Correlation and Calibration of Soil Potassium Availability with Soybean Yield and Trifoliolate Potassium

Abstract

The ability of soil tests to identify nutrient‐deficient soils and recommend fertilizer rates that optimize agronomic yield is essential for profitable soybean [ Glycine max (L.) Merr.] production. Our objectives were to correlate relative soybean yield to Mehlich‐3 and 1 mol L −1 HNO 3 –extractable soil K and trifoliolate‐leaf K concentration at the R1 to R2 development stage and calibrate the K rates for Mehlich‐3‐extractable soil K. Experiments were established on silt loams at 34 site‐years planted with a Maturity Group IV or V cultivar and fertilized at five K rates (0–148 kg K ha −1 ). Mehlich‐3‐extractable soil K ranged from 46 to 167 mg K kg −1 and produced relative soybean yields of 59 to 100% when no K was applied. Eleven sites had Mehlich‐3‐extractable K < 91 mg K kg −1 and all responded positively to K fertilization. Soybean grown in soil having 91 to 130 mg K kg −1 responded positively at nine of 15 sites. Mehlich‐3 soil K explained 76 to 79% of the variability in relative yields and had critical concentrations of 108 to 114 mg K kg −1 , depending on the model. The linear‐plateau model predicted the critical HNO 3 –extractable soil K to be 480 mg K kg −1 Trifoliolate‐leaf K concentration increased significantly, positively, and linearly as Mehlich‐3‐ and HNO 3 –extractable soil K increased, but Mehlich‐3 soil K explained only 49 to 53% of the variation in trifoliolate‐leaf K. Mehlich‐3‐extractable K is an excellent predictor of soil K availability for soybean grown on silt loams in eastern Arkansas.