2 3.8 18 10.6 34 50 24.0 

3 4.3 19 11.0 35 17.7 51 24.4 

4 4.7 20 11.4 36 18.1 52 24.8 

5 5.1 21 11.8 37 18.6 53 25.3 

6 5.5 22 12.2 38 19.0 54 25.7 

7 6.0 23 12.7 39 19.4 55 26.1 

8 6.4 24 13.1 40 19.8 56 26.5 

9 6.8 25 13.5 41 20.2 57 27.0 

10 7.2 26 14.0 42 20.6 58 27.4 

11 7.6 27 14.4 43 21.0 59 27.8 

12 8.0 28 14.8 44 21.5 60 28.2 

13 8.5 29 15.2 45 21.9 61 28.6 

14 8.9 30 15.6 46 22.4 62 29.0 

15 9.3 31 16.0 47 22.8 63 29.5 ____________________________________________________________________________________________________________ 

1

%CC = percent calcium carbonate in a sample 

2

CA = ml of 10% citric acid needed to be diluted to 30-ml volume with RODI water and added 

to sample 

7.3 If the soil contains no free CaCO3, add 30 mL of 1% citric acid solution to the sample. 

7.4 Cap the bottles, place in a shaker and shake for 16 h at 100 oscillations min-1. 

7.5 Remove the sample from shaker and filter. 

538
7.6 Pipet 1 mL of sample extract into a 50-ml oakridge tube. Add 4mL of ammonium 

molybdate solution to all samples and standards. Bring up to 25 ml mark with DDI water. Add 

2 ml stannous chloride. Shake to mix and allow to stand 20 min for color development. 

7.7 Set the spectrophotometer to read at 660 nm. Set the zero against distilled water (blank). A 

blank has all reagents contained in the sample extract except the soil. 

7.8 Record the percent transmittance to the nearest 0.01 unit for the sample extract and each 

SPCS. 

8. Calculations

8.1 Transmittance of a solution is the fraction of incident radiation transmitted by the solution, 

i.e., T = P/Po and is often expressed as a percentage, i.e., %T = P/Po x 100. The absorbance of a 

solution is directly proportional to concentration and is defined by the equation, A = -log10 T. 

These relationships are derived from Beer's law. 

Calibration Calculations

8.2 Use transmission of each SPCS to either construct a calibrated curve to plot P2O5 or use a 

least squares analysis to calculate P2O5. The P2O5 is reported in ppm. 

8.3 Calibration Curve: Plot the transmittances against the ppm P2O5 of each SPCS on semilog 

graph paper or convert to absorbances and plot on linear graph paper. Construct the calibration 

curve by finding the "best" line that fits the plotted SPCS. 

8.4 Linear Squares Analysis: Use a least squares criterion, i.e. best moving average. Refer to a 

statistical analysis book for additional information on least squares analysis. To facilitate data 

manipulation in a least squares analysis, the following SPCS curve is developed using the 

concentration of SPCS as a f[ln(%T]. Final calculated analyte concentration with either log10

or ln base would be the same. Refer to procedure 6S3 for an example of least squares analysis. 

Analyte Calculation 

8.5 Calibration Curve: Read the P2O5 (ppm) directly from the calibration curve. 

8.6 Least Squares Analysis: Refer to procedure 6S3 for an example of least squares analysis. 

8.7 Convert the extract P2O5 (ppm) to soil P2O5 (ppm or lbs/A) as follows: 

Soil P2O5 = Extract P2O5 x DR x 100 x AD/OD/Sample Weight (g) 

where: 

Soil P2O = P2O5 in soil (ppm) 

Extract P2O5 = P2O5 in extract (ppm) 

DR = Dilution ratio, if necessary, otherwise 1 

100 = Conversion factor 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report the 1% citrate acid extractable P2O5 in mg kg-1 (ppm) to nearest whole number. 

10. Precision

Precision data are not available for this procedure. 

539
11. References 

Dyer. 1894. Trans. Chem. Soc. 65:115-167. 

Metson, A.J. 1956. Methods of chemical analysis for soil survey samples. Soil Bureau 

Bulletin no. 12. NZ Dept. Sci. and Industrial Res. 

Snell, F.D., and C.T. Snell. 1949. Colorimetric methods of analysis. Phosphorus. Vol 2. 

3rd ed. p.630-681. D. Van Nostrand Co., Inc. 

Soil Survey Staff. 1975. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. USDA-SCS Agric. Handb. 436. Appendix III: Tests of 

organic materials. p. 483. U.S. Govt. Print. Office. Washington, DC. 

Soil Survey Staff. 1994. Keys to soil taxonomy. 6th ed. USDA-SCS. Govt. Print. Office, 

Washington DC. 

MINERALOGY (7) 

Instrumental Analyses (7A) 

X-Ray Diffraction (7A2) 

Phillips XRG-300 X-Ray Diffractometer 

Thin Film on Glass, Resin Pretreatment II (7A2i) (Mg Room Temp, Mg Glycerol Solvated, K 300°C, K 500°C)

1. Application

Clay fractions of soils are commonly composed of mixtures of one or more 

phyllosilicate minerals together with primary minerals inherited directly from the parent 

material (Whittig and Allardice, 1986). Positive identification of mineral species and 

quantitative estimation of their proportions in these polycomponent systems usually require the 

application of several complementary qualitative and quantitative analyses (Whittig and 

Allardice, 1986). One of the most useful methods to identify and to make semiquantitative 

estimates of the crystalline mineral components of soil is X-ray diffraction analysis. 

The operational strategy at the SSL and the preceding Lincoln Soil Survey Laboratory 

has been to adjust instrumental parameters to keep peak intensity of a soil reference constant 

from 1964 to present through the evolution of instrumentation. The intent is to keep the same 

quantitative interpretations consistent from sample to sample. 

2. Summary of Method

Soils are dispersed and separated into fractions of interest. Sands and silts are mounted 

on glass slides as slurries or on double sticky tape for analysis. Clay suspensions are placed on 

glass slides to dry and to preferentially orient the clay minerals. The soil clay minerals of 

greatest interest are phyllosilicates, e.g., kaolinite, mica (illite), smectite, vermiculite, hydroxyinterlayered vermiculite, and chlorite. 

Generally, no two minerals have exactly the same interatomic distances in three 

dimensions and the angle at which diffraction occurs is distinctive for a particular mineral 

(Whittig and Allardice, 1986). These interatomic distances within a mineral crystal result in a 

unique array of diffraction maxima, which help to identify that mineral. When several minerals 

are present in a sample, species identification is usually accomplished most easily and 

positively by determining the interatomic spacings that give rise to the various maxima and by 

comparing these with known spacings of minerals (Whittig and Allardice, 1986). 

X-ray diffraction produces peaks on a chart that correspond to 2θ angles on a 

goniometer. The angle of incidence of the goniometer is relative to the surface plane of the 

sample. Standard tables to convert θ or 2θ angles to crystal "d" spacings are published in the 

U.S. Geological Survey Circular 29 (Switzer et al., 1948) and in other publications (Brown, 

1980). At the SSL, conversions are made by the analysis program on the Philips 

diffractometer, d-spacings are recorded on an IBM-compatible 486 DOS-based computer 

system, and hard copies are printed for interpretation and filing. The crystal "d" spacings of 

540
minerals, i.e., the interval between repeating planes of atoms, can be calculated by Bragg's Law 

as follows: 

nλ = 2d sin θ

where: 

n = order of diffraction (integer) 

λ = x-radiation wavelength (Angstroms, A) 

d = crystal "d" spacing (A) 

θ = angle of incidence 

When n = 1, diffraction is of the first order. The wavelength of radiation from an X-ray tube is 

constant and characteristic for the target metal in the tube. Copper radiation (CuKa) with a 

wavelength of 1.54 A (0.154 nm) is used at the SSL. Because of similar structures of layer 

silicates commonly present in soil clays, several treatments which characteristically affect the 

"d" spacings are necessary to identify components. At the SSL, four treatments are used, i.e., 

Mg2+ (room temperature); Mg2+-glycerol (room temperature); K+ (300°C); and K+ (500°C). 

3. Interferences

Intimate mixtures of similar phyllosilicate minerals on a fine scale cause problems in 

identification. The mixtures, differences in crystal size and purity, and background or matrix 

interferences affect quantification. No pretreatments other than dispersion with sodium 

hexametaphosphate are used for separation and isolation of the crystalline clay fraction. 

Impurities such as organic matter and iron oxides may act as matrix interferences causing peak 

attenuation during X-ray analysis or may interfere with clay dispersion and separation. The 

separation procedure to isolate the clay fraction from the other size fractions of the soil skews 

the <2-μm clay suspension toward the fine clay, but it minimizes the inclusion of fine silt in the 

fraction. Dried clay may peel from the XRD slide. One remedy is to rewet the peeled clay on 

the slide with 1 drop of glue-water mixture (1:7). Other remedies are as follows: 

a. Place double sticky tape on the slide prior to adding the dried clay. 

b. Dilute the suspension by half, if thick. 

c. Crush with ethanol and dry, and then add water to make a slurry slide. 

d. Roughen the slide surface with a fine grit sand paper. 

Sufficient glycerol on the slides is required to solvate the clay, i.e., to expand smectites 

to 18 A. X-ray analysis should be performed 1 to 2 days after glycerol addition. If excess 

glycerol is applied to the slide and free glycerol remains on the surface, XRD peaks are 

attenuated. Some suggestions to dry the slides and achieve optimum glycerol solvation are as 

follows: 

a. Use a desiccator to dry slide, usually when the clay is thin. 

b. If the center of slide is whitish and dry, usually with thick clay, brush slide with glycerol or 

add an additional drop of glycerol. 

4. Safety

Operate the centrifuge with caution. Keep the centrifuge lid closed when in operation. 

Ensure that all hangers and tubes are seated firmly in proper location. Use tongs and 

appropriate thermal protection when operating the muffle furnace. The diffraction unit presents 

an electrical and radiation hazard. Analysts must receive radiation safety training before 

541
operating the equipment. Employees must wear a radiation film badge while in the room when 

the diffraction unit is in operation. 

5. Equipment

5.1 Teaspoon (5 g) 

5.2 Dispenser, 5 mL, for sodium hexametaphosphate solution 

5.3 Centrifuge, International No. 2, with No. 240 head and carriers for centrifuge tubes, 

International Equip. Co., Boston, MA 

5.4 Centrifuge tubes, plastic, 100 mL, on which 10-cm solution depth is marked 

5.5 Rubber stoppers, No. 6, for centrifuge tubes 

5.6 Mechanical shaker, reciprocal, 120 oscillations min-1

5.7 Plastic cups, 60 mL (2 fl. oz.) with lids 

5.8 Label machine 

5.9 Hypodermic syringes, plastic, 12 mL, with tip caps 

5.10 Screen, 80 mesh, copper 

5.11 Dropper bottle, plastic, 30 mL (1 fl. oz.), for a 1:7 glycerol:water mixture 

5.12 Muffle furnace 

5.13 X-ray diffractometer, Philips XRG-300, with PW-1170 automated sample changer 

5.14 PC-APD, Philips, software for Automatic Powder Diffraction (PW-1877), Version 3.5 

5.15 Computer, IBM-compatible 486, Gateway 2000 4D X2-66V 

5.16 Printer, Hewlett Packard LaserJet IV 

5.17 Plotter, Hewlett Packard 7550 Plus 

5.18 XRD slides, glass, 14 x 19 mm 

5.19 XRD sample preparation board, wood, with 32 places for glass XRD slides 

5.20 Slide holder. Accepts 14 x 19 mm XRD glass slides. Modified so slide surfaces rest 

flush with surface of holder. 

5.21 Magazine for slide holder, 35 positions 

5.22 Reference slides: quartz and clay from reference soil 

6. Reagents

6.1 Distilled deionized (DDI) water 

6.2 Sodium hexametaphosphate solution. Dissolve 35.7 g of sodium hexametaphosphate 

(NaPO3)6 and 7.94 g of sodium carbonate (Na2CO3) in 1 L DDI water. 

6.3 Potassium chloride (KCl), 1.0 N. Dissolve 74.60 g KCl in 1 L DDI water or 671.40 g 

KCl in 9 L DDI water. 

6.4 Magnesium chloride (MgCl2), 1.0 N. Dissolve 47.61 g MgCl2 in 1 L DDI water or 428.49 

g MgCl2 in 9 L DDI water. 

6.5 Glycerol:water mixture (1:7). Add 4 mL of glycerol to 28 mL DDI water plus 2 drops of 

toluene. 

6.6 Exchange resin, Rexyn 101 (H), analytical grade. Pretreatment of resin as follows: 

6.6.1 Divide equally Rexyn 101 (H), approximately 250-g portions, into two 600-mL beakers 

labelled K and Mg and add appropriate salt solution ( 1.0 N KCl or 1.0 N MgCl2). Cover 

resin with salt solution. 

6.6.2 Stir, let settle for 10 min, decant clear solution, and add salt solution. Repeat 3 times. 

Leave resin covered in salt solution for 8 to 12 h. 

6.6.3 Repeat step 6.6.2 second day. Resin is ready for syringes. Saturated resin not used 

initially for syringes can be saved for future use. 

6.7 White glue, diluted 1:7 with DDI water 

542
7. Procedure

Preparation (Recharge) of Resin-Loaded Syringes

7.1 Place a small circle of 80-mesh screen in a 12-mL syringe and add 4 cm3 of exchange resin 

from which salt solution has been drained. Our procedure requires each sample to have 2 Mg 

and 2 K slides prepared, so we produce our syringes in sets of two. 

7.2 Saturate the resin in each of the four syringes with 4 mL of the appropriate 1.0 N salt 

solution (MgCl2 or KCl) and expel. Repeat saturation of resin. 

7.3 Fill syringe completely with the salt solution and allow to equilibrate for 4 to 20 h. 

7.4 Rinse syringe twice with 4 mL of DDI water and rinse tip cap. 

7.5 Completely fill syringe with DDI water and allow to equilibrate for 4 to 20 h. 

7.6 Rinse syringe twice with DDI water. 

7.7 Expel water, cap syringe, and store. 

Preparation of Clay Suspension

7.8 Place ≈ 5 g (1 tsp) of air-dry <2-mm soil in a 100-mL plastic centrifuge tube. If the sample 

appears to be primarily sand, use 10 g (2 tsp) of <2-mm soil to obtain sufficient clay. 

7.9 Add 5 mL of sodium hexametaphosphate solution. If the soil contains gypsum or is 

primarily calcium carbonate, use 10 mL of sodium hexametaphosphate dispersing agent. 

7.10 Fill tube to 9.5-cm height with DDI water. 

7.11 Place rubber stopper in tube and shake overnight in mechanical shaker. 

7.12 Remove stopper from tube and rinse stopper and sides of tube with enough water to bring 

the volume to the 10-cm mark. 

7.13 Balance the pairs of tubes and place in centrifuge. Centrifuge at 750 rpm for 3.0 min. 

7.14 If the clay is dispersed, carefully decant 30 mL of suspension into a labelled, 60-mL, 

plastic cup. Place cap on cup. 

7.15 If the clay did not disperse after being shaken overnight, remove the rubber stopper and 

carefully decant the clear supernatant liquid. 

7.16 Add an additional 10 mL of sodium hexametaphosphate dispersing agent to sample and 

then add DDI water to 9.5-cm depth. 

7.17 Stopper and shake overnight to disperse the clay. Rinse stopper and fill tube to 10-cm 

mark. 

7.18 Centrifuge, decant, and store clay suspension. 

7.19 Use the clay suspension for X-ray diffraction analysis and HF plus aqua regia dissolution 

analysis. Dry clay suspension for use in thermal analysis. 

543
Thin Film on Glass, Resin Pretreatment

7.20 The SSL uses a sample board which holds 32 slides, i.e., 8 samples x 4 treatments. 

Prepare the sample board with glass XRD slides to receive the following 4 treatments per clay 

suspension sample. 

Mg2+ - room temperature 

Mg2+ - glycerol (room temperature) 

K+ - 300°C (heated for 2 h) 

K+ - 500°C (heated for 2 h) 

7.21 Place one small drop of the glycerol:water mixture (1:7) on each Mg2+-glycerol slide. 

7.22 Draw 1 mL of <2-μm clay suspension into the resin-loaded syringe and invert back and 

forth to facilitate cation exchange. 

7.23 Dispense 3 drops to clear the tip. 

7.24 Dispense ≈ 0.1 mL (6 to 10 drops) to cover the appropriate XRD slide. Draw DDI water 

into the syringe and expel 3 times to remove all of the clay suspension. Recharge the syringe 

after 10 times of use. 

7.25 When the clay suspension has dried, transfer the slides with the K+

-saturated clays to 

transite plates and heat for a minimum of 2 h in a muffle furnace. 

7.26 Heat the following sample slides on the XRD sample board. 

K+-300°C - slides 3, 7, 11, 15, 19, 23, 27, and 31 

K+-500°C - slides 4, 8, 12, 16, 20, 24, 28, and 32 

7.27 After heating, remove the transite plate from the furnace, cool to air temperature, and 

return slides to XRD sample board. 

X-ray Diffraction Operation

7.28 The X-ray analysis of the glycerol slide must be done within 1 to 2 days after the slide 

dries. If this is not possible, skip Step 7.21 when slide is prepared. Add one small drop of 

glycerol:water mixture (1:7) to dry slide 24 h prior to X-ray analysis. 

7.29 Transfer the slides (1 to 32) from XRD sample board to slide holders (1 to 32) and place in 

slots (1 to 32) in a magazine for the automated sample changer. 

7.30 Analyze one reference soil sample in each run. Place this sample in slot 33. 

7.31 Analyze one quartz standard for 2θ and intensity calibrations in each run. Place this 

sample in slot 34. Intensity is measured at peak maximum at or near 26.66° 2θ for 10 s. 

7.32 The 32 samples from one XRD board constitute one run on the diffraction unit. Prepare a 

run sheet for samples on each XRD sample board. Refer to example run instruction (7.33). 

Refer to the manufacturer's manual for operation of the X-ray diffractometer. 

7.33 Place the magazine in the automated sample changer. Confirm that the XRD shutter is off 

when changing magazines. Set the XRD unit parameters as follows: 

CuKa radiation, λ: 1.54 A (0.154 nm) 

544
Scan range: 2° to 34° 2θ

Generator settings: 40 kv, 20 ma 

Divergence slit: 1° 

Receiving slit: 0.2 mm 

Monochrometer: Yes 

Step size and scan speed vary depending on intensity of X-rays generated from tube. Adjust 

settings to maintain same long-term peak intensities on standard reference clay and quartz 

standard regardless of tube intensities. 

7.34 Enter run instruction from the keyboard. Create a batch file for the automated run. File 

names specified are of the sample number. An example run instruction is as follows: 

Batch File Name: Project number (e.g., CP95LA022) 

Raw Data File Name: Run number 

First Sample: 1 

Last Sample: 33 

(reference soil clay) 

7.35 Activate program. The run stores raw data on the hard disk under the subdirectory 

designated by project type and year, e.g., CP95. Refer to example run instruction (7.34). 

7.36 Print a hard copy of the "Detected Peaks File" for each sample and perform level 1 

smoothing on diffraction patterns. 

7.37 Prepare and print a 4-color graphics chart. The 4 colors are blue (Mg2+); green (Mg2+- glycerol); pink (K+

 300°C); and red (K+ 500°C). Stamp chart with label; enter run parameter 

information, and complete soil information, e.g., soil name, horizon designation, and depth. 

File hard copies of detected peaks and graphics chart in pasteboard binders by state, county, 

and chronology. 

7.38 Record "d" spacing and intensity of quartz standard in the logbook. Record the peak 

intensities for designated peaks for the reference soil clay. 

7.39 File the detected peaks printout and graph for the reference soil in the reference soil-clay 

folder. 

Interpretation of X-ray Diffraction Data 

7.40 The angle in degrees two theta (2θ) measured in X-ray diffraction analyses is converted to 

angstroms (A) using tables complied according to Bragg's Law. Refer to summary of method. 

Angstroms convert to nanometers (nm) by a factor of 0.1, e.g., 14 A = 1.4 nm. 

7.41 Use the following X-ray diffraction criteria to identify some common crystalline minerals. 

The reported "d" values are for 00l basal spacings. The Miller index (hkl) specifies a crystal 

face which has some orientation to the three crystallographic axes of a, b, and c. The Miller 

index (00l) indicates a crystal face that is parallel to the a and b axes, e.g., phyllosilicate 

minerals. The following X-ray diffraction criteria also has some questions (Q) that may aid the 

analyst in interpreting the diffraction patterns. These questions are a suggested procedural 

approach to help the analyst identify the relative locations of a few peaks and to confirm key 

criteria. 

545
X-Ray Diffraction Criteria

1. Kaolinite and Halloysite

a. Crystal structure missing at 500°C. 

b. 7 A (7.2 to 7.5 A) with all other treatments 

Q. Is there a 7 A peak? Is it destroyed at 500°C? Kaolinite or Halloysite. 

Q. Is the peak sharp and at ~ 7.1 A? Kaolinite. 

Q. Is the peak broad and at 7.2 to 7.5 A? Halloysite. 

2. Mica (Illite)

a. 10 A with all treatments. 

b. 10 A with Mg2+-saturation 

Q. Is there a 10 A peak with Mg2+-saturation? Mica (Illite). 

3. Chlorite a. Crystal structure of Fe-chlorites destroyed at 650 to 700°C. 

b. 14 A with all other treatments. 

c. 14 A at 500°C. 

d. Generally also has strong 7 A peak. 

Q. Is there a 14 A peak when heated to 500°C? Chlorite. 

4. Vermiculite

a. 14 A with Mg2+-saturation. 

b. 14 A with Mg2+-glycerol solvation.

c. Nearly 10 A with K+

saturation. 

d. 10 A when K+-saturated and heated to 300°C. 

Q. Is there an enhanced 10 A peak with K+-saturation in comparison to Mg2+saturation that 

cannot be attributed to smectitie? Vermiculite. 

5. Smectite

a. 14 A with Mg2+-saturation 

b. 12 to 12.5 A with K+- or Na+-saturation. 

c. 17 to 18 A with Mg2+-glycerol solvation. 

d. 10 A with K+-saturation and heating to 300°C. 

Q. Is there a 17 to 18 A peak upon solvation? Smectite. 

6. Gibbsite

a. Peak at 4.83 A with Mg2+ and Mg2+-glycerol but destroyed when heated to 300°C. 

7. Goethite

a. Peak at 4.18 A with Mg2+ and Mg2+-glycerol but destroyed when heated to 300°C. 

8. Hydroxy-interlayed Vermiculite or Smectite 

a. Incomplete collapse to 10 A of smectite or vermiculite when K+-saturated and heated to 

300°C. 

9. Quartz

a. Peaks at 4.27 A and 3.34 A with all treatments (only 3.34 if small amounts). 

10. Lepidocrocite

a. Peak at 6.2 to 6.4 A with Mg2+ and Mg2+-glycerol but destroyed when heated to 300°C. 

11. Potassium Feldspar

a. Peak at 3.24 A with all treatments. 

546
12. Plagioclase Feldspar

a. Twin peaks between 3.16 and 3.21 with all treatments. 

13. Calcite

a. Peak at 3.035 A with all treatments. 

14. Dolomite

a. Peak at 2.88 to 2.89 A with all treatments. 

15. Gypsum

a. Peak at 4.27 A with Mg2+ and Mg2+-glycerol, but destroyed when heated to 300°C. 

16. Mixed Layer Vermiculite-Mica

a. Peak at 11 to 13 A with Mg2+ that does not expand with Mg2+-glycerol. 

b. Peak collapses to 10 A with K+-saturation and heating to 300°C. 

17. Mixed Layer Smectite-Mica

a. Peak at 11 to 13 A with Mg2+ that expands to 14-16 A with Mg-glycerol. 

b. Peak collapses to 10 A with K+-saturation and heating to 300°C. 

18. Mixed Layer Chlorite-Mica

a. Peak at 14 A with Mg2+ and Mg2+-glycerol.

b. Peak collapses toward 10 A with K+-saturation and heating to 300°C, and more completely 

with heating to 500°C, but never to 10 A. 

19. Mixed Layer Chlorite-Smectite

a. Peak at 11 to 13 A with Mg2+-saturation that expands to about 16 A with Mg2+-glycerol. 

b. Collapses to about 12 A with K+-saturation and heating to 300°C and 500°C. 

7.42 Use the X-ray diffraction criteria, i.e., diagnostic basal 00l spacings (A), in Table 1 for 

identification and ready reference of some common crystalline minerals as affected by 

differentiating sample treatments. 

7.43 Preferential orientation of clay mineral samples enhances diffraction from the basal (00l) 

spacing and tends to minimize the number and intensity of peaks from diffraction by other hkl

planes. With preferential orientation, second, third, and fourth order peaks may be recorded in 

addition to the basal first order peaks. Groups of associated peaks that differ by order of 

diffraction are as follows: 

Smectite (Mg2+-glycerol): 

a. 17 to 18 A. 

b. 8.5 to 9 A (weak). 

Chlorite, vermiculite, and smectite: 

a. 14, 7, 4.7, and 3.5 A. 

b. 7, 4.7, and 3.5 A weak for smectite. 

Mica:

a. 10, 5 (weak in biotites and moderate in muscovites), and 3.3 A. 

Kaolinite: 

a. 7 and 3.5 A. 

547
7.44 The differentiation of kaolinite and halloysite in a sample can be aided by the use of 

formamide (Churchman et al., 1984). The intercalation and expansion of halloysite to a dspacing of ≈ 10.4 A is relatively rapid (20 to 30 min), whereas kaolinite expansion requires ≈ 4 

h upon treatment. The procedure is as follows: 

a. Lightly spray formamide as an aerosol on the dried Mg2+-saturated slide. 

b. Wait 15 min but not more than 1 h and X-ray approximately 7.6 to 13.5° 2θ (d = 11.6 to 6.55 

A). 

c. Halloysite will expand to ≈ 10.4 A, whereas kaolinite will remain unchanged. 

d. Heating the sample to 110°C for 15 min will collapse the halloysite to ≈ 7 A. 

e. The total amount of kaolinite and halloysite can be determined by thermal analysis. The 

intensity ratio of the 10.4 to 7.2 A peaks of the formamide-treated sample can be used to 

determine the relative percentage of halloysite and kaolinite. 

8. Calculations

X-ray diffraction produces peaks on a chart that corresponds to 2θ angle on a 

goniometer. Standard tables to convert θ or 2θ to crystal "d" spacings are published in the U.S. 

Geological Survey Circular 29 (Switzer et al., 1948) and in other

publications (Brown, 1980). The crystal "d" spacings of minerals, i.e., the interval between 

repeating planes of atoms, can be calculated by Bragg's Law. Refer to summary of method. 

548
Table 1. X-ray diffraction parameters of common soil clay minerals. 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Mineral Treatment 

 Na+ Mg2+ Mg2+ K+ K+ K+ K+

 Gly 300°C 500°C 700°C 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 00l diffraction spacing in angstroms 

Kaolinite 7 7 7 7 7 LD1/ LD 

Halloysite 7B2/ 7B 7B 7B 7B LD LD 

Mica (Illite) 10 10 10 10 10 10 10 

Chlorite 14*3/ 14* 14* 14* 14* 14* T4/

Vermiculite 14 14 14 10 10 10 10 

Smectite 12.5 14 18 12.5 10 10 10 

Gibbsite 4.85 4.85 4.85 4.85 LD LD LD 

Goethite 4.18 4.18 4.18 4.18 LD LD LD 

Interlayer 10-14 10-14 10-18 10-14 10-14 10-14 10-14 

Quartz 3.14 and 4.27 for all treatments 

Calcite 3.035 for all treatments 

Dolomite 2.88 for all treatments 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ 1/ LD = Lattice destroyed 

2/ B = Broad peak is common 

3/ * = Sometimes <14A 

4/ T = Temperature of decomposition varies with chemical composition, particle-size, and 

heating conditions. 

549
9. Report

From the "Detected Peaks File" and graphics chart, identify the minerals present 

according to the registered "d" spacings. As a first approximation, use the following peak 

intensities, i.e., peak heights above background in counts s-1, to assign each layer silicate 

mineral to one of the 5 semiquantitative classes. 

Class Peak Height 

 above Background 

 (counts sec-1) 

5 (Very Large) >1.88 X 103

4 (Large) 1.12 to 1.88 X 103

3 (Medium) 0.36 to 1.12 X 103

2 (Small) 0.11 to 0.36 X 103 

1 (Very Small) <0.11 X 103

Adjust class placement to reflect area under the curve if peak is broad relative to peak 

height or if thermal, elemental, clay activity data, or other evidence warrant class adjustment. 

If there are no peaks or no evidence of crystalline components, place the sample in NX class 

(noncrystalline). 

10. Precision Precision data are not available for this procedure. Procedure 7A2i (X-ray diffraction) 

is semiquantitative. 

11. References

Brown, G. 1980. Appendix I (Tables for the determination of d in A from 2θ for the KA 

and KB radiations of copper, cobalt, and iron). In G.W. Brindley and G. Brown (eds.) 

Crystal structures of clay minerals and their x-ray identification. Mineralogical Soc. 

Monograph No. 5. Mineralogical Soc. Great Britain. pp 439-475. 

Churchman, G.J., J.S. Whitton, G.G.C. Claridge, and B.K.G. Theng. 1984. Intercalation 

method using formamide for differentiating halloysite from kaolinite. Clays and Clay 

Minerals. 32:241-248. 

Switzer, G., J.M. Axelrod, M.L. Lindberg, and E.S. Larsen 3d. 1948. U.S. Dept. Interior. 

Geological Survey. Circular 29. Washington, DC. 

Whittig, L.D., and W.R. Allardice. 1986. X-ray diffraction techniques. In A. Klute (ed.) 

Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. 

Agronomy 9:331-362. 

Total Analysis (7C) 

HF Plus Aqua Regia (HF + HNO3 + HCl) Dissolution (7C4a) 

1. Application 

Prior to the development of modern analytical techniques, e.g., X-ray diffraction and 

thermal analysis, identification of minerals was based on elemental analysis and optical 

properties (Washington, 1930; Bain and Smith, 1994). Chemical analysis is still essential to 

determine mineral structural formulas and to identify and quantify specific mineral species 

through elemental allocation to minerals. Many clay mineral groups are subdivided based on 

composition. 

Analysis of the entire fine earth (<2-mm) fraction or specific particle-size separates 

provides information on parent material uniformity, pedon development, and mineral 

weathering within or between pedons. This interpretation is determined from differences 

between horizons or pedons in elemental concentrations, elemental ratios such as Si/Al, 

550
Si/Al+Fe, or Ti/Zr, or from differences in total elemental concentrations compared to 

concentrations determined by selective dissolution techniques. 

The inherent fertility of a soil derived from its parent material can be examined by 

determination of the basic cations relative to the Si or Al content. Phosphorus fertility of a soil 

and potential water quality problems can be better understood by measurements of total P, 

especially when compared to other P measurements, such as water-soluble or Bray-extractable 

P. 

Hydrofluoric acid (HF) is efficient in the digestion and dissolution of silicate minerals 

for elemental dissolution (Bernas, 1968; Sawhney and Stilwell, 1994). Aqua regia (HNO3 and 

HCl) aids in digestion of soil components, especially the organic fraction. Procedure 7C4a is a 

digestion of 100 mg of dried clay suspension, the fine earth (<2-mm) fraction, or other particle 

size separate with HF and aqua regia. Closed digestion vessels (Parr Bombs) are heated in the 

oven at 110°C for at least six hours. Elemental concentration of the digestate is determined by 

inductively coupled plasma-atomic emission spectrometry (ICP-AES). 

2. Summary of Method 

A clay suspension (procedure 7A2i) containing approximately 100 mg of clay material 

is pipeted into a Teflon digestion container and dried at 110°C. A equal amount of suspension 

is pipeted into a tared aluminum-weighing dish and dried at 110°C to obtain a dried sample 

weight. An oven-dry 100-mg soil sample (<80 mesh) or a specific particle-size separate may 

be substituted for the clay suspension. The P and Na content of the clay fraction is not 

measurable when the soil is dispersed in sodium hexametaphosphate (procedure 7A2i). Total P 

and Na are measurable on the fine-earth fraction or other particle-size separates not dispersed in 

Na or P-containing reagents, and the analyses are included as a part of this procedure. 

Following evaporation of the aqueous portion of the suspension, 0.75 mL HNO3, 0.25 

mL HCl, and 5 mL HF are added. The vessel is inserted into a stainless steel retainer vessel, 

heated, cooled, and 15 mL of 2.5 percent boric acid solution is added to neutralize the excess 

HF acid. The digestate is quantitatively transferred with boric acid solution, diluted to 100 mL, 

shaken, and allowed to stand overnight. Approximately 60 mL are saved for analysis. The 

concentration of Fe, Mn, Al, Ca, Mg, Na, K, P, Si, Zr, Cu, Zn, As, Ti, Se, Cd, and Pb are 

determined by ICP analysis in procedures 6C7b, 6D6a, 6G11b, 6N5b, 6O5b, 6P3b, 6Q3b, 

6S6a, 6V1b, 8K1a, 8L1a, 8M1a, 8N1a, 8O1a, 8P1a, 8Q1a, and 8R1a, respectively. Data are 

reported in procedure 7C4a. 

3. Interferences 

Insoluble fluorides of various metals may form. Formation of SiF4 results in gaseous 

losses of Si, but additions of boric acid retards formation of this molecule as well as dissolves 

other metal fluorides. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated acids to the fume hood. Keep HF acid refrigerated and 

avoid contact with skin of all acids. Wash hands thoroughly after handling reagents. Filling 

the Teflon cup of the acid digestion bomb to greater than 25 percent of the free volume or 

adding organic reagents or oxidizing agents to the cup may result in explosion of the digestion 

bomb. 

5. Equipment 

5.1 Pipet(s) capable of delivering 5, 0.75, and 0.25 mL 

5.2 Volumetric flasks, nalgene, 100 mL 

5.3 Polypropylene bottles, 60 mL, with cap 

5.4 Electronic balance, ±0.1 mg sensitivity 

5.5 Acid digestion bombs: 25-mL Teflon containers with stainless steel retainer vessels 

5.6 Oven, 110°C 

551
5.7 Desiccator with P2O5 drying agent 

5.8 Disposable aluminum-weighing dishes 

6. Reagents 

6.1 Deionized distilled (DDI) water 

6.2 Hydrofluoric acid (HF), 48%, low trace metal content 

6.3 Concentrated hydrochloric acid (HCl), 12 N. Use instrumental grade reagents which 

contain low levels of impurities. 

6.4 Concentrated nitric acid (HNO3), 16 N. Use instrumental grade reagents which contain 

low levels of impurities. 

6.5 Boric acid solution, 2.5 percent. Dissolve 25.0 g low trace metal, granular boric acid 

(H3BO3) in 1000 mL DDI water. 

7. Procedure 

HF plus Aqua Regia Dissolution

7.1 Prepare Na-saturated clay as in procedure 7A2i, Preparation of Clay Suspension, Steps 7.8 

to 7.19. Clay dispersion by this method eliminates quantitative analysis of Na and P in the clay 

due to dispersion by sodium hexametaphosphate. Digestion of the entire fine earth (<2-mm) 

fraction or any fraction not derived by dispersion with sodium hexametaphosphate (or other Na 

and P-containing dispersing agents) can be quantitatively analyzed for Na and P. Dispersion of 

clays and cleaning of test tubes and dishware should be with DDI water. 

7.2 Pipet a known aliquot of clay suspension containing approximately 100 mg clay into a 25-

mL Teflon container. The milliliters of suspension required depends on the clay concentration 

of the suspension but is generally from 2 to 6 mL. More dilute suspensions should be partially 

evaporated under a fume hood to concentrate the clay prior to transfer to the Teflon container. 

Fine-earth (<2-mm) or a specific particle size separate ground to <80-mesh may be used instead 

of clay. Samples with greater than 3 percent organic C should be ashed in a muffle furnace at 

400°C for 2 h prior to analysis to destroy the organic matter. Oven-dry the sample (110°C), 

cool over P2O5, and weigh to 100 ±0.1 mg. If a clay suspension is used, Steps 7.3 to 7.4 are 

performed. Proceed to Step 7.5 if using fine-earth or other oven-dried material. 

7.3 Pipet a duplicate aliquot of suspension (as used in Step 7.2) into a tared Al weighing dish, 

dry at 110°C, cool in a desiccator with P2O5, and weigh to the nearest 0.1 mg. Use this value as 

the sample weight in the calculations. 

7.4 Dry the Teflon container and clay suspension in an oven for 4 h or until the aqueous portion 

of the suspension is completely evaporated. Remove from oven and cool on the bench top or in 

a fume hood. Cooling in a desiccator is not required. 

7.5 Pipet 0.75 mL HNO3 and 0.25 mL HCl into the sample and allow to completely wet and 

then pipet 5 mL HF into sample. 

7.6 Place covered Teflon container in stainless steel retainer vessel. Place sample in oven at 

110°C for a minimum of 6 h. Samples can be left in the oven overnight at 110°C. 

7.7 Remove samples from oven and cool for at least 4 h. 

7.8 Under a hood, remove Teflon container from steel retainer vessel, open the Teflon 

container, and add 15 mL 2.5 percent boric acid solution. 

7.9 Quantitatively transfer contents of Teflon container to a 100 mL nalgene volumetric flask 

and adjust to volume with 2.5 percent H3BO3. 

552
7.10 Cap flask and mix well by inverting at least three times. Allow to stand overnight to 

dissolve any metal fluorides. 

7.11 Invert the volumetric flask to mix and decant approximately 60 mL into a labeled 

polypropylene container. 

7.12 Prepare working standards of a blank, a clay suspension from a SSL reference soil sample, 

and a National Institute of Standards and Technology (NIST) standard reference material by the 

same digestion method. Run one of these standards with each set of 20 samples. 

7.13 Solutions and standards are analyzed by ICP spectrometry. Refer to procedures 6C7b, 

6D6a, 6G11b, 6N5b, 6O5b, 6P3b, 6Q3b, 6S6a, 6V1b, 8K1a, 8L1a, 8M1a, 8N1a, 8O1a, 8P1a, 

8Q1a, and 8R1a for analysis of Fe, Mn, Al, Ca, Mg, Na, K, P, Si, Zr, Cu, Zn, As, Ti, Se, Cd, 

and Pb, respectively. 

8. Calculations 

8.1 Data are transferred as an ASCII file from the ICP computer onto a 3.5-in floppy disk via 

"Report Writer" in the TJA software ThermoSpec, Version 5.06. 

8.2 On a MS-DOS based PC computer, import the ASCII file of ICP data into the DOS editor 

and strip off unnecessary headers and data from standards. Save the file after editing, renaming 

using a format that can be imported into LOTUS, e.g., rename to .wk3 file for LOTUS 123, 

Version 3.1. 

8.3 Import the file into an established total analysis spreadsheet in LOTUS 123. The 

spreadsheet has columns for sample number, soil fraction digested, soil weight, concentration 

of each element in ppm, and the calculated elemental percent. Each line of elemental data for a 

sample is imported as a single data string. 

8.4 Parse the components of each data string into separate columns. Rearrange the data set in 

order to have all elemental values on a single line for a particular sample. Move the data into 

the correct columns of the spreadsheet. 

8.5 Insert values for elements requiring dilution into the original line of sample data and replace 

all negative values with zero. 

8.6 Input sample weights, or if possible, import sample weights (dried soil weights) from the 

ASCII file generated by computer attached to balance via RS-232. 

8.7 Calculate the percent of an element in the soil from ppm in solution as shown in the Si 

example as follows: 

Si (ppm) in solution = 75.2 ppm (75.2 μg/mL) 

Volume extract = 100 mL 

Sample weight (110°C) = 100.0 mg 

Calculate as follows: 

% Si = 75.2μg mL-1 x 100 mL x (1 g/ 106

 μg) x (1/0.1 g soil) x 100 = 7.52 % 

8.8 The fraction digested needs to be identified with each sample. Use proper SSL database 

abbreviations. 

553
8.9 Delete the Na and P data for clay samples dispersed in sodium hexametaphosphate. 

8.10 Prepare the file to send to CMS. Save the file as an unformatted ASCII file using LOTUS. 

8.11 Enter data for Si, Al, Fe, Mg, Mn, K, Ti, Ca, Zr, P, and Na into the SSL CMS database on 

a 110°C weight basis as percent of the element in the fraction digested. Data are converted to 

the oxide form on the data sheet. 

8.12 The factor for converting from an elemental form to an oxide form is based on the atomic 

weights of the element and oxygen. An example is as follows: 

Atomic weight Si = 28.09 

Atomic Weight O = 16.0 

Molecular weight SiO2 = 60.09 

Calculate percent Si in SiO2 as follows: 

Si (%) = (28.09/60.09) x 100 = 46.7 % 

There is 46.7 percent Si in SiO2. To convert from percent Si to percent Si oxide (SiO2) in the 

soil, divide the percent Si by 0.467 or multiply by the inverse of this value. The following table 

lists the element, the oxide form, and the elemental percent in the oxide form. 

Element 

Form 

Oxide Elemental 

% 

Si SiO2 46.7 

Al Al2O3 52.9 

Fe Fe2O3 69.9 

Mg MgO 60.3 

Mn MnO 77.4 

K K2O 83.0 

Ti TiO2 59.9 

Ca CaO 71.5 

Zr ZrO2 74.0 

P P2O5 43.6 

Na Na2O 74.2 

9. Report 

Data are reported as percent to the nearest tenth for Fe, Al, Mg, Na, K, and Si; to the 

nearest hundredth for Mn, Ca, P, and Ti; and to the nearest thousandth for Zr. The remaining 

trace elements (Cu, Zn, As, Se, Cd, and Pb) are reported in mg kg-1 (ppm). 

10. Precision 

The mean, standard deviation, and C.V. are calculated for each element for both the 

NIST standard and the SSL reference standard. 

11. References 

Bain, D.C., and B.F.L. Smith. 1994. Chemical analysis. (In) M.J. Wilson ed., Clay 

Mineralogy: Spectroscopic and Chemical Determinative Methods. pp. 300-332. 

Chapman and Hall, Inc. London, England. 

Bernas, B. 1968. A new method for decomposition and comprehensive analysis of silicates 

by atomic absorption spectrometry. Anal. Chem. 40:1682-1686. 

554
Sawhney, B.L., and D.E. Stilwell. 1994. Dissolution and elemental analysis of minerals, 

soils, and environmental samples. (In) J.E. Amonette and L.W. Zelazny, eds., 

Quantitative methods in soil mineralogy. pp. 49-82. Soil Sci. Soc. Am. Miscellaneous 

Publ. Madison, WI. 

Washington, H.S. 1930. The chemical analysis of rocks. 4th ed. John Wiley and Sons, Inc., 

New York, NY. 

Surface Area (7D) 

Ethylene Glycol Monoethyl Ether (EGME) Retention (7D2) 

1. Application

Surface area determines many physical and chemical properties of materials. Water 

retention and movement, cation exchange capacity, pesticide adsorption, and many biological 

processes are closely related to specific surface (Carter et al., 1986). Soils vary widely in their 

reactive surface area because of differences in mineralogical and organic composition and in 

their particle-size distribution (Carter et al., 1965). Specific surface, defined as surface area per 

unit mass of soil, is usually expressed in units of m2 g

-1

 or cm

2

 g

-1 soil. Specific surface has 

been measured for several clays, e.g., 810 m2

 g

-1 for smectite and 20 to 40 m2

 g

-1 for kaolinite 

and mica. 

2. Summary of Method

Ethylene glycol monoethyl ether (EGME) retention is a surface-area determination. A 

soil sample is dried over phosphorus pentoxide (P2O5). The sample is saturated with EGME. 

A monomolecular layer of EGME is established by desorbing the EGME by vacuum over 

EGME-saturated CaCl2. The solvate of CaCl2 and EGME helps to maintain an EGME vapor 

pressure in the desiccator which results in the formation of a monomolecular layer of EGME on 

sample surfaces. 

The weight of a monomolecular layer of EGME on the sample is determined by 

weighing the dried sample. EGME is determined by weighing the sample and sample plus 

EGME (Carter et al., 1965). The SSL determines EGME retention by procedure 7D2. The 

SSL reports EGME retention as mg EGME per g of soil to the nearest mg on a <2-mm base. 

3. Interferences

The loss or contamination of sample and the variation in sample weight may cause 

erroneous results. Handle the weighing vessels with finger cots or tongs to prevent vessel 

contamination and the resulting weighing errors. High relative humidity in the laboratory may 

result in high moisture absorption by sample. 

4. Safety

Wear protective clothing (e.g., coats, aprons, and gloves) and eye protection (e.g., face 

shields, goggles, or safety glasses) when handling reagents and working with vacuum 

desiccators. Follow standard laboratory safety procedures in handling reagents and vacuum 

devices. The P2O5 is corrosive and reacts violently with water. Use caution in cleaning P2O5

spills. The EGME is combustible and harmful is swallowed, inhaled, or absorbed through the 

skin. Keep samples and desiccators with EGME under fume hood at all times. 

5. Equipment

5.1 Electronic balance, ±0.1-mg sensitivity, Mettler AE 160 

5.2 Vacuum desiccator, 250 mm, Nalgene No. 5310, with desiccator plate, 230 mm 

5.3 Laboratory vacuum or vacuum pump, 0.65 to 0.75 bars 

5.4 EGME trap, anhydrous CaCl2 in a large tube between desiccator and vacuum source 

5.5 Syringe, polypropylene, 3 mL 

5.6 Weighing bottle, cylindrical, low form, 50 x 30 mm 

555
6. Reagents

6.1 Ethylene glycol monoethyl ether (EGME), reagent 

6.2 Phosphorus pentoxide (P2O5), anhydrous 

6.3 Calcium chloride (CaCl2), pellets, 40 mesh, reagent grade 

7. Procedure

7.1 Dry 3 to 5 g of <2-mm, air-dry soil in a weighing bottle in a vacuum desiccator over P2O5

for 2 days. 

7.2 Prepare solvated CaCl2 by weighing 100 g oven-dried CaCl2, without cooling, into a large 

beaker. Add 20 g EGME and mix by stirring. Transfer to a desiccator in which EGMEsaturated samples equilibrate. 

7.3 Weigh the P2O5-dried soil sample to the nearest 0.1 mg. When working outside the 

desiccator, cover the sample to avoid moisture adsorption from the atmosphere. 

7.4 Use a 3-mL syringe to saturate the soil with EGME. Add 5 drops in excess of saturation. 

7.5 Place the uncovered, EGME-soil mixture in a vacuum desiccator over solvated CaCl2. Use 

a laboratory vacuum of 0.65 to 0.75 bar pressure. 

7.6 Loosely cover the tops of weighing bottles with a piece of aluminum foil that is smaller 

than the inside diameter of desiccator. 

7.7 Apply suction for 16 to 24 h. 

7.8 Carefully release the suction. Remove weighing bottles and weigh the EGME-soil mixture. 

7.9 If a 3-g sample is used, the difference between the EGME-soil mixture and P2O5-dry soil is ≈ 10 mg EGME/g P2O5-dry soil. When this difference is <10 mg, reduce the vacuum time to 1 

h day-1 and weigh twice daily. 

7.10 Repeat the vacuum and weighing procedure until a constant weight is attained. Constant 

weight is defined as three successive daily weighings within 1 mg of EGME per gram P2O5-dry 

soil. When a constant weight is attained, make calculations. 

