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KINETICS OF PHOSPHATE RELEASE IN SOME FOREST AND SAVANNA SOILS
Abstract:
The rate at which phosphate (P) is desorbed from the soil surface into soil solution is a key factor that regulates the continuous supply of P to crops. Understanding the kinetics of P desorption is paramount for effective P management in order to boost agricultural production and to minimize environmental degradation and pollution. The objectives of this study were to compare several kinetic models for describing P desorption rates in savanna soils of varying lithogenic origins, and to determine the effect of soil properties on P release rate. Phosphate desorption patterns were measured from soils derived from three different parent materials using anion exchange resin. The desorption patterns included an initial fast reaction that lasted for about 500 mins, followed by a slow release that continued up to 1200 mins. Phosphorus desorption rates by anion exchange resins were best described by three empirical kinetic models: Elovich equation, the parabolic diffusion equation and the fractional power equation in that order. However, when P was added to the soils, the first-order rate equation gave a satisfactory description of the experimental data from soils derived from Shale and Basement complex, indicating that P release rates in these soils were related to the quantity of P sorbed reversibly to the surface. The rate coefficients varied widely among soils from the same parent materials and between parent materials due probably to variations in the properties of the soils. The rate coefficients from the Elovich equation, parabolic diffusion equation and the fractional power model were best predicted from soil organic carbon (OC), clay, pH, and extractable Al and Fe oxides. These soil properties together explained between 93 and 99% of the variance in the rate coefficients of P desorption in the soils.
KINETICS OF PHOSPHATE RELEASE IN SOME FOREST AND SAVANNA SOILS
