ñ<iS H V^ U -3 AH 525/4/78

LABORATORY METHODS

RECOMMENDED

FOR CHEMICAL ANALYSIS

OF MINED-LAND SPOILS

AND OVERBURDEN

IN WESTERN UNITED STATES

A-íAvííÍJNITÉD STATES AGRICULTURE PREPARED BY

ffyJtSDEPARTMENT OF HANDBOOK SCIENCE AND

"^^^ AGRICULTURE NUMBER 525 EDUCATION

ADMINISTRATION
ABSTRACT

Sandoval, F. M. and Power, J. F. 1977. Laboratory methods recommended for chemical analysis of mined-land spoils and overburden in

western United States. U.S. Department of Agriculture, Agriculture

Handbook No. 525.

Guidelines are suggested for sampling and for chemical

analysis of mine spoils and overburden samples. The handbook was compiled to meet an urgent need for uniform

laboratory methods to evaluate plant growth capabilities

and limitations associated with coal lands in western

United States. Salinity associated with sodium and nutritional deficiencies commonly characterize these materials, therefore the procedures were selected accordingly.

The authors drew heavily from methods recommended by

the U.S. Salinity Laboratory, Riverside, Calif., and terminology common to saline-sodic soil technology was used.

The procedures selected are those with which the authors

have experience and which they believe are most widely

accepted as reference or standard procedure for western

mined lands and associated spoils. Other methods may be

equally applicable, but those presented have been related

to plant growth responses and may be used as a reference

against which other methods may be compared.

Key words and phrases :

Laboratory analyses ; chemistry of mine spoils ; reclamation of mined-land; reclamation of saline-sodic spoils;

diagnosis of mined land ; salt-affected spoils ; procedures

of analyses.

On January 24, 1978, four USDA agencies—

Agricultural Research Service (ARS),

Cooperative State Research Service (CSRS),

Extension Service (ES), and

National Agricultural Library (NAL)—

merged to become a new organization.

Science and Education Administration (SEA),

U.S. Department of Agriculture.

This publication was prepared by the Science and

Education Administration's Federal Research Staff,

which was formerly the Agricultural Research Service,
PREFACE

The material in this pubhcation is intended to provide

guidelines on acceptable methods for chemical analyses of

mine spoils and overburden materials associated with the

major coalfields in v^estern United States. The methods

selected are those which, in the judgment and experience

of the authors, will provide data that can be interpreted

in terms of plant growth potentials. Individuals with interest other than revegetation will undoubtedly be aware

of other methods. Numerous methods of analyses were

omitted from this publication either because they were not

thought closely related to the subject or because we beHeved the methods selected were more appropriate.

In 1974, the authors prepared a preliminary Hsting of

suggested laboratory procedures for the USDA Forest

Service, Surface Environment and Mining (SEAM) Program, to serve as a guide for laboratories and agencies

involved in the SEAM Program. To meet a later request

from the U.S. Environmental Protection Agency (EPA),

this publication was prepared by revising and further developing the 1974 draft. The authors acknowledge the

interest and support from EPA for the development of

this publication.

For sale by the Superintendent of Documents, U.S. Government Printing OfBce

Washington, D.C. 20402

Stock No. 001-000-03763-3
CONTENTS

Introduction 1

Need for uniform procedures 1

Principles of evaluation 2

Sampling method and sample preparation 3

Methods on earth samples 4

1. Soil-water content 4

2. Saturation extract and saturation percentage 4

3. Alkaline-earth carbonates from acid neutralization, calcium carbonate equivalent . 6

4. pH Determination of water saturated paste 6

5. Extractable and exchangeable cations 7

6. Exchangeable cations and exchangeable sodium percentage 9

7. Gypsum 10

8. Organic carbon (Walkley-Black method) 12

9. Sodium bicarbonate soluble phosphorus (Olsen method) 13

10. Total nitrogen (Macro-Kjeldahl method) 14

11. Inorganic nitrogen 16

12. Hot-water soluble boron 20

Analyses of soil extracts and water solutions 22

1. Electrical conductivity to estimate soluble salt concentration 22

2. Cations calcium, magnesium, sodium, and potassium by atomic absorption

spectroscopy 24

3. Cations sodium and potassium by flame emission photometry 25

4. Cations calcium and magnesium by titration with EDTA 25

5. Carbonate and bicarbonate 27

6. Chloride 28

7. Sulfate 29

References 31

Washington, D.C. Issued April 1978
Laboratory Methods Recommended

For Chemical Analysis of Mined-Land Spoils

And Overburden in Western United States

F. M. Sandoval and J. F. Power'

INTRODUCTION

Need for Uniform Procedures

The need is urgent for a uniform set of laboratory procedures to use

in the evaluation of plant growth capabilities and limitations of minedland spoils in the Western States. For analytical data on properties of

spoils collected from one laboratory to be directly comparable with

those from another laboratory, as many laboratories as possible should

agree on a uniform set of analytical procedures. The adoption of uniform methods would increase the value of laboratory data acquired by

the different laboratories—Federal, State, commercial, or industry

owned. Although different procedures may result in similar conclusions

regarding the relative revegetation potential of mine spoils, with uniform methods, reclamation specialists from Government and industry

will be better able to define and directly compare land restoration problems and results.

Much laboratory work is needed to characterize and evaluate the

wide array of land and management treatments associated with the

restoration of plant growth potential to mined land in the Western

United States. Information available shows that high salinity, sodic

conditions, and plant nutrient deficiencies characterize many mine

spoils. The laboratory methods suggested are selected with this fact in

mind. Although we recommend specific procedures, we acknowledge

that other procedures may also give acceptable data. Some individuals

may prefer a different procedure, so long as the results are comparable.

For this reason, we are also suggesting that a few standard soils be

made available and their laboratory analyses be compiled and distributed to interested people.

Although the authors recognize the traditional distinction between

soil and other materials from deeper depths, the procedures described

^Soil scientists, Northern Great Plains Research Center, Agricultural Research Service,

U.S. Department of Agriculture, Mandan, N. Dak.

1
apply equally to soil and mine spoils regardless of their original depth ;

therefore, "soil" in this pubhcation includes all materials evaluated.

Most of the laboratory procedures suggested here are those recommended by the U.S. Salinity Laboratory (5)^ and the American Society

of Agronomy (i, 2), More detailed laboratory methodology is described

in the references indicated at the beginning of each procedure.

Principles of Evaluation'

The term soluble salts, as applied to soils, refers to the inorganic

constituents that are appreciably soluble in water. The determination

of soluble salts consists essentially of two steps : the preparation of a

soil-water extract and the measurement of the salt concentration of

the extract.

The choice of a method for preparing a soil-water extract and for

measuring its salt concentration depends upon the purpose of the determination and the accuracy required. In general, the higher the water

content at which the extract is obtained, the easier to remove the extract but the less representative the extract is of the solution to which

plant roots are exposed in the soil. Thus, if the purpose is to correlate

soluble-salt concentration with plant growth, the extract should be

obtained at a water content similar to that at which plants grow. The

water content of soils in which plants grow fluctuates between a lower

limit at which plants wilt permanently (the permanent wilting percentage) and an upper limit (the field capacity), which, for most soils,

is approximately two times the water content at the permanent wilting

percentage.

A satisfactory method for appraising the soluble salt content of soils

in relation to plant growth must, therefore, take into account the variable water-retention characteristics of soils. Moreover, the method

should use an extract having a composition as representative of the soil

solution as possible. An ideal method would measure the salt concentration of an extract obtained at field capacity water content, but the

difficulty of obtaining such extracts prohibits their routine use. The

next higher feasible and readily identifiable water content is that at

which the soil is mixed with water to a saturated paste.

On some soil materials, laboratory analyses may be feasibly conducted on soil : water ratio extracts wider than saturation and then

arithmetically corrected to saturation (when the saturation percentage

is known). This procedure assumes that the change in solubihty of the

salts present is linearly related to the soil : water ratio—an assumption

^ Numbers in parentheses refer to references listed, p. 31,

^ Abstracted in part from Bower and Wilcox In Black Ql ).
that may or may not be true. Consequently, in many cases, deviation

from saturation may lead to considerable error in the estimate of concentration and composition of salts. Medium- to coarse-textured, chloride-dominant materials are in the first category ; fine-textured, highsulfate (especially if gypsiferous) materials are in the second category.

In 1954, the U.S. Salinity Laboratory developed, and has since recommended, the saturated paste extract as the best solution for soil

sahnity appraisal (5). Research to date suggests that this also applies

for laboratory analyses of solutions extracted from spoils and overburden connected with strip mining.

The quantity of water required to mix a soil to a saturated paste that

has certain definable characteristics is reasonably reproducible. It also

quantitatively equals about four times the quantity of water held by

the soil at permanent wilting and about twice that held at field capacity. The salt concentration of water in the paste, therefore, tends

to be about one-fourth the concentration of that in the soil solution at

the lower limit of field-water content and about one-half the concentration at the upper limit. Measurement of the salt concentration in

water extracted from a saturated soil paste thus provides a quantitative value that automatically reflects the field water-holding characteristics of the soil and which can be related to plant response.

Sampling Method and Sample Preparation

Samples of overburden and spoils can be collected and prepared by

many methods varying with available resources, time, and purposes.

In selecting the method used, care must be exercised that the chemical

properties of the samples are not altered during sampling and before

analysis. No simple answers exist to the problem of collecting or to the

question of frequency of sampling. Good judgment and experience are

required.

