The partitioning of P in soil determines the fluxes and deliveries of labile P in soil solution

Abstract

Phosphorus (P) is an increasingly limited resource for food production, which necessitates studying soil factors controlling rates of P release to soil solution. Phosphorus use efficiency is among other, affected by the plants, the plant root induced displacement of P equilibrium in soil during uptake and the following rates of replenishment from geochemically active P stores in soil. Here, soil P partitioning and flux data collected from a 50year field trial, based on application of differing P masses, was investigated using a diffusive gradients in thin films (DGT) technique and “DGT-induced fluxes in sediments” (DIFS) model. Partitioning of P in soil was accomplished by deploying DGT at increasing contact times (6h to 120h). DGT induced P fluxes increased with soil P, and they were highest the first hours after installation. A Langmuir adsorption approach to determine Kd concealed accumulated P labile stores, whereas Kd estimations from ammonium lactate (AL) extractions did not. The estimated fluxes in the latter situation stabilized after 24h deployment, and they were more clearly reflecting the long term P treatments. The two Kd approaches showed the importance of considering inherent P-stores for calculating fluxes and deliveries of labile P available for plants during P-uptake. The use of DGT and DIFS in combination enabled good estimations of fluxes. Such fluxes may be used to estimate, In Situ, critical soil solution P concentrations available for plants during growth, in different soil types.