The document discusses the goals, methods, and considerations for routine soil testing, including collecting representative soil samples, using appropriate sampling techniques and numbers of samples, analyzing samples for nutrient levels, and interpreting results to make meaningful fertilizer recommendations through calibration of soil test levels to crop yields. Routine soil testing aims to provide rapid, inexpensive, and broadly applicable analysis to predict crop nutrient needs.

1. The art and science of
routine soil testing
http://www.labsafety.com/search/LaMotte/+-1399/24528163/221700/?isredirect=true

2. What is “routine”
soil testing ?

3. Goals of routine soil testing
Rapid
Cheap
Predictive
Broadly
applicable
Very different from soil science research

4. Routine soil testing starts with the
collection of "representative" soil samples

5. How many samples
should be collected
from each 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

6. What is a
composite
sample?
The U of Illinois currently
recommends collecting
1 composite sample per
2.5-acres.
120 acre field

7. Composite
sampling
Multiple sub-
samples are
collected from
each management
unit and mixed
together

8. 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.

9. 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??

10. Lack of precision in soil sampling
= unrepeatable results
*
* *
*
How do you know if soil test results
are accurate?
Inaccurate results => inappropriate fertilizer recommendations

11. Grid vs. Zone Sampling
"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."

12. 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."

13. Soil management zones
A management zone
approach is only
possible if knowledge
Soil 3
of soil variation is
preexisting. Soil
Soil 4
1
Knowledge of soil variation:
County soil survey maps Soil 2
Old field boundaries
Past management records

14. How well do soil survey mapping units
relate to crop productivity ?
Sometimes very well… other times not so well

15. 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.

16. 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

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

18. 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

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

20. Many labs will only accept samples
in official sample bags or boxes

21. Field moist soil samples should be delivered to a
lab ASAP or dried prior to storage

22. Samples should be accompanied
by a submittal form specifying
desired analyses and crop and soil
management information

23. When samples arrive at a high
throughput lab, they are entered
into a tracking system and then
prepped for extraction.

24. Sample prep generally consists
of drying and grinding.

25. 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.

26. 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

27. Mehlich 3 extractant
most widely used universal extractant
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)
Would this extracting solution be useful for measuring plant available N?

28. Ion exchange resins
Plant root simulator probes –
an alternative method of nutrient extraction

29. Traditionally sample extracts were analyzed
using different methods for different nutrients
but many labs now use sophisticated
instruments that can analyze many nutrients
simultaneously.

30. Most large labs use an Inductively Coupled Plasma Atomic Emission
spectrometer to analyze soil extracts for multiple elements
I am an ICP!

31. 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.

32. moisture temperature microbial activity
Extractable nutrient levels are not
directly related to most of the factors
controlling nutrient availability during
a growing season.
rooting depth root health

33. Meaningful interpretation of soil test results
requires field calibration
100 %
yield
Field sites are
needed that vary
widely in soil
50 % test levels of the
yield nutrient of
interest but have
few other
limiting factors
Soil test P concentration (ppm)
http://www.ipm.iastate.edu/ipm/icm/2003/11-17-2003/mehlich3.gif

34. 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 !

35. Rates of P2O5 or K2O to apply based on soil test index value and crop-specific equation *
Soil Test Index
Eq. #
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 In North Carolina, 25
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 different crop response
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 equations are used to
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 make P and K
0 0 0 0 0 0 0 0 0 0
17
18
140
120
120
90
100
60
80
40
70
20
50
0
recommendations
40
0
30
0
20
0
10
0
10
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

36. Different response equations are used for different crops

37. Results may be reproducible but have
limited meaning without local field calibration
http://www.lamotte.com/

39. 20 labs actually29 member labsIL 2008
located in in
2008 ISTA Members (alphabetical)
A K
A&L Great Lakes Laboratories, Inc. Key Agricultural Services
Lois K. Parker Dean Wesley
3505 Conestoga Dr. 114 Shady Lane
Ft. Wayne, IN 46808 Macomb, IL 61455
Tel: 260-483-4759 Tel: 309-833-1313
Fax: 260-483-5274 Fax: 309-833-3993
Additional member: Julie Bruggner Additional members: Tad Wesley
AgriEnergy Resources KSI Laboratory
Gary Cambpell David Brummer
21417-1950 E. St. 202 S. Dacey Dr.
Princeton, IL 61356 Shelbyville, IL 62565
815-872-7790 Tel: 217-774-2421
815-872-1928 Fax: 217-774-2866
gcampbell@agrienergy.net ksilabdbrummer@consolidated.net
Additional member:
Ann Berry - aberry@agrienergy.net M
M & R Ag Services
AgSource Cooperative Services Mick Capouch
Steve Peterson 16747 W 200N
106 N. Cecil St., PO Box 7

41. Quality Control
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).

42. Good labs include standard (aka check) samples in every
analytical run. This allows them to quickly identify problems.

44. Choose a lab and stick with it !
Different labs
often use
different
analytical and
interpretation
methods

45. Recommendations
Analytical results
So what do the
numbers mean ???

46. Analytical results
Recommendations

47. Analytical results can be obtained
without recommendations

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

49. 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?

50. 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

51. 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

52. Build and maintenance approach
Critical Level

53. Soil is a black box !!!!
Maintenance applications of fertilizer
(i.e., replacing nutrients removed in
harvested crops)
make sense conceptually
**but**
do not necessarily make sense
economically !

54. Regional variation in soil test K
http://soilfertility.unl.edu/Materials%20to%20include/2001%20NCR%20potassium_files/image008.g
if

55. 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

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

58. Soil Test K
Change between 2005 and 2010 % of samples below critical level

59. Soil Test P
Change between 2005 and 2010 % of samples below critical level

61. 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

62. 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

63. 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

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

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

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

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

69. 2.5 acre grid sampling vs.
high density on the fly sensing

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

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

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

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

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

75. Soil pH and lime requirement often vary
widely within fields
Is a high density pH map all you need
for variable rate lime application?

78. Variable rate P and
K is based on false Variable rate is only
assumptions and
does not pay. I likely to pay in fields
only do variable with large variability
rate lime on my including levels
farm now.
above and below
critical levels.
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.”

81. 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.