POTASSIUM RELEASE KINETICS AND PLANT-RESPONSE IN CALCAREOUS SOILS

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//4OAc exchangeable K were monitored. Calcium resin extractable K was determined in the laboratory (7000 h extraction) on the less than 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 related 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. Refs.