We investigated the release of K from 10 surface and subsurface soil horizons at different K concentrations, and used four kinetic equations (Elovich, modified Freundlich, parabolic diffusion, and first-order) to describe the desorption rate data. The results demonstrate the successful use of the first-order equation to describe K desorption rates. The choice of the first-order equations among others investigated was based on the goodness of fit (lower standard error of estimate obtained) and on the more realistic theoretical assumptions of the equation.
The relationship between first-order equation constants and the selected physical and chemical properties of the studied soils was investigated. Correlation coefficients relating first-order equation constants to most of the selected soil properties were low, but the interaction between organic C and exchangeable K variables was high. Multiple linear regression models relating first-order parameters to soil variables were highly significant. The ratio of organic C to exchangeable K (OC/Ex. K) was a strong contributor in the first-order constants models. The regression models were successful in predicting the first-order equation constants, as well as the K desorbed from soils.
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