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Effect of Exchangeable Potassium Level and Drying on Release and Fixation of Potassium by Soils as Related to Clay Mineralogy¹

ABSTRACT

The effect of exchangeable K level and drying over H₂SO₄ upon K release and fixation by six soil series was studied in the laboratory. Differences in behavior seemed to be related very closely to clay mineralogy of the soils. Illite appeared to be the source of K released by drying, whereas fixation at moisture levels higher than 4% was associated with vermiculite and fixation at lower moisture levels with montmorillonite.

Further evidence indicates the moist K equilibrium value of these soils to be 0.45 ± 0.10 me. exchangeable K per 100 g. of soil. When exchangeable K values are above that level for field-moist samples, K is fixed on drying, whereas it is released when the initial K level is lower. The magnitude of release or fixation appears to be directly related to the clay mineralogy.

¹ Contribution of the Agronomy Department, University of Kentucky, Lexington. Published with approval of the Director of the Kentucky Agr. Exp. Sta. Appreciation is expressed to the American Potash Institute for partial support of this research.

² Former Graduate Assistant and Associate Professor of Agronomy, respectively.

Received for publication March 8, 1962. Accepted for publication May 22, 1962.