1. Soil and Plant Sampling and Analysis

2. Interpretation of lab results
Lime and fertilizer
recommendations
Sampling
Soil
Soil acidity
Available plant nutrients

3. Interpretation of lab results
Lime and fertilizer
recommendations
Soil acidity
Available plant nutrients

4. First stool leg Sampling Soil Soil acidity Available plant nutrients
Interpretation of lab results

5. Sample in Management Zones

6. Precision Ag sampling

7. Sampling Depth
Tilled
Non-Tilled
3-4”
6-8”

8. Second stool leg Sampling Soil Soil acidity Available plant nutrients
Interpretation of lab results

9. Target pH
Most agronomic crops
Tobacco
Alfalfa

10. Laboratory results for
Soil pH
Buffer pH
Water pH
They measure……
Active acidity
Active and
Residual acidity

12. Soil pH measures Active acidity
pH electrode - K+
Mg2+ H+ -
Mg2+ K+
Ca2+ H+ H+ H+
Na+ H+ - K+
Mg2+ K+ K+ - H+ H+
Mg2+ - H+ H+ -
Ca2+
Ca2+
Na+ - K+ H+
Ca2+
Mg2+
Ca2+ -
10 g soil + 10 ml water
Soil pH measures Active acidity

13. B B B B B H B B B H H H H H H H H H soil particle - - - - - + - - - +

14. + H + H
soil particle + H

15. Acidity (meq/100g) = 6.2 x (7.5 – Buffer pH)
SMP Buffer
Active and Residual acidity
pH of buffer alone
7.5 x
6.8
Soil Buffer pH y
6.4
Soil Buffer pH
Acidity (meq/100g) = 6.2 x (7.5 – Buffer pH)

16. UK standard Sikora buffer SMP buffer Mehlich buffer
Initial pH
7.5
Sikora buffer
UK standard
7.5
SMP buffer
6.6
Mehlich buffer
8.0
Adam and Evans buffer
Woodruff buffer
7.0

17. Third stool leg Sampling Soil Soil acidity Available plant nutrients
Interpretation of lab results

18. Laboratory results for
Phosphorus
Potassium P K
They measure……
Concentration of P and K in soil that is proportional to plant-available P and K

19. Phosphorus Adsorption
Al and Fe oxides
clays P P-

20. Precipitation of Inorganic Phosphorus Compounds
at low pH (below 7)
Al3+ + H2PO4-
Fe-P and Al-P
Fe3+ + H2PO4-

21. Precipitation of Inorganic Phosphorus Compounds
at high pH (above 7)
Ca-P
Ca2+ + H2PO4-

22. Potassium Retention in SoilK+ K+

23. Calcium and Magnesium Retention in Soil
Mg2+
Mg2+

24. 50%
Solids
Plant roots extract nutrients from soil solution
25%
Water
25%
Air

25. Extractants release a portion of nutrients into solution
chemical extractant P K+
Ca2+
Mg2+

28. Ammonium Acetate (for K)
Common soil extractants
Bray I (for P)
Bray II (for P)
Mehlich I
Mehlich III
UK standard
Ammonium Acetate (for K)

29. WHY THERE IS NO SOIL TEST FOR N:

30. different extractants different units expressing results
Confusion when comparing
different soil test reports because of..
different extractants
different units expressing results

31. proportional to amount available to plant
SOIL
Extractable
nutrient
proportional to amount available to plant
whole pie is total P or K

32. Different extractants, different soil test results
Mehlich I =
Mixture of
2 acids
whole pie is total P

33. Different extractants, different soil test results
Mehlich III
Mixture of
1 acid
+ fluoride
+ salt
+ chelate
+ pH buffer
whole pie is total P

34. Comparison of 4 extractants for soil test P
P (lbs/acre)
Bray I
112
Bray II
212
Mehlich I 46
Mehlich III 90
NAPT sample : Rozetta silt loam from Bureau Co., IL. Soil pH = 6.5, CEC = 8.3

35. Comparison of 4 extractants for soil test K
K (lbs/acre)
Bray I
272
Mehlich I
250
Mehlich III
332
Am. Acet.
330
NAPT sample : Rozetta silt loam from Bureau Co., IL. Soil pH = 6.5, CEC = 8.3

36. different units expressing results
Variation in how 45 Laboratories in North America report Mehlich III Soil Test P and K
20 labs report as mg/kg
15 labs report as lbs/acre
1 lab reports as lbs/acre-6 inches
2 labs report as lbs/ppm
2 labs report as ppm/lbs/acre
1 lab repors an index
3 labs reports as kg/ha
1 lab reports as mg/L
Source - NAPT, 2nd quarter 2000

37. Mehlich III in lbs/acre
UK standard for P and K
Mehlich III in lbs/acre
mg/kg x 2 = lbs/acre

38. Fourth stool leg Sampling Soil Soil acidity Available plant nutrients
Interpretation of lab results

39. Relative Sources of Nutrients
Soil Test
Sufficiency
Level
Level
High
soil
100%
Med
soil
fert.
70-100%
Low
soil
fertilizer
50-70%
V.Low
soil
fertilizer
<50%
Nutrients
External
available
nutrients
from soil
required

40. Agronomic Threshold Yield (% of maximum) Soil Test P (lbs/acre)
110
100
High
Med 90
Low 80
Yield (% of maximum)
V.low 70 60 50 40 1 60 30 5
Soil Test P (lbs/acre)
Soil Test P (lbs/acre)

41. Environmental Threshold
110
100 90 80
Limited Risk
of P runoff
Potential Risk
Yield (% of maximum) 70 60 50 40
Soil Test P (lbs/acre)
400
Soil Test P (lbs/acre)

42. in sufficiency approach

43. 2 philosophies with a low soil test
Sufficiency
Agronomic Threshold
9 lb/ac P2O5 remaining in soil increases soil test 1 lb/ac
Soil test P or K
4 lb/ac K2O remaining in soil increases soil test 1 lb/ac
Time (years)

44. 2 philosophies with a low soil test
Rapid Build-up
Agronomic Threshold
Soil test P or K
Time (years)

45. 3 philosophies with a high soil test
buildup
maintenance
sufficiency
Agronomic Threshold
Soil test P or K
Time (years)

46. Fertilizer costs for Corn Production
* Data from H.J. Savoy, Univ. of Tenn.

47. * Data from H.J. Savoy, Univ. of Tenn.
Corn Yields
* Data from H.J. Savoy, Univ. of Tenn.

48. Interpretation of lab results
Lime and fertilizer
recommendations
Sampling
Soil
Soil acidity
Available plant nutrients

49. Plant Tissue Testing