Soil Quality

Test Kit Guide

United States

Department of

Agriculture

Agricultural

Research Service

Natural Resources

Conservation Service

Soil Quality Institute

August 1999
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by the Department or the Natural Resources Conservation Service over comparable products that are

not named.

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(voice and TDD). USDA is an equal opportunity provider and employer.
Table of Contents

 Preface ..........................................................................................................................

Section I - Test Procedures:

 1. Measuring Soil Quality - discusses sampling and site

characterization ......................................................................................................

 2. Soil Respiration Test - indicates the soil's biological

activity.....................................................................................................................

 3. Infiltration Test - measures the soil's ability

to take in water through the soil surface .................................................................

 4. Bulk Density Test - measures the soil's compaction

or pore space.............................................................................................................

 5. Electrical Conductivity (EC) Test - measures the salt

concentration in the soil...........................................................................................

 6. pH Test - measures the soil's acidity or alkalinity..................................................

 7. Soil Nitrate Test - measures the soil's

nitrate levels ...........................................................................................................

 8. Aggregate Stability Test - measures the amount of

water stable aggregates............................................................................................

 9. Slake Test - estimates the stability of soil

fragments in water .................................................................................................

 10. Earthworm Test - measures the number of earthworms

in the soil .................................................................................................................

 11. Soil Physical Observations and Estimations - shows how

to observe soil structure and root patterns and how to estimate topsoil

depth, penetration resistance, and soil texture in the soil profile..........................

 12. Water Quality Tests estimates salinity and

nitrate/nitrite levels in water...................................................................................

Page

iii

1

4

7

9

14

15

16

18

20

22

23

28

i
Appendix:

 A. References...............................................................................................................

 B. Soil Respiration (alternative method)..................................................................

 C. EC and pH Meter Maintenance and Calibration..................................................

 D. Building a Soil Quality Test Kit ..............................................................................

 E. Site Description Data Sheet.....................................................................................

 F. Soil Quality Data Worksheets.................................................................................

Section II - Background & Interpretive Guide for Individual Tests:

 Introduction ..................................................................................................................

 1. Soil Respiration .....................................................................................................

 2. Infiltration ............................................................................................................

 3. Bulk Density ...........................................................................................................

 4. Electrical Conductivity (EC) ...............................................................................

 5. Soil pH ....................................................................................................................

 6. Soil Nitrate ...........................................................................................................

 7. Aggregate Stability ...............................................................................................

 8. Soil Slaking ............................................................................................................

 9. Earthworms............................................................................................................

 10. Soil Physical Observations and Estimations ......................................................

 11. Water Quality .......................................................................................................

Salinity of water

Nitrate/nitrite levels in water

ii

Page

30

31

33

35

41

43

51

52

55

57

59

63

67

69

72

73

75

79
PREFACE

Soil quality is simply defined as “the capacity of a specific kind of soil to function.” It is

generally assessed by measuring a minimum data set of soil properties to evaluate the soil’s ability

to perform basic functions (i.e., maintaining productivity, regulating and partitioning of water and

solute flow, filtering and buffering against pollutants, and storing and cycling nutrients). This

guide describes a kit of selected field procedures to evaluate or indicate the level of one or more

soil functions.

When measuring soil quality, it is important to evaluate the physical, chemical, and biological

properties of the soil. Physical properties addressed by the kit include bulk density, water content,

infiltration rate, aggregate stability, slaking, and morphological estimations. Biological properties

measured include soil respiration and earthworms. Soil chemical properties measured include pH,

electrical conductivity (EC), and soil nitrate levels. The chemical tests are also useful to evaluate

water quality of well-water, tile drainage waters, and other water bodies related to farm activities.

Section I of this guide provides a list of supplies and instructions for conducting a number of

on-farm tests to assess soil quality. Section II provides background and interpretive information

for each test described in Section I. These tests, or indicators, are designed as a screening tool to

provide immediate results for comparing management systems, monitoring changes in soil quality

over time, and for diagnosing possible soil health problems due to land use and management.

 These tests can be easily conducted on the farm by NRCS field personnel or by landowners

themselves to assess the quality of their soil. Use of the kit allows NRCS staff to be an active

participant with the landowner in the assessment of soil health. The assessment will provide the

opportunity to discuss management options when the need arises.

The kit was developed by John Doran and associates, Agricultural Research Service, Lincoln,

NE. The Soil Quality Institute has continued the development, enhancement and testing of the kit

(with NRCS field staff) by adding tests, modifying the manual, and writing an interpretations

guide. The Soil Quality Test Kit Guide is a dynamic document. The Institute welcomes suggestions for additional tests and interpretive information to incorporate in future versions of the guide.

The Institute gratefully acknowledges the contributions of the following individuals: John

Doran, USDA-ARS, Lincoln, NE, for the development of the original soil quality test kit from

which this guide is based. Bob Grossman, USDA-NRCS, NSSC, Lincoln, NE, for the development

of the soil structure index and penetration resistance tests. Jeff Herrick, USDA-ARS, Las Cruces,

NM, for the development of the soil slake test procedure and aggregate stability test design. Dennis Linden, USDA-ARS, St. Paul, MN, for the development of the earthworm procedure. Bob

Hanafin, Auburn University, for the development of the design and layout of this guide. Cathy

Seybold and Lee Norfleet, USDA-NRCS, Soil Quality Institute, for the development of this guide

and testing of kit procedures.

The mission of the Soil Quality Institute is to cooperate with partners in the development,

acquisition, and dissemination of soil quality information and technology to help people conserve

and sustain our natural resources and the environment.

For more information about the Soil Quality Institute and its products and services, visit our

website at http://soils.usda.gov/sqi.

Soil Quality Institute Staff

iii

1

1. Measuring Soil Quality

Soil quality integrates the physical, chemical, and biological components of soil and their interactions. Therefore, to capture the holistic nature of soil quality or health, all of the parameters in the

kit should be measured. However, not all parameters have equal relevance to all soils and situations. For example, the EC test for salinity may not be useful in the eastern part of the U.S. where

salinity is not a problem. A minimum data set of soil properties, or indicators, from each of the

three soil components are selected based on their ability to indicate the capacity of the soil to

function for a specific land use, climate, and soil type. Indicators in the soil quality kit are selected

primarily for agricultural soil quality assessments. The kit should be used as a screening tool to

give the general trend or direction of soil quality--whether current management systems are maintaining, enhancing, or degrading the soil. Proper use of the kit and interpretation of results depends

on how well the indicators are understood with respect to the land use and environmental goals.

There are two fundamental ways to assess soil quality:

• take measurements periodically over time to monitor changes or trends in soil quality;

• compare measured values to a standard or reference soil condition.

By making use of the two ways of assessing soil quality, the kit can be used to:

 make side-by-side comparisons of different soil management systems to determine their

relative effects on soil quality;

 take measurements on the same field over time to monitor trends in soil quality as affected

by soil use and management;

 compare problem areas in a field to the non-problem areas;

 compare measured values to a reference soil condition or to the natural ecosystem.

Field or Site Characterization

It is important to gain as much information about the area and soils as possible. Indicators of soil

quality must be evaluated within the context of site and climatic characteristics. A "Soil Quality

Site Description" recording sheet, located in the appendix, should be completed during the soil

quality assessment. The following are items that should be considered when making an on-farm

soil quality assessment:

Soil series - The soil series name can be found in the county soil survey.

Signs of erosion - Signs of erosion include gullies, rills, development of pedestals, exposed

areas of subsoil, damage to plants caused by wind blown materials, etc.

Management history - This item includes a description of past and present land and crop

management; kind, amount, and method of fertilization; prior tillage; and land leveling.

Slope and topographical features of the field - Record percent slope at the sampling sites

within the field, and note any hills, knolls, ridges, potholes, depressions, etc.

Location of the field and sampling areas - Record longitude and latitude (if GPS unit is

available), a description of the location (feet from landmarks), and a drawing of the field

showing sampling areas.

Climatic information - This item includes precipitation and high and low average tempera-
2

Sampling Guidelines

Important: When, where, and how deep to sample and how many samples to take is primarily

dependent on the questions being asked or problems being addressed by the farm or land manager.

When to sample?

Timing of sampling is important, because soil properties vary within a season and with management operations, such as tillage. In general, for the overall assessment of soil quality, an annual

sampling of the field is recommended. Sampling once a year will allow for the detection of longterm changes in soil quality. A good time of year to sample is when the climate is most stable and

there have been no recent disturbances, such as after harvest or the end of the growing season.

Where to sample?

An important consideration in determining where to sample in a field is the variability of the area.

Soil properties naturally vary across a field and even within the same soil type. Soil variability

across a field is also affected by management operations. General field characteristics to consider

are:

 row versus inter-row areas,

 differences in soil type,

 differences in management,

 wheel versus non-wheel tracked areas,

 differences in crop growth,

 salt affected versus non-salt affected

areas,

 eroded versus non-eroded areas,

 differences in slope, and

 wet versus non-wet areas (drainage).

Some general guidelines on selecting sampling sites are as follows:

(1) For a general assessment of soil quality, select sample sites within a field

that are representative of the field.

Refer to soil maps of the area (Soil

Survey) to identify soil type differences

and variations within the map unit Figure 1.1

 tures for each month (data from a county or watershed level will often be sufficient).

Location of environmentally sensitive areas - This item includes location of ponds, creeks,

wetlands, or other environmentally fragile sites adjacent to the field.
3

 (Figure 1.1). A hand auger can be used

to make a number of borings to establish locations of the most representative

areas of the field.

(2) For assessment of trouble spots within

a field, sample areas that are representative of the trouble spots (Figure 1.2).

(3) When comparing management systems,

make sure sites selected for comparison

have the same soil type and are located

on the same topographical features in

both fields. For example, if sites are

 measured in the wheel tracks in one

field, wheel tracks sites should be

 selected in the comparison field.

(4) When monitoring changes in soil

quality over time, make sure the same

sites within the field are measured at

each sampling time. Also, try to take

measurements at the same soil moisture

conditions at each sampling time to

reduce variability.

In some cases it might be helpful to compare sampling points if the field is sampled

at different points across gradients of soil

type, soil moisture, slope, or other factors

rather than just at a fixed point (Figure 1.3).

How many samples?

The number of samples or measurements to

take will depend on the variability of the field.

It is recommended that a minimum of three samples or measurements be collected on any one

soil type and management combination. In general, the greater the variability of the field, the

greater the number of measurements are needed to get a representative value at the field scale.

When measuring EC, pH, and soil nitrates at the field scale, eight or nine sample cores from across

the field could be bulked and mixed, and two subsamples from the mixed cores could be analyzed.

When taking cores from across the field, stay away from areas that are distinctly different and are

not representative of the field, such as farm lanes and field borders, fertilizer bands, areas within

150 feet of a gravel road, potholes, eroded spots, etc.

Figure 1.2

Figure 1.3

Sampling points

Soil type gradient

Soil types

Trouble spots
4

2. Soil Respiration Test

For efficient sampling, the soil respiration test is performed first, followed by the infiltration test

(Chapter 3) without removing the 6-inch diameter ring. The best time to run the soil respiration

test is when soil moisture is at field capacity (the amount of water the soil can hold after drainage).

Otherwise, soil respiration should be measured before and after the infiltration measurement or

soil wetting (6 to 24 hours after wetting).

Materials needed to measure respiration:

 6-inch diameter ring

 lid with rubber stoppers

 hand sledge and wood block

 soil thermometer

 two sections of plastic tubing

 2 needles

 Draeger tubes

 140 cc syringe

 stopwatch or timer

Considerations: Microbial activity is greatest when the soil is moist (at or near field capacity).

If the soil is dry, a second respiration measurement should be made at a minimum of six hours

(preferably 16 to 24 hours later) after the infiltration test or wetting of the soil. If the soil is

saturated, soil respiration is inhibited, and this test should not be run.

Drive Ring into Soil

 Clear the sampling area of surface residue, etc. If the

site is covered with vegetation, trim it as close to the

soil surface as possible.

 Using the hand sledge and block of wood, drive the 6-

inch diameter ring, beveled edge down, to a depth of

three inches (line marked on outside of ring) Figure 2.1.

 If the soil contains rock fragments, and the ring can not be inserted to depth, gently

push the ring into the soil until it hits a rock fragment. Measure the height from the soil

surface to the top of the ring in centimeters (cm). [See note below]

NOTE: For a more accurate measurement of soil respiration, the chamber head-space should

be measured. Inside the ring, take four measurements (evenly spaced) of the height from the

soil surface to the top of the ring, and calculate the average. Record average on the Soil Data

worksheet.

1

Figure 2.1

Did You Know?

Soil breathes! Soil respiration is an indicator

of biological activity (i.e., microbial and

root), or soil life. This activity is as important to the soil ecosystem as healthy lungs are

to us. However, more activity is not always

better; it may indicate an unstable system

(i.e., after tillage).
5

Cover Ring with Lid and Wait

 Cover the ring with the lid as depicted in

Figure 2.2 and note the time.

 Wait exactly 30 minutes* (to allow CO2

 to

accumulate in the chamber).

[If this is the SECOND respiration measurement,

briefly remove the lid and replace it before timing

to allow the release of gases that have built up

over the 6-24 hour waiting period. Proceed with Step 3.]

*NOTE: During the 30-minute wait, other tests such as Bulk Density (Chapter 4) can be run.

Insert Soil Thermometer

 Insert the soil thermometer into the soil adjacent to the ring with lid (about one inch

away from ring and one inch deep). If the thermometer can easily be inserted into the

rubber stoppers, insert it into one of them to a 1-inch depth into the soil.

Assemble Draeger Tube Apparatus

 Assemble the Draeger tube apparatus just before

the end of the 30-minute wait.

 Connect a needle to one of the sections of

tubing.

 Break open both ends of a CO2

 Draeger tube,

either by using the hole at the end of the syringe

handle as depicted in Figure 2.3, or by clipping

the tube ends with a finger nail clipper.

 Connect the Draeger tube to the other end of the

needle’s tubing. The arrow on the side of the

Draeger tube should point away from the needle.

 With the second piece of tubing, connect the

Draeger tube to the syringe as shown in Figure

2.4

4

Figure 2.2

3

2

Figure 2.4

Figure 2.3
6

Insert Apparatus Needle into Stopper

After 30 minutes, insert the Draeger tube apparatus

needle into a stopper as shown in Figure 2.5. Insert

a second needle into one of the other stoppers on

the lid to allow air flow into the head space during

the gas sampling. The second needle should be

inserted just before the head space is sampled.

Draw Head Space Sample

Over a 15-second span, draw the syringe handle back to the 100 cc reading (1 cc = 1 mL) as

shown in Figure 2.5. [If the reading is less than 0.5%, take four additional 100 cc samples

of the head space through the same Draeger tube. To do this, disconnect the tube from the

syringe to remove the air, and reconnect the tube to the syringe. Take another 100 cc

sample. Repeat.]

Record Soil Temperature and % CO2

On the Soil Data worksheet, record the temperature in Celsius at the

time of sampling. On the Draeger tube, read the "n=1" column if 100

cc was sampled or the "n=5" column if 500 cc was sampled. The %

CO2

 reading should be an estimate of the highest point that the

purple color can be easily detected. Enter this reading on the Soil

Data worksheet. In the example in Figure 2.6, the reading would be

approximately 0.75%.

Remove Lid

Remove the thermometer, Draeger

apparatus needle, air flow needle, and

the lid from the ring.

If this is the first respiration measurement,

leave the ring in the soil for the infiltration

measurement (Chapter 3).

7

8

CALCULATIONS:

Soil Respiration (lb CO2-C/acre/day) = PF x TF x (%CO2 - 0.035) x 22.91 x H

PF = pressure factor = 1

TF = temperature factor = (soil temperature in Celsius + 273) ÷ 273

H = inside height of ring = 5.08 cm (2 inches)

5

6 Figure 2.5

Figure 2.6

Maintenance Tips: Seal any holes in the

chamber lid that may

cause leakage. Also to

prevent leaks, replace the

stoppers in the lid if they

become worn or loose.
7

3. Infiltration Test

The infiltration test is generally performed after the first respiration measurement. The same 6-

inch diameter ring left in place from the soil respiration test can be used for the infiltration test. If

soil respiration was not determined, follow the instructions in Step 1 of the soil respiration procedure (Chapter 2) for inserting the 6-inch diameter ring.

Materials needed to measure infiltration:

 6-inch diameter ring (left in soil from respiration test)

 plastic wrap

 500 mL plastic bottle or

 graduated cylinder

 distilled water

 stopwatch or timer

Considerations: If the soil is saturated, infiltration will not occur. Wait for one or two days to

allow for some drying. Also, if the respiration test is not performed, make sure the sampling area

is free of residue and weeds or that vegetation is trimmed to the soil surface before inserting the

ring.

Firm Soil

With the 6-inch diameter ring in place, use your finger to gently firm the soil surface only

around the inside edges of the ring to prevent extra seepage. Minimize disturbance to the

rest of the soil surface inside the ring.

Line Ring with Plastic Wrap

Line the soil surface inside the ring with a sheet of

plastic wrap to completely cover the soil and ring

as shown in Figure 3.1. This procedure prevents

disturbance to the soil surface when adding water.