8. Calculations

8.1 The EGME retention is calculated as follows: 

Retention of EGME (mg g-1) = (Wt1 - Wt2) x (1000/Wt3) 

where: 

Wt1 = Soil weight with monomolecular layer of EGME + Tare weight of bottle 

Wt2 = Soil weight after drying with P2O5 + Tare weight of bottle 

Wt3 = Soil weight after drying with P2O5 - Tare weight of bottle 

1000 = Conversion factor (mg g-1) 

The surface area in units of mg EGME per g of soil is converted to m2 g-1, the convention 

commonly used in clay mineralogy. The conversion is as follows: 

Surface area (m2 g-1) = (EGME retention (mg g-1))/0.286 

where: 

556
0.286 = Conversion factor (mg EGME m-2) 

The constant, 0.286, is the amount of EGME (mg) that is required to cover a m2 of clay 

surface with a monomolecular layer (Carter et al., 1986). This value is calculated from the 

measured value of 231.7 mg EGME per g of pure montmorillonite assumed to have 810 m2 g

-1

on the basis of other measurements. 

9. Report 

Report EGME as mg EGME per g of soil to the nearest mg. 

10. Precision

Precision data are not available for this procedure. Two quality control checks, a high 

and a low standard, are routinely analyzed in EGME. The mean (mg EGME per g soil), 

standard deviation, and C.V. for the quality control check sample are as follows: 

 Mean n Std. 

Dev. 

C.V. 

High Std 109.0 10 7.4 7.3 

Low Std. 37.5 10 0.64 4.8 

11. References 

Carter. D.L., M.D. Heilman, and C.L. Gonzalez. 1965. Ethylene glycol monoethyl ether 

for determining surface area of silicate minerals. Soil Sci. 100:356-360. 

Carter, D.L., M. M. Mortland, and W.D. Kemper. 1986. Sampling. In A. Klute (ed.) 

Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. 

Agronomy 9:413-423. 

MISCELLANEOUS (8) 

Ratios and Estimates (8D) 

To Noncarbonate Clay (8D2)

Divide the CEC-7 (procedure 5A8c), extractable Fe (procedure 6C2), or 15-bar water 

retention (procedure 4B2a or 4B2b) by the noncarbonate clay percentage. Noncarbonate clay is 

determined by subtracting the carbonate clay (procedure 3A1d or 3A2d) from total clay 

(procedure 3A1 or 3A2). 

Ratios and Estimates (8D) 

Ca to Mg (extractable) (8D3) 

Divide extractable Ca2+ (procedure 6N2) by extractable Mg2+ (procedure 6O2). 

Ratios and Estimates (8D) 

Estimated Clay Percentage (8D4) 

For most soils, clay percentage can be approximated as 2.5 x 15-bar water percentage 

(procedure 4B2a or 4B2b). Use caution in applying this factor to any particular situation, 

especially if organic matter or other amorphous material is present in significant quantities. 

Ratios and Estimates (8D) 

Estimated Total Salt (8D5) 

557
Use the charts and graphs available in U.S. Salinity Laboratory Staff (1954) to estimate 

total salt content from the electrical conductivity (ECs) of the saturation extract (procedure 

8A3a). The essential relations are summarized in the equations as follows: 

Log total salt in soil (ppm) = 0.81 + 1.08 x Log ECs (mmhos cm-1) + Log SP 

where: 

ECs = Electrical conductivity of saturation extract 

SP = Saturation percentage of saturation extract 

Total salt in soil (%) = Total salt (ppm) x 10-4

These equations are applicable to saturation extracts with an ECs <20 mmhos cm-1. Deviations occur at higher salt concentrations. 

Ratios and Estimates (8D) 

Iron Plus Aluminum, Pyrophosphate Extractable to Dithionite-Citrate 

Extractable (8D6) 

Divide the sum of the pyrophosphate-extractable Fe plus Al (procedures 6C8a and 

6G10a, respectively) by the sum of dithionite-citrate-extractable Fe plus Al (procedures 6C2 

and 6G7, respectively). Pyrophosphate and dithionite-citrate extractable Fe and Al are former 

criteria for spodic placement (Soil Survey Staff, 1975). 

Ratios and Estimates (8D) 

Index of Accumulation (8D7)

Subtract 1/2 the clay percentage (procedure 3A1 or 3A2) of a subhorizon from the CEC 

at pH 8.2 (procedure 5A3a) and multiply the remainder by the thickness of subhorizon (cm). 

The combined index of accumulation of amorphous material is a former criterion for spodic 

placement (Soil Survey Staff, 1975). 

References

Soil Survey Staff. 1975. Soil Taxonomy: A basic system of soil classification for making and 

interpreting soil surveys. USDA-SCS Agric. Handb. 436. U.S. Govt. Print. Office, 

Washington, DC. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of saline 

and alkali soils. 160 p. U.S. Dept. of Agric. Handb. 60. U.S. Govt. Print. Office, 

Washington, DC. 

558
Use Table 1 with the SSL preparation procedures 1B1, 1B2, 1B5, 1B6, and 1B7. 

Gravel codes are also defined in Table 1. In the "Code" column, "Char" refers to 

characterization sample. Laboratory preparation and >2-mm porosity are defined in footnotes 

on laboratory data sheet. 

---------------------------------------------------------------------------------------------------------------- 

Table 1. Laboratory preparation codes and procedural summaries. 

 Code Laboratory Preparation

Char >2mm 

S Blank Weigh sample at field-moisture content and record weight. Airdry, weigh, and record weight. Sieve >2-mm fractions, weigh, 

record weights, and discard. Report all analytical results on <2-

mm basis. Refer to procedure 1B1, Standard Air-dry. 

S P Lab preparation is same as S-blank. However, report clod 

parameters and Cm (correction factor for >2-mm content moist 

soil) on an whole-soil basis. Refer to procedure 1B1, Standard 

Air-dry. 

N Blank Lab preparation is same as S-blank except do not record the 

weight of the >2-mm fraction. All analytical results are reported 

on a <2-mm basis. Refer to procedure 1B1, Standard Air-dry. 

M Blank Lab preparation is same as S-blank except sieve <2-mm moist 

subsample for 15-bar moist analysis. Use <2-mm air-dry soil for 

all other analyses. Report all analytical results on <2-mm basis. 

Refer to procedure 1B2, Field-moist. 

S K Lab preparation is same as S-blank except grind the 2- to 20-mm 

fraction to <2 mm and keep for CO3 analyses, etc. Report the 

analytical results for the ground 2- to 20-mm fraction on a 2- to 

20-mm basis and all other analytical results on a <2-mm basis. 

Refer to procedure 1B5, Coarse Fragments. 

S R Lab preparation is same as S-blank except recombine the 2- to 

20-mm fraction with the <2-mm fraction and grind the entire 

sample to <2 mm. Report all analytical results for ground sample 

on a <2-mm basis. Refer to procedure 1B5, Coarse Fragments 

G P Weigh sample at field-moisture content and record weight. Airdry, weigh, and record weight. Grind entire sample to <2 mm. 

Report all analytical results for ground sample on a whole-soil 

basis. Refer to procedure 1B6, Whole-soil. 

W P Weigh sample at field-moisture content and record weight. Airdry, weigh, and record weight. Sieve >2-mm fractions, weigh, 

and record weights. Recombine the >2-mm fractions with the <2-

mm fraction and grind entire sample to <2 mm. Report all 

analytical results on a whole-soil basis. This procedure is no 

longer performed at the SSL. 

559
Table 1. Laboratory preparation codes and procedural summaries (continued). 

Code Laboratory Preparation

Char >2mm

H Blank Obtain a moist whole-soil subsample for Histosol analysis. 

Obtain a <2-mm moist subsample for 15-bar moist analysis. 

Weigh remaining sample at field-moisture content and record 

weight. Air-dry, weigh, and record weight. Sieve >2-mm 

fractions, weigh, record weights, and discard. Pulverize 

subsample of <2-mm air-dry soil to a <80-mesh size and use for 

lab analyses. Use <80-mesh air-dry for all analyses except 

AD/OD, 15-, 1/10- and 2-bar analyses. For the AD/OD, 15-, 

1/10- and 2-bar analyses, use <2-mm air-dry soil. Use <2-mm 

moist subsample for 15-bar moist. Report all analytical results 

except fabric on a <2-mm basis. Refer to procedure 1B7, 

Organic Material. 

A (L) Blank Lab preparation is same as N-blank except pulverize subsample 

of <2-mm air-dry soil to a <80-mesh size and use for lab 

analyses. Use <80-mesh air-dry for all analyses except AD/OD 

and 15-bar analyses. For the AD/OD and 15-bar analyses, use 

<2-mm air-dry soil. All analytical results are reported on a <2-

mm basis. Refer to procedure 1B1, Standard Air-dry. ---------------------------------------------------------------------------------------------------------------- 

Gravel codes

P = porous >2-mm material that is considered soil is used for clod or core measurements. 

V = volume estimate is used to calculate the weight percentage of a >2-mm fraction. If 

that fraction is porous (P), code the samples with "P" rather than with "V". 

 

560
PART II: 

SSIR NO. 42, SOIL SURVEY LABORATORY METHODS 

MANUAL, VERSIONS 1.0 - 2.0 (1989, 1992, respectively) 

ION EXCHANGE ANALYSES (5) 

Cation Exchange Capacity (5A) 

NH4Oac, pH 7.0 (5A8) Automatic Extractor (CEC-7) 

Steam Distillation (5A8b)

1. Application 

The CEC determined with 1 N NH4OAc buffered at pH 7.0, is a commonly used 

method and has become a standard reference to which other methods are compared (Peech et 

al., 1947). The advantages of using this method are that the extractant is highly buffered so that 

the extraction is performed at a constant, known pH (7.0) and that the NH4+ on the exchange 

complex is easily determined. 

 

2. Summary of Method

Displacement after washing is the basis for this procedure. The CEC is determined by 

saturating the exchange sites with an index cation (NH4+); washing the soil free of excess 

saturated salt; displacing the index cation (NH4+) adsorbed by the soil; and measuring the 

amount of the index cation (NH4+). A sample is leached using 1 N NH4OAc and a mechanical 

vacuum extractor (Holmgren et al., 1977). The extract is weighed and saved for analyses of the 

cations. The NH4

+

 saturated soil is rinsed with ethanol to remove the NH4

+

 that was not 

adsorbed. Steam distillation and titration are used to determine the NH4

+

 adsorbed on the soil 

exchange complex. The CEC by NH4OAc, pH 7 is reported in meq/100 g oven-dry soil in 

procedure 5A8b (Soil Conservation Service, 1984). 

3. Interferences 

Incomplete saturation of the soil with NH4

+

 and insufficient removal of NH4

+

 are the 

greatest interferences to this method. Ethanol removes some adsorbed NH4

+

 from the exchange 

sites of some soils. Isopropanol rinses has been used for some soils in which ethanol removes 

adsorbed NH4

+

. Soils that contain large amounts of vermiculite can irreversibly "fix" NH4

+

. 

Soils that contain large amounts of soluble carbonates can change the extractant pH and/or can 

contribute to erroneously high cation levels in the extract. 

4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

and bases. Dispense concentrated acids and bases in a fume hood. Thoroughly wash hands 

after handling reagents. Use the safety showers and eyewash stations to dilute spilled acids and 

bases. Use sodium bicarbonate and water to neutralize and dilute spilled acids. 

Ethanol is flammable. Avoid open flames and sparks. Standard laboratory equipment 

includes fire blankets and extinguishers for use when necessary. Follow the manufacturer's 

safety precautions when using the vacuum extractor and the Kjeltec Auto 1030 Analyzer. 

561
5. Equipment 

5.1 Mechanical vacuum extractor, 24 place, Centurion International, Inc., Lincoln, NE 

5.2 Syringes, polypropylene, disposable, 60 mL, for sample tube, extractant reservoir, and 

tared extraction syringe. 

5.3 Rubber tubing, 3.2 ID x 6.4 OD x 25.4 mm (1/8 ID x 1/4 OD x 1 in) for connecting 

syringe barrels. 

5.4 Polycons, Richards Mfg. Co. 

5.5 Kjeltec Auto 1030 Analyzer, Tecator, Fisher Scientific Inc. 

5.6 Digestion tubes, straight neck, 250 mL 

5.7 Analytical filter pulp, Schleicher and Schuell, no. 289 

5.8 Plunger, modified. Remove rubber and cut plastic protrusion from plunger end. 

5.9 Electronic balance, ±1-mg sensitivity 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Ammonium acetate solution (NH4OAc), 1 N, pH 7.0. Add 1026 mL of glacial acetic acid 

(CH3COOH) to 15 L DDI water. Add 1224 mL of conc. ammonium hydroxide 

(NH4OH). Mix and cool. Dilute with DDI water to 18 L and adjust to pH 7.0 with 

CH3COOH or NH4OH. 

6.3 Ethanol (CH3CH2OH), 95%, U.S.P. 

6.4 Nessler's reagent. Add 4.56 g of potassium iodide (KI) to 30 mL DDI water. Add 5.68 g 

of mercuric iodide (HgI2). Stir until dissolved. Dissolve 10 g of sodium hydroxide 

(NaOH) in 200 mL of DDI water. Transfer NaOH solution to a 250-mL volumetric flask 

and slowly add K-Hg-I solution. Dilute to volume with DDI water and thoroughly mix. 

Solution should not contain a precipitate. Solution can be used immediately. 

6.5 Sodium chloride (NaCl), reagent, crystal. 

6.6 Antifoam agent, slipicone release spray, Dow Chemical Corp. Alternatively, mix equal 

parts of mineral oil and n-octyl alcohol. 

6.7 Boric acid, 4% (w:v), with bromcresol green-methyl red indicator (0.075 % bromcresol 

green and 0.05% methyl red), Ricca Chemical Co. 

6.8 Hydrochloric acid (HCl), 0.1 N, standardized. Dilute 148 mL of conc. HCl in 16 L of DDI 

water. 

6.9 NaOH, 1 M. Add 500 mL of 50% NaOH solution to 8 L of DDI water. Dilute to 9 L 

with DDI water. 

7. Procedure 

Extraction of Bases 

7.1 Prepare sample tube by tightly compressing a 1-g ball of filter pulp into the bottom of a 

syringe barrel with a modified plunger. 

7.2 Weigh 2.50 g of <2-mm, air-dry soil and place in sample tube. Prepare one quality control 

check sample per 48 samples. 

7.3 Place sample tube on upper disk of the extractor and connect a tared extraction syringe. 

Use 25.4-mm (1 in) length rubber tubing and insert the plunger in the slot of the stationary disk 

of the extractor. 

7.4 Use a squeeze bottle to fill sample tube to the 20-mL mark with NH4OAc solution (≈ 10 

mL). Thoroughly wet the sample. Let stand for at least 20 min. 

562
7.5 Put reservoir tube on top of the sample tube. Rapidly extract the NH4OAc solution to a 0.5- 

to 1.0-cm height above sample. Turn off extractor. Add ≈ 45 mL of NH4OAc solution to the 

reservoir tube. Set extractor for an overnight (12 to 16 h) extraction. 

7.6 Next morning turn off the extractor. Pull the plunger of the syringe down. Do not pull 

plunger from the barrel of the syringe. Carefully remove the syringe containing the extract. 

Leave the rubber tubing on the sample tube. Weigh each syringe containing the NH4OAc 

extract to the nearest 0.01 g. 

7.7 Mix the extract in each syringe by manually shaking. Fill a polycon with extract solution 

and discard the excess. The solution in the polycon is reserved for analyses of extracted cations 

(procedures 6N2e, 6O2d, 6P2b, and 6Q2b). 

Removal of Excess Ammonium Acetate 7.8 Return the extractor to starting position. Attach syringe to the sample tube and rinse the 

sides of the sample tube with ethanol from a wash bottle. Fill the sample tube to the 20-mL 

mark with ethanol and let stand for 15 to 20 min. 

7.9 Place reservoir tube on the sample tube. Rapidly extract the ethanol level to a 0.5- to 1.0-

cm height above the sample. Turn off the extractor and add 55 to 60 mL of ethanol to the 

reservoir. Extract at a 45-min rate. 

7.10 After the extractor has stopped, turn off the switch. Pull the plunger of the syringe down. 

Do not pull the plunger from the syringe barrel. Remove the syringe and discard the ethanol. 

7.11 Repeat the ethanol wash. 

7.12 After the second wash, collect a few drops of ethanol extract from the sample tube on a 

spot plate. Test for NH4

+

 by using Nessler's reagent. A yellow, red to reddish brown 

precipitate is a positive test. If the test is positive, repeat the ethanol wash and retest with 

Nessler's reagent. Repeat until a negative test is obtained. 

Steam Distillation: Samples and Reagent Blanks 

7.13 Remove the sample tube and transfer the sample with filter pulp to a 250-mL digestion 

tube. Add 6 to 7 g of NaCl to the digestion tube. Use a gentle flow of compressed air to blow 

the filter pulp and sample out of the syringe. Wash the tube with DDI water and use a rubber 

policeman to complete transfer. The amount of distilled water that is added depends on the 

amount that is required to complete the transfer of tube contents. 

7.14 Perform the same transfer and addition of reagents for blanks as for samples. 

7.15 Spray silicone antifoam agent (or 2 drops of octyl alcohol) into the digestion tubes for 

each of the samples and reagent blanks. 

7.16 When using new reagents, e.g., boric acid, reagent blanks are distilled in 2 sets of 6, one 

set per Kjeltec machine. Each set of 6 is averaged and recorded on bench worksheet and 

manually set on each machine. During the steam distillation, the mean reagent blank titer is 

automatically subtracted from the sample titer. 

7.17 On bench worksheet, record the normality of standardized acid, i.e., ≈ 0.1 N HCl. 

7.18 Connect the tube to the distillation unit. Close the safety door. Distillation and titration 

are performed automatically. Record the titer in mL of titrant. 

563
8. Calculations 

CEC (meq/100g) = (Titer x N x 100 x AD/OD)/(Weight) 

where 

Titer = Titer of sample (mL) 

N = Normality of HCl titrant 

Weight = Sample weight (g) 

100 = Conversion factor to 100 g basis 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report CEC-7 in units of meq/100 g of oven-dry soil to the nearest 0.1 meq/100 g. 

10. Precision 

Precision data are not available for this procedure. A quality control check sample is 

run with every batch of 48 samples. With 113 observations of the quality control check 

sample, the mean, standard deviation, and C.V. for the CEC are 27.1, 0.57, and 2.1%, 

respectively. 

11. References 

Holmgren, George G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically 

controlled variable rate leaching device. Soil Sci. Amer. J. 41:1207-1208. 

Peech, M., L.T. Alexander, L.A. Dean, and J.F. Reed. 1947. Methods of soil analysis for 

soil fertility investigations. U.S. Dept. Agr. Circ. 757, 25 pp. 

Soil Conservation Service. 1984. Procedures for collecting soil samples and methods of 

analysis for soil survey. USDA-SCS Soil Surv. Invest. Rep. no. 1. U.S. Govt. Print. 

Office, Washington, DC. 

NH4Cl, pH 7.0 (5A9) Steam Distillation (5A9b) 

1. Application

The CEC determined with a neutral unbuffered salt, e.g., 1 N NH4Cl, is an estimate of 

the "effective" CEC (ECEC) of the soil (Peech et al., 1947). For a soil with a pH of <7.0, the 

ECEC value should be < CEC measured with a buffered solution at pH 7.0. The NH4Cl CEC is 

≈ equal to the NH4OAc extractable bases plus the KCl extractable Al for noncalcareous soils. 

2. Summary of Method

Displacement after washing is the basis for this procedure. The CEC is determined by 

saturating the exchange sites with an index cation (NH4+

); washing the soil free of excess 

saturated salt; displacing the index cation (NH4+) adsorbed by the soil; and measuring the 

amount of the index cation (NH4+). A sample is leached using 1 N NH4Cl and a mechanical 

vacuum extractor (Holmgren et al., 1977). The extract is weighed and saved for analyses of the 

cations. The NH4

+

 saturated soil is rinsed with ethanol to remove the NH4

+

 that was not 

adsorbed. Steam distillation and titration are used to determine the NH4

+

 adsorbed on the soil 

exchange complex. The CEC by NH4Cl is reported in meq/100 g oven-dry soil in procedure 

5A9b (Soil Conservation Service, 1984). 

3. Interferences 

Incomplete saturation of the soil with NH4

+

 and insufficient removal of NH4

+

 are the 

greatest interferences to this method. Ethanol removes some adsorbed NH4

+

 from the exchange 

sites of some soils. Isopropanol rinses have been used for some soils in which ethanol removes 

564
adsorbed NH4

+

. Soils that contain large amounts of vermiculite can irreversibly "fix" NH4

+

. 

Soils that contain large amounts of soluble carbonates can change the extractant pH and/or can 

contribute to erroneously high cation levels in the extract. 

4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses) when preparing reagents, especially concentrated acids 

and bases. Dispense concentrated acids and bases in a fume hood. Thoroughly wash hands 

after handling reagents. Use the safety showers and eyewash stations to dilute spilled acids and 

bases. Use sodium bicarbonate and water to neutralize and dilute spilled acids. 

Ethanol is flammable. Avoid open flames and sparks. Standard laboratory equipment 

includes fire blankets and extinguishers for use when necessary. Follow the manufacturer's 

safety precautions when using the vacuum extractor and the Kjeltec Auto 1030 Analyzer. 

5. Equipment 

5.1 Mechanical vacuum extractor, 24 place, Centurion International, Inc., Lincoln, NE 

5.2 Syringes, polypropylene, disposable, 60 mL, for sample tube, extractant reservoir, and 

tared extraction syringe. 

5.3 Rubber tubing, 3.2 ID x 6.4 OD x 25.4 mm (1/8 ID x 1/4 OD x 1 in), for connecting 

syringe barrels. 

5.4 Polycons, Richards Mfg. Co. 

5.5 Kjeltec Auto 1030 Analyzer, Tecator, Fisher Scientific Inc. 

5.6 Digestion tubes, straight neck, 250 mL 

5.7 Analytical filter pulp, Schleicher and Schuell, no. 289 

5.8 Plunger, modified. Remove rubber and cut plastic protrusion from plunger end. 

5.9 Electronic balance, ±1-mg sensitivity 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Ammonium chloride solution (NH4Cl), 1 N. Dissolve 535 g of NH4Cl reagent in DDI 

water and dilute to 10 L. 

6.3 Ethanol (CH3CH2OH), 95%, U.S.P. 

6.4 Nessler's reagent. Add 4.56 g of potassium iodide (KI) to 30 mL DDI water. Add 5.68 g 

of mercuric iodide (HgI2). Stir until dissolved. Dissolve 10 g of sodium hydroxide 

(NaOH) in 200 mL DDI water. Transfer NaOH solution to a 250-mL volumetric flask 

and slowly add K-Hg-I solution. Dilute to volume with DDI water and thoroughly mix. 

Solution should not contain a precipitate. Solution can be used immediately. 

6.5 Sodium chloride (NaCl), reagent, crystal. 

6.6 Antifoam agent, slipicone release spray, Dow Chemical Corp. Alternatively, mix equal 

parts of mineral oil and n-octyl alcohol. 

6.7 Boric acid, 4% (w:v), with bromcresol green-methyl red indicator (0.075 % bromcresol 

green and 0.05% methyl red), Ricca Chemical Co. 

6.8 Hydrochloric acid (HCl), 0.1 N, standardized. Dilute 148 mL of conc. HCl in 16 L of DDI 

water. 

6.9 NaOH, 1 M. Add 500 mL of 50% NaOH solution to 8 L of DDI water. Dilute to 9 L 

with DDI water. 

7. Procedure 

Extraction of Bases 

7.1 Prepare sample tube by tightly compressing a 1-g ball of filter pulp into the bottom of a 

syringe barrel with a modified plunger. 

565
7.2 Weigh 2.50 g of <2-mm, air-dry soil and place in sample tube. Prepare one quality control 

check sample per 48 samples. 

7.3 Place sample tube on upper disk of the extractor and connect a tared extraction syringe. 

Use 25.4-mm (1 in) length rubber tubing and insert the plunger in the slot of the stationary disk 

of the extractor. 

7.4 Use a squeeze bottle to fill sample tube to the 20-mL mark with NH4Cl solution (~ 10 mL). 

Thoroughly wet the sample. Let stand for at least 20 min. 

7.5 Put reservoir tube on top of the sample tube. Rapidly extract the NH4Cl solution to a 0.5- to 

1.0-cm height above sample. Turn off extractor. Add ≈ 45 mL of NH4Cl solution to the 

reservoir tube. Set extractor for an overnight (12 to 16 h) extraction. 

7.6 Next morning turn off the extractor. Pull the plunger of the syringe down. Do not pull 

plunger from the barrel of the syringe. Carefully remove the syringe containing the extract. 

Leave the rubber tubing on the sample tube. Weigh each syringe containing the NH4Cl extract 

to the nearest 0.01 g. 

7.7 Mix the extract in each syringe by manually shaking. Fill a polycon with extract solution 

and discard the excess. The solution in the polycon is reserved for analyses of extracted cations 

(procedures 6N2e, 6O2d, 6P2b, and 6Q2b). 

Removal of Excess Ammonium Chloride

7.8 Return the extractor to starting position. Attach syringe to the sample tube and rinse the 

sides of the sample tube with ethanol from a wash bottle. Fill the sample tube to the 20-mL 

mark with ethanol and let stand for 15 to 20 min. 

7.9 Place reservoir tube on the sample tube. Rapidly extract the ethanol level to a 0.5- to 1.0-

cm height above the sample. Turn off the extractor and add 55 to 60 mL of ethanol to the 

reservoir. Extract at a 45-min rate. 

7.10 After the extractor has stopped, turn off the switch. Pull the plunger of the syringe down. 

Do not pull the plunger from the syringe barrel. Remove the syringe and discard the ethanol. 

7.11 Repeat the ethanol wash. 

7.12 After the second wash, collect a few drops of ethanol extract from the sample tube on a 

spot plate. Test for NH4

+

 by using Nessler's reagent. A yellow, red to reddish brown 

precipitate is a positive test. If the test is positive, repeat the ethanol wash and retest with 

Nessler's reagent. Repeat until a negative test is obtained. 

Steam Distillation: Samples and Reagent Blanks 

7.13 Remove the sample tube and transfer the sample with filter pulp to a 250-mL digestion 

tube. Add 6 to 7 g of NaCl to the sample. Use a gentle flow of compressed air to blow the 

filter pulp and sample out of the syringe. Wash the tube with DDI water and use a rubber 

policeman to complete transfer. The amount of distilled water that is added depends on the 

amount that is required to complete the transfer of tube contents. 

7.14 Perform the same transfer and addition of reagents for blanks as for samples. 

7.15 Spray silicone antifoam agent (or 2 drops of octyl alcohol) into the digestion tubes for 

each of the samples and reagent blanks. 

566
7.16 When using new reagents, e.g., boric acid, reagent blanks are distilled in 2 sets of 6, one 

set per Kjeltec machine. Each set of 6 is averaged and recorded on bench worksheet and 

manually set on each machine. During the steam distillation, the mean reagent blank titer is 

automatically subtracted from the sample titer. 

7.17 On bench worksheet, record the normality of standardized acid, i.e., ≈ 0.1 N HCl. 

7.18 Connect the tube to the distillation unit. Close the safety door. Distillation and titration 

are performed automatically. Record the titer in mL of titrant. 

8. Calculations 

CEC (meq/100g) = (Titer x N x 100 x AD/OD)/(Weight0 

where 

Titer = Titer of sample (mL) 

N = Normality of HCl titrant 

Weight = Sample weight (g) 

100 = Conversion factor to 100 g basis 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report neutral salts CEC in units of meq/100 g of oven-dry soil to the nearest 0.1 

meq/100 g. 

10. Precision 

Precision data are not available for this procedure. A quality control check sample is 

run with every batch of 48 samples. With 19 observations of the quality control check sample, 

the mean, standard deviation, and C.V. for the CEC are 26.0, 0.37, and 1.4%, respectively. 

11. References 

Holmgren, George G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically 

controlled variable rate leaching device. Soil Sci. Amer. J. 41:1207-1208. 

Peech, M., L.T. Alexander, L.A. Dean, and J.F. Reed. 1947. Methods of soil analysis for 

soil fertility investigations. U.S. Dept. Agr. Circ. 757, 25 pp. 

CHEMICAL ANALYSES (6) 

Total Carbon (6A) 

Dry Combustion (6A2) 

LECO CR-12 Carbon Analyzer (6A2d)

1. Application

Total C in soils is the sum of organic and inorganic C. Most of the organic C is 

associated with the organic matter fraction, and the inorganic C is generally found with 

carbonate minerals. The organic C in mineral soils generally ranges from 0 to 12%. 

Total C is quantified by two basic methods, i.e., wet or dry combustion. The SSL uses 

dry combustion. In total C determinations, all forms of C in a soil are converted to CO2

followed by a quantification of the evolved CO2. Total C can be used to estimate the organic C 

content of a soil. The difference between total and inorganic C is an estimate of the organic C. 

Organic C also can be determined directly (procedure 6A1c). The inorganic C should be 

567
equivalent to carbonate values measured by CO2 evolution with strong acid (Nelson and 

Sommers, 1982). 

Organic C defines mineral and organic soils. In Soil Taxonomy, organic C is also used 

at lower taxonomic levels, e.g., ustollic and fluventic subgroups (Soil Survey Staff, 1975). 

2. Summary of Method

An 80-mesh soil sample is oxidized at high temperatures. The released gases are 

scrubbed, and the CO2 in the combustion gases is measured by using an infrared detector. 

Percent total C is reported on an oven-dry soil basis. 

3. Interferences 

This procedure simultaneously measures inorganic and organic C.

4. Safety

Wear protective clothing and safety glasses. Magnesium perchlorate may form 

explosive mixtures. Magnesium perchlorate may contain traces of perchloric acid, which 

remain from manufacturer's operations. This acid is anhydrous because of the strong 

desiccating capability of the salt. Avoid prolonged contact with oxidizable material or material 

capable of forming unstable perchlorate esters or salts. Remove magnesium perchlorate by 

using an excess of water to thoroughly dilute the material. 

The use of high temperatures in the oxidation of samples requires that extreme caution 

be used to prevent burns and fires. Follow standard laboratory procedures when handling 

compressed gases. Oxygen is highly flammable. Avoid open flames and sparks. Standard 

laboratory equipment includes fire blankets and extinguishers for use when necessary. Follow 

the manufacturer's safety precautions when using the carbon analyzer. 

5. Equipment

5.1 Carbon analyzer, Leco Model CR-12 781-600 Carbon System, Leco Corp., St. Joseph, 

MI 

5.2 Data transmit card, part no. 772-573, Leco Corp., St. Joseph, MI 

5.3 Combustion boats, part no. 529-203, Leco Corp., St. Joseph, MI 

5.4 Single-stage regulator, oxygen service, part no. E11-W-N115Box, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 18105 

5.5 Electronic balance, ±1-mg sensitivity 

6. Reagents

6.1 Anhydrone, anhydrous magnesium perchlorate, granular 

6.2 Glass wool 

6.3 Compressed oxygen, >99.5% @ 30 psi 

6.4 Calcium carbonate, CaCO3, reagent grade. 

7. Procedure

7.1 Use a fine-ground 80-mesh, air-dry soil 

7.2 Weigh sample in a tared combustion boat. The sample size is dependent upon the C 

content. The product of sample weight (g) multiplied by C percentage should not be >10%. In 

most cases, the sample size is 1.00 g, unless the C content is >10%. 

7.3 Refer to the manufacturer's manual for operation of carbon analyzer. 

7.4 Combust sample in an O2 atmosphere in which the C is oxidized to CO2. Moisture and dust 

are removed by the instrument, and the CO2 gas is then measured by a solid state infrared 

detector. The microprocessor formulates the analytical results (Ci) by combining the outputs of 

568
the infrared detector and the system ambient sensors with pre-programmed calibration, 

linearization and weight compensation factors. Analytical results are displayed and printed on 

the control console. 

8. Calculations

C (%) = Ci x AD/OD 

where: 

C (%) = C (%), oven-dry basis 

Ci = C (%) instrument 

AD/OD = air-dry/oven-dry ratio (procedure 4B5) 

9. Report

Report total C percentage on an oven-dry basis to the nearest 0.1%. 

10. Precision

Precision data are not available for this procedure. A quality control check sample is 

included in every batch of ten samples. For 41 observations of the quality control check 

sample, the mean, standard deviation, and C.V. for total carbon are 11.38, 0.062, and 5.5%, 

respectively. 

11. References 

Nelson, D.W., and L.E. Sommers. 1982. Total carbon, organic carbon, and organic matter. 

In A.L. Page, R.H. Miller, and D.R. Keeney (eds.) Methods of soil analysis. Part 2. 

Chemical and microbiological properties. 2nd ed. Agronomy 9:539-579. 

Soil Survey Staff. 1975. Soil taxonomy: A basic system of soil classification for making 

and interpreting soil surveys. USDA-SCS Agric. Handb. 436. U.S. Govt. Print. Office, 

Washington, DC. 

Nitrogen (6B) 

Kjeldahl Digestion II (6B3) 

Ammonia Steam Distillation, Automatic Titrator (6B3a) 

1. Application 

The total N content of the soil may range from <0.02% in subsoils, 2.5% in peats, and 

0.06 to 0.5% in surface layers of many cultivated soils (Bremmer and Mulvaney, 1982). The 

total N data may be used to determine the soil C:N ratio, the soil potential to supply N for plant 

growth, and the N distribution in the soil profile. The C:N ratio generally ranges between 10 to 

12. Variations in the C:N ratio may serve as an indicator of the amount of soil inorganic N. 

Uncultivated soils usually have higher C:N ratios than do cultivated soils. 

Soils with large amounts of illites or vermiculites can "fix" significant amounts of N 

compared to those soils dominated by smectites or kaolinites (Young and Aldag, 1982; 

Nommik and Vahtras, 1982). Since the organic C of many soils diminishes with depth while 

the level of "fixed" N remains constant or increases, the C:N ratio narrows (Young and Aldag, 

1982). The potential to "fix" N has important fertility implications as the "fixed" N is slowly 

available for plant growth. 

2. Summary of Method

A soil sample is digested using the Kjeldahl technique. The digest is made alkaline, the 

steam is distilled to release NH4

+

-N, and the NH4

+

-N is complexed with boric acid. The 

complexed NH4

+

-N is titrated with HCl, and the total N is calculated against a reagent blank 

(Soil Conservation Service, 1984). 

569
3. Interferences 

The total N that is measured by the Kjeldahl method does not distinguish among the 

types of N that are present in the soil. Practically all of the N is measured, but some forms of 

N are not recovered. Generally, soils have small amounts of N in the nonrecoverable forms, 

i.e., NO3

-

 and NO2

-

. Soils with significant amounts of NO3

-

 or NO2

-

 are usually saline. The 

anion analysis of the saturated paste extracts measures NO3

-

 and NO2

-

 (procedures 6M1c and 

6W1a, respectively). 

The most significant error in the Kjeldahl method is the heating of the digestion mixture 

over 400°C. Loss of N occurs when the temperature of the digestion is >400°C (Bremmer and 

Mulvaney, 1982). 

4. Safety 

Wear protective clothing (coats, aprons, sleeve guards and gloves) and eye protection 

(face shields, goggles, or safety glasses) when handling acids and bases. Use heat resistant 

gloves when handling hot digestion tubes during digestion and steam distillation. Use the 

provided safety showers and eyewash stations to dilute spilled acids and bases. Use sodium 

bicarbonate and water to neutralize and dilute spilled acids. Digestion blocks are used at high 

temperatures, i.e., 250 and 400°C. Standard laboratory equipment includes fire blankets and 

extinguishers for use when necessary. Use the fume hood and fume aspiration devices to 

control and dispose of the acid fumes when digesting samples. 

Boric acid is toxic and must not be ingested. Hengar granules contain Se which is toxic. 

Concentrated H2SO4 reacts violently with water and must be handled with caution. The 50% 

NaOH solution is very corrosive. Follow prudent laboratory safety precautions when handling 

these chemicals. Follow the manufacturer's safety precautions when using the Kjeltec Auto 

1030 Analyzer. 

5. Equipment

5.1 Electronic balance, ±0.001-g sensitivity 

5.2 Digestion tubes, 250 mL, with constricted neck, Ace Glass Co., Inc. 

5.3 Digestion blocks, 250 and 400°C 

5.4 Dispenser, Zippette, 30 mL or equivalent, for conc. sulfuric acid (H2SO4), Brinkmann 

Instruments Inc. 

5.5 Kjeltec Auto 1030 Analyzer, Tecator, Fisher Scientific Inc. 

6. Reagents 

6.1 Distilled water 

6.2 Distilled deionized (DDI) water 

6.3 Hydrochloric acid (HCl), conc., 12 N

6.4 Sodium hydroxide (NaOH), 50% (w:v), reagent 

6.5 Hengar granules (selenized) 

6.6 Digestion salt mixture. Mix 1000 g of potassium sulfate powder, 55 g of ferrous sulfate 

powder (anhydrous), and 32 g of copper II sulfate powder (anhydrous) in a tumbling mill 

for at least 30 min. 

6.7 Antifoam, silicone spray bottle, Slipicone release spray, Dow Chemical Corp. 

6.8 Boric acid, 4% (w:v), with bromcresol green-methyl red (0.075% bromcresol green and 

0.05% methyl red) indicator, Ricca Chemical Co. 

6.9 HCl, 0.1 N, standardized. Dilute 148 mL of conc. HCl in 16 L of DDI water. 

6.10 Sucrose 

7. Procedure 

Kjeldahl Digestion of Sample 

7.1 Weigh 3.000 g of <2-mm, air-dry soil into a 250-mL digestion tube. Refer to Table 1 for 

sample size. 

570
7.2 Prepare 3 to 5 reagent blanks in every batch of 20 analyses. Reagent blanks contain 0.5 g 

of sucrose plus all reagents used in sample analysis, i.e., 12 mL of H2SO4, 4.5 g of digestion 

salt mixture, and 1 or 2 Hengar granules. Samples do not receive the 0.5 g of sucrose. Reagent 

blanks are run as samples and are not automatically subtracted during distillation procedure. 

7.3 Use a dispenser to add 5 mL of distilled water to sample tube. Shake the tube to wet the 

sample. 

7.4 Use a dispenser to add 12 mL of conc. H2SO4 to sample. 

7.5 Allow sample to stand overnight. 

7.6 Use a calibrated scoop to add 4.5 g of digestion salt mixture to sample. 

7.7 Add 1 or 2 Hengar granules to sample. 

7.8 Preheat one digestion heating block to 250°C and the other to 400°C. 

7.9 Place the tube in the 250°C block, attach a fume aspirator, and digest for at least 30 min. 

7.10 Remove the tube, place in the 400°C block, and digest sample for 1 h. 

7.11 Remove the tube, place on a cooling board, and allow sample to cool for at least 15 min. 

7.12 Remove the aspirator. Add 50 mL of distilled water. 

Table 1. Sample size for total N based on volume of titrant (FeSO4) used in organic C analysis 

(procedure 6A1c). 

Fe2SO4 (mL) Sample Size (g) 

 

>6.00 3.0 

4.00 to 5.00 2.0 

3.00 to 4.00 1.5 

<2.00 1.0 

If >10.00 mL of K2Cr2O7 (procedure 6A1c) is used and/or sample size is <1.00 g, then divide 

the volume of FeSO4 by 2 and then use Table 1. To obtain a representative sample, do not use 

a sample size <0.5 g for total N analysis. 

Ammonia Steam Distillation, Automatic Titrator 

7.13 Spray silicone antifoam solution (or 2 drops of octyl alcohol) into the digestion tube and 

connect to the distillation unit. 

7.14 Close the safety door. 

7.15 Distillation and titration are performed automatically. 

7.16 On bench worksheet, record the mL that are titrated for samples and reagent blanks. On 

bench worksheet, also record the normality of standardized HCl. 

571
8. Calculations 

N (%) = [(Titersample - Titerblank) x N X 1.4 X AD/OD]/(Sample Weight) 

where 

Titersample = Titer of sample (mL) 

Titerblank = Average titer of reagent blank (mL) 

N = Normality of HCl titrant solution 

1.4 = Conversion factor 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report total N as a dimensionless value to the nearest 0.001 unit on an oven-dry basis. 

10. Precision 

Precision data are not available for this procedure. For 105 observations of the quality 

control check sample, the mean, standard deviation, and C.V. for total N are 0.143, 0.004, and 

2.7%, respectively. 

11. References 

Bremmer, J.M., and C.S. Mulvaney. 1982. Nitrogen - Total. In A.L. Page, R.H. Miller, and 

D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological 

properties. 2nd ed. Agronomy 9:595-624. 

Nommik, H., and K. Vahtras. 1982. Retention and fixation of ammonium and ammonia in 

soils. In F.J. Stevenson (ed.) Nitrogen in agricultural soils. Agronomy 22:123-171. 

Soil Conservation Service. 1984. Procedures for collecting soil samples and methods of 

analysis for soil survey. USDA-SCS Soil Surv. Invest. Rep. no. 1. U.S. Govt. Print. 

Office, Washington, DC. 

Young, J.L., and R.W. Aldag. 1982. Inorganic forms of nitrogen in soil. In F.J. Stevenson 

(ed.) Nitrogen in agricultural soils. Agronomy 22:43-66. 

Iron, Aluminum, and Potassium (6C, 6G, and 6Q) 

HF Dissolution (6C7, 6G11, and 6Q3) 

Atomic Absorption (6C7a, 6G11a and 6Q3a) 

1. Application

Historically, elemental analysis was developed for the analysis of rocks and minerals 

(Washington, 1930). The elemental analysis of soils, sediments, and rocks necessitates their 

decomposition into soluble forms. Hydrofluoric acid (HF) is efficient in the digestion and 

dissolution of silicate minerals for elemental decomposition. Elemental concentrations of Fe, 

Al, and K are determined by atomic absorption using 100 mg of clay suspension contained in a 

closed vessel with boric acid (H3BO3) to neutralize excess acid (Berdanier, Lynn, and 

Threlkeld, 1978; Soil Conservation Service, 1984). 

2. Summary of Method

To 100 mg of clay suspension (procedure 7A2i), 5 mL of HF acid are added. The 

solution is heated, cooled, and 2 to 3 g of H3BO3 are added to neutralize excess acid. The 

solution is diluted to 100 mL, allowed to stand overnight, and 20 mL are decanted (procedure 

7C3). The concentrations of Fe, Al, and K are determined by atomic absorption (AA) in 

procedures 6C7a, 6G11a, and 6Q3a, respectively. Data are reported in procedure 7C3. 

572
3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in AA 

analyses of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. 

The stable matrix system (HBF4-H3BO3-ionic constituents of silicates) provides a 

suitable salt-free single matrix that greatly diminishes the chemical ionization, matrix, and 

instrumental interferences for AA determinations. One of the principal advantages of this 

technique is that all elements may be determined from a single sample solution (Lim and 

Jackson, 1982). 

4. Safety

There are no significant hazards to analyst by this procedure. Wear protective clothing, 

e.g., coats and aprons. Follow standard laboratory practices when handling compressed gases. 

Gas cylinders should be chained or bolted in an upright position. Acetylene gas is highly 

flammable. Follow the manufacturer's safety precautions when using the AA. 

5. Equipment

5.1 Atomic Absorption spectrophotometer (AA), Perkin-Elmer Corp., Norwalk, CT 

5.2 Autosampler, AS-50, Perkin-Elmer Corp., Norwalk, CT 

5.3 Microcomputer, 7500 Professional Computer, Perkin-Elmer Corp., Norwalk, CT 

5.4 Dot matrix printer, P-132, Interdigital Data Systems, Inc. 

5.5 Digital diluter/dispenser, product no. 100004, with hand probe and actuator, product no. 

230700, Hamilton Co., P.O. box 10030, Reno, NV, 89510 

5.6 Syringes, 10000 and 1000 μL, 1001 DX an 10110-TEL LL gastight, Hamilton Co., P.O. 

Box 10030, Reno, NV, 89510 

5.7 Centrifuge tubes, polystyrene, 15 mL, conical bottom, graduated, part no. 2087, for 

sample dilution and sample changer, Becton Dickinson Labware, Becton Dickinson and 

Co., 2 Bridgewater Lane, Lincoln, Park, NJ 07035 

5.8 Containers, polypropylene or teflon 

6. Reagents

6.1 Distilled Deionized (DDI) water 

6.2 Sodium chloride (NaCl) solution, 1143 ppm Na. Dissolve 5.81 g of NaCl in 2 L of DDI 

water. 

6.3 Boric acid, H2BO3

6.4 Hydrofluoric acid (HF) solution, 2.47 N. Fill a polyethylene volumetric flask 1/3 full 

with DDI water. In hood, slowly and carefully add 49.36 g of HF. Slowly and carefully 

add 20 g of H2BO3. Hot reaction. May not completely dissolve. Make to 1-L volume 

with DDI water. Store HF solution in refrigerator. Use HF solution as reagent blank. 

6.5 Fe stock solution, 1000 ppm. Commercial. Weigh 1.0000 g of Fe wire, dissolve in HCl, 

and make to 1-L volume with DDI water. Store in polypropylene container. 

6.6 Al stock solution, 1000 ppm. Commercial. Weigh 1.0000 g of Al wire, dissolve in HCl, 

and make to 1-L volume with DDI water. Store in polypropylene container. 

6.7 K stock solution, 50 meq L-1. Dissolve 3.7279 g of KCl in 1 L of DDI. Store in 

polypropylene container. 

6.8 Fe standard, 200 ppm. To 50 ml of Fe stock solution, add 12.34 ml of HF solution and 5 

g of H2BO3. Make to 250-ml volume with DDI water. Store in polypropylene container. 

6.9 Al standard, 200 ppm. To 50 ml of Al stock solution add 12.34 ml of HF solution and 5 g 

of H2BO3. Store in polypropylene container. 

6.10 K standard, 1 meq L-1. Add 12.34 ml of HF solution and 5 g of H2BO3 to 10 ml of K 

stock solution. Store in polypropylene container. 

6.11 NaCl solution (1143 ppm Na). Dissolve 2.54 g of NaCl in DDI and make to 1-L volume. 

573
7. Procedure

Dilution of Sample Extracts and Standards

7.1 Set the digital settings at 60 for the diluent (NaCl solution) and 99 for the HF sample, 

calibration reagent blanks, and calibration standards. 

7.2 Dilute 1 part HF sample with 7 parts of NaCl solution (1:7 dilution). 

7.3 Dilute 1 part calibration reagent blank (HF solution) with 7 parts NaCl solution (1:7 

dilution). 

7.4 Dilute 1 part of each calibration standard (200 ppm Fe, 200 ppm Al, and 1 meq-1 K) with 7 

parts of NaCl solution (1:7 dilution). 

7.5 Dispense the diluted solutions into 15-mL conical polystyrene centrifuge tubes. Place tubes 

in carousels of the sample changer. 

AA Calibration

7.6 Use calibration reagent blank (HF solution) and calibration standards to calibrate the AA. 

The AA program requires a blank and a standard, in that order, to establish a single point 

calibration curve for element determination. During AA determinations, perform one 

calibration, i.e., blank plus standard, for every 8 samples. 

