soil testing

The art and science of

routine soil testing

http://www.labsafety.com/search/LaMotte/+-1399/24528163/221700/?isredirect=true

What is “routine”

soil testing ?

Goals of routine soil testing

Rapid

Cheap

Predictive

Broadly

applicable

Very different from soil science research

Routine soil testing starts with the

collection of "representative" soil samples

How many samples

should be collected

from each field ?

120 acre field

The optimum number of

soil samples is a

compromise between

what should be done (to

accurately represent the

field) and what can be

done (time/cost).

120 acre field

The U of Illinois currently

recommends collecting

1 composite sample per

2.5-acres.

What is a

composite

sample?

Composite

sampling

Multiple sub-

samples are

collected from

each management

unit and mixed

together

This does not mean that we should all be collecting 20 cores per

composite sample but using only 5 cores per composite is a major compromise.

If we don’t collect enough sub-samples or collect

sub-samples at different depths or times… our

soil sampling will lack precision

Accuracy vs. precision??

Lack of precision in soil sampling

= unrepeatable results

How do you know if soil test results

are accurate?

***

*

Inaccurate results => inappropriate fertilizer recommendations

"We've been moving in circles for years," says Gyles

Randall, soil scientist, University of Minnesota. "Grid

sampling was the hottest thing going, but it was

expensive. The question was if growers were getting

their money's worth. If land is owned or under a long-

term rental agreement, I like grid-based sampling, but

under a short-term rental basis, you can hardly justify it."

Grid vs. Zone Sampling

Matt Duncan, Key Agricultural Services, Macomb, Ill., is a strong believer

in grid sampling. However, it is only one part of the equation. "We found

that after multiple soil test cycles using grid sampling based variable rate

applications, in many cases highs were getting higher and lows were

getting lower," says Duncan. "When we looked at the GPS yield data

history, we noticed the crop yields were consistently higher in the field

areas with decreasing soil test values and lower in the areas of increasing

soil test levels."

Soil management zones

Soil

1

Soil 2

Soil 3

Soil 4

A management zone

approach is only

possible if knowledge

of soil variation is

preexisting.

Knowledge of soil variation:

County soil survey maps

Old field boundaries

Past management records

How well do soil survey mapping units

relate to crop productivity ?

Sometimes very well… other times not so well

Monitoring change over time will be much easier

if soil samples are collected from the same

locations each time the field is sampled.

Sampling locations can be identified using GPS

equipment or by more traditional methods such as a

measuring wheel.

The U of Illinois recommends compositing 5 soil

cores from within a 10-foot radius to represent each

sampling location.

Important soil sampling considerations

Avoid sampling areas that are clearly not representative

(old manure piles, eroded knolls…)

Use clean sampling tools

Collect samples from a depth that is

appropriate for your soil management system:

conventional tillage = 6-8”

no-till or lawn = 4”

Multiple sampling depths (e.g., 0-2” & 2-8”)

is often desirable for long term NT systems

Nutrient Stratification and No-till – Is it a problem??

Late summer and fall are often recommended as

the best times for collecting soil samples

- the soil samples used for soil test correlation are normally

collected in the late summer/fall

- potassium test results are most reliable during the late

summer/fall

- nutrient uptake by summer crops has occurred

- soil is more likely to be dry

Keep in mind that soil testing labs are normally

the busiest in the late summer and fall

If possible, sample at ~ the same time every year !

Many labs will only accept samples

in official sample bags or boxes

Field moist soil samples should be delivered to a

lab ASAP or dried prior to storage

Samples should be accompanied

by a submittal form specifying

desired analyses and crop and soil

management information

When samples arrive at a high

throughput lab, they are entered

into a tracking system and then

prepped for extraction.

Sample prep generally consists

of drying and grinding.

Small sub-samples of prepped

soils are isolated (normally

volumetrically) and then

extracted.

Extraction is a process of

briefly washing a soil. It is not

intended to simulate the

process of root uptake or

remove all available nutrients.

A variety of soil extractants are

used by soil testing labs in the

Midwest region.

Examples of extractants: Bray 1, Olsen,

Ammonium acetate, Hot water, DTPA,

Mehlich 1, Mehlich 3

The Mehlich 3 extractant was developed by Dr. Adolph Mehlich

to estimate plant availability of macronutrients and micronutrients

in soils with a wide range of physical and chemical properties.

Adopted by the NCDA soil testing lab in 1981, the Mehlich 3

extractant has reduced analytical costs by replacing multiple

extraction methods.

Reference: Mehlich A. 1984. Mehlich-3 soil test extractant: a

modification of Mehlich-2 extractant. Commun Soil Sci Plant Anal

15(12):1409–16.

Composition: (0.2N CH3COOH + 0.25N NH4NO3 + 0.013N HNO3

+ 0.015N NH4F + 0.001M EDTA)

Mehlich 3 extractant most widely used universal extractant

Would this extracting solution be useful for measuring plant available N?