Caution should be exercised in transporting and processing samples

for laboratory analyses. Polyethylene plastic bags are recommended for

transporting samples from the field. Canvas (unless Hned) and ordinary paper bags are not recommended because these materials may

absorb soluble salts from wet samples, and the glue in the paper bag

may interfere with accurate analysis for boron. Galvanized equipment

should be avoided if zinc is to be analyzed. Samples to be analyzed for

nitrate-nitrogen cannot be stored moist under warm conditions. Moist

or wet samples should be immediately frozen or spread to dry on waxed

paper or similar water-proof material, ground to 2-mm size, and stored

in closed water-resistant containers until analyzed. Knowledge of potential sources of contamination and chemical transformations that

may occur in samples is required. Erroneous data are generally more
harmful than no data. The principles of sampling are discussed by

Peterson and Calvin in detail in ASA Monograph, Part 1, In Black (J).

Sampling by drilling methods that involves a circulating fluid may

have a potential to affect the composition of soluble constituents in

the sample, either by leaching out salts or by impregnating the sample

with contaminants from the circulating fluid. This problem is particularly acute in sampling overburden and spoils in the Western United

States. The authors of this publication have shown that the drilling

method affects the chemical composition of overburden samples (4).

Drilling fluids that used saline water (about 5 milhmhos/cm electrical

conductivity (EC)) or sodium bentonite as the drilHng mud, or both,

increased salinity and adsorbed sodium in samples, whereas drilling

with air (pneumatic) or using water of relatively low salinity (about

1 millimhos/cm EC) did not appreciably change the sample composition. The use of an organic polymer developed for drilling fluid use did

not appreciably change sample composition. In this work, laboratory

data of samples collected directly from a freshly exposed highwall a

few meters away were assumed to represent tme values.

METHODS ON EARTH SAMPLES

1. Soil-Water Content

Procedure: Transfer a representative subsample of the soil to a

tarred can with Hd. For accuracy, use at least a 25-g sample. Weigh,

oven dry to constant weight at 105° C, and weigh again.

Calculations:

A. Water content percent (weight basis) = (loss in weight on drying) X 100/(weight

of oven-dried soil).

B. Water content percent (volume basis) = water content percent, weight basis X bulk

density, g/cc.

2. Saturation Extract and Saturation Percentage

References: (Complete citations, page 31.)

USDA Handbook 60, pp. 84, 107.

ASA Monograph No. 9, chap. 62-1.3.

Reagent: Sodium hexametaphosphate solution, 0.1 percent: Dissolve

0.1 g of sodium hexametaphosphate [(NaP03)6] in water and dilute to

100 ml with distilled water.

Procedure: Weigh 200 to 1,000 g of air-dry soil of known water content and transfer it to a suitable container with a Hd. Weigh the container and contents. Weighing is not necessary if the Saturation Percentage (SP) is omitted. Add distilled water to the soil and stir the

mixture with a spatula until a condition of saturation is reached. Consolidate the mixture from time to time during the mixing process by
tapping the container on the workbench. At saturation, the soil paste

glistens as it reflects light, flows slightly when the container is tipped,

and slides freely and cleanly off a spatula for all soils except those of

high clay content.

After the mixing has been completed, cover the container and allow

the sample to stand for 1 hr or more; then recheck the criteria for

saturation. If the paste has stiffened markedly or lost its glisten, add

more water and mix it again. Alternatively, if free water has collected

on the surface of the paste, add an additional weighed quantity of dry

soil and mix it again. Weigh the container and contents. Record the

increase in weight as water added.

Calculate the SP from the weight of oven-dry soil and the sum of

the weights of water added and that originally present in the air-dry

sample. The SP may also be determined by oven-drying a subsample

of the saturated soil paste, in which case recording the quantity of

water and soil used is not necessary.

After allowing the saturated soil paste to stand 4 or more hours,

pH may be determined (see Method 4, p. 6). Then transfer the paste

to a Büchner or Richards filter funnel, fitted with low-ash, highly retentive filter paper. Apply vacuum and collect the filtrate in a test tube

or small bottle. About one-fourth of the water in the paste can be extracted with ordinary laboratory suction filtration. If the initial filtrate

is turbid, refilter or discard it. Terminate the filtration when air begins

to pass through the filter. Add 1 drop of 0.1 percent sodium hexametaphosphate solution for each 25 ml of extract to prevent the precipitation of calcium carbonate (CaCOa) on standing. This will increase the

sodium content < 0.5 ppm, which is more acceptable than the loss of

CaCOa by precipitation.

Comments on the saturation point : When sulfate content is minor,

or when the extraction is made to make a broad general sahnity evaluation, the extraction can take place a few minutes after preparation of

the saturated paste. However, if the soil contains gypsum (CaSOé • 2

H2O), ionic content may increase by 10 or 20 meq/hter (1 or 2 millimhos/cm electrical conductivity) upon standing. Therefore, to allow

for the presence of gypsum, allow the paste to stand several hours as

suggested.

Special precautions must be taken with soils of extreme properties.

Highly sodic-clay soils of low, organic-matter content puddle easily,

frequently have a high affinity for water, and the saturation endpoint

is difficult to obtain. To minimize puddling, and thus obtain a more

definite endpoint with such soils, the water should be added initially

with a minimum of stirring. Sands have a low saturation percentage ;

unless caution is taken, too much water will be added.
The saturation extract may be used for the following determinations : electrical conductivity ; calcium, magnesium, sodium, potassium,

calculation of the sodium adsorption ratio (see exchangeable sodium

percentage Method 6, p. 9), carbonates, bicarbonates, chlorides, and

sulfates. See respective Analysis section for these determinations.

3. Alkaline-Earth Carbonates

from Acid Neutralization, Calcium Carbonate Equivalent

References: (Complete citations, page 31.)

USDA Handbook 60, pp. 84-88, 105-107.

ASA Monograph 9, Part 2, chap. 91-4.2.

Reagents:

1. Hydrochloric acid (HCl), 0.5 A", standardized.

2. Sodium hydroxide (NaOH), 0.25 .Y, standardized.

3. Phenolphthalein, 1 percent in 60 percent ethanol.

Procedure: Place 1 to 5 g of oven-dried soil in a 150-ml beaker, add

50 ml of reagent 1 by means of a pipet. Cover with a watchglass and

boil gently for 5 min. Cool, filter, and wash all the acid from the soil

with distilled water. Determine the amount of unused acid by adding

2 drops of reagent 3 and back-titrating with 2.

Calculation :

Calcium carbonate CCaC03) equivalent in percent

= (meq HCl added minus meq NaOH used) X 5/weight of sample in grams.

Note: The calculation gives the CaCOa equivalent. This is the amount

of CaCOa required to react with the acid. The value is often somewhat

high because soil constituents other than CaCOs may react with the

acid.

4. pH Determination of Water Saturated Paste

References: (Complete citations, page 31.)

USDA Handbook 60, pp. 17-18 and 102.

ASA Monograph 9, Part 2, chap. 60.

Equipment : pH meter with glass electrode ; standard pH buffers.

Procedure : Standardize the pH meter against known, standard buffer solutions having pH values approximately those of the samples.

Prepare a saturated paste with distilled water as directed in Method 2,

page 4, and allow the paste to stand at least 1 hr. Insert the electrodes

into the paste and raise and lower repeatedly until a representative pH

reading is obtained.

Note: Opinions vary as to the best way for making pH readings.

The pH of soil suspensions frequently increase upon dilution by increasing the soil : water ratio. For this reason, we recommend the saturated paste method with water at the CO2 pressure of the atmosphere

after equilibrium with the soil.

6
5. Extractable and Exchangeable Cations

References: (Complete citations, page 31.)

USDA Handbook 60, p. 101.

ASA Monograph 9, Part 2, chap. 57-2.1 and 57-3.2.

The procedure described below is by saturation with ammonium and

is taken from the first reference Hsted. A slightly different ammonium

saturation procedure is described in the second reference, as well as a

method by sodium saturation.

A. Extractable cations (exchangeable plus soluble cations)

Apparatus: Centrifuge, 50-ml round-bottom, narrow-neck centrifuge

tubes and reciprocating shaker.

Reagents :

1. Ammonium acetate solution, 1.0 A^ To 700 or 800 ml of water

add 57 ml of concentrated acetic acid (CH3COOH) and then 68 ml of

concentrated ammonium hydroxide (NH4OH). Dilute to volume of 1

Hter and adjust to pH 7 or to pH 8 by the addition of more ammonium

hydroxide or acetic acid. pH 7 solution is used on noncalcareous soils ;

pH 8 solution is used on calcareous materials.

2. Nitric acid (HNO3), concentrated.

3. Hydrochloric acid (HCl), concentrated.

4. Acetic acid, approximately 0.1 N.

Procedure: Ammonium acetate extractable cations: Samples for this

determination should be approximately 4 g for medium- and fine-textured soils and 6 g for coarse-textured soils. Weigh samples to an accuracy of 1 percent and correct for the air-dry moisture content. Place

the sample in a centrifuge tube. Add 33 ml of reagent 1 to the tube,

stopper, and shake for 5 min. Remove the stopper and centrifuge at

relative centrifugal force (RCF) = 1,000 until the supernatant hquid

is clear. This usually requires 5 min. Decant the supernatant hquid as

completely as possible into a 100-ml volumetric flask. Extract with reagent 1, a total of three times by this procedure, decanting into the

same flask. Dilute to volume, mix, and determine the amounts of the

various extracted cations by flame photometric or chemical methods.