AA Operation

7.7 The following parameters are only very general guidelines for instrument conditions for the 

analyte. 

Element Wavelength Angle Fuel/ 

Oxidant 

 

Fe 302.1 Parallel C2H2/Air 

20/25 

Al 308.2 Parallel C2H2/N2O 

30/17 

K 766.5 30° C2H2/Air 

20/25 

7.8 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.9 If a sample exceeds the calibration standard, dilute the sample (dilution ratio in calculation) 

with appropriate matrix and record the dilution. Remember to keep the matrix the same after 

dilution. 

8. Calculations 

Calculations are reported in procedure 7C3. 

9. Report

Report concentrations of Fe, Al, and K by atomic absorption. Elemental concentrations 

are converted to percent oxides. Data are reported in procedure 7C3. 

10. Precision

Precision data are not available for this procedure. 

574
11. References 

Berdanier, C.R., W.C. Lynn, and G.W. Threlkeld. 1978. Illitic mineralogy in Soil 

Taxonomy: X-ray vs. total potassium. Agron. Absts. 1978 Annual Mtgs. 

Lim, C.H., and M.L. Jackson. 1982. Dissolution for total elemental analysis. In A.L. Page, 

R.H. Miller, and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and 

microbiological properties. 2nd ed. Agronomy 9:1-12. 

Soil Conservation Service. 1984. Procedures for collecting soil samples and methods of 

analysis for soil survey. USDA-SCS Soil Surv. Invest. Rep. no. 1. U.S. Govt. Print. 

Office, Washington, DC. 

Washington, H.S. 1930. The Chemical analysis of rocks. 4th ed. John Wiley and Sons, 

Inc., New York, NY. 

Iron, Aluminum, and Silicon (6C, 6G, and 6V) 

Ammonium Oxalate Extraction (6C6, 6G12, and 6V2) 

Inductively Coupled Plasma Spectrometry (6C9a, 6G12a, 6V2a) 

Optical Density (8J) 

(of ammonium oxalate extract) 

1. Application 

Oxalic acid-ammonium oxalate (acid oxalate) is used as a selective dissolution 

extractant for organically complexed Fe and Al, noncrystalline hydrous oxides of Fe and Al, 

allophane, and amorphous aluminosilicates (Wada, 1989). Acid oxalate is a poor extractant of 

imogolite and layer silicates and does not extract crystalline hydrous oxides of Fe and Al, opal, 

or crystalline silicate (Wada, 1989). A more reliable and accurate estimation of soil properties 

and a better understanding of soil exchange complex is provided when acid oxalate extraction 

is used in conjunction with other selective dissolution procedures, thermal techniques, and 

chemical tests. In Soil Taxonomy, acid oxalate extractable Fe and Al are criteria for andic soil 

properties (Soil Survey Staff, 1990). 

2. Summary of Method 

A soil sample is extracted with a mechanical vacuum extractor (Holmgren et al., 1977) 

in a 0.2 M acid oxalate solution buffered at pH 3.0 under darkness. The acid oxalate extract is 

weighed. The acid oxalate extract is diluted with 0.1 N HCl. The diluted extract is vaporized 

and atomized by a inductively coupled plasma emission spectrophotometer (ICP). The atoms 

or ions of the analyte are energized in high temperatures, resulting in the movement of valence 

electrons to higher orbits from the nucleus. As the electrons fall back to a lower orbit, 

electromagnetic energy at a specific wavelength for a given atom is emitted in measurable 

amounts (Soltanpour et al., 1982). Data are automatically recorded by a microcomputer and 

printer. The percent acid oxalate extractable Fe, Al, and Si are reported in procedures 6C9a, 

6G12a, and 6V2a, respectively (Soil Conservation Service, 1984). On a less routine basis, Mn 

is also measured. To date, however, a National Soil Survey Laboratory (NSSL) method code 

has not been assigned to the Mn determination by acid oxalate extraction. In procedure 8J, the 

optical density of the extract is measured with a UV spectrophotometer at 430 nm. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

ICP analyses of these elements. These interferences vary in importance, depending upon the 

particular analyte chosen. 

The acid oxalate buffer extraction is sensitive to light, especially UV light. The 

exclusion of light reduces the dissolution effect of cystalline oxides and clay minerals. If the 

sample contains large amounts of amorphous material (>2% Al), an alternate method should be 

used, i.e., shaking with 0.275 M acid oxalate, pH 3.25, 1:100 soil:extractant. 

575
4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Follow standard laboratory 

practices when handling compressed gases. Gas cylinders should be chained or bolted in an 

upright position. Follow the manufacturer's safety precautions when using the UV 

spectrophotometer and ICP. 

5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Mechanical vacuum extractor, 24 place, Centurion International, Inc., Lincoln, NE 

5.3 Syringes, polypropylene, disposable, 60 mL, for sample tube, extractant reservoir, and 

tared extraction syringe 

5.4 Rubber tubing, 3.2 ID x 6.4 OD x 25.4 mm (1/8 ID x 1/4 OD x 1 in) for connecting 

syringe barrels 

5.5 Polycons, Richards Mfg. Co. 

5.6 Plunger, modified. Remove rubber and cut plastic protrusion from plunger end. 

5.7 UV-visible spectrophotometer, DU-7, Beckmann Instruments, Inc. 

5.8 Cuvettes, disposable, polystrene, 1-cm light path 

5.9 Inductively coupled plasma spectrophotometer (ICP), Perkin-Elmer model 6000 

5.10 Autosampler, AS-50, Perkin-Elmer Corp., Norwalk, CT 

5.11 Microcomputer, 7500 Professional Computer, Perkin-Elmer Corp., Norwalk, CT 

5.12 Dot matrix printer, P-132, Interdigital Data Systems, Inc. 

5.13 Single-stage regulator, high-purity, high-flow, argon, product no. E11-X-N145DHF, Air 

Products and Chemicals, Inc., Box 538, Allentown, PA 18105 

5.14 Digital diluter/dispenser, product no. 100004, with hand probe and actuator, product no. 

230700, Hamilton Co., P.O. Box 10030, Reno, NV, 89510 

5.15 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gastight, Hamilton Co., P.O. 

Box 10030, Reno, NV, 89510 

5.16 Centrifuge tubes, polystyrene, 15 mL, conical, graduated, part no. 2087, for sample 

dilution and sample changer, Becton Dickinson Labware, Becton Dickinson and Co., 2 

Bridgewater Lane, Lincoln Park, NJ 07035 

5.17 Containers, polyproylene 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Hydrochloric acid (HCl), conc. 12 N

6.3 HCl, 1:1 HCl:DDI, 6 N. Carefully mix 1 part of conc. HCl to 1 part DDI water. 

6.4 HCl, 1% wt. Carefully dilute 25 mL of conc. HCl to 1 L with DDI water. 

6.5 HCl, 0.1 N. Add 8.33 mL of conc. HCl to DDI water and make to 1-L volume. 

6.6 Acid oxalate buffer solution, 0.2 M, pH 3.0. Solution A (base): Dissolve 284 g of 

(NH4)2C2O4·H2O in 10 L of DDI water. Solution B (acid): Dissolve 252 g of 

H2C2O4·H2O in 10 L of DDI water. Mix 4 parts solution A with 3 parts solution B. 

Adjust acid oxalate solution pH by adding either acid or base solution. Store in a 

polypropylene bottle. 

6.7 pH buffers, pH 4.00 and 7.00, for electrode calibration. 

6.8 Primary Fe standard, 1000 ppm. Dissolve 1.000 g of Fe wire in a minimum volume of 

1:1 HCl:DDI. Dilute to 1-L volume in a volumetric flask using 1% HCl. Store in a 

polypropylene bottle. 

6.9 Primary Al standard, 1000 ppm. Dissolve 1.000 g of Al wire in a minimum volume of 

1:1 HCl:DDI. Dilute to 1-L volume in a volumetric flask using 1% HCl water. Store in a 

polypropylene bottle. 

6.10 Primary Si standard, 1000 ppm. Fuse 0.2139 g of SiO2 with 2 g of Na2CO3 in a platinum 

crucible. Dissolve the melt with DDI water and transfer to a 100-mL volumetric flask. 

Dilute to 1-L volume with DDI water. Store in a polypropylene bottle. 

576
6.11 Primary Mn standard, 1000 ppm. Dissolve 1.000 g of Mn wire in a minimum volume of 

1:1 HCl:DDI. Dilute to 1-L volume in a volumetric flask using 1:1 HCl:DDI. Store in a 

polypropylene bottle. 

6.12 High calibration standard. Mix 30 mL of each primary standard (Al, Fe, and Si) with 5 

mL of primary Mn standard. Add 50 mL of 0.4 M acid oxalate solution, 20 mL of conc. 

HCl, and make to 1-L volume with DDI water. Resulting solution contains 5 ppm Mn 

and 30 ppm each of Al, Fe, and Si. Store in a polypropylene bottle. 

6.13 Low calibration standard. Mix 10 mL of each primary standard (Al, Fe, and Si) with 2 

mL of primary Mn standard. Add 30 mL of 0.4 M acid oxalate solution, 20 mL of conc. 

HCl, and make to 1-L volume with DDI water. Resulting solution contains 2 ppm Mn 

and 10 ppm each of Al, Fe, and Si. Store in a polypropylene bottle. 

6.14 Calibration reagent blank solution. Add 30 mL of 0.4 M acid oxalate solution, 20 mL of 

conc. HCl, and make to 1-L volume with DDI water. 

6.15 Argon gas, purity 99.9% 

7. Procedure 

Extraction of Fe, Al, Si, and Mn

7.1 Prepare sample tube by tightly compressing a 1-g ball of filter pulp into the bottom of a 

syringe barrel with a modified plunger. 

7.2 Weigh 0.500 g of <2-mm, air-dry soil and place in sample tube. Prepare two reagent blanks 

(no sample in tube) per set of 48 samples. 

7.3 Place the sample tube on the upper disk of the extractor and connect a tared extraction 

syringe. Use 25.4-mm (1-in) length rubber tubing to insert the handle of the plunger in the slot 

of the stationary extractor disk. 

7.4 Use a dispenser to add 15.00 mL of acid oxalate buffer to the sample tube. Make sure that 

the sample is thoroughly wetted. During the addition, wash sides of the tube and wet the 

sample. Shaking, swirling, or stirring may be required to wet organic samples. Allow sample 

to stand for at least 30 min. 

7.5 Set extractor for 30-min extraction rate and extract until the acid oxalate buffer solution is 

at a 0.5 to 1.0-cm height above sample. Turn off extractor. 

7.6 Put reservoir tube on top of the sample tube. 

7.7 Add 35 mL of acid oxalate buffer to the reservoir tube. 

7.8 Cover the extractor with a black plastic bag to exclude light. Adjust the extraction rate for a 

12-h extraction. 

7.9 After the extraction, shut off the extractor and pull plunger of syringe down. Do not 

remove the plunger from syringe barrel. Carefully remove the syringe with extract leaving the 

rubber tubing on the sample tube. 

7.10 Weigh each syringe containing acid oxalate extract to the nearest 0.01 g. 

7.11 Mix extract in each syringe by manually shaking. Fill a polycon with extract solution. 

This solution is reserved for determinations of Fe, Mn, Al, and Si. If optical density is to be 

measured, fill a disposable cuvette with extract solution. Discard excess solution. 

577
Determination of Optical Density of Extract

7.12 Place 4 mL of acid oxalate extract in disposable cuvette. 

7.13 Place 4 mL of acid oxalate reagent blank in disposable cuvette. 

7.14 On DU-7 spectrophotometer, select a 430-nm wavelength. Select normal slit width and 

height. 

7.15 Use the acid oxalate extract reagent blank to set spectrophotometer. 

7.16 Record optical density of acid oxalate extract to nearest 0.000. 

Dilution of Sample Extracts and Standards

7.17 For better nebulization, add one drop of DDBSA solution to each tube (sample extracts, 

calibration standards, and reagent blanks) to reduce surface tensions. Add DDBSA to tube 

before the addition of diluted solution. 

7.18 Set the digital settings of the Hamilton diluter at 63 for the diluent (0.1 N HCl) and 70 for 

the acid oxalate extracts for a 1:10 dilution. Calibration reagent blanks and calibration 

standards are not diluted. 

7.19 Dilute 1 part acid oxalate sample extract with 10 parts of 0.1 N HCl (1:10 dilution). 

7.20 Dispense the diluted solutions into 15-mL conical polystyrene centrifuge tubes which have 

been placed in carousels of the sample changer. 

ICP Calibration

7.21 Use high calibration standard and calibration reagent blank to calibrate ICP. The ICP 

requires a standard and a blank, in that order, for calibration. During ICP determinations, 

perform one calibration, i.e., standard plus blank, for every 6 samples. 

7.22 Use the low calibration standard as a check sample. 

ICP Set-up and Operation

7.23 The following parameters are only very general guidelines for instrument conditions for 

the various analytes. 

Parameter Value 

ICP power 1250 W 

Plasma gas flow Ar 12 L min-1

Nebulizer gas flow Ar 0.5 L min-1

Auxiliary gas flow Ar 0.05 to 1 L min-1

Use a high solids nebulizer instead of the cross flow nebulizer. 

7.24 Analyte data for some elements are reported at 2 wavelengths which serve as data checks. 

578
Analyte Wavelength 

Low 

Stamdards 

High 

Standards 

 

Fe 238.204/ 

239.562 

30.00 10.00 

Al 394.400/ 

396.150 

30.00 10.00 

Si 212.412/ 

251.611 

30.00 10.00 

Mn 257.610 5.00 2.00 

7.25 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. The instrument readings are usually programmed in ppm. 

7.26 If sample exceeds calibration standard, dilute the sample (dilution ratio in calculation) 

with appropriate matrix and record dilution. Remember to keep the matrix the same after 

dilution by diluting with 0.1 N HCl at the 1:1 ratio. 

8. Calculations

Analyte (%) = [ICP x (Syrfin -Syrinit) x DR x AD/OD]/[Sample x 10000 x Density]

where 

ICP = ICP analyte concentration (ppm) 

Syrfin = Weight of syringe + extract (g) 

Syrinit = Tare weight of syringe (g) 

DR = Dilution ratio of samples over calibration range 

Sample = Weight of sample (g) 

Density = Density of acid oxalate solution (1.007) 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report the percent acid oxalate extractable Fe, Al, and Si to the nearest 0.01%. Percent 

acid oxalate extractable is also reported. To date, however, no method code has been assigned 

to Mn determination by acid oxalate extraction. Report the optical density of the acid oxalate 

extract to the nearest 0.001 unit. 

10. Precision 

Precision data are not available for this procedure. The mean, standard deviation, and 

CV for Fe, Al, Si, and optical density for both the low and high standards are as follows: 

High 

Std 

n Mean Std. 

Dev. 

C.V. 

 

Optical 

Density 

18 0.18 0.03 14.2 

Fe 17 0.94 0.17 18.2 

Al 17 2.6 0.19 7.6 

Si 17 1.2 0.09 7.3 

 

(nm) (ppm) (ppm) 

579
Low 

Std 

N Mean Std. 

Dev. 

C.V. 

 

Optical 

Density 

25 0.06 0.00 7.5 

Fe 24 0.26 0.03 9.7 

Al 25 0.17 0.01 8.4 

Si 26 0.02 0.01 53.2 

11. References 

Holmgren, G.G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically controlled 

variable rate leaching device. Soil Sci. Amer. J. 41:1207-1208. 

Soil Conservation Service. 1984. Procedures for collecting soil samples and methods of 

analysis for soil survey. USDA-SCS Soil Surv. Invest. Rep. no. 1. U.S. Govt. Print. 

Office, Washington, DC. 

Soil Survey Staff. 1990. Keys to soil taxonomy. 4th ed. SMSS technical monograph no. 6. 

Blacksburg, VA. 

Soltanpour, P.N., J.B. Jones Jr., and S.M. Workman. 1982. In A. Klute (ed.) Methods of 

soil analysis. Part 2. Chemical and microbiological properties. 2nd ed. Agronomy 9:29-

65. 

Wada, K. 1989. Allophane and imogolite. In J.B. Dixon and S.B. Weed (eds.). Minerals in 

soil environment. 2nd ed. Soil Sci. Soc. Amer. No. 1. p. 1051-1087. 

Manganese and Aluminum (6D and 6G) 

1 N KCl Extractable, Automatic Extractor (6D3 and 6G9) Inductively Coupled Plasma Spectrometry (6D3 and 6G9b) 

1. Application 

The Al extracted by 1 N KCl approximates exchangeable Al and is a measure of the 

"active" acidity present in soils with a 1:1 water pH <5.5. Above pH 5.5, precipitation of Al 

occurs during analysis. This method does not measure the acidity component of hydronium 

ions (H3O+). If Al is present in measurable amounts, the hydronium is a minor component of 

the active acidity. Because the 1 N KCl extractant is an unbuffered salt and usually affects the 

soil pH one unit or less, the extraction is determined at or near the soil pH. The KCl 

extractable Al is related to the immediate lime requirement and existing CEC of the soil. The 

"potential" acidity is better measured by the BaCl2-TEA method (procedure 6H5a) (Thomas, 

1982). 

2. Summary of Method 

A soil sample is leached with 1 N KCl using the mechanical vacuum extractor 

(Holmgren et al., 1977). The leachate is weighed. The KCl extracted solution is diluted with 

0.5 N HCl. The diluted extract is vaporized and atomized by a inductively coupled plasma 

emission spectrophotometer (ICP). The atoms or ions of the analyte are energized in high 

temperatures, resulting in the movement of valence electrons to higher orbits from the nucleus. 

As the electrons fall back to a lower orbit, electromagnetic energy at a specific wavelength for a 

given atom is emitted in measurable amounts (Soltanpour et al., 1982). Data are automatically 

recorded by a microcomputer and printer. The Mn and Al are reported in meq/100 g ovendry 

soil in procedures 6D3 and 6G9b (Soil Conservation Service, 1984). 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

ICP analyses of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. 

580
The soil:extractant ratio must remain constant. A soil:extractant ratio of 1:10 (w:v) for 

batch procedures is most commonly used. Using a leaching technique, a 1:20 (w:v) ratio gives 

comparable results. If the sample size is changed, the amount of extractable Al is changed. No 

other significant interferences have been identified for this procedure. 

4. Safety

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Follow standard laboratory 

practices when handling compressed gases. Gas cylinders should be chained or bolted in an 

upright position. Follow the manufacturer's safety precautions when using the ICP. 

5. Equipment

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Analytical filter pulp, Schleicher and Schuell, no. 289 

5.3 Mechanical vacuum extractor, 24 place, Centurion International, Inc., Lincoln, NE 

5.4 Syringes, polypropylene, disposable, 60 mL, for sample tube, extractant reservoir, and 

tared extraction syringe. 

5.5 Rubber tubing, 3.2 ID x 6.4 OD x 25.4 mm (1/8 ID x 1/4 OD x 1 in), for connecting 

syringe barrels 

5.6 Plunger, modified. Remove rubber and cut plastic protrusion from plunger end. 

5.7 Wash bottle, 20 mL, to dispense KCl. 

5.8 Polycons, Richards Mfg. Co. 

5.9 Inductively coupled plasma (ICP) atomic emission spectrophotometer, Perkin-Elmer 

model 6000 

5.10 Autosampler, AS-50, Perkin-Elmer Corp., Norwalk, CT 

5.11 Microcomputer, 7500 Professional Computer, Perkin-Elmer Corp., Norwalk, CT 

5.12 Dot matrix printer, P-132, Interdigital Data Systems, Inc. 

5.13 High-purity, high-flow, single-stage regulator, argon, product no. E11-X-N145DHF, Air 

Products and Chemicals, Inc., Box 538, Allentown, PA 18105 

5.14 Digital diluter/dispenser, product no. 100004, with hand probe and actuator, product no. 

230700, Hamilton Co., P.O. Box 10030, Reno, NV, 89510 

5.15 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV, 89510 

6. Reagents

6.1 Distilled deionized (DDI) water 

6.2 Hydrochloric acid (HCl), conc., 12 N

6.3 HCl, 1:1 HCl:DDI, 6 N. Carefully mix 1 part of conc. HCl to 1 part DDI water. 

6.4 HCl, 1% wt. Carefully dilute 25 mL of conc. HCl to 1 L with DDI water. 

6.5 HCl, 0.5 N. Add 1 part of conc. HCl to 24 parts DDI water (1:25 dilution). 

6.6 Potassium chloride solution (KCl), 1.0 N. Dissolve 1342 g of KCl reagent in 16 L DD 

water. Allow solution to equilibrate to room temperature. Dilute to 18 L with DDI 

water. Use 1.0 N KCl for Al and Mn extraction. 

6.7 Potassium chloride solution (KCl), 2.0 N. Dissolve 298.24 g of KCl reagent in 1.5 L DDI 

water. Allow solution to equilibrate to room temperature. Dilute to 2 L with DDI water. 

Use 2.0 N KCl for standards. 

6.8 Primary Al standard, 2248.5 ppm (250 meq L-1). Dissolve 2.2485 g of Al wire in a 

minimum volume of 1:1 HCl:DDI. This is a very slow reaction. Dilute to 1 L in a 

volumetric flask using 1% HCl solution. Store in polypropylene container. 

6.9 Primary Mn standard, 1000 ppm (36 meq L-1). Commercial. Dissolve 1.000 g of Mn 

metal in a minimum volume of 1:1 HCl:DDI. When dissolved, dilute to 1 L in a 

volumetric flask using 1% HCl solution. Store in a polypropylene container. 

581
6.10 Mn standard, 250 ppm (9 meq L-1). Mix 25 mL of primary Mn standard (1000 ppm) with 

10 mL of 1:1 HCl:DDI and dilute to 100-mL volume with DDI water. Store in 

polypropylene bottle. 

6.11 Calibration Al and Mn standard, 10 meq L-1 Al and 5 ppm Mn. Mix 10 mL of primary Al 

standard (250 meq L-1) with 125 mL 2.0 N KCl solution. Add 5 mL of Mn standard (250 

ppm). Make to 250-mL volume with DDI water. Store in polypropylene container. 

6.12 Calibration Al and Mn check standard, 5 meq L-1 Al and 2 ppm Mn. Mix 5 mL of 

primary Al standard (250 meq L-1) with 125 mL 2.0 N KCl solution. Add 2 mL of Mn 

standard (250 ppm). Store in polypropylene container. 

6.13 Calibration reagent blank solution, 1.0 N KCl. Add 125 mL of 2.0 N KCl to a volumetric 

flask and make to 250-mL volume with DDI water. Store in polypropylene container. 

6.14 Dodecylbenzenesulfonic acid (DDBSA), tech 97%. Working stock is 0.1 M. Dilute 25 

mL of 0.1 M DDBSA to 1-L volume with DDI water. 

6.15 Argon gas, purity 99.9% 

7. Procedure

Extraction of Al and Mn

7.1 Prepare sample tube by tightly compressing a 1-g ball of filter pulp into the bottom of a 

syringe barrel with a modified plunger. 

7.2 Weigh exactly 2.50 g of <2-mm, air-dry soil and place in sample tube. Prepare one quality 

control check sample per 48 samples. 

7.3 Place the sample tube on the upper disk of the extractor and connect a tared extraction 

syringe. Use 25.4-mm (1-in) length rubber tubing to insert the handle of the plunger in the slot 

of the stationary extractor disk. 

7.4 Use a squeeze bottle and fill sample tube to the 20-mL mark with 1.0 N KCl solution (≈ 10 

mL). Make sure that the sample is thoroughly wetted. During the addition, wash sides of the 

tube and wet the sample. Shaking, swirling, or stirring may be required to wet organic samples. 

Allow sample to stand for at least 30 min. 

7.5 Put reservoir tube on top of the sample tube. Set extractor for fast extraction rate and 

extract until the KCl solution is at a 0.5- to 1.0-cm height above sample. Turn off extractor. 

7.6 Add 45 mL KCl solution to reservoir tube. Set extractor for 45-min extraction. 

7.7 After the extraction, shut off extractor and pull plunger of syringe down. Do not remove 

the plunger from syringe barrel. Carefully remove the syringe with extract leaving the rubber 

tubing on the sample tube. 

7.8 Weigh each syringe containing KCl extract to the nearest 0.01 g. 

7.9 Mix extract in each syringe by manually shaking. Fill a polycon with extract solution and 

discard the excess. This solution is reserved for extractable Al and Mn analyses. 

Dilution of Extracts and Standards

7.10 For better neubilization, add one drop of DDBSA solution to KCl sample extracts, 

calibration reagent blanks and calibration standards to reduce surface tensions. Add DDBSA to 

tube before adding diluted solution. 

582
7.11 Set the digital settings at 40 for the diluent (0.5 N HCl) and 99 for the KCl sample 

extracts, calibration reagent blanks, calibration standards, and calibration check standards for a 

1:5 dilution as follows: 

7.12 Dilute 1 part KCl sample extract with 4 parts of 0.5 N HCl (1:5 dilution). 

7.13 Dilute 1 part calibration reagent blank with 4 parts of 0.5 N HCl (1:5 dilution). 

7.14 Dilute 1 part calibration standard (10 meq L-1 Al and 5 ppm Mn) with 4 parts of 0.5 N HCl 

(1:5 dilution). 

7.15 Dilute 1 part calibration check standard (5 meq L-1 Al and 2 ppm Mn) with 4 parts of 0.5 

N HCl (1:5 dilution). 

7.16 Dispense the diluted solutions into 15-mL conical polystyrene centrifuge tubes which have 

been placed in carousels of the sample changer. 

ICP Calibration

7.17 Use calibration standard (10.00 meq L-1 Al and 5.00 ppm Mn,) and calibration reagent 

blank (1.0 N KCl) to calibrate ICP. The ICP requires a standard and a blank, in that order, for 

calibration. During ICP determinations, perform one calibration, i.e., standard plus blank, for 

every 6 samples. 

7.18 Use the calibration check standard (5.00 meq L-1 Al and 2.00 ppm Mn) as a check sample. 

ICP Set-up and Operation 7.19 The following parameters are only very general guidelines for instrument conditions for 

the analytes. 

Parameter Al Fe 

Plasma flow (ml Ar min-1) 12.0 12.0 

Nebulizer flow (mL Ar min-1) 0.5 0.5 

Auxiliary flow (mL Ar min-1) 0.5 0.5 

Viewing Height (nm) 15.0 15.0 

 Wavelength 1 

Wavelength (nm) 394.400 259.373 

Scan speed (s) 2.0 1.0 

Bkg. Correction (nm) -0.069, +0.055 0.0 

 

 Wavelength 2 

Wavelength (nm) 396.152 294.920 

Scan speed (s) 2.0 2.0 

Bkg. Correction (nm) -0.069, +0.055 -0.046, +0.049 

High solids nebulizer has a 20 s read delay. 

7.20 Load sample tubes in the carousel so that the calibration standard, reagent blank, 

calibration check standard, and 6 unknown samples are determined in order. Determine a set of 

24 unknown samples with each carousel. 

583
7.21 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.22 If a sample exceeds the calibration standard, dilute the sample (dilution ratio in 

calculation) with appropriate matrix and record dilution. Remember to keep the matrix the 

same after dilution by diluting with the 0.5 N HCl solution (1:5 dilution). 

7.23 Analyze one quality control check sample for every 48 samples. 

8. Calculations

8.1 The instrument readings are the analyte concentration (meq L-1 Al and ppm Mn) in 

undiluted extract. Use these values to calculate the analyte concentration on an oven-dry soil 

basis (meq/100 g). 

Analyte (meq/100 g) = [ICP x (Wtsyr+ext - Wtsyr) x DR x 100 x AD/OD]/[Smp.Wt. x 1.0412 x 

1000]

where 

ICP = ICP analyte reading 

Wtsyr+ext = Weight of extraction syringe & extract (g) 

Wtsyr = Weight of tared extraction syringe (g) 

DR. = Dilution ratio of samples over calibration range 

Smp. Wt = Sample weight (g) 

1.0412 = Density of 1 N KCl @ 20°C 

1000 = g L-1

100 = Conversion factor (100-g basis) 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

9. Report

Report KCl extractable Al and Mn in units of meq/100 g of oven-dry soil to the nearest 

0.01 meq/100 g. 

10. Precision

Precision data are not available for this procedure. 

11. References

Holmgren, George G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically 

controlled variable rate leaching device. Soil Sci. Amer. J. 41:1207-1208. 

Soil Conservation Service. 1984. Procedures for collecting soil samples and methods of 

analysis for soil survey. USDA-SCS Soil Surv. Invest. Rep. no. 1. U.S. Govt. Print. 

Office, Washington, DC. 

Soltanpour, P.N., J.B. Jones Jr., and S.M. Workman. 1982. In A. Klute (ed.) Methods of 

soil analysis. Part 2. Chemical and microbiological properties. 2nd ed. Agronomy 9:29-

65. 

Thomas, G.W. 1982. Exchangeable cations. In A. Klute (ed.) Methods of soil analysis. Part 

2. Chemical and microbiological properties. 2nd ed. Agronomy 9:159-165. 

Aluminum (6G) 

KCl, Automatic Extractor (6G9) 

Atomic Absorption (6G9a) 

1. Application 

584
The Al extracted by 1 N KCl approximates exchangeable Al and is a measure of the 

"active" acidity present in soils with a 1:1 water pH <5.5. Above pH 5.5, precipitation of Al 

occurs during analysis. This method does not measure the acidity component of hydronium 

ions (H3O+). If Al is present in measurable amounts, the hydronium is a minor component of 

the active acidity. Because the 1 N KCl extractant is an unbuffered salt and usually affects the 

soil pH one unit or less, the extraction is determined at or near the soil pH. The KCl 

extractable Al is related to the immediate lime requirement and existing CEC of the soil. The 

"potential" acidity is better measured by the BaCl2-TEA method (procedure 6H5a) (Thomas, 

1982). 

2. Summary of Method 

A soil sample is leached with 1 N KCl using the mechanical vacuum extractor 

(Holmgren et al., 1977). The leachate is weighed. The KCl extract is diluted with distilled 

deionized (DDI) water. The diluted extract is aspirated into an atomic absorption 

spectrophotometer (AA). The analyte is measured by absorption of the light from a hollow 

cathode lamp. An automatic sample changer is used to aspirate a series of samples. The AA 

converts absorption to analyte concentration. The data are automatically recorded by a 

microcomputer and printer. The Al is reported in meq/100 g ovendry soil in procedure 6G9a. 

3. Interferences 

There are four types of interferences (matrix, spectral, chemical, and ionization) in the 

AA analyses of these cations. These interferences vary in importance, depending upon the 

particular analyte selected. 

The soil:extractant ratio must remain constant. A soil:extractant ratio of 1:10 (w:v) for 

batch procedures is most commonly used. Using a leaching technique, a 1:20 (w:v) ratio gives 

comparable results. If the sample is changed, the amount of extractable Al is changed. No 

other significant interferences have been identified for this procedure. 

4. Safety 

Wear protective clothing and eye protection. When preparing reagents, exercise special 

care. Restrict the use of concentrated HCl to a fume hood. Many metal salts are extremely 

toxic and may be fatal if ingested. Follow standard laboratory practices when handling 

compressed gases. Gas cylinders should be chained or bolted in an upright position. Acetylene 

gas is highly flammable. Avoid open flames and sparks. Standard laboratory equipment 

includes fire blankets and extinguishers for use when necessary. Follow the manufacturer's 

safety precautions when using the AA. 

5. Equipment 

5.1 Electronic balance, ±1-mg sensitivity 

5.2 Mechanical vacuum extractor, 24 place, Centurion International, Inc., Lincoln, NE 

5.3 Syringes, polypropylene, disposable, 60 mL, for sample tube, extractant reservoir, and 

tared extraction syringe. 

5.4 Rubber tubing, 3.2 ID x 6.4 OD x 25.4 mm (1/8 ID x 1/4 OD x 1 in) for connecting 

syringe barrels 

5.5 Wash bottle, 20 mL, to dispense KCl. 

5.6 Plunger, modified. Remove rubber and cut plastic protrusion from plunger end. 

5.7 Polycons, Richards Mfg. Co. 

5.8 Atomic absorption spectrophotometer (AA), Perkin-Elmer model 5000 

5.9 Autosampler, AS-50, Perkin-Elmer Corp., Norwalk, CT 

5.10 Microcomputer, 7500 Professional Computer, Perkin-Elmer Corp., Norwalk, CT 

5.11 Dot matrix printer, P-132, Interdigital Data Systems, Inc. 

5.12 Single-stage regulator, acetylene service, part number E11-0-N511A, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 18105 

585
5.13 Heated regulator, single-stage, nitrous oxide, stock number 808 8039, Airco Welding 

Products, P.O. Box 486, Union, NJ 07083 

5.14 Digital diluter/dispenser, product no. 100004, with hand probe and actuator, product no. 

230700, Hamilton Co., P.O. Box 10030, Reno, NV, 89510 

5.15 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV, 89510 

5.16 Centrifuge tubes, polystyrene, 15 mL, conical bottom, graduated, part no. 2087, for 

sample dilution and sample changer, Becton Dickinson Labware, Becton Dickinson and 

Co., 2 Bridgewater Lane, Lincoln Park, NJ 07035 

5.17 Containers, polyproylene or teflon 

6. Reagents 

6.1 Distilled deionized (DDI) water 

6.2 Hydrochloric acid (HCl), conc., 12 N

6.3 HCl, 1:1 HCl:DDI, 6 N. Carefully mix 1 part of conc. HCl to 1 part DDI water. 

6.4 HCl, 1% wt. Carefully dilute 25 mL of conc. HCl to 1 L with DDI water. 

6.5 Potassium chloride solution (KCl), 1.0 N. Dissolve 1342 g of KCl reagent in 16 L DDI 

water. Allow solution to equilibrate to room temperature. Dilute to 18 L with DDI 

water. Use 1.0 N KCl solution for Al extraction. 

6.6 Potassium chloride solution (KCl), 2.0 N. Dissolve 298.24 g of KCl reagent in 1.5 L DDI 

water. Allow solution to equilibrate to room temperature. Dilute to 2 L with DDI water. 

Use 2.0 N KCl solution for standards. 

6.7 Primary Al standard, 2248.5 ppm (250 meq L-1). Dissolve 2.2485 g of Al wire in a 

minimum volume of 1:1 HCl:DDI. This is a very slow reaction. Dilute to 1 L in a 

volumetric flask using 1% HCl solution. Store in polypropylene bottle. 

6.8 Calibration Al standard, 10 meq L-1. Mix 10 mL of primary Al standard (250 meq L-1) 

with 125 mL of 2.0 N KCl solution. Make to 250-mL volume with DDI water. Store in 

polypropylene bottle. 

6.9 Calibration Al check standard, 5 meq L-1. Mix 5 mL of primary Al standard (250 meq L1

) with 125 mL of 2.0 N KCl solution. Make to 250-mL volume with DDI water. Store 

in polypropylene bottle. 

6.10 Calibration reagent blank solution, 1.0 N KCl. Add 125 mL of 2.0 N KCl to a volumetric 

flask and make to 50-mL volume with DDI water. Store in polypropylene bottle. 

6.11 Nitrous oxide gas, compressed 

6.12 Acetylene gas, compressed, purity 99.6% 

6.13 Compressed air with water and oil traps 

7. Procedure 

Extraction of Al 

7.1 Prepare sample tube by tightly compressing a 1-g ball of filter pulp into the bottom of a 

syringe barrel with a modified plunger. 

7.2 Weigh exactly 2.50 g of <2-mm, air-dry soil and place in sample tube. Prepare one quality 

control check sample per 48 samples. 

7.3 Place the sample tube on the upper disk of the extractor and connect a tared extraction 

syringe. Use 25.4-mm (1-in) length rubber tubing to insert the handle of the plunger in the slot 

of the stationary extractor disk. 

7.4 Use a squeeze bottle and fill sample tube to the 20-mL mark with 1.0 N KCl solution (~ 10 

mL). Make sure that the sample is thoroughly wetted. During the addition, wash sides of the 

586
tube and wet the sample. Shaking, swirling, or stirring may be required to wet organic samples. 

Allow sample to stand for at least 30 min. 

7.5 Put reservoir tube on top of the sample tube. Set extractor for fast extraction rate and 

extract until the KCl solution is at a 0.5- to 1.0-cm height above sample. Turn off extractor. 

7.6 Add 45 mL KCl solution to reservoir tube. Set extractor for 45-min extraction. 

7.7 After the extraction, shut off extractor and pull plunger of syringe down. Do not remove 

the plunger from syringe barrel. Carefully remove the syringe with extract leaving the rubber 

tubing on the sample tube. 

7.8 Weigh each syringe containing KCl extract to the nearest 0.01 g. 

7.9 Mix extract in each syringe by manually shaking. Fill a polycon with extract solution and 

discard the excess. This solution is reserved for extractable Al analysis. 

Dilution of Sample Extracts and Standards

7.10 No ionization suppressant is required as the K in the extractant is present in sufficient 

quantity. Set the digital settings at 40 for the diluent (DDI water) and 99 for the KCl sample 

extracts, calibration reagent blanks, calibration standards, and calibration check standards for a 

1:5 dilution as follows: 

7.11 Dilute 1 part KCl sample extract with 4 parts of DDI water (1:5 dilution). 

7.12 Dilute 1 part calibration reagent blank with 4 parts of DDI water (1:5 dilution). 

7.13 Dilute 1 part calibration standard (10 meq L-1 Al) with 4 parts of DDI water (1:5 dilution). 

7.14 Dilute 1 part calibration check standard (5 meq L-1 Al) with 4 parts of DDI water (1:5 

dilution). 

7.15 Dispense the diluted solutions into 15-mL conical polystyrene centrifuge tubes which are 

placed in carousels of the sample changer. 

AA Calibration

7.16 Use calibration reagent blank (1.0 N KCl) and calibration standard (10 meq L-1 Al) to 

calibrate the AA. The AA program requires a blank and a standard, in that order, to establish a 

single point calibration curve for element determination. During AA determinations, perform 

one calibration, i.e., blank plus standard, for every 12 samples. 

7.17 Use the calibration check standard (5 meq L-1 Al) as a check sample. 

AA Set-up and Operation

7.18 The following parameters are only very general guidelines for instrument conditions for 

the analyte. 

Element Head = Al 

Wavelength (nm) = 309.3 

Burner head & angle = 5 cm Parallel 

Fuel/Oxidant (C2H2/N2O) = 30/17 

Typical read delay is 6 s, and integration by peak area is 8 s. 

587
7.19 Use the microcomputer and printer to set instrument parameters and to collect and record 

instrument readings. 

7.20 If a sample exceeds the calibration standard, dilute the sample (dilution ratio in 

calculation) with appropriate matrix and record dilution. Remember to keep the matrix the 

same after dilution by diluting with DDI water (1:5 dilution). 

7.21 Analyze one quality control check sample for every 48 samples. 

8. Calculations

8.1 The instrument readings are the analyte concentration (meq L-1 Al) in undiluted extract. 

Use these values to calculate the analyte concentration on an oven-dry soil basis (meq/100 g). 

Al (meq/100 g) = [AAAl x (Wtsyr+ext - Wtsyr) x DR x 100 x AD/OD]/[Smp. Wt. x 1.0412 x 1000]

where 

AAAl = AA Al reading (meq L-1) 

Wtsyr+ext = Weight of extraction syringe and extract (g) 

Wtsyr = Weight of tared extraction syringe (g) 

DR= Dilution ratio for samples over calibration range 

Smp.Wt = Sample weight (g) 

1.0412 = Density of 1 N KCl @ 20°C 

1000 = g L-1

100 = Conversion factor (100-g basis) 

AD/OD = Air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report KCl extractable Al in units of meq/100 g of oven-dry soil to the nearest 0.1 

meq/100 g. 

10. Precision 

Precision data are not available for this procedure. A quality control check sample is 

run with every batch of 48 samples. For 21 observations of the quality control sample, the 

mean, standard deviation, and C.V. for extractable Al are 3.1, 0.18, and 5.7 %, respectively. 

11. References 

Holmgren, George G.S., R.L. Juve, and R.C. Geschwender. 1977. A mechanically 

controlled variable rate leaching device. Soil Sci. Amer. J. 41:1207-1208. 

Thomas, G.W. 1982. Exchangeable cations. In A. Klute (ed.) Methods of soil analysis. Part 

2. Chemical and microbiological properties. 2nd ed. Agronomy 9:159-165. 

Chloride, Sulfate, Nitrate, Fluoride, and Nitrite (6K, 6L, 6M, 6U, and 6W) Saturation Extract (6K1, 6L1, 6M1, 6U1, and 6W1) Chromatograph (6K1c, 6L1c, 6M1c, 6U1a, and 6W1a) 

1. Application 

The soluble anions that are commonly determined in saline and alkali soils are 

carbonate, bicarbonate, sulfate, chloride, nitrate, nitrite, fluoride, phosphate, silicate, and borate 

(Khym, 1974; U.S. Salinity Laboratory Staff, 1954). Carbonate and bicarbonate are 

determined by titration in procedures 6I1b and 6J1b, respectively (Soil Conservation Service, 

1984). Phosphate, silicate, and borate usually are not determined because they are found only 

occasionally in measurable amounts in soils. Chloride, sulfate, nitrate, fluoride, and nitrite are 

measured in solution in procedures 6K1c, 6L1c, 6M1c, 6U1a, and 6W1a, respectively (Soil 

588
Conservation Service, 1984). In saline and alkali soils, carbonate, bicarbonate, sulfate, and 

chloride are the anions that are found in the greatest abundance. In general, soluble sulfate is 

usually more abundant than soluble chloride. 

2. Summary of Method 

The saturation extract is diluted according to its electrical conductivity (ECs). The 

diluted sample is injected into the ion chromatograph, and the anions are separated. A 

conductivity detector is used to determine the anion. A chart recording is made of the 

chromatograph. Standard anions are used to calibrate the system. A calibration curve is 

determined, and the anion concentrations are calculated. The saturated extract anions, Cl-, SO4

2

, NO3

-

, F-, and NO2

-

 are reported in meq L-1 in procedures 6k1c, 6L1c, 6M1c, 6U1a, and 

6W1a, respectively (Soil Conservation Service, 1984). 

3. Interferences 

Some saturation extracts contain suspended solids. Filtering after dilution removes the 

particles. Saturation extracts of acid soils that contain Fe and/or Al may precipitate and clog 

the separator column. Saturation extracts of very high pH may contain organic material which 

may clog or poison the column. Low molecular weight organic anions will co-elute with 

inorganic anions from the column. 

4. Safety 

Wear protective clothing and safety glasses. When preparing reagents, exercise special 

care. Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash 

hands after handling these metal salts. Follow the manufacturer's safety precautions when 

using the chromatograph. 

5. Equipment 

5.1 Ion chromatograph, Series 2110i, with conductivity detector, Dionex Corp., 1228 Titan 

Way, Sunnyvale, CA 94086 

5.2 HPIC AS3 analytical column, P/N 030985, Dionex Corp., 1228 Titan Way, Sunnyvale, 

CA 94086 

5.3 HPIC AG3 analytical guard column, P/N 030986, Dionex Corp., 1228 Titan Way, 

Sunnyvale, CA 94086 

5.4 Anion micro membrane suppressor, P/N 037072, Dionex Corp., 1228 Titan Way, 

Sunnyvale, CA 94086 

5.5 Automated sampler, Dionex Corp., 1228 Titan Way, Sunnyvale, CA 94086 

5.6 Poly-vials, 5 mL, P/N 038008, Dionex Corp., 1228 Titan Way, Sunnyvale, CA 94086 

5.7 Poly-vials, filtercaps, 5 mL, P/N 038009, Dionex Corp., 1228 Titan Way, Sunnyvale, CA 

94086 

5.8 Chart recorder, Honeywell Corp., chart speed 0.5 cm min-1, span 1000 mV F.S. 

5.9 Digital diluter/dispenser, product number 100004, with hand probe and actuator, product 

number 230700, Hamilton Co., P.O. Box 10030, Reno, NV 89510 

5.10 Syringes, gas tight, Hamilton 1001 DX and 1010-TEF LL, Hamilton Co., P.O. Box 

10030, Reno, NV 89510 

5.11 Syringes, disposable, polypropylene, 12 mL 

5.12 Disposable 0.2-μm pore size, 25-mm filter assembly, Gelman Sciences, Inc., 674 South 

Wagner Road, Ann Arbor, MI 48106. Use for saturation extracts and standards. 

5.13 Disposable 0.2-μm pore size, Ultipor N66 DFA3001NAEY, Pall Trinity Micro Corp., 

Cortland, NY 13045. Use for filtering distilled deionized (DDI) water. 

6. Reagents 

6.1 Distilled deionized (DDI) filtered water 

6.2 Sulfuric acid (H2SO4), conc., reagent 

6.3 Toluene 

589
6.4 Isopropanol to de-gas column 

6.5 Regenerant solution for membrane suppressor columns, 0.025 N H2SO4. Carefully mix 

22.92 g of conc. H2SO4 with filtered DDI water and dilute to 18-L volume. Store in a 

clean glass carboy with a solid stopper. Cover the carboy top with aluminum foil to 

protect the contents from dust. 

6.6 Stock NaHCO3 solution, 0.480 M. Mix 40.34 g of dried NaHCO3 with filtered DDI water 

and dilute to 1-L volume. 

6.7 Stock Na2CO3 solution, 0.3838 M. Mix 40.68 g of dried Na2CO3 with filtered DDI water 

and dilute to 1-L volume. 

6.8 Working eluent solution. Mix 112.5 mL of 0.480 M NaHCO3 and 112.5 mL of 0.3838 M

Na2CO3 with filtered DDI water and dilute to 18-L volume. Add 3 drops of toluene to 

retard microbial growth. 

6.9 Primary SO4

2- standard, 0.5 M (1.0 N). Mix 17.7560 g of Na2SO4 with filtered DDI water 

and dilute to 250-mL volume. 

6.10 Primary Cl- standard, 1.0 M (1.0 N). Add 18.6392 g of KCl with filtered DDI water and 

dilute to 250-mL volume. 

6.11 Primary F- standard, 0.125 M (0.125 N). Add 1.3122 g of NaF with filtered DDI water 

and dilute to 250-mL volume. 

6.12 Primary NO3

-

 standard, 1.0 M (1.0 N). Add 25.2770 g of KNO3 with filtered DDI water 

and dilute to 250-mL volume. 

6.13 Primary mixed standard. Prepare 1 primary mixed standard by taking aliquots of each of 

the proceeding primary standards and diluting the combined aliquots to a 1-L volume 

with working eluent as follows: 

Primary 

Stds. 

Aliquot Final 

Conc. 

Vol. 

w/Eluent 

 mL mL Meq/L 

 

Na2SO4 50 1000 50 

KCl 10 1000 10 

NaF 100 1000 12.5 

KNO3 30 1000 30 

Add eight drops of toluene to primary mixed standard to retard microbial growth and store in a 

glass container. 

6.14 Mixed calibration standards. Prepare 4 mixed calibration standards (0.5, 1.0, 3.0, and 7.0 

readings) by taking aliquots of primary mixed standard and diluting each aliquot to 100-

mL volume with working eluent as follows: 

Primary 

Mixed Stds. 

Final Vol. 

w/Eluent 

SO4

2- Cl-

 F- NO3

-

(mL) (mL) meq L-1 meq L-1 meq L-1 meq L-1

 

0.5 100 0.25 0.05 0.0625 0.15 

1.0 100 0.50 0.10 0.125 0.30 

3.0 100 1.5 0.30 0.375 0.90 

7.0 100 3.5 0.70 0.875 2.1 

6.15 NaNO2, Baker reagent grade, 99.5% purity 

590
6.16 Primary NO2

-

 standard, 1 N (1000 meq L-1). Mix 69.3568 g of reagent grade NaNO2 with 

filtered DDI water and dilute to 1-L volume. Take 5 mL aliquot of primary NO2

-

standard and dilute with 500 mL of filtered DDI water (10 meq L -1). Add eight drops of 

toluene to primary NO2

-

 standard to retard microbial growth and store in a glass 

container. 

6.17 NO2

-

 calibration standards. Prepare 4 NO2

-

 calibration standards (0.5, 1.0, 3.0, and 7.0 

readings) by taking aliquots of primary NO2

-

 standard (10 meq L-1) and diluting each 

aliquot to 100-mL volume with working eluent as follows: 

Primary 

Mixed Stds. 

Final Vol. 

w/Eluent 

NO2

- 

 

(mL) (mL) meq L-1

 

0.5 100 0.5 

1.0 100 1.0 

3.0 100 3.0 

7.0 100 7.0 

7. Procedure

Dilution of extracts 

7.1 To estimate the total soluble anion concentration (meq L-1), multiply the ECs (procedure 

8A3a) by 10. Subtract the CO3

2- and HCO3-

 concentrations (procedures 6I1b and 6J1b) from 

the total anion concentration. The remainder is the ≈ concentration (meq L-1) of anions to be 

separated by ion chromatography. 

Anion concentration (meq L-1) = ECs x 10 - (HCO3

-

 + CO3

2-) 

7.2 Dilute the saturation extract with the working eluent. Some typical dilutions are as follows: 

ECs (mmhos cm-1) Dilution Factor 

0.0 to 0.4 1:3 

0.4 to 0.7 1:5 

0.8 to 1.2 1:9 

1.2 to 1.8 1:17 

1.8 to 2.9 1:39 

3.0 to 5.5 1:80 

5.5 to 7.5 1:150 

7.5 to 9.7 1:200 

9.7 to 13.5 1:290 

13.5 to 15.5 1:350 

15.5 to 25.0 1:660 

25.0 to 40.0 1:1100 

40.0 to 55.0 1:2100 

55.0 to 75.0 1:4800 

+75.0 1:15500 

7.3 Place the diluted samples in 12-mL syringes. Cap syringes to prevent evaporation or 

contamination. 

7.4 Place the mixed calibration standards in 12-mL syringes. 

591
Set-up and Operation of Ion Chromatograph (IC) 

7.5 Because any number of factors may cause a change in IC operating conditions, only a 

general set-up of the Dionex 2110i ion chromatograph is presented. Individual analysts may 

modify some or all of the operating conditions to achieve satisfactory results. The uS cm-1

units are equivalent to mmhos cm-1. Typical operation parameters are as follows: 

Parameter Range 

Conductivity cell range 3 uS cm-1 full scale to 100 

uS cm-1

Auto Offset “On” 

Analytical pump flow rate 2.0 to 2.5 mL min-1

Low pressure limit 200 

High pressure limit 1000 

Regenerant flow 3 to 4 mL min-1

Injector loom 0.50 mL 

Air pressure 3 to 6 psi 

Chart recorder speed 0.5 cm min-1 

Chart recorder span 1000 mV full scale 

7.6 Initial IC operation should be long enough to establish a stable baseline. 

7.7 Inject the most concentrated standard. The IC adjustment may be necessary to obtain 

adequate stability, resolution, and reproducibility. 

7.8 Inject standards in random order to detect if memory effects are evident. 

7.9 Analyze blanks at frequent intervals. 

7.10 The injection loop requires complete flushing, i.e., 3 to 5x the loop volume. 

7.11 Inject samples, standards, and blanks in the IC after achievement of stability. The analyst 

may change the detector range to suit the sample. 

7.12 The analyst records the detector range and peak height for each detected anion. The anion 

identity may be determined by comparison to standards. Peak height is determined from the 

baseline to the peak. 

8. Calculations 

Calibration Calculations 

8.1 Use the peak height of each anion standard to either construct a calibrated curve to plot 

anion concentration or use a least squares analysis to calculate anion concentration. The 

analytes are reported in meq L-1. 

8.2 Calibration Curve: Plot the peak height against the meq L-1 of each anion standard on graph 

paper. Construct the calibration curve by finding the "best" line that fits the plotted standards. 

8.3 Linear Squares Analysis: Use a least squares criterion, 

i.e. best moving average. Refer to a statistical analysis book for additional information on least 

squares analysis. An example for the anion Cl- is as follows: 

592
Cl-

 (meq L-1) = Y = 0.1 1.5 4.0 

Peak height = X = 8.43 170.0 441.5 

Number of standards = n = 3 

∑Yi = 5.6 ∑Xi = 619.93 

∑Yi/n = Y = 1.866 ∑Xi/n = X = 206.6433 

∑XiYi = 2021.843 ∑Xi

2

 = 223893.31 

∑Xi∑Yi = 3471.608 

b = ∑XiYi - ∑Xi∑Yi/n = ⎯⎯⎯⎯⎯⎯⎯⎯⎯ ∑Xi

2

 - (∑Xi)

2

/n 

2021.843 - 1157.2027 

⎯⎯⎯⎯⎯⎯⎯⎯⎯ = 0.0090265 

223893.31 - 128104.4 

b = slope of the line, i.e., the amount that Y changes when X changes by 1 unit. 

The equation is as follows: 

Y = ⎯Y + b (X - ⎯X) 

Y = 1.866 + 0.0090265 (X) - 1.8653 

Analyte Calculation 

8.4 Calibration curve: Read the analyte concentration (meq L-1) directly from the calibration 

curve. 

8.5 Linear regression: Put the peak height in the preceding equation and solve for analyte 

concentration (meq L-1). Thus, if sample extract has 204 peak height, the 

preceding equation is as follows: 

Y = 1.866 + 0.0090265 (204) - 1.8653 = 1.84 meq L-1 

8.6 Repeat the calibration set and analyte calculation for each anion. 

9. Report

Report the saturation extract anions in units of meq L-1 to the nearest 0.1 meq L-1. 

10. Precision

Precision data are not available for this procedure. 

11. References 

Khym, J.X. 1974. Analytical ion-exchange procedures in chemistry and biology: theory, 

equipment, techniques. Prentice-Hall, Inc., Englewood Cliffs, NJ. 

593
Soil Conservation Service. 1984. Procedures for collecting soil samples and methods of 

analysis for soil survey. USDA-SCS Soil Surv. Invest. Rep. no. 1. U.S. Govt. Print. 

Office, Washington, DC. 

U.S. Salinity Laboratory Staff. 1954. L.A. Richards (ed.) Diagnosis and improvement of 

saline and alkali soils. U.S. Dept. of Agric. Handb. 60. U.S. Govt. Print. Office, 

Washington, DC. 

Total Sulfur (6R) 

SO2 Evolution, Infrared (6R3) LECO SC-132 Sulfur Analyzer (6R3b)

1. Application 

Organic and inorganic S forms are found in soils, with the organic S fraction accounting 

for >95% of the total S in most soils from humid and semi-humid (Tabatabai, 1982). 

Mineralization of organic S and its conversion to sulfate by chemical and biological activity 

may serve as a source of plant available S. Total S typically ranges from 0.01 to 0.05% in most 

mineral soils. In organic soils, total S may be >0.05%. 

In well-drained, well-aerated soils, most of the inorganic S normally occurs as sulfate. 

In marine tidal flats, other anaerobic marine sediments, and mine spoils, there are usually large 

amounts of reduced S compounds which oxidize to sulfuric acid upon exposure to the air. In 

arid regions, significant amounts of inorganic S are found as sulfates such gypsum and barite. 

The typical use of total S is as an index of the total reserves of this element, which may 

be converted to plant available S. The SSL uses the combustion technique (LECO sulfur 

analyzer) for analysis of total S (procedure 6R3b). Extractable sulfate S (SO4

2

-S) is an index of 

readily plant-available S. Reagents that have been used for measuring SO4

2

-S include water, 

hot water, ammonium acetate, sodium carbonate and other carbonates, ammonium chloride and 

other chlorides, potassium phosphate and other phosphates, and ammonium fluoride (Bray-1). 

Extractable SO4

2

-S does not include the labile fraction of soil organic S that is mineralized 

during the growing season (Tabatabai, 1982). Extraction reagents for organic S include 

hydrogen peroxide, sodium bicarbonate, sodium hydroxide, sodium oxalate, sodium peroxide, 

and sodium pyrophosphate. There other methods available for determination of soil S, 

especially for total S and SO4

2

-S. The investigator may refer to the review by Beaton et al. 

(1968). 

2. Summary of Method 

A fine-ground (<80-mesh) soil sample is oxidized at high temperature. The gases 

released are scrubbed, and the SO2 in the combustion gases are measured using an infrared 

detector. Percent S is reported on an oven-dry soil basis. 

3. Interferences 

No significant interferences are known to affect the oxidizable S measurement. 

4. Safety 

Wear protective clothing and safety glasses. Magnesium perchlorate may form 

explosive mixtures. Magnesium perchlorate may contain traces of perchloric acid, which 

remain from manufacturer's operations. This acid is anhydrous because of the strong 

desiccating capability of the salt. Avoid prolonged contact with oxidizable material or material 

capable of forming unstable perchlorate esters or salts. Remove magnesium perchlorate by 

using an excess of water to thoroughly dilute the material. 

The use of high temperatures in the oxidation of samples requires that extreme caution 

be used to prevent burns and fires. Follow standard laboratory procedures when handling 

compressed gases. Oxygen is highly flammable. Avoid open flames and sparks. Standard 

laboratory equipment includes fire blankets and extinguishers for use when necessary. Follow 

the manufacturer's safety precautions when using the sulfur analyzer. 

594
5. Equipment 

5.1 Sulfur analyzer, Leco Model SC-132 781-400 Sulfur System, Leco Corp., St. Joseph, MI 

5.2 Data transmit card, part no. 772-573, Leco Corp., St. Joseph, MI 

5.3 Combustion boats, part no. 529-203, Leco Corp., St. Joseph, MI 

5.4 Single-stage regulator, Oxygen Service, Part No. E11-W-N115BOX, Air Products and 

Chemicals, Inc., Box 538, Allentown, PA 18105 

5.5 Electronic balance, ±1-mg sensitivity 

6. Reagents 

6.1 Anhydrone, anhydrous magnesium perchlorate, granular 

6.2 Glass wool 

6.3 Compressed oxygen, >99.5% @ 30 psi 

7. Procedure 

7.1 Weigh an air-dry, fine-ground (<80-mesh) soil sample in a tared combustion boat. Sample 

size depends upon S content. The product of sample weight in g multiplied by the S percent 

must not be >2. In most cases, the sample size is 1.00 g, unless the S content is >2%. 

7.2 Refer to the manufacturer's manual for operation of sulfur analyzer. An overview of the 

sulfur analyzer is as follows: 

a. Samples are combusted in an O2 atmosphere in which the S is oxidized to SO2. 

b. Moisture and dust are removed, and the SO2 gas is then measured by a solid state infrared 

detector. 

c. The microprocessor formulates the analysis results. The control console displays and prints 

results by combining the outputs of the infrared detector and system ambient sensors with preprogrammed calibration, linearization, and weight compensation factors. 

8. Calculations

S (%) = Si x AD/OD 

where: 

S (%) = S (%) on oven-dry basis 

Si = S (%) instrument 

AD/OD = air-dry/oven-dry ratio (procedure 4B5) 

9. Report 

Report total S as a percentage of oven-dry weight to the nearest 0.1%. 

10. Precision

Precision data are not available for this procedure. A quality control check sample is 

run in every batch of 12 samples. A blank (crucible only) and a rerun of one of the 12 samples 

(unknowns) also are run in every batch. For 27 observations of the quality control check 

sample, the mean, standard deviation, and C.V. for total S are 0.57, 0.02, and 4.3%, 

respectively. 

595
11. References 

Beaton, James D., G.R. Burns, and J. Platou. 1968. Determination of sulfur in soils and 

plant material. Tech. Bull. No. 14. The Sulfur Inst., 1725 K Street, N.W., Washington, 

D.C. 20006 

Tabatabai, M.A. 1982. Sulfur. In A.L. Page, R.H. Miller, and D.R. Keeney (eds.) Methods 

of soil analysis. Part 2. Chemical and microbiological properties. 2nd ed. Agronomy 

9:501-538. 

Phosphorus (6S)

New Zealand P Retention (6S4)

1. Application 

In Soil Taxonomy, the P retention of soil material is a criterion for andic soil properties 

(Soil Survey Staff, 1990). Andisols and other soils that contain large amounts of allophane and 

other amorphous minerals have capacities for binding P (Gebhardt and Coleman, 1984). The 

factors that affect soil P retention are not well understood. However, allophane and imogolite 

have been considered as major materials that contribute to P retention in Andisols (Wada, 

1985). Phosphate retention is also called P absorption, sorption, or fixation. 

2. Summary of Method

A 5-g soil sample is shaken in a 1000-ppm P solution for 24 h. The mixture is 

centrifuged at 2000 rpm for 15 min. An aliquot of the supernatant is transferred to a 

colorimetric tube to which nitric vanadomolybdate acid reagent (NVAR) is added. The percent 

transmittance of the solution is read using a colorimeter. The New Zealand P retention is 

reported as percent P retained. 

3. Interferences 

No significant problems are known to affect the P retention measurement. 

4. Safety

Wear protective clothing (coats, aprons, sleeve guards, and gloves) and eye protection 

(face shields, goggles, or safety glasses). When preparing reagents, exercise special care. 

Many metal salts are extremely toxic and may be fatal if ingested. Thoroughly wash hands 

after handling these metal salts. Restrict the use of concentrated HNO3 to a fume hood. Use 

safety showers and eyewash stations to dilute spilled acids and bases. Use sodium bicarbonate 

and water to neutralize and dilute spilled acids. 

5. Equipment

5.1 Electronic balance, ±0.01-g sensitivity 

5.2 Shaker, Eberbach 6000 power unit, reciprocating speed of 60 to 260 epm, with 6040 

utility box carrier and 6110 floor stand, Eberbach Corp., Ann Arbor, MI 

5.3 Digital diluter/dispenser, product no. 100004, with hand probe and actuator, product no. 

230700, Hamilton Co., P.O. Box 10030, Reno, NV, 89510 

5.4 Syringes, 10000 and 1000 μL, 1001 DX and 1010-TEL LL gas tight, Hamilton Co., P.O. 

Box 10030, Reno, NV, 89510 

5.5 Diluter/dispenser, 25 mL 

5.6 Calorimeter, Baush and Laumb 

5.7 Calorimeter tubes, glass, 10 mL, 1-cm light path, Baush and Laumb 

5.8 Centrifuge, International no. 2, Model V, with no. 250 A head, International Equip. Co., 

Boston, MA 

5.9 Trunions, International no. 320, International Equip. Co., Boston, MA 

5.10 Centrifuge tubes, 50 mL, Oak-Ridge, polyallomer, Nalgene 3119, Nalge Co., Box 20365, 

Rochester, NY 14602. 

5.11 Plastic cups, 2 fl. oz. 

596
5.12 Pipets, volumetric, class A, glass, various sizes of 1 to 20 mL 

6. Reagents

6.1 Distilled deionized (DDI) water 

6.2 Nitric acid (HNO3), conc. 

6.3 P retention solution, 1000 ppm P. Dissolve 8.80 g of KH2PO4 and 32.8 g of sodium 

acetate (CH3COONa) in DDI water. Add 23 mL of glacial acetic acid. Dilute to 2 L with 

DDI water in a volumetric flask. The solution pH should range between 4.55 and 4.65. 

6.4 Molybdate solution. Dissolve 16 g of ammonium molybdate (VI) [(NH4)6MO7O24·4H2O] 

in 50°C DDI water. Allow the solution to cool to room temperature and dilute to 1 L 

with DDI water. 

6.5 Nitric acid solution. Carefully and slowly dilute 100 mL of conc. HNO3 to 1 L of DDI 

water. Add the acid to the water. 

6.6 Nitric vanadomolybdate acid reagent (NVAR), vanadate solution. Dissolve 0.8 g of 

NH4VO3 in 500 mL of boiling DDI water. Allow the solution to cool to room 

temperature. Carefully and slowly add 6 mL of conc. HNO3. Dilute to 1 L with DDI 

water. Mix the nitric acid solution with the vanadate solution and then add the molybdate 

solution. Mix well. 

6.7 Stock P standard solution (SPSS), 4000 ppm P. Dissolve 17.6 g K2HPO4 in DDI water. 

Dilute to 1 L with DDI water. 

6.8 Standard P calibration P solutions (SPCS), 100, 80, 60, 40, 20, and 0% P retained. Dilute 

the SPSS with a solution that contains 32.8 g of sodium acetate (CH3COONa) and 23 mL 

of glacial acetic acid diluted to 2 L with DDI water as follows: 100% = DDI water (0 

ppm); 80% = 1:20 (200 ppm); 60% = 1:10 (400 ppm); 40% = 3:20 (600 ppm); 20% = 1:5 

(800 ppm); and 0% = 1:4 (1000 ppm). The percent amount refers to percent P retention. 

7. Procedure

7.1 Weigh 5.00 g of air-dry soil into a 50-mL centrifuge tube. 

7.2 Use the dispenser to add 25.0 mL of P-retention solution to centrifuge tube. 

7.3 Cap centrifuge tube and place in shaker and shake for 24 h at room temperature (20°C). 

7.4 Add 2 to 3 drops of Superfloc, 0.02% w/v to each tube. 

7.5 Centrifuge sample at 2000 rpm for 15 min. 

7.6 Pour sample supernatant into plastic cup. 

7.7 Use the digital diluter to add the nitric vanadomolybdate acid reagent (NVAR) to each 

sample supernatant and to each SPCS. To fill a 10-mL Calorimeter tube, the diluter setting is 

66 for diluent (NVAR) and 35 for sample (1:20 dilution). 

7.8 The color reaction requires a minimum of 30 min before the analyst records readings. 

7.9 Set the Calorimeter (blue bulb) to read at 466 nm. Set the zero against DDI water (blank). 

A blank has all reagents contained in the sample extract except the soil. 

7.10 Record the percent transmittance to the nearest 0.01 unit for the sample extract and each 

SPCS. 

597
8. Calculations

8.1 Transmittance of a solution is the fraction of incident radiation transmitted by the solution, 

i.e., T = P/Po and is often expressed as a percentage, i.e., T = P/Po x 100. The absorbance of a 

solution is directly proportional to concentration and is defined by the equation, A = -log10 T. 

These relationships are derived from Beer's law. 

Calibration Calculations

8.2 Use the transmittance of each SPCS to either construct a calibrated curve to plot P or use a 

least squares analysis to calculate P. The P is reported in percent retained. 

8.3 Calibration Curve: Plot the transmittances against the ppm P of each SPCS on semilog 

graph paper or convert to absorbances and plot on linear graph paper. Construct the calibration 

curve by finding the "best" line that fits the plotted SPCS. 

8.4 Least Squares Analysis: Use a least squares criterion, i.e. best moving average. Refer to a 

statistical analysis book for additional information on least squares analysis. To facilitate data 

manipulation in a least squares analysis, the following standard curve is developed using the 

concentration of SPCS as a f[ln(%T]. Final calculated analyte concentration with either log10

or ln base would be the same. Refer to procedure 6S3b for an example of least squares 

analysis. 

Analyte Calculation 

8.5 Calibration Curve: Read the percent P directly from the calibration curve. 

8.6 Least Squares Analysis: Refer to procedure 6S3 for an example of least squares analysis. 

9. Report

Report the percent New Zealand P retention to the nearest whole number. 

10. Precision

Precision data are not available for this procedure. 

11. References

Gebhardt, H., and N.T. Coleman. 1984. Anion adsorption of allophanic tropical soils: III. 

Phosphate adsorption. p. 237-248. In K.H. Tan (ed.) Anodosols. Benchmark papers in 

soil science series. Van Nostrand Reinhold, Co., Melbourne, Canada. 

Soil Survey Staff. 1990. Keys to soil taxonomy. 4th ed. SMSS technical monograph no. 6. 

Blacksburg, VA. 

Wada, K. 1985. The distinctive properties of Andosols. p. 173-229. In B.A. Stewart (ed.) 

Adv. Soil Sci. Springer-Verlag, NY. 

MINERALOGY (7) Instrumental Analyses (7A) 

Thermal Gravimetric Analysis (7A4)

Perkin-Elmer 7 Series (7A4b) 

1. Application

Thermal analysis defines a group of analyses that determine some physical parameter, 

e.g., energy, weight, or evolved substances, as a dynamic function of temperature (Tan et al., 

1986). Thermogravimetric analysis (TGA) is a technique for determining weight loss of a 

sample as it is being heated at a controlled rate. The weight changes are recorded as a function 

598
of temperature, i.e., a thermogravimetric curve, and provide quantitative information about 

substances under investigation, e.g., gibbsite (Al(OH)3), kaolinite (Al2Si2O5(OH)4), and 2:1 

expandable minerals (smectite and vermiculite). 

2. Summary of Method 

A 5- to 10-mg sample of soil clay is weighed into a platinum sample pan and placed in 

the TGA balance. The instrument records the initial sample weight. The analyst zeros the 

balance. The sample is then heated from a temperature of 30 to 900°C at a rate of 20°C min-1

in a flowing N2 atmosphere. The computer collects weight changes as a function of 

temperature and records a thermogravimetric curve. Gibbsite and kaolinite are quantified by 

noting the weight loss between 250 to 350°C and 450 to 550°C, respectively, and then relating 

these data to the theoretical weight loss of pure gibbsite or kaolinite (Soil Conservation Service, 

1984). The weight loss is due to dehydroxylation, i.e., loss of crystal lattice water. Though not 

presently performed by the National Soil Survey Laboratory (NSSL), quantification of the 2:1 

expandable minerals (smectite + vermiculite) is related to weight loss at <250°C, i.e., loss of 

adsorbed water (Karanthasis and Hajek, 1982; Tan et al., 1986). At this low temperature, 

adsorbed water is proportional to the specific area of the sample (Jackson, 1956; Karathanasis 

and Hajek, 1982; Mackenzie, 1970; Tan and Hajek, 1977). 

3. Interferences

Organic matter is objectionable because it has a weight loss by dehydrogenation and by 

oxidation to CO2 between 300 to 900°C (Tan, et al., 1986). Analysis in an inert N2 atmosphere 

alleviates this problem. Mineral salts that contain water of crystallization also may be 

interferences. Samples should be washed free of any soluble salts. 

A representative soil sample is important as sample size is small (<10 mg). Avoid large 

aggregates in sample, the presence of which may cause thermal interferences, i.e., differential 

kinetics of gas diffusion through the sample and physical movement of sample in a reaction. 

In general, the same reactions that interfere with DSC/DTA also interfere with TGA 

determinations of kaolinite, gibbsite, and 2:1 expandable minerals. However, TGA is more 

sensitive to small water losses at slow rates, whereas DSC/DTA is more sensitive to large water 

losses at rapid rates (Tan, et al., 1986). This sensitivity difference may help to explain why 

kaolinite and gibbsite quantifications in TGA vs. DSC/DTA often are not equivalent, i.e., TGA 

estimates tend to be greater than the corresponding DSC/DTA estimates. In TGA, there is a 

greater probability of measuring water losses in specific temperature regimes that are not 

specifically associated with dehydroxylation reactions of interest. This problem is particularly 

apparent with illitic samples, which characteristically contain more "structural" water than ideal 

structural formulae would indicate (Rouston, et al., 1972; Weaver and Pollard, 1973). 

Even though it is well established that various minerals lose the major portion of their 

crystal lattice water at different temperature ranges (Tan et al., 1986), there are overlaps in 

these weight loss regions (WLR) of minerals which interfere in the identification and 

measurement of the minerals of interest. The goethite WLR (250 to 400°C) overlaps the 

gibbsite WLR (250 to 350°C) (Mackenzie and Berggen, 1970). The illite WLR (550 to 600°C) 

overlaps the high end of the kaolinite WLR (450 to 550°C) (Mackenzie and Caillere, 1975). 

The WLR of hydroxy-Al interlayers in hydroxy-Al interlayered vermiculite (HIV) (400 to 

450°C) overlaps the low end of the kaolinite WLR (450 to 550°C), especially in the poorly 

crystalline kaolinites (Mackenzie and Caillere, 1976). Similarly, the dehydroxylation of 

nontronites, Fe-rich dioctahedral smectites, (450 to 500°C) may interfere with kaolinite 

identification and measurement (Mackenzie and Caillere, 1975). 

4. Safety

Secure high pressure N2 tanks and handle with care. When changing the tanks, protect 

valves with covers. Do not program the analyzer for >950°C because it may present a safety 

hazard during sample analysis and cleaning cycles. Do not heat aluminum sample pans 

>600°C. Aluminum melts at 660°C, and the pans alloy with and destroy the sample holders. 

599
Always use high quality purge gases with the TGA. Minimum purity of 99.9% is 

recommended. 

5. Equipment

5.1 Thermal analysis system, Perkin-Elmer 7 series, 7500 computer, TAC7 instrument 

controllers 

5.2 Thermogravimetric analyzer module, TGA7, Hewlett-Packard digital plotter 

5.3 Pressure tanks (2), N2, purity 99.99% 

5.4 Two-stage gas regulators (2), 50 psi outlet pressure 

5.5 One-stage gas regulator for compressed air 

5.6 Electronic balance, ±0.1-mg sensitivity, Mettler AE160 

5.7 Forceps, flat-tipped 

5.8 Weighing spatula 

5.9 Desiccator, glass 

5.10 Mortar and pestle 

5.11 Sieves, 100 mesh or 80 mesh 

5.12 Kaolinite, standard, poorly crystalline, Georgia Kaolinite, Clay Minerals Society, Source 

Clay Minerals Project, sample KGa-2. 

5.13 Gibbsite, standard, Surinam Gibbsite, National Soil Survey Laboratory (NSSL), 67L022. 

6. Reagents

6.1 Magnesium nitrate saturated solution [Mg(NO3)2·6H2O] 

6.2 Ethanol 

7. Procedure

Derive <2μm Clay Fractions

7.1 Prepare Na-saturated clay as in procedure 7A2i, preparation of clay suspension, 7.8 to 7.19. 

7.2 Dry the clay suspension and transfer to mortar. Moisten sample with ethanol and grind 

with pestle to make a homogeneous slurry. 

7.3 Air-dry sample using flowing air in hood. Lightly grind sample with pestle to make a 

homogeneous powder. 

7.4 Sieve sample with 80-mesh screen. Equilibrate sample overnight over a saturated 

magnesium nitrate solution (55% rh) in a glass desiccator. 

TGA Operation

7.5 Set-up the instrument and calibrate. 

7.6 Turn on the N2 purge gases and set to 6 and 3.5 psi for balance and sample purge, 

respectively. The balance purge pressure should always be greater than the sample purge 

pressure. 

7.7 Turn on compressed air and set to 25 psi. 

7.8 Place the platinum sample pan in the balance stirrup. Use the computer to raise the furnace 

tube and to zero the balance. Lower the furnace tube. 

7.9 Remove the sample pan from the stirrup. Weigh ≈ 5 mg of sample, i.e., <100-mesh wholesoil or derived <2-μm clay fraction, into tared sample pan. Refer to section on derived <2-μm 

clay fractions, 7.1 to 7.4. 

600
7.10 Use flat-tipped forceps to remove the sample pan from the analytical balance. Tap the 

sample pan against a hard surface several times to uniformly distribute the sample. 

7.11 Carefully place sample pan in the stirrup of the TGA microbalance. 

7.12 The standard sample run heating program has a heating rate of 20°C min-1, a starting 

temperature of 30°C, and an ending temperature of 900°C. 

7.13 Raise the furnace tube and allow it to seat. Press "Read Weight" key (usually twice) until 

a relative weight percentage of 100.0% is displayed. The computer then reads the weight. 

7.14 Immediately start the "Run" program. 

7.15 At the end of the sample run (≈ 45 min), remove the sample pan from the microbalance 

stirrup. The furnace tube is lowered automatically at the end of run. 

7.16 To store data, enter the appropriate file name on the computer for the completed run. If 

data are not stored by appropriate file name, data are stored under a default file name of "gsav". 

Only four of these files can be saved at any one time, after which files are overwritten. Once a 

file is named, it cannot be changed. 

8. Calculations 

8.1 The thermogravimetric curve is displayed on the computer monitor. The ordinate (Y) is 

expressed in a relative weight percentage, i.e., the initial sample weight is 100.0%. Use the 

computer to calculate the total change in sample weight (∆ Y), within the predetermined 

temperature range, as a 8 sample weight percent. 

% Kaolinite = [(∆ sample weight % 450-550°C)/14] x 100 

 14 

where 

∆ sample weight = total ∆ in sample weight expressed as relative percent 

14 = percent weight of hydroxyl water Lost from pure kaolinite 

% Gibbsite = [(∆ sample weight % 250-350°C)/ 34.6] x 100 

where 

∆ sample weight = total ∆ in sample weight expressed as relative percent 

34.6 = percent weight of hydroxyl water lost from pure gibbsite 

The percent weights of hydroxyl water lost from kaolinite and gibbsite are derived from the 

following assumed dehydroxylation reactions. 

Si2Al2O5(OH)4 ---> 2SiO2 + Al2O3 + 2H2O 

 (kaolinite) 

2Al(OH)3 ---> Al2O3 + 3H2O 

 (gibbsite) 

Using kaolinite as an example, percent weight of hydroxyl water lost is calculated from the 

following formula weights. 

Si2Al2O5(OH)4 = 258 g mol-1

601
2H2O = 36 g mol-1

Percent weight of hydroxyl water lost = (36/258) x 100 = 34.6% 

9. Report

Report percent gibbsite and/or kaolinite to nearest whole number. 

10. Precision

Precision data are not available for this procedure. 

11. References 

Jackson, M.L. 1956. Soil chemical analysis. Advan. course. M. L. Jackson, Madison, WI. 

Karathanasis, A.D., and B.F. Hajek. 1982. Revised methods for rapid quantitative 

determination of minerals in soil clays. Soil Sci. Soc. Am. J. 46:419-425. 

Mackenzie, R.C. 1970. Simple phyllosilicates based on gibbsite- and brucite-like sheets. p. 

498-537. In R. C. Mackenzie (ed.) Differential thermal analysis. Vol. 1. Acad. Press, 

London. 

Mackenzie, R.C., and G. Berggen. 1970. Oxides and hydroxides of higher-valency 

elements. p. 272-302. In R.C. Mackenzie (ed.) Differential thermal analysis. Acad. 

Press, NY. 

Mackenzie, R.C., and S. Caillere. 1975. The thermal characteristics of soil minerals and the 

use of these characteristics in the qualitative and quantitative determination of clay 

minerals in soils. p. 529-571. In J.E. Gieseking (ed.) Soil components. Vol. 2. Inorganic 

components. Springer-Verlag, NY. 

Mackenzie, R.C., and B.D. Mitchell. 1972. Soils. p. 267-297. In R.C. Mackenzie (ed.) 

Differential thermal analysis. Vol. 2. Acad. Press. London. 

Rouston, R.C., J.A. Kittrick, and E.H. Hope. 1972. Interlayer hydration and the broadening 

of the 10A x-ray peak in illite. Soil Sci. 113:167-174. 

Soil Conservation Service. 1984. Procedures for collecting soil samples and methods of 

analysis for soil survey. USDA-SCS Soil Surv. Invest. Rep. no. 1. U.S. Govt. Print. 

Office, Washington, DC. 

Tan, K.H., and B.F. Hajek. 1977. Thermal analysis of soils. p. 865-884. In J.B. Dixon and 

S.B. Weed (eds.) Minerals in soil environments. 2nd ed. SSSA Book Series 1. SSSA, 

Madison, WI. 

Tan, K.H., and B.F. Hajek, and I. Barshad. 1986. Thermal analysis techniques. p. 151-183. 

In A. Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical properties. 

2nd ed. Agronomy 9:151-183. 

Weaver, C.E., and L.D. Pollard. 1973. The chemistry of clay minerals. Elsevier Sci. Publ. 

Co., Amsterdam. 

Instrumental Analyses (7A) 

Differential Scanning Calorimetry (7A6) 

1. Application 

Calorimetry measures specific heat or thermal capacity of a substance. Differential 

scanning calorimetry (DSC) is a calorimetric technique in which the rate of heat flow between 

a sample and a reference material is measured as materials are held isothermal to one another. 

The DSC directly measures the magnitude of an energy change (H, enthalpy or heat content) in 

a material undergoing an exothermic or endothermic reaction. DSC is commonly used to 

quantify gibbsite (Al(OH)3) and kaolinite (Al2Si2O5(OH)4) in soils and clays by measuring the 

magnitude of their dehydroxylation endotherms which are between 250 to 350°C and 450 to 

550°C, respectively (Karathanasis and Hajek, 1982; Jackson, 1956; Mackenzie and Berggen, 

1970; Mackenzie, 1970). 

602
2. Summary of Method

An 8 mg sample of soil clay is weighed into an aluminum sample pan and placed in the 

DSC sample holder. The sample and reference are heated under flowing N2 atmosphere from a 

temperature of 30 to 600°C at a rate of 10°C min-1. Data are collected by the computer and a 

thermogram is plotted. Gibbsite and kaolinite are quantified by measuring the peak area of any 

endothermic reactions between 250 to 350°C and 450 to 550°C, respectively, and by 

calculating the H of the reaction. These values are related to the values for the respective 

known quantities of the two minerals (gibbsite and kaolinite). 

3. Interferences 

Organic matter is objectionable because it produces irregular exothermic peaks in air or 

O2, commonly between 300 to 500°C, which may obscure important reactions from the 

inorganic components of interest (Schnitzer and Kodama, 1977). Analysis in an inert N2

atmosphere alleviates this problem. Mineral salts that contain water of crystallization also may 

be interferences. Samples should be washed free of any soluble salts. 

Use a representative soil sample as sample size is small (<10 mg). Avoid large 

aggregates in sample, the presence of which may cause thermal interferences because of 

differential kinetics of gas diffusion through the sample and physical movement of sample in a 

reaction. 

The dehydroxylation of goethite is between 250 to 400°C and may interfere with the 

identification and integration of the gibbsite endotherm (250 to 350°C) (Mackenzie and 

Berggen, 1970). The dehydroxylation of illite is between 550 to 600°C and partially overlaps 

the high end of the kaolinite endotherm (450 to 550°C), resulting in possible peak integrations 

(Mackenzie and Caillere, 1975). The dehydroxylation of hydroxy-Al interlayers in hydroxy-Al 

interlayered vermiculite (HIV) is between 400 to 450°C and may interfere with the low end of 

the kaolinite endotherm (450 to 550°C), especially in the poorly crystalline kaolinites 

(Mackenzie and Caillere, 1976). Similarly, the dehydroxylation of nontronites, Fe-rich 

dioctahedral smectites is between 450 to 500°C and may interfere with kaolinite identification 

and measurement (Mackenzie and Caillere, 1975). 

4. Safety 

Secure high pressure N2 tanks and handle with care. When changing the tanks, valves 

should be protected with covers. Do not program the analyzer for >950°C because it may 

present a safety hazard during sample analysis and cleaning cycles. Do not heat aluminum 

sample pans >600°C. Aluminum melts at 660°C, and the sample pans alloy with an destroy the 

sample holders. Always use high quality purge gases with the DSC. Minimum purity of 

99.9% is recommended. 

5. Equipment

5.1 Thermal analysis system, Perkin-Elmer 7 series, 7500 computer, TAC7 instrument 

controllers 

5.2 Differential scanning calorimeter module, DSC7, Hewlett-Packard digital plotter 

5.3 Pressure tanks (2), N2, purity 99.99% 

5.4 Two-stage gas regulators (2), 50 psi outlet pressure 

5.5 Electronic balance, ±0.1-mg sensitivity, Mettler AE160 

5.6 Forceps, flat-tipped 

5.7 Weighing spatula 

5.8 Desiccator, glass 

5.9 Mortar and pestle 

5.10 Sieves, 100 mesh or 80 mesh 

5.11 Kaolinite, standard, poorly crystalline, Georgia Kaolinite, Clay Minerals Society, Source 

Clay Minerals Project, sample KGa-2. 

5.12 Gibbsite, standard, Surinam Gibbsite, National Soil Survey Laboratory (NSSL), 67L022. 

603
6. Reagents

6.1 Magnesium nitrate saturated solution [Mg(NO3)2·6H2O] 

6.2 Ethanol 

7. Procedure 

Derive <2μm Clay Fractions

7.1 Prepare Na-saturated clay as in procedure 7A2i, preparation of clay suspension, 7.8 to 7.19. 

7.2 Dry the clay suspension and transfer to mortar. Moisten sample with ethanol and grind 

with pestle to make a homogeneous slurry. 

7.3 Air-dry sample using flowing air in hood. Lightly grind sample with pestle to make a 

homogeneous powder. Transfer to original container for storage until use. 

7.4 Prior to TGA analysis, sieve sample with 80-mesh screen. Equilibrate sample overnight 

over a saturated magnesium nitrate solution (55% rh) in a glass desiccator. 

DSC Operation

7.5 Set-up the instrument and calibrate. 

7.6 Weigh ≈ 8 mg of sample, i.e., <100-mesh whole-soil or derived <2-μm clay fraction, into 

tared aluminum sample pan. Refer to section on derived <2-μm clay fractions, 7.1 to 7.4. 

7.7 Use flat-tipped forceps to remove aluminum sample pan from balance. Drop sample from a 

4- to 5-mm height to uniformly distribute sample in pan. Return the sample pan with sample to 

the balance and record weight to nearest ±0.1 mg. This weight is entered into computer in 

appropriate menu. 

7.8 Carefully place aluminum sample pan in the center of DSC platinum sample side (left side) 

of sample holder. Place platinum two-hole lid on holder that covers the sample pan. Align lid 

holes with purge gas exit hole in DSC head. 

7.9 Place empty aluminum sample pan in reference side (right side) of sample holder. Place 

remaining platinum two-hole lid on holder that covers the sample pan. Align lid holes as in 

previous step. 

7.10 Close DSC head cover and lock. 

7.11 The standard sample run heating program has a heating rate of 10°C min-1, 5.3 min data 

delay, 5.0 min N2 purge. 

7.12 Start the "Run" program. 

7.13 Observe the milliwatts (mW) readout on the computer display terminal and when reading 

stabilizes (≈ 5 to 10 s), remove the sample pan and sample from the sample side of sample 

holder. Do not disturb the reference side. 

7.14 To store data, enter the appropriate file name on the computer for the completed run. If 

data are not stored by appropriate file name, data are stored under a default file name of "gsav". 

Only four of these files can be saved at any one time, after which files are overwritten. Once a 

file is named, it cannot be changed. 

604
8. Calculations 

The thermogram is displayed on the computer monitor. The area under the DSC curve 

is proportional to the enthalpy (H). Use the computer to calculate the H or enthalpy of reaction 

per g of kaolinite and/or gibbsite (joules g-1) as appropriate. 

8.1 % Kaolinite weight = H/12.62 

where: 

12.62 = factor obtained from standard curve of kaolinite mixtures using China clay of 

undetermined purity 

8.2 % Gibbsite weight = H/15.03 

 

where: 

15.03 = factor obtained from standard curve of gibbsite values using deferrated Surinam 

gibbsite of undetermined purity 

9. Report

Report percent kaolinite and/or gibbsite to the nearest whole number. 

10. Precision

Precision data are not available for this procedure.

11. References 

Karathanasis, A.D., and B.F. Hajek. 1982. Revised methods for rapid quantitative 

determination of minerals in soil clays. Soil Sci. Soc. Am. J. 46:419-425. 

Mackenzie, R.C. 1970. Simple phyllosilicates based on gibbsite- and brucite-like sheets. p. 

498-537. In R. C. Mackenzie (ed.) Differential thermal analysis. Vol. 1. Acad. Press, 

London. 

Mackenzie, R.C., and G. Berggen. 1970. Oxides and hydroxides of higher-valency 

elements. p. 272-302. In R.C. Mackenzie (ed.) Differential thermal analysis. Acad. 

Press, NY. 

Mackenzie, R.C., and S. Caillere. 1975. The thermal characteristics of soil minerals and the 

use of these characteristics in the qualitative and quantitative determination of clay 

minerals in soils. p. 529-571. In J.E. Gieseking (ed.) Soil components. Vol. 2. Inorganic 

components. Springer-Verlag, NY. 

Mackenzie, R.C., and B.D. Mitchell. 1972. Soils. p. 267-297. In R.C. Mackenzie (ed.) 

Differential thermal analysis. Vol. 2. Acad. Press. London. 

Rouston, R.C., J.A. Kittrick, and E.H. Hope. 1972. Interlayer hydration and the broadening 

of the 10A x-ray peak in illite. Soil Sci. 113:167-174. 

Schnitzer, M., and H. Kodama. 1977. Reactions of minerals with soil humic substances. In

J.B. Dixon and S.B. Weed (eds.) Minerals in soil environments. 2nd ed. SSSA Book 

Series 1. SSSA, Madison, WI. 

Tan, K.H., and B.F. Hajek. 1977. Thermal analysis of soils. p. 865-884. In J.B. Dixon and 

S.B. Weed (eds.) Minerals in soil environments. 2nd ed. SSSA Book Series 1. SSSA, 

Madison, WI. 

Tan, K.H., and B.F. Hajek, and I. Barshad. 1986. Thermal analysis techniques. p. 151-183. 

In A. Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical properties. 

2nd ed. Agronomy 9:151-183. 

605
Total Analysis (7C) 

HF Dissolution (7C3)

1. Application 

Historically, elemental analysis was developed for the analysis of rocks and minerals 

(Washington, 1930). The elemental analysis of soils, sediments, and rocks necessitates their 

decomposition into soluble forms. Hydrofluoric acid (HF) is efficient in the digestion and 

dissolution of silicate minerals for elemental decomposition. Procedure 7C3 is an HF acid 

digestion. Elemental concentration is determined by atomic absorption using 100 mg of clay 

suspension contained in a closed vessel with boric acid (H3BO3) to neutralize excess acid 

(Berdanier, Lynn, and Threlkeld, 1978; Soil Conservation Service, 1984). 

2. Summary of Method 

To 100 mg of clay suspension (procedure 7A2i), 5 mL of HF acid are added. The 

solution is heated, cooled, and 2 to 3 g of H3BO3 are added to neutralize excess acid. The 

solution is diluted to 100 mL, allowed to stand overnight, and 20 mL are decanted. The 

concentrations of Fe, Al, and K are determined by atomic absorption in procedures 6C7a, 

6G11a, and 6Q3a, respectively. Data are reported in procedure 7C3. 

3. Interferences 

Organic material may remain as a residue with this method. 

4. Safety

Perform procedure in hood. Keep HF acid refrigerated and avoid contact with skin. 

5. Equipment

5.1 Pipet, 5 mL, 

5.2 Volumetric flask, nalgene, 100 mL 

5.3 Polyethylene container, 25 mL, with cover 

5.4 Electronic balance, ±0.1-mg sensitivity 

6. Reagents

6.1 Distilled water 

6.2 Hydrofluoric acid (HF), 48%, 

6.3 Boric acid, (H3BO3), granular 

7. Procedure

HF Dissolution 7.1 Prepare Na-saturated clay as in procedure 7A2i, preparation of clay suspension, 7.8 to 7.19. 

7.2 Pipet 2 mL of clay suspension into a 25-mL Teflon cup and add 5 mL of HF. A 100 mg of 

100-mesh whole-soil sample may be substituted for the clay suspension. 

7.3 Pipet a duplicate sample into a weighing dish, dry at 105°C, and weigh. Use this sample for 

calculations. 

7.4 Place covered Teflon cup in stainless steel retainer and tighten Teflon cap. Place sample in 

oven at 105°C for ≈ 4 h. 

7.5 Turn off oven, open door and let stand overnight to cool. 

7.6 Remove sample from oven. 

606
7.7 Under a hood, remove Teflon cup from steel retainer vessel and add 2 to 3 g of H3BO3 acid. 

7.8 Rinse contents of Teflon cup into a 100-mL nalgene volumetric flask and adjust to volume 

with distilled water. Allow to stand overnight. 

7.9 Decant ≈ 20 mL into a 25-mL polyethylene container for elemental analysis by atomic 

absorption. Refer to procedures 7C7a, 6G11a, and 6Q3a. 

8. Calculations 

Use the MR 2.0 to perform calculations. Inputs are as follows: project number; sample 

number; tare value; tare + sample value; Al and Fe readings (mg L-1); and K readings (meq L1

). Review data for internal consistency. Request a rerun, if necessary, at this time. Store data 

on a data disk. 

The following example illustrates the conversion calculations of atomic absorption 

readings or element concentrations of Fe, Al, and K to appropriate oxide forms. The 

concentrations of Fe and Al (mg L-1), and K (meq L-1) are converted to percent Fe2O3, Al2O3, and K2O, respectively. Refer to procedure 4A5 for air-dry/oven-dry ratio (AD/OD). 

Sample weight = S = 0.1071 g 

Fe reading = [Fe] =34.2 mg L-1

Fe2O3 molecular weight = Fe2O3 =159.70 

Fe atomic weight = Fe = 55.85 

Al reading = [Al]= 72.8 mg L-1 

Al2O3 molecular weight = Al2O3 = 101.94 

Al atomic weight = Al = 26.98 

K reading weight =[K] = 0.61 meq L-1

K2O molecular weight = K2O = 94.19 

K atomic weight = K = 39.10 

K equivalent weight = 39 = 39 

AD/OD =1.024 = AD/OD 

100 mL/1000 mL= dil. factor = 100/1000 

1/1000 mg g-1 = conv. factor = 1/1000 

100/1 P/100 pts. = conv. factor = 100/1 

% Fe2O3 = 

[Fe] x 1/S x 100/1000 x 1/1000 x 100/1 x AD/OD x Fe2O3/Fe = 

34.2 x 1/0.1071 x 0.1 x 0.001 x 100 x 1.024 x 159.7/111.70 

% Fe2O3 = 4.68 

% Al2O3 = 

[Al] x 1/S x 100/1000 x 1/1000 x 100/1 x AD/OD x Al2O3/Al = 

72.8 x 1/0.1071 x 0.1 x 0.001 x 100 x 1.024 x 101.94/53.96 

% Al2O3 = 13.15% 

% K2O = 

[K] x 1/S x 100/1000 x 1/1000 x 100/1 x AD/OD x K2O/K x 39 = 

0.61 x 1/0.1071 x 0.1 x 0.001 x 100 x 1.024 x 94.19/78.2 x 39 = 

% K2O = 2.74 

9. Report

Report data to nearest whole percent. 

607
10. Precision 

Precision data are not available for this procedure. A quality control check sample is 

routinely run in HF analyses. For 38 observations of the quality control check sample, the 

mean, standard deviation, and C.V. for percent Fe, Al2O3, and K2O are as follows: 

Analyte Mean Std. Dev. C.V. 

 

% Fe 2.8 0.40 14 

% Al2O3 12.1 1.04 9 

% K2O 2.4 0.38 16 

11. References 

Berdanier, C.R., W.C. Lynn, and G.W. Threlkeld. 1978. Illitic mineralogy in Soil 

Taxonomy: X-ray vs. total potassium. Agron. Absts. 1978 Annual Mtgs. 

