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Potassium Release Kinetics and Plant Response in Calcareous Soils¹

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 NH₄OAc 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 NH₄OAc-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 NH₄OAc-K soil test was an adequate measure of long-term K supply in these soils.

¹ Contribution from the Dep. of Agronomy, Colorado State Univ. Exp. Stn., Ft. Colins, CO 80523, and published as Scientific Series Paper no. 2752. This research was supported in part by the Potash and Phosphate Institute, Atlanta, GA 30329 and the Colorado Experiment Station.

² Former Graduate Research Assistant and Professor, Dep. of Agronomy, Colorado State Univ., respectively. The senior author is currently Assistant Professor, Soil Science, Univer. of Nebraska, Scottsbluff, NE 69361

Received for publication October 24, 1984. Accepted for publication October 18, 1985.

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