Add Water

• Fill the plastic bottle or graduated cylinder to

the 444 mL mark with distilled water.

 Pour the 444 mL of water (1" of water) into the ring

 lined with plastic wrap as shown in Figure 3.1.

2

3

1

 Did You Know?

Infiltration rate is a measure of how fast

water enters the soil. Water entering too

slowly may lead to ponding on level fields or

to erosion from surface runoff on sloping

fields.

Figure 3.1
8

Remove Wrap and Record Time

 Remove the plastic wrap by gently pulling it

out, leaving the water in the ring (Figure 3.2).

Note the time.

 Record the amount of time (in minutes) it takes

for the 1" of water to infiltrate the soil. Stop

timing when the surface is just glistening.

 If the soil surface is uneven inside the ring,

count the time until half of the surface is exposed and just glistening (Figure 3.3).

 Enter the amount of time in minutes on the Soil

Data worksheet.

Repeat Infiltration Test

In the same ring, perform Steps 2, 3, & 4 with a second inch of water. On the Soil Data

worksheet, enter the number of minutes elapsed for the second infiltration measurement. If

soil moisture is at or near field capacity, the second test is not necessary.

[The moisture content of the soil will affect the rate of infiltration; therefore, two

infiltration tests are usually performed (if soil is dry). The first inch of water wets the

soil, and the second inch gives a better estimate of the infiltration rate of the soil.]

Replace Lid

If a second respiration measurement will be performed, set the lid loosely on the ring and

leave it covered for preferably 16 to 24 hours (6-hour minimum) before beginning the

second test (Chapter 2). (Remove lid and replace it before beginning the second soil respiration measurement).

Reminder: If you still need to perform the second

respiration measurement, remember to loosely place !the lid back on the ring before leaving the field.

4

5

Figure 3.2

Figure 3.3

6
9

4. Bulk Density Test

The bulk density measurement should be performed at the soil surface and/or in a compacted zone

(plow pan, etc.) if one is present . Measure bulk density near (between 1 and 2 feet) the site of the

respiration and infiltration tests. To get a more representative bulk density measurement of the

area, additional samples may be taken.

Materials needed to measure bulk density:

 3-inch diameter ring

 hand sledge

 wood block

 garden trowel

 flat-bladed knife

 sealable bags and marker pen

 scale (0.1 g precision)

 1/8 cup (30 mL) measuring scoop

 paper cups

 18-inch metal rod

 access to a microwave oven

Considerations: For rocky or gravelly soils, use the alternate procedure on page 11.

Drive Ring into Soil

• Using the hand sledge and block of wood, drive

the 3-inch diameter ring, beveled edge down, to a

depth of 3 inches (Figure 4.1).

• The exact depth of the ring must be determined

for accurate measurement of soil volume. To do

this, the height of the ring above the soil should

be measured. Take four measurements (evenly

spaced) of the height from the soil surface to the

top of the ring and calculate the average. Record

the average on the Soil Data worksheet.

NOTE: Use the metal rod to probe the soil for depth to a compacted zone. If one is found, dig

down to the top of this zone and make a level surface. Proceed with Step 1.

Remove 3-inch Ring

Dig around the ring and with the trowel underneath it, carefully lift it out to prevent any

loss of soil.

Did You Know?

Bulk density is the weight

of soil for a given volume. It is used to measure compaction. In

general, the greater the

density, the less pore

space for water movement, root growth and

penetration, and seedling

germination.

1

2

Figure 4.1
10

Remove Excess Soil

Remove excess soil from the sample with a flatbladed knife. The bottom of the sample should be flat

and even with the edges of the ring (see Figure 4.2).

Place Sample in Bag and Label

Touch the sample as little as possible. Using the flatbladed knife, push out the sample into a plastic

sealable bag. Make sure the entire sample is placed in the

plastic bag. Seal and label the bag.

NOTE: Steps 5-7 can be done in a lab or office if a scale is not available in the field. Step 8

requires access to a microwave.

Weigh and Record Sample

• Weigh the soil sample in its bag. [If the sample is too heavy for the scale, transfer about

half of the sample to another plastic bag. The weights of the two sample bags will need

to be added together. Enter the weight (sum of two bags, if applicable) on the Soil Data

worksheet.

• Weigh an empty plastic bag to account for the weight of the bag. Enter the weight (sum

of two bags, if applicable) on the Soil Data worksheet.

Extract Subsample to Determine Water Content and Dry Soil Weight

• Mix sample thoroughly in the bag by kneading it with your fingers.

• Take a 1/8-cup level scoop subsample of loose soil (not packed down) from the plastic

bag and place it in a paper cup (a glass or ceramic cup may be used).

Weigh and Record Subsample

 Weigh the soil subsample in its paper cup. Enter the weight on the Soil Data worksheet.

 Weigh an empty paper cup to account for its weight. Enter the weight on the Soil Data

worksheet.

Dry Subsample

Place the paper cup containing the subsample in a microwave and dry for two or more fourminute cycles at full power. Open the microwave door for one minute between cycles to

allow venting. Weigh the dry subsample in its paper cup and enter the weight on the Soil

Data worksheet.

5

6

7

8

4

3

Figure 4.2
11

Bulk Density Test for Gravelly and Rocky Soils

This method is to be used when rocks or gravels prevent sampling bulk density by the core method

described in the first part of this Chapter. This excavation method will require the user to sieve out

the coarse material greater than 2 mm in size.

Materials needed to measure bulk density:

 Plastic wrap

 140-cc syringe

 water

 garden trowel

 sealable bags and marker pen

 2-mm sieve

 scale (0.1 g precision)

 1/8-cup (30 mL) measuring scoop

 paper cup or bowl

 access to a microwave oven

Considerations: Choose a spot that is as level as possible to allow water to fill the hole evenly.

If the soil is too wet to sieve, ignore the part in Step 2 about replacing rocks, and proceed to Step 3.

Soil will have to be dried and sieved later. The volume of gravel will need to be determined and

subtracted from the total volume of the soil sample taken in the field.

Dig Hole

• Dig a bowl shaped hole three inches deep and

approximately five inches in diameter using the

trowel (Figure 4.3). Avoid compacting the soil in

the hole while digging. Place all of the soil and

gravel removed from the hole in a plastic bag.

• Using the 2-mm sieve, sieve the soil in the plastic

bag to separate the gravel. Collect the soil in a

plastic sealable bag. Put the gravel aside to be

used in Step 2. Seal and label the plastic bag.

[Note: See Considerations above if soil is wet.]

1

NOTE: To determine if the soil is dry, weigh the sample and record its weight after each 4-

minute cycle. When its weight does not change after a drying cycle, then it is dry.

CALCULATIONS (See page 13)

Figure 4.3
12

Line the Hole

Line the hole with plastic wrap as shown in Figure

4.4. Leave some excess plastic wrap around the edge

of the hole. Place the sieved rocks and gravel carefully in the center of the hole on top of the plastic

wrap. Assure that the pile of rocks do not protrude

above the level of the soil surface.

Add Water to Hole

• Use the 140 cc syringe to keep track of how much water is needed to fill the lined hole.

The level of the water should be even with the soil surface.

• The amount of water represents the volume of soil removed. Record the total amount of

water in cubic centimeters (1 cc = 1 cm3

) on the Soil Data worksheet.

NOTE: Steps 4-6 can be done in a lab or office if a scale is not available in the field. Step 7

requires access to a microwave.

Weigh and Record Sample

• Weigh the soil sample in its bag. [If the sample is too heavy for the scale, transfer about

half of the sample to another plastic bag. The weights of the two sample bags will need

to be added together. Enter the weight (sum of two bags, if applicable) on the Soil Data

worksheet.

• Weigh an empty plastic bag to account for the weight of the bag. Enter the weight (sum

of two bags, if applicable) on the Soil Data worksheet.

Extract Subsample to Determine Water Content and Dry Soil Weight

• Mix sample thoroughly in the bag by kneading it with your fingers.

• Take a 1/8-cup level scoop subsample of loose soil (not packed down) from the plastic

bag and place it in a paper cup (a glass or ceramic cup may be used).

Weigh and Record Subsample

 Weigh the soil subsample in its paper cup. Enter the weight on the Soil Data worksheet.

 Weigh an empty paper cup to account for its weight. Enter the weight on the Soil Data

worksheet.

4

5

6

3

2

Figure 4.4
13

CALCULATIONS (for both bulk density methods):

Soil water content (g/g) = (weight of moist soil - weight of oven dry soil)

 weight of oven dry soil

Soil bulk density (g/cm3

) = oven dry weight of soil

volume of soil

Soil water-filled pore space (%) = volumetric water content x 100

 soil porosity

Volumetric water content (g/cm3) = soil water content (g/g) x bulk density (g/cm3)

Soil porosity (%) = 1 - soil bulk density

 2.65

Volume of Rocks (cm3

) = Fill 1/3 of a graduated cylinder with water, and record the amount.

Add the rocks to the cylinder and record the change in the water level. The difference is the

volume of rocks (1 mL = 1 cm3).

Volume of Soil (cm3) = Total soil volume - volume of rocks

( )

Dry Subsample

Place the paper cup containing the subsample in a microwave and dry for two or more fourminute cycles at full power. Open the microwave door for one minute between cycles to

allow venting. Weigh the dry subsample in its paper cup and enter the weight on the Soil

Data worksheet.

NOTE: To determine if the soil is dry, weigh the sample and record its weight after each 4-

minute cycle. When its weight does not change after a drying cycle, then it is dry.

7
14

5. Electrical Conductivity Test

Soil samples for the electrical conductivity (EC) test are taken from the 0- to 3-inch depth. Bulked

soil samples from across the field can be collected, and two subsamples can be taken for analysis

(See Chapter 1, Sampling Guidelines). Electrical conductivity, pH, and soil nitrate are all

measured from the same soil subsample.

Materials needed to measure electrical conductivity (EC):

 1/8-cup (30 mL) measuring scoop

 120-mL plastic containers with lid

 EC pocket meter (blue with black cap)

 squirt bottle

 calibration solution (0.01 M KCl)

 distilled water

Extract Subsample

The soil sample should be thoroughly mixed before taking a subsample. Measure a 1/8-cup

level scoop subsample of soil and place it in the plastic container. If soil nitrates will be

measured on this subsample (Chapter 7), weigh the subsample for a more accurate estimate

of soil nitrates. Enter the subsample weight on the Soil Data worksheet.

Add Water to Subsample and Mix

 Add 1/8-cup (30 mL) of distilled water to

the container with the subsample. The

resulting soil/water mixture equates to a

1:1 soil to water ratio on a volume basis.

 Put the lid on the container and shake

vigorously about 25 times.

Measure and Record EC (See Calibration Tip)

 Open the container and insert the EC pocket meter into the soil-water mixture. Take the

reading while the soil particles are still suspended in solution. To keep the soil particles

from settling, stir gently with the EC pocket meter. Do not immerse the meter above

the immersion level (See Appendix C, Figure 1c). Allow the reading to stabilize (stays

the same for about 10 seconds).

 Enter the EC reading on the Soil Data worksheet in decisiemens per meter (dS/m). The

DiST WP 4 meter gives readings directly in dS/m. For the Microsensor 4 meter, divide

the reading by 10, and for the Microsensor 3 meter, divide the reading by 100 to get

readings in dS/m.

 Save the soil-water mixture for the pH measurement (Chapter 6).

Turn the meter off. Thoroughly rinse meter with distilled water and replace cap.

Calibration Tip: Make sure the EC

meter is calibrated before

making a measurement.

See Appendix C for calibration instructions.

1

2

3

4

 Did You Know?

Excess salts in soil can be a

detriment to plant health. Salts

can also hamper water movement into the soil and increase

the occurrence of surface compaction.
15

6. Soil pH Test

Use the same soil-water mixture prepared in the EC test to conduct the pH Test. If you are starting with a fresh soil sample, read the introduction and follow Steps 1-3 in the EC Test Chapter

on preparing the sample.

Materials needed to measure pH:

 1/8-cup (30 mL) measuring scoop

 plastic specimen bottle

 calibration buffer solutions

 squirt bottle

 pH pocket meter (red with black cap)

 distilled water

Considerations: If the soil sample is saturated or very wet, a 1:1 ratio, on a volume basis, of soil

to water will not be obtained in the soil-water mixture (See Step 2, Chapter 5). Let the soil dry

before proceeding with Step 1 in Chapter 5. Also, a small amount of salts diffuse out of the pocket

pH meter; therefore, EC measurements should always be taken first when measuring both EC

and pH on the same sample.

Measure and Record pH

 Make sure to periodically calibrate your pH meter (See Appendix C for instructions). If

the meter has not been used in a while, place the meter in tap water for about 5 minutes

before calibrating or taking a reading.

 Wait about 10 to 15 minutes after the EC measurement before measuring the pH. This

gives the soil particles time to settle. Insert the pH pocket meter into the topmost

portion of the solution and turn the meter on. Wait until the reading stabilizes (0-30

seconds), and record the digital reading on the Soil Data worksheet.

Rinse Pocket Meter

 Thoroughly rinse the electrode with distilled water.

 Store the electrode with a few drops of the pH 7 buffer solution and replace the cap.

(See Appendix C on storage of pH meter)

 Did You Know?

Soil acidification can also be an

indication of excessive N fertilizer

applications and N leaching loss.

Maintenance Tips: Check the batteries

and calibrate the EC and

pH meters periodically.

Be sure to clean the

meters thoroughly to keep

them working properly.

1

2
16

7. Soil Nitrate Test (NO3

-

)

Use the same sample prepared for the EC and pH tests to measure soil nitrates. If you are starting

with a fresh soil sample, read the introduction and follow Steps 1-3 in the EC Test Chapter on

preparing the sample.

Materials needed to measure soil nitrate:

 filter paper

 120-mL plastic container with lid

 eye dropper

 nitrate/nitrite test strips

 stopwatch or timer

 distilled water

Fold Filter

Fold the filter paper in half (into a semicircle).

Fold it again, but not quite into a quarter-circle.

Leave the edges a little uneven as in Figure 7.1

(A black line is drawn for demonstration purposes.)

Insert Filter Paper into Subsample

Open the filter paper into the shape of a cone and push

it (pointed part first) quickly into the jar with the

soil/water mixture until it touches the bottom of the

jar (Figure 7.2). Wait until about an eye dropperfull of the solution has seeped through to the inside

of the filter paper. (Note: Inserting the filter

paper quickly prevents it from wetting up and

tearing as it is inserted.)

[For Steps 3 & 4, it would be helpful to first

familiarize yourself with the directions on the

side of the bottle of nitrate strips.]

Place Drops on Nitrate Strips

Using the eye dropper and one nitrate/nitrite test strip, place 1 or 2 drops of the filtered

solution on each of the strip's two pads. Note the time.

NOTE: One pad measures the amount of nitrite, and the other measures the amount of

nitrite and nitrate combined. Nitrite rarely occurs in measurable amounts in soils, so nitrite

readings from the test strips are not recorded.

1

3

2

Figure 7.2

 Did You Know?

Soil nitrates are good measures of

plant-available nitrogen, but they

can be readily lost from the soil by

leaching and volatilization.

Figure 7.1
17

Measure and Record Nitrate

 Align the nitrate/nitrite test strip with the bottom of the bottle with your thumb corresponding to the diagram on the bottle.

 After 60 seconds, compare the first pad (furthest from your thumb) along the nitrate scale

as shown in Figure 7.3. Estimate the nitrate

amount according to the degree of color change.

Enter the value from the nitrate scale on the Soil

Data worksheet in ppm. This value is an estimate of nitrate-N concentration in the extract.

Did You Know?

Water samples may be taken from drinking water, well water, tile drainage, drainage

ditches, and ponds. Dip a nitrate/nitrite test strip into the water and estimate the nitrate or

nitrite concentration from the color chart on the test strip bottle. This test can give you an

idea of how much N fertilizer is lost from the soil. (See Chapter 12).

CALCULATIONS:

Estimated (lb NO3

-N/acre) =

(ppm extract NO3-N) x (depth of soil sampled in cm) x bulk density x 0.89

 10

Exact (lb NO3

-N/acre) =

(ppm NO3-N) x (volume water used) x (depth of soil sampled, cm) x bulk density x 0.89

 (dry weight of soil) x 10

Volume water used = 30.0 mL + [dry weight of soil x soil water content (g/g)]

Note: The maximum nitrate-N reading on the nitrate/nitrite test strip container is 50 ppm. If the

sample reading falls into the 50 ppm category, the sample can be diluted to get a better estimate of

the actual amount over 50 ppm. To dilute the sample, fill the eye dropper with filtered solution and

place five drops in a plastic container. Add five drops of distilled water; mix gently by swirling the

container. Take a reading with a new test strip as stated in Step 4. Multiply the estimated nitrate-N

in ppm by 2 before using the calculations. If the nitrate reading falls into the category of 50 ppm

again, repeat the dilution steps, and multiply the estimated nitrate-N in ppm by 4.

Figure 7.3

4

NOTE: The nitrate test strips have a shelf-life.

Check the expiration date on the bottle.
18

8. Aggregate Stability

Aggregate stability measures the amount of stable aggregates against flowing water. It is recommended that aggregate stability be determined on the top three inches of surface soil. The soil

sample should be air-dried before determining aggregate stability.