Soil Conservation Service. 1984. Procedures for collecting soil samples and methods of 

analysis for soil survey. USDA-SCS Soil Surv. Invest. Rep. no. 1. U.S. Govt. Print. 

Office, Washington, DC. 

Washington, H.S. 1930. The Chemical analysis of rocks. 4th ed. John Wiley and Sons, 

Inc., New York, NY. 

Whittig, L.D., and W.R. Allardice. 1986. X-ray diffraction techniques. In A. Klute (ed.) 

Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. 

Agronomy 9:331-362. 

608
SSIR No. 1, PROCEDURES FOR COLLECTING SOIL 

SAMPLES AND METHODS OF ANALYSIS FOR SOIL 

SURVEY (1972, 1982, 1984) 

SAMPLE COLLECTION AND PREPARATION (1) 

Laboratory Preparation of Soil Samples (1B) Carbonate-Containing Material (1B3) 

Procedure

Prepare dialysis membrane sacks from 5 1/2-inch cellulose casing (Visking Company), 

using large rubber bands to tie the bottoms. Place the sample (as much as 6 kg if very gravelly 

and highly calcareous) in a dialysis membrane and add about 1 L pH 5, N NaOAc buffer. Tie 

the top of the dialysis membrane around a glass breather tube 4 in long and hang the assembly 

in a 60-L reservoir of buffer held in a 20-gal plastic garbage can. If carbonate is dissolving, 

knead the membrane to release bubbles of CO2. When bubbles of CO2 no longer form on 

kneading, open the dialysis membrane and use strong acid to check the coarser material for 

carbonate coatings (carbonate remains longer in the coarser material). When sample is free of 

carbonate, desalt it by dialysis against tap water flowing continuously through a large plastic 

garbage can. Check the ionic concentration inside the membrane by measuring conductivity of 

a small volume of the supernatant liquid poured out through the breather tube. Continue 

dialysis until the salt concentration is less than 10 meq/L. 

The procedure used to dry the sample depends on whether the particles larger than 2 

mm have been removed before buffer treatment. If they have been removed, withdraw excess 

water from the sample in the membrane with filter candles. Knead the membrane to mix the 

sample and place it in contact with ethanol to desiccate further. Remove the sample from the 

membrane and air-dry. 

If the buffer-treated sample contains particles larger than 2 mm, wet sieve the sample 

through a 2-mm sieve. Then dry sieve the material remaining on the sieve (>2 mm) and add the 

<2-mm fraction from this sieving to the <2-mm fraction separated by the wet sieving. Remove 

most of the water from the <2-mm fraction with filter candles. Use ethanol to transfer the 

samples to shallow pans and dry. Ethanol prevents aggregation of clay into durable flakes 

during drying. 

Discussion

The time required for carbonate removal varies greatly, depending on particle size, 

percentage and type of carbonate, and sample size. Samples from horizons strongly cemented 

by carbonate have required as long as 2 months. The concentration of alkaline-earth ions in the 

buffer greatly affects the rate of carbonate removal. Changing the buffer in the reservoir well 

before the buffer capacity has been exhausted, thereby keeping the alkaline-earth ion 

concentration low, increases the rate markedly. Desalting usually takes about 4 days. 

For carbonate-cemented horizons, the whole sample, not just the <2-mm material, must 

be buffer treated. Furthermore, for horizons without carbonate cementation, buffer treatment of 

the whole sample has the advantage of washing the >2-mm skeletal material free of adhering 

fines and organic material. This problem is considered further in 1B4. 

For very gravelly horizons, large samples (several kilograms) are necessary for buffer 

treatment because of the small amount of <2-mm material. Using large samples also increases 

precision of the >2-mm percentage. 

609
References 

Grossman and Millet (1961). 

Carbonate-Indurated Material Containing Coarse Fragments (1B4)

Break the field sample to get several representative subsamples. Remove the carbonate 

from one subsample by acid treatment and separate the coarse fragments from the fine earth 

(1B3). Weigh the two fractions. Use the noncarbonate fine earth for the standard 

characterization and mineralogical measurements (sections 6-7). 

Grind another subsample of the whole field sample to pass 80-mesh sieve. Determine 

the carbonate content (weight) of this whole ground subsample (6E). 

These weights can be used to calculate the CaCO3 percentage of the fine earth. Any 

analytical value based on the noncarbonate fine earth can be converted to the whole-soil basis 

as well as to the basis of the carbonate-containing fine earth. 

PARTICLE-SIZE ANALYSIS (3) 

Particles < 2mm (Pipet Method) (3A) 

An automated balance system, consisting of a Radio Shack Model II microcomputer 

interfaced to a Mettler PL2000 electronic balance (for sand) and a Mettler AE160 electronic 

balance (for silt and clay), is used for determining, storing, and processing sample weights. 

Air-Dry Samples (3A1) 

Apparatus

Fleaker, 300 ml (tare to 1 mg). 

Pasteur-Chamberlain filter candles, fineness "F". 

Shaker, horizontal, 120 oscillations per minute. 

Cylinders, 1000 ml. 

Stirrer, motor-driven 

Stirrer, hand. Fasten a circular piece of perforated plastic to one end of a brass rod. 

Shaw pipet rack. 

Pipets, 25 ml automatic (Lowy with overflow bulb). 

Polyurethane foam, pipe-insulating cover. 

Shaker with 1/2-in vertical and lateral movements and 500 oscillations per minute. 

Accommodates a nest of sieves. 

Wide-mouth glass pill bottles with screw caps, 90 ml (tare to 1 mg). 

Electronic balance (0.1-mg sensitivity). 

Set of sieves. Square mesh woven phosphor bronze wire cloth. U.S. Series and Tyler Screen 

Scale equivalent designations as follows: 

610
Sand Size Opening 

(mm) 

U.S. No. Tyler Mesh 

Size 

VCS 1.0 18 16 

CS 0.5 35 32 

MS 0.25 60 60 

FS 0.105 140 150 

VFS 0.047 300 300 

Reagents

Hydrogen peroxide (H2O2), 30 to 35 percent. 

Sodium hexametaphosphate (NaPO3)6. Dissolve 35.7 grams of (NaPO3)6 and 7.94 grams of 

Na2CO3 per liter of water. 

Demineralized water. 

Procedure

Removing organic matter.--Place about 10 air-dry soil containing no particles larger 

than 2 mm in a tared Fleaker. Add about 50-ml of demineralized water (referred to 

subsequently as water) and then add 5 ml of H2O2. Cover the fleaker with a watchglass. If a 

violent reaction occurs, repeat the cold H2O2 treatment periodically until no more frothing 

occurs. Heat the Fleaker to about 90°C on an electric hot plate. Add H2O2 in 5-ml quantities at 

45-min intervals until the organic matter is destroyed, as determined visually. Continue heating 

for about 30 min to remove any excess H2O2. Removing cementing agents (optional).--Treat the sample with about 200 ml of 1 N

sodium acetate buffered at pH 5 to remove carbonates. When CO2 bubbles are no longer 

evident, wash free of salts with a filter candle system. Highly calcareous samples may need a 

second treatment. 

Remove siliceous cementing agents by soaking the sample overnight in 0.1 N NaOH. 

Iron oxide cementing agents are removed by shaking overnight in sodium dithionite (6C2). 

Wash free of salts with filter candle system before proceeding. 

Removing dissolved mineral and organic components.--After the H2O2 treatment, place 

the Fleaker in a rack and add about 150 ml of water in a jet strong enough a short PasteurChamberlain filter of "F" fineness. Five such washings and filterings are usually enough except 

for soils containing much coarse gypsum. Remove soil adhering to the filter by gentle back 

pressure; use finger as policeman. Dry the sample overnight in an oven at 105°C, cool in a 

desiccator, and weigh to the nearest milligram. Use the weight of the ovendry, H2O2-treated 

sample as the base weight for calculating percentages of the various fractions. 

Dispersing the sample.--Add 10 ml of sodium hexametaphosphate dispersing agent to 

the Fleaker containing ovendry treated sample. Make the volume to approximately 200 ml. 

Stopper and shake overnight on a horizontal reciprocating shaker at 120 oscillations per minute. 

Separating sands from silt and clay.--Wash the dispersed sample with water on a 300-

mesh sieve. Silt and clay pass through the sieve into a 1-L cylinder. Use a clamp and stand to 

hold the sieve above the cylinder. Avoid using jets of water in washing the sample. Gently tap 

the sieve clamp with the side of the hand to facilitate sieving. Continue washing until the 

suspension volume in the cylinder is about 800 ml. Sand and some coarse silt remain on the 

sieve. It is important to wash all particles of less than 20μ diameter through the sieve. Remove 

the sieve from the holder, wash the sands into an evaporating dish with water, and dry at 105 to 

110°C. Bring the silt and clay suspension in the cylinder to 1 L with water and cover with a 

watchglass. 

Pipeting.--First pipet the <20μ fraction at a 10-cm depth. Vary sedimentation times 

according to temperature. Next, pipet the <2μ fraction after a predetermined setting time 

(usually 4 1/2 to 6 1/2 hr). Vary depth according to time and temperature. Use a Lowy 25-ml 

automatic pipet and regulate filling time to about 12 s. Before each pipeting, stir material in the 

611
sedimentation cylinder, and stir the suspension for 30 s with a hand stirrer, using an up-anddown motion. Note the time at completion of stirring. About 1 min before sedimentation is 

complete, lower the tip of the pipet slowly into the suspension to the proper depth with a Shaw 

pipet rack. At the appropriate time, fill the pipet and empty into a 90-ml, wide-mouth bottle. 

Rinse the pipet into the bottle once. Dry in an oven overnight at 105°C. Cool in a desiccator 

containing phosphorus pentoxide (P2O5). Weigh. 

Sieving and weighing the sand fractions.--Transfer the dried sands to a nest of sieves. 

Shake for 3 min on a shaker that has 1/2-in vertical and lateral movements and oscillates at 500 

strokes per minute. Record the weights of the individual sand fractions. 

Calculations

Pipetted fractions: 

Percentage of pipetted fractions = (A - B)KD 

where 

A = Weight (g) of pipetted fraction 

B = Weight correction for dispersing agent (g) 

K = 1000/(ml in pipet) 

D = 100/(g of H2O2-treated ovendry total sample) 

The <20-μ fraction minus the <2-μ fraction equals fine silt. 

Sand fractions: 

Percentage of sieved fractions = weight (g) of fraction on sieve times D. 

Coarse silt fraction: 

Obtain by difference. Subtract the sum of the percentages of sand plus the <20-μ fraction from 

100. 

References

Kilmer and Alexander (1949), Kilmer and Mullins (1954), Tyner (1939), and Grossman and 

Millet (1961). 

Carbonate and Noncarbonate Clay I (3A1a) 

Apparatus

Warburg manometer. 

1/4-oz (5-ml) gelatin capsules. 

30-ml plastic cups. 

Reagents

Hydrochloric acid (HCl), 6 N. 

Procedure

If carbonate is present, use the glass 

bottle containing clay residue from regular pipet analysis and determine carbonate as in 6E1b. 

Use Warburg manometer. 

Calculations

Cc = {[(A - B - C) x Factor]/D} x 100 

612
where 

Cc = Carbonate clay (pct <2 mm) 

A = Upper reading 

B = Lower reading 

C = Blank 

Factor = Factor derived from standard curve and includes pipette volume factor 

D = Total sample weight (3A1) 

Nc = Total clay - Cc 

where: 

Nc = Noncarbonate clay (pct <2mm) 

Cc = Carbonate clay (pct <2mm) 

References

Shields and Meyer (1964). 

Moist Samples (3A2)

If drying affects dispersion of treated sample, ovendrying may be avoided by removal 

of a pipet sample to estimate the total weight of the sample. Pipet 50 ml at a depth of 20 cm at 

time zero while the suspension is still turbulent. Use the ovendry weight of the aliquot to 

calculate the total weight of the <0.05-mm fraction. Add this weight to the total weight of the 

sands to obtain the total weight of the sample. 

An optional procedure is to carefully weigh out two identical samples and pretreat to 

remove organic matter and dissolved mineral matter. The first sample is continued through the 

standard procedure, excluding ovendrying. The second sample is ovendried, weighed, and 

discarded. The ovendry weight of the second sample is substituted in the calculations for the 

first sample. 

Carbonate and Noncarbonate Clay (3A2a)

Proceed as in 3A1a except use field-moist sample. 

FABRIC-RELATED ANALYSES (4) 

Bulk Density (4A) 

Density is defined as mass per unit volume. Soil density as commonly used differs from 

most density measurements in that the volume of interparticle space is included but the mass of 

the liquid phase is excluded. Therefore, soil density has been called bulk density, Db, to 

distinguish it from the more usual density that is based on intraparticle volume only. Since the 

volume of a shrinking-swelling soil changes with a change in its water content, subscripts are 

added to designate the moisture condition when the measurement was made. Thus, Dbm is the 

bulk density of a moist sample, Db1/3 is the bulk density of a clod sample equilibrated at 1/3-bar 

tension, and Dbd is the bulk density of a dry sample. 

Saran-Coated Clods (4A1) 

Reagents

Methyl ethyl ketone. 

613
Dow Saran F310.--The saran resin dissolves readily in acetone or methyl ethyl ketone. In this 

method, methyl ethyl ketone is used as a solvent because it is less soluble in water than is 

acetone and there is less penetration of the Saran-solvent solution into a moist clod. However, 

acetone is adequate for a first (field) coat and is more readily available. Saran-solvent ratios of 

1:4 to 1:7 are used, depending on the porosity of the soil to be coated. 

Coating solution.--To prepare the solution, fill a weighted container with a solvent to about 

three-fourths its volume. From the weight of the solvent, calculate the weight of resin required 

to obtain a predetermined resin-solvent ratio and add to the solvent. Since the solvent is 

flammable and its vapors form explosive mixtures with air, mix the components with an airpowered or nonsparking electric stirrer under an exhaust hood. Information on the safe 

handling and use of methyl ethyl ketone is available in Chemical Safety Data Sheet SD-83, 

Manufacturing Chemists' Association, Inc., 1825 Connecticut Avenue NW, Washington, D.C. 

The threshold limits of methyl ethyl ketone are 200 ppm as given in OSHA standards, Part 2, 

Section 1910.93, table G1. 

If a high-speed stirrer is used, the resin dissolves in about 1 hr. In the field, mix with a wooden 

stick. Metal cans (1 gal) are satisfactory containers for mixing and storing the plastic. Keep the 

containers tightly closed to prevent evaporation of the solvent. 

Procedure

Collect natural clods (three per horizon) of about 100 to 200 cm3

 in volume (fist-sized). 

Remove a piece of soil larger than the clod from the face of a sampling pit with a spade. From 

this piece prepare a clod by directly cutting or breaking off protruding peaks and material 

sheared by the spade. If roots are present, they can be cut conveniently with scissors or side 

cutters. In some soils, clods can be removed directly from the face of a pit with a knife or 

spatula. No procedure for taking clod samples fits all soils; the procedure must be adjusted to 

meet the conditions in the field at the time of sampling. 

The clods are tied with the fine copper wire or placed in hairnets and suspended from a 

rope or string, hung out like a clothesline. Moisten dry clods with a fine mist spray. The 

suspended clods are dipped by raising a container of the dipping mixture upward around each 

clod, so it is immersed momentarily. The saran-coated clods should be allowed to dry for 30 

min or longer. Clods coated in this way can be transported to the laboratory and examined 

microscopically in an undisturbed state. For convenience, either of two concentrations of 

plastic solution is usually used--a 1:7 solution for most soil samples or a 1:4 solution for clods 

that have larger pores. If bulk density at field-moisture content is desired, store the clods in 

waterproof plastic bags as soon as the coating dries since the coating is permeable to water 

vapor. Although the coating keeps the clods intact, they may be crushed in transport unless they 

are packed in rigid containers. 

In the laboratory, additional coatings of plastic are applied to make the clod waterproof 

and to prevent its disruption during wetting. Then weigh the clod, either in its natural moisture 

condition or in an adjusted moisture condition (e.g., 1/3-bar tension) in air and in water to 

obtain its volume by Archimedes' principle. Subsequent changes in moisture condition and 

volume of the soil sample can be followed by reweighing the coated clod in air and in water. 

Finally, weigh the ovendry clod in air and in water. 

Be careful not to lose any soil material because the weight of material lost is calculated 

as soil moisture, and calculated bulk densities depend on the final ovendry weight of the clod. 

Bulk-density values determined by this method are reported on the basis of fine-earth 

fabric. Weight and volume measurements are made on clod samples that may contain particles 

>2 mm; however, after the measurements are made, the weight and volume of the coarse 

fraction are subtracted. The remainder consists of the weight of <2-mm material and the 

volume of these fine-earth particles and the pore space associated with them. 

614
Sometimes it is necessary to correct bulk density for weight and volume of the plastic 

coating. The coating has a density of about 1.3 g/cm3 and it loses 10 to 20 percent of its air-dry 

weight on ovendrying at 105°C. Thus, the amount of correction becomes smaller as bulk 

density of the soil approaches the density of the coating and as moisture content of the soil 

approaches the weight loss of the coating. 

Calculations

Db1/3 = wtclodod - wt>2mm - tcoatod

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ volclod1/3 - vol>2mm - vol coat 

Dbod = wtclodod - wt>2mm - wtcoatod

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ volclodod - vol>2mm - vol coat 

W1/3 = wtclod1/3 -wtclodod - (wtclodad -wtcoatod) x 100 

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 wtclodod - wt>2mm - wtcoatod

where 

Db1/3 = bulk density of <2-mm fabric at 1/3-bar tension in grams per cubic centimeter 

Dbod = bulk density of <2-mm fabric at ovendryness in grams per cubic centimeter 

W1/3 = the weight percentage of water retained at 1/3-bar tension 

wt clodod = weight of ovendry coated clod 

wt clod1/3 = weight of coated clod equilibrated at 1/3-bar tension

vol clodod = volume of ovendry coated clod 

vol clod1/3 = volume of coated clod equilibrated at 1/3-bar tension 

vol >2 mm = volume of material >2 mm separated from clod after ovendrying 

wt > 2 mm = weight of material > 2mm separated from after ovendrying 

wt coatad = weight of Saran coating before ovendrying 

wt coatod = weight of Saran coating after ovendrying 

vol coat = volume of Saran coating (estimated) 

The field coat (initial coat) of plastic penetrates the clod to some extent. Weight of the field coat, estimated to 1.5 

times the weight of each additional coat, is computed by: 

Wtcoatinit = (WtclodB -WtclodA) x 1.5 

 ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 3 

615
where 

Wtcoatinit = Weight of field (initial) coat 

WtclodA = Weight of clod with one coat of plastic

WtclodB = Weight of clod with three additional coats of plastic 

References

Brasher et al. (1966). 

Air-Dry (Dbd) (4A1b)

After measuring field-state volume, place clods in a drying room kept at 90° F. Weigh a 

few clods each day until they reach a constant weight. Assume then that all the clods are airdry. 

Coat them again with Saran and measure "airdry" volume as described in 4A1a. Determine 

ovendry weight and calculate bulk density as described in 4A1. 

30-cm Absorption (Db30) (4A1c)

After measuring airdry volume, remove a patch of the Saran coating from one side of 

each clod. Next place the clods on a sand tension table with the exposed side in contact with 

very fine sand that has been equilibrated to 30-cm water tension. Again weigh a few clods each 

day until they reach constant weight and assume that all the clods are at 30-cm water tension. 

Most clods reach equilibrium in 7 to 10 days. Remove the clods from the tension table and coat 

with Saran until waterproof. Measure volume of the clods and calculate bulk density as 

described in 4A1. 

1/3-Bar Desorption II (Db1/3) (4A1e)

Cut a flat surface on the coated field-moist clods with a sharp knife or diamond saw. 

Seat the clods on saturated ceramic plates with the flat surface in contact with the plates. Place 

the plates in pans and add water to just cover the surface of the plates. After the clods become 

wet by capillary movement, place the plates in a pressure cooker and equilibrate at 1/3 bar. 

After equilibration, carefully remove the clods from the plates and dip in Saran until 

waterproof. Measure volume of the clods and calculate bulk density as described in 4A1. 

1/3-Bar Desorption III (Db1/3) (4A1f)

Proceed as in 4A1e except prewet the clods at 10-cm tension on porous bricks 

(cheesecloth layer between clod and brick) instead of saturating them on ceramic plates. 

1/10-Bar Desorption (Db1/10) (4A1g)

Proceed as in 4A1d, e, or f except make final desorption at 1/10 bar. 

Parafffin-Coated Clods (4A2)

Ovendry (Dbd) (4A2a)

Ovendry the clods, coat with paraffin, and weigh in water and in air. Calculate bulk 

density as follows: 

616
Dbd (g/cc) = Wtair - Wt>2mm 

 ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Wtair - WtH2O - (Wt>2mm/2.65) 

where 

Wtair = Weight in air 

Wt>2mm = Weight of >2-mm fraction in clod 

WtH2O = Weight in water 

Nonpolar-Liquid Saturated Clods (4A4)

Procedure Place a natural clod in a nonpolar liquid of low viscosity, e.g., high-purity kerosene. 

Evacuate under vacuum until bubbles cease to appear and weigh the clod suspended in the 

nonpolar liquid. Remove the clod, place it on a sand table under 3-cm tension against the 

nonpolar liquid to drain off excess nonpolar liquid, and weigh it in air. The difference in weight 

of the clod in air and suspended in the nonpolar liquid divided by the density of the nonpolar 

liquid is the clod volume. Determine the ovendry weight and calculate bulk density as in 4A1. 

The difference between the clod's initial weight before immersion in the nonpolar liquid and its 

ovendry weight is the moisture content. 

References

Rennie (1957). 

FABRIC-RELATED ANALYSES (4)

Water Retention (4B) 

Pressure-Plate Extraction (4B1) 

After measuring the 1/3-bar volume (4A1d), the Saran coating is removed from the flat 

surface of the clods. The clods are allowed to air-dry (4 to 6 days) and then placed in the drying 

room 2 or 3 days. They are then placed on a tension table of very fine sand and equilibrated to 

5-cm tension as in 4A1d. After about 2 weeks, some of the highly organic clods that have not 

rewetted are placed in a pan of free water overnight to make certain that wetting is complete. 

The clods are again desorbed to 1/3-bar as in 4A1d and volume measurements of the clod are 

made and bulk density is calculated as described in 4A1. 

Soil Pieces (4B1b)

Procedure

Make desorption measurements of soil pieces concurrently with the sieved-sample 

measurements. Cover the sieved samples in retainer rings with small squares of industrial 

tissues (Kimwipes). Place the soil pieces (about 2.5 cm in diameter) on the tissues before 

adding water to the plate. Proceed as in 4B1a. If the soil pieces contain >2-mm material, wet 

sieve and weigh the ovendry >2-mm material. Report moisture content as percentage of 

ovendry weight of <2mm material. 

 

References

Young (1962). 

Sand-Table Absorption (4B3)

617
Saran-coated clods that have been equilibrated on a sand table to determine bulk density 

(4A) can also be used to determine water content at these tensions. 

FABRIC-RELATED ANALYSES (4)

Micromorphology (4E) 

Thin Sections (4E1) 

Moved-Clay Percentage (4E1c)

Apparatus

Diamond tile saw. 

Thin-section equipment. 

Point-counting eyepiece. 

Reagents

Aroclor 5460 (Monsanto). 

Polyester resin. 

Styrene. 

Procedure Impregnate an undisturbed field sample with Aroclor (4E1b). With a diamond saw cut 

the clods into pieces about 3 by 1 by 1 cm. Mount about 10 pieces side by side with polyester 

resin (use a little styrene) to form a block. Cut this assembly to form slices 3 by 1 by 1 cm. 

Slice all the field sample, composite, and withdraw subsamples of 10 to 15 slices. Stack these 

slices, tape them together, and mount in plastic (polyester resin plus styrene). Cut a section 

through the stack parallel to the direction of stacking and along the longer of the two remaining 

axes. Mount one such section from each stack on a glass slide and prepare a thin section. 

To estimate the moved-clay volume insert a point-counting eyepiece into the 

microscope and run a transect along each strip. Keep the transect length and the number of 

fields in a transect constant. Count the number of points that fall on moved clay. Divide this 

number by the total number of points to get an estimate of the proportion of moved clay. To 

convert these volume estimates to weight estimates, multiply by the ratio of the bulk density of 

the moved clay to the bulk density of the appropriate dry fabric. Assume that the moved clay 

has a bulk density of 2.00 g per cubic centimeter. 

References

Grossman (1964). 

Scanning Electron Microscopy (4E2)

Electronically reproduced images of fabric surfaces can be obtained at magnifications 

ranging from 50 to 30,000 diameters. Depth of focus by this technique is large compared to that 

by light microscope. Stereoscopic pictures can be taken to give three-dimensional viewing. 

Procedure

Take a sample of fabric up to 10 mm in diameter and 2 to 3 mm thick. Coat with a thin 

metallic layer and insert in the instrument. The image is displayed on a cathode ray tube. 

618
ION EXCHANGE ANALYSES (5) 

Cation Exchange Capacity (CEC) (5A) 

NH4OAc, pH 7.0 (Buchner funnel) (5A1)

Reagents

Ammonium acetate (NH4OAc), 1 N, pH 7.0. Mix 68 ml ammonium hydroxide (NH4OH), 

specific gravity 0.90, and 57 ml 99.5-percent acetic acid (CH3COOH) per liter of solution 

desired. Cool, dilute to volume with water, and adjust to pH 7.0 with CH3COOH or NH4OH. 

Optionally prepare from NH4OAc reagent salt and adjust pH. 

Ethanol (CH3CH2OH), 95-percent, U.S.P. 

Nessler's reagent (optional). Prepare according to Yuen and Pollard. 

Procedure

Weigh 25 g airdry <2-mm soil (some early work was done with 50-g samples) into a 

250-ml Erlenmeyer flask and add 35 to 50 ml NH4OAc solution. Stopper, shake the flask for 

several minutes, and allow to stand overnight. Transfer contents of the flask to a Buchner 

funnel (Coors No. 1) fitted with moist Whatman No. 42 filter paper. Filter, using gentle suction 

if needed. Leach with 200 ml NH4OAc, adding small amounts at a time so that leaching 

requires no less than 1 hour. Transfer leachate from suction flask to volumetric flask and retain 

for analysis of NH4OAc-extractable cations (methods 6N2, 6O2, 6P2, 6Q2). 

Add 95-percent ethanol in small amounts to the ammonium-saturated soil remaining on 

the Buchner funnel until the leachate gives a negative test for ammonia with Nessler's reagent 

or leach with 100 ml ethanol. 

References

Peech et al. (1947) and Yuen and Pollard (1952). 

Direct Distillation of Adsorbed Ammonia, Kjeldahl (5A1a)

Reagents

Sodium chloride (NaCl). 

Antifoam mixture. Mix equal parts of mineral oil and n-octyl alcohol. 

Sodium hydroxide (NaOH), 1 N. 

Hydrochloric acid (HCl), 0.2 N, standardized. 

Boric acid (H3BO3), 4-percent. 

Mixed indicator. Mix 1.250 g methyl red and 0.825 g methylene blue in 1 liter 95-percent 

ethanol. 

Brom cresol green, 0.1-percent, aqueous solution. 

Procedure

Transfer the soil plus filter paper from method 5A1 to a Kjeldahl flask. Add 400 ml 

water and about 10 g NaCl, 5 drops antifoam mixture, a gram or two of granular zinc, and 40 

ml 1 N NaOH. Connect the flask with the condenser and distill 200 ml into 50 ml 4-percent 

H3BO3 solution. Titrate the distillate to the first tinge of purple with 0.2 N HCl, using 10 drops 

mixed indicator and 2 drops brom cresol green. 

619
Calculations

CEC(meq/100 g) =(A/B) x N x 100 

where 

A = Volume HCl (mL) 

B = Sample weight (g) 

N = Normality of acid 

Report on ovendry basis. 

References

Peech et al. (1947). 

Displacement of Adsorbed Ammonia, Semimicro Kjeldahl (5A1b) 

Reagents

Sodium chloride (NaCl), acidified, 10-percent. Dissolve 100 g NaCl, reagent-grade, ammoniafree, in 750 ml warm water; add 25 ml 2 N hydrochloric acid (HCl) and bring to 1000-ml 

volume. 

 

Sodium hydroxide (NaOH), 1 N. 

Boric acid (H3BO3), 2-percent. 

Sulfuric acid (H2SO4), 0.01 N, standardized. 

Ethanol, 95-percent. 

Mixed indicator. Dissolve 0.1 g methyl red and 0.1 g brom cresol green in 250 ml ethanol. 

Procedure

Leach soil from method 5A1 with 240 ml 10-percent acidified NaCl solution, using 

small increments. Drain completely between each increment. Transfer the leachate to a 250-ml 

volumetric flask and adjust volume to mark. Pipet a suitable aliquot of the leachate into a 

micro-Kjeldahl distillation flask and attach to steam-distillation apparatus. Start steam 

distillation and slowly add 10 ml 1 N NaOH. Catch distillate in a 250-ml Erlenmeyer flask 

containing 10 ml H3BO3 and 10 drops of mixed indicator. Distill for 5 minutes after H3BO3

turns green, lower receiving flask, and rinse condenser and outlet hose into receiving flask. 

Titrate the ammonia with 0.01 N H2SO4 to a red end point, using a blank for comparison. 

Calculations

CEC(meq/100 g) = (A/B) x N x (C/D) x 100 

where 

A = Volume H2SO4 (mL) 

B = Sample weight (g) 

N = Normality of acid 

C = Volume leachate (mL) 

D = Volume aliquot (mL) 

Report on ovendry basis. 

620
NaOAc, pH 8.2 (5A2) Centrifuge Method (5A2a) 

Reagents

Sodium acetate (NaOAc), 1 N, pH 8.2. 

Ethanol, 95-percent. 

Ammonium acetate (NH4OAc), 1 N, pH 7.0. Add 57 ml concentrated acetic acid and 68 ml 

concentrated NH4OH, specific gravity 0.90, to about 800 ml water. Cool and dilute to 1 liter 

and adjust to pH 7.0 by adding more NH4OH or acetic acid. 

Procedure

Weigh 5-g samples to an accuracy of 1 percent and place in centrifuge tubes. Add 33 ml 

NaOAc, stopper the tubes, and shake for 5 minutes. Remove stopper and centrifuge until the 

supernatant liquid is clear (usually 5 min). Decant the supernatant liquid as completely as 

possible and discard. Repeat four times, discarding the supernatant liquid each time. After the 

last saturation, wash the rubber stoppers and use absorbent paper to remove any acetate crystals 

remaining on lip of centrifuge tube. Add about 30 ml ethanol to each tube, stopper, shake for 5 

minutes, remove stopper, and centrifuge until the supernatant liquid is clear. Decant and discard 

the supernatant liquid. Continue washing until the electrical conductivity of the supernatant 

liquid from the last washing is between 55 and 40 μmho per centimeter. Optionally, decrease 

volume by about 5 ml each washing. Replace the absorbed sodium from the sample by 

extracting with three 30-ml portions of NH4OAc solution. Dilute to 100 ml and determine the 

sodium concentration as described in 6P2a. 

Calculations

CEC (meq/100 g) = (A/B) x dilution x 10 

where 

A = Na from curve (meq/L) 

B = Sample weight (g) 

Report on ovendry basis. 

References

Richards (1954). 

KOAc, pH 7.0 (5A4)

Procedure 

Proceed as in 5A1 except substitute 1 N KOAc, pH 7.0, for NH4OAc. Determine 

potassium with flame photometer. 

BaCl2, pH 8.2 (5A5)

Apparatus

Leaching tubes. 

Flame photometer. 

621
Reagents

Buffer solution. Barium chloride (BaCl2), 0.5 N, and triethanolamine (TEA), 0.2 N. Adjust to 

pH 8.2 with HCl. Protect from CO2 of the air by attaching a drying tube containing soda lime 

(sodium calcium hydrate) to the air intake. 

Replacement solution. Barium chloride (BaCl2), 0.5 N. Add 0.4 ml buffer solution per liter and 

mix. Protect from CO2 with soda-lime tube. 

Magnesium nitrate (Mg(NO3)2), 1 N. 

Procedure

Transfer a 5-g sample to a leaching tube. For field-moist samples use a sample large 

enough to give an ovendry weight of about 5 g. Leach with 50 ml BaCl2-TEA solution, 

controlling the leaching rate to give at least 4 hours of soil:solution contact time. Follow with 

100 ml BaCl2 replacement solution, controlling the leaching rate so that the soil and BaCl2

solutions are in contact for a total of 20 to 24 hours. Rinse walls of leaching tube with 15 to 20 

ml H2O, collecting this washing with leachates from BaCl2 solutions. Extractable acidity can be 

determined by using this solution (6H1a). Place leaching tube on a clean flask and wash with 

methanol until free of chloride ion. For many samples 100 ml methanol is enough, but more 

methanol may be needed for some soils, particularly those of heavy texture and containing 

large amounts of hydrous oxides. Leach with 100 ml 0.001 N BaCl2 to remove methanol. 

Disconnect leaching tube and flask, rinse underside of leaching tube, place over a 250-

ml volumetric flask, and leach with 100 ml 1 N Mg(NO3)2 solution. Control leaching rate to 

give a soil-solution contact time of 16 hours or more. Rinse walls of leaching tube with 15 to 

20 ml H2O; collect rinse in the Mg(NO3)2 leachate. Make to volume. 

Barium by Flame Photometry (5A5a)

Make standards in 1 N Mg(NO3)2. Determine barium by flame photometry at 489 mμ. 

Calculations

CEC(meq/100 g) = (A/B) x dilution x 25 

where 

A = Ba from curve (meq/L) 

B = Sample weight (g) 

NH4OAc, pH 7.0, Leaching Tube (5A6)

Apparatus

Allihn leaching tubes or 50-ml plastic syringe barrels. 

Reagents

Same as in 5A1. 

Procedure

Prepare the Allihn tubes by placing either filter paper (Reeve Angel No. 934 AH, 3-cm 

fiber glass) or filter paper pulp on the fritted glass plate. If the syringe barrel is used as a 

leaching tube, compress the filter paper pulp in the barrel bottom with the syringe plunger. 

Place a Gooch perforated plate over the filter paper to permit stirring the soil without damage to 

the filter. (This plate is not necessary if an adequate pulp pad is used.) Place 5 or 10 g soil and a 

teaspoon of Celite into the tubes. (Optionally place a layer of Celite under the soil.) Add 25 ml 

N NH4OAc; stir and leach. Add an additional 25 ml N NH4OAc and let stand overnight. Stop 

622
the leaching with a pinch clamp or by stoppering the leaching tube. Add the NH4OAc directly 

to the leaching tube or use a constant level device (refer to Fig. 8, procedure 6N3)

volumetric flask can be substituted for the 250-ml Erlenmeyer flask and tubing. 

Make the leachate to volume if a volumetric flask is used or, if tared suction flasks are 

used, make to the appropriate calibrated weight for 100 ml NH4OAc. Set aside the leachate for 

further analysis. Add about 10 ml ethanol to the soil pad, stir, and leach. Leach with 100 ml 

ethanol and check for NH4

+

 in leachate. If NH4

+

 is present, leach with an additional 100 ml 

ethanol. Some soils, particularly those containing amorphous material, require as much as 400 

ml ethanol to clear the ammonia from the leachate. 

Direct Distillation (5A6a) 

Transfer soil cake to Kjeldahl flask and determine ammonia as described in 5A1a. 

NH4Cl, pH 7.0, Mechanical Extraction (5A7) Direct Distillation (5A7a) 

Determine ammonia by Kjeldahl distillation as described in 5A1a. 

NH4OAc, pH 7.0, Automatic Extractor (5A8) Direct Distillation (5A8a)

Reagents 

Sodium chloride (NaCl). 

Antifoam mixture. Mix equal parts of mineral oil and n-octyl alcohol. 

Sodium hydroxide (NaOH), 1 N. 

Hydrochloric acid (HCl), 0.2 N, standardized. 

Boric acid (H3BO3), 4 percent. 

Procedure

Transfer the soil plus filter pulp from methods 5A8 or 5A9 to a Kjeldahl flask. Add 400 

ml water and about 10 g NaCl, 5 drops antifoam mixture, a gram or two of granular zinc, and 

40 ml of 1 N NaOH. Connect the flask with the condenser and distill 140 ml into 50 ml of 4-

percent H3BO3 solution in 250-ml titrator beaker. Titrate with automatic titrator to end point pH 

setting of 4.60. 

Calculations

CEC(meq/100g) = (A/B) x N x 100 

where 

A = Volume HCl (mL) 

B = Sample weight (g) 

N = Normality of acid 

Report on ovendry basis. 

References 

Peech et al. (1947). 

. A 

623
NH4Cl, pH 7.0, Automatic Extractor (5A9) 

Direct Distillation (5A9a)

Determine ammonia by Kjeldahl distillation as described in 5A8a. 

Extractable Bases (5B) NH4OAc, pH 7.0, Buchner Funnel (5B1)

Procedure

Analyze the NH4OAc leachate from method 5A1 a for calcium, magnesium, sodium, 

and potassium (methods 6N2, 6O2, 6P2, 6Q2). 

Uncorrected (extractable) (5B1a)

If a soil does not contain soluble salts, the extractable bases are presumed to equal the 

exchangeable bases. They are, however, reported as extractable bases. 

Corrected (exchangeable) (5B1b) 

If a soil contains soluble salts, estimate their amount from the saturation extract as 

follows. Multiply cation concentration in the saturation extract (meq/L) by the saturation 

percentage (divided by 1000) to convert to milliequivalents per 100 g. Subtract this quantity 

from the concentration of the extracted cation. This procedure is not valid for calcium and 

magnesium in the presence of carbonates or for calcium in the presence of gypsum because 

these salts are soluble in NH4OAc. 

References

Peech et al. (1947). 

KCl-Triethanolamine Extraction, pH 8.2 (5B2)

Reagents 

Buffer solution. Potassium chloride (KCl), 1.0 N, and triethanolamine (TEA), 0.2 N, pH 8.2. 

Procedure

Proceed as in 5B1 except leach with 1 N KCl buffered at pH 8.2 with triethanolamine. 

Determine calcium by method 6N4, magnesium by 6O4. 

References

North-Central Regional Research Committee (1955). 

KCl-Triethanolamine Extraction, pH 8.2 (revised) (5B3)

Reagents

Buffer solution. Potassium chloride (KCl), 1.0 N, and triethanolamine (TEA), 0.2 N, pH 8.2. 

Procedure

Weigh 10-g samples and transfer to 100-ml beakers. Add 40 ml buffer solution. Stir 

thoroughly at least three times over a period of not less than 1 hour. Filter the suspension and 

collect the leachate in a 100-ml volumetric flask. 

Analyze the leachate for Ca and Mg by an appropriate procedure (6N4, 6O4). 

624
Uncorrected (extractable) (5B3a) 

If a soil does not contain soluble salts, the extractable bases are presumed to equal the 

exchangeable bases. They are, however, reported as extractable bases. 

Corrected (exchangeable) (5B3b)

If a soil contains soluble salts, estimate their amounts from the saturation extract and 

correct as in 5B1b. 

NH4OAc, pH 7.0, Leaching Tube (5B4) 

Analyze the NH4OAc leachate from method 5A6 for Ca, Mg, Na, and K (methods 6N2, 

6O2, 6P2, 6Q2). 

Uncorrected (extractable) (5B4a)

If a soil does not contain soluble salts, the extractable bases are presumed to equal the 

exchangeable bases. They are, however, reported as extractable bases. 

Corrected (exchangeable) (5B4b)

If a soil contains soluble salts, estimate their amounts from the saturation extract and 

correct as in 5B1b. 

NH4OAc, pH 7.0, Automatic Extractor (5B5) Corrected (exchangeable) (5B5b) 

If a soil contains soluble salts, estimate their amount from the saturation extract as 

follows. Multiply cation concentration in the saturation extract (meq/L) by the saturation 

percentage (divided by 1000) to convert to milliequivalents per 100 g. Subtract this quantity 

from the concentration of the extracted cation. This procedure is not valid for calcium and 

magnesium in the presence of carbonates that contain those elements, or for calcium in the 

presence of gypsum, because these compounds are soluble in NH4OAc. 

ION EXCHANGE ANALYSES (5)

Base Saturation (5C) 

NaOAc, pH 8.2 (5C2)

Divide sum of NH4OAc-extracted bases by the exchange capacity determined by 

method 5A2a. 

Exchangeable Sodium Percentage (ESP (5D) NaOAc, pH 8.2 (5D1)

Divide exchangeable sodium (meq/100 g) by the exchange capacity determined by 

method 5A2a. 

625
Calcium Saturation (Exchangeable-Calcium Percentage) (5F) NH4OAc, pH 7.0 (5F1) 

Divide the NH4OAc-extracted calcium by the exchange capacity determined by 

procedure 5A1 or 5A6. 

Organic Carbon (6A) 

Determine carbon for each horizon that may contain organic matter. Report as carbon 

percentage by weight of <2-mm material. 

To calculate total carbon per unit area, convert these weight percentages to volume 

percentages. Multiply each value by the bulk density Dbm, where m is usually 1/3 bar or 30 

cm, and by the thickness (inches) of that horizon. If coarse fragments are present, further 

multiply by Cm (4A). Sum the organic-matter percentages and multiply by 0.254 to convert to 

kilograms of carbon per square meter. 

Acid-Dichromate Digestion (6A1) 

FeSO4 Titration (6A1a)

Reagents

Potassium dichromate (K2Cr2O7), 1.00 N (49.04 g per liter). 

Ferrous sulfate, 1.0 N. Dissolve 280 g reagent-grade FeSO4·7H2O in water, add 80 ml 

concentrated H2SO4, cool, and dilute to 1 liter. Standardize this reagent each day by titrating 

against 10 ml N K2Cr2O7 as directed. 

Barium diphenylaminesulfonate indicator, 0.16 percent aqueous solution. 

Orthophenanthroline-ferrous complex (optional), 0.025 M solution of one of the phenanthroline-ferrous complex indicators. 

H2SO4, at least 96-percent. 

Phosphoric acid (H3PO4), 86-percent. 

Procedure Transfer 1 g (0.5 g or less if high in organic matter) soil ground to pass an 80-mesh 

sieve to a 500-ml Erlenmeyer flask. Add 10 ml N K2Cr2O7. Add 20 ml concentrated H2SO4

rapidly, directing the stream into the solution. Immediately swirl vigorously or place in wristaction shaker for 1 minute. Let the flask stand on a sheet of asbestos for about 30 minutes. Add 

200 ml water and 10 ml H3PO4. Add 0.5 ml barium diphenylaminesulfonate just before 

titrating. Titrate by adding FeSO4 drop by drop to a light green end point. If more than 8 ml of 

the available 10 ml K2Cr2O7 are reduced, repeat the determination, using less soil. If 

orthophenanthroline-ferrous complex is the indicator, it is not necessary to add H3PO4. 

Calculations

Organic carbon (pct.) = ((A - B)/C) x N x (0.30/0.77) 

where 

A = Volume FeSO4 blank (mL) 

B = Volume FeSO4 sample (mL) 

C = Sample weight (g) 

N = Normality of FeSO4

626
0.77 = Recovery factor proposed by Walkley (1935) 

Report on ovendry basis. 

References

Peech et al. (1947) and Walkley (1935). 

CO2 Evolution, Gravimetric (6A1b)

Apparatus

See Fig. 4. 

Reagents

Digestion-acid mixture. Mix 600 ml concentrated H2SO4 and 400 ml 85-percent H3PO4. 

Potassium dichromate (K2Cr2O7), reagent grade. 

Potassium iodide (KI). Dissolve 100 g KI in 100 ml water. 

Silver sulfate (Ag2SO4), saturated aqueous solution. 

Concentrated sulfuric acid (H2SO4). 

Other reagents. Indicarb or Mikohbite, soda lime, 30-mesh zinc, and anhydrone (anhydrous 

magnesium perchlorate). 

 

627
Procedure 

Place a soil sample containing 20 to 40 mg carbon (usually 0.5 to 3 g ovendry soil) in 

digestion flask and add 1 to 2 g K2Cr2O7. Wash the neck of the flask with 3 ml water and 

connect the flask to reflux condenser. Attach the weighed Nesbitt bulb to the system and open 

the valve at the top. Pour 25 ml digestion-acid mixture into funnel, let it enter the flask, and 

close the stopcock immediately to prevent loss of CO2. Use digestion-acid mixture to lubricate 

the funnel stopcock. The tip of the air-delivery tube should extend about 0.5 cm below the 

surface of the acid during digestion. Adjust the "carrier stream" to a flow rate of one or two 

bubbles per second and maintain this rate during digestion. Heat with a gas flame of sufficient 

intensity to bring the sample to boiling in 3 to 4 min. Continue gentle boiling for a total heating 

period of 10 min (avoid excessive frothing). Heating is too rapid if white fumes of SO3 are 

visible above the second bulb of the reflux condenser during boiling. At the end of the 

digestion period remove the flame and aerate for 10 min at the rate of six to eight bubbles per 

second. Then close the stopcock on the Nesbitt bulb, disconnect the bulb from the system, and 

weigh. 

Calculations 

Organic carbon (pct.) = ((A - B)/C) x 27.3 

where 

A = Final bulb weight (g) 

B = Initial bulb weight (g) 

C = Sample weight (g) 

Report on ovendry basis. 

References

Allison (1960). 

Dry Combustion (6A2) 

CO2 Evolution, Gravimetric I (6A2a)

Apparatus

See Fig. 5. 

628
Reagents

Powdered manganese oxide (MnO2). 

Procedure 

Place 0.5 to 1.5 g soil that has been ground to 80 mesh in an Alundum boat containing 

0.25 g powdered MnO2. Insert the boat into the quartz tube of the multiple-unit combustion 

furnace shown. Before inserting the soil, preheat the long part of the quartz tube to 900°C or 

more (1000° or 1,100°C) and clear of CO2 by passing CO2free oxygen through the combustion 

train until the weighing bottle shows a constant weight. While oxygen is passing slowly 

through the apparatus, heat to a temperature of 900° C or higher (15 to 30 min). Continue 

heating in a streaming oxygen atmosphere for 30 minutes more or until the Nesbitt absorption 

bulb has reached a constant weight. 

Calculations

Report on ovendry basis as in 6A1b. 

References

Robinson (1930) 

CO2 Evolution, Gravimetric II (6A2b)

Apparatus

See Fig. 6. 

629
Procedure 

Heat tube to approximately 950°C. Sweep with oxygen until weight of Nesbitt bulb is 

constant. Remove rubber stopper in the oxygeninlet end of the tube and insert the boat 

containing 0.5 to 1.5 g soil. Reinsert the stopper and use the push rod to move the boat into the 

hot zone. Heat for 10 minutes, remove bulb, and record weight gain. Remove boat and repeat 

process with fresh sample, using the same Nesbitt bulb. 

Calculations

Report on ovendry basis as in 6A1b. 

References

Robinson (1930) and Post. (Post, G.J. A study of three methods for determination of organic 

carbon in Ohio soils of several great soil groups and the profile distribution of carbon-nitrogen 

ratios. M.Sc. thesis. The Ohio State University, 34 pp. 1956.) 

