Soil and Plant Sampling and Analysis

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

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

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

Sample in Management Zones

Precision Ag sampling

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

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

Target pH Most agronomic crops 6.4 Tobacco 6.6 Alfalfa 6.8

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

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

B B B B B H B B B H H H H H H H H H soil particle - - - - - + - - - +

+ H + H soil particle + H

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)

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

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

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

Phosphorus Adsorption Al and Fe oxides clays P P-

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

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

Potassium Retention in Soil K+ K+

Calcium and Magnesium Retention in Soil Mg2+ Mg2+

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

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

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)

WHY THERE IS NO SOIL TEST FOR N:

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

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

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

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

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 2003-110: Rozetta silt loam from Bureau Co., IL. Soil pH = 6.5, CEC = 8.3

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 2003-110: Rozetta silt loam from Bureau Co., IL. Soil pH = 6.5, CEC = 8.3

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

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

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

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

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)

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)

in sufficiency approach

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)

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

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

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

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

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

Plant Tissue Testing