Materials needed to measure aggregate stability:

 2-mm sieve (3-inch diameter)

 0.25-mm sieves (2.5-inch diameter)

 terry cloths

 400-watt hair dryer and drying chamber

 calgon solution (about 2 tbsp of calgon

per 1/2 gallon of tap water)

 bucket or pan

 scale (0.1 g precision)

 distilled water

Considerations: If the soil is moist, air-dry a sample before determining aggregate stability.

When taking a soil sample, care should taken not to disrupt the soil aggregates.

Sieve the Soil Sample

Transfer about a 1/4 cup of air-dried soil to the 2-

mm sieve. Shake the sieve gently and collect the

soil passing through the sieve. Try to pass all of the

soil through the sieve by gently pressing the soil

through with your thumb (Figure 8.1).

Weigh Sieved Soil Sample

Weigh the 0.25-mm sieve, and record its weight on

the Soil Data worksheet. Weigh out about 10 g of

the sieved soil from Step 1 (make sure the soil is

mixed well before taking a subsample). Record the

exact weight on the Soil Data worksheet.

Slowly Wet the Soil Sample in Sieve

Saturate one of the terry cloth sheets with distilled

water and lay it flat. Place the 0.25-mm sieve

containing the soil on the wet cloth, allowing the

soil to wet up slowly (Figure 8.2). Wet the soil for five minutes.

NOTE: A container (bucket or pan) of distilled water is needed for Step 4. The water temperature should be at or near the temperature of the soil.

1

2

3

 Did You Know?

Soil aggregates protect organic

matter within their structure

from microbial attack. Formation and preservation of aggregates allows organic matter to

be preserved in the soil.

Figure 8.1

Figure 8.2

Terry cloth

Sieves
19

Wet Sieve the Soil

• Place the 0.25-mm sieve with soil in the container filled with distilled water, so that the

water surface is just above the soil sample.

• Move the sieve up and down in the water through a vertical distance of 1.5 cm at the

rate of 30 oscillations per minute (one oscillation is an up and down stroke of 1.5 cm in

length) for three minutes. Important: Make

sure the aggregates remain immersed in

water on the upstroke.

Dry Aggregates

After wet sieving, set the sieve with aggregates on a

dry piece of terry cloth, which will absorb the

excess water from the aggregates in the sieve. Then

place the sieve containing the aggregates on the

drying apparatus (Figure 8.3). Allow the samples

to dry using the low power setting.

NOTE: Be careful when drying the soil to prevent particles from blowing out of the sieves. It

may be necessary to put a cover over the top of the sieves to keep aggregates in place.

Weigh Aggregates

After drying, allow the aggregates and sieve to cool for five minutes. Weigh the sieve

containing the aggregates. Record the weight of the sieve plus aggregates on the Soil Data

worksheet.

Disperse Aggregates in Calgon Solution

• Prepare calgon solution. Immerse the sieve containing the dried aggregates in the

calgon solution (do not completely immerse the sieve). Allow the aggregates in the

sieve to soak for five minutes, moving the sieve up and down periodically. Only sand

particles should remain on the sieve.

• Rinse the sand on the sieve in clean water by immersing the sieve in a bucket of water

or by running water through the sieve.

Dry and Weigh Sand

• Remove excess water by first placing the sieve containing the sand on the dry terry

cloth, then placing it on the drying apparatus. Allow sand to dry.

• After drying, allow the sand and sieve to cool for five minutes. Weigh the sieve containing the sand. Record the weight of the sieve plus sand on the Soil Data worksheet.

5

6

7

8

CALCULATIONS:

Water Stable Aggregates (% of soil > 0.25mm) = (weight of dry aggregates - sand)

 (weight of dry soil - sand)

4

Figure 8.3

seives

drying chamber

x 100
20

9. Slake Test

The slake test measures the stability of soil when exposed to rapid wetting. This test is qualitative

and should be measured on air-dried soil fragments or aggregates.

Materials needed to measure slaking:

 complete soil stability kit

 sampling scoop

 distilled water (1 L)

Considerations: The soil should be air-dry when performing this test. If the soil is not dry,

collect surface fragments as described in Step 1 and allow them to dry. Be careful not to destroy

the soil fragments while sampling.

Collect Surface Fragments

• Carefully remove soil fragments or aggregates

from the soil surface. If there is a surface crust,

carefully sample pieces of it. Use the flat end

(handle) of the scoop to lift out surface and

subsurface fragments. If the soil has been

tilled, collect some aggregates (about 1 cm in

size). Be careful not to shatter the soil fragments or aggregates while sampling.

• Collect 16 separate soil fragments. If there is a

surface crust, collect eight fragments of the

crust and eight fragments from below the crust.

Fill Box with Water

• Remove all sieve baskets from the stability kit.

• Fill the compartments in the box with water.

The water should be 2 cm deep and at approximately the same temperature as the soil.

Test Soil Fragments

• Place soil fragments in the sieve baskets

(Figure 9.1).

• Lower one of the sieves into a box compartment filled with water (Figure 9.2).

1

2

3

 Did You Know?

Soil stability serves as a qualitative indicator of soil biological

activity, energy flow, and nutrient cycling. Binding of soil

particles must constantly be

renewed by biological processes.

Figure 9.1

Figure 9.2
21

5

Observe Fragments

• Observe the soil fragment for five minutes. Refer to the stability class table below to

determine classes 1 and 2.

• After five minutes, raise the basket out of the water, then lower it to the bottom. It

should take one second for the basket to clear the surface and one second to return to the

bottom.

• Repeat immersion four times (total of five immersions). Refer to the stability class

table below to determine classes 3 through 6.

Record Ratings

• Soil stability is rated according to the time required for the fragment to disintegrate

during the five-minute immersion and the proportion of the soil fragment remaining on

the mesh after the five extraction-immersion cycles. [See table below.]

 Record the stability ratings for all 16 soil fragments or aggregates on the Soil Data

worksheet.

4

Stability class Criteria for assignment to stability class (for “Standard Characterization”)

0 Soil too unstable to sample (falls through sieve).

1 50 % of structural integrity lost within 5 seconds of insertion in water.

2 50 % of structural integrity lost 5 - 30 seconds after insertion.

3 50 % of structural integrity lost 30 - 300 seconds after insertion or < 10 % of

soil remains on the sieve after 5 dipping cycles.

4 10 - 25% of soil remaining on sieve after 5 dipping cycles.

5 25 - 75% of soil remaining on sieve after 5 dipping cycles.

6 75 - 100% of soil remaining on sieve after 5 dipping cycles.
22

10. Earthworms

Earthworms are most active during the spring and fall, which are the best times to observe their

activity.

Materials needed to measure the number of earthworms:

 tap water (2 L)

 hand trowel or shovel

 large jar or container for worm collection

 and cleaning

 mustard solution (2 tablespoons mustard

 powder in 2 liters of tap water)

Considerations: When examining the soil for earthworms, avoid places where their populations

might be affected, such as near mulch or compost piles. The abundance of earthworms is usually

patchy within a field and varies with season. Therefore, count earthworms several times during a

season and use the average to gauge changes from year to year.

Dig Plot

Measure a square-foot plot and dig down 12 inches

with the hand trowel or shovel (Figure 10.1). Try

to minimize the number of cuts with the shovel to

avoid damage to the earthworms. Dig the hole

first, then sort for earthworms.

Count the Number of Earthworms

Sort the soil samples against a pale-colored background to help locate the earthworms. Separate

and count the number of earthworms.

Add Mustard Solution (optional)

To facilitate extraction of deep burrowing earthworms, add two liters of mustard solution to the

hole. First, make sure the bottom of the hole is

level. The deep burrowing worms should appear

within five minutes (Figure 10.2). Count the

number of worms.

Record Total Number of Earthworms

Record the total number of earthworms (those found in the hole and after adding the mustard solution) on the Soil Data worksheet. [The mustard solution should not harm the

worms. Rinse them in water before returning them to the soil.]

1

2

3

4

 Did You Know?

Earthworm burrowing improves

infiltration and their casts

improve aggregation. Earthworms also break down larger

bits of residue for use by other

soil organisms.

Figure 10.2

Figure 10.1
23

11. Soil Physical Observations and Estimations

Materials needed in observing the soil physical properties:

 tape measure

 sharpshooter spade or shovel

 18-inch metal rod

 tap water

Dig hole

Dig a hole to a depth of 1 foot. Make it wide enough to cut out a slice of soil.

Cut Slice of Soil

Using the shovel, cut a slice of soil from a wall of the hole and

lay it on the ground.

Measure Depth of Topsoil

• Measure the depth of the topsoil. Look for color changes

from the soil surface downward through the soil profile.

The topsoil is usually distinguished by a darker color than

the underlying material (See Figure 11.1).

• Record the depth of topsoil on the Soil Data worksheet.

Observe Plant Roots

• Observe plant roots in the hole and the slice of soil. To get a better look at the roots, dig

down along a plant stem. The roots should be well branched with lots of fine root hairs.

• Things to look for are balled up roots or roots growing sideways. A lack of fine root

hairs indicates oxygen deprivation in the root zone. Lateral root growth indicates a

hardpan, or compacted layer.

Determine Resistance

• Use the metal rod to probe one of the side walls,

starting from the soil surface to the bottom of

the hole. Determine changes or differences in

penetration resistance as you probe the side wall

(See Figure 11.2).

• Look for compacted layers that may restrict

root growth and water movement.

1

2

3

4

5

Figure 11.2

Figure 11.1

aaaaaa aaaa

Topsoil

Soil surface
24

Examine Soil Structure

Observe soil structure in the slice of soil to a depth of about 12 inches. Measure and mark,

starting at the surface and moving downward; depth increments of 0 to 4 inches, 4 to 8

inches, and 8 to 12 inches. Note and record the type, size, and grade of the soil structural

units or aggregates for each depth increment.

Note: Soil structure is how particles of soil are grouped together in stable collections or

aggregates.

Note the type of soil structure at each of the three depth increments.

• The three general types of soil structure are granular (Figure 11.3), blocky (Figure

11.4), and platy (Figure 11.5).

• If there are no noticeable aggregates or peds, the soil has no structure. It is either single

grained (Figure 11.6) or massive (Figure 11.7).

• Record on the Soil Data worksheet the type of structure observed for each depth increment.

Figure 11.3 Granular:

imperfect spheres, usually

sand-size.

Figure 11.4 Blocky:

imperfect cubes with

angular or rounded edges.

Figure 11.5 Platy:

a flattened or compressed

appearance.

6a

Figure 11.6 Single grain:

unconsolidated mass such

as loose sand.

Figure 11.7 Massive:

cohesive mass.

6
25

Note the size of the aggregates or peds at the different depths.

• Estimate the general size of the aggregates or peds. If the structure is granular, choose

from fine (Figure 11.8), medium (Figure 11.9) and coarse (Figure 11.10) granule sizes.

• If the structure is blocky, choose from very fine (Figure 11.11), fine (Figure 11.12),

and medium (Figure 11.13) block sizes.

• If structure is platy, choose from thin (Figure 11.14), medium (Figure 11.15), and thick

(Figure 11.16) plate sizes.

• Record on the Soil Data worksheet the size of the aggregates or peds observed for each

depth increment.

6b

Figure 11.8

Fine: < 2 mm.

Figure 11.9

Medium: 2 to 5 mm.

Figure 11.10

Coarse: 5 to 10 mm.

Figure 11.11

Very fine: < 5 mm.

Figure 11.12

Fine: 5 to 10 mm.

Figure 11.13

Medium: 10 to 20 mm.

Figure 11.14

Thin: < 2 mm.

Figure 11.15

Medium: 2 to 5 mm.

Figure 11.16

Thick: 5 to 10 mm.
26

Note the distinctness (grade) of the aggregates in place and when removed from the

slice of soil.

The distinctness of the aggregates is either weak, moderate, or strong.

Weak structure:

• Aggregates or peds are barely observable in

place in moist soil.

• When removed, the structure breaks into a few

observable aggregates or peds (Figure 11.17).

Moderate structure:

• Aggregates or peds are moderately well-formed

and distinct in place.

• When removed, many well-formed aggregates

are observable (Figure 11.18).

Strong structure:

• Aggregates or peds are well-formed and very

evident in place.

• When disturbed, the structure breaks into quite

evident aggregates or peds (Figure 11.19).

Record on the Soil Data worksheet the grade of the

aggregates or peds observed for each depth increment.

Determine soil textural class

• Perform the Texture by Feel procedure (See page 27) on the top three inches of soil.

• Record on the Soil Data worksheet the soil textural class.

6c

7

Figure 11.17

Figure 11.18

Figure 11.19
27

TEXTURE BY FEEL

PROCEDURE

Place approximately 25 grams in palm. Add

water dropwise and knead the soil to break down

all aggregates. Soil is at the proper consistency

when plastic and moldable, like moist putty.

Does soil remain in a

ball when squeezed? Is the soil too dry? Is the soil too wet?

Place ball of soil between thumb and forefinger, gently push the soil with the thumb, squeezing

it upward into a ribbon. Form a ribbon of uniform thickness and width. Allow the ribbon to

emerge and extend over the forefinger, breaking from its own weight.

Does the soil form a ribbon?

Does soil make a weak

ribbon less than 1 inch long

before breaking?

Does soil make a strong

ribbon two inches or longer

before breaking?

Does soil make a ribbon 1 inch

long before breaking?

Add dry soil to soak

up water

Excessively wet a small pinch of soil in palm and rub with forefinger.

 Clay

Loam

Silty

Clay

Loam

Loam Clay

Silt

Loam

Sandy

Clay

Loam

Silty

Clay

Sandy

Clay

Sandy

Loam

 Sand

Loamy

Sand

Does soil

feel very

gritty?

Does soil

feel very

gritty?

Does soil

feel very

gritty?

Does soil

feel very

smooth?

Does soil

feel very

smooth?

Does soil

feel very

smooth?

Neither

gritty nor

smooth?

Neither

gritty nor

smooth?

Neither

gritty nor

smooth?

Yes

Yes Yes

Yes

Yes Yes Yes

Yes Yes Yes

Yes Yes

Yes

Yes Yes Yes

No

No

No

No

No

No

No No

No

No No No

Making a Ribbon
28

12. Water Quality Tests

A. Estimation of Water Nitrate and Nitrite levels

Materials needed to determine water nitrate (NO3

-

) and nitrite (NO2

-

) levels:

 filter paper

 120-mL plastic containers with lids

 eye dropper

 nitrate/nitrite test strips

 stopwatch or timer

Considerations: Water samples may be taken from drinking water, well water, tile drainage,

drainage ditches, and ponds. Sample surface runoff from fields, which may be a contributing

source of contaminates.

Filter Water Sample (if cloudy)

 Collect water sample in the plastic container. Fill to about 1/3 full.

 Fold a piece of filter paper as described in Chapter 7--Soil Nitrate Test. Insert filter

paper into the jar and allow the water to seep through the filter paper to the inside. [If

the water sample is clear (no cloudiness or suspended particles), the sample does

not need to be filtered.]

Place Drops on Nitrate and Nitrite Strips

Using the eye dropper, collect a sample of the filtered water. Place 1 or 2 drops of the

filtered solution on each of the strip's two pads. Note the time.

[One pad measures the amount of nitrite and the other measures the amount of nitrite

and nitrate combined.]

Measure and Record Nitrate and Nitrite.

 After 30 seconds, measure and record nitrite.

Estimate the nitrite amount according to the degree of color change. Enter the value on

the Soil Data worksheet in ppm from the nitrite scale on the bottle.

 After 60 seconds, measure and record nitrate.

Estimate the nitrate amount according to the degree of color change. Enter the value on

the Soil Data worksheet in ppm from the nitrate scale on the bottle.

[Note: Estimate results if colors on test pads fall between two color patches.]

1

2

3
29

B. Estimated Water Salinity Levels

Materials needed to estimate water salinity levels:

 EC pocket meter

 120-mL plastic containers and lids

 distilled water

Considerations: Water samples may be taken from drinking water, well water, tile drainage,

ditches, irrigation water, and ponds.

Collect Sample

Collect water sample in plastic container. Fill to about 1/3 full.

Measure Electrical Conductivity

 Insert the EC pocket meter into the water sample. Allow the reading to stabilize (stays

the same for about 10 seconds). Note the digital reading.

 Enter the EC reading on the Soil Data worksheet in decisiemens per meter (dS/m). The

DiST WP 4 meter gives readings directly in dS/m. For the Microsensor 4 meter, divide

the reading by 10, and for the Microsensor 3 meter, divide the reading by 100 to get

readings in dS/m. Insert the EC pocket meter into the water sample until the reading

stabilizes (stays the same for about 10 seconds). Note digital reading.

Rinse Pocket Meter

Turn off the meter. Thoroughly rinse the meter with distilled water, and replace cap.

2

3

1

 Did You Know?

Healthy soil not only improves crop

performance, it also cleans and stores

water; and prevents runoff and erosion;

and uses nutrients more efficiently,

reducing the need for pesticides.
30

A. References

Arshad, M.A., B. Lowery, and B. Grossman. 1996. Physical tests for monitoring soil quality. p.123-

142. In: J.W. Doran and A.J. Jones (eds.) Methods for assessing soil quality. SSSA Spec.

Publ. 49. Soil Science Society of America, Inc., Madison, Wisconsin, USA.

