Potassium Release Kinetics and Plant Response in Calcareous Soils

Abstract

Abstract Greenhouse and laboratory experiments were conducted to characterize the K supply and nonexchangeable K release kinetics in calcareous soils. Twelve soils were exhaustively cropped with alfalfa ( Medicago sativa L.) in the greenhouse for 584 d (16 cuttings). Yield, K uptake, and changes in NH 4 OAc exchangeable K were monitored. Calcium resin extractable K was determined in the laboratory (7000 h extraction) on the <0.25 mm fraction of each soil. Nonexchangeable K release was calculated from the greenhouse and laboratory data. Cumulative K release to Ca‐resin was mathematically described by a power function equation and the empirical constants releated to alfalfa yield, K uptake, and exchangeable K levels. Results indicated that clay soils had a long‐term supply of plant available K while light‐textured soils did not. After 16 cuttings the exchangeable K levels in the clay, loam, and sand textured soils declined 44, 33 and 58%, respectively. Both independent methods of measuring nonexchangeable K release were highly correlated with each other ( r = 0.91). Potassium release was also highly correlated to initial NH 4 OAc‐K and to cumulative or relative K uptake and yield. Intercept and slope constants of the power function kinetic equation were significantly correlated to alfalfa yield, K uptake, and initial exchangeable K. Results also indicated that the NH 4 OAc‐K soil test was an adequate measure of long‐term K supply in these soils.