Changes in some soil phosphorus availability parameters as induced by phosphorus addition and soil sorption properties

Abstract

Changes in agronomic and environmental soil phosphorus (P) availability parameters, i.e., Mehlich‐ and Olsen‐extractable P, reversibly‐adsorbed P, soil‐solution P, and equilibrium‐P concentration were determined following equilibration of 13 Italian soils with five rates of P application (0, 12.5, 25, 50, and 100 mg P kg‐1 soil). Soil P availability as determined by each parameter increased with added P. The relative change in soil P availability with added P was a function of soil sorption index silicon (SI), according to the equation DP=(Padded)a*exp(b+g*SI). This equation accounted for 94 to 98% of the variance in soil‐P availability. The inclusion of SI in a soil testing program may increase the reliability in assessing both soil‐P fertilizer requirements and the vulnerability of a soil to P loss in runoff following land application of fertilizer or manure P.