CO2 Evolution III (6A2c) 

Apparatus

LECO 70-second carbon analyzer, model 750-100. 

LECO induction furnace, model 521-000. 

Reagents 

Manganese dioxide. 

Antimony. 

1-g standard sample rings containing 0.870 percent carbon. 

1-g standard sample rings containing 0.073 percent carbon. 

Metal accelerator. 

Iron chip accelerator. 

Anhydrone. 

Procedure 

For noncalcareous soils, weigh approximately 1/2 g of <2-mm soil into crucibles in 

duplicate. Add to the soil in the crucibles one scoop of copper accelerator and one scoop of iron 

chip accelerator. Mix by stirring. Add an additional scoop of iron chips to the stirred mixture. 

Four standard soils containing 0.8, 2.1, 3.5, and 6.5 percent organic carbon are run with each 

group of soils. Follow LECO instruction manuals for instrument operation. Record readings 

from digital voltmeter as percent carbon. 

References

Tabatabai and Bremner (1970). 

630
Peroxide Digestion (6A3)

Gravimetric Weight Loss (6A3a)

Reagents

Hydrogen peroxide (H2O2), 6-percent. 

Procedure

Digest soil for several hours in a covered beaker with 6-percent H2O2. Remove soluble 

material by washing three to five times with a Pasteur-Chamberlain clay filter, "F" fineness. 

Dry the beaker and soil, and weigh. 

Calculations

Organic matter (pct.) = ((A + B)/C) x 100 

where 

A = Weight loss on heating (g) 

B = Weight of dry matter in solution (g) 

C = Sample weight (g) 

Note that organic matter differs from organic carbon (see 6A1a). 

References

North-Central Regional Research Committee on soils (1955). 

Nitrogen (6B) 

Kjeldahl Digestion I (6B1)

Reagents

Concentrated sulfuric acid (H2SO4). 

Salt mixture: 

Potassium sulfate (K2SO4), 1000 g. 

Ferrous sulfate (anhydrous) FeSO4, 55 g. 

Copper sulfate (anhydrous) CuSO4, 32 g. 

Hengar granules (selenized). 

Procedure

Weigh 5 g soil into 800-ml Kjeldahl flask, add 20 ml distilled water and let stand 

overnight. Add 10 g salt mixture, 2 or 3 Henger granules, and 30 ml H2SO4. Digest on Kjeldahl 

digestion heaters, rotating flasks frequently. Continue digestion 1 hr after mixture is clear. 

References

Association of Official Agricultural Chemists (1945). 

Ammonia Distillation (6B1a)

Reagents 

Mixed indicator. Methyl red, 0.125-percent, and methylene blue, 0.0825-percent, in 95-percent 

ethanol. 

631
Methyl red (optional), 0.25-percent. 

Brom cresol green, 0.1-percent aqueous solution. 

Boric acid (H3BO3), 4-percent. 

HCl, standardized, 0.1 N or 0.05 N. 

Procedure

Cool digestion flask (6B1) and dilute contents with about 400 ml water. Add 2 to 3 g 

mossy zinc, 5 drops antifoam mixture, and 70 ml concentrated NaOH solution. Connect flask to 

condenser and distill ammonia into 25 or 50 ml H3BO3 solution. Titrate with standard HCl to 

purple end point, using 10 drops mixed indicator and 2 drops brom cresol green or 3 drops 

brom cresol green and 1 drop methyl red. 

Calculations

N (pct) = ((A - B)/C) x N x 1.4 

where 

A = Volume HCl sample (mL) 

B = Volume HCl blank (mL) 

C = Sample weight (g) 

N = Normality of HCl 

Report on ovendry basis. 

Ammonia Distillation, Automatic Titrator (6B1b)

Reagents

Boric acid (H3BO3), 4 percent. 

HCl, standardized, 0.1 N or 0.05 N. 

Concentrated sodium hydroxide (NaOH) solution, 50 percent. 

Antifoam mixture: Equal parts n-octyl alcohol and mineral oil. 

Mossy zinc. 

Procedure

Cool digestion flask (6B1) and dilute contents with about 400 ml water. Add 2 to 3 g 

mossy zinc, 5 drops antifoam mixture, and 70 ml concentrated NaOH solution. Connect flask to 

condenser and distill ammonia into 250-ml titrator beaker containing 50 ml H3BO3 solution. 

Titrate with standard HCl to end point pH setting of 4.60 on automatic titrator. 

Calculations

N (pct.) = ((A - B)/C) x N x 1.4 

where 

A = Volume HCl sample (mL) 

632
B = Volume HCl blank (mL) 

C = Sample weight (g) 

N = Normality of acid 

Report on ovendry basis. 

Semimicro Kjeldahl (6B2) 

Apparatus

Aminco-Koegel semimicro rotary digestion rack and steam-distillation apparatus. 

Reagents

Concentrated sulfuric acid (H2SO4). 

H2SO4, 0.01 N, standardized. 

Sodium hydroxide (NaOH), 50-percent. 

Boric acid (H3BO3), 2-percent. 

Mixed indicator. Mix 0.1 g methyl red and 0.1 g brom cresol green and dissolve in 250 ml 

ethanol. 

Salt mixture. Mix 790 g potassium sulfate (K2SO4), 100 g ferrous sulfate (FeSO4), 100 g copper 

sulfate (CuSO4), and 10 g selenium metal. 

Procedure

 Using an analytical balance, weigh on a cigarette paper either 0.500 or 1.000 g ovendry soil 

that has been ground to about 0.2 mm. Roll soil in cigarette paper and drop into a 100-ml 

digestion-distillation flask. Add 2 g salt mixture 1 ml water, and 5 ml concentrated H2SO4. Swirl vigorously and digest, rotating the flask frequently until fumes are emitted. Continue 

digestion for at least 1 hour after mixture becomes white. Cool to room temperature and add 15 

ml water. Shake until the contents of the flask are thoroughly mixed. 

Ammonia Distillation (6B2a) 

Procedure Measure 10 ml 2-percent H3BOa with an automatic pipet into a 125-ml flask and add 

0.5 ml mixed indicator. Place this flask under delivery tube. Connect digestion-distillation flask 

containing soil digested according to method 6B2 to the distillation unit by the ground-glass 

connection. Start steam passing through the system and slowly add 15 ml 50-percent NaOH. 

Distill for 12 minutes, add 0.5 ml more mixed indicator, and titrate the absorbed ammonia with 

0.01 N H2SO4. 

Calculations

N (pct) = (A/B) x N x 1.4 

where 

A = Volume H2SO4 (mL) 

B = Sample weight (g) 

N = Normality of H2SO4 

Report on ovendry basis. 

633
Iron (6C) 

Dithionite-Extraction (6C1)

Reagents

Sodium dithionite powder (Na2S2O4). 

Hydrochloric acid (HCl), 10-percent. 

Apparatus

8-oz Pyrex nursing bottles or 250-ml flat-bottomed centrifuge bottles. 

Procedure

Place 4 g soil, ground to 80 mesh, in a nursing or centrifuge bottle. Add 4 g Na2S2O4

and 75 ml water. Stopper and shake overnight or for 16 hours. Then adjust the pH to 3.5 to 4.0, 

if necessary, with 10-percent HCl. Let stand for no less than 1 hour, stirring four or five times. 

Transfer the suspension to a graduated cylinder, dilute to 200 ml with water, and mix. 

Centrifuge or filter a part of the suspension and transfer 50 ml of the clear solution to a 250-ml 

beaker. 

References

Kilmer (1960). 

Dichromate Titration (6C1a)

Reagents

Hydrogen peroxide (H2O2), 35-percent. 

Ammonium hydroxide (NH4OH), 1:1. 

Hydrochloric acid (HCl), 1:1. 

Stannous chloride (SnCl2). Dissolve 1 g SnCl2 in 2 to 4 ml concentrated HCl and dilute to 50 

ml with water; prepare fresh each time. 

Mercuric chloride (HgCl2), saturated aqueous solution. 

Phosphoric acid (H3PO4), 85-percent. 

Potassium dichromate (K2Cr2O7), 0.100 N, standard. 

Barium diphenylaminesulfonate, 0.16-percent aqueous solution. 

Procedure

Add 10 to 15 ml H2O2 (6C1) to the solution to destroy any excess reducing agent. Cover 

the beaker with a watchglass and warm on a hot plate until the reaction starts. Set the solution 

aside until the reaction subsides and then boil for 10 to 15 minutes. Add a slight excess of 1:1 

NH4OH and boil the solution for 15 to 20 minutes to insure complete removal of H2O2. 

Dissolve Fe(OH)3 by adding 1:1 HCl through the lip of the beaker. Usually 10 to 15 ml are 

enough. Heat the solution to 90° C and reduce by adding SnCl2 by drops, stirring until the 

yellow color just disappears. Add three to four drops more. Cool the solution to room 

temperature and add 15 ml HgCl2 solution all at once. A light silky precipitate of Hg2Cl2 forms 

if the proper amount of SnCl2 has been added. Dilute the solution to 100 to 150 ml and add 5 

ml H3PO4. Add 10 drops of barium diphenylaminesulfonate and titrate the solution with 

standard K2Cr2O7 to a violet-blue end point. 

634
Calculations

Fe (pct.) = (A/B) x N x (C/D) x 5.58 

where 

A = Volume K2Cr2O7 (mL) 

B = Sample weight (g) 

N = Normality of K2Cr2O7

C = Volume extract (mL) 

D = Volume aliquot (mL) 

Fe2O3 (pct.) = Fe (pct.) x 1.43 

Report on ovendry basis. 

EDTA Titration (6C1b)

Reagents

Hydrogen peroxide (H2O2), 35-percent. 

Ammonium persulfate ((NH4)2S2O8). 

Salicylic acid, 1-percent in 95-percent ethanol. 

EDTA, standardized as g iron per ml EDTA. Prepare EDTA as described in 6N1a. 

 

Iron standard, 0.500 g iron per liter. 

Procedure

Pipet a 5- to 25-ml aliquot from the centrifuge tube of procedure 6C1 into a 250-ml 

beaker. Add 50 ml water to the beaker. Then add by drops 5 ml H2O2 and digest over low heat 

until bubbling from the decomposing H2O2 ceases. Remove immediately to avoid precipitation 

of Fe2O3 in samples high in iron. Caution: Add H2O2 slowly to prevent liberation of elemental 

sulfur from any remaining Na2S2O4. Keep the volume in the beaker to about 50 ml during the 

digestion by adding water if necessary. Remove from heat and cool. Adjust the pH between 2.0 

and 3.0 with a pH meter, using either concentrated acetic acid or a 20-percent NaOAc solution. 

Add a few milligrams (NH4)2S2O8 to the solution to insure total oxidation of iron. Then add 1 

ml indicator (1-percent salicylic acid) and titrate with 0.02 N EDTA to a pale yellow or 

colorless end point. 

Calculations

Fe (pct.) = (A/B) x V x (C/D) x 100 

where 

A = Volume EDTA (mL) 

B = Sample weight (g) 

V = Titer of EDTA in g Fe/ml EDTA 

C = Volume extract (mL) 

D = Volume aliquot (mL) 

Fe2O2 (pct.) = Fe (pct.) x 1.43 

Report on ovendry basis. 

635
References

Cheng, Bray, and Kurtz (1953). 

Dithionite-Citrate Extraction (6C2)

Reagents

Sodium dithionite (Na2S2O4) 

Sodium citrate 

Superfloc flocculating agent, 0.2 percent in water 

Procedure

Weigh 1 to 4 g of soil (approximately 0.2 g maximum extractable iron) into an 8-oz 

nursing bottle. Add 2 g sodium dithionite and 20 to 25 g sodium citrate. Make up to 4 oz with 

water, and shake overnight in a reciprocating shaker. Add 2 ml Superfloc solution to the 

suspension, make up to 8 oz with water, shake vigorously for 15 s and allow to settle for at 

least 1 hr. This extract is used for analysis of iron (6C2b), aluminum (6G7a), and manganese 

(6D2a). 

References

Holmgren (1967). 

Orthophenanthroline Colorimetry (6C2a)

Apparatus

Seligson pipet, 0.1-ml. 

Reagents

Orthophenanthroline, 0.25-percent. 

Iron solution, 1000 mg per liter, standard. 

Sodium dithionite powder (Na2S2O4). 

Sodium citrate crystals. 

Superfloc flocculating agent, 0.2-percent, in water. 

Procedure

Add 5 drops Superfloc solution to the dithionite-treated soil suspension (6C2) and make 

to 8 oz. Shake vigorously for about 15 seconds and allow to settle. Pipet a 0.1-ml aliquot with 

a Seligson pipet into a 25-ml volumetric flask. Add water to about 10 ml. Using a small scoop, 

tap a pinch of dithionite and a pinch of sodium citrate into the flask. Add 0.5 ml 0.25-percent 

orthophenanthroline and make to volume. Shake and read in a colorimeter at 508 Mμ after 1 

hour. To prepare the standards, pipet 5-, 10-, 25-, 50-, 100-, 150-, and 200-ml aliquots of 

standard iron solution (1000 mg/L) into 8-oz shaking bottles and make to 8 oz after adding 

reagents as in 6C2. Transfer 0.1-ml aliquots to 25-ml volumetrics and develop color by the 

above procedure. 

Plot the standard curve as milligrams iron per 8-oz bottle against percentage 

transmission. 

Calculations

636
Fe (pct.) = (A/B) x 10-1 

A = Fe in bottle (mg) 

B = Sample weight (g) 

Fe2O3 (pct.) = Fe (pct.) x 1.43 

Report on ovendry basis. 

References

Holmgren (1967). 

Dithionite-Citrate-Bicarbonate Extraction (6C3) 

Reagents

Sodium bicarbonate (NaHCO3), 1 M. Sodium citrate, 0.3 M. 

Sodium chloride (NaCl), saturated solution. 

Acetone. 

Procedure

Weigh 4 g soil (1 g clay) into a 100-ml centrifuge tube. Add 40 ml 0.3 M Na-citrate and 

5 ml 1 M NaHCO3. Bring temperature to 80°C in water bath. Add 1 g solid Na2S2O4, stir 

constantly for 1 minute and occasionally for 15 minutes. Add 10 ml NaCl solution and 10 ml 

acetone to promote flocculation. Mix, warm in water bath, and centrifuge 5 minutes at 1,600 to 

2,200 rpm. Decant clear supernatant into 500-ml volumetric flask and make to volume. 

References

Mehra and Jackson (1960). 

Potassium Thiocyanate Colorimetry (6C3a)

Apparatus Colorimeter. 

Reagents

Hydrochloric acid (HCl), 6 N. 

Potassium thiocyanate (KSCN), 20-percent. 

Hydrogen peroxide (H2O2), 30-percent. 

Procedure

Transfer suitable aliquot (0.5 to 3 ppm iron in final solution) to 50 ml-volumetric flask. 

Add water to 35 ml, 1 drop H2O2, 5 ml HCl, and 5 ml KSCN solution. Make to volume and 

read at 490 mμ in colorimeter. 

Calculations

Fe (pct.) = (A/B) x (C/D) x 0.005 

where 

637
A = Fe from curve (mg) 

B = Sample weight (g) 

C = Volume extract (mL) 

D = Volume aliquot (mL) 

Fe2O3 (pct.) = Fe (pct.) x 1.43 

Report on ovendry basis. 

References Jackson (1958). 

Pyrophosphate-Dithionite Extraction (6C4) 

Reagents

Pyrophosphate solution. Dissolve 89.2 g Na4P2O7·10H2O in 800 to 900 ml water. Adjust the pH 

of this solution to 8.0 by adding hydrogensaturated exchange resin. Decant or filter, wash the 

resin, and dilute the solution to 1000 ml to make 0.2 M Na4P2O7. 

Sodium dithionite (Na2S2O4). 

Digestion acid. 10 Parts concentrated HNO3, 4 parts concentrated H2SO4, and 4 parts 

concentrated HClO4. 

Procedure

Mix 80 ml pyrophosphate solution and 2.0 g solid sodium dithionite in a beaker and add 

this solution to 4 g soil in a centrifuge tube (pH 8.0 pyrophosphate solution and dithionite 

combined in this ratio result in a solution having a pH of about 7.3). Continue the extraction for 

30 minutes at 50°C, shaking the suspension in the tube every 5 minutes. Centrifuge the 

suspension 5 to 10 minutes at 2000 rpm. Dilute the extract to 100 ml (solution A). 

Immediately transfer 5 ml solution A to a beaker. Add 1 to 2 ml digestion acid and heat 

on a hot plate until almost dry to destroy the organic and hydrolyze pyrophosphate to 

orthophosphate. Allow to cool, dissolve the salts in HCl, and dilute to 100 ml (solution B). 

Determine iron and aluminum in solution B by appropriate methods, such as 6C3a and 6G1a. 

References

Franzmeier, Hajek, and Simonson (1965). 

Sodium Pyrophosphate Extraction (6C5) 

Reagents

Sodium pyrophosphate (Na4P2O7), 0.1 M. 

Superfloc solution, 0.4 percent. 

Procedure

Place 2 g soil into 250-ml centrifuge bottle (polypropylene). Add 200 ml 0.1 M

Na4P2O7, cap, and shake overnight. Add 5 to 10 drops 0.4-percent Superfloc, shake, and 

centrifuge at 2000 rpm (Int. No. II centrifuge). Transfer the supernatant liquid to a plastic or 

glass container and reserve for Fe and Al analyses. 

The supernatant liquid must be clear in reflected light. If fine colloids are visible, repeat 

the procedures. If fine colloids are still present, spin the suspension in a super centrifuge until 

the supernatant liquid is clear. Foam rubber can be used in the centrifuge cups as a cushion for 

the 250-ml flat-bottom plastic bottles. 

638
References

Bascomb (1968). 

Atomic absorption (6C5a)

Apparatus

Atomic absorption spectrophotometer. 

Reagents

Standard Fe solution, 0 to 50 ppm. 

Procedure

Establish standard curve and match readings from extract to curve readings. Dilute 

where necessary. 

Calculations

Fe (pct.) = A x (B/C) x (1/10000) x dilution 

where 

A = Fe (ppm) 

B = Volume extract (mL) 

C = Sample weight (g) 

Report on ovendry basis. 

Ammonium Oxalate Extraction (6C6)

Reagents

Ammonium oxalate (NH4)2C2O4 0.2 M, pH 3.0. 

Adjust the pH of 0.2 M (NH4)2C2O4 to 3.0 with 0.2 M oxalic acid (H2C2O4). 

Superfloc solution, 0.4 percent. 

Procedure

Place 2 g soil into 250-ml centrifuge bottle (polypropylene). Add 200 ml 0.2 M

(NH4)2C2O4, cap, and shake immediately in the dark for 4 hours. Add 5 to 10 drops 0.4-percent 

Superfloc, shake, and centrifuge at 2000 rpm (Int. No. II centrifuge). Transfer the supernatant 

liquid to a plastic or glass container. Store in the dark and reserve for Fe and Al analyses. 

The supernatant liquid must be clear in reflected light. If fine colloids are visible repeat 

the procedure. If fine colloids are still present, spin the suspension in a supercentrifuge until the 

supernatant liquid is clear. 

References

McKeague and Day (1965). 

Atomic Absorption (6C6a)

Proceed as in 6C5a except use extract from 6C6. 

639
Manganese (6D) 

Dithionite Extraction (6D1) 

Extract 4.00 g soil as described in 6C1. 

Permanganate Colorimetry (6D1a)

Reagents

Concentrated nitric acid (HNO3). 

Hydrogen peroxide (H2O2), 30-percent. 

Phosphoric acid (H3PO4), 85-percent. 

Sodium para periodate (Na3H2IO6) or sodium meta periodate (NaIO4). 

Purified water diluent. Add 100 ml 80-percent H3PO4 and 1 g Na3H2IO6 to 1 liter water (Mnfree); heat to boiling and digest for 1 hour; stopper with foil-covered stopper. About 85 ml of 

this diluent is needed for each sample. 

KMnO4, standard. 

Procedure 

Take a 10- to 25-ml aliquot from the dithionite extract and place in a 150-ml beaker. 

Add 5 ml 30-percent H2O2, digest on hot plate, and evaporate until dry. Cool beaker and 

contents and add 3 ml concentrated HNO3 and 2 ml 30-percent H2O2. Digest on hot plate for 

30 minutes, using a close fitting cover glass, then raise cover glass, and evaporate until dry. 

Take up residue with 10 ml 85-percent H3PO4, heat to boiling, remove, and cool to about 50°C. 

Dilute with 10 ml water and add 0.2 g Na3H2IO6. Cover beaker and heat to boiling. Cool to 

50°C and add 62 ml purified water diluent and 0.1 g Na3H2IO6. Digest at 90° C for 40 minutes 

or until no further color develops. Transfer the hot solution to a 100-ml volumetric flask, using 

purified water diluent to rinse the beaker. Cool, make up to volume with the diluent, stopper, 

and shake. Determine percentage transmittance with a photoelectric colorimeter at 540 mμ. 

Interpolate concentration from a standard absorbance concentration. 

Calculations

Mn (pct.) = (A/B) x (C/D) x 54.9 

where 

A = MnO4

-

 (meq/L) 

B = Sample weight (g) 

C = Volume extract (mL) 

D = Volume aliquot (mL) 

MnO (pct.) = Mn (pct.) x 1.291 

Report on ovendry basis. 

References

Jackson (1958). 

640
Calcium Carbonate (6E) 

HCl Treatment (6E1) 

Gas Volumetric (semiquantitative) (6E1a)

This procedure uses a simple leveling device to measure the volume of gas released 

when the soil is treated with HCl. It has an inherent error caused by the solubility of CO2 in the 

HCl solution. Data on file at the laboratory at Lincoln, Nebr., indicate that the results are about 

10 percent (8 to 12 percent) low for CaCO3 equivalents ranging from 40 percent to 6 percent 

(1-g basis). For 1-percent equivalents the values are about 20 percent low and for less than 1 

percent, the values have doubtful significance. 

References

Association of Official Agricultural Chemists (1945). 

Manometric (6E1b) 

Apparatus

Wide-mouth prescription bottles, 3-oz, with bakelite cap; drill 7/16-in hole in cap for serum 

bottle stopper. Rubber gasket, 1 3/8 in OD x 15/16 in ID. 

Serum bottle stopper. 

Mercury manometer and a 26-gauge hypodermic needle attached to manometer tube. 

Gelatin capsule. 1/4 oz. 

Reagents

Hydrochloric acid (HCl), 6 N. 

Glycerin. 

Procedure

Place 2 g of soil in prescription bottle and add 5 ml water. Moisten lip of bottle with a 

drop of glycerin to ensure a good seal with rubber gasket. Fill gelatin capsule with HCl, put cap 

in place and invert to seal cap on capsule. Place, capsule in bottle and immediately cap the 

bottle. In a minute or two the HCl will dissolve the capsule. After 1 hr insert hypodermic 

needle through serum stopper and read manometer. Compare reading with those for standards 

prepared by treating aliquots of standard Na2CO3 solution in same manner as samples. 

Vary sample weight according to CaCO3 content as follows: For <25 percent CaCO3, 

use 2 g soil; for 25 to 50 percent CaCO3, 1 g soil; and for >50 percent CaCO3, 0.5 g soil. For 

trace amounts, add a few drops 6 N HCl to soil and observe under binocular microscope. 

Evolution of gas bubbles indicates the presence of CaCO3. 

References

Williams (1948). 

Gravimetric (weight loss) (6E1c) 

Apparatus

See Fig. 7. 

641
Reagents

Hydrochloric acid (HCl), 6 N. 

Anhydrone (Mg(ClO4)2). 

Procedure

Assemble apparatus as shown in Fig. 7. Place a sample of soil containing less than 1 g 

CaCO3 equivalent in a 125-ml Erlenmeyer flask. Wash down the sides of the flask with 10 ml 

water. Place 7 ml 6N HCl into vial C and then place the vial upright in the flask without 

spilling any acid. Moisten stopper G with glycerin, sprinkle with a small amount of 180-mesh 

abrasive to overcome slipperiness, and place the apparatus with stopcocks D and E, tubes I and 

J, attached firmly in position in the flask. Close stopcocks D and E. Place the apparatus beside 

the balance. Wait 30 minutes before weighing to allow temperature of the apparatus to 

equilibrate with temperature of air in the balance. Do all weighing with stopcock D open since 

a change in temperature of the flask with the stopcock closed results in a change in weight of 

the apparatus. Use tongs to place apparatus on the weighing pan, open stopcock D, weigh to 

0.1 mg, and then immediately close stopcock D. Check the weight 10 minutes later to be 

certain that the weight of the flask has stabilized. Open stopcock D and then shake apparatus to 

upset the vial, allowing the acid to react with the carbonates. After 10 minutes, attach the 

rubber tube from the airdrying vessel to stopcock E. Open stopcock E and apply suction at 

stopcock D to give 5 to 10 bubbles per second at the base of tube J to sweep out CO2. Shake 

the flask after 10 minutes and again after 20 minutes. After 30-minutes sweeping time, stop the 

suction and close stopcocks D and E. Return apparatus to the balance. Delay weighing for 1 

hour to allow the heat generated by absorption of water by the anhydrone to be dissipated. 

Weigh apparatus with stopcock D open. Check the weight after 10 minutes. 

Calculations

Carbonate as CaCO3 (pct.) = ((A - B)/C) x 228 

642
where 

A = Initial weight of flask (g) 

B = Final weight of flask (g) 

C = Sample weight (g) 

Report on ovendry basis. 

References

Erickson et al. (1947). 

Gravimetric (weight gain) (6E1d)

Proceed as in 6E1c except add additional trap containing CO2-absorbing Ascarite to end 

of gas train. Weigh Ascarite bulb before and after CO2 evolution. Weight gain equals the CO2

evolved from the sample. Better results are obtained if the Ascarite is size-graded so that CO2

passes through the coarser material first. Indicarb can be used in place of Ascarite. 

Titrimetric (6E1e)

Reagents

Hydrochloric acid (HCl), 0.5 N, standardized. 

Sodium hydroxide (NaOH), 0.25 N, standardized. 

Phenolphthalein, 1 percent in 60-percent ethanol. 

Procedure

Place 5 to 25 g soil in a 150-ml beaker, add exactly 50 ml HCl, cover with a watchglass, 

and boil gently for 5 minutes. Cool, filter, and wash all the acid from the soil with water. 

Determine the amount of unused acid by adding 2 drops of phenolphthalein and back-titrating 

with NaOH. 

Calculations

Carbonate as CaCO3 (%) = ((50 x A - B x C)/D) x 5 

where 

A = Normality of HCl 

B = Volume NaOH (mL) 

C = Normality of NaOH 

D = Sample weight (g) 

Report on ovendry basis. 

References

Richards (1954) 

Warburg Method (6E1f)

Apparatus

Warburg manometer, mercury filled. 

643
Warburg reaction vessel, 15-ml capacity, with vented stopper for sidearm. 

Constant temperature bath. 

Reagents

HCl, 1:1. Na2CO3 solution for standard curve. Dissolve 1.06 g Na2CO3 in water and make to 1 

liter. Solution contains 1.06 mg Na2CO3 per ml or the equivalent of 1 mg CaCO3 per ml. Obtain 

standard curve by measuring CO2 pressure from 1, 2, 4, 6, 8, and 10 ml Na2CO3 solution. 

Procedure

Weigh 100 mg sample of finely ground soil and transfer to Warburg reaction vessel. Be 

careful not to get any sample in center well. Pipet 1 ml water into vessel and mix well with 

sample. Pipet 1 ml 1:1 HCl into sidearm, insert greased stopper, and leave in vent-open 

position. Attach reaction vessel to manometer and fasten with rubber bands or spring supports. 

Place reaction vessel in constant temperature bath at 25°C for 5 to 10 minutes to bring flask 

contents to temperature of water bath. Remove flask from bath, close stopper vent, and fasten 

with rubber bands or springs. Tilt flask to allow acid to flow from sidearm into reaction vessel, 

mix contents, and return vessel to water bath. Let stand for at least 30 minutes before reading 

manometer. Use the standard curve to convert the difference between the two manometer arm 

readings (mm), to milligrams CaCO3. Gently tap the manometer holder occasionally to 

prevent low readings caused by mercury adhering to manometer walls. 

Sensitive Qualitative Method (6E2) 

Visual, Gas Bubbles 6E2a)

Add few drops 6 N H2SO4 to soil and observe under binocular microscope. Evolution of 

gas bubbles indicates the presence of CaCO3. 

H2SO4 Treatment (6E3) Gravimetric (weight gain) (6E3a)

Apparatus

See Fig. 4, procedure 6A1b. 

Reagents

Sulfuric acid (H2SO4). Dissolve 57 ml concentrated H2SO4 and 92 g of FeSO4·7H2O in 600 ml 

water, cool, and dilute to 1000 ml. This solution is approximately 2 N in acidity and contains 5-

percent FeSO4 as antioxidant. Keep well stoppered. 

Procedure

Place a 1- to 5-g sample of ovendry soil in the digestion flask E and connect condenser 

D. Weigh the Nesbitt bulb, attach to the system, and adjust the carrier stream to a flow rate of 1 

or 2 bubbles per second. Pour 25 ml of the acid solution into the funnel and let it enter the 

digestion flask E. Close the stopcock immediately. Apply heat slowly and bring contents of 

flask to a boil in about 4 minutes. Continue gentle boiling for exactly 3 minutes more for a total 

heating period of 7 minutes. Remove the flame, adjust the carrier stream to 6 or 8 bubbles per 

second, and continue aerating for 10 minutes. Disconnect the Nesbitt bulb and weigh. 

Calculations

Carbonate as CaCO3 (%) = ((A - B)/C) x 227 

where 

A = Final weight of bulb (g) 

644
B = Initial weight of bulb (g) 

C = Sample weight (g) 

Report on ovendry basis. 

References

Allison (1960). 

Gypsum (6F) 

Water Extract (6F1) 

Indirect Estimate (6F1b) 

Add a weighed quantity of soil to enough water to dissolve all the gypsum by overnight 

shaking. The concentration of sulfate in this dilute soil:water extract should be <10 meq/L. 

Gypsum can be estimated by method 6F2. If crystals are observed or estimated gypsum content 

is >5 percent, the <2-mm sample should be ground to approximately 80 mesh. Determine total 

sulfate in this extract by any appropriate procedure. Also determine Ca and S04 in a saturation 

extract by any appropriate procedure. 

Calculations

Gypsum = (SO4)DE - (SO4)non-gypsum SE

but S04 non-gypsum SE = (SO 4) SE - (SO 4) gypsum SE

∴gypsum = (SO4)DE + (SO4)gypsum SE - (SO4)SE

(SO4)DE = S04 in dilute water extract 

(SO4)SE = S04 in saturation extract 

(SO4)gypsum SE = 30 meq/L if S04 and Ca are > 30 meq/L 

= (SO4)SE if (Ca)SE > (SO4)SE

= (Ca)SE if (Ca)SE < (SO4)SE

All quantities are reported in meq/100 g. 

Gypsum (%)=Gypsum (meq/100g) x 0.0861 (g/meq) 

References

Lagerwerff, Akin, and Moses (1965). 

Ion Chromatograph (6F1c) 

Apparatus

DIONEX Model 2110i ion chromatograph 

Recorder (1 volt input). 

Voltage stabilizer. 

645
Reagents

0.1 M Na2CO3. 

0.003 M NaHCO3. 

0.0024 M Na2CO3. 

1 N H2SO4. 

Mixed standard solutions: 

Fluoride 0.0125 to 5.0 meq/L. 

Chloride 0.01 to 4.0 meq/L. 

Nitrate 0.025 to 10.0 meq/L. 

Sulfate 0.05 to 20.0 meq/L. 

All solutions are filtered through a polycarbonate membrane having 0.4μm pore size. Soil 

extracts are filtered with a disposable filter unit (MillixTM) having 0.22μm pore size. 

Procedure

The soil extract is obtained as described in 6F1a. Fill a plastic syringe (3 to 10 cc) with 

a solution having a concentration within the range of the sulfate standard. Baseline is 

established using a full-scale μmhos setting of 3 before each determination. This setting is 

adjusted as needed, keeping in the range used for making the determinations on the mixed 

standard. Peak height readings are made on the mixed standard using eight concentrations. A 

curve fitting linear regression equation [y(meq/L) = a1 (PKH) + a0] is established for the sulfate 

standards. Sulfate concentration in the soil extracts is determined by this equation. 

Calculations

See 6F1b. 

Weight Loss (6F2)

Apparatus

Vacuum desiccator. 

Aluminum dish. 

Balance, 0.001-g sensitivity. 

Reagents

Phosphorus pentoxide (P2O5). 

Procedure

Place about 10 g of soil in a tared (Wt A) aluminum dish. Saturate sample with water 

and let stand overnight to air-dry. Place in a vacuum desiccator with P2O5 desiccant. Evacuate 

desiccator and allow to stand 48 hr. Remove dish from desiccator and weigh (Wt B), then place 

in oven at 105° C for 24 hr. Allow dish to cool in desiccator and weigh (Wt C). 

646
Calculations

Gypsum (%) = ((WtB - WtC) x 100)/((WtB - WtA) x 0.1942) 

The theoretical crystal water content of gypsum is 20.91 percent. However, Nelson et al. have 

determined that, in practice, this content averages 19.42 percent. 

References 

Nelson, Klameth, and Nettleton (1978). 

Gypsum Requirement (6F5)

The amount of gypsum needed to replace all of the sodium on the exchange complex 

with calcium is the gypsum requirement. 

Reagents 

Saturated gypsum solution. Place about 25 g gypsum (CaSO4-2H2O) in 5 L water in a large 

flask, stopper, and shake by hand periodically for 1 hr or more. Let settle and decant through a 

filter into storage bottle. Determine calcium concentration by titration of an aliquot with 

standard EDTA solution using Eriochrome black T as indicator. 

EDTA solution. Dissolve 1.25 g di-sodium ethylenediamine tetraacetate in water and dilute to 1 

L. Standardize against solutions containing known concentrations of Ca and Mg. 

Buffer solution. Dissolve 6.75 g ammonium chloride in about 400 ml water. Add 570 ml 

concentrated ammonium hydroxide and dilute to 1 L with distilled water. 

Eriochrome black T indicator. Dissolve 1 g Eriochrome black T in 100 ml triethanolamine. 

Procedure

Weigh 5 g soil into flask, add 100 ml saturated gypsum solution, stopper, and shake for 5 min 

in mechanical shaker. Filter through folded filter paper, discarding the first few milliliters of 

filtrate, which may be cloudy. Pipet a 5-ml aliquot of filtrate into a 125-ml Erlenmeyer flask 

and dilute to 25 or 30 ml with distilled water. Add 10 drops of buffer solution, 2 drops 

Eriochrome black T indicator, and titrate with standard EDTA solution to blue end point. 

Calculations

Gypsum requirement (meq/100 g) = (A - B) x 2 

where 

A = Ca concentration of gypsum solution (meq/L) 

B = Ca + Mg concentration of filtrate (meq/L) 

References 

Richards (1954). 

Aluminum (6G) 

KCl Extraction I (30 min) (6G1) 

Reagents

Potassium chloride (KCl), 1 N. 

647
Procedure

Weigh 10-g soil samples into 125-ml Erlenmeyer flasks. Add 50 ml 1 N KCl to each 

flask, mix several times, and let stand for 30 minutes. Filter through 5.5-cm Whatman No. 42 

filter paper in Buchner funnel, using suction as necessary. Leach each sample as rapidly as 

possible with about five 9-ml portions of KCl, using the first to help transfer the remaining soil 

in the Erlenmeyer flasks to the Buchner funnels. Transfer the extract to 100-ml volumetric 

flasks and dilute to volume with the extracting solution. Or use Allihn leaching tubes and bring 

to standard weight in tared suction flasks. 

References

Lin and Coleman (1960) and Pratt and Bair (1961). 

Aluminon Colorimetry I, Hot Color Development (6G1a)

Reagents

Thioglycolic acid (HSCH2COOH). Dilute 1 ml purified acid to 100 ml with water. 

Aluminon reagent. Dissolve in separate containers 0.75 g 

Aluminon (ammonium aurine tricarboxylate), 15 g gum acacia, and 200 g NH4OAc crystals. To 

the NH4OAc solution add 189 ml concentrated HCl, then the gum acacia, and finally the 

Aluminon. Mix, filter, and dilute to 1,500 ml with water. To get the gum acacia in suspension, 

add slowly to boiling water while stirring constantly. 

Aluminum standard. Add 2.24 g AlCl3·6H2O per liter of water. This solution should be nearly 

250 ppm aluminum. Check concentration of an aliquot containing 10 ppm aluminum by 

analyzing for chloride. 

Procedure

If samples contain less than 5 meq per 100 g aluminum, pipet a 1-ml aliquot of each 

extract into numbered and calibrated test tubes. If more aluminum is present, dilute before the 

aliquot is taken. Dilute to approximately 20 ml with distilled water. Add 2 ml dilute 

thioglycolic acid to each tube, stopper, and shake all the tubes. Pipet 10 ml Aluminon into each 

tube and dilute to exactly 50 ml. The pH should be between 3.7 and 4.0. Stopper and shake all 

tubes. Place tubes in a rack and heat in a boiling-water bath for 4 minutes. Cool in running 

water to room temperature. Transfer samples to reading tubes and measure light transmittance 

at 535 mμ and compare with a standard curve. 

Calculations

Al (meg/100g) = (A/B) x (C/D) x (9/5) 

where 

A = Al from curve (mg/L) 

B = Sample weight (g) 

C = Volume extract (mL) 

D = Volume aliquot (mL) 

Report on ovendry basis. 

References

Chenery (1948) and Yoe and Hill (1927). 

648
Aluminon Colorimetry II, HCl Predigestion (6G1b) 

Procedure

Proceed as in 6G1a but first add 3 ml N HCl to the aliquot and heat for 30 minutes at 80 to 90° 

C. 

References

Hsu (1963). 

Aluminon Colorimetry III, Overnight Color Development (6G1c) 

Proceed as in 6G1a except eliminate boiling-water bath, adjust pH to 4.0, and allow 

color to develop overnight before reading. 

Fluoride Titration (6G1d) 

Reagents

Potassium fluoride (KF), 1 N. Titrate with NaOH to a phenolphthalein end point. This 

eliminates the need for a blank correction in the Al titration. 

Sodium hydroxide (NaOH), 0.1 N, standardized. 

Sulfuric acid (H2SO,), 0.1 N, standardized. 

Phenolphthalein, 0.1 percent. 

Procedure

Add 6 to 8 drops phenophthalein to the leachate in the suction flask (6G1). Titrate with 

standard NaOH to a pink color that persists for 30 seconds or more. Correct for a KCl blank to 

obtain KCl extractable acidity. Then add 10 ml KF, and titrate with standard H2SO4 until the 

pink color disappears. Set aside while other samples are titrated and then complete to a lasting 

colorless end point. If there is a considerable amount of Al, add a few more drops of 

phenolphthalein. 

Calculations

Acidity (meq/100 g) = (A/B) x N x 100 

where 

A = Volume NaOH (mL) 

B = Sample weight (g) 

N = Normality of NaOH 

Al(meq/100) = (A/B) x N x 100 

where 

A = Volume H2SO4 (mL) 

B = Sample weight (g) 

N = Normality of H2SO4

References

Yuan (1959). 

649
Atomic absorption (6G1e)

Apparatus

Perkin-Elmer Model 290 atomic absorption spectrophotometer with nitrous oxide burner 

attachment. 

Reagents

Standard Al solution, 0 to 5 meq per liter. 

Procedure

Dilute sample to within range of standard curve. Compare absorbance with standard 

curve. 

Calculations

Al (meq/100 g) = (A/B) x dilution x (C/10) 

where 

A = Al from curve (meq/L) 

B = Sample weight (g) 

C = Volume extract (mL) 

KCl Extraction II, Overnight (6G2) 

Weigh 10 g soil into 125-ml Erlenmeyer flask. Add 50 ml 1 N KCl and let stand 

overnight. In the morning transfer to filter funnels and leach with an additional 50 ml KCl. 

Aluminon Colorimetry I (6G2a)

Follow procedure for aluminum analysis described in 6G1a. 

NH4OAc Extraction (6G3) 

Prepare soil as described in 5A1. 

Aluminon Colorimetry III (6G3a) 

Follow procedure of 6G1c. 

NaOAc Extraction (6G4) 

Prepare soil as described in 5A2. 

Aluminon Colorimetry III (6G4a)

Follow procedure of 6G1c. 

Sodium Pyrophosphate Extraction (6G5) 

Prepare extract as described in 6C5. 

650
Atomic Absorption (6G5a)

Apparatus

Atomic absorption spectrophotometer. 

Reagents 

Standard Al solution, 0 to 50 ppm or 0 to 160 ppm. 

Procedure

Establish standard curve and match readings from extract to curve readings. Dilute 

where necessary. 

Calculations

Al (pct.) = A x (B/C) x (1/10000) x dilution 

where 

A = Al (ppm) 

B = Volume extract (mL) 

C = Sample weight (g) 

Report on ovendry basis. 

Ammonium Oxalate Extraction (6G6)

Prepare extract as described in 6C6. 

Atomic absorption (6G6a)

Analyze extract as described in 6G5a. 

NH4Cl, Automatic Extractor (6G8) 

Prepare extract as described in 5A9. 

Atomic Absorption (6G8a) 

Apparatus

Atomic absorption spectrophotometer. 

Reagents

Standard Al solutions, 0 to 6 meq/L 

Procedure

Compare absorbance of samples from 5A9 with that of standards at 309.3 nm, diluting 

if necessary. 

Calculations

Al (meq/100 g) = (A/B) x dilution x (C/10) 

where 

A = Al (meq/L) 

651
B = Sample weight (g) 

C = Volume extract (mL) 

Report on ovendry basis. 

Extractable Acidity (6H)

BaCl2-Triethanolamine I (6H1) 

Extractable acidity data are reported on some data sheets as exchange acidity and on 

others as extractable H+. 

Reagents

Buffer solution. Barium chloride, 0.5 N, and triethanolamine, 0.2 N. Add about 90 ml, 1 N HCl 

per liter to adjust pH to 8.2. Protect the buffer solution from CO2 of the air by attaching a 

drying tube containing soda lime (sodium calcium hydrate) to the air opening at the top of the 

solution bottle. 

Replacement solution. Barium chloride, 0.5 N. Add 5 ml buffer solution per liter. Protect the. 

replacement solution from CO2 of the air by attaching a drying tube similar to that used for the 

buffer solution. 

Procedure

Weigh 5 g soil into a 125-ml Erlenmeyer flask. Add 15 ml buffer solution and let stand 

for 30 minutes, swirling occasionally to mix. Use 35 ml buffer solution to transfer all the soil 

solution to a No. 4 Gooch crucible containing a moist Whatman No. 540 filter paper and filter 

into a 500-ml suction flask. The rate of filtration should be such that at least 30 minutes is 

needed to complete the filtering and leaching. Then leach the soil with 100 ml of the 

replacement solution, adding small amounts at a time. It may be necessary to use a larger 

amount of buffer solution to leach allophanic soils high in organic matter with extractable 

acidity of more than 35 meq per 100 g. 

Back-Titration with HCl (6H1a)

Reagents

Hydrochloric acid (HCl), 0.2 N, standardized. 

Brom cresol green, 0.1-percent aqueous solution. 

Mixed indicator. Dissolve 1.250 g methyl red indicator and 0.825 g methylene blue in 1 liter 

90-percent ethanol. 

Procedure

Run a blank by adding 100 ml replacement solution, 2 drops brom cresol green, and 10 

drops mixed indicator to 50 ml buffer solution. Titrate with HCl to a chosen end point in the 

range from green to purple. Add 2 drops brom cresol green and 10 drops mixed indicator to the 

leachate and titrate to the same end point chosen for the blank. Calculate exchange acidity (EA) 

as follows. 

Calculations

EA (meq/100 g) = ((A - B)/C) x N x 100 

where 

A = Volume HCl blank (mL) 

652
B = Volume HCl sample (mL) 

C = Sample weight (g) 

N = Normality of HCl 

Report on ovendry basis. 

References

Peech et al. (1947). 

BaCl2-Triethanolamine II (6H2) 

Apparatus

Sulfur absorption tubes. 

Whatman No. 41 filter paper or glass-fiber filter paper cut to fit sulfur absorption tubes. 

Reagents

Buffer solution. BaCl2, 0.5 N, and triethanolamine, 0.2 N as in 6H1. 

Mixed indicator. Dissolve 1.250 g methyl red and0.825 g methylene blue in 1 liter 90 percent 

ethanol. 

Celite. 

Procedure

Stopper bottom of sulfur absorption tubes with medicine-dropper bulbs and fit to a 300-

ml suction flask with a rubber stopper. Place Whatman No. 41 filter paper in bottom of 

absorption tube, cover with 1/4 inch of acid-washed sand, and add exactly 25 ml buffer 

solution. Weigh 10 g soil and mix with teaspoonful of Celite. Add to the absorption tube by 

means of a funnel. After 30 minutes remove the medicine-dropper bulbs, wash bulbs out with a 

little water, and add washings to absorption tubes. Leach with 25 ml more buffer solution and 

then leach with 100 ml replacement solution in small increments. If necessary, use suction to 

facilitate leaching. 

Back-Titration with HCl (6H2a)

Reagents

Same as in 6H1a. 

Procedure

Titrate with standard HC1, using either 2 drops brom cresol green and 10 drops methyl red or 

10 drops mixed indicator. Use same end point as that chosen for a blank run by leaching sand 

and Celite with 50 ml buffer solution and 100 ml replacement solution. 

Calculations

Use same calculation as in 6H1a. 

KCl-Triethanolamine (6H3)

Back-titration with NaOH (6H3a)

Procedure

Leach 10 g soil with 50 ml KCl-triethanolamine solution and follow by washing with 50 

ml unbuffered 1 N KCL. Add a known volume of standard acid to leachate and washings and 

653
back-titrate with standard alkali (NaOH). Titrate an equal volume of acid to the same end point 

for a blank. 

Calculations

EA (meq/100 g) = ((A - B)/C) x N x 100 

where 

EA = Extractable acidity 

A = Volume NaOH sample (mL) 

B = Volume NaOH blank (mL) 

C = Sample weight (g) 

N = Normality of NaOH 

References

North-Central Regional Research Committee (1955). 

BaCI2-Triethanolamine III (6H4)

Apparatus

60-ml plastic syringe barrels. 

Reagents

Buffer solution. Barium chloride, 0.5 N, and triethanolamine, 0.2 N. Add l N HCl (about 90 

ml/L) to adjust pH to 8.2. Protect the buffer solution from CO2 of the air by attaching a drying 

tube containing soda lime (sodium calcium hydrate) to the air opening at the top of the solution 

bottle. 

Replacement solution. Barium chloride, 0.5 N. Add 5 ml of above buffer solution per liter. 

Protect the replacement solution from CO2 of the air by attaching a drying tube similar to that 

used for the buffer solution. 

"Celite" filter pulp. 

Procedure

Prepare syringe barrels as leaching tubes by forcing a 1-g ball of filter pulp into bottom 

of barrel with syringe plunger. Measure 1.5 g celite and 5 g soil sample into tube. Attach pinch 

clamp to delivery tube of syringe barrel and add approximately 25 ml buffer solution to sample. 

Let stand 30 min, stirring occasionally. Remove pinch clamp and filter with low suction into 

titrator beaker using a total of 50 ml buffer solution followed by 100 ml replacement solution. 