Flame photometric analyses (emission or atomic absorption) may be

made directly upon ahquots of the extract.

If chemical methods are to be employed for the determination of

cations, pretreat the extract in the following manner: Transfer to a

250-ml beaker and evaporate to dryness on a hot plate or steam bath.

Wash down the walls of the beaker with a small quantity of distilled

water and again evaporate to dryness. Add 1 ml of reagent 2 and 3 ml

of 3, evaporate, and dissolve the residue in 20 ml of reagent 4. Filter
through low-ash content filter paper into a 50-ml volumetric flask,

using water to wash the beaker and filter paper. Dilute to volume.

Soluble cations: Prepare a saturated soil paste as described in

Method 2, page 4, using a 200- to 1,000-g sample of soil. The weight of

soil will depend upon the number of cations to be determined, the analytical methods employed, and the salt content of the soil. Determine

the saturation percentage and obtain the saturation extract as described in Method 2, page 4, and determine the soluble cation concentrations by flame photometric or chemical methods.

Calculations :

Ammonium acetate extractable cations in meq/100 g

= (cation concentration of extract in meq/liter X 10)/(wt of sample in g).

Soluble cations in meq/100 g

= (cation concentration of saturation extract in meq/liter) X (saturation

percentage) /1,000.

Exchangeable cations in meq/100 g

= (extractable cations in meq/100 g) minus (soluble cations in meq/100 g).

Note: To complete the calculations, determine the soluble cation

content.

B. Cation exchange capacity

Apparatus: Centrifuge, 50-ml round-bottom, narrow-neck, centrifuge

tubes, and reciprocating shaker.

Reagents :

1. Sodium acetate solution, 1.0 N, Dissolve 136 g of sodium acetate

trihydrate in water and dilute to a volume of 1 hter. The pH value of

the solution should be approximately 8.2.

2. Ethanol, 95 percent.

3. Ammonium acetate solution, 1.0 A". To 700 or 800 ml of water

add 57 ml of concentrated acetic acid and then 68 ml of concentrated

ammonium hydroxide. Dilute to volume of 1 Hter and adjust to pH 7

or 8 as under (A-1) for extractable cations.

Procedure: Samples for this determination should be approximately

4 g for medium- and fine-textured soils and 6 g for coarse-textured

soils. Weigh samples to an accuracy of 1 percent and correct for the

air-dry moisture content. Place the sample in a centrifuge tube. Add

33 ml of reagent 1, stopper the tube, and shake for 5 min. Unstopper

and centrifuge at RCF = 1,000 until the supernatant Uquid is clear.

This usually requires 5 min. Decant the supernatant Hquid as completely as possible and discard. Treat the sample in this manner with

33-ml portions of reagent 1, a total of four times, discarding the supernatant liquid each time. Add 33 ml of reagent 2 to the tube, stopper,

shake for 5 min, unstopper, and centrifuge until the supernatant Uquid

8
is clear. Decant and discard the supernatant liquid. Wash the sample

with 33-ml portions of reagent 2 a total of three times. The electrical

conductivity of the supernatant liquid from the third washing should

be less than 40 micromhos/cm. Replace the adsorbed sodium from the

sample by extraction with three 33-ml portions of reagent 3 and determine the sodium concentration of the combined extracts after dilution

to 100 ml as described under Method 5-A.

Calculation :

Cation-exchange capacity in meq/100 g

= (Na concentration of extract in meq/liter X 10)/Cwt of sample in g).

6. Exchangeable Cations

and Exchangeable Sodium Percentage

References: (Complete citations, page 31.)

USDA Handbook 60, pp. 101-103.

Wilcox, L. v., 1963. Factors for calculating the sodium absorption ratio. U.S.

Salinity Laboratory, Riverside, Calif., Publ. No. 376.

A, Direct determination

Procedure: Determine the exchangeable-cation content and the cation-exchange capacity (CEC), using A and B from Method 5, page 6.

Calculation :

Exchangeable-cation percentage

= (exchangeable cation content in meq/100 g X 100)/(cation exchange

capacity in meq/100 g).

B. Soluble cations or empirical method

Procedure: Prepare a saturation extract of the soil as described in

Method 2, page 4. Determine the calcium, magnesium (or Ca plus

Mg), and sodium concentrations of the saturation extract, using methods described in Analyses of Soil Extracts and Water Solutions, page

22.

Calculations:

Exchangeable sodium percentage, ESP

ESP = 1QQC-Q-Q^26 + 0.01475X)

1 + (0.0126+ 0.01475X)

where X is equal to the sodium adsorption ratio.

Sodium adsorption ratio, SAR

SAR = Na/ V (Ca + Mg)/2

where ionic concentrations are expressed in milliequivalents per liter.

A nomogram which relates soluble sodium and calcium plus magnesium concentrations to the SAR is given in USDA Handbook 60,

page 103. Included on the nomogram is a scale for estimating the corresponding ESP. A helpful set of factors to facihtate accurate calculation of the SAR has been prepared by Wilcox of the U.S. Sahnity Laboratory (5).

259-697 O - 78
7. Gypsum

Reference: (Complete citation, pag"e 31.)

USDA Handbook 60, pp. 102-104.

A. Precipitation with acetone (qualitative)

Reagent: Acetone.

Procedure: Weigh 10 to 20 g of air-dried soil into an 8-oz bottle and

add a measured volume of water sufficient to dissolve the gypsum

present. Stopper the bottle and shake by hand six times at 15-min intervals or agitate for 15 min in a mechanical shaker. Filter the extract

through paper of medium porosity. Place about 5 ml of the extract in a

test tube, add an approximately equal volume of acetone, and mix. The

formation of a precipitate indicates the presence of gypsum in the soil.

Remarks: The soil should not be oven-dried because heating promotes the conversion of gypsum (CaSOé • 2 H2O) to the half-hydrate

form (CaS04 • 0.5 H2O). The latter hydrate has a higher solubility in

water for an indefinite period following its solution.

B. Precipitation with acetone (quantitative)

Apparatus: Centrifuge, 50-ml conical centrifuge tubes, conductivity

cell, and electrical conductivity bridge.

Reagent: Acetone.

Procedure : Transfer a 20-ml ahquot of the filtered extract obtained

as described under A into a 50-ml conical centrifuge tube. Add 20 ml

of acetone and mix. Let stand until the precipitate flocculates. This

usually requires 5 to 10 min. Centrifuge at relative centrifugal force

(RCF) = 1,000 for 3 min, decant the supernatant Hquid, invert the

tube, and drain on filter paper for 5 min. Disperse the precipitate and

rinse the wall of the tube with a stream of 10 ml of acetone blown

from a pipet. Again, centrifuge for 3 min, decant supernatant Hquid,

invert tube and drain on filter paper for about 5 min. Add exactly 40

ml of distilled water to the tube, stopper, and shake until the precipitate is completely dissolved. Measure the electrical conductivity of the

solution, using Analysis 1, page 22, and correct the conductivity reading to 25° C. Determine the concentration of gypsum in the solution

by reference to a graph showing the relationship between the concentration and the electrical conductivity of gypsum solutions. This graph

may be constructed by means of the following data from the International Critical Tables, Vol. VI.

10
Electrical conductivity

CaS04 concentration ^^ ^^ ° ^'

Meq/liter Millimhos/cm

1 0.121

2 226

5

.500

10 900

20 1-584

30.5 2.205

Calculations :

Milliequivalents of CaSO, in aliquot

= (meq/liter of CaS04 from conductivity reading) X (ml of water used to

dissolve precipitate)/1,000.

Milliequivalents of gypsum per 100 g of soil

= 100x(meq of CaSO* in aliquot)/(soil:vi^ater ratio X ml of soil-water

extract used).

Remarks: Sodium and potassium sulfates when present in sufficiently high concentrations are also precipitated by acetone. The maximum concentrations of sodium sulfate and of potassium sulfate that

may be tolerated are 50 and 10 meq/hter.

At a 1: 5 soil-water ratio, water will dissolve approximately 15 meq

of gypsum per 100 g of soil. If the gypsum content of the soil is found

to approach 15 meq/100 g by use of a 1: 5 soil-water extract, the determination should be repeated, using a more dilute extract.

C. Increase in soluble calcium plus magnesium content upon dilution

Procedure : Determine the saturation percentage and obtain a saturation extract of the soil using method described in Method 2, page 4.

Prepare another water extract of the soil, using a moisture content

sufficient to dissolve the gypsum present as described under method A.

Determine the calcium plus magnesium concentrations of the two extracts by methods described in Analyses of Soil Extracts and Water

Solutions.

Calculations :

Soluble Ca + Mg at the saturation percentage in meq/100 g

= (Ca+ Mg concentration of saturation extract in meq/liter) X (saturation

percentage)/1,000.

Soluble Ca + Mg at the high moisture percentage in meq/100 g

= (Ca + Mg concentration of dilute extract in meq/liter) X (moisture

percentage)/1,000.

Gypsum in meq/100 g of soil

= (soluble Ca + Mg at the high moisture percentage in meq/100 g)

— (soluble Ca + Mg at the saturation percentage in meq/100 g).

11
8. Organic Carbon (Walkley-Black Method)

References: (Complete citations, page 31.)

ASA Monograph No. 9, Part 2, pp. 1373-1376.

Jackson, M. L., Soil Chemical Analysis, pp. 219-222.

Apparatus : Magnetic stirrer, burette, and appropriate glassware.

