Effect of potassium depletion on potassium-calcium exchange equilibria in soils1
1986
Mehta, S. C. | MITTAL, S. B. | Singh, A. P.
We conducted a laboratory experiment to study the K-Ca exchange equilibria in some soils from semiarid regions of India. The soils were depleted of their available and fixed K prior to exchange studies in order to understand the exchangeability and availability of applied K in such soils. Various exchange selectivity equations were also tested for consistency of the relevant exchange selectivity coefficients. In light-textured and relatively low K soils, about 50% of the exchange sites preferred K; this figure was reduced drastically, to about 5%, upon fixed K depletion. The values of standard free energy change of the exchange reactions, ΔG°, were negative in all the soils and decreased with depletion of fixed K, indicating the reduced specificities for K. The Gapon selectivity coefficient, KG, decreased with increased K saturation. NH4OAc treatment enhanced KG values at all exchangeable K percentages. None of the selectivity coefficients tested remained constant throughout the exchange isotherm.
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