References

Peech (1947). 

Back-Titration with HCl, Automatic Titrator (6H4a)

Reagents

Hydrochloric acid (HCl), 0.33 N, standardized. 

Procedure

Titrate the leachate contained in the 250-ml beaker to an end-point pH setting of 4.60 

with automatic titrator. Carry reagent blank through procedure. 

654
Calculations

EA (meq/100 g) = ((A - B)/C) x N x 100 

where 

EA = Extractable acidity 

A = Volume HCl blank (mL) 

B = Volume HCl sample (mL) 

C = Sample weight (g) 

N = Normality of HCl 

Report on ovendry basis. 

Carbonate (6I) 

Saturation Extract (6I1) 

Acid titration (6I1a)

Reagents

Sulfuric acid (H2SO4), 0.05 N, standardized. 

Phenolphthalein. 

Procedure

Pipet an appropriate aliquot of saturation extract into a 250-ml Erlenmeyer flask or a 

porcelain crucible. The electrical conductivity (EC X 103) of the saturation extract (8A1a) can 

be used to determine the aliquot to be used for carbonate, bicarbonate, and chloride 

determinations. Where EC X 103 is 1.0 or less, use a 10-ml aliquot; if 1.0 to 10.0, use a 5-ml 

aliquot; if more than 10.0, use a 2-ml aliquot. 

Make volume to 50 ml (10 ml for porcelain crucible) with water. To the 50 ml in the 

Erlenmeyer flask, add a drop or two of phenolphthalein. If a pink color is produced, titrate with 

0.05 N H2SO4, adding a drop every 2 or 3 seconds until the pink color disappears. Use this 

solution to determine bicarbonate (6J1a). 

Calculations

Carbonate (meq/L) = (A/B) x N x 2000 

where 

A = Volume H2SO4 (mL) 

B = Volume aliquot (mL) 

N = Normality of H2SO4

References

Association of Official Agricultural Chemists (1945) and Richards (1954). 

Bicarbonate (6J) 

Saturation Extract (6J1) 

Acid Titration (6J1a)

Reagents

Sulfuric acid (H2SO4), 0.05 N, standardized. 

Methyl orange, 0.01-percent aqueous solution. 

655
Procedure

Use solution remaining from carbonate titration (6I1a). To the colorless solution from 

this titration or to the original solution if no color is produced with phenolphthalein, add 4 

drops methyl orange and continue titration to the methyl orange end point without refilling the 

buret. Retain this solution for the chloride determination (6K1a). Make a blank correction for 

the methyl orange titration. 

Calculations

Bicarbonate (meq/L) = ((A - (2 x B))/C) x N x 1000 

where 

A = Total volume H2SO4 (mL) 

B = Volume H2SO4 from 6I1a (mL) 

C = Volume aliquot (mL) 

N = Normality of H2SO4

References

Association of Official Agricultural Chemists (1945) and Richards (1954). 

Chloride (6K) Saturation Extract (6K1) 

Mohr Titration (6K1a)

Reagents

Potassium chromate (K2CrO4) indicator. Dissolve 5 g K2CrO4 in water and add a saturated 

solution of AgNO3 until a permanent slight red precipitate is produced, filter, and dilute to 100 

ml. 

Silver nitrate (AgNO3), 0.05 N, standardized. 

Sodium bicarbonate (NaHCO3), saturated solution (optional). 

Nitric acid (HNO3), 0.1 N (optional). 

Procedure

To the solution from the bicarbonate titration (6J1a) add 6 drops K2CrO4 indicator and 

titrate with AgNO3 to a reddish-orange end point. Make a correction with a blank of 50 ml 

water containing the indicators of both titrations. The laboratory at Riverside, Calif., modifies 

this procedure by adding saturated NaHCO3 solution to a pink end point and neutralizing to a 

colorless end point with HNO3 before adding the indicator. 

Calculations 

Chloride (meq/L) = ((A - B)/C) x N x 1000 

where 

A = Volume AgNO3 sample (mL) 

B = Volume AgNO3 blank (mL) 

C = Volume aliquot (mL) 

N = Normality of AgNO3

References

Association of Official Agricultural Chemists (1945). 

656
Potentiometric Titration (6K1b)

Apparatus

Silver Billet combination electrode, No. 39187. 

Zeromatic pH meter (expanded scale). 

Reagents

Standard silver nitrate (AgNO3), 0.025 N. 

Buffer solutions. Either potassium acid phthalate or trisodium citrate and citric acid. To prepare 

phthalate buffer, weigh 37.5 g potassium acid phthalate and bring to a volume of 500 ml with 

water; 4 ml of this buffer added to a 46-ml solution brings the pH to about 4. To prepare 

trisodium citrate buffer, weigh 43.8 g trisodium citrate and 43.3 g citric acid into 500-ml 

volumetric flask and bring to volume with water. Add a small amount of toluene to the solution 

for storage; 10 ml of this buffer added to a 40-ml solution brings pH to about 4. 

Procedure

Standardize the pH meter by adjusting the needle to a convenient setting (about 0.8) on 

the expanded scale when the electrode is immersed in buffer solution (4 or 10 ml made to 50 

ml) without chloride. To titrate the sample, pipet an aliquot containing as much as 2.0 meq 

chloride into a beaker and add 4 ml buffer. Make to 50 ml. Immerse the electrode and buret tip 

into the beaker and titrate with AgNO3 to the end point previously established for the buffer 

without chloride. 

Calculations

Chloride (meq/L) = (A/B) x N x 1000 

where 

A = Volume AgNO3 (mL) 

B = Volume aliquot (mL) 

N = Normality of AgNO3

Sulfate (6L) 

Saturation Extract (6L1) 

Gravimetric, BaSO4 Precipitation (6L1a) 

Reagents

Concentrated hydrochloric acid (HCl). 

Barium chloride (BaCl2), 10-percent. 

Methyl orange, 0.01-percent. 

Procedure

Pipet an aliquot of saturation extract into a 250-ml beaker. Dilute to approximately 100 

ml with water. Add 2 drops methyl orange and 0.5 ml concentrated HCl to the beaker. Heat to 

boiling and add BaCl2 solution by drops, stirring constantly until precipitation is complete. Let 

stand on hot plate for several hours. Remove from heat and let samples stand overnight. Filter 

through Gooch crucibles, which have been ignited and weighed. Dry in 105°C oven and ignite 

in muffle furnace at 1,200°F (650°C) for 30 minutes. Cool in desiccator and weigh. 

657
Calculations

SO4 (meq/L) = (A/B) x 8.568 

where 

A = BaSO4 (mg) 

B = Volume aliquot (mL) 

References

Richards (1954). 

EDTA Titration (6L1b) 

Apparatus

Repipet, automatic dilutor, pipet range 0.1 to 1.0 ml. 

Titration assembly including a 10-ml buret with magnetic stirrer. 

Reagents

Thymol blue indicator, 0.04-percent. 

Nitric acid (HNO3), 0.4 N. 

Calcium nitrate (Ca(NO3)2), 0.05 N. Dissolve 5.90 g Ca(NO3)2·4H2O in 1 liter CO2-free water. 

EC is 5.15 ± 0.15 mmhos per cm at 25°C. 

Acetone, reagent grade, boiling range 55.5 to 57.5°C 

Ethanol, 95-percent, reagent grade. 

Hydrochloric acid (HCl), 0.01 N. 

EDTA solution, 0.02 N. Standardize against CaCl2. 

Procedure Pipet an aliquot containing 0.01 to 0.05 meq SO4 from soil-water extracts and transfer 

to a 100-ml beaker. Bring volume to 7.5 ± 0.5 ml with water. Add 2 drops 0.04-percent thymol 

blue and 0.4 N HNO3 drop by drop until color changes from yellow to distinct red. Add 2 ml 

0.05 N Ca(NO3)2, 20 ml acetone, and stir. Allow 30 minutes for the precipitate to flocculate. 

Place a 9.0-cm Whatman No. 42 filter paper in a 5.0-cm fluted funnel and fit snugly with water. 

Wash the sides of filter paper with 5 ml 95-percent ethanol from a wash bottle. Transfer the 

precipitate and supernatant to the filter paper with alcohol. Rinse the beaker twice and wash 

filter paper three times, using 3 to 5 ml ethanol per rinse. Allow the alcohol in the filter paper 

to evaporate. Wash the funnel stem thoroughly with water. Place the beaker that contained the 

CaSO4 precipitate under the funnel and wash the filter paper with 3 to 5 ml portions of 0.01 N

HCl until approximately 25 ml is leached. Proceed as in 6N1a, except eliminate carbamate and 

add an extra drop 4 N NaOH to neutralize the 25 ml 0.01 N HCl. 

The amount of sulfate is determined from the Ca++ content in the CaSO4 precipitate. 

Calculations

SO4 (meq/L) = (A/B) x N x 1000 

where 

658
A = Volume EDTA (mL) 

B = Volume aliquot (mL) 

N = Normality of EDTA 

References

Bower and Wilcox (1965), Lagerwerff, Akin, and Moses (1965), and Nelson (1970). 

NH4OAc Extraction (6L2) 

Obtain extract by procedure 5B1. 

Gravimetric, BaSO4 Precipitation (6L2a)

Proceed as in 6L1a. A greater quantity of acid will be needed to lower the pH. 

Otherwise the procedures are the same. 

Nitrate (6M) 

Saturation Extract (6M1) 

Phenoldisulfonic Acid Colorimetry (6M1a)

Reagents

Phenoldisulfonic acid. Dissolve 25 g phenol in 150 ml concentrated H2SO4, add 75 ml fuming 

H2SO4 (13 to 15 percent SO3), and heat at 100°C for 2 hours. 

Standard potassium nitrate (KNO3), 0.010 N. 

Silver sulfate (Ag2SO4), 0.020 N. 

Ammonium hydroxide solution (NH4OH), 1:1, approximately 7 N. Calcium oxide (CaO). 

Procedure

First determine the chloride concentration in an aliquot of saturation extract as directed 

in 6K1a. Pipet another aliquot containing 0.004 to 0.04 meq of nitrate into a 25-ml volumetric 

flask. Add an amount of Ag2SO4 equivalent to the amount of chloride present, dilute to volume, 

and mix. Separate the precipitate by centrifuging the suspension in a 50-ml centrifuge tube. 

Transfer the solution to another centrifuge tube, flocculate any suspended organic matter by 

adding about 0.1 g CaO, and clear by centrifuging again. Pipet a 10-ml aliquot into an 8-cm 

evaporating dish. Evaporate the aliquot to dryness, cool, and dissolve the residue in 2 ml 

phenoldisulfonic acid. After 10 minutes, add 10 ml water and transfer to a 100-ml volumetric 

flask. Make alkaline by adding NH4OH, dilute to volume, and mix. Measure light transmission 

through a 460 mμ filter of solution in an optical cell against that of water in a similar cell. 

Prepare a calibration curve by pipetting 0-, 0.2, 0.4-, 0.8-, 1.2-, and 1.6-ml aliquots of 

standard KNO3 into evaporating dishes and treating as for sample except for additions of 

Ag2SO4 and CaO and the clarifying procedure. 

Calculations

NO3 (meq/L) = (A/B) x 1000 

where 

A = NO3 from curve (meq/L) 

B = Volume aliquot (mL) 

659
References

Richards (1954). 

Diphenylamine (qualitative) (6M1b)

Use this procedure to test for nitrates if there is a significant excess of cations over 

anions in the extract. A quantitative measurement can be made if there is a positive indication 

of NO3 (6M1a). 

Reagents

Diphenylamine in H2SO4. Dissolve 0.05 g diphenylamine in 25 ml concentrated sulfuric acid. 

Store in polyethylene dropper bottle. 

Procedure

Place a drop of extract in a spot plate and add 3 or 4 drops diphenylamine reagent. 

Nitrate is present if a blue color develops. 

References

Treadwell and Hall (1943). 

Calcium (6N) 

Saturation Extract (6N1) 

EDTA titration (6N1a)

Reagents

Sodium hydroxide (NaOH), approximately 4 N. 

Calcium chloride (CaCl2), 0.02 N. Dissolve calcite crystals in HCl and make to volume. 

Murexide. Thoroughly mix 0.5 g ammonium purpurate with 100 g powdered potassium sulfate 

(K2SO4). 

EDTA solution, 0.02 N. Standardize against CaCl2

Sodium diethyldithiocarbamate, 1-percent. 

Procedure

Pipet an aliquot containing 0.02 to 0.20 meq of calcium into a beaker. Add 5 drops 

carbamate, 1 drop NaOH for each 5-ml aliquot, and a suitable amount (15 to 20 mg for a 10-ml 

aliquot) of murexide, mixing after each addition. A magnetic stirrer is helpful. Titrate with 

EDTA to a lavender end point. A blank containing NaOH, murexide, carbamate, and a drop or 

two of EDTA helps to distinguish the end point. If the sample is overtitrated with EDTA, it can 

be back-titrated with standard CaCl2. Retain solution for magnesium determination (6O1a). 

Calculations

Ca (meq/L) = (A/B) x N x 1000 

where 

A = Volume EDTA (mL) 

B = Volume aliquot (mL) 

N = Normality of EDTA 

660
References

Cheng and Bray (1951). 

NH4OAc Extraction (6N2)

Prepare NH4OAc extract as described in 5A1. EDTA-alcohol extraction. 

EDTA-Alcohol Separation (6N2a) 

Reagents

Standard calcium chloride (CaCl2), 5 mg per ml. Dissolve calcite crystals in HCl and make to 

volume. 

Ethanol, 95-percent. 

Standard EDTA. Dissolve 1.25 g disodium ethylenediaminetetraacetate in water and dilute to a 

volume of 1 liter. Standardize against solutions containing known amounts of calcium and 

magnesium. Run the standards through the separation procedure before titrating. 

Sodium hydroxide (NaOH), 10-percent aqueous solution. 

Calcon. Dissolve 1 g Calcon (Eriochrome Blue Black R) in 100 ml triethanolamine. 

Procedure

Pipet 25-ml aliquots from the pH 7, NH4OAc extracts obtained in the total exchangecapacity procedure (5A1) into 100-ml beakers and evaporate to dryness at moderate heat. Cool 

and add 3 ml N HNO3 to dissolve the residue. Transfer the solution quantitatively to 50-ml 

conical centrifuge tubes with ethanol, using a wash bottle with a fine delivery tip. Add 1 ml 6 N

H2SO4. While mixing the contents of the tube by swirling, add approximately 34 ml 95-percent 

ethanol. Cover the tubes and let stand overnight. The next morning remove the covers and 

centrifuge the tubes at about 2000 rpm (Int. No. II centrifuge) for 15 minutes. Decant the 

alcohol solution into 250-ml Erlenmeyer flasks and retain for the magnesium determination. 

Use the CaSO4 precipitate for calcium determination. 

Break up the CaSO4 precipitate with a small steam of water from a wash bottle and 

transfer the precipitate and solution to 250-ml Erlenmeyer flasks. Dilute the solution to a total 

volume of about 100 ml. Place the sample on a magnetic stirrer, add 5 ml 10-percent NaOH, 2 

drops Calcon indicator solution, and titrate with the standard EDTA solution to the blue color 

of a blank carried through the procedure. The pH of the solution should be about 12.5. The 

color change is from red to clear blue. Titrate until the color in the sample and in the blank are 

the same. 

Calculations

Ca (meq/100 g) = (A/B) x N x (C/D) x 100 

where 

A = Volume EDTA (mL) 

B = Sample weight (g) 

N = Normality of EDTA 

C = Volume extract (mL) 

D = Volume aliquot (mL) 

References

661
Barrows and Simpson (1962). 

Oxalate Precipitation I, KMnO4 Titration (6N2b)

Reagents

Oxalic acid (C2H2O4), 5-percent aqueous solution. 

Brom cresol green, 0.04-percent aqueous solution. 

Ammonium hydroxide (NH4OH), 1 N. 

Sulfuric acid (H2SO4), 1 N. 

Standard potassium permanganate (KMnO4), 0.05 N 

Wash solution, saturated calcium oxalate (CaC22O4) 

Asbestos. Digest asbestos in 1 N HNO3 solution containing just enough KMnO4 to give a deep 

purple color. Add more permanganate if the color disappears; digest for 24 hours or until the 

permanganate color is permanent. Destroy the excess permanganate with oxalic acid and wash 

thoroughly on a Buchner funnel. 

Procedure

Transfer an aliquot of the filtrate (5A1) to a 400-ml Pyrex beaker and evaporate to 

complete dryness. Cool, cover the beaker with a watchglass, and slowly add through the lip 10 

ml concentrated HNO3 and 2 ml concentrated HCl. Warm until the reaction has subsided and 

no more brown fumes are given off. Rinse the watchglass into the beaker. Evaporate to dryness 

at low heat to prevent spattering and continue to heat for about 10 minutes to dehydrate the 

salts. Then place the beaker in an electric muffle furnace at about 150°C, heat to 390° ± 10°, 

and hold at this temperature for about 20 minutes. Remove the beaker from the muffle furnace 

and cool. Treat the residue with 3 ml 6 N HCl, evaporate to dryness at low heat, and continue 

heating for about 30 minutes longer to dehydrate silica. Cool and dissolve the residue in 0.1 N

HNO3, using a rubber policeman to loosen the residue. 

Add 5 ml oxalic acid, heat the contents of the beaker almost to boiling, and add 1 ml 

brom cresol green. Adjust the pH of the hot solution to approximately 4.6 by slowly adding 1 N

NH4OH, stirring constantly. Let digest at about 80° C for 1 hour or until the supernatant liquid 

is clear. Collect the CaC2O4 precipitate on a compact asbestos pad in a Gooch crucible or in a 

Whatman No. 42 filter paper in filter funnel. Rinse the beaker four times with water or water 

saturated with CaC2O4 and pour the washings into the crucible. Wash the precipitate five more 

times with water saturated with CaC2O4. 

Remove the Gooch crucible from its holder, rinse the outside, and replace crucible in 

the beaker. If filter paper is used, pierce the paper and wash most of the precipitate into the 

beaker with 3.6 N H2SO4. Wash off excess H2SO4 with water and place filter paper on 

watchglass. Add 100 ml water and 7 ml concentrated H2SO4. Heat to 90°C and stir until 

CaC2O4 is dissolved. Titrate with standard KMnO4 solution to a pink color. Add filter paper to 

solution and titrate to a permanent pink color. 

Calculations

Ca (meq/100 g) = (A/B) x N x (C/D) x 100 

where 

A = KMnO4 (mL) 

B = Sample weight (g) 

662
N = Normality of KMnO4

C = Volume extract (mL) 

D = Volume aliquot (mL) 

Report on ovendry basis. 

References Peech et al. (1947). 

Oxalate Precipitation II, KMnO4 Titration 

(Fe, Al and Mn removed) (6N2c) 

Proceed as in 6N2b but after muffle treatment and before oxalate precipitation, remove 

iron, aluminum, and manganese by the following procedure. 

Reagents

Hydrochloric acid (HCl), 6 N. 

Ammonium hydroxide (NH4OH), 2 N. 

Bromine water, saturated. 

Ammonium chloride (NH4Cl), 6 N. 

Concentrated nitric acid (HNO3). 

Procedure Dissolve salts and oxides by adding 5 ml 6 N HCl and heating on a hot plate until all 

salts and oxides are in solution. Add 75 to 100 ml water and heat the solution until it is nearly 

boiling. Immerse the pH electrodes into the hot solution and precipitate the hydroxides of iron, 

aluminum, and titanium by slowly adding 2 N NH4OH until the meter indicates a pH of 6.2 to 

6.4. Add 2 more drops of NH4OH to neutralize the acidifying effect of the 15 ml saturated 

bromine water, which is slowly added next to precipitate manganese hydroxide. Since bromine 

water lowers the pH of the solution, readjust it to 6.2 to 6.4 with 2 N NH4OH. Heat the solution 

with precipitate until it just begins to boil (l or 2 min on a Bunsen burner) and remove from the 

heat. 

Place on a hot plate at a temperature of 80° to 90°C for 1 hour. Filter when the breaker 

has cooled enough to handle easily. Use an 11-cm Whatman No. 42 filter paper or its 

equivalent. Collect the filtrate in a beaker of the same size as those used for precipitating 

calcium. Wash and police the beaker containing the precipitate with hot 2-percent NH4Cl. 

Wash the precipitate on the filter with the same solution. Five washings are usually enough. To 

the filtrate add 10 ml concentrated HNO3 and evaporate to dryness; add 5.0 ml 6 N HCl, take to 

dryness, and use high heat to dehydrate silica. Proceed with the calcium precipitation (6N2b). 

References

Washington (1930) and Fieldes et al. (1951). 

Oxalate Precipitation, Cerate Titration (6N2d)

Proceed as in 6N2b except substitute the following for the permanganate titration. 

Reagents

663
Ammonium hexanitrate cerate ((NH4)2Ce(NO3)) in molar perchloric acid (HClO4), 0.1 N. Add 

85 ml 70- to 72-percent perchloric acid to 500 ml water. Dissolve 56 g ammonium hexanitrate 

cerate in the acid solution and dilute to 1 liter. 

Ammonium hexanitrate cerate in molar perchloric acid, 0.05 N. Follow the directions for the 

preparation of the 0.1 N solution but use only 28 g cerate. 

Perchloric acid (HClO4), 2 N. Add 170 ml 70 to 72-percent perchloric acid to 500 ml water and 

dilute to 1 liter. 

Nitro-ferroin indicator solution. Dilute a solution of nitro-orthophenanthroline ferrous sulfate 

with water to a convenient working strength. Two to four drops of the solution should give a 

sharp color change at the end point. 

Standardize the cerate solutions against accurately weighed quantities of primary standardgrade 

sodium oxalate. Convenient weights of sodium oxalate are 0.10 to 0.11 g for the 0.05 N

solution and 0.10 to 0.18 g for the 0.1 N cerate solution. Dissolve the sodium oxalate in 100 to 

150 ml 2 N perchloric acid and titrate as directed in the following procedure. 

Procedure

Dissolve the filtered and washed (use water) calcium oxalate in 100 to 200 ml 2 N

perchloric acid. If a paper filter has been used, macerate it before titration. Add 2 to 4 drops of 

nitro-ferroin indicator solution and titrate with 0.05 N or 0.1 N cerate solution, depending upon 

the amount of oxalate present. The solution changes from red to colorless at the end point. 

Calculations

Ca (meq/100g) = (A/B) x N x (C/D) x 100 

where 

A = Volume Cerate (mL) 

B = Sample weight (g) 

N = Normality of Cerate 

C = Volume extract (mL) 

D = Volume aliquot (mL) 

Report on ovendry basis. 

NH4Cl-Ethanol Extraction (calcareous soils) (6N3)

Apparatus

See Fig. 8. 

664
Reagents

Ammonium chloride (NH4Cl), 1 N, in 60-percent ethanol. To make 9 liters of extraction 

solution, dissolve 482 g NH4Cl in 2,835 ml water and add 5,985 ml 95-percent ethanol. Adjust 

pH to 8.5 with 140 to 145 ml NH4OH. 

Celite. 

Procedure 

Fill extraction tube with water, set tube upright in holder, and let most of the water drain 

out. Close screw clamp and place filter paper on plate with a stirring rod. Let remainder of the 

water drain out of tube. The filter paper provides enough tension to keep the bottom part of the 

tube filled with water. Place tube on the rack and add about 1 1/2 teaspoons washed sand. Place 

an extra perforated plate (inverted) on top of the sand and cover the plate with more sand. Place 

heaping teaspoon of Celite on the sand and pour about 20 ml extraction solution into the tube. 

Pour remainder of 400 ml extraction solution into a 500-ml Erlenmeyer flask. Add soil sample 

slowly and then stir with a rod to mix soil and Celite. Allow sample to settle and then place 

filter paper on top of the soil column. Put upper tube in place, stopper, and let stand overnight. 

In the morning, place a 500-ml volumetric flask under the delivery tip and open screw 

clamp on lower extraction tube slowly. When level of liquid is a few milliliters above the soil, 

invert the 500-ml Erlenmeyer flask containing remainder of extraction solution (delivery tube 

in place), place glass tip in the upper tube, and open the pinch clamp. Use the screw clamp on 

lower tube to adjust flow rate through soil column. When all the extraction solution has passed 

through the soil column, remove volumetric flask, make to volume with water, and mix. 

665
EDTA Titration (6N3a)

Pipet a 50-ml aliquot for determination of Ca and Mg into a 100-ml beaker and 

evaporate to dryness. Add 10-ml concentrated HNO3 and 1 or 2 ml concentrated HCl. Cover 

with watchglass, place on hot plate, and heat until no more brown fumes are evolved. Remove 

cover glass, rinse into beaker, and evaporate solution to dryness. Take up residue with 3 ml N

HNO3. Quantitatively transfer solution with ethanol to a 50-ml conical centrifuge tube and 

proceed with determination of Ca according to 6N2a. 

References

Tucker (1954). 

KCl-Triethanolamine Extraction (6N4)

Prepare extract as in procedure 5B2. 

Oxalate-Permanganate Titration (6N4a)

Proceed as in 6N2b. 

EDTA Titration (6N4b)

Reagents

Sodium hydroxide (NaOH), 4 N

EDTA 0.02 N. Dissolve 3.723 g disodium dihydrogen ethylenediamine tetraacetate in water 

and dilute to 1 liter. Standardize the solution against standard CaCl2 prepared in the TEA buffer 

solution. 

Ammonium purpurate (murexide) indicator. Thoroughly mix 0.5 g ammonium purpurate with 

100 g powdered potassium sulfate. 

Eriochrome Black T (Erio T) indicator. Dissolve 0.5 g Erio T in 100 ml of triethanolamine. 

Procedure

Pipet a 5-ml aliquot of extract from procedure 5B3 into a 100-ml beaker. Add 20 ml 

water, 5 drops 4 N NaOH, and 50 mg murexide. Titrate with standard EDTA using a 10-ml 

microburet. Approach the end point slowly (orange-red to lavender or purple). Save the 

solution for the Mg++ determination. 

Calculations

Ca (meq/100 g) = (A/B) x N x (C/D) x 100 

where 

A = Volume EDTA (mL) 

B = Sample weight (g) 

N = Normality of EDTA 

C = Volume extract (mL) 

D = Volume aliquot (mL) 

References

Bower and Wilcox (1965). 

666
Atomic Absorption (6N4c)

Proceed as in 6N1b except use sample from KCl-TEA extraction. 

HF Dissolution (6N5)

Obtain extract as in 7C3. 

Atomic Absorption (6N5a) 

Apparatus Diluter. 

Atomic absorption spectrophotometer. 

Reagents

Standard Ca solutions, 0 to 30 meq/L. 

Procedure

Dilute HF extracts from 7C3 and Ca standards fivefold to twentyfold with water. 

Compare absorbance of samples with that of standards at 442.7 nm. 

Calculations

Ca (pct.) = (A x 10 x dilution x 20.04 mg/meq)/B 

where 

A = Ca (meq/L) 

B = Sample weight (mg) 

CaO (pct.) = Ca (pct.) x 1.40 

Report on ovendry basis. 

Magnesium (6O) 

Saturation Extract (6O1) 

EDTA Titration (6O1a)

Reagents

Buffer solution. Mix 33.75 g NH4Cl with 285 ml concentrated (15 N) NH4OH, add 5 g 

disodium Mg-versenate and dilute to 500 ml. 

Eriochrome Black T indicator. Dissolve 0.5 g Eriochrome Black T (F241) and 4.5 g 

hydroxylamine hydrochloride (NH2OH·HCl) in 100 ml 95-percent ethanol or dissolve 1.0 g 

Eriochrome Black T in 100 ml triethanolamine. 

EDTA 0.02 N. Standardize with magnesium solution. 

Procedure

To the sample just titrated for calcium (6N1a) add 3 or 4 drops concentrated HCl, stir 

until the murexide is destroyed, add 1 ml NH4Cl·NH4OH buffer solution, 1 or 2 drops 

Eriochrome Black T indicator, and complete the titration for magnesium, using EDTA. The end 

point should be a clear blue with no tinge of red. 

667
Calculations

Mg (meq/100 g) = (A/B) x N x (C/D) x 100 

where 

A = Volume EDTA (mL) 

B = Sample weight (g) 

N = Normality of EDTA 

C = Volume extract (mL) 

D = Volume aliquot (mL) 

Report on ovendry basis. 

References

Cheng and Bray (1951). 

NH4OAc Extraction (6O2)

Prepare NH4OAc extraction as described 

EDTA Titration, Alcohol Separation (6O2a)

Reagents

Buffer solution. Dissolve 67.5 g NH4Cl in about 400 ml water. Add 570 ml concentrated 

NH4OH and dilute to 1 liter with water. 

Hydroxylamine hydrochloride (NH2OH·HCl), 5-percent aqueous solution. Prepare fresh 

solution every 10 days. 

Potassium ferrocyanide (K4Fe(CN)6·3H2O), 4-percent aqueous solution. 

Triethanolamine, U.S.P. 

Eriochrome Black T. Dissolve 1 g Eriochrome Black T 

(Superchrome Black TS) in 100 ml triethanolamine. 

Standard magnesium solution, 5.0 mg per milliliter. Transfer 2.500 g unoxidized reagent-grade 

magnesium metal to a 500-ml volumetric flask. Add 150 ml water and 20 ml concentrated HCl. 

When in solution, make to volume with water and mix. Dilute an aliquot of this solution to get 

a solution containing 0.5 mg magnesium per milliliter. 

EDTA, 0.02 N. Standardize with magnesium standard solution. 

Procedure

Place the Erlenmeyer flasks containing the alcohol solution retained from the CaSO4

separation (6N2a) on a hot plate and evaporate the alcohol at moderate heat. Do not evaporate 

to complete dryness. Cool and dilute to 100 ml with water and add 5 ml buffer solution and 10 

drops each of hydroxylamine hydrochloride, potassium ferrocyanide, and triethanolamine. Stir 

and let stand 5 to 10 minutes. Place the sample on the stirrer, add 2 drops Eriochrome Black T, 

and titrate with standard EDTA to the ice-blue end point. The color change is from red through 

wine to ice blue. A blank carried through this procedure usually requires 0.3 to 0.8 ml EDTA to 

668
get the proper ice-blue color. Correct for a blank carried through this procedure and use the 

corrected titration to calculate the magnesium in the sample. 

Calculations

Mg (meq/100 g) = (A/B) x N x (C/D) x 100 

where 

A = Volume EDTA (mL) 

B = Sample weight (g) 

N = Normality of EDTA 

C = Volume extract (mL) 

D = Volume aliquot (mL) 

Report on ovendry basis. 

References Barrows and Simpson (1962). 

Phosphate Titration (6O2b)

Reagents

Sodium hydroxide (NaOH), 0.1 N, standardized. Protect from CO2 of the air with a sodalime 

trap. 

Sulfuric acid (H2SO4), 0.1 N. 

Ammonium hydroxide (NH4OH), concentrated. 

Diammonium hydrogen phosphate ((NH4)2 HPO4), 10-percent solution. 

Brom cresol green, 0.1-percent aqueous solution. 

Hydrochloric acid (HCl), 1:1. 

Carbon-dioxide-free water. Boil water in a 5-liter round-bottom boiling flask for about 15 

minutes. Cool and protect from CO2 of the air with a sodalime trap. 

Procedure

Transfer the filtrate from the calcium determination (6N2b, 6N2c, or 6N2d) to a 400-ml 

beaker, add 10 ml concentrated HN3, cover with a 3.5-inch Speedyvap watchglass and 

evaporate to dryness. Dissolve the residue in 5 ml 1:1 HCl and transfer to a 250-ml Erlenmeyer 

flask, policing twice and rinsing the beaker twice after final policing. The volume of solution 

should be about 75 ml or more. Using 3 to 4 drops brom cresol green indicator, neutralize the 

solution with concentrated NH4OH added by drops. Add 5 ml 10-percent (NH4)2HPO4 and 10 

ml concentrated NH4OH. Heat the solution just to boiling, cool, stopper, and let stand 

overnight. 

Filter through a 9-cm Whatman No. 40 filter paper, pouring the solution down a stirring 

rod. Rinse the flask five times with 1 N NH4OH and pour the rinsings onto the filter. Wash the 

precipitate on the filter five more times with 1 N NH4OH. Place the wet filter paper with 

precipitate on a watchglass and let dry at no more than 40°C until free of ammonia. Place the 

dry filter in the original flask, add 5 drops brom cresol green and 10 ml 0.1 N H2SO4 or more if 

necessary to dissolve the precipitate. The solution should be yellow. After most of the 

precipitate has dissolved, add 50 ml CO2-free water, stopper the flask, and shake vigorously 

669
until the filter paper is macerated. Remove the stopper and rinse it and the flask walls with 

CO2-free water. Back-titrate with standard 0.1 N NaOH to pH 4.5. To determine the correct 

end point, prepare a color standard by pipetting 5 ml potassium dihydrogen phosphate (2-

percent solution) into a 250-ml Erlenmeyer flask, adding 65 ml water, 5 drops brom cresol 

green, and a macerated filter paper. 

Calculations

Mg (meq/100 g) = ((A - B)/C) x N x (D/E) x 100 

where 

A = Volume NaOH blank (mL) 

B = Volume NaOH sample (mL) 

C = Sample weight (g) 

N = Normalitiy of NaOH 

D = Volume extract (mL) 

E = Volume aliquot (mL) 

Report on ovendry basis. 

References

Peech et al. (1947). 

Gravimetric, Magnesium Pyrophosphate (6O2c)

Reagents

Diammonium hydrogen phosphate ((NH4)2HPO4), 10-percent solution. 

Nitric acid (HNO3), concentrated. 

Ammonium hydroxide (NH4OH), concentrated. 

Ammonium hydroxide (NH4OH), 1:1. 

Hydrochloric acid (HCl), 6 N. 

Procedure

Continue analysis on filtrate from oxalate precipitation (6N2b). This filtrate will 

probably fill a 150-ml beaker. Place cover glass on filtrate and heat at a low temperature. When 

volume has been reduced, add 20 ml concentrated HNO3. Evaporate to complete dryness and 

wash cover glass and sides of beaker with water. Dissolve residue in 5 ml 6 N HCl and then 

dilute to about 75 ml. Add 2 or 3 drops brom cresol green and bring pH to 4.6 with 1:1 

NH4OH. Add 5 ml 10-percent diammonium hydrogen phosphate (make up fresh each time). 

Add 10 ml concentrated NH4OH, stir solution vigorously until a precipitate forms, and let stand 

overnight. 

On the next day filter on a 11.0-cm Whatman No. 42 filter paper, rinse beaker five 

times with 1 N NH4OH, and pour washings into the filter. Wash the precipitate in the filter five 

more times with 1 N NH4OH. Place filter in oven to dry (2 to 3 hours) and evolve NH4OH to 

prevent any explosion in the muffle furnace. Place crucibles (Coors 000) with filters containing 

magnesium precipitate in muffle furnace. Raise temperature gradually to 1000°C and hold at 

1000°C for 1 hour. Allow muffle furnace to cool down and remove crucibles. Place in 

desiccator and dry over phosphorus pentoxide (P2O5). Weigh Mg2P2O7 and record. 

670
Calculations

Mg (meq/100 g) = (A/B) x (C/D) x 1.797 

where 

A = Mg2P2O7 (mg) 

B = Sample weight (g) 

C = Volume extract (mL) 

D = Volume aliquot (mL) 

NH4Cl-Ethanol Extraction (calcareous soils) (6O3)

Proceed as in 6N3. 

EDTA Titration (6O3a) 

Proceed as in 6N3a except determine magnesium in alcohol extract by method 6O2a. 

KCl-Triethanolamine Extraction (6O4)

Prepare extract as described in 5B2 or 5B3. 

Phosphate Titration (6O4a)

Proceed as in 6O2b except use extract from 5B2 or 5B3. 

EDTA Titration (6O4b)

Reagents

Concentrated hydrochloric acid (HCl). 

Concentrated ammonium hydroxide (NH4OH). 

EDTA 0.02 N. Dissolve 3.723 g disodium dihydrogen ethylenediaminetetraacetate in water and 

dilute to a volume of 1000 ml. Standardize the solution against standard MgCl2. 

Eriochrome Black T (Erio T) indicator. Dissolve 0.5 g Erio T in 100 ml triethanolamine. 

Procedure

Add 4 or 5 drops concentrated HCl to the solution used for the calcium determination 

(6N4b). Set aside until the murexide turns colorless. Add 15 to 20 drops concentrated NH4OH. 

This should bring the pH between 10.0 and 10.3. Add 1 drop Erio T and titrate with EDTA to a 

clear blue end point. 

Calculations

Mg(meq/100g) = (A/B) x N x (C/D) x 100 

where 

A = Volume EDTA (mL) 

B = Sample weight (g) 

N = Normality of EDTA 

C = Volume extract (mL) 

D = Volume aliquot (mL) 

671
Report on ovendry basis. 

Atomic Absorption (6O4c) 

Proceed as in 6O1b except use samples from the KCl-TEA extract. 

HF Dissolution (6O5)

Obtain extract as in 7C3. 

Atomic Absorption (6O5a) 

Apparatus

Diluter. 

Atomic absorption spectrophotometer. 

Reagents

Standard Mg solutions, 0 to 10 meq/L. 

Procedure

Dilute HF extracts from 7C3 and Mg standards fivefold to twentyfold with water. 

Compare absorbance of samples with that of standards at 285.2 nm. 

Calculations

Mg (pct.) = (A x 10 x dilution x 12.16 mg/meq)/B 

where 

A = Mg (meq/L) 

B = Sample weight (mg) 

MgO (pct.) = Mg (pct.) x 1.66 

Report on ovendry basis. 

Sodium (6P) 

Saturation Extract (6P1) 

Flame Photometry (6P1a) 

Apparatus

Beckman Model DU spectrophotometer with flame attachment. 

Reagents

Standard sodium solutions, 0.0 to 2.0 meq per liter. 

Concentrated hydrochloric acid (HCl). 

Hydrochloric acid (HCl), 6 N. 

Hydrochloric acid (HCl), 0.4 N. 

Concentrated nitric acid (HNO3). 

672
Procedure

Pipet an aliquot of appropriate size (5 to 25 ml) of the saturation extract into a 100-ml 

beaker and evaporate to dryness on a hot plate. Treat the residue with 1 ml concentrated HCl 

and 3 ml concentrated HNO3 and again evaporate to dryness on the hot plate. Repeat the acid 

treatment on the residue. Add 5 ml 6 N HCl to the residue and bring to dryness. Then raise the 

temperature to high for 20 minutes to render the silica insoluble. Wash and filter the residue 

into 50-ml volumetric flasks, using 0.4 N HCl. Determine flame luminosity of samples 

appropriately diluted and compare with luminosity of standard solutions made up with 0.4 N

HCl. The evaporation and dehydration steps are used only where there is enough silica to clog 

the burner. If they are not used, merely dilute the sample. 

Calculations

Na (meq/L) = A x dilution 

where 

A = Na from curve (meq/L) 

NH4OAc Extraction (6P2) Flame Photometry (6P2a)

Proceed as in 6P1a except make standard solutions in NH4OAc. The evaporation and 

dehydration steps can be eliminated. 

Calculations

Na (meq/100 g) = (A/B) x dilution x (C/10) 

where 

A = Na from curve (meq/L) 

B = Sample weight (g) 

C = Volume extract (mL) 

Report on ovendry basis. 

References

Fieldes et al. (1951). 

HF Dissolution (6P3)

Obtain extract as in 7C3. 

Atomic Absorption (6P3a)

Apparatus

Diluter. 

Atomic absorption spectrophotometer. 

Reagents

Standard Na solutions, 0 to 20 meq/L in HF and boric acid. 

Procedure

673
Dilute HF extracts from 7C3 and Na standards fivefold to twentyfold with water. 

Compare absorbance of samples with that of standards at 589 nm. 

Calculations

Na (pct.) = (A x dilution x 23.00 mg/meq)/B 

where 

A = Na (meq/L) 

B = Sample weight (mg) 

Na2O (pct.) = Na (pct.) x 1.35 

Report on ovendry basis. 

Potassium (6Q) 

Saturation Extract (6Q1) 

Flame photometry (6Q1a)

Apparatus

Beckman Model DU spectrophotometer with flame attachment. 

Reagents 

Standard potassium chloride (KCl) solutions ranging from 0.0 to 1.0 meq per liter. 

Procedure

Proceed as in 6P1a. Determine flame luminosity of potassium at 768 mμ and compare 

with that of the standard solutions. 

Calculations

K (meq/L) = A x dilution 

where 

A = K from curve (meq/L) 

References

Fieldes et al. (1951). 

NH4OAc Extraction (6Q2) Flame Photometry (6Q2a) 

Proceed as in 6Q1a except make up standards in NH4OAc solution. 

Calculations

K (meq/100 g) = (A/B) x dilution x (C/10) 

where 

A = K from curve (meq/L) 

B = Sample weight (g) 

C = Volume extract (mL) 

Report on ovendry basis. 

674
Sulfur (6R) 

NaHCO3 Extract, pH 8.5 (6R1) Methylene Blue Colorimetry (6R1a)

References

Kilmer and Nearpass (1960). 

HCl Release (sulfide) (6R2)

Apparatus

Nitrogen tank (water pumped). 

Scrubber. 250-ml Erlenmeyer flask equipped with three-hole rubber stopper to accommodate 

entry and exit for sweep gas, and a 4-foot glass tube to serve as a manometer. 

Reaction flask. 250-ml Erlenmeyer equipped with three-hole rubber stopper to accommodate 

entry and exit for sweep gas, and a buret for adding acid. Reaction flask sits on a magnetic 

stirrer. 

Collection bottles. Two 500-ml bottles (No. 8 rubber stopper), each fitted with a two-hole 

rubber stopper to accommodate entry and exit tubes for sweep gas. The entry tubes should be 

detachable below the rubber stopper (Fig. 9). Attach a pinch clamp to the exit tube to help 

control the flow rate of gases. 

Procedure

Place 10 ml zinc acetate solution in collection flask. Add water to 150 ml volume and 

place flask in train. Add moist sample (collected as in 1A2b) in tared reaction flask (250-ml 

Erlenmeyer), introduce N2 gas (unless sample is run immediately), stopper, and weigh. 

Determine moisture content on a separate sample. Place flask in collection train. Sweep with N2

gas for about 5 minutes. Reduce flow until pressure drops enough so that 50 to 60 ml of 6 N

HCl can be added to reaction flask. Adjust flow of N2 to about 4 bubbles per second in 

collection flask and turn on stirrer. Collect sample for 45 to 60 minutes. Second collection 

bottle should be a blank. Cut flow, disconnect entry tube but leave in collection bottle, remove 

collection bottles, and stopper until ready to titrate. 

Iodine Titration (6R2a)

Apparatus

Iodine applicator, approximately a 50-ml reservoir with stopcock delivery in a two-hole rubber 

stopper (No. 8). Fit a glass tube for air exit through the stopper. 

Buret for thiosulfate. 

Magnetic stirrer. 

Reagents

Iodine 0.1 N, standardized. 

Sodium thiosulfate 0.1 N, standardized. 

Starch indicator. 

Hydrochloric acid (HCl), 6 N. 

675
Procedure

Mix an aliquot of standardized iodine solution and 5 ml of 6 N HCl in iodine applicator. 

Place applicator on bottle and add acidified iodine. Wash contents of applicator, quantitatively, 

into bottle. Remove applicator, stopper bottle, and swirl so that iodine enters the top of the 

entry tube from collection train. Any white precipitate of ZnS should dissolve off entry tube. 

Remove stopper and titrate with standardized thiosulfate until iodine color becomes faint. Add 

1 or 2 ml starch indicator and titrate until blue color changes to clear. The end point is abrupt. 

Stopper bottle and again swirl so that solution passes through the entry tube. Blue color should 

reappear. Again titrate to the end point. Magnetic stirrer can be used to mix the sample. 

Calculations

S (meq/100 g) = ((A - B)/C) x N x 100 

where 

A = Volume thio for blank (mL) 

B = Volume thio for sample (mL) 

C = Sample weight (g) 

N = Normality of thio 

References

Pierce and Haenisch (1955), Johnson and Ulrich (1959), and Chapman and Pratt (1961). 

SO2 Evolution (6R3) 

KIO3 titration (6R3a)

Apparatus

LECO induction furnace model 521. 

LECO automatic sulfur titrator model 532. 

LECO crucibles and lids. 

Oxygen tank and regulator. 

LECO starch dispenser and 0.2-ml scoop. 

Reagents

Potassium iodate (KIO3). 

Potassium iodide (KI). 

Arrowroot starch. 

Hydrochloric acid (HCl) 7.7 N. 

Hydrochloric acid (HCl) 0.18 N. 

Magnesium oxide, (MgO). 

Iron-chip accelerator. 

676
Copper metal accelerator. 

Procedure

Into a tared crucible, weigh approximately 1/2 g of 60-mesh soil, recording gross 

weight. Where high sulfur content might be present, either 1/4 or 1/10 g sample should be run. 

Add 2 scoops of MgO and a scoop of iron chips. Mix thoroughly. Add a half scoop of copper 

accelerator and a scoop of iron chips. Magnesium oxide scoops are heaping; all others are level. 

A cover is placed on the crucible, which is placed on the pedestal and raised into the 

combustion tube for ignition. The LECO instruction manual is followed in setting up the 

furnace and titrator. The timer is set to 8 min and grid tap switch to midposition. These settings 

should be adjusted as needed to get complete fusion of the mixture in the crucible; however, 

plate current should not exceed 350 mA. When the burette reading does not change for 2 min 

and plate current has achieved 300 to 350 mA, the titration is complete and the titer is recorded. 

A blank is run using all ingredients except soil. Sulfate removal before analysis may be 

desirable in some instances. Sample is leached with 50 ml of 7.7 N HCl followed by 500 ml of 

distilled water. 

Calculations

The KIO3 burette is direct reading in percent for a 1-g sample containing up to 0.2 

percent sulfur, provided the KIO3 concentration is 0.444 g/L. With 1.110 g KIO3/L, multiply 

burette readings by 5 (1/2-g sample, 0.005 to 1.00-percent sulfur range). 

References

Smith (1974). 

Phosphorus (6S) 

Perchloric Acid Digestion (6S1) 

Perchloric acid is extremely hazardous and 

subject to explosion if improperly handled. Do not attempt this procedure unless the hazards 

are well understood and the laboratory is specially equipped to handle perchloric acid digestion.

Reagents

Perchloric acid (HClO4), 60-percent. 

Concentrated nitric acid (HNO3). 

Concentrated hydrochloric acid (HCl). 

Procedure

Weigh 2.000 g ovendry soil, ground to approximately 100 mesh, into a 300-ml 

Erlenmeyer flask, add 30 ml 60-percent HClO4, and boil until the soil is white. Continue 

boiling 20 minutes longer to insure complete extraction. Soils high in organic matter should be 

pretreated with HNO3 and HCl to destroy the readily oxidize organic matter. 

Molybdovanadophosphoric Acid Colorimetry (6S1a)

Apparatus

Spectrophotometer. 

Reagents

Solution I. Dissolve 20 g ammonium molybdate ((NH4)6Mo7O24·4H2O) in 250 ml water. 

677
Solution II. Dissolve 1.25 g ammonium metavanadate (NH4VO3) in 300 ml boiling water, cool, 

and add 425 ml 60-percent HClO4. Mix solution I and II and dilute to 1 liter in a volumetric 

flask. Store in a brown bottle. 

