Formulation of a first-order kinetic model and release of added phosphorus in a savanna soil

Adsorption–desorption of added phosphorus (P) was studied in a batch experiment using anion-exchange resin. Total P sorbed by adding 400 mg P kg^?1 by Nigerian soil ranged from 10.8 mg kg^?1 in the Idofian Basement complex to 35.5 mg kg^?1 in Alkaleri Sandstone, representing 3 and 9% of applied P. Phosphorus release kinetics was apparently described by the first-order, second-order, Elovich, parabolic diffusion and fractional power equations, but not in soils derived from sandstone. The mechanism underlying the release pattern was concluded to be dissolution followed by diffusion of sorbed P from the good fit to the Elovich and parabolic diffusion equations. The inability to clearly relate the P sorbed by the soil to OH^- and SO₄ ^2- released into the soil solution during the adsorption process further corroborated the above conclusion, thereby overruling the possibility of ligand exchange as a dominant mechanism in the sorption/desorption of P in these soils.