Phosphorus sorption capacity and availability along a toposequence of agricultural soils: effects of soil type and a decade of fertilizer applications

Abstract

AbstractSoil type and changes in soil properties due to long‐term fertilizer application are each known to alter phosphorus (P) availability. Our aim was to determine the respective effects of soil type and fertilizer application on the available P content and proportion of inorganic P (Pi) vs. organic P (Po). Five field trials where mineral and organic fertilizers were applied for a decade along a toposequence (two andosols, one andic cambisol, one nitisol and one arenosol) were investigated. Legacy P (i.e. P accumulated in soil with fertilizer applications minus P lost by plant uptake, erosion and leaching) was used to study the effect of fertilizer application rate. P availability was determined by classic extractions and by the diffusive gradients in thin films technique (Pi‐DGT). The solid‐solution Pi (Kd) partