Description of the phosphorus sorption and desorption processes in coarse calcareous sandy soils

In order to understand and predict the behavior of phosphorus (P) in calcareous sandy soils, sorption and desorption studies were carried out. Two main processes were distinguished: a fast, reversible phosphate reaction (within 1 day), which can be described by the Langmuir equation, and a precipitation reaction, which can be described by a time-dependent Freundlich equation. The maximum phosphate sorption capacity in the top 50 cm of the soil ranged from 3 to 6 t P2O5·ha-1. About 85% to 95% of the maximum amount of P bound was poorly soluble; the remaining portion of bound P determines the ortho-P concentration in soil solution under desorption conditions. The breakthrough curves of the two column experiments were described reasonably well by the proposed process description and the associated parameters, which were derived from batch experiments.