Reagents:

1. Potassium dichromate (K2Cr207), 1 A : Dissolve 49.04 g of reagent-grade K2Cr207 (dried at 105° C) in water, and dilute to 1 liter.

2. Sulfuric acid (H2SO4), concentrated (not less than 96 percent) :

if chloride is present, add silver sulfate (Ag2S04) at the rate of 15 g

per liter of acid.

3. Orthophosphoric acid (H3PO4), concentrated.

4. o-phenanthroline-ferrous complex, 0.025 A^: Dissolve 14.85 g of

o-phenanthrohne monohydrate (C12H8N2 • H2O) and 6.95 g of ferrous

sulfate (FeS04 • 7 H2O) in distilled water, and dilute to 1 Hter.

5. Barium diphenylamine sulfonate [((36H5NHC6H4-4-S03)2 Ba]

solution: Prepare a 0.16 percent aqueous solution. This reagent is an

optional substitute for No. 4.

6. Ferrous sulfate solution, 0.5 A^: Dissolve 140 g of reàgent-grade

FeS04 • 7 H2O in distilled water, add 15 ml of concentrated H2SO4, cool

the solution, and dilute to 1 liter. Standardize this reagent daily by

titrating it against 10 ml of 1 A" K2CR2O7, as directed below.

Procedure: Grind material to pass a 0.5-mm sieve, avoiding iron or

steel mortars. Transfer a weighed sample, containing 10 to 25 mg of

organic-C, but not in excess of 10 g total weight, into a 500-ml widemouth Erlenmeyer flask.^ Add 10 ml of 1 A" K2Cr207, and swirl the

flask gently to disperse the material in the solution. Then rapidly add

20 ml of concentrated H2SO4, directing the stream into the suspension.

Immediately swirl the flask gently until soil and reagents are mixed,

then more vigorously for a total of 1 min. Allow the flask to stand on a

sheet of asbestos for about 30 min. Then add 200 ml of water to the

flask and filter the suspension if experience shows that the endpoint of

the titration cannot otherwise be clearly discerned. Add three to four

drops of o-phenanthrohne indicator and titrate the solution with 0.5 A^

FeS04. As the endpoint is approached, the solution takes on a greenish

cast and then changes to dark green. At this point, add the ferrous

sulfate drop by drop until the color changes sharply from blue to red

(maroon in reflected light against a white background). Make a blank

determination in the same manner, but without soil, to standardize the

''Trade names are used in this pubHcation solely for the purpose of providing specific

information and do not constitute a warranty of the product by the U.S. Department of

Agriculture or an endorsement over products not mentioned.

12
dichromate ion (Cr207-'). Repeat the determination with less soil if

more than 75 percent of the dichromate is reduced.

Calculation :

Calculate the results according to the following formula, using a correction factor

f = 1.33 or a more suitable value found experimentally:

(meq K^Cr-.O; - meq FeSOO X 0.003 X 100

Organic-C, percent = -7^ X U)-

soil wt, g

Note: This method is not well suited for determining organic carbon

contents of spoils in which coal fragments are intermixed because carbon in coal, lignite, charcoal, or other resistant forms is only partially

oxidized.

9. Sodium Bicarbonate Soluble Phosphorus

(Olsen Method)

References: (Complete citations, page 31.)

ASA Monograph No. 9, Part 2, pp. 1044-1047.

Jackson, M. L., Soil Chemical Analysis, pp. 162-165.

Murphy, J. and J. P. Riley. 1962. A modified single solution method for the determination of phosphate in natural water. Analytica Chimica Acta. 27:31-36.

Apparatus: Shaker, colorimeter.

Reagents :

1. Sodium bicarbonate (NaHCOa) solution, 0.5 N: Adjust pH to

8.5 with 1 .V sodium hydroxide (NaOH). Add mineral oil (about 1 cm

layer) to avoid exposure of the solution to the air. Prepare a fresh solution if it has been standing over 1 month in a glass container. The

solution may be stored in a polyethylene container for longer periods,

but check pH monthly.

2. Carbon black : Use carbon black G as received.

3. Ammonium molybdate solution: Dissolve 15 g of ammonium

molybdate [(NH4)6Mo7024 • 4 H2O] in 300 ml of warm distilled water.

Filter the mixture, if necessary, and allow to cool ; add 342 ml of concentrated HCl gradually with mixing and dilute to 1 liter with distilled

water. This solution contains an extra 50 ml of concentrated HCl to

neutraHze the NaHCOs in a 5-ml ahquot.

4. Stannous chloride (SnCb • 2 H2O), concentrated solution: Dissolve 10 g of stannous chloride in 25 ml of concentrated HCl. Prepare a

fresh solution every 2 months or less. Use large crystals of SnCk •

2 H2O rather than fine powder. Store solution in a refrigerator.

5. Stannous chloride, dilute solution: Add 0.5 ml of the concentrated SnCl2 solution to 66 ml of distilled water. Prepare the dilute

solution for each set of determinations.

6. Standard phosphorus (P) solution: Weigh 0.4393 g of monobasic potassium phosphate (KH2PO4) into a 1-hter, volumetric flask.

13
Add 500 ml of distilled water and shake until the salt dissolves. Dilute

to 1 liter with distilled water. Add 5 drops of toluene to diminish microbial activity. This solution contains 0.1 mg of P per ml.

7. Dilute P solution: Dilute 20 ml of the standard P solution to

1 liter with distilled water. This solution contains 2 [;-g of P per ml.

Procedure: Add 5 g of soil, 1 tsp of carbon black, and 100 ml of the

extracting solution (reagent 1) to a 250-ml Erlenmeyer flask. Shake

the flask for 30 min with a suitable shaker. Filter the suspension

through Whatman No. 40 paper. Add more carbon black if necessary

to obtain a clear filtrate. Shake the flask immediately before pouring

the suspension into the funnel.

Place a 5-ml aliquot of the extract in a 25-ml volumetric flask.

Slowly add 5 ml of the ammonium molybdate solution directly into the

flask. After rapid evolution of CO2 has ceased, shake the flask gently

to mix contents. Wash down the neck of the flask with distilled water

to avoid direct contact of the SnCk solution with the concentrated

ammonium molybdate solution. Dilute the contents to about 22 ml with

distilled water. Add 1.0 ml of the dilute SnCk solution to one or two

flasks, dilute the solution to volume and mix the contents immediately.

Measure the transmittance of the solution in the colorimeter 10 min

after addition of the stannous chloride solution. Use 660 nm incident

light in the colorimeter.

Calculation: Prepare a standard curve as follows: Pipet ahquots of

the dilute P solution containing from 2 to 25 ¡ig of P into 25-ml volumetric flasks and add 5 ml of the NaHCOa extracting solution to each

flask. Develop the color as stated above. Plot percentage transmittance

against P concentration on single-cycle, semilog, graph paper. Express

the results of P in ppm of soil, that is, [xg of P per 5 ml of the unknown

X 4 equals ppm of P for the procedure described here.

Note: Ascorbic acid may be substituted for the SnCl2 • 2 H2O reagent. However, with spoil materials, continue to use carbon-black even

with ascorbic acid to prevent discolored extract giving erroneous colorimeter readings.

10. Total Nitrogen (Macro-Kjeldahl Method)

References: (Complete citations, page 31.)

ASA Monograph No. 9, Part 2, pp. 1162-1164.

Jackson, M. L., Soil Chemical Analysis, pp. 183-190.

Apparatus: Macro-Kjeldahl digestion and distillation apparatus with

fume exhaust, associated glassware.

Reagents:

1. Sulfuric acid (H2SO4), concentrated.

2. Potassium sulfate (K2SO4).

14
3. Copper sulfate (CUSO4 • 5H2O).

4. Selenium (Se).

5. Sodium hydroxide (NaOH), approximately 10 N: Place 4.2 kg

of NaOH in a heavy-walled 10-Hter Pyrex flask, add 4 liters of water,

and swirl the flask until the alkaH is dissolved. Place a rubber stopper

on the flask while cooUng* to prevent absorption of atmospheric carbon

dioxide (CO2) and allow to stand for several days to permit any sodium

carbonate (Na2C03) present to settle. Siphon the clear supernatant

liquid into a large Pyrex bottle which contains about 1.5 hters of CO2-

free water and is marked to indicate a volume of 10 Hters, and make

the solution to 10 liters by addition of C02-free water. Then swirl the

bottle vigorously to mix the contents, and fit the neck with some arrangement which permits the alkali to be stored and dispensed with

protection from atmospheric CO2.

6. Boric acid-indicator solution: Place 80 g of pure boric acid

(H3BO3) in a 5-hter flask marked to indicate a volume of 4 liters, add

about 3,800 ml of water, and heat and swirl the flask until the H3BO3

is dissolved. Cool the solution and add 80 ml of mixed indicator solution

prepared by dissolving 0.099 g of bromocresol green and 0.066 g of

methyl red in 100 ml of ethanol. Then cautiously add 0.1 .V NaOH until

the solution assumes a reddish-purple tint (about pH 5.0), and make

the solution to 4 liters by addition of water. Mix thoroughly before use.

7. Sulfuric (or hydrochloric) acid (H2SO4 or HCl), 0.05 N standard.

Procedure: Place a sample containing about 10 mg of N in a dry

Macro-Kjeldahl flask, add 20 ml of water; and, after swirHng the flask

for 5 to 10 min, allow it to stand for an additional 30 min. Then add

10 g of K2SO4, 1 g of CUSO4 • 5H2O, 0.1 g of Se, and 30 ml of concentrated H2SO4, and heat the flask cautiously on the digestion stand.