Dick, R.P., D.R. Thomas, and J.J. Halvorson. 1996. Standardized methods, sampling, and sample

pretreatment. p.107-122. In: J.W. Doran and A.J. Jones (eds.) Methods for assessing soil

quality. SSSA Spec. Publ. 49. Soil Science Society of America, Inc., Madison, Wisconsin,

USA.

Gershuny, G. and J. Smillie. 1995. The soul of soil: A guide to ecological soil management. 3rd ed.

agAccess, Davis, California, USA.

Parkin, T.B. and J.W. Doran. 1996. Field and laboratory tests of soil respiration. p.231-246. In: J.W.

Doran and A.J. Jones (eds.) Methods for assessing soil quality. SSSA Spec. Publ. 49. Soil

Science Society of America, Inc., Madison, Wisconsin, USA.

Powell, D. and J. Pratley. 1991. Sustainability kit manual. Centre for Conservation Farming.

Charles Sturt University-Riverina, PO Box 588, Wagga Wagga 2650, Australia.

Rowell, D.L. 1994. Soil science: methods and applications. Longman Scientific & Technical,

Singapore.

Sarantonio, M., J.W. Doran, M.A. Liebig, and J.J. Halvorson. 1996. On-farm assessment of soil

quality and health. p.83-106. In: J.W. Doran and A.J. Jones (eds.) Methods for assessing soil

quality. SSSA Spec. Publ. 49. Soil Science Society of America, Inc., Madison, Wisconsin,

USA.

Smith, J.L. and J.W. Doran. 1996. Measurement and use of pH and electrical conductivity. p.169-

186. In: J.W. Doran and A.J. Jones (eds.) Methods for assessing soil quality. SSSA Spec.

Publ. 49. Soil Science Society of America, Inc., Madison, Wisconsin, USA.
31

B. Soil Respiration (Alternative Method)

This alternative method uses a kit produced by Woods End1 known as the Solvita Soil Life Kit1.

Instead of the Draeger tube apparatus, this procedure uses "paddles" inserted into a plastic container with the soil sample (See procedure on page 32). The use of this method eliminates the need

for the Draeger tube (carbon dioxide adsorption tube), needle, and syringe. With the Solvita kits,

results are given in 24 hours instead of 30 minutes with the Draeger method. The color change of

the paddles may also be easier to distinguish than reading the color change off the Draeger tubes.

The Solvita kit also requires the soil to be disturbed and will falsely stimulate microbial activity

similar to the action of tillage. However, when used to compare sites, both soils are disturbed and

the relative differences are noted. This procedure also reduces the effects of root respiration.

Picking out as many roots from the sample as possible will further eliminate their CO2

 contribution. The Solvita kit may be preferred if immediate results are not necessary and the microbial

activity differences without the influence of plant roots are desired.

The Solvita kit comes with well written and user friendly instructions and interpretations. There is

also a trouble shooting guide to help the user. The kit consists of four parts: the sample jar to hold

the correct volume of soil for the test (Figure 1b); a foil-pack containing a special color gel paddle

(Figure 2b); instruction manual; and a color key for reading results (Figure 2b).

Solvita Soil Life kits can be obtained from Woods End Research, Mt. Vernon, ME;

solvita@woodsend.org.

Figure 1b Figure 2b

Paddle

1

Trade names are used solely to provide specific information. Mention of a trade name does not constitute a guarantee of the

product by the U.S. Department of Agriculture nor does it imply endorsement by the Department or the Natural Resources

Conservation Service over comparable products that are not named.
32

The following is part of the instructions from the SOLVITA SOIL LIFE KIT1:

1

Trade names are used solely to provide specific information. Mention of a trade name does not constitute a guarantee of the

product by the U.S. Department of Agriculture nor does it imply endorsement by the Department or the Natural Resources

Conservation Service over comparable products that are not named.
33

C. EC and pH Meter Maintenance and Calibration

EC meter maintenance:

· Do not immerse the EC meter above the immersion

level (Figure 1c). Under no circumstances should the

meter be immersed above the display level.

· When not in use, switch off the meter and replace the

protective cap.

· To improve performance, clean the stainless steel

electrodes periodically by rinsing them in alcohol for a

few minutes.

· Replace all four batteries if the display becomes faint

or disappears or if the readings are unstable or constant.

· To change batteries for DiST WP1 models, unscrew the

top with a coin and replace the batteries (Figure 2c).

EC meter calibration:

· Immerse the meter into the calibration solution (1.41

dS/m).

· Allow the reading to stabilize. Using a small screwdriver, turn the Calibration Trimmer to match the

solution value, 1.41 dS/m (normally at 25 C).

pH meter maintenance:

· Crystals may appear around the cap (Figure 3c). This

condition is normal. The crystals will dissolve when

rinsed with water.

· After use, rinse the electrode with water to

minimize contamination.

· Store the electrode with a few drops of storage solution (HI 70300L) or pH 7 solution in the

protective cap. DO NOT STORE IN DISTILLED OR DEIONIZED WATER.

· Always replace the protective cap after use.

Figure 2c.

Figure 3c.

Calibration

Trimmer

Batteries

Figure 1c.

Immersion

Level

Crystals
34

· Large differences in pH readings (± 0.5 pH) could be

due to lack of calibration, dry electrode, or rundown

batteries.

· If the pH meter cannot be switched on or if the display

fades, unscrew the battery compartment and replace all

four batteries, paying attention to their polarity (Figure

4c).

pH meter calibration (pHep 31):

· Prepare buffer solutions. Only 2 buffers are needed, pH 7 and 4 or 10, depending on the pH

range of your soils (see Figure 5c).

· Switch the unit on by pressing the ON/OFF button.

· With the meter on, press and hold the ON/OFF button for about three seconds. The display will

start blinking "7.0o" to confirm that you have entered the calibration mode.

· Immerse the pH meter in the pH 7 buffer solution. Stir gently and wait approximately 20

seconds.

· If "Ec" appears on the display, the pH 7 solution is not fresh, or the electrode is not conditioned.

· The pHep 31 meter automatically confirms the pH 7 calibration after the meter is adjusted. The

display will blink "4.0o". After a few seconds, it will display "Ec" to prompt you to use a

second buffer solution.

· Rinse the electrode with water and immerse in pH 4 for acidic samples or pH 10 for alkaline

samples. Allow approximately 20 seconds for the meter to auto-confirm the reading. Once the

display stops blinking, the meter is calibrated and ready to use. ALWAYS USE FRESH BUFFERS FOR CALIBRATION.

Figure 5c.

1

Trade names are used solely to provide specific information. Mention of a trade name does not constitute a guarantee of the

product by the U.S. Department of Agriculture nor does it imply endorsement by the Department or the Natural Resources

Conservation Service over comparable products that are not named.

Figure 4c.

Battery

compartment

Immersion

level
35

D. Building a Soil Quality Test Kit

Kit Inventory:

____ Two 6-inch diameter infiltration rings, 5 inches tall;

cut from 1/8-inch thick aluminum irrigation pipe;

beveled edge on one side (Figure 1d). Mark a line

around the outside of the ring, 2 inches from the top.

____ 12-inch wide roll of plastic wrap.

____ Two 500-mL plastic graduated cylinders. As a substitute, 500-mL plastic bottles or 16 oz. plastic soft

drink containers can be used (Figure 2d). Mark a

line around the bottle at the 444 mL level.

____ 2-lb hand sledge or rubber mallet (Figure 3d).

____ 7 3/4-inch long wood block, 2" by 4" (Figure 3d).

____ Two 6-inch lids with septa (stoppers) for respiration

chamber; 6-inch diameter stove-top caps can be used

(Figure 4d). As an alternative, the bottoms from a

#10 can (coffee can) can be cut (1 inch lip) and used

(Figure 5d). The lids should be white or silver to

reduce absorption of heat. Three holes fitted with red

rubber stoppers, for serum or vaccine bottles, are

drilled through the top of the lid to allow for gas

sampling.

____ Two 6-inch long latex tubing (3/16" x 1/16").

____ Three 18- to 22-guage, 1.5-inch hypodermic needles.

____ 140-cc (mL) plastic syringe (Figure 6d). A 2-mm

hole can be drilled at the end of the syringe handle.

____ Pack of 10 Draeger tubes (0.1% CO2

 detection tubes)

[Figure 6d].

____ Soil thermometer (Celsius).

____ Two 3-inch diameter sampling tubes, 5 inches tall;

cut from 1/8-inch thick aluminum irrigation pipe;

beveled edge on one side (Figure 1d). Mark a line

around the outside of the ring, 2 inches from the top.

____ Flat-bladed knife.

____ Garden trowel (heavy duty) [Figure 7d].

____ 1-qt sealable plastic storage bags.

____ 18-inch long metal rod, 1/8-inch in diameter. As a

substitution, a straightened coat hanger can be used.

____ Calibrated scoop, 30.0 mL (1/8 cup) [Figure 7d].

____ Squirt bottle.

____ Four 120-mL plastic containers with lids (Figure 7d).

As an alternative, any container with lid of similar

size can be used; e.g., baby food jars.

____ Electrical conductivity meter (0.01-9.99 mS range)

Figure 2d

Figure 1d

Figure 3d

6-inch ring

3-inch tube

Figure 4d

Stoppers

[Figure 8d].
36

____ EC calibration standard, 1.41 dS/m (0.01 M KCl).

____ Small screw driver (for EC meter).

____ pH meter (model pHep31) [Figure 8d].

____ Packets of 4, 7 and 10 pH buffers (Figure 9d).

____ Bottle of 25 AquaChek1 nitrate/nitrite test strips

(Figure 10d).

____ Box of filter paper, 12.5-cm diameter, Grade 2 - 5 can

be used (Figure 11d).

____Three standard plastic eyedroppers.

____Tape measure; 6-foot (metric and English units).

____ Small calculator

____ Permanent marker pen

____ 400-watt hair dryer (Figure 12d).

____ 2-mm sieve, 3-inch diameter (Figure 13d).

____ Two 0.25-mm sieves, 2-inch diameter (Figure 14d).

____ Drying chamber, holds two 2-inch sieves (Fig. 15d).

____ Two 6" x 6" sheets of terry cloth.

____ Calgon1 (crystal form).

____ Soil stability kit (18 section tackle box with 18 1.5-

mm sieve baskets) [Figure 16d].

____ Stopwatch or timer.

____ Finger nail clipper.

____ Paper cups.

Other items needed:

____ Bucket or pan.

____ Mustard powder (optional).

____ Sharpshooter spade or shovel

____ Distilled water.

The kit requires the use of a scale with 0.1 g precision.

1

Trade names are used solely to provide specific information. Mention of a trade name does not constitute a guarantee of the

product by the U.S. Department of Agriculture nor does it imply endorsement by the Department or the Natural Resources

Conservation Service over comparable products that are not named.

Figure 6d

Draeger

tubes

Syringe

Needle

Latex

tubing

Figure 5d

Figure 7d

Scoop

Plastic vial Garden

trowel

Figure 8d

EC pH

Figure 9d
37

The list on the previous pages describes all the equipment

necessary for building a kit. The following are some listed

items that can be easily constructed.

Construction of 2-mm sieves

1. The 2-mm-opening sieve can be made from No. 10

screens (2-mm openings) cut into discs approximately

75 mm in diameter.

2. The disc periphery is soldered with acid-core solder

and mounted on the lip of 3-inch diameter PVC bushings.

3. A section of PVC (sleeve), dimensions 75 mm in

diameter by 38 mm high (280 lb per inch rating), is

made.

4. PVC cement is placed on the outside wall of the PVC

sleeve, and on the inside wall of the PVC bushing. The

PVC sleeve is pushed down firmly in to the PVC

bushing, so they are cemented together (Figure 13d).

Construction of 0.25-mm sieves

The 0.25-mm opening sieves can be made from No. 60

screens (hardware store) cut and mounted on the bottom of

2-inch diameter PVC joints (hardware or plumbing supply

stores) using PVC cement, epoxy, or other thick glue

(Figure14d).

Construction of drying chamber

1. Any plastic container can be used. The container used

here is a 4" x 6" plastic container with lid (Figure 15d).

2. Drill two 21⁄4-inch holes in the bottom of the container

(for insertion of 2-inch sieves).

3. Drill four 1⁄4-inch holes in each side of the container,

and a 1-inch hole on one side for insertion of the hair

dryer. A 1-inch rubber grommet can be used to line the

1-inch hole to create a good seal when the hair dryer is

inserted (See Figure 15d).

To accommodate the drying of more sieves (efficient for a

large number of samples), a bigger container can be used

with more 21⁄4-inch holes (Figure 18d). The container

pictured in Figure 18d is a small, trunk-style tackle box

(13.5 x 8 x 6 inches). The inside tray was removed.

Figure 11d

Figure 13d

Figure 10d

Figure 12d
38

Construction of Soil Stability Kit

Construction of Box

1. Obtain a “parts” or “tackle” box with a lid; 18 cells,

each cell at least 11⁄4" x 11⁄4" x 11⁄2" deep (Figure 16d).

[sporting goods or hardware store].

2. Seal individual cells in the box with a small bead of

silicone glue or caulk.

Construction of Sieve Baskets (Figure 17d)

Materials:

· PVC, 1-inch in diameter, thin wall, about 21⁄2 feet long.

· Aluminum window screen (1.5-mm openings), 4" x 8"

piece (hardware store).

· Adhesive (epoxy or thick glue) [grocery or hardware

store].

Instructions:

1. Beginning at left end of the PVC pipe, make marks at

11⁄2-inch intervals; 20 marks are needed.

2. Make a smaller mark 1⁄4 to 3/8 inches to the left of all

the first marks.

3. Beginning at left end, cut 3⁄4 of the way through the tube

at the first small mark using a hacksaw or bandsaw.

4. Beginning at the left end, use tin snips to make two

lengthwise cuts through the tube, leaving a 1⁄4" diameter

“tab” (See Figure 17d).

5. Using tin snips or hacksaw, cut through the tube at the

first large (11⁄2 inch) interval mark.

6. Repeat steps 6-8 for each of the 20 sieves.

7. Cut 20 11⁄4" x 11⁄4" squares of aluminum window screen.

8. Glue a window screen square to the bottom of each

sieve.

9. After allowing glue to dry, carefully trim screen to

edge of sieves.

Figure 15d

Figure 16d

Figure 17d

Figure 14d Figure 18d
39

Outlet for kit items include:

Supplier1

Gempler's Inc.

100 Countryside Dr.

P.O. Box 270

Belleville, WI 53508

(608) 424-1544 or (800) 382-8473

http://www.gemplers.com

Fisher Scientific

Pittsburgh, PA

Ph. (800) 766-7000

Scientific Industries

227 Blue Bell Ave.

Boulder, CO 80302

Ph. (303) 443-7087

Spectrum Technologies

23839 W. Andrew Rd.

Plainfield, IL 60544

Ph. (800) 248-8873

Whatman Labsales

P.O. Box 1359

Hillsboro, OR 97123

Ph. (800) 942-8626

Walgreens

Forestry Suppliers, Inc.

PO Box 8397

Jackson, MS 39284

Ph. (800) 647-5368

ATM Test Sieves

West Allis, WI

Ph. (800) 511-2096

Veterinary or medical supply

Hardware store

Grocery or

discount stores

Items Supplied1

A soil quality test kit as described in this manual.

All kit items.

Draeger tubes

Filter paper, pH and EC meters, scales, graduated cylinders,

500-mL bottles, plastic containers, latex tubing, hypodermic needles

Draeger tubes

AquaChek nitrate/nitrite test strips

pH and EC meters

scales

EC standard solution (500-mL bottle, 1413 microsiemens)

pH buffer capsules (pH 4, 7 and 10)

Filter paper, pH and EC meters, scales

graduated cylinders, 500-mL bottles, plastic containers

400-watt hair dryer

Sieves, scales

0.25 mm screen (60 mesh)

2.0 mm screen (10 mesh)

140-cc syringe

2-lb hand sledges, tape measures, hand trowels, small screw drivers

Plastic-wrap, 1-qt. sealable bags, 30-mL calibrated scoop

1

Trade names are used solely to provide specific information. Mention of a trade name does not constitute a guarantee of the

product by the U.S. Department of Agriculture nor does it imply endorsement by the Department or the Natural Resources

Conservation Service over comparable products that are not named.
40
Site Description DATE:

Map Location State: County:

Geographic Location Longitude: Latitude:

Field or site location

Landowner

Soil Information

Soil Series

Slope %

Erosion

Mean Annual Temp.

Mean Annual Precip.

Present Management

Cropping System

(Rotations, cover crops, etc)

Fertilizers/Pesticides

(N inputs, pesticide use, etc)

Tillage/Residue Cover

(Type, depth, frequency, timing,

% cover, etc)

Irrigation

(Pivot, gravity, amount and

timing, etc)

Other

Past Management History

Cropping System

(Rotation/fallow history, etc)

Fertilizers/Pesticides

(N inputs, pesticide use, etc)

Tillage/Residue Cover

(Past tillage, frequency and

type)

Irrigation

(past irrigation, how long?)