Plant root simulator probes –

an alternative method of nutrient extraction

Ion exchange resins

Traditionally sample extracts were analyzed

using different methods for different nutrients

but many labs now use sophisticated

instruments that can analyze many nutrients

simultaneously.

Most large labs use an Inductively Coupled Plasma Atomic Emission

spectrometer to analyze soil extracts for multiple elements

I am an ICP!

By themselves, extractable

nutrient levels are not informative.

Extractable nutrient levels provide an index of

nutrient availability that can be interpreted

using results from field experiments.

Extractable nutrient levels are not

directly related to most of the factors

controlling nutrient availability during

a growing season.

moisture temperature microbial activity

rooting depth root health

Meaningful interpretation of soil test results

requires field calibration

100 %

yield

50 %

yield

http://www.ipm.iastate.edu/ipm/icm/2003/11-17-2003/mehlich3.gif

Soil test P concentration (ppm)

Field sites are

needed that vary

widely in soil

test levels of the

nutrient of

interest but have

few other

limiting factors

Relationship between crop yield and soil test K

Response curves are derived from

calibration data – response curves do

not describe all the variation in

calibration data !

Rates of P2O5 or K2O to apply based on soil test index value and crop-specific equation *

Eq. #Soil Test Index

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

1 900 780 660 550 460 370 290 220 160 110 70 40 10 0 0 0

2 500 440 380 330 280 230 190 150 120 90 70 40 30 10 0 0

3 300 270 230 200 180 150 130 100 80 70 50 40 20 10 10 0

4 300 260 220 180 150 120 100 70 60 40 30 20 20 20 20 10–30

5 300 250 210 170 130 100 80 50 30 20 0 0 0 0 0 0

6 300 240 190 140 100 60 30 10 0 0 0 0 0 0 0 0

7 250 220 190 160 140 110 90 70 50 40 30 10 0 0 0 0

8 250 210 160 130 90 60 30 10 0 0 0 0 0 0 0 0

9 220 190 160 140 120 100 80 60 50 30 20 10 10 0 0 0

10 200 170 150 120 100 80 60 50 30 20 10 10 0 0 0 0

11 200 160 120 90 60 40 20 0 0 0 0 0 0 0 0 0

12 180 160 140 130 110 90 80 70 50 40 30 20 20 10 0 0

13 165 140 110 90 70 50 30 20 10 0 0 0 0 0 0 0

14 150 120 100 80 60 40 30 10 0 0 0 0 0 0 0 0

15 150 120 90 70 40 30 10 0 0 0 0 0 0 0 0 0

16 150 110 70 40 10 0 0 0 0 0 0 0 0 0 0 0

17 140 120 100 80 70 50 40 30 20 10 10 0 0 0 0 0

18 120 90 60 40 20 0 0 0 0 0 0 0 0 0 0 0

19 100 80 70 60 40 30 20 10 0 0 0 0 0 0 0 0

20 80 60 40 20 0 0 0 0 0 0 0 0 0 0 0 0

21 20.0 17.0 14.0 11.5 9.5 7.5 5.5 4.0 2.5 1.5 0.5 0 0 0 0 0

22 11.0 9.5 8.0 7.0 6.0 5.0 4.0 3.0 2.5 2.0 1.0 1.0 0.5 0 0 0

23 9.0 7.5 6.5 5.5 4.5 3.5 2.5 2.0 1.5 1.0 0.5 0 0 0 0 0

24 8.0 6.5 5.0 4.0 2.5 2.0 1.0 0 0 0 0 0 0 0 0 0

25 6.5 5.0 4.0 3.0 2.0 1.0 0.5 0 0 0 0 0 0 0 0 0

In North Carolina, 25

different crop response

equations are used to

make P and K

recommendations

Different response equations are used for different crops

http://www.lamotte.com/

Results may be reproducible but have

limited meaning without local field calibration

2008 ISTA Members (alphabetical)

A

A&L Great Lakes Laboratories, Inc.

Lois K. Parker

3505 Conestoga Dr.

Ft. Wayne, IN 46808

Tel: 260-483-4759

Fax: 260-483-5274

Additional member: Julie Bruggner

AgriEnergy Resources

Gary Cambpell

21417-1950 E. St.

Princeton, IL 61356

815-872-7790

815-872-1928

[email protected]

Additional member:

Ann Berry - [email protected]

AgSource Cooperative Services

Steve Peterson

106 N. Cecil St., PO Box 7

Bonduel, WI 54107

K

Key Agricultural Services

Dean Wesley

114 Shady Lane

Macomb, IL 61455

Tel: 309-833-1313

Fax: 309-833-3993

Additional members: Tad Wesley

KSI Laboratory

David Brummer

202 S. Dacey Dr.

Shelbyville, IL 62565

Tel: 217-774-2421

Fax: 217-774-2866

[email protected]

M

M & R Ag Services

Mick Capouch

16747 W 200N

Medaryville, IN 47597

29 member labs in 200820 labs actually located in IL

mailto:[email protected]


















Members of ISTA are required to participate in a quality

control program referred to as the Split Sample Soil

Test Comparison Program. In this process, six samples

are sent quarterly to all member labs. The labs test the soil

and return the raw data to an independent accounting firm.

