KINETIC DESORPTION OF NATIVE PHOSPHORUS FROM SOILS OF VARYING LITHOGENIC ORIGINS IN THE NIGERIAN SAVANNA

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Abstract

We determined the kinetic desorption of native phosphorus (P) from some savanna soils of varying lithogenic origin. Our objective was to determine whether soils of different lithogenic origins in the Nigerian savanna have different rates of P release to resin sinks. Soils derived from Basement Complex, Sandstone, and Shale were sampled for this study. The P desorption patterns for the soils was biphasic: an initial fast reaction followed by a slow release that lasted up to 1200 min. There were no significant differences between soils of the same or different parent materials. The time-dependent P desorption trends were satisfactorily described by a fractional power equation and also by the Elovich and parabolic diffusion kinetic equations, as judged from the coefficient of determination (r2) and the SE of fitting the linear forms of the kinetic expressions to the experimental data. None of the rate coefficients of the different kinetic equations differed significantly between soils of the same parent materials, but a significant difference was, however, observed in the rate parameters between soils of different parent materials. The conformity of the experimental data to either the Elovich or parabolic diffusion kinetic equation was indicative of diffusional limitation. This was supported by the failure of the fractional power, the Elovich, and the parabolic diffusion kinetic equations to model the P desorption patterns on reducing the soil particle size from greater than 2 mm to less than 0.2 mm. Reduction of the soil particle size eliminated the intra-aggregate diffusion paths from the soils to the resin sink.

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