Unusual Events

(Floods, fires, land-leveling)

Soil Quality Evaluation Site Description
Additional Specifications and Notes:

Aerial view of field showing sampling sites and location of environmentally sensitive areas,

such as ponds, creeks, wetlands, and other fragile sites adjacent to the field.

Scale 1 inch = _________ ft. (NA indicates sketch not to scale).
NOTES:

Soil Respiration (at Initial Field Water Content)

Sample

site

(H)

Ring

height

(cm)

Start

time

End

time

(A)

Soil temp.

(Celsius)

(B)

Draeger tube

%CO2 (n=1)

*

Soil Respiration

lbs CO2-C/acre/day

1

23

4

Soil Respiration (at least 6 hours after irrigation or soil wetting)

1

23

4

* Soil respiration = PF x ((A + 273)/273) x (B - 0.035) x 22.91 x H = lbs CO2-C/acre/day

PF = Pressure Factor = 'raw' barometric pressure in inches Hg/29.9 inches.

Note: This adjustment is necessary at elevations > 3,000 ft.; otherwise PF = 1

Conversion: Degrees Celsius = 5/9 x (Degrees Fahrenheit - 32)

DATE: T

(B)

Draeger tub

%CO2 (n=5

89884444

8448484844

H = 5.08 cm HhrHyH
NOTES:

Infiltration (for 1 inch of water)

Sample

site

1st inch of water (W)

1st

Infiltration

time

(minutes)

*

1st

Infiltration

(in/hr)

2nd inch of water

Start

time

End

time

Start

time

End

time

1

23

4

* Conversion of infiltration time to inches per hour (in/hr); in/hr = (1/W) x 60

DATE:

(W)

2nd

Infiltration

time

(minutes)

7777

g
Bulk Density and Soil Water Status (core method) DATE:

Sample

site

(h)

Heightof ring

above

soil (cm)

(E)

Weight of

field moist

soil + bag

(grams)

(F)

Weight

of bag

(grams)

Subsample for determinng soil water content

(G)

Weight of

paper cup

(grams)

(I)

Weight of

paper cup

+ soil (g)

(K)

Dry

weight of

soil + cup

* (L)

Dry weight

of soil

(grams)

1

23

4

*Dry wt. of soil subsample = (K - G) **Soil H2O content = (I - K)/L

***Soil bulk density = [(E - F)/(1 + M)]/[(12.7 - h) x 42.52] h = 5.08 cm (2 inches) if not measured;

Bulk Density and Soil Water Status for Gravelly Soils (excavation method)

Sample

site

(n)

Volume

of water

(cm3

)

(E)

Weight of

field moist

soil + bag

(grams)

(F)

Weight

of bag

(grams)

Subsample for determinng soil water content

(G)

Weight of

paper cup

(grams)

(I)

Weight of

paper cup

+ soil (g)

(K)

Dry

weight of

soil + cup

* (L)

Dry weight

of soil

(grams)

1

23

4

*Dry wt. of soil subsample = (K - G) **Soil H2O content = (I - K)/L

***Soil bulk density = [(E - F)/(1 + M)]/(n) n = volume of soil in cm3

T

So

c

6666

volu

So

c

666666
Soil Electrical Conductivity, pH, and Nitrate (NO3

-

) DATE:

Sample

site

(X)

Weight of

field moist

soil

(grams)

Readings for 1:1 soil:water mix. *

Estimated

Soil NO3-N

(1b NO3-N/acre)

**

Exact

Soil NO3-N

(1b NO3-N/acre)

EC

(dS/m) pH

(Y)

Soil NO3

-N

ppm (est.)

1

2

3

4

*Estimated: lb NO3-N/acre = Y x [depth of soil in cm /10] x soil bulk density x 0.89

Depth of soil = depth of soil sampled in centimeters; for kit it is 0 to 3 inches = 7.6 cm

**Exact: lb NO3

-N/acre = Y x C.F. x [depth of soil in cm /10] x soil bulk density x 0.89

C.F. = [30 mL + ((X/(1 + M)) x M)]/[X/(1 + M)] M = decimal soil water content (g/g)

Depth of soil = depth of soil sampled in centimeters; for kit it is 0 to 3 inches = 7.6 cm

Water Quality Measurements DATE:

Sample site Salinity

(dS/m)

Water Nitrite

(ppm)

Water Nitrate

(ppm)

1

2

3

4

NOTES:
Aggregate Stability DATE:

Sample

site

(A)

Weight of

sieve

(grams)

(B)

Weight of

sieve +

aggregates

(grams)

(C)

Weight of

sieve + dry

aggregates

(grams)

(D)

Weight of

sieve + dry

sand

(grams)

*

Percent

water stable aggregates

(% of soil > 0.25mm)

1

2

3

4

* % Water stable aggregates = (C - D)/(B - D) x 100

Slake Test DATE:

Sample

site

Individual

Soil Slake Ratings

*

Average

Soil Slake Rating

1

2

3

4

* Soil Slake Rating = (add all of the individual ratings and divide by the total number)

Earthworms DATE:

Sample

site

Surface

dwelling

earthworms

Deep

dwelling

earthworms

Total Earthworms

(no. per square foot)

1

2

3

4

NOTES:
NOTES:

1

12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901

2345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901

12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901 Classes for Structure Index Structure 

Type Size Gra

Granular Fine, Medium, Coarse Weak Granular Fine, Medium, Coarse Moderate Granular Fine, Medium, Coarse Strong 

Blocky Very fine, Fine, Med. Weak Blocky Very fine, Fine Moderate Blocky Very fine, Fine, Med. Strong Blocky Medium Moderate Platy Thin, Medium, Thick Very friable

Platy Thin, Medium, Thick Friableb Platy Thin, Medium, Thick Firm or Stro

Massive 

Single Grain 

Note: a Class 5 is the best. b Substitute horizontal m

Soil Structure DATE:

Depth

(inches) Type Size Grade (A) Class (B) (A) x (B) Structure index*

0 - 4 3

4 - 8 2

8 - 12 1

*Structure index = ((Total - 6)/24) x 100 Total =

Soil Observations and Estimations DATE:

Description

Top soil depth (inches)Plant roots

Compaction layerSoil textureOther
49

Soil Quality Test Kit

SECTION II

Background & Interpretive Guide

for Individual Tests
50

Section II

 Introduction ..........................................................................................................

Background & Interpretive Guides:

 1. Soil Respiration .....................................................................................................

 2. Infiltration ............................................................................................................

 3. Bulk Density ...........................................................................................................

 4. Electrical Conductivity (EC) ...............................................................................

 5. Soil pH ....................................................................................................................

 6. Soil Nitrate ...........................................................................................................

 7. Aggregate Stability ...............................................................................................

 8. Soil Slaking ............................................................................................................

 9. Earthworms............................................................................................................

 10. Soil Physical Observations and Estimations ......................................................

 11. Water Quality .......................................................................................................

Salinity of water

Nitrate/nitrite levels in water

Page

51

52

55

57

59

63

67

69

72

73

75

79
51

INTRODUCTION

Soil quality assessment or interpretation should be considered a process through

which soil resources are evaluated on the basis of soil function (what the soil does)

and change in soil function in response to a specific natural or introduced stress, or

management practice. Five vital soil functions have been proposed. They are: (1)

sustaining biological activity, diversity, and productivity; (2) regulating and partitioning of water and solute flow; (3) filtering, buffering, degrading, immobilizing, and

detoxifying organic and inorganic materials, including industrial and municipal byproducts and atmospheric deposition; (4) storing and cycling of nutrients and other

elements within the Earth’s biosphere; and (5) providing support of socioeconomic

structures and protection for archeological treasures associated with human habitation

(Karlen et al., 1997).

It is also important to emphasize that soil quality evaluations must consider

biological, chemical, and physical properties and processes. For interpretation, the

measurements must be evaluated with respect to their long-term trends or signs of

sustainability. A general sequence of how to evaluate soil quality is to (1) define the

soil functions of concern, (2) identify specific soil processes associated with those

functions, and (3) identify soil properties and indicators that are sensitive enough to

detect changes in the functions or soil processes of concern (Carter et al., 1997).

Section II provides background and interpretive information for each test described in Section I. Each test is considered to be an indication of the level of functioning. However, indicator data is not meaningful unless a baseline or some reference condition is available for comparison or unless relative comparisons between

management systems are made.

References

Carter, M.R., E.G. Gregorich, D.W. Anderson, J.W. Doran, H.H. Janzen, and F.J. Pierce.

1997. Concepts of soil quality and their significance. p. 1-20. In: E.G. Gregorich

and M.R. Carter. (eds.) Soil quality for crop production and ecosystem health.

Elsevier Science, Amsterdam.

Karlen, D.L., M.J. Mausbach, J.W. Doran, R.G. Cline, R.F. Harris, and G.E. Schuman.

1997. Soil quality: A concept, definition, and framework for evaluation. Soil

Sci. Soc. Amer. J. 61:4-10.

Soil Processes

Soil Functions

Indicators
52

1. Soil Respiration

Introduction

Soil respiration is the production of carbon dioxide (CO2

) as a result of biological activity in the

soil by microorganisms, live roots, and macroorganisms such as earthworms, nematodes, and insects

(Parkin et al., 1996). Carbon dioxide emitted from soil is a colorless and odorless gas that enters the

atmosphere and annually exceeds the amount emitted by all human activities (Volk, 1994). The activity

of organisms in the soil is considered to be a positive attribute for soil quality.

Soil respiration is highly variable both spatially and seasonally, and is strongly affected by

moisture and temperature conditions. Because this variability can complicate interpretations, certain

sampling precautions must be taken.

Knowing the history of the sampling site and characteristics of nearby soils becomes very

important when evaluating respiration. Soil color may provide some assistance when interpreting

respiration rates. A light colored soil with a high respiration rate may be indicative of a soil being

depleted of organic matter. A relatively darker soil with the same rate could be considered healthy.

The dark color indicates the presence of organic matter. Tillage or cultivation can result in loss of

soil carbon (C) and increases in the amount of CO2 released. The soil is loosened, which creates

better accessibility of oxygen necessary for organic matter decomposition and respiration, resulting in CO2

 release (Reicosky and Lindstrom, 1995).

Interpretations

When comparing soil respiration rates from different sites or from the same site at different times,

differences in soil temperature and soil water content must be taken into account. Soil temperature

corrections can be performed using the general rule that biological activity increases by a factor of 2

with each 10EC increase in temperature (Parkin et al., 1996). The following equation can be used to

standardize (to 25EC) for differences in soil temperatures that are between 15 and 35EC:

Standardized soil respiration rate = soil respiration rate x 2[(25-T)÷10]

For soil temperatures between 0 and 15EC, the following equation is used:

Standardized soil respiration rate = soil respiration x 4[(25-T)÷10]

For example, if you had a soil respiration rate of 15 CO2-C lbs/a/d and soil temperature of 22EC,

the first equation listed above would be used, and the standardized soil respiration rate would be

calculated as follows:

1. [(25 - 22) ÷ 10] = 0.3

2. 20.3 = 1.2

3. (15 CO2-C lbs/a/d) x 1.2 = 18 CO2-C lb/a/d (standardized respiration rate at 25EC)

Standardization for differences in soil water content must also be taken into account. Maximum
53

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microbial activity generally occurs when 60% of the soil pores are filled with water (Parkin et

al., 1996). The amount of water in the pore space is referred to as water-filled pore space (WFPS),

and gives an indication of how well aerated the soil is at the time of sampling.

 Water-filled pore space (%) = (volumetric water content x 100) ÷ [1 - (soil bulk density ÷ 2.65)]

Soil respiration can be adjusted to equivalent values at 60% WFPS through the following equation for

WFPS values between 30 and 60% (Parkin et al., 1996):

Soil respiration60 = soil respiration rate x (60 ÷ measured %WFPS)

For WFPS values between 60 and 80%, the following equation is used:

Soil respiration60 = soil respiration rate ÷ [(80 - %WFSP) x 0.03] + 0.4

When the soil water content or WFPS exceeds 80%, soil respiration may be restricted by the wet

conditions and should not be measured. The relationship between WFPS and soil respiration has been

evaluated primarily in the laboratory and remains to be tested in the field (Parkin et al., 1996).
54

A high soil respiration rate, indicative of high biological activity, can be a good sign of rapid

decomposition of organic residues into nutrients available for plant growth. However, decomposition

of the stable organic matter is detrimental to many physical and chemical processes such as aggregation, cation exchange, and water holding capacity. Also, immediately following a tillage operation,

CO2 evolution can rise dramatically due to exposure of organic matter to organisms and oxygen. Also,

soil respiration can rise dramatically after rainfall (Rochette et al., 1991). The rise in soil respiration

is affected by the length of time the soil is dry before the rainfall event.

Under dry conditions, soil respiration tends to be higher in the crop row than in the interrow

(Rochette et al., 1991). The higher respiration rates are attributed to the contribution from plant roots.

Under wet conditions, there tends to be no difference in respiration between the row and interrow.

When the soil interrow is compacted (wheel track) and the soil is wet, soil respiration tends to be

lower than in the row. The lower soil porosity accounts for the lower respiration rate under compacted conditions.

Biological activity is a direct reflection of the degradation of organic matter in the soil. This

degradation indicates that two processes are occurring: (1) loss of soil carbon and (2) turnover of

nutrients (Parkin et al., 1996). Some optimum soil respiration rate, that balances the long-term detrimental aspects of soil carbon loss and soil nutrient turnover, must be defined .

Conversions

kg CO2-C/ha/d = lbs CO2-C/a/d x 1.12

g CO2-C/m2/d = lbs CO2-C/a/d ÷ 11.2

kg CO2

-C/ha/d = g CO2-C/m2/d x 10

References

Doran, J.W., T. Kettler, M. Liebig, and M. Tsivou. 1997. Solvita soil test evaluation, personal

communication.

Parkin, T.B, J.W. Doran, and E. Franco-Vizcaino. 1996. Field and laboratory tests of soil respiration. p.231-246. In: J.W. Doran and A.J. Jones (eds.) Methods for assessing soil quality. Soil

Sci.Soc. Am. Spec. Publ. 49. SSSA, Madison, WI.

Prochette, P., R.L. Desjardins, and E. Pattey. 1991. Spatial and temporal variability of soil respiration in agricultural fields. Can. J. Soil Sci. 71:189-196.

Volk, T. 1994. The soil’s breath. Natural History November/94.

Woods End Research. 1997. Guide to solvita testing and managing your soil. Woods End Research

Laboratory, Inc., Mt. Vernon, ME.
55

2. Infiltration

Introduction

Infiltration is the process of water entering the soil. The rate at which water enters the soil is the

infiltration rate, which is dependent on the soil type; soil structure, or amount of aggregation; and the

soil water content (Lowery et al., 1996). The initial soil water content at time of measurement affects

the ability of the soil to pull additional water into the soil. Therefore, the infiltration rate will be

higher when the soil is dry than when it is wet. This factor is important when comparing infiltration

measurements of different soils. The soils should have similar moisture content when taking the

measurements.

Tillage will affect the infiltration rate. Immediately after tillage, improved infiltration may occur

due to the loosening of surface crusts or compacted areas. Tillage fluffs up the soil. However, tillage

further disrupts aggregates and soil structure, creating the potential for compaction, surface crusting,

and loss of continuous surface connected pores. Compacted soils will have less pore space, resulting

in lower infiltration rates. Soils that tend to form surface crusts, which seal the soil surface, can have

severely reduced infiltration rates.

Interpretations

Since infiltration is affected by the initial water content at the time of measurement, it is important

that the soil water content be similar when comparing infiltration rates from different sites. The

infiltration test in the soil quality kit requires two 1-inch depths of water to be applied consecutively.

Application of the first inch of water is used to wet the soil, and the second inch of water determines

the infiltration rate. This procedure is an attempt to standardize the soils for differences in initial

water content. Infiltration rates are best determined when the soil is at or near field capacity, usually

12 to 48 hours after the soil has been thoroughly wetted (i.e., soaking rain or irrigation).

The infiltration rate is sensitive to near-surface conditions and is subject to significant change

with soil use, management, and time. It is affected by the development of plant roots, earthworm

burrows, soil aggregation, and by overall increases in stable organic matter (Sarrantonio et al., 1996).

Infiltration is rapid into large continuous pores in the surface. Infiltration is decreased when the size

Table 2. Steady infiltration rates for general soil texture

groups in very deeply wetted soil (Hillel, 1982).

Soil type

Steady

infiltration rate

(inches per hour)

Sands > 0.8

Sandy and silty soils 0.4 - 0.8

Loams 0.2 - 0.4

Clayey soils 0.04 - 0.2

Sodic clayey soils < 0.04
56

References

Donahue, R.L., R.W. Miller, J.C. Shickluna. 1977. Soils: An introduction to soils and plant growth.

Prentice Hill, Englewood, New Jersey.

Hillel, D. 1982. Introduction to soil physics. Academic Press, San Diego, CA.

Lowery, B., M.A. Arshad, R. Lal, and W.J. Hickey. 1996. Soil water parameters and soil quality.

p.143-157. In: J.W. Doran and A.J. Jones (eds.) Methods for assessing soil quality. Soil Sci.