When water has been removed (frothing has ceased), increase heat

until the digest clears, and thereafter boil the mixture gently up to

5 hr. Regulate the heating during this boihng so that the H2SO4 condenses about one-third of the way up the neck of the flask. Time of

boiling varies somewhat with materials and may need to be determined

independently for different materials. Temperature of the solution

while boiling should be maintained in the 350° to 410° C range.

After completion of digestion, allow the flask to cool, and add about

100 ml of water (slowly, and with shaking). Then cool the flask under

a cold-water tap and transfer the contents to a 1-Hter conical (or 800-

ml Kjeldahl) flask for distillation. As far as practicable, retain sandy

residue in the digestion flask during this transfer because sand can

cause severe bumping during Kjeldahl distillation. Four washings of

15
the sandy residue with 50 ml of water are usually adequate for quantitative transfer of the ammonium in the digest.

To determine the ammonium-N liberated by digestion, place a 500-ml

Erlenmeyer flask containing 50 ml of boric acid-indicator solution under the condenser of the distillation apparatus so the end of the condenser is below the surface of the H3BO3. Then hold the distillation

flask at a 45° angle, add a teaspoonful of pumice, and pour about 150

ml of 10 N NaOH down the neck so the alkali reaches the bottom of

the flask without mixing appreciably with the digest. Attach the flask

as quickly as possible to the distillation apparatus, mix the contents

thoroughly by swirling, and immediately commence distillation. Regulate the heating to prevent suck-back of H3BO3 and to minimize frothing or bumping during distillation and check that the flow of cold

water through the condenser is sufficient to keep the temperature of

the distillate < 35° C.

When about 150 ml of distillate have been collected, lower the receiver flask so the end of the condenser is above the surface of the

distillate, and after rinsing the end of the condenser with water, remove the flask and stop distillation. Determine ammonium-N in the

distillate by titration with 0.05 A^ H2SO4 using a 25-ml burette graduated at 0.1-ml intervals (1 ml 0.05 N H2SO4 0=^ 0.7 mg ammonium-N).

The color change at the end point is from green to pink.

Calculation :

Percent N in sample = (T — B) X N X 1.4/s

where T = ml standard acid used in sample titration,

B = ml standard acid used in blank titration,

N = normality of standard acid, and

s = oven dry weight of sample in grams.

Note : Many alterations of the basic method are commonly employed,

particularly in respect to apparatus, sample size, and catalysts. Material should be ground to pass at least a 40-mesh sieve to insure

thorough digestion, especially when semi-micro methods are used. Also

procedure may be modified to include nitrates and nitrites if desired.

11. Inorganic Nitrogen

A. Nitrate-nitrogen by phenoldisulfonic acid method

References: (Complete citations, page 31.)

ASA Monograph No. 9, Part 2, pp. 1216-1218.

Soil Chemical Analysis, pp. 197-201.

Apparatus: Colorimeter, appropriate glassware.

Reagents:

1. Calcium sulfate (CaS04 • 2H2O), reagent-grade, powdered.

2. Phenoldisulfonic acid: Dissolve 25 g of pure, white phenol in

16
150 ml of concentrated sulfuric acid (H2SO4) (sp gr 1.84) in a 500-ml

Erlenmeyer flask. Then add 75 ml of fuming H2SO4 (13 percent SO3),

mix, and place the flask (loosely stoppered) in boihng water for 2 hr.

Store the resulting solution of phenoldisulfonic acid in a glass-stoppered, amber bottle. Alternatively, dissolve 25 g of pure, white phenol

in 225 ml of concentrated H2SO4, and heat the solution in a loosely

stoppered bottle or flask in boiling water for 6 hr. Store the product

in a glass-stoppered, amber bottle.

3. Ammonium hydroxide solution (NH4OH) : Prepare by mixing

1 liter of reagent-grade NH4OH (sp gr 0.89 to 0.90) with 1 liter of

water.

4. Calcium carbonate (CaCOa), reagent-grade, finely powered.

5. Standard nitrate solution : Dissolve 0.722 g of potassium nitrate

(KNO3) in water, and dilute to a volume of 1,000 ml in a volumetric

flask. If pure, dry KNO3 is used, this solution contains 100 [xg of nitrate-N per ml. Store the solution in a refrigerator.

6. Silver sulfate (Ag2S04), reagent-grade, powdered.

7. Calcium hydroxide [Ca(0H)2], reagent-grade, powdered.

8. Magnesium carbonate (MgCOs), reagent-grade powdered.

Procedure : Preparation of soil extract. Place 50 g of soil in a 500-ml,

wide-mouth bottle and add 0.5 g of CaS04 and 250 ml of water. Stopper

the bottle and shake it for 10 min on a mechanical shaker. Allow the

suspension to settle for a few minutes and decant and filter the supernatant liquid through a large, dry, fluted filter paper (Whatman No. 42

or Schleicher and Schull No. 597 paper) .^ If the first portion of the

filtrate is not clear, return it to the filter and collect the filtrate in a

clean receiver flask.

Pipet an ahquot (usually 25 ml) of the extract into a 150-ml beaker

(or an 8-cm evaporating dish), add about 0.05 g of CaCOs, and evaporate the sample to dryness on a steam plate. Perform the evaporation

in an atmosphere free of nitric acid (HNO3) fumes and do not continue

heating beyond the point of dryness. Allow the beaker to cool and add

2 ml of phenoldisulfonic acid from a rapid-dehvery pipet. Rotate the

beaker so that the phenoldisulfonic acid comes into contact with the

entire residue in the beaker. After allowing the beaker to stand for

10 min, add 20 ml of water and stir with a glass rod until the residue

is in solution. Then add NH4OH solution (slowly and with stirring)

from a dispensing burette until the solution is shghtly alkahne (as

indicated by the development of a yellow color) and add an additional

2 ml to ensure an excess of this reagent. Transfer the solution to a

100-ml volumetric flask and dilute to volume with water. Then mix

thoroughly and measure color intensity at 420 nm against a reagent

blank solution.

17
Determine the nitrate content of the sample by reference to a calibration graph plotted from the results obtained with samples containing 0, 10, 20, 40, 70, and 100 i^g of nitrate-N. To prepare this graph,

dilute 10 ml of the standard nitrate solution (reagent 5) to 100 ml with

water in a volumetric flask and mix thoroughly. Then add 0-, 1-, 2-, 4-,

7-, and 10-ml volumes of this diluted standard solution (from a 10-ml

burette graduated at 0.02-ml intervals) to 150-ml Pyrex beakers and

measure the intensities of the colors obtained with these samples by

the procedure described for analysis of the extract.

Calculation :

ppm NO3-N in soil

= ppm from standard curve X aliquot dilution X soil dilution

= ppm from standard curve X ml final volume/ml aliquot X ml extracting

solution/gm oven dry soil

100 250 + ml soil water

= ppm from standard curve X X

25 50 — ml soil v^ater

Note: If high chlorides are suspected, remove with AgS04 first.

Procedure is capable of high precision and is frequently used as a

standard method to which results from other methods are commonly

referred.

B. Nitrogen by steam distillation method

(ammonium, nitrate, and nitrite)

References: (Complete citations, page 31.)

ASA Monograph No. 9, Part 2, pp. 1195-1201.

Apparatus: Steam-distillation apparatus, 100-ml Pyrex distillation

with side-arm, microburette, and other appropriate glassware.

Reagents :

1. Magnesium oxide (MgO) : Heat heavy powder MgO in an electric muffle furnace at 600° to 700° C for 2 hr. Cool the product in a

desiccator containing potassium hydroxide (KOH) pellets and store it

in a tightly stoppered bottle..

2. Boric acid-indicator solution: Dissolve 20 g of pure H3BO3 in

about 700 ml of hot water and transfer the cooled solution to a 1-liter

volumetric flask containing 200 ml of ethanol and 20 ml of mixed indicator solution prepared by dissolving 0.330 g of bromocresol green

and 0.165 g of methyl red in 500 ml of ethanol. After mixing the contents of the flask, cautiously add approximately 0.05 N sodium hydroxide (NaOH) until a color change from pink to pale green is just detectable when 1 ml of the solution is treated with 1 ml of water. Then

dilute the solution to volume with water and mix thoroughly.

3. Devarda alloy: Prepare this reagent by ball-milling, reagent

grade, Devarda alloy until the product will pass a 100-mesh screen and

18
at least 75 percent of it will pass a 300-mesh screen. Store the finely

ground alloy in a tightly stoppered bottle.

4. Sulfamic acid (NH2SO3H) : Purify sulfamic acid by crystallization from hot water and dissolve 2 g of the purified reagent in 100 ml

of water. Store the solution in a refrigerator.

5. Sulfuric acid (H2SO4), 0.005 .Y standard.

6. Standard (ammonium + nitrate)-N solution: Dissolve 0.236 g

of (NH4)2S04 and 0.361 g of potassium nitrate (KNO3) in water, dilute

to a volume of 1,000 ml in a volumetric flask, and mix thoroughly. If

pure, dry reagents are used, this solution contains 50 ¡i^g of ammoniumN and 50 \).g of nitrate-N per ml. Store the solution in a refrigerator.

