Soil Testing Methods: How they affect fertilizer and lime recommendations

1. Soil Testing Methods: How they affect fertilizer and lime recommendations 20th annual Kentuckiana Crop Production Seminar Dec. 9-10, 2003 Executive Inn – Owensboro, Kentucky F.J. Sikora, Ph.D. University of Kentucky

2. Interpretation of lab results Nutrient recommendations Available plant nutrients Soil acidity

3. Interpretation of lab results Nutrient recommendations Available plant nutrients Soil acidity

4. Interpretation of lab results Nutrient recommendations Available plant nutrients

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

6. Target pH Most agronomic crops 6.4 Tobacco 6.6 Alfalfa 6.8

7. Soil pH Buffer pH Water pH They measure…… Active acidity Residual acidity

9. 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

10. - - B - - B - B B B + - H B - - B + B H + H + H + H soil particle + H + + H H + H + H

11. + H + H soil particle + H

12. 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)

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

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

15. Phosphorus Potassium K P They measure…… Concentration of P and K in soil that is related to plant-available P and K

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

19. SOIL Mehlich I = Mixture of 2 acids whole pie is total P

20. SOIL Mehlich III Mixture of 1 acid + fluoride + salt + chelate + pH buffer whole pie is total P

21. Comparison of 6 extractants for soil test P NAPT sample 2003-110: Rozetta silt loam from Bureau Co., IL. Soil pH = 6.5, CEC = 8.3

22. Comparison of 6 extractants for soil test K NAPT sample 2003-110: Rozetta silt loam from Bureau Co., IL. Soil pH = 6.5, CEC = 8.3

23. 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

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

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

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

27. Agronomic Threshold High Med Low 5 30 60 V.low 110 100 90 80 Yield (% of maximum) 70 60 50 40 0 1 Soil Test P (lbs/acre) Soil Test P (lbs/acre)

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

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

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