Soc. Am. Spec. Publ. 49. SSSA, Madison, WI.

or amount of pore space is reduced from conditions such as structure breakdown, pore clogging

by lodged particles, or slower movement of deeper water as it reaches denser subsoils (Donahue et

al., 1977).

Texture, or the percentage of sand, silt, and clay will affect the infiltration rate. Usually sandy

soils will have rapid infiltration rates. Some typical values for steady infiltration rates (After long

continuous wetting, the rate of infiltration becomes steady.) for general soil texture groups are shown

in Table 2. However, the values in Table 2 can be considerably higher in well aggregated or cracked

soils and during initial stages of wetting; these values can be lower if surface crusting occurs (Hillel,

1982). Soil structure greatly influences the movement of water into the soil.

Table 3 shows the infiltration rate in minutes per inch and inches per hour and the associated

infiltration class. These classes are the soil permeability classes historically used in Soil Survey.

Classes are estimated from soil properties and indicate a steady infiltration rate.

Table 3. Infiltration rates and classes.

Infiltration rate

(minutes per inch)

Infiltration rate

(inches per hour) Infiltration class

< 3 > 20 Very rapid

3 to 10 6 to 20 Rapid

10 to 30 2 to 6 Moderately rapid

30 to 100 0.6 to 2 Moderate

100 to 300 0.2 to 0.6 Moderately slow

300 to 1,000 0.06 to 0.2 Slow

1,000 to 40,000 0.0015 to 0.06 Very slow

> 40,000 < 0.0015 Impermeable
57

3. Bulk Density

Introduction

Bulk density is defined as the ratio of oven-dried soil (mass) to its bulk volume, which includes

the volume of particles and the pore space between the particles. It is dependent on the densities of

the soil particles (sand, silt, clay, and organic matter) and their packing arrangement. Mineral particle

densities usually range from 2.5 to 2.8 g/cm3, while organic particles are usually less than 1.0 g/cm3.

Bulk density is a dynamic property that varies with the structural condition of the soil. This condition

can be altered by cultivation; trampling by animals; agricultural machinery; and weather; i.e., raindrop

impact (Arshad et al., 1996). Compacted soil layers have high bulk densities, restrict root growth, and

inhibit the movement of air and water through the soil.

Interpretations

Soil bulk density can serve as an indicator of compaction and relative restrictions to root growth

(See Table 4). Typical soil bulk densities range from 1.0 to 1.7 g/cm3

, and generally increase with

depth in the soil profile (Arshad et al., 1996). In soils containing high amounts of swelling clays, bulk

densities will vary with the water content, which should be measured at the time of sampling.

Table 4. General relationship of soil bulk density to root growth based on soil

texture.

Soil texture Ideal bulk densities

(g/cm3)

Bulk densities that may

affect root growth

(g/cm3)

Bulk densities that

restrict root growth

(g/cm3)

sands, loamy sands < 1.60 1.69 > 1.80

sandy loams, loams < 1.40 1.63 > 1.80

sandy clay loams,

loams,

clay loams

< 1.40 1.60 > 1.75

silts, silt loams < 1.30 1.60 > 1.75

silt loams, silty clay

loams < 1.40 1.55 > 1.65

sandy clays, silty

clays,

some clay loams

(35-45% clay)

< 1.10 1.49 > 1.58

clays (> 45% clay) < 1.10 1.39 > 1.47
58

Comments

Bulk density values are also required for converting soil water content in percent by weight (gravimetric) to percent by volume (volumetric):

Volumetric water content (g/cm3

) = soil water content (g/g) x bulk density (g/cm3)

and to calculate porosity, which is the amount of pore space in the soil:

soil porosity (%) = 1 - (soil bulk density ÷ 2.65).

References

Arshad, M.A., B. Lowery, and B. Grossman. 1996. Physical tests for monitoring soil quality. p.123-

142. In: J.W. Doran and A.J. Jones (eds.) Methods for assessing soil quality. Soil Sci. Soc. Am.

Spec. Publ. 49. SSSA, Madison, WI.
59

4. Electrical Conductivity

Introduction

The electrical conductivity (EC) of soil-water mixtures indicates the amount of salts present in

the soil. All soils contain some salts, which are essential for plant growth. However, excess salts

will hinder plant growth by affecting the soil-water balance. Soils containing excess salts occur

both naturally and as a result of soil use and management. Salt-affected soils are largely found in

the western arid and semiarid areas of the country, where the annual rainfall is low, allowing salts

to accumulate in the soil profile. The electrical conductivity measurement detects the amount of

cations or anions (salts) in solution; the greater the amount of anions or cations, the greater the

electrical conductivity reading. The ions generally associated with salinity are Ca2+, Mg2+, K+, Na+,

H+ (cations), or NO3

-

, SO4

-

, Cl-, HCO3

-

, OH- (anions).

Interpretations

In general, EC1:1 values between 0 and 0.8 dS/m are acceptable for general crop growth. Site

specific interpretations for soil quality will depend on specific land use and crop tolerance. Table 5

shows the soil salinity class and general crop and microbial responses for each class.

Table 5. Electrical conductivity measurement and salinity classes for a 1:1

soil:water suspension.

Electrical

Conductivity

(dS m-1 at 25 C)

Salinity class Crop response Microbial response

0 - 0.98 Non saline Almost negligible

effects Few organisms affected

0.98 - 1.71 Very slightly saline Yields of very sensitive

crops restricted

Selected microbial processes

altered

(nitrification/denitrification)

1.71 - 3.16 Slightly saline Yields of most crops

restricted

Major microbial processes

influenced

(respiration/ammonification)

3.16 - 6.07 Moderately saline Only tolerant crops

yield satifactorily

Salt tolerant microorganisms

predominate (fungi,

actinomycetes, some bacteria)

> 6.07 Strongly saline Only very tolerant crops

yield satisfactorily

A select few halophilic

organisms are active

Adapted from Soil Survey Staff (1993), Janzen (1993), and Smith and Doran (1996). Conversions

from the saturation paste extract to the 1:1 soil:water suspensions were perfomed using the

regression equation (y = 2.75 x -0.69) developed by Hogg and Henry (1984).
60

Table 6 provides general salt tolerance ratings for selected crops. These ratings apply to soils

in which chloride (Cl-) is the predominant anion. The EC of soils containing gypsum will tolerate

1 dS/m higher than those listed in this table (Tanji, 1990). Consult a local Soil Survey to determine

if gypsum is present in the soil of interest.

Table 6. Salt tolerance of selected crops (Tanji, 1990).

Crop Rating Crop Rating Crop Rating

Alfalfa

Alkali grass, Nuttall

Alkali sacaton

Almond

Apple

Apricot

Artichoke

Asparagus

Avocado

Barley 

Barley (forage)

Bean

Beet, red

Bentgrass

Bermuda grass

Blackberry

Bluestem, Angleton

Boysenberry

Broad bean

Broccoli

Brome, mountain

Brome, smooth

Brussels sprouts

Buffelgrass

Burnet

Cabbage

Canary grass, reed

Carrot

Castorbean

Cauliflower

Celery

Cherimoya

Cherry, sweet

Cherry, sand

Clover, alsike

Clover, berseem

Clover, hubam

MS

T

T

S

S

S

MT

T

S

T

MT

S

MT

MS

T

S

MS

S

MS

MS

MT

MS

MS

MS

MS

MS

MT

S

MS

MS

MS

S

S

S

MS

MS

MT

Clover, iadino

Clover, red

Clover, strawberry

Clover, sweet

Clover, white Dutch

Corn

Corn (forage)

Corn, sweet

Cotton

Cowpea

Cowpea (forage)

Cucumber

Currant

Dallis grass

Date palm

Eggplant

Fescue, tall

Fescue, meadow

Fig

Flax

Foxtail, meadow

Gooseberry

Grama, blue

Grape

Grapefruit

Guar

Guayule

Harding grass

Jojoba

Jujube

Kale

Kaller grass

Kenaf

Kohlrabi

Lemon

Lettuce

Lime

MS

MS

MS

MT

MS

MS

MS

MS

T

MT

MS

MS

T

MS

T

MS

MT

MT

MT

MS

MS

S

MS

MS

S

T

T

MT

T

MT

MS

T

MT

MS

S

MS

S

Loquat

Love grass

Mango

Milkvetch, Cicer

Millet, foxtail

Muskmelon

Oat grass, tall

Oats (forage)

Okra

Olive

Onion

Orange

Orchard grass

Panic grass, blue

Papaya

Rape

Parsnip

Passion fruit

Pea

Peach

Pear

Pepper

Persimmon

Pineapple

Plume, prune

Pomegranate

Potato

Pummelo

Pumpkin

Radish

Rescue grass

Raspberry

Rhodes grass

Rice, paddy

Rose apple

Rye

Rye (forage)

S

MS

S

MS

MS

MS

MS

MS

S

MT

S

S

MS

MT

MT

MT

S

S

S

S

S

MS

S

MT

S

MT

MS

S

MS

MS

MT

S

MT

S

S

T

MS
61

Considerations

The electrical conductivity of a solution is affected by temperature. Generally the electrical

conductivity of a solution increases with temperature at a rate of approximately 1.9% per 1EC

increase (Rhoades, 1993). The conductivities in Table 5 are standardized at 25EC. Most EC meters

adjust for deviations from 25EC within a specific temperature range. Therefore, conductivity

measurements must be taken within this temperature range (Refer to instructions packaged with

the meter.) to avoid under- or overestimating the electrical conductivity.

Generally, the effects of soil moisture on the EC measurement will be negligible when soil

water content is at or below field capacity. If water content is above field capacity, adjustments

should be made to maintain a 1:1 ratio of soil to water. Another approach would be to air-dry the

soil if it is too wet.

Excess salts affect plant growth by (1) direct toxicities; e.g., boron; (2) disrupting the ionic

balance in the plant; (3) interfering with nutrient uptake; e.g., blossom-end rot of tomatoes due to

high salt interference with calcium uptake; and (4) reducing the availability of water by lowering

the osmotic potential (Fitter and Hay, 1987). Excess sodium (Na+), often expressed as exchangeable sodium percentage (ESP), can deteriorate soil structure by dispersing soil clays.

Table 6. Continued.

Crop Rating Crop Rating Crop Rating

Ryegrass, perennial

Safflower

Salt grass, desert

Sapote, white

Sesame

Sesbania

Sirato

Sorgham

Soybean

Sphaerophysa

Spinach

Squash, scallop

Squash, zucchini

Strawberry

MT

MT

T

S

S

MS

MS

MT

MT

MS

MS

MS

MT

S

Sudan grass

Sugar beet

Sugarcane

Sunflower

Sweet potato

Tangerine

Timothy

Tomato

Trefoil, narrowleaf

Triticale

Turnip

Vetch, common

Watermelon

Wheat

MT

T

MS

MS

MS

S

MS

MS

MT

T

MS

MS

MS

MT

Wheat, semidwarf

Wheat, durum

Wheat, durum (forage)

Wheat (forage)

Wheat grass, standard

Wheat grass, fairway

Wheat grass, interm.

Wheat grass, slender

Wheat grass, tall

Wheat grass, western

Wild rye, Altai

Wild rye, beardless

Wild rye, Canadian

Wild rye, Russian

T

T

MT

MT

MT

T

MT

MT

T

MT

T

MT

MT

T

Rating EC range for 1:1 soil:water suspension

for which yield reductions occur

S = Sensitive > 0.90 dS/m

MS = Moderately sensitive > 1.40 dS/m

MT = Moderately tolerant > 2.50 dS/m

T = Tolerant > 4.00 dS/m
62

When distilled water is not available, tap or rain water can be used. Measure the conductivity of the water source, and subtract the water source EC value from the sample EC value.

The relationship between electrical conductivity and salt concentration is only approximate.

General relationships that have been established are (Rhoades, 1996):

1) Total cation (or anion) concentration: meq/L  10 x EC (dS/m).

2) Total dissolved solids: mg/L  640 x EC (dS/m).

3) Osmotic pressure: kPa (at 25EC)  0.36 x EC (dS/m).

Where NO3

-

 is the predominant ion in the soil solution, a very useful relationship has been

established between the EC (in 1:1 soil to water mixture) readings and soil nitrate (NO3

-

) concentrations (Smith and Doran, 1996).

 EC (dS/m) x 140  mg NO3

-

-N/kg of soil

This relationship assumes the complete extractability of NO3

-

 in water and that NO3

-

 is the major

anion in the soil solution.

Conversions

1 dS/m (decisiemens per meter) = 1 mmhos/cm (millimhos per centimeter)

1 dS/m (decisiemens per meter) = 1000 FS/cm (microsiemens per centimeter)

1000 FS/cm (microsiemens per centimeter) = mS/cm (millisiemens per centimeter)

References

Fitter, A.H. and R.K.M. Hay. 1987. Environmental physiology of plants. Academic Press, London.

Hogg, T.J. and J.L. Henry. 1984. Comparison of 1:1 suspensions and extracts with the saturation

extract in estimating salinity in Saskatchewan soils. Can. J. Soil Sci. 64:699-704.

Janzen, H.H. 1993. Soluble salts. p. 161-166. In: M.R. Carter (ed.) Soil sampling and methods of

analysis. Canadian Society of Soil Science. Lewis Publ., Boca Raton.

Rhoades, J.D. 1993. Electrical conductivity methods for measuring and mapping soil salinity. p.

201-251. In: D.L. Sparks (eds.) Advances in agronomy, Vol. 49. Academic Press, Inc., San

Diego, CA.

Rhoades, J.D. 1996. Salinity: Electrical conductivity and total dissolved solids. p.417-435. In: D.L.

Sparks (ed.) Methods of soil analysis: Part. 3-chemical methods. Book Series no. 5. SSSA

and ASA, Madison, WI.

Smith, J.L. and J.W. Doran. 1996. Measurement and use of pH and electrical conductivity for soil

quality analysis. p. 169-185. In: J.W. Doran and A.J. Jones (eds.) Methods for assessing soil

quality. Soil Sci. Soc. Am. Spec. Publ. 49. SSSA, Madison, WI.

Soil Survey Staff. 1993. Soil survey manual. United States Department of Agriculture. Hnbk no.

18. U.S. Gov. Printing Office, Washington, DC.

Tanji, K.K. (ed.). 1990. Agricultural salinity assessment and management (Manual No. 71). Prepared by Subcommittee on Salinity Manual of the Committee on Water Quality of the Irrigation and Drainage Division of the American Society of Civil Engineers. American Society of

Civil Engineers, New York.
63

5. Soil pH

Introduction

Soil pH is a measure of the acidity or alkalinity of a soil, which affects the availability of plant

nutrients, activity of microorganisms, and the solubility of soil minerals. Major factors affecting

soil pH are temperature and rainfall, which control the intensity of leaching and soil mineral

weathering. Acidity is generally associated with leached soils; alkalinity generally occurs in drier

regions. However, agricultural practices, such as liming or addition of ammonium fertilizers, can

alter soil pH. The pH measurement is actually measuring the hydrogen ion activity [H+] in the soil

solution.

Interpretations

In general, pH values between 6 and 7.5 are optimum for general crop growth. Site specific

interpretations for soil quality will depend on specific land use and crop tolerance.

Figure 1. Soil pH, ranges for pH classes, and associated soil conditions. Adapted from the National

Soil Survey Manual (1993) and Troeh and Thompson (1993).
64

4.5 5.0 5.5 6.0 6.5 7.0 7.5

Table 7. Suitable soil pH ranges for selected crops (Whittaker et al., 1959).

Crops Soil pH ranges

Alfalfa

Alsike clover

Apples

Asparagus

Azalea

Barley

Beans, lima

Beans, snap

Beans, velvet

Blueberries

Buckwheat

Cabbage

Carrots

Clover, crimson

Clover, red

Clover, sweet

Clover, white

Corn

Cotton

Cowpeas

Cucumber

Grasses

Hydrangea, blue flowered

Iris, blueflag

Juniper, Irish
65

4.5 5.0 5.5 6.0 6.5 7.0 7.5

Table 7. Continued.

Crops Soil pH ranges

Kale

Lettuce

Mustard

Oats

Onions

Parsnips

Peas

Peppers

Pine, longleaf

Pine, yellow

Potatoes, sweet

Pototoes, white

Radishes

Rye

Sorghum

Soybeans

Spinach

Squash

Strawberries

Sudan grass

Timothy

Tobacco

Tomatoes

Trefoil, birdsfoot

Vetch

Wheat
66

References

Brady, N.C. 1990. The nature and properties of soils. 10th ed. Macmillan Publ., New York.

Smith, J.L. and J.W. Doran. 1996. Measurement and use of pH and electrical conductivity for soil

quality analysis. p. 169-185. In: J.W. Doran and A.J. Jones (eds.) Methods for assessing soil

quality. Soil Sci. Soc. Am. Spec. Publ. 49. SSSA, Madison, WI.

Soil Survey Staff. 1993. Soil survey manual. United States Department of Agriculture. Hnbk no.

18. U.S. Gov. Printing Office, Washington, DC.

Thomas, G.W. 1996. Soil pH and soil acidity. p.475-489. In: D.L. Sparks (ed.) Methods of soil

analysis: Part 3-chemical methods. Book Series no. 5. SSSA and ASA, Madison, WI.

Treoh, F.R. and L.M. Thompson. 1993. Soils and soil fertility. 5th ed. Oxford Univ. Press, New

York.

Whittaker, C.W., M.S. Anderson, and R.F. Reitemeier. 1959. Liming soils, an aid to better farming.

USDA Farmers Bul. 2124.

Nutrient Availability

Soil pH affects the availability of nutrients

to plants or crops (Figure 2). Nutrient

availability is affected by changes in the

solubility of soil minerals. Most minerals

are more soluble in acid soils than in

neutral or slightly basic soils. The greatest

availability for most nutrients is between

pH 6 and 7 (Figure 2). Where nutrients are

shown interlocking in Figure 2, those

nutrients at that pH combine to form

insoluble compounds, reducing their

availability. Soil pH also affects the

activity of beneficial microorganisms,

which affects nutrient availability. In

general, fungi function at a wide pH range,

but bacteria and actinomycetes function

better at intermediate and higher pH.

Comments

The presence of salts affects soil pH

by decreasing the reading by 0.2 to 0.3 pH

units (Thomas, 1996). To mask the effects

of salts, a 0.01 M CaCl2

 solution has been

commonly used instead of distilled water.

Declining pH is a sign of inefficient N

use where ammonia based fertilizers are

used (see Smith and Doran, 1996).

Figure 2. Nutrient availability based on pH of

mineral soils (Soils Handbook, Kentucky Agr. Exp.

Stn. Misc. 383, 1970, p.28).
67

6. Soil Nitrate

Introduction

Soil nitrate (NO3

-

) is a form of inorganic nitrogen (N) that is available for use by plants. It

forms from the mineralization (by microorganisms) of organic forms of N (i.e., soil organic matter,

crop residue, and manure) in the soil. The rate of N mineralization is dependent on the amount of

soil organic N, water content, temperature, pH, and aeration. Crop needs are met by soil-derived

mineral-N and by fertilizer-N. Efficient management of soil N requires knowledge of crop needs

for N and the amount of soil-derived N. Nitrate is mobile in soil, so it can be leached with percolating water below the root zone. All soils lose a small amount of nitrate to groundwater, including

soils under natural vegetation. When amounts leach that are greater than what occurs naturally, we

need to be concerned. Nitrate is not a contaminant until it leaches below the root zone or is transported off-site in surface runoff. When leached to groundwater, there is a human and animal health

risk. In surface water systems, nitrate can contribute to euthrophication.

Interpretations

The amount of residual nitrate-N in the soil at any one time is a function of the rate at which

microorganisms decompose soil organic matter (Figure 3). This rate is dependent on temperature,

moisture, aeration, type of organic residues, pH, and other factors (Dahnke and Johnson, 1990).

Also, once soil nitrate has formed, it is subject to leaching, fixation, denitrification, and plant

uptake (Figure 3). Therefore, it is difficult to interpret the nitrate-N content in terms of how much

and when N will be available to meet crop needs. However, residual nitrate-N tests can be useful in

determining fertilizer-N needs of crops in certain regions during specific times of the year and at

specific crop growth stages (Dahnke and Johnson, 1996). For interpretations of residual nitrateN tests for crop needs, consult local or regional calibrations.

Any amount of nitrate in the soil that is not used by the crop may potentially be leached from

the root zone and become an environmental liability. Nitrate is not adsorbed on to soil particles

unless they have a positive charge. Therefore, nitrate can readily move with percolating water out

of the root zone and into groundwater or into surface waters through subsurface flow (Figure 3).

Acidic soils of the humid tropics contain a significant amount of positively charged soil particles

which can hold nitrate and keep it from leaching.

Nitrogen Cycling

In general, soil nitrate levels will change significantly during the course of the year and from

week to week. Soil nitrogen is continuously cycling, moving from one form to another (Figure 3).

It is derived primarily from atmospheric nitrogen gas (N2

). Soil microorganisms fix N2 to produce

organic nitrogen, which becomes part of the soil organic matter. The decomposition of organic

matter converts some organic nitrogen into mineral nitrogen (mineralization). Ammonium (NH4

+

)

produced by mineralization (an intermediate step) can be converted to nitrate by specific microorganisms (nitrification). The nitrate formed is then available for uptake by plants or microorganisms and is converted to organic forms of nitrogen (immobilization). Under water logged or

anaerobic conditions, nitrate may be substituted for oxygen and ultimately released to the atmo
68

Comments

The nitrate/nitrite test strips can determine both nitrate and nitrite concentrations (two test

pads on each test strip). Nitrite levels in soils are usually not detectable (in a transition state);

therefore, its measurement is not warranted. The nitrate test pad on the test strip measures the sum

of both nitrate-N and nitrite-N present in the sample. If nitrite is detected in the sample, the

amount can be subtracted from the nitrate reading to get the actual amount of nitrate-N in the

sample.

Spring soil nitrate-N tests can be used to assess the effectiveness of soil and cropping management practices in providing sufficient N for optimal crop yields. For example, for corn in the

Midwest, values of 20-25 ppm nitrate-N in top foot (30 cm) of soil are needed (14-16 ppm is the

threshold for soils receiving manure or having alfalfa or soybeans as the previous crop) [Allan et

al., 1996; page 196].

References

Allan, D.L. and R. Killorn. 1996. Assessing soil nitrogen, phosphorus, and potassium for crop

nutrition and environmental risk. p.187-201. In: J.W. Doran and A.J. Jones (eds.) Methods for

assessing soil quality. Soil Sci. Soc. Am. Spec. Publ. 49. SSSA, Madison, WI.

Dahnke, W.C. and G.V. Johnson. 1990. Testing soils for available nitrogen. p.127-139. In: R.L.

Westerman (ed.) Soil testing and plant analysis. 3rd ed. SSSA Book Series 3. SSSA, Madison,

WI.

Primary fates of nitrates:

· utilization by microorganisms or

plant roots (immobilization)

· leached below the root zone

· moved off-site in surface runoff

· microbial conversion of nitrate-N to nitrogen gas

Primary sources of nitrates:

· addition of fertilizers

containing nitrate,

· microbial conversion of

ammonium fertilizers to

nitrate-N,

· microbial conversion of

organic N (i.e., soil

organic matter and

manures) to nitrate-N.

sphere as elemental nitrogen or nitrous oxide gas (N2

 or N2O) [denitrification]. Each N transformation depends on the activity and abundance of a specific population of microorganisms that

require different sets of optimal environmental conditions.

Figure 3. Generalized soil nitrogen cycle.
69

7. Aggregate Stability

Introduction

Aggregate stability is a measure of the vulnerability of soil aggregates to external destructive

forces (Hillel, 1982). An aggregate consists of several soil particles bound together. The destructive force in this test is flowing water. Aggregates that stand up to the forces of water are called

water stable aggregates (WSA). In general, the greater the percentage of stable aggregates, the less

erodible the soil will be. Soil aggregates are a product of the soil microbial community, the soil

organic and mineral components, the nature of the above-ground plant community, and ecosystem

history. They are important in the movement and storage of soil water and in soil aeration, erosion,

root development, and microbial community activity (Tate, 1995). Breakdown of aggregates is the

first step to crust development and surface sealing, which impedes water infiltration and increases

erosion. Soil aggregation can change over a period of time, such as in a season or year. Aggregates

can form, disintegrate, and reform periodically (Hillel, 1982).

Interpretations

The percentage of water stable aggregates indicates the amount resistant to disturbance by flowing

water. In general, greater amounts of stable aggregates are better for soil quality.

Aggregates improve soil quality by:

· protecting soil organic matter entrapped in the aggregates from exposure to air and microbial

decomposition,

· decreasing soil erodibility,

· improving water and air movement (Aggregates increase the amount of large pore spaces.),

· improving the physical environment for root growth,

· improving soil organism habitat.

Aggregate stability is affected by the amount and type of the following soil constituents (Kemper,

1966):

Soil Organic Matter content:

Aggregate stability generally increases with organic matter content (Table 1). The effect is

more pronounced in soils containing small amounts of clay. Generally, increases in organic

matter above 2% do not increase aggregate stability appreciably.

Soil Clay content:

Aggregate stability is affected by the amount and type of clay in the soil and generally

increases with clay content (Table 1). This effect decreases at higher clay contents (Table

1). In general, high surface-area clays (i.e., montmorillonite) tend to cause greater aggregation than low surface-area clays (i.e., kaolinite).

Aluminum and Iron Oxide content:

Aggregate stability generally increases with free iron oxide content. In general, free aluminum oxides do not appreciably increase aggregate stability.

Calcium Carbonate content:

The calcium carbonate content generally does not appreciably affect aggregate stability.
70

Exchangeable Sodium content:

Aggregate stability decreases with increasing amounts of exchangeable sodium. In general,

water stable aggregates are nonexistent in soils with greater than 20% exchangeable Na+.

Table 8 contains suitable values for aggregate stability based on soil organic matter and clay

content. A suitable range of values could be developed for a soil using the aggregate stability

values for the organic matter content and clay content as end members to the range. For example,

for a soil with 2% organic matter and 10% clay, the suitable aggregate stability range (taken from

Table 8) would be 65 to 75% water stable aggregates.

Soil aggregates are divided into two general groups based on aggregate size (diameter):

· Microaggregates (less than 250 Fm) consist of primary soil particles and smaller

microaggregates bound together. Binding agents include:

humified organic matter (organic polymers)

polyvalent metals or cations

roots and fungal hyphae

polysaccharides

plant and microbial debris (encrusted)

iron and aluminum amorphous oxides

· Macroaggregates (> 250 Fm) consist of microaggregates bound together. Major binding

agents are:

fungal hyphae

fibrous roots

polysaccharides

Table 8. Suitable values for % water stable aggregates based on

clay and organic matter content (Kemper, 1966). Water stable

aggregates for % clay should be read independently of %

organic matter in this table.

Organic Matter

(%)

Water Stable

Aggregates (%)

Clay

(%)

Water Stable

Aggregates (%)

0.4 53 5 60

0.8 66 10 65

1.2 70 20 70

2 75 30 74

4 77 40 78

8 81 60 82

12 85 80 86

Aggregate stability values are based on 519 soil samples from the arid,

semiarid, and subhumid regions of the United States and Canada. The

majority of the samples were from cultivated areas, but a large number were

taken from virgin or replanted grasslands (Kemper, 1966).
71

Considerations and Comments

The temperature of the water used to sieve the soils should be maintained within the range of

22 to 25EC (71.5 to 77EF). At higher water temperatures, aggregate stability tends to decrease.

To make observational estimations of aggregate stability or relative comparisons, weighing

and drying of the aggregates are not necessary.

When dry aggregates are wetted up too quickly at atmospheric pressure, disintegration and

slaking can result. Upon rapid wetting, capillary water entering the pores causes air entrapped

inside the aggregate pores to increase in pressure causing them to rupture (Kemper and Rosenau,

1986).

References

Angers, D.A. and G.R. Mehuys. 1993. Aggregate stability to water. p. 651-658. In: M.R. Carter

(ed.) Soil sampling and methods of analysis. Canadian Soc. Soil Sci., Lewis Publ., Boca

Raton.

Arshad, M.A., B. Lowery, and B. Grossman. 1996. Physical tests for monitoring soil quality. p.123-

142. In: J.W. Doran and A.J. Jones (eds.) Methods for assessing soil quality. Soil Sci. Soc.

Am. Spec. Publ. 49. SSSA, Madison, WI.

Hillel, D. 1982. Introduction to soil physics. 2nd ed. Academic Press, San Diego, CA.

Kemper, W.D. 1966. Aggregate stability of soils from western United States and Canada. USDAARS. Technol. Bull. no. 1355. U.S. Gov. Print. Office, Washington, D.C.

Kemper, W.D. and R.C. Rosenau. 1986. Aggregate stability and size distribution. p. 425-442. In: A.

Klute (ed.) Methods of soil analysis: Part I, physical and mineralogical methods. American

Society of Agronomy, Madison, WI.

Tate, R.L. 1995. Soil microbiology. John Wiley & Sons, New York.

Tisdall, J.M. and J.M. Oades. 1982. Organic matter and water-stable aggregates in soils. J. Soil Sci.

33:141-163.

iron and aluminum oxides (soils that contain more than 10% iron and aluminum oxides)

The size of the water stable aggregates measured in the soil quality kit are macroaggregates.

Macroaggregates form readily under the following conditins:

· under pasture or forage grasses (dense, fibrous root mass),

· where organic residues have been added,

· where large amounts of microaggregates (< 250 Fm diameter) are present.

Differences between micro- and macroaggregates include the following:

· Macroaggregates are more sensitive to changes in management than microaggregates and thus,

are considered a better indicator of changes in soil quality. Macroaggregate stability depends

on management because of the transient nature of the binding agents.

· Macroaggregates form more rapidly than microaggregates.

· Carbon is more stable in microaggregates than in macroaggregates.

· Microaggregates are more water stable than macroaggregates.

· When the proportion of macro- to microaggregates increases, soil quality increases.
72

8. Soil Slaking

Introduction

Slaking is the process of fragmentation that occurs when aggregates are suddenly immersed in

water (Chan and Mullins, 1994). Slaking occurs because the aggregates are not strong enough to

withstand the stresses of rapid water uptake. At fast rates of wetting, internal stresses arise from

differential swelling and air entrapment in the soil aggregate (Kay, 1998). These stresses may be

released through the creation of an increasingly extensive network of failure zones in the soil

fragments or aggregates. The differences between tests of aggregate stability and slaking are the

type of stress applied and the size of aggregates or soil fragments used. The slake test is a qualitative and simpler test to perform. The two tests may not necessarily yield the same results.

Interpretations

The slake test in the kit yields a stability rating of 0 to 6 (Herrick, 1998). Soil fragments or

aggregates which fall into classes 0 to 3 are relatively unstable. Class 4 indicates some stability, but

very little strength. Classes 5 and 6 represent relatively stable soil fragments or aggregates. Soil

strength relates to the ability of the soil to resist loss of its structure.

Stability ratings of soil surface crust fragments are interpreted differently. Soil crust formation in

agricultural systems reduces the capacity of the soil to function (i.e., soil crusts can reduce air and

water movement into the soil and can inhibit seedling germination). In general, weakly formed or

unstable crusts are better than very strong or stable crusts, which have a greater potential to lower soil

quality. The subsurface fragments or aggregates directly beneath the crust are tested to provide an

indication of the potential for future slaking and crusting of the soil (potential of crust formation).

Slaking is affected by:

· the soil water content,

· rate of wetting,

· texture,

· clay mineralogy, and

· organic matter content.

Slaking is more severe when the soil is initially dry than when it is moist. For loamy soils, the

pressure of entrapped air has been shown to be more important. For clayey soils, differential swelling

was shown as the more important process (Chan and Mullins, 1994). In general, organic matter can

influence both the rate of wetting and the resistance to stress generated during wetting (Kay, 1998).

The stability of aggregates is strongly dependant on the rate of wetting; therefore, aggregate stability

declines as the rate of wetting increases.

References

Chan, K.Y. and C.E. Mullins. 1994. Slaking characteristics of some Australian and British soils.

European J. of Soil Sci. 45:273-283.

Herrick, J.E. 1998. Manual for monitoring and assessing rangeland health. USDA-ARS.

Kay, B.D. 1998. Soil structure and organic carbon: A review. p.169-197. In: R. Lal, J.M. Kimble, R.F.

Follett, and B.A. Stewart (ed.) Soil processes and the carbon cycle. CRC Press, Boca Raton.
73

9. Earthworms

Introduction

Earthworm populations may vary with site characteristics (food availability and soil conditions), season, and species. Populations are highly variable in space and time, which can range

from less than 10 to greater than 10,000 individuals per square meter (Curry, 1998). However, not

all areas or soils support earthworms. Either they were not introduced, or environmental conditions are not favorable. Earthworms generally increase soil microbial activity and soil chemical

fertility and enhance soil physical properties.

Interpretations

About 10 earthworms per square foot of soil (100 worms/m2

) is generally considered a good

population in agricultural systems. Populations generally do not exceed 20 per square foot of soil

(200 worms/m2) in cultivated systems (Edwards, 1983). In grassland systems, populations can

generally range up to about 50 per square foot of soil (500 worms/m2

) [Edwards, 1983]. The hand

digging method does not capture certain deep-burrowing or fast moving earthworm species. However, hand digging is one of the best methods available.

Earthworms improve soil quality by:

· increasing the availability of nutrients. (Available plant nutrients (N, P, & K) tend to be higher

in fresh earthworm casts than in the bulk soil.) [Edwards et al., 1995];

· accelerating the decomposition of organic matter by incorporating litter into the soil and

activating both mineralization and humification processes;

· improving soil physical properties, such as aggregation and soil porosity;

· suppressing certain pests or disease organisms; and

· enhancing beneficial microorganisms.

Earthworms and soil aggregation processes:

· Fresh earthworm casts are often highly dispersed, nearly saturated masses of soil, which are

unstable and susceptible to erosion (Edwards et al., 1995). As earthworm casts age, they can

become more stable. The organic matter content, wet-dry cycles, and fungal hyphae and other

microbial products help to stabilize casts over time and improve the aggregation of soil.

