We investigated the release of P from 10 surface and subsurface soil horizons, using 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 rate equation to describe P-desorption rates. The choice of the first-order rate equation over others investigated was based on the goodness of fit (lower standard error of estimate obtained) and on the more scientific theoretical assumptions of the equation.
We also investigated the relationship between first-order equation constants and the selected physical and chemical properties of the studied soils. Multiple regression models relating first-order equation constants to soil variables yielded high R2 values. The ratios of exchangeable A1/clay and Fe2O3/organic C were strong contributors in the first-order constants models. The regression models were successful in predicting the first-order equation constants, as well as the P desorbed from soils.
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