7. Standard (ammonium + nitrate + nitrite)-N solution: Dissolve 0.236 g of (NH4)2S04, 0.123 g of NaN02, and 0.361 g of KNO3 in

water, dilute the solution to a volume of 1,000 ml in a volumetric flask

and mix thoroughly. If pure, dry reagents are used, this solution contains 50 [xg of ammonium-N, 25 ¡kg of nitrite-N and 50 \).g of nitrate-N

per ml. Store the solution in a refrigerator.

Procedure (using 2 N KCl soil extracts): The steam required for

distillation is generated by heating distilled water in a 5-liter flask,

which contains pumice or glass beads (to promote smooth boihng)

and a small amount of H2SO4 (to trap any ammonium in the distilled

water). Before use, the distillation apparatus should be steamed out

for about 10 min to remove traces of NH3, and the rate of steam generation should be adjusted so that 7 to 8 ml of distillate are collected per

min. The flow of cold water through the condenser of the apparatus

should be such that the temperature of the distillate obtained using

this rate of distillation does not exceed 22° C. The desired rate of distillation is obtained if the steam generator flask is heated by an electric

heating mantle and if the power supply to the mantle is controlled by

a variable transformer. A trap at the base of the water jacket on the

condenser is used to prevent water condensing on the external surface

of the condenser from entering the flask used to collect the distillate.

Ammonium-N. Add 5 ml of HsBOs-indicator solution to a 50-ml Erlenmeyer flask, which is marked to indicate a volume of 30 ml, and

place the flask under the condenser of the steam-distillation apparatus

so that the end of the condenser is about 4 cm above the surface of the

H3BO3. Pipet an aliquot (usually 10 to 20 ml) of a 2 N KCl soil extract

(10 ml per 100 g soil) into a distillation flask and add 0.2 g of MgO

through a dry powder funnel having a long stem that reaches down

into the bulb of the flask. Attach the flask to the steam-distillation

apparatus and immediately commence steam distillation. When the distillate reaches the 30-ml mark on the receiver flask, stop the distillation, rinse the end of the condenser, and determine ammonium-N in the

19
distillate by titration with 0.005 N H2SO4 from a microburette (1 ml

of 0.005 N H2SO4 c^ 70 |jLg of ammonium-N). The color change at the

endpoint is from green to a permanent, faint pink.

(Nitrate + Nitrite)-N. After removal of ammonium-N from the

sample as described in the previous section, remove the stopper from

the side-arm of the flask, add 0.2 g of Devarda alloy rapidly through a

dry powder funnel that reaches down into the flask to about the base

of the side-arm and immediately replace the stopper in the neck of the

side-arm. Then determine the amount of ammonium-N hberated by

steam distillation as described above.

(Ammonium + Nitrate + Nitrite)-N. Proceed as described for ammonium-N but add 0.2 g of Devarda alloy to the distillation flask

immediately after the addition of MgO and before connection of the

flask to the distillation apparatus.

(Ammonium + Nitrate)-N. Proceed as described in the previous

paragraph, but treat the sample in the distillation flask with 1 ml of

sulfamic acid solution and swirl the flask for a few seconds to destroy

nitrite before addition of MgO and Devarda alloy.

Nitrate-N. Follow the procedure described for determination of (nitrate + nitrite)-N, but perform the analysis on a sample which has

been treated with sulfamic acid to destroy nitrite as described in the

previous paragraph.

Note: Steam distillation procedures are especially suited to operations in the small- and medium-sized laboratories where up to a few

thousand analyses are anticipated annually. Cost of equipment is nominal, and precision of the method is generally adequate for most purposes. The procedure for nitrates described gives results that agree

closely with those obtained by the phenoldisulfonic acid method

(Method 11-A, page 16). This procedure has the advantage that the

three forms of inorganic N (ammonium, nitrate, and nitrite) can be

determined on the same soil extract.

12. Hot-Water Soluble Boron

References: (Complete citations, page 31.)

ASA Monograph 9, Part 2, pp. 1062-1063.

Apparatus:

Low-boron glassware.

Reagents :

1. Ethyl alcohol, 95 percent.

2. Curcumin-oxahc acid reagent: Dissolve 0.04 g finely ground

curcumin and 5 g oxalic acid in 100 ml of 95 percent ethyl alcohol and

store in refrigerator in stoppered low-boron bottle.

20
3. Calcium hydroxide [Ca(0H)2]: Add 0.4 g reagent-grade

Ca(0H)2 to 100 ml of distilled water.

4. Hydrochloric acid (HCl),2.5iV.

5. Phenolphthalein indicator.

6. Standard solution A: Dissolve 0.5716 g of boric acid (H3BO3)

in distilled water and dilute to 1 liter in a volumetric flask. 1 ml contains 0.1 mg Boron.

7. Standard solution B : Transfer 10 ml of solution A to a 1-liter

volumetric flask and dilute to volume with water. One ml contains

0.001 mg Boron.

8. Barium chloride (BaCh), 10 percent solution.

Procedure: Place 20 g of air-dry, 20-mesh soil in a 250-ml, Corning,

low-boron, Erlenmeyer flask and add 40 ml of distilled water and 0.5 ml

of 10 percent BaCk solution. Attach a water-cooled reflux condenser.

Heat the flask until the first sign of boihng and then reflux the contents for exactly 5 min. Allow the flask to cool without removing the

condenser. Decant the suspension into a 50-ml, round-bottom, centrifuge tube and centrifuge the suspension for 15 min at 1,500 to 2,000

rpm. Transfer an aliquot containing 1 to 5 [xg of boron to a Coors evaporating dish. The usual aliquot sizes range from 1 to 20 ml. If the

aliquot size exceeds 1 ml, evaporate the aUquot with 5 ml of Ca(0H)2

suspension as directed below in the discussion of standards. Add 4 ml

of the curcumin-oxaUc acid solution and rotate the dish to bring the

solution in contact with all the sample.

Place the dish on a mesh support located about 1.5 cm below the

water surface in a water bath at 55° dz 3° C. If a controlled water

bath is not available, regulate the temperature by a gas burner. Allow

the dish to bake for 15 min after drying before removing it from the

bath. Moisten the residue with alcohol, using a wash bottle with a fine

nozzle. After a few minutes, transfer the contents to a 15-ml centrifuge

tube with additional alcohol, using a poHceman to aid in the transfer.

(At this stage of the procedure, low-boron glassware is not required

because no additional color will develop if the solution is contaminated

with boron.) Centrifuge the tube for 10 min at 1,500 rpm. Decant the

solution into a 25-ml volumetric flask and add alcohol to bring the total

volume to 25 ml. (The trace of solution remaining in the centrifuge

tube is not added to either unknowns or standards.)

Place the blank solution in a colorimeter equipped with a green filter

(approximately 540 nm) and adjust the galvanometer to indicate zero

absorbence or 100 percent transmittance. Then measure the absorbence

of the test solution without readjusting the galvanometer. Find the

concentration of boron in the test solution by reference to a calibration

21
curve and calculate the content of boron in the original soil sample.

The color is stable for a period of 1 to 2 hr.

Prepare a calibration curve by pipetting 0-, 1-, 2-, 3-, 4-, and 5-ml

quantities of standard solution B into separate 75-mm evaporating

dishes. Then treat each member of the series as follows : Add 5 ml of

Ca(0H)2 suspension and evaporate the contents to dryness. Allow the

dish to cool and then add one drop of phenolphthalein indicator. Add

2.5 A^ HCl dropwise until the color of the indicator disappears and then

add 0.5 ml of acid in excess. Add 4 ml of curcumin-oxaHc acid solution

and rotate the dish to bring the solution into contact with all the sample. Continue the procedure in the manner described above for soil

samples, setting the galvanometer to indicate zero absorbence or 100

percent transmittance with the solution to which no boron has been

added. Plot the absorbence or percentage transmittance against the

quantities of boron added to obtain a cahbration curve.

Note: In laboratories with atomic absorption (AA) equipment, use

of AA spectroscopy for boron analysis is probably more convenient

than the method described.

ANALYSES OF SOIL EXTRACTS

AND WATER SOLUTIONS^

1. Electrical Conductivity

To Estimate Soluble Salt Concentration

References: (Complete citations, page 31.)

USDA Handbook 60, pp. 7-13, 89-90.

ASA Monograph No. 9, Part 2, chap. 62-2.

Apparatus :

1. Electrical conductivity (EC) bridge, alternating-current (a.c.)

type, suitable for EC measurements : This may be an older 1,000-cycle,

a.c. bridge with telephone. receivers, a 60-cycle, a.c. bridge with an

a.c. galvanometer, or one of the newer bridges employing a cathode

ray tube as the null indicator. Battery-operated bridges are also

available that give satisfactory readings.

2. EC cell, pipet-type, with platinized platinum electrodes: The

cell constant should be approximately 1.0 reciprocal cm. A higher cell

constant of 10 reciprocal cm will increase the working EC range, which

may be helpful when highly saline soils are analyzed. Keep cells clean

and rinse them thoroughly after use. When not in use, keep cells filled

with distilled water. Refer to references and manufacturers' instructions for replatinizing cells and how to clean dirty cells.

'Also see Method 2, page 4.

22
Reagents: An array of standard solutions of known salt concentration and EC should be prepared. Salts of reagent grade that may be

used are sodium chloride (NaCl) and potassium chloride (KCl). Solutions of KCl of 10 and 100 meq/liter (0.01 and 0.10 A^) will have EC^s

of 1.41 and 12.86 millimhos/cm, respectively, at 25° C. To prepare a

0.01 N KCl solution, dissolve 0.7456 g/liter of distilled water; for a

0.10 N KCl solution, dissolve 6.456 g/liter.

Procedure: Allow the standard salt solutions and samples of soil:

water extracts to adjust uniformly to room temperature. The specific

temperature within the range 20° to 30° C is not important, but the

standard solution and samples must be at the same temperature. When

greater precision is required, bring the standard solution and samples

to a temperature of 25° in a thermostat or constant temperature room.

Depending on the EC meter used, the EC determination is obtained

by either manually correcting for temperature on the meter or by multiplying the meter reading by the appropriate temperature factor to

correct to the standard 25° C.

Comments: EC (also called specific conductance) readings on solutions are highly correlated with total ionic concentration and thus the

osmotic potential of water extracts. The units of conductivity recomTABLE 1.—Temperature correcting factors for electrical

conductivity data to standard 25° C

c° Factor C° Factor C° Factor

18.0 1.163 23.2 1.038 27.0 0.960

19.0 1.136 23.4 1.034 27.2 0.956

19.5 1.124 23.6 1.029 27.4 0.953

20.0 1.112 23.8 1.025 27.6 0.950

20.2 1.107 24.0 1.020 27.8 0.947

20.4 1.102 24.2 1.016 28.0 0.943

20.6 1.097 24.4 1.012 28.2 0.940

20.8 1.092 24.6 1.008 28.4 0.936

21.0 1.087 24.8 1.004 28.6 0.932

21.2 1.082 25.0 1.000 28.8 0.929

21.4 1.078 25.2 0.996 29.0 0.925

21.6 1.073 25.4 0.992 29.2 0.921

21.8 1.068 25.6 0.988 29.4 0.918

22.0 1.064 25.8 0.983 29.6 0.914

22.2 1.060 26.0 0.979 29.8 0.911

22.4 1.055 26.2 0.975 30.0 0.907

22.6 1.051 26.4 0.971 30.5 0.899

22.8 1.047 26.6 0.967 31.0 0.890

23.0 1.043 26.8 0.964 32.0 0.873

23
mended are millimhos per cm (EC X 10^) for extracts from soil materials and micromhos per cm (EC X 10^) for waters. For water solutions associated with mined lands in the West, we found the following

empirical conversion factors useful :

EC, millimhos/cm X Factor = mg/liter (ppm)

Oto 3 650 (ppm expressed on solution basis, not on soil basis.)

3 to 7 700

7 to 15 750

15 to 25 800

2. Cations Calcium, Magnesium, Sodium, and Potassium

by Atomic Absorption Spectroscopy

References: (Complete citations, page 31.)

Analytical Methods Handbook available from manufacturer for specific instrument

used.

ASA Monograph No. 9, Part 2, chap. 54, 55, 62.

Robinson, J. W. 1966. Atomic Absorption Spectroscopy. Marcel Dekker, Inc., New

York, N.Y. 204 pp.

Slavin, W. 1968. Atomic Absorption Spectroscopy. Interscience Publishers, New

York, N.Y. 305 pp.

Atomic absorption (AA) spectroscopy techniques and instrumentation are invaluable for identifying and measuring metals in soil and

water solutions and are recommended to analyze for calcium (Ca),

magnesium (Mg), sodium (Na), and potassium (K). The principle of

AA is simple in theory but not in actual practice. Use of AA instrumentation requires a competent analyst to recognize and compensate

for light-scattering errors that are introduced. Samples in solution are

sprayed into a flame to dissociate the sample into atoms. Then a light

source is beamed in, and depending on the wave length used, the individual atoms of a particular metal selectively absorb the light. The

wave length absorbed by a particular metal is specific for the metal

and therefore identifies it. The amount of light absorbed is proportional

to the metal concentration and therefore determines quantity.

Detailed procedures of AA analysis vary depending on the type of

instrument and burners employed and on other factors. A review of

the instrument methods handbook plus other references is necessary.

Apparatus, principal:

1. AA instrument with appropriate lamps and hooked up with airacetylene for the flame, adequately vented in a room free of noxious

fumes and dusts.

2. Equipment for preparing accurate dilutions.

3. Miscellaneous laboratory glass and hardware.

Procedure (generalized) : Prepare a single-standard solution containing the standard elements of determination. This minimizes standard

24
preparation time and storage requirements. Like all analytical procedures, a minimum and a maximum concentration range of application

exists. Generally, low range analyses present minor problems, and detection is a function of concentration limits under optimum conditions.

High concentration limits frequently present problems but often can be

manipulated. The upper limit can be extended by three methods: (1)

The sample solution is diluted until the concentration is in a good analytical range; (2) use of long path burners and changing the position

of the burner. By placing the burner perpendicular, or at an angle, to

the light path rather than parallel to it, much of the flame is taken out

of the light path, and the number of absorbing atoms is reduced, however, there is a loss of sensitivity; and (3) use of secondary absorption

wave length lines with low oscillator strengths. For example : with Na,

3320 Angstrom (A) instead of the more sensitive 5890 A; with Ca,

2399 A instead of the primary line at 4227 A.

During analysis, a good technique is to run one or more standard

samples with each group of unknowns because results are varied by

such things as sample feed rate caused by salt incrustations on the

burner or change in Hquid viscosity caused by temperature. Unsuspected errors may also be detected and compensated for if frequent

calibration checks are performed.

3. Cations Sodium and Potassium

by Flame Emission Photometry

Apparatus: Flame spectrophotometer and associated equipment.

The monovalents, sodium (Na) and potassium (K) can be accurately

determined by using emission flame photometry techniques. Interferences are much less of a problem with Na and K than with the divalents, Ca and Mg. For this reason, analysis for the divalents is not

popular with emission flame spectrophotometers. Detailed procedures

for the analyses vary depending on the type of instrument used and

on other factors. A review of the instrument methods handbook is necessary plus references like those suggested. The most prominent emission lines of Na and K and the radiations most usable for analysis of

soil and water solution work are the doublets at 5890 A and 5896 A

for Na and at 7665 A and 7699 A for K. A series of standards of known

Na and K content containing similar reagents as the unknowns are

prepared.

4. Cations Calcium and Magnesium

by Titration With EDTA

References: (Complete citations, page 31.)

USDA Handbook 60, pp. 94-95.

ASA Monograph No. 9, Part 2, chap. 62, 68-3.2.

25
Apparatus: Magnetic stirrer, 10-ml titration assembly, and other

miscellaneous lab ware.

Reagents:

1. Ammonium chloride (NH4CI)-ammonium hydroxide (NH4OH)

buffer solution: Dissolve 33.76 g of NH4CI in 285 ml of concentrated

(15 N) NH4OH, add 5 g of disodium magnesium ethylenediamine tetraacetate (Na2Mg EDTA) and dilute the solution to a volume of 500 ml.

2. Sodium hydroxide (NaOH), approximately 4 N: Dissolve 40 g

of NaOH in water, and dilute the solution to a volume of 250 ml.

3. Standard calcium chloride (CaCl2) solution, 0.02 A': Dissolve

1.000 g of pure calcite crystals (CaCOs) in 20 ml of approximately 3 A'

hydrochloric acid (HCl) and dilute the solution to a volume of 1 Hter.

4. Eriochrome Black T indicator solution: Dissolve 0.5 g of reagent grade Eriochrome Black T powder and 4.5 g of hydroxylamine

hydrochloride (NH2OH • HCl) in 100 ml of 95 percent ethyl alcohol.

Alternatively, prepare a somewhat more stable solution by dissolving

0.5 g of Eriochrome Black T in 100 ml of diethanolamine [ (HOCH2

CH2)2NH].

5. Murexide (acid ammonium purpúrate) indicator: Thoroughly

mix 0.5 g of murexide (CgHgNeOe • H2O) with 100 g of powdered potassium sulfate (K2SO4).

6. Standard disodium dihydrogen ethylenediamine tetraacetate

(EDTA) solution, 0.02 A^: Dissolve 3.723 g of reagent grade disodium

ethylenediamine tetraacetate dihydrate (Na2CioHi408N2 • 2 H2O) in

water and dilute the solution to a volume of 1 liter. Standardize this

EDTA solution against the standard CaCk solution (reagent 3), following the titration procedure for Ca -f Mg given below.

7. Sodium diethyldithiocarbamate solution : Dissolve 1 g of reagent

grade sodium diethyldithiocarbamate [(C2H5)2 NCSS Na*3 H2O] in

100 ml of water. Because this solution decomposes rapidly, some

workers prefer to add the crystals directly to the sample. The quantity

is not critical, but 5 mg are adequate. This reagent complexes the

heavy-metal ions and thus reduces or eliminates interference from

these ions.

8. Hydrochloric acid (HCl), concentrated (12 A^.

Procedure: To measure calcium (Ca) concentration, pipet an aliquot

of the soil-water extract containing 0.02 to 0.20 meq of Ca into a

beaker. Place the beaker in the titration assembly and start the stirrer.

Add 5 drops of the sodium diethyldithiocarbamate solution (reagent 7),

1 drop of NaOH (reagent 2) for each 5 ml of aliquot, and a suitable

amount (about 5 to 10 mg per 5 ml aliquot) of murexide indicator

(reagent 5), mixing the solution after the addition of each reagent.

Titrate the solution with the standard EDTA (reagent 6). The color

26
change at the end point is from pink to purple. As the end point is

approached, add the titrant slowly—a drop every 5 to 10 seconds. At

the end point, the addition of a small increment of titrant will not

cause a deepening of the purple color. Reserve the solution for the

determination of magnesium (Mg).