· In general, the more sensitive the soil is to physical disturbance, the more effective casting is

for stable aggregation but less effective for tensile strength (Schrader and Zhang, 1997).

Factors affecting earthworm populations include the following (Curry, 1998):

Tillage

• Tillage generally kills about 25% of the earthworm population. The indirect effects of

tillage affects the remaining population. These indirect effects include increases in surface

temperature, decreased soil moisture regimes, reduced litter input, and more rapid oxidation (decomposition) of crop residues.

• Earthworm populations are often greater under no-till than under conventional tillage.

Large populations of both surface-dwelling and deep-burrowing earthworms are often
74

References

Curry, J.P. 1998. Factors affecting earthworm abundance in soils. p.37-64. In: C.A. Edwards (ed.)

Earthworm ecology. CRC Press, Boca Raton.

Edwards, C.A. 1983. Earthworm ecology in cultivated systems. p.123-137. In: J.E. Satchell (ed.)

Earthworm ecology: From Darwin to vermiculture. Chapman and Hill, London.

Edwards, C.A., P.J. Bohlen, D.R. Linden, and S. Subler. 1995. Earthworms in agroecosystems.

p.185-206. In: P.F. Hendrix (ed.) Earthworm ecology and biogeography. Lewis, Boca Raton.

Schrader, S. and J. Zhang. 1997. Earthworm casting: stabilization or destabilization of soil structure. Soil Biol. Biochem. 29:469-475.

associated with improved soil physical conditions. Higher infiltration rates often occur in notill than in conventional tillage systems due to (in part) the large number of macropores

from earthworm activity.

Temperature

The optimum temperature range for earthworms is between 10 and 20EC. The upper lethal

range is 25 to 35EC. Few species can tolerate temperatures below 0EC. Many species have

behavioral and/or physiological adaptations that enable them to survive unfavorable conditions.

Soil Properties

• Medium textured soils are more favorable for earthworms than sandy or clayey soils.

• Depth of aeration in soils affects the deep-burrowing species.

• Soil pH affects earthworm populations. Earthworms are usually absent in soils with pH

less than 3.5 and are scarce in soils with pH between 3.5 and 4.5. The majority of the

earthworms live in soils with pH between 5.0 and 7.4.

• Quality and amount of food (organic matter) affect earthworm distribution and abundance.

Food Source

Litter, or organic, residue on the soil surface is the primary food source for earthworms in most

ecosystems. However, dead roots and root exudates can also be important food sources. If the

physical and chemical environments are not limiting, the quality and quantity of litter input

frequently determines earthworm abundance.

Soil Disturbance

• Earthworm populations are generally higher in undisturbed soil systems.

• Population size depends on the severity and frequency of soil disturbance.

• If the soil disturbance is not repeated, earthworm populations can recover fairly rapidly

(within a few years).

Soil Moisture

Soil moisture restrictions generally determine earthworm distributions and their activity.

Agrochemicals

• Pesticides, especially insecticides, can affect earthworm populations. The majority of

triazine herbicides (i.e., atrazine, simazine, and cyanizine) are slightly toxic. Carbamatebased fungicides (i.e., carbendazim, benomyl, and thiophanate-methyl) are very toxic.

Organophosphates (i.e., phorate, isozophos, chlorpyrifos, and ethoprophos) and most of the

carbamate-based insecticides (i.e., carbaryl, carbofuran, methomy, and methiocarb) are

toxic. Most of the nematicides (i.e., D-D, metham-sodium, and methyl bromide) have been

reported to be toxic to earthworms (Edwards et al., 1995).

• Regular use of ammonium sulfate and anhydrous ammonia and sulfate coated urea has been

shown to decrease earthworm populations (Edwards et al., 1995).
75

10. Soil Physical Observations and Estimations

Topsoil Depth

Topsoil depth is important for water storage and nutrient supply for plant growth. Generally,

removal of the topsoil will result in loss of soil fertility, water-holding capacity, soil organic

carbon content, and productivity. Measurements of topsoil depth over time provide a good estimate of soil loss (erosion).

Interpretations

Change in topsoil thickness is usually a result of wind erosion, water erosion, deposition of

material, or land leveling. Eroded soils will commonly have a reduced Ap horizon (plow layer) or

topsoil thickness. Natural erosion occurs in the absence of human disturbances. However, it is the

accelerated erosion caused by plowing, burning, overgrazing, and other management practices that

remove the protective vegetative cover and results in loss of soil quality.

Root Growth

Depth of soil to a layer that would restrict root growth strongly affects crop production. Factors that influence rooting depth include high salt content and depth to bedrock, stone layer, hard

pan, frozen layer, and water table (Arshad et al., 1996).

When continuous pores are present in the soil, roots will grow through these pores as a result

of the low mechanical impedance. The distribution of roots in the soil profile is a function of soil

depth, thickness, and mechanical resistance of the root-impeding soil layers (Bennie, 1996).

Interpretations

Roots growing through restrictive soil layers undergo morphological changes, particularly

root stunting and thickening (Bennie, 1996). Impeded roots are generally shorter, thicker, and

more irregularly shaped. The shorter root system will exploit a smaller soil volume for plant

nutrients and water, causing the plant to maintain a higher than normal uptake rate of nutrients and

water per unit of root length. Also, more photosynthetic energy is needed to sustain root length

increases that do occur. All of these factors can result in plant stress, which may eventually result

in reduced crop growth and productivity.

Penetration Resistance

Penetration resistance is a measure of the ease with which an object can be pushed into the soil

(Bradford, 1986). It gives an indication of root-impeding layers in the soil and can be used in

comparing relative strengths among similar soil types. It can also be used for determining hardpans, zones of compaction, or dense soil layers.

Interpretations

Soil compaction that results in severely restricted root growth is caused mainly by trampling

of animals, use of farm and tillage equipment, and vehicular traffic. The type of root system will
76

determine the ability of a root to penetrate the soil. Figure 4 shows typical locations of compaction zones in cultivated soils.

Penetration resistance depends strongly on the soil water content: the dryer the soil, the greater

the resistance to penetration. Therefore, the water content of the soil should be noted when taking

a measurement. Penetration resistance is best determined when the soil is at field capacity, which

is a uniform condition that can be reproduced from season to season.

Soil Structure

Soil structure is the arrangement and organization of particles in the soil. It is strongly affected by changes in climate, biological activity, and soil management practices. Soil structure

affects the retention and transmission of water and air in the soil as well as the mechanical properties of the soil. Observing and describing soil structure in the field is subjective and qualitative.

Interpretations

For plant growth it is desirable to have a physical condition in which the soil is an optimally

loose, friable, and porous assemblage of aggregates permitting free movement of water and air,

easy cultivation and planting, and unobstructed germination and root growth (Hillel, 1982). The

soil structure index is a general quality placement that indicates the closeness to the condition

described above. In general, the higher the index value the better the soil's capacity to transmit

water and air and to promote root growth and development.

Soil processes involved in the development of soil structure are as follows (Rowell, 1994):

· drying and wetting, which cause shrinking and swelling, creating cracks and channels;

· freezing and thawing, which creates spaces as ice is formed;

· the action of roots (removal of water, release of exudates (organic materials), and formation of

root channels);

· the action of soil animals (moving soil material around, creating burrows, and bringing soil

Figure 4. General position of soil compaction zones in cultivated systems (Bennie,

1996)

Zone 1: Surface crusting, which may impede seedling

emergence and water infiltration.

Zone 2: Low impedance zone for roots; loosened by

tillage.

Zone 3: Plowed or deeply loosened cultivated soil

that has been recompacted by vehicular traffic.

Zone 4: Subsoil compaction by wheel traffic and

tillage implement-soil interactions during tillage.

Zone 5: May contain high mechanical impedance due

to inherent factors, such as duripans, fragipans,

ortstein layers, petrocalcic layers, etc., which may

occur near the surface if topsoil is not present.

CULTIVATED

LAYER

(9 inches)

1

2

3

4

SUBSOIL 5
77

mineral and organic materials into close association); and

· the action of microorganisms (breaking down plant and animal residues and creating soil

organic matter and humus as a binding material).

Soil Texture

Soil texture refers to the distribution of sand, silt, and clay sized mineral particles in the soil.

Texture is one of the most stable attributes of the soil, being modified only slightly by cultivation

and other practices that cause mixing of the different soil layers.

Interpretations

 This test is routinely used by soil scientists and provides reliable estimates of soil texture.

The textural class places the soil in one area of the triangular diagram based on the distribution of

sand, silt and clay in the soil (Figure 5). Texture is an important characteristic, because it influences fertility and helps determine water intake rates, water storage in the soil, ease of tillage, and

amounts of aeration. For example, clay soils will retain more water and nutrients than a sandy soil.

Mineral Particles Soil is composed of mineral particles that vary in size. There are three general

classifications (or soil separates) of mineral particles:

· sand particles - 2.0 mm (very coarse) to .05 mm (very fine);

· silt particles - .05 mm to .002 mm;

· clay particles - smaller than .002 mm.

Figure 5. Soil textural triangle showing the percentages of clay, silt, and sand in the textural classes.
78

Twelve Soil Textural Classes. Definitions of the 12 textural classes are based on the relative

proportion, or weight, of these three particle classifications. Sandy soil, for example, has a greater

proportion of sand particles than silt or clay. In reading the textural triangle (Figure 5), any two

particle size percentages will locate the textural class. For example, a soil containing 20% clay

and 40% sand is located in the loam textural class (Figure 5).

References

Arshad, M.A., B. Lowery, and B. Grossman. 1996. Physical tests for monitoring soil quality. p.123-

142. In: J.W. Doran and A.J. Jones (eds.) Methods for assessing soil quality. Soil Sci. Soc.

Am. Spec. Publ. 49. SSSA, Madison, WI.

Bennie, A.T.P. 1996. Growth and mechanical impedance. p.453-470. In: Y. Waisel, A. Eshel, and U.

Kafkafi (eds.) Plant roots: The hidden half. 2nd ed. Mercel Dekker, Inc., New York.

Bradford, J.M. 1986. Penetrability. p.463-478. In: A. Klute (ed.) Methods of soil analysis. Part 1

Physical and mineralogical methods. Agronomy No. 9. Am. Soc. Agron., Madison, WI.

Hillel, D. 1982. Introduction to soil physics. 2nd ed. Academic Press, London.

Rowell, D.L. 1994. Soil science: Methods & applications. Longman Scientific & Technical,

Singapore.
79

11. Water Quality

The quality of water is relative to the purpose for which the water is used; therefore, specific

use conditions will determine the suitability of a water body (James et al., 1982).

Water Electrical Conductivity

Introduction

Water salinity levels, as measured by electrical conductivity, can be used to assess irrigation

water quality. Other water quality concerns about saline waters include possible physiological

effects on humans and animals and mineral taste. Also, high concentrations of certain mineral

salts can cause corrosion damage in water systems. The measurement of electrical conductivity is

an indicator of the total dissolved solids (TDS) in water. The relationship of EC to TDS will vary

depending upon the distribution of major constituent elements present in the water.

Interpretations

Tables 9 and 10 contain safe salinity limits for human and livestock drinking water. Table 11

contains general guidelines for salinity in irrigation waters. For aquatic plant growth, salinity

levels should be kept as close to natural conditions as possible (US EPA, 1973).

Table 9. Safe limits for drinking water (US EPA) and average salinity levels

for river waters of the world (James et al., 1982)

Water EC2

(dS/m 25°C)

Total Dissolved Solids

(mg/L)

Drinking water

SMCL1 0.78 500

Livestock and poultry

US EPA recommendation 4.7 3000

Average salinity levels in river waters

North America 0.23 146

Europe 0.28 182

Australia 0.09 59

World 0.19 120

1 SMCL = secondary maximum contaminant levels are unenforceable Federal

guidelines regarding taste, odor, color, and other non-aesthetic effects in drinking water.

2

 EC estimated from total dissolved solids (TDS); EC = TDS/640
80

Table 10. Use of saline waters for livestock and poultry (US EPA, 1973)

Comment EC1

(dS/m 25°C)

Total Dissolved

Solids

(mg/L)

Relatively low level of salinity. Excellent for all classes

of livestock and poultry. < 1.6 < 1,000

Very satisfactory for all classes of livestock and poultry.

May cause temporary and mild diarrhea in livestock not

accustomed to them or watery droppings in poultry.

1.6 - 4.7 1,000 - 3,000

Satisfactory for livestock, but may cause temporary

diarrhea or be refused first by animals not accustomed to

them. Poor waters for poultry, often causing watery

feces, increased mortality, and decreased growth,

especially in turkeys.

4.7 - 7.8 3,000 - 5,000

Can be used with reasonable safety for dairy and beef

cattle, for sheep, swine, and horses. Avoid use for

pregnant or lactating animals. Unfit for poultry and

probably for swine.

7.8 - 10.9 5,000 - 7,000

Considerable risk in using for pregnant or lactating cows,

horses, or sheep, or the young of these animals. In

general, use should be avoided although older ruminants,

horses, poultry, and swine may subsist on them under

certain conditions.

10.9 - 15.6 7,000 - 10,000

Risks are too great and are not recommended for use

under any conditions. >15.6 > 10,000

1

 EC estimated from total dissolved solids (TDS); EC = TDS/640

Table 11. General purpose guidelines for salinity in irrigation water for

arid and semi-arid regions (US EPA, 1973).

Classification EC dS/m TDS mg/L

Water for which no effects are usually noticed 0.75 500

Water that can have detrimental effects on

sensitive crops 0.75-1.50 500-1,000

Water that can have adverse effects on many

crops: requires careful management 1.50-3.00 1,000-2,000

Water that can be used for tolerant plants on

permeable soils with careful management 3.0-7.50 2,000-5,000
81

Water Nitrate and Nitrite Levels

Introduction

Nitrate in water is of concern in regards to human and animal health and to environmental

quality of ground and surface waters. Nitrate in drinking water can cause methemoglobinemia

(“blue baby syndrome”) in infants under six months of age and can have toxic effects in livestock

and poultry. The toxicity occurs with the conversion of nitrate to nitrite after it has been consumed. Nitrite has a more rapid and pronounced toxicity effect than nitrate in drinking water.

Fortunately, nitrite concentrations in water sources are usually very low. Nitrate in surface waters

can cause accelerated growth of algae and aquatic plants, causing depletion of dissolved oxygen

and general degradation of the water body (eutrophication). Eutrophication jeopardizes the use of

water for recreation, sport and commercial fishing, agriculture, industry, and municipal supply.

Also, nitrates can adversely impact aquatic ecosystems. Nitrate entering surface and groundwater

is from non-point sources; both urban and agricultural runoff and leachate are recognized as contributors.

Interpretations

The levels of N required to induce eutrophication will vary depending on the nitrogen to

phosphorous ratio. Excesses of either or both N and P can lead to eutrophication. Excessive

growth of algae has been shown to occur when total phosphorus (mostly phosphate) levels exceed

0.10 ppm. Table 12 shows commonly used values for total nitrogen (mostly nitrate or ammonia).

Eutrophication is defined as an increase in the nutrient status of natural waters that causes accelerated growth of algae or water plants, depletion of dissolved oxygen, increased turbidity, and general degradation of water quality (Pierzynski et al., 1994).

Table 12. Human, animal, and environmental limits of nitrate and nitrite in

water (Pierzynski et al., 1994; US EPA, 1973).

Description Limit or threshold

US EPA maximum contaminant level for nitrate-N

in public drinking water 10 mg NO3

-N L-1

US EPA maximum contaminant level for nitrite-N

in public drinking water 1 mg NO2

-N L-1

Recommended safe level for livestock and poultry

drinking water 40 mg NO3

-N + NO2-N L-1

Recommended safe level for Nitrite-N alone in

livestock and poultry drinking water 10 mg NO2

-N L-1

Threshold for eutrophication in fresh water

environments 0.5-1.0 mg N L-1

Threshold for eutrophication in marine

environments > 0.6 mg N L-1
82

Comments

The nitrate/nitrite test strips can determine both nitrate and nitrite concentrations (two test

pads on each test strip). The nitrate test pad on the test strip measures the sum of both nitrate-N

and nitrite-N present in the sample. If nitrite is detected in the sample, the amount can be subtracted from the nitrate reading to get the actual amount of nitrate-N in the sample. However,

nitrite is rarely found in drinking waters at levels above 0.1 mg L-1 (Manahan, 1993).

1 ppm (parts per million) = 1 mg L-1 (milligram per liter)

References

James, D.W., R.J. Hanks, and J.J. Jurinak. 1982. Modern irrigated soils. John Wiley & Sons, New

York.

Manahan, S.E. 1993. Fundamentals of environmental chemistry. Lewis Publ., Ann Arbor, MI.

Pierzynski, G.M., J.T. Sims, and G.F. Vance. 1994. Soils and environmental quality. Lewis Publ.,

Boca Raton, FL.

US EPA. 1973. Water quality criteria 1972. PB-236 199/6BE. National Academy of Sciences -

National Academy of Engineers. US Environmental Protection Agency, Washington, DC.