Standard phosphorus solution. Weigh out 0.2194 g ovendry KH2PO4 and dilute to 1 liter. This 

solution contains 50 ppm phosphorus. 

Concentrated nitric acid (HNO3) for samples high in organic matter only. 

Concentrated hydrochloric acid (HCl) for samples high in organic matter only. 

Procedure

Transfer the extract into 250-ml volumetric flasks, bring to volume, and let residue 

settle out. Pipet a 25-ml aliquot into a 50-ml volumetric flask, add 10 ml molybdovanadate 

reagent, bring to volume, and mix. 

After 10 minutes, the color is fully developed on most samples and can be read at 460 

mμ. Prepare a standard curve covering the range O to 5 ppm phosphorus in 50 ml solution. Plot 

on semilog paper. 

Calculations

Total P (pct.) = (A/400) x (250/B) 

where 

A = P from curve (ppm) 

B = Volume aliquot (mL) 

Comments 

The color developed is molybdovanadophosphoric acid and is very stable, lasting 2 

weeks or more. 

To destroy organic matter in samples high in organic matter, add 15 ml HNO3 and 5 ml 

HCl. When brown fumes stop coming off, add HClO4, and follow the usual procedure. 

Sediment disturbance during aliquot removal makes it impossible to take more than one 

aliquot a day. If more aliquots are necessary, remove the sediment by filtering the suspension 

into a 250-ml volumetric flack, using Whatman No. 50 filter paper. 

Comparison of results by Na2CO3 fusion and by perchloric acid on lava samples 

indicates that extraction may not be complete for some silicate minerals. Extraction by HClO4

should be complete on common phosphate minerals. 

The volume of molybdo-vanadate reagent added is not critical but must be constant. 

The presence of chlorides slows down color development but does not interfere otherwise. 

References

Sherman (1942), and Kitson and Mellons (1944), and Jackson (1956). 

Adsorption Coefficient (6S2)

Apparatus

Automatic extractor, 24 place. 

Syringes, 60 cc polypropylene; use one sample tube and one extraction syringe per sample. 

678
Reagents

Extractant. Dissolve 4.5 g ammonium fluoride (NH4F) and 85.6 g ammonium chloride (NH4Cl) 

in about 4 L of distilled water, add 92 ml glacial acetic acid and 10 ml concentrated HCl, make 

to 8 L and mix. 

Sulfuric-molybdate-tartrate solution. Dissolve 100 g ammonium molybdate 

[(NH4)6Mo7O24·4H2O] and 2.425 g antimony potassium tartrate [K(SbO)C4H4O6·1/2H2O] in 

500 ml distilled water, heating if necessary but not to exceed 60°C. Slowly add 1,400 ml 

concentrated H2SO4 and mix well. Cool, dilute to 2 L with water and store in refrigerator in 

polyethelene or Pyrex bottle. 

Ascorbic acid solution. Dissolve 88.0 g ascorbic acid in distilled water, dilute to 1 L, mix, and 

store in glass bottle in refrigerator. 

Phosphorus stock standard, 100 ppm. Weigh 0.4394 g dried monobasic potassium phosphate 

(KH2PO4) into a 1-L volumetric flask, dissolve, and make to volume with extractant solution. 

Phosphorus working standards, 2 to 10 ppm. Pipette 2, 4, 6, 8, and 10-ml aliquots of 

phosphorus stock standard into a series of 100-ml volumetric flasks and make to volume with 

extractant solution. The standards contain 2, 4, 6, 8, and 10 ppm P. 

Saturate stock solution. Dissolve 4.394 g dried monobasic potassium phosphate (KH2PO4) in 

distilled water and make to 1 L. 

Saturate working solution. Pipette 20 and 80-ml aliquots of Saturate stock solution into two 1-L 

volumetric flasks. The resulting solutions contain 20 and 80 ppm P. 

Color solution. Measure 40 ml ascorbic solution and 80 ml sulfuric-molybdate-tartrate solution 

into 2 L of distilled water. Bring to 4 L, mix, and store in refrigerator. 

Apparatus

Colorimeter. 

Automatic extractor. 

Shaker. 

Procedure

A. Saturation

Weigh three 2-g subsamples of ovendried soil into 50-ml Erlenmeyer flasks. To the first add 2 

ml distilled water. To the second add 2 ml 20 ppm P solution. To the third add 2 ml 80 ppm P 

solution. Let stand for 1 hr then place in oven at 60° C and dry overnight. 

B. Extraction

To each of the dried samples in the 50-ml Erlenmeyer flasks, add 20 ml extractant 

reagent, and shake for 20 min (Burrell shaker). Extract samples using the automatic extractor. 

C. Developing the color 

Standard curve. Using 50-ml Erlenmeyer flasks, pipette aliquots from the phosphorus 

working standards as follows: 

Flask 1--2 ml extractant 

Flask 2--2 ml 2 ppm P 

679
Flask 3--2 ml 4 ppm P 

Flask 4--2 ml 6 ppm P 

Flask 5--2 ml 8 ppm P 

Flask 6--2 ml 10 ppm P 

Samples. For each sample extracted in part B, pipette 2 ml of extract into clean 50-ml 

Erlenmeyer flasks corresponding with sample numbers. To all flasks, standards, and samples, 

add 25 ml of color solution, swirl to mix, and let stand for 15 min to allow color to develop. 

After color has developed fully, transfer to colorimeter tubes. 

D. Reading the color

Using a wavelength setting of 880 μm, set colorimeter to 100 percent transmittance (T) with 

No. 1 standard containing 2 ml extractant. Read percent transmittance of remaining standards 

and samples. Generally, the standard curve is around the following values: 

(ppm) %T 

 

0 100 

2 77 

4 59 

6 45 

8 33 

10 24 

E. Calculations

1. Develop standard curve by the least squares analysis using concentration of standards as a 

f(ln%t). This results in the equation: 

concentration = m(ln%t) + b 

2. Use this equation to determine solution concentrations of unknowns (leachate). 

Concentration of leachate x 10 is desorbed P in ppm of dry soil. 

3. P retained of that added = P added (desorbed P at that conc. minus desorbed P at zero P 

addition). 

4. Pa (adsorption coefficient) is the slope of the least square regression of P retained as a 

function of phosphorus added, f(P added). 

Example

P T Added P T 

(ppm) (%) (ppm) (%) 

 

0 100 

2 77 

4 59 

6 45 0 84 

8 33 20 73 

10 24 80 45 

 

1. Conc.= -7.023(ln%t) + 32.5158 

680
2. Concentration 

= -7.023 (ln84) + 32.5158 = 1.40 

= -7.023 (ln73) + 32.5158 = 2.38 

= -7.023 (In45) + 32.5158 = 5.78 

Desorbed P (ppm) of dry soil = 1.40 x 10 = 14.0 

= 2.38 x 10 = 23.8 

= 5.78 x 10 = 57.8 

3. P (ppm) retained of that added 

= 0 - (14.0 - 14.0) = 0 

= 20 - (23.8 - 14.0) = 10.2 

= 80 - (57.8 - 14.0) = 36.2 

4. y = 0.4478(P added) + 0.5083 

Pα= 0.4478 

References

Mehlich (1978). 

Boron (6T)

Saturation Extract (6T1) 

Carmine Colorimetry (6T1a)

Refer to USDA Handbook 60, method 17 (p. 100) and method 73b (p. 142). 

Silicon (6V) 

HF Dissolution (6V1)

Obtain extract as in 7C3. 

Atomic Absorption (6V1a)

Apparatus

Diluter. 

Atomic absorption spectrophotometer. 

Reagents

Standard Si solutions, 400 and 800 mg/L in HF. 

Procedure

Dilute HF extracts from 7C3 and Si standards fivefold to twentyfold with water. 

Compare absorbance of samples with that of standards at 252 nm. 

Calculations

Si (pct.) = (A x 10 x dilution)/B 

where 

A = Si (mg/L) 

B = Sample weight (g) 

681
SiO 2 (pct) = (pct) x 2.14 

Report on ovendry basis. 

MINERALOGY (7) 

Instrumental Analyses (7A) 

Preparation (7A1) 

The treatment to be used in preparing samples depends on analysis objective and 

sample composition. 

Carbonate Removal (7A1a)

Reagents

Sodium acetate (NaOAc), N, pH 5.0. Dissolve 82 g NaOAc, 27 mL glacial acetic acid L-1, adjust to pH 5.0. 

Procedure

Place 5 g soil in a 90-ml centrifuge tube, add 40 ml N NaOAc, pH 5.0, and heat at 95°C 

for 30 minutes, stirring occasionally. Centrifuge at 1,600 rpm for 5 minutes and decant 

supernatant liquid. Repeat if necessary until carbonates are removed. Wash twice with N

NaOAc, pH 5.0. Save decantates for calcium and magnesium analysis. One washing is enough 

to prepare neutral or basic noncalcareous soils for optimum hydrogen peroxide treatment. 

References

Jackson (1956). 

Organic-Matter Removal (7A1b)

Reagents

Hydrogen peroxide (H2O2), 30- to 35-percent. 

Procedure

Transfer sample to a 250-ml tall breaker, using a minimum of water, and add 5 ml 

H2O2. When frothing subsides, heat at 90° C. Continue to watch for frothing. Add 5- to 10-ml 

aliquots of H2O2 each hour until 25 to 30 ml H2O2 has been used. Wash five times, removing 

water by filter candles. Transfer to a 90-ml centrifuge tube. 

References

Kilmer and Alexander (1949). 

Iron Removal (7A1c) 

Reagents

Sodium bicarbonate (NaHCO3), N. 

Sodium citrate (Na3C6H5O7), 0.3 M. 

Sodium dithionite (Na2S2O4) powder. 

682
Procedure

If iron reduction is intended, add 5 ml N NaHCO3 and as much as 40 ml 0.3 M sodium 

citrate. Heat to 70°C (not above 80°C) in a water bath and add 1 to 2 g Na2S2O4, stir for 1 

minute, and then stir intermittently for 15 minutes. Decant supernatant liquid and save for iron 

analysis. Repeat treatment as needed if soil is high in iron. Wash twice with 0.3 M sodium 

citrate. 

References

Aguilera and Jackson (1953) and Mehra and Jackson (1960). 

Disaggregation and Particle-Size Fractionation (7A1d)

Reagents

Sodium bicarbonate (NaHCO3), pH 9.5 to 10.0. 

Sodium metaphosphate (NaPO3). Prepare as in 3A1. 

Procedure

Use NaHCO3 solution or sodium hexametaphosphate-sodium bicarbonate as a 

dispersing agent. Use hexametaphosphate carefully with amorphous materials since phosphates 

may be precipitated. A dilute HCl treatment may be useful for some highly allophanic soils. Do 

not use mechanical blenders for disaggregation if silt and sand are to be studied because they 

fracture large quartz grains. Separate sand from silt with a 300-mesh sieve and further separate 

the sands, using a nest of sieves (3A1). Separate clay (<2μ) from silt by centrifuging at 750 rpm 

for 3 minutes (International No. 2 centrifuge with No. 240 head and solution depth of 10 cm). If 

silt and sand are to be studied, save these fractions in small vials after drying and weighing. If 

interested in separating fine clay (<0.2μ) from the coarse clay (0.2μ to 2μ), centrifuge at 2,400 

rpm for 30 minutes with a solution depth of 10 cm. Adjust time according to temperature. Add 

50-ml aliquots of clay suspension after each centrifugation until the required amount of clay is 

obtained. Make each suspension of coarse and fine clay to known volume and determine its 

concentration and the concentration of the whole clay. 

References

Kilmer and Alexander (1949) and Jackson (1956). 

Particle-Size Distribution Analysis (PSDA) Pretreatment (7A1e) 

Mineralogical analysis can be performed on samples from the particle-size distribution 

analysis (3A1). These samples have undergone peroxide digestion and sodium metaphosphate 

dispersion. 

X-ray Diffraction (7A2) 

The minerals in soil clays of greatest interest are mostly flaky or platy, e.g., kaolinite, 

illite (mica), vermiculite, chlorite, and montmorillonite. They are most readily identified and 

distinguished from one another by observing the effect of different treatments on the 

interplanar spacings along the axis perpendicular to the platy surfaces. X-ray diffraction 

produces peaks on a chart corresponding to the various angles (2R) of goniometer from which 

the crystallographic spacing of the mineral or minerals can be calculated by Bragg's law. Tables 

of spacings corresponding to angles have been published in U.S. Geological Survey Circular 29 

(Switzer et al. 1948). 

The pretreatment used to distinguish montmorillonite from vermiculite and chlorite and 

to identify illite is saturation of the exchange complex of the clay with magnesium and 

treatment with ethylene glycol or glycerol. With this treatment, montmorillonite has a 

683
distinctive interplanar spacing of 17 Angstroms (17 A) to 19 A. Chlorite and vermiculite keep a 

14 A spacing and mica a spacing of 10 A. To distinguish vermiculite from chlorite and to 

identify kaolinite, which has a 7 A spacing, the pretreatment consists of saturating the clay with 

potassium and heating on a glass slide at 500°C. Intermediate heat treatments 110 and 250°C, 

can be used to study interlayering in the collapsing minerals or other special problems. After 

the 500°C treatment, vermiculite and montmorillonite collapse completely to 10 A kaolinite 

becomes amorphous and chlorite still shows 14 A and sometimes 7 A peaks. Interstratified 

forms of these minerals are indicated by spacings intermediate between those of the individual 

components. 

Clay suspensions are dried as thin films so that the plates are parallel to one another 

(preferred orientation). This results in greater X-ray diffraction peak intensities. For 

identification and semiquantitative estimation of nonplaty minerals such as quartz, feldspars, 

and crystalline iron and aluminum oxides, randomly oriented dry-powder samples can be used. 

This dry-powder method was used for nearly all analysis, including clay fractions, before 1951. 

Various techniques are used to prepare the ion-saturated clays and to improve their 

parallel orientation. Details can be obtained from the soil survey laboratories. 

References

Brindley (1951), Brown (1961), Brunton (1955), Grim (1953), Jackson (1956), and Switzer et 

al. (1948). 

Thin film on Glass, Solution Pretreatment (7A2a)

Reagents

Potassium chloride (KCl), N. 

Magnesium acetate (Mg(OAC)2), N. 

Magnesium chloride (MgCl2), 1 N. 

Glycerol, 10-percent in ethanol by volume. 

Procedure

Place an aliquot containing 50 mg clay in a 50-ml centrifuge tube. All a few ml 1 N

KCl, centrifuge, and discard the clear supernatant. Combine sediments if necessary to get 50 

mg in the tube. Wash four times by suspending and centrifuging in 20-ml portions N KCl. 

After the last washing with N KCl, wash with water until some of the clay remains suspended 

after centrifuging. Add a few drops of acetone or centrifuge at higher speed, or both, to 

flocculate the clay. Discard the supernatant. Clays are now free of chloride. Suspend the 

sediment in water and adjust the volume of the suspension to yield the desired weight of clay 

per slide. For most clays 50 mg per slide (27 by 46 mm) gives maximum intensity of reflection 

with minimum peeling of clay films. For amorphous clays, 25 mg per slide is adequate if glass 

slides are dried in a low-humidity atmosphere. 

For magnesium saturation and glycerol solvation place an aliquot containing 100 mg 

clay in a 50-ml centrifuge tube. Wash twice with N Mg(OAC)2 acetate and then three times 

with N MgCl2. Wash the suspension free of chloride or until clay disperses. Place 2.5 ml clay 

suspension containing 50 mg clay on a glass slide (25 mg clay if the clay is amorphous). 

Solvate the remaining clay in the test tube with glycerol (about 1/2 ml of 10-percent glycerol in 

ethanol per 50 mg clay). Mix well and pipet 50 mg clay onto the glass slide. The slide should 

be moist but not wet. Or prepare the glycerol slide by adding 10-percent glycerol, a drop at a 

time, to the slides until the clay film is moist. 

684
Thin Film on Glass, Resin Pretreatment (7A2b)

Reagents

Potassium-charged resin (Dowex 50W-X8). 

Magnesium-charged resin (Dowex 50W-X8). 

Glycerol, 10-percent in ethanol by volume. 

Procedure

Add 1/4 teaspoon K-charged resin to 50 mg clay in a 1 ml volume in a 50-ml centrifuge 

tube. Mix and transfer a 1-ml aliquot to a glass slide (27 by 46 mm). Take the aliquot from the 

top of the suspension to avoid removing the resin. 

Magnesium-clay and Mg-glycerol-clay slides can be prepared using a Mg-charged 

cation exchange resin. Add 1/2 teaspoon Mg-charged resin to the clay suspension (100 mg clay 

in a 4-ml volume) in a 50-ml centrifuge tube. Mix with the suspension, remove 1-ml aliquot, 

and place it on a glass slide. Add approximately 1/2 ml 10-percent glycerol in ethanol to the 

tube. Mix and transfer a 1-ml aliquot to a glass slide or use a Mg-clay slide for both Mg and 

Mg-glycerol solvated slides. Record a diffraction pattern for the Mg-saturated clay film. After 

solvating the clay film with 10-percent glycerol solution, record a second X-ray pattern. 

References Rex (1967). 

Thin film on Glass, Sodium Metaphosphate Pretreatment (7A2c)

Shake soil overnight in sodium metaphosphate solution (3A2). Centrifuge to separate 

the clay or siphon off the clay. Pipet about 50 mg clay to a glass slide (47 by 26 mm). 

Concentrate the clay suspension if necessary. Scan the clay film at room temperature, again 

after heating to 500°C. The clay film is Na+ saturated. The sodium metaphosphate peaks do not 

interfere with peaks of the more common clay minerals in this quick check method. 

Thin Film on Tile, Solution Pretreatment (7A2d)

Apparatus

Ceramic tile (porous precipitate drying plate, sawed into 27- by 46- by 7-mm blocks). 

Procedure

Prepare clay suspensions as in 7A2a except dry the suspensions on ceramic tile blocks. 

Clay suspensions dry in a few seconds on tile, preventing particle-size segregation. Partly 

immerse the Mg-saturated clay films in a 10-percent glycerol solution. The porous tile rapidly 

transfers the glycerol to the clay film. Blot off excess glycerol before recording the X-ray 

pattern. 

Thin Film on Tile, Resin Pretreatment (7A2e)

Prepare clay suspensions as in 7A2b. Dry on ceramic tile blocks as in 7A2d. Solvate 

with glycerol as in 7A2d. 

Thin Film on Tile, Sodium Metaphosphate Pretreatment (7A2f)

Prepare the sample as in 7A2c. Pipet the clay onto ceramic tile blocks as in 7A2d. 

Follow method 7A2c for the other treatments. Or solvate with glycerol as in 7A2d. 

685
Powder Mount, Diffractometer Recording (7A2g)

Distinguishing dioctahedral and trioctahedral minerals requires random orientation of 

the sample. There is no completely satisfactory method for preparing a random mount, but 

several techniques are used. 

Pack the sample in a box mount against a glass slide. When the box is full, tape the 

back of the box. Invert the box and remove the slide to expose the sample to X-rays. For more 

random packing, sprinkle the dry sample (ground to <100 mesh) on double stick tape fixed on a 

glass slide or on a thin film of Vaseline on a glass slide. Scan the sample by X-ray and 

measure the reflections with a geiger, proportional, or other counter. 

Quick checks for whole samples, particularly for nonlayered minerals, can be made 

with a modified powder mount. Form the sample into a thick slurry, apply to a glass slide, and 

let dry. This for convenience rather than random orientation. 

Powder Mount, Camera Recording (7A2h)

Photographic plates are still the best means of identifying minerals. Mount the sample 

in the center of a circular X-ray camera. Record the X-ray reflections on photographic film 

placed in a cylindrical film holder inside the camera. All diffraction peaks are recorded 

simultaneously. 

Thin Film on Glass, NaPO3 Pretreatment II (7A2j) 

Apparatus

Hypodermic syringe (1.0 cc). 

Glass slides 24 x 46 mm or 14 x 19 mm. 

International No. 2 centrifuge with a No. 240 head. 

100-ml centrifuge tubes (plastic). 

Reagents

Glycerol-water mixture (1:8 glycerol-water). 

Sodium hexametaphosphate solutions. 

Procedure

Shake approximately 5 g ovendried soil (<2 mm) overnight with 5 ml sodium 

hexametaphosphate solution (3A1) and 35 ml of water in a 100-ml centrifuge tube, centrifuge 

at 750 rpm for 3 min for a 10-cm suspension depth, and decant clays. Draw about 0.5 cc of clay 

suspension into the syringe. Expel approximately 0.2 cc of the clay suspension onto an area 

approximately 20 x 27 mm in a band across the middle of a 46- x 27-mm slide or expel 

approximately 0.1 cc of clay suspension, containing approximately 6 mg of clay, onto and 

covering the 14- x 19-mm slide. Prior to the deposition of the clay suspension, one small drop 

of glycerol-water mixture is placed on the slide which is to be solvated. Prepare four slides for 

X-ray diffraction: 1) Na+

--room temperature, 2) Na+--solvated, 3) Na+--heated 2 hr at 300°C, 

and 4) Na+--heated for 2 hr at 500°C. 

Powder Mounts (7A2k)

Two procedures are used for random orientation of mineral separates. In the first 

procedure, double-stick tape is affixed to a glass slide, a surplus of the sample is sprinkled onto 

the tape, the excess material is removed, and the slide is scanned by X-ray analysis. In the 

second procedure, a <2-mm soil sample is ground finer than 100 mesh prior to slide 

686
preparation. A thin film of Vaseline is applied to a glass slide, the 100-mesh sample is added, 

the excess removed, and the slide is scanned by X-ray analysis. 

For quick check of a <2-mm sample, particularly for nonlayered minerals, a small 

portion is ground to less than 100 mesh and placed on a glass slide. Water is applied a little at a 

time until a thick slurry is formed. The slurry is allowed to dry and the slide is scanned by Xray analysis. This method is also applicable for specific mineral separates, very fine sands or 

silts. 

References

Brown (1961), Jackson (1956). 

Differential Thermal Analysis (7A3)

Differential thermal analysis (DTA) is a measurement of the difference in heat absorbed 

by or evolved from a sample of soil material and a thermally inert material as the two are 

heated simultaneously at a constant rate. Thermocouples are in contact with two platinum pans; 

one pan contains an unknown and the other pan contains an inert material of similar 

composition. If a reaction occurs, a difference in temperature is registered on a stripchart 

recorder or photographically. The magnitude of the difference depends on the nature of the 

reaction and amount of reacting substance in the unknown. The temperature at which the 

reaction occurs identifies the substance if enough is known about the sample to predict the 

possibilities. 

Apparatus

Columbia scientific instrument (CSI) system 200. 

Mortar and pestle. 

Analytical balance. 

Desiccator. 

Reagents

Reference sample, calcined kaolinite, 2 to 20 μ. 

Ethyl alcohol, 95 percent. 

Magnesium nitrate (Mg(NO3)2·6H20 

Procedure

The decanted clay from 7A2i or 7A2j is air-dried, ground in alcohol to approximately 

100 mesh, and stored in a desiccator with Mg(N03)2·6H2O. A 3- to 7-mg sample is placed on a 

small platinum pan in the sample holder. The temperature of the kaolinite reference sample and 

clay sample is increased at a rate of 20°C per minute to a maximum of 900°C. The sample can 

be heated in air or nitrogen. 

The common endothermic reactions studied or recorded are loss of structural water in 

gibbsite, goethite, and kaolin and loss of carbon dioxide in carbonates. Change of state or 

rearrangement of crystal lattices can be either exothermic or endothermic. Oxidation reactions 

such as burning of carbon and oxidation of ferrous iron are exothermic. 

Loss of structural hydroxyls can be measured quantitatively by calibrating areas of 

peaks of known mixtures of standard minerals, as is done commonly to determine the 

percentage of kaolin and gibbsite in soils. The standard curves are prepared by running the 

known mixtures under the same conditions as the unknowns. Kaolin has an endotherm at 500° 

to 600°C and gibbsite, at 310°C. Each worker should prepare a set of standard curves. 

687
Endotherms at about 120°C indicate surface-adsorbed water. Montmorillonite produces 

a double peak at a low temperature if saturated with a divalent cation. The proportion of this 

mineral can be estimated if samples are kept in an atmosphere with a high (70 to 80 percent) 

relative humidity for 24 hr or more before analysis. Allophane has a broad endotherm at about 

160°C. 

Samples can be any well-powdered material, whole-soil, or separated fractions. Organic 

matter is objectionable because it produces irregular exothermic reactions that obscure the 

important peaks. If a clay separate is used, it must be washed free of hygroscopic salts or salts 

containing water of crystallization. 

References

Grim (1968), McKenzie (1957), and Tan and Hajek in Dixon and Weed (1977). 

Thermal Gravimetric Analysis (7A4) 

CSI Stone Model 10002B (7A4a)

Thermal gravimetric analysis is the detection and measurement of weight changes in a 

sample of soil material as the sample is being heated or cooled over a specific temperature 

range. 

Apparatus

CSI Stone Model lOOOB used in conjunction with an RC-202 recorder-controller. Furnace is 

water cooled, with a rapid cooling Kanthal element. Furnace is capable of operation at 

temperatures of up to 1,200°C. 

Procedure

Prepare sample as described in 7A3 and place in balance pan suspended above 

thermocouple assembly. Heat sample at rate of 20°C/min to desired temperature. If a weight 

loss occurs, it is registered on a stripchart recorder. The magnitude of the weight loss depends 

on the reaction and the amount of reacting substance in the unknown. The temperature at which 

the reaction occurs usually identifies the substance. 

Infrared Analyses (7A5)

Soil or clay samples (7A2j) are incorporated into a potassium bromide (KBr) pellet for infrared 

analyses. Sample concentration in the pellet ranges from 0.1 to 1 percent. 

Reagents

Potassium bromide, spectroscopic grade. 

Apparatus

Infrared spectrometer. Perkin Elmer Model 283. 

Pellet die. 

Hydraulic press. 

Analytical balance. 

Procedure

Mix 0.30 g KBr and 1 mg of sample in mortar and pestle. Transfer the mixture to the 

pellet die, and place die in hydraulic press. Apply 8 tons of pressure for 1 min. Place pellet in 

instrument holder and scan for 12 min. Peaks produced on chart recorder are used to identify 

the substance. 

688
References

J. L. White in Dixon and Weed (1977). 

Optical Analyses (7B) 

Grain Studies (7B1) 

Grain mounts, Canada balsam (7B1b) 

For Canada balsam, heat slide plus balsam for 15 min at 125°C. Add mineral grains, 

stir, heat for an additional 5 min, place cover glass in position and press firmly, remove slide 

from hot plate, and cool. 

The refractive index of Canadian balsam is close to that of quartz, which helps to 

distinguish quartz from other colorless minerals, particularly the feldspars. Other available 

commercial media cover the refractive index range of 1.53 to 1.55. Piperine with a refractive 

index of 1.68, which is close to that of many of the common heavy minerals, is best for 

mounting them. 

Electron Microscopy (7B2)

Electron microscopy gives information on particle size and morphology of clay-size 

particles. Evidence of clay formation or weathering can also be seen. Positive identification of 

halloysite often depends on observation of rolled structures under the electron microscope. 

Procedure

Place a drop of dilute clay suspension on a 200-mesh copper grid. After drying, insert 

this grid in the microscope. 

Total Analysis (7C)

Chemical (7C1)

The procedures follow the standard procedures for rock analysis set forth by Hillebrand 

and Lundell (1929) and modified by Robinson (1920) and by Shapiro and Brannock (1956). 

X-ray Emission Spectrography (7C2)

X-ray emission spectrography is elemental analysis by measuring the X-ray 

fluorescence produced by bombarding a sample with high-energy X-rays. Each element yields 

fluorescent radiation of unique wave lengths, one of which is selected for measurement by 

using an analyzing crystal that diffracts according to Bragg's law. The intensity of the 

fluorescent radiation is generally proportional to the amount of the element present, but this is 

affected by sample homogeneity, particle size, and the absorption and enhancement of radiation 

by any other elements present in the sample (matrix effects). These effects can be overcome or 

compensated for by (1) comparing the intensities with those of standards of similar 

composition prepared in a similar manner, (2) fusing both samples and standards in borax or 

lithium borate to eliminate particle-size effects and to reduce matrix effects, and (3) making 

matrix corrections by calculation the absorption-enhancement coefficient of the sample for the 

particular radiation being measured. 

References

Vanden Heuvel (1965). 

689
Surface Area (7D)

Glycerol retention (7D1) 

Apparatus

Weighing cans. 

Reagents

Glycerol, 2-percent. 

Procedure

Ovendry a clay sample (about 0.2 g) at 110°C for 2 hours. Cool and weigh. Add 5 ml 

2-percent glycerol solution and mix. Heat in oven containing free glycerol at 110°C to constant 

weight. Record weight. 

Calculations

To calculate the percent of glycerol retained subtract weight of ovendry sample from 

weight of glycerol and ovendry sample, divide by weight of ovendry sample, and multiply by 

100. For the surface area of noncollapsible minerals (m2/g), multiply glycerol retained by 19.1. 

References

Kinter and Diamond (1958). 

MISCELLANEOUS (8) 

Saturation Extract, Mixed (8A)

Saturation Extract (8A1)

Apparatus

Richards or Buchner funnels. 

Filter rack or flask. 

Filter paper. 

Vacuum pump. 

Extract containers such as test tubes or 1-oz bottles. 

Procedure

Transfer the saturated soil paste to a filter funnel with a filter paper in place and apply 

vacuum until air begins to pass through the filter. Collect the extract in a bottle or test tube. If 

carbonate and bicarbonate are to be determined on the extract, add 1 drop of 1000 ppm sodium 

hexametaphosphate solution for each 25 ml of extract to prevent precipitation of calcium 

carbonate on standing. 

References

Richards (1954). 

Conductivity of Saturation Extract (8A1a)

Apparatus

Conductivity bridge. 

690
Conductivity cell. 

Procedure

Determine temperature of the saturation extract obtained by methods 8A1 or 8B1. 

Draw the extract into the cell and read the meter. Correct for temperature and cell constant 

using Table 1 (Table 15, Richards 1954) and report as electrical conductivity, mmhos per 

centimeter at 25°C. If the instrument fails to balance, dilute the extract 1:9 with distilled water 

and redetermine. The conductivity of the diluted extract is approximately one-tenth the 

conductivity of the saturation extract. 

References

Richards(1954). 

Conductivity of Saturation Extract (quick test) (8A1b) 

Apparatus

Extractor, miniature Richards-type (Fig. 10). 

Conductivity cell, micropipet. 

Filter paper, glass fiber, 3.0 cm. 

Vacuum pump. 

Procedure

Add 1 tablespoon soil to a 100-ml beaker or container. Make a saturated paste as in 8A. 

Place filter paper in recess of extractor and moisten with water. Insert the tip of the pipet 

691
conductivity cell through the other end of the extractor and into the paste. Apply suction to the 

cell until full. Proceed as in 8A1a. 

Bureau of Soils Cup, Resistance (8A2)

Apparatus

Wheatstone bridge. 

Bureau of Soils electrode cup. 

Procedure

Rinse the soil cup with water, dry, and fill with soil paste (8A). Jar cup to remove air 

bubbles strike off excess paste so the cup is level full, and connect cup to the bridge. Record 

resistance (ohms) and temperature of soil paste (°F). 

Calculations

Convert resistance of the soil paste in ohms to percentage of soluble salt by using the 

tables and formulas on pages 346-349, Soil Survey Manual. 

References

Richards (1954) and Soil Survey Staff (1951). 

Saturated, Capillary Rise (8B)

Apparatus

Sand table. Mariotte bottle. 

Filter paper. 

Polyethylene dish with lid. 

Procedure

Weigh 250 g airdry soil into cups made from Whatman No. 52 (15-cm) filter paper and 

place them on a sand table wetted at 5-cm tension with water. The sand table used consists of 

two nested plastic dishpans. The outer pan holds distilled water, which is kept at a constant 

level by a Mariotte bottle. The inner pan, containing medium to fine (35 to 80 mesh) pure 

quartz sand, rests on rubber stoppers and is suspended in the distilled water. Its perforated 

bottom is covered with a fine cloth-mesh screen that permits water to move upward by 

capillarity through the sand to the table surface. The sand on the table surface is then smoothed 

and covered with an absorbent paper towel. Lightweight porous firebricks can be used in place 

of the sand table. 

Keep the samples on the sand table 16 to 18 hours, remove them, and weigh. Water 

adsorption drops rapidly after an initial wetting of 2 hours and the rate becomes very slow after 

6 to 9 hours. Moisture moves toward the top and center of the sample, which is wetted last, 

insuring retention of soluble salts in the soil. Calculate moisture at saturation from the wet- and 

dry-soil weights, correcting for the wet and dry filter paper weights. Add airdry moisture 

percentage to moisture at saturation and report on ovendry basis. After the wet weighing, 

transfer the sample to a pint polyethylene refrigerator dish, mix briefly with a spatula, and 

determine the pH. Keep a lid on the dish whenever possible to reduce evaporation. 

References

Longenecker and Lyerly (1964). 

Saturation Extract (8B1) 

692
Proceed as in 8A1, using the saturated paste obtained by method 8B. 

Conductivity of Saturation Extract (8B1a)

Proceed as in method 8A1a except use saturation extract obtained by method 8B1. 

Reaction pH (8C) 

Soil Suspensions (8C1) 

Water dilution (8C1a) 

Procedure

For 1:1 dilution add an equal weight of water to 20 or 30 g soil in a 50-ml beaker or 

paper cup. Stir at regular intervals for about an hour. Measure pH of the soil suspension with a 

glass electrode, stirring well just before immersing the electrodes in the suspension. For other 

dilutions vary the amount of soil, keeping the volume of water constant. 

KCl (8C1c)

Procedure

Proceed as in method 8C1a except use N KCl instead of water. 

CaCl2 (8C1e)

Proceed as in 8C1a except use 0.01 M CaCl2. This procedure can be combined with 

8C1a by adding an equal volume of 0.02 M CaCl2 to the soil suspension prepared for the water 

pH. Stir twice at 15-minute intervals before reading. The soil-solution ratio will be 1:2, but the 

pH difference between 1:1 and 1:2 suspensions is negligible. 

References

Schofield and Taylor (1955) and Peech (1965). 

Literature Cited 

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696
697

SOIL Hayter silt loam SOIL Nos. S63Ky-74-6 LOCATION McCreary County, Kentucky

SOIL SURVEY LABORATORY Beltsville, Maryland LAB Nos. 63776-63781

 1Blb Size class and particle diameter (mm) 3A1 

 Total Sand Silt 3B2 Coarse fragments 3B1 

 >2, Vol >2, Wt 

 Very Very 2-20 20-75 

Depth Hori- Sand Silt Clay Course Course Med. Fine Fine Int. III Int. II pct. of pct. of pct. of 

(in) Zon (2- (0.05- (< (0.5- (0.25- (0.1- (0.05- (0.02- (0.2- whole whole <--- ---> 

 0.05) 0.002) 0.002) (2-1) (1-0.5) 0.25) 0.1) 0.05) 0.02) 0.002) 0.02) (2-0.1) soils soils <75 mm 

 <---------------------------------------------------------------------- Pct. of < 2 mm --------------------------------------------------------------------> 

1/2-5 Ap2 15.0 59.0 26.0 3.8 1.9 0.6 1.6 7.1 15.7 43.3 23.9 7.9 23 36 21 -- 

5-10 B1 15.0 57.4 27.6 3.0 1.9 0.6 1.1 8.4 14.6 42.8 23.7 6.6 36 52 22 4 

10-19 B21 15.6 57.0 27.4 3.4 1.9 0.6 1.5 8.2 14.7 42.3 24.0 7.4 34 47 17 2 

19-34 B22t 14.3 57.0 28.7 3.4 2.1 0.8 1.2 6.8 13.4 43.6 20.9 7.5 26 37 12 -- 

34-48 B23t 15.9 53.7 30.4 4.8 2.9 1.0 1.6 5.6 9.2 44.5 15.7 10.3 47 59 16 18 

48-60 B3t 24.1 50.8 25.1 8.1 4.9 1.7 2.8 6.6 9.5 41.3 17.8 17.5 51 62 27 7 

 

 6A1a 6B2a 6Cla Bulk density Water content pH 

Depth Organ- Nitro- C/N Carbo- Ext. 4Ale 4A1h6 4D1 4B1c 4B2 4C1 8C1c 8C1a 

(in.) Ic gen nate iron 1/3 Oven 1/3 15 

 Carbon as as bar drt LE bar bar WRD (1:1) (1:1) 

 CaCO3 Fe KCl H2O 

 Pct. Pct. Pct. g/cc g/cc g/cc Pct. Pct. Pct. Pct. in/in IN. 

1/2-5 1.86 0.180 10 2.9 1.36 1.39 0.7 26.6 12.0 0.15 4.4 4.9 

5-10 .87 .100 9 2.9 1.35 1.39 0.6 26.8 11.5 0.13 3.9 4.6 

10-19 .35 .058 6 2.3 1.54 1.61 0.9 21.6 11.1 0.11 3.9 5.4 

19-34 .21 2.4 1.57 1.63 0.9 21.5 12.0 0.11 3.9 5.4 

34-48 .22 2.5 1.60 1.63 0.3 21.7 12.4 0.08 3.8 5.4 

48-60 .10 2.9 1.68 1.75 0.6 18.4 10.1 0.07 3.8 5.3 

 

Extractable bases 5B1a 6H2a CEC 6G1d Base saturation 

 6N2d 6O2b 6P2a 6Q2a Ext. 5A3a A1 5C3 

Depth Ca Mg Na K acidity cations Sum 

(in.) cations 

 <------------------------------------------------ meq/100g ----------------------------------------------> Pct. Pct. 

1/2-5 4.3 1.5 0.1 0.5 12.8 19.2 0.4 33 

5-10 1.6 1.1 0.1 02 10.8 13.8 1.5 22 

10-19 1.8 1.6 0.1 02 7.8 11.5 0.7 32 

19-34 1.4 2.4 0.1 .2 7.8 11.9 1.0 34 

34-48 1.5 3.2 Tr. .2 7.6 12.5 1.2 38 

48-60 1.1 3.0 Tr. .2 6.9 13.0 1.2 33 

 

Figure 1. Laboratory data sheet for Hayter silt loam, McCreary County, KY. 
698

Soil Type: Hayter silt loam 

Soil No.: S63Ky-74-6 

Location: McCreary County, Kentucky, North off Hwy. 759 about 2 miles east of U.S. Hwy. 

27. 

Vegetation and 

land use: Hickory, persimmon, yellow poplar. 

Slope and 

land form: 50 percent. 

Drainage: Well drained. 

Parent Material: Colluvium from sandstone and shale. 

Sampled by and 

date: D.P. Franzmeier, E.J. Pedersen, C.R. Gass, L. Manhart, G. Chapman; 

October 15, 1963. 

Described by: J.H. Winsor, C.K. Losche. 

Horizon and 

Beltsville 

Lab. No. 

01 1-1/2 to 0 inches. Hardwood leaf litter. 

Ap1 0 to 1/2 inch. Very dark grayish brown (10YR 3/2) silt loam; moderate fine 

granular structure; very friable; 12 percent sandstone fragments (> 3 in. 

diameter); many roots; pH 7.0. 

Ap2 1/2 to 5 inches. Brown (10YR 4/3) silt loam; weak medium granular structure; 

63776 very friable; 12 percent sandstone fragments; many roots; pH 5.0. 

B1 5 to 10 inches. Brown (7.5YR 4/4) silt loam; weak to moderate fine subangular 

63777 blocky structure; friable; 25 percent sandstone fragments; many roots; pH 5.0. 

B21 10 to 19 inches. Brown (7.5YR 4/4) silt clay loam / silt loam; moderate medium 

63778 blocky structure; friable; 25 percent sandstone fragments; common roots; 

pH 5.0. 

B22t 19 to 34 inches. Brown to dark brown (7.5YR 4/4 - 3/2) silty clay loam; 

63779 moderate medium blocky structure; friable; common clay films; 20 percent 

sandstone fragments; few roots; pH 5.0. 

B23t 34 to 48 inches. Brown (7.5YR 4/4) silty clay loam; moderate medium 

63780 subangular blocky structure; friable to firm; 30 percent sandstone fragments; 

common clay films; few roots; pH 5.0. 

B3t 48 to 60 inches. Brown (7.5YR 5/4) silty clay loam; weak to moderate medium 

63781 subangular blocky structure; friable to firm; common clay films; 35 percent 

sandstone fragments; few roots; pH 5.0. 

Notes: Colors are given for moist soil. The B21 and B23t layers were sampled for the Bureau of Public 

Roads. Reaction was determined by Soiltex. 

Figure 2. Profile description of Hayter silt loam, McCreary County, KY. 
SUBJECT INDEX: CURRENT METHODS ONLY

Acetate 294, 358 

Acidity 

 BaCl2-TEA, pH 8.2 extractable acidity 191 

 1 N KCl extractable aluminum 197 

Activity 204 

Aggregate stability 163 

Air-dry/oven-dry ratio (ADOD) 33, 132 

Aluminum 197, 249, 341, 365 

Aluminum saturation 204 

Ammonium oxalate extraction 312 

Anaerobic incubation 265 

Antimony 324 

Aqueous extraction 223, 273, 277, 

Arsenic 249, 324 

Atterberg Limits 167 

Barium 249, 324 

Base saturation 

 NH4OAc, pH 7 (CEC-7), 202 

 NH4Cl , 203 

 Sum Cations (CEC-8.2), 203 

 Sum NH4OAC bases + 1 N KCl extractable 

 aluminum, 203 

Beryllium324 

Bicarbonate 299, 363 

Biological analyses 375 

Bromide 294, 358 

Bulk density 

 Saran-coated clods 75 

 Field-state 75 

 33 kPa 80 

 Oven-dry 86 

 Rewet 89 

 Reconstituted 99 

 33 kPa 99 

 Oven-dry 99 

 Ring excavation 100 

 Field-state 100 

 Frame excavation 102 

 Field-state 102 

 Soil cores 104 

 Field-state 104 

Cadmium 249, 324 

Calcium 184, 249, 290, 341 

Calcium carbonate 269, 381 

Carbon 347, 368, 376, 379 

 Active 379 

 Hot water extractable 376 

 Organic 347, 376 

 Total 347 

 Mineral 368 

Carbonate 299, 363 

Cation exchange capacity (CEC) 173, 181, 202 

 NH4OAc, pH 7 173 

 NH4Cl 181 

 Sum Cations (CEC-8.2) 202 

 Sum NH4OAc extractable bases + 1 N 

 KCl extractable aluminum 202 

Chemical analyses 173 

 Soils 173 

 Water 352 

Chloride 294, 358 

Chromium 249, 324 

Clay mineralogy 398 

Cobalt 294, 324 

Coefficient of Linear Extensibility (COLE) 135 

Conventions 31 

Copper 249, 324 

Correction for crystal water 33, 132 

Data sheet symbols 33 

Data types 32 

Differential scanning colorimetry 410 

Differential thermal analysis 415 

Dithionite-citrate extraction 307 

Effective cation exchange capacity (ECEC) 202 

Electrical conductivity 277, 284, 353 

Exchangeable sodium percentage (ESP) 301 

Extractable bases 184, 201 

Fabric-related analyses 34, 140 

Fiber volume 371 

Field-moist/oven-dry ratio (FMOD) 33, 132 

Fluoride 294, 358 

Froth flotation 439 

Fumigation incubation 388 

Geomorphology 1 

Glass counts 422 

Grain studies 422 

Gypsum 269 

Histosol analysis 368, 369, 371 

Iron 249, 307, 312, 317, 341, 365 

Lead 249, 324 

Magnesium 184, 249, 290, 341 

Magnetic separation 434 

Manganese249, 307, 312, 317, 324, 365 

Major elements 341 

Melanic Index 374 

Mercury 336 

Methods 31 

Method codes 31 

Mineral content 368 

Microbial biomass 388 

Microbiology 388 

Mineralizable nitrogen 265, 347, 388 

Mineralogical analysis 398 

Molybdenum 324 

New Zealand P retention 257 

Nickel 249, 324 

699
SUBJECT INDEX: CURRENT METHODS ONLY

Nitrate 260, 294 

 1 M KCl extraction 260 

 Saturated paste extraction 294 

Nitrite 260, 294 

 1 M KCl extraction 260 

 Saturated paste extraction 294 

Nitrogen, total 347 

Optical density, ammonium oxalate extraction 

 (ODOE) 312 

Organic soils or materials analyses 368 

Particle density 165 

Particle-size distribution analysis 34, 66 

 <2-mm Fraction 34 

 >2-mm Fraction 66 

Particulate organic matter (POM) 385 

Pedon sampling 1 

Pipet analysis 34 

Phosphorus 219, 294, 312, 324, 341, 365 

 Ammonium oxalate extraction 312 

 Aqueous extraction 219 

 Bray P-1 extraction 231 

 Bray P-2 extraction 239 

 Citric acid soluble 253 

 Mehlich No. 3 extraction 246 

 New Zealand P Retention 257 

 Olsen sodium-bicarbonate extraction 242 

 Saturated paste extraction 294 

 Total 324, 341 

Physical analyses 34 

Plant analysis 375 

Platy minerals 434 

Potassium 184, 249, 290, 341 

Pyrophosphate color 369 

Reaction 204, 352 

 1 N NaF, pH 7.5 – 7.8 205 Trace elements 249, 324 

 Saturated Paste pH 207 Tungsten 324 

 Oxidized pH 209 Vanadium 324 

 Organic Materials pH, Final Solution 

 ≈ 0.01 M CaCl2 pH 211 Zirconium 341 

 1:1 water pH 213 Water analysis352 

 1:2 0.02 M CaCl2 pH 213 Water retention 105 

 1 M KCl pH 215 6 kPa 106 

Resistant minerals 398, 442, 443 

Resistivity 286 

Ratios and Estimates 132, 201, 301 

 Physical 132 

 Chemical 201, 301 

Rock fragments 24, 66 

Root analysis 394 

Root biomass 394 

Salt prediction (Predict) 277 

Samples 16, 29, 30 

 Soils 16 

 Water 29 

 Biological materials 30 

Sample collection 1, 16 

 Field 1 

 Laboratory 16 

Sample preparation 1, 16 

 Field 1 

 Laboratory 16 

Sample weight 33 

Saturated paste 277 

Selective dissolutions 303 

Selenium 249, 324 

Separation by heavy liquids 428 

Significant figures 33 

Silicon 312, 341, 365 

Site selection field 1 

Sodium 184, 249, 290, 341 

Sodium Adsorption Ratio (SAR) 303 

Sodium pyrophosphate extraction 317 

Soil test analyses 219 

Soluble salts 277 

Static tube separation 437 

Surface area 418 

Sulfur 294, 347 

 Saturated paste extraction 294 

 Total 347 

Strontium 324 

Thallium 324 

Thermal analysis 398, 410 

Tin 324 

Titanium 341 

Total analysis 324, 341 

Total salt 303 

Zinc 249, 324 

 10 kPa 106 

 33 kPa 106 

 100 kPa 106 

 200 kPa 106 

 1500 kPa 125 

 Field-state 131 

Water Retention Difference (WRD) 137 

Water soluble anions 294 

Water soluble cations 290 

X-ray diffraction analysis 399

700