Calculation :

1,000

Meq of Ca per liter == X (ml of standard EDTA X normality of EDTA).

ml of sample

To measure the Mg concentration, add 3 or 4 drops of concentrated

HCl (reagent 8) to the sample just titrated for Ca and stir the solution until the murexide is destroyed. Add 1 ml of the NH4CI-NH4OH

buffer solution (reagent 1) and 1 or 2 drops of Eriochrome Black T

indicator (reagent 4) and titrate the solution with the standard EDTA

(reagent 6). The color at the end point should be clear blue with no

tinge of red.

Calculation :

1,000

Meq of Mg per liter = X (ml of standard EDTA X normality of EDTA).

ml of sample

To measure the Ca + Mg concentration, pipet an ahquot containing

0.02 to 0.20 meq of Ca + Mg into a beaker. Place the beaker in the

titration assembly and start the stirrer. Add 5 drops of the sodium

diethyl-dithiocarbamate solution (reagent 7), 1 ml of the NH4CINH4OH solution (reagent 1), and 1 or 2 drops of the Eriochrome

Black T .ndicator solution (reagent 4). Titrate the solution with the

standard EDTA (reagent 6). The color change at the end point is from

wine red to clear blue.

Calculation :

1,000

Meq of Ca + Mg per liter = X (ml of standard EDTA X normality of EDTA).

ml of sample

5. Carbonate and Bicarbonate

References: (Complete citations, page 31.)

USDA Handbook 60, pp. 98-99.

ASA Monograph No. 9, chap. 62-3.4.

Apparatus: Magnetic stirrer, 10-ml titration burette assembly, and

other miscellaneous lab ware.

Reagents :

1. Phenolphthalein indicator: Dissolve 0.25 g of phenolphthalein

powder in 100 ml of 50 percent alcohol.

2. Methyl orange indicator: Dissolve 0.1 g of methyl orange powder in 100 ml of water.

3. Sulfuric acid (H2SO4), standard, 0.01 .¥.

27
Procedure: Pipet an aliquot (usually 5 ml) of the soil-water extract,

containing not more than 0.05 meq of bicarbonate (HCO3) into a

beaker. Place the beaker in the titration assembly and start the stirrer.

Add 2 drops of phenolphthalein (reagent 1), and, when a pink color is

produced, titrate the solution with standard H2SO4 (reagent 3), adding

a drop every 2 or 3 sec, until the pink color disappears. Note the

burette reading. To the colorless solution from this titration, or

to the original solution if no color is produced with phenolphthalein,

add 1 or 2 drops of methyl orange (reagent 2), and continue the titration to the methyl orange end point. Note the total volume of standard

H2SO4 used from the burette. Reserve the solution for the determination of chloride (Cl). Make blank determinations after adding the

appropriate reagents to C02-free water, and make corrections if necessary.

Calculation :

Meq of carbonate (COs^') per liter

1,000

= —-— — X C2P X normality of standard H2SO4)

ml of sample

where P = ml of standard H2SO4 required to reach the phenolphthalein

end point.

Calculation :

Meq of bicarbonate (HCOs") per liter

1,000

= __^ (T — blank — 2P) X (normality of standard H2SO4)

ml of sample

where T = total ml of standard H2SO4 required to reach the methyl

orange end point, and P = ml of standard H2SO4 required to reach the

phenolphthalein end point.

Note: Water extracts from sodic mine spoils are often so dark in

color that titration with color indicators are difficult. Under such conditions the titration can be made by using a pH meter and glass

electrode—carbonate to pH 8.2 and bicarbonate to pH 4.5.

6. Chloride

A. Titration with silver nitrate

References:

USDA Handbook 60, pp. 98-99.

ASA Monograph No. 9, chap. 62-3.5.

Apparatus:..Magnetic stirrer, 10-ml titration assembly, and other

miscellaneous lab ware.

Reagents :

1. Potassium chromate (K2Cr04) indicator: Dissolve 5 g of K2Cr04

in approximately 75 ml of water. Add a saturated solution of silver

nitrate (AgNOs) until a small quantity of red silver chromate

28
(Ag2Cr04) precipitates. Set the solution in the dark for 24 hr. Then

filter it to remove the Ag2Cr04 and make the volume to 100 ml.

2. Standard AgNOa solution, 0.025 A^: Dissolve 4.2472 g of reagent

grade AgNOa in water and dilute the solution to a volume of 1 liter.

Check the normality by titrating an aliquot of the 0.01 A' potassium

chloride (KCl) conductivity reference solution reagent (Analysis 1,

page 22).

3. Sodium bicarbonate (NaHCOs) saturated solution: Renew the

solution every few weeks because it has a tendency to lose CO2 and

become too alkaline. Dispense the solution from a dropping bottle.

Procedure: Place the solution from the carbonate-bicarbonate titration (Analysis 5, p. 27) in the titration assembly and start the stirrer.

If this solution is not available, take a new aUquot of the sample.

Adjust the pH with NaHCOa solution (reagent 3) so the solution is

alkaline to methyl orange^ but acid to phenolphthalein. Usually a single

drop of the NaHCOs solution is sufficient. Add K2Cr04 indicator

(reagent 1), 1 drop per 5-ml aliquot, and titrate the solution with the

standard AgNOa solution (reagent 2) until the appearance of a red or

reddish-brown precipitate.

Determine a blank correction by titrating a Hke volume of chloridefree distilled water. The normal blank correction is 0.02 to 0.05 ml,

depending on the final volume.

Calculation :

Meq of chloride (Cl~) per liter

1,000

= -7-7 r- X (ml of AgNOs - blank) X normality of AgNOa. ml ot sample

B. Potentiometric or coulometric methods

Reference :

ASA Monograph No. 9, chap. 81-3.

Frequently, some extracts from sodic mine spoils are highly colored

and are difficult to analyze colorimetrically ; such samples can best be

analyzed by potentiometric titration using equipment and the procedure such as described in the above reference.

Chloride determinations are also made by using specialized automatic titrator equipment which employs the principle of coulometric

generation of reagent (a silver wire) and amperometric indication of

the endpoint.

7. Sulfate

A. Precipitation as barium sulfate

References :

USDA Handbook 60, p. 99.

ASA Monograph No. 9, chap. 62-3.1.

29
Apparatus: Centrifuge and 12-ml conical tubes.

Reagents:

1. Methyl orange, 0.01 percent in water.

2. Hydrochloric acid (HCl), approximately 1 .V.

3. Barium chloride, approximately 1 A^ Dissolve 122 g of barium

chloride dihydrate (BaCk • 2 H2O) in water and dilute to 1 hter.

4. Ethanol, 50 percent by volume.

Procedure: Pipet an aliquot containing 0.05 to 0.5 meq of sulfate

(SO4"-) into a clean 12-ml conical centrifuge tube of known weight.

Dilute or evaporate to about 5 ml. Add 2 drops of reagent 1, then 2

dropwise until pink, and then 1 ml of 2 in excess. Heat to boiling in

water bath. While twirling the tube, add 1 ml of 3 dropwise. Return to

the hot-water bath for 30 min and then cool at least 1 hr in air.

Centrifuge at RCF == 1,000 for 5 min. Carefully decant and let drain

by inversion on filter paper for 10 min. Wipe the mouth of the tube

with a clean towel or lintless filter paper.

Stir the precipitate and rinse the sides of the tube with a stream of

5 ml of reagent 4 blown from a pipet. If necessary, loosen precipitate

from bottom of tube with a bent wire. Centrifuge for 5 min and decant

but do not drain. Repeat this washing and decanting operation once.

Wipe the outside of tube carefully with chamois and do not subsequently touch with fingers. Dry overnight in an oven at 105° C. Cool

in a desiccator and weigh.

Calculation :

Meq per liter of sulfate CSO4) = (mg of BaS04 precipitate X 8.568)/Cml in aliquot).

Note: Care must be taken in the preparation or concentration of

the unknowns so as not to precipitate foreign material that might be

weighed as BaS04.

B. Content calculation by difference

Estimating sulfate concentration is often adequate as the difference

between the sum of the determined cations and the sum of the determined anions expressed in meq per hter. When nitrate content is

significant, it should also be subtracted.

SO. = (Ca + Mg + Na + K) -(CO, + HCO3 + Cl)

30
REFERENCES

(i) Black, C. A., (ed.) 1965. Methods of soil analysis. American Society of Agronomy (ASA), Monograph 9, Part 1, Madison, Wis.

(^) . 1965. Methods of soil analysis. American Society of Agronomy, Monograph 9, Part 2. Madison, Wis.

(5) Jackson, M. L. 1958. Soil chemical analysis. Prentice-Hall, Inc., Englewood

CHfFs, N.J.

(4) Power, J. F. and F. M. Sandoval. 1976. Effects of sampUng methods on results of

chemical analysis of overburden samples. Mining Congress Journal 62:37-41.

(5) U.S. Salinity Laboratory. 1954. Diagnosis and improvement of saline and alkah

soils. U.S. Department of Agriculture, Agriculture Handbook No. 60.

31

us. GOVERNMENT PRINTING OFFICE : 1978 O—259-697
0)

•o

PI

z

>

CO

<^

» >

5?

^ 2

> KÎ 2 H 2 TÏ

H S >

5 Sí aï

m ig

2 i -I

r 3 >

> 5 O

i|5

o C

>i r

• -I ^ c

PI

c m m

m H c/>