This information is then gathered yearly and used in a

Reliability/Repeatability report. A level of proficiency is

required to receive a Certificate of Good Standing from

ISTA. This certificate is the member's accreditation and is

their clients' assurance that the information they receive is

reliable, consistent and accurate.

Some ISTA member labs also participate in an additional

National Proficiency Testing Program (NAPT).

Quality Control

Good labs include standard (aka check) samples in every

analytical run. This allows them to quickly identify problems.

Choose a lab and stick with it !

Different labs

often use

different

analytical and

interpretation

methods

Recommendations

So what do the

numbers mean ???

Analytical results

Analytical results

Recommendations

Analytical results can be obtained

without recommendations

Analytical results are commonly presented as

concentrations of extractable nutrients

(e.g., ppm or lbs/ac) but are sometimes

presented as unit-less index values

As stated earlier, by themselves, extractable

nutrient levels are not informative.

Extractable nutrient levels provide an index of

nutrient availability that can be interpreted using

results from field experiments.

As a general rule, ppm * 2 = lbs/ac(assuming a plow layer weighs 2 million lbs)

Have any of you ever had to run a 40

as part of a try-out for a team?

How well does your

40 time predict your

ability to play the

game?

Turning analytical results into recommendations

- the sufficiency approach

Critical levels of extractable nutrients have been identified using field experiments

The critical levels identified across the US vary because of differences in soil

properties and also because of differences in the interpretation of field experiments

Build and maintenance approach

Critical Level

Maintenance applications of fertilizer

(i.e., replacing nutrients removed in

harvested crops)

make sense conceptually

**but**

do not necessarily make sense

economically !

Soil is a black box !!!!

Regional variation in soil test K

http://soilfertility.unl.edu/Materials%20to%20include/2001%20NCR%20potassium_files/image008.g

if

Changes in soil test results between 2001 and 2005

Some of these trends are a little surprising !

Increased use of conservation tillage may be responsible

http://www.ipni.net/ppiweb/bcrops.nsf

Soil Test K

Change between 2005 and 2010 % of samples below critical level

Soil Test P

Change between 2005 and 2010 % of samples below critical level

Nutrient balancing concepts

Nutrients interact in plant and soil systems. Some

important nutrient interactions include ammonium-

calcium, phosphorus-iron, phosphorus-copper,

phosphorus-zinc, and potassium-magnesium-calcium.

Some consultants and private labs place great

emphasis on “base cation ratios”.

Typical target ratios: 65-75% Ca : 10-15% Mg : 2-5% K

Nutrient interactions and proper nutrient

balance should be considered in relation to

nutrient supply – i.e. the availability of nutrients

in the soil.

Nutrient supply is important because

“recommended nutrient ratios" in soil or

plant tissue are possible even when

nutrients are deficient or excessively high.

As we have discussed earlier in the semester, nutrient

imbalance can be a problem (e.g., competitive ion effects

and other types of antagonistic nutrient interactions) but

nutrient balance in animal diets is probably more important

than in soil because of the selective abilities of plant roots

Some day soon

soil testing

may consist of

on-the-fly “sensing”

of soil hundreds to

thousands of times

per acre like a

yield monitor

http://bse.unl.edu/adamchuk/presentations/

a


“The Soil Doctor”The original electrical conductivity/resistivity system

2.5 acre grid sampling vs.

high density on the fly sensing

Soil pH and lime requirement often vary

widely within fields

Is a high density pH map all you need

for variable rate lime application?

Illinois corn and soybean producer Ken Dalenberg (Mansfield IL) was

recently named 2010 Farmer of the Year in the PrecisionAg Awards Of

Excellence program. His deliberate approach to honest evaluation has helped

him build relationships with universities and industry… he is frequently involved

in advanced evaluation of equipment for John Deere and other companies. He

is frequently invited to speak at conferences throughout the U.S. and other

countries. Ken understands the importance of proper scientific methodology

and is willing to expend the extra efforts and costs to do it right…even though it

means delays in getting his farm work done.”

Variable rate P and

K is based on false

assumptions and

does not pay. I

only do variable

rate lime on my

farm now.

Variable rate is only

likely to pay in fields

with large variability

including levels

above and below

critical levels.

MISS has incorporated EC, NDVI readers and soil testing so that the client can rest

assured that low application amounts prior to planting will not hurt the crop yield. By

going a step further and taking stalk nitrate tests at those same locations of soil

testing, the client is able to further define the management map and customize the

following nitrogen applications to occur.

soil testing

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