Phosphorus sorption-desorption kinetics of soil under contrasting land uses

.In watersheds with a high density of animal production, the land application of large amounts of manure has led to P accumulation in soils, thereby increasing the risk of P leaching. The objective of this study was to characterize P sorption-desorption kinetics of a soil under contrasting land uses, The A, B, and C horizons of a Typic Humaquept were sampled from a forest (F) and in hay fields of farms with no surplus (D) or a known surplus of manure (SN). Leaching experiments, using a 0.01 M KCl solution containing 5 mg P L(-1) for the sorption phase and a P-free electrolyte solution for the desorption phase, were conducted in glass columns. From the incremental model used, it was estimated that the available P sorption capacities were 50% lower in the agricultural A horizons than in the forest soil. In the B horizon, the P sorption capacities were comparable for all soils. In the C horizon, the available P sorption capacity was 75% lower in the SN than in the two other soils. After P saturation of the samples, the potential amounts of desorbable P in the A and B horizons of agricultural soils were two-fold greater than those of forested soil. A significant relationship (P < 0.05) was established between soil Al,, content and the number of pore volumes necessary to decrease the P concentration of the effluent to 1 mg P L(-1). The results of this study suggest that soils associated with high animal density were more at risk to leach P into drainage waters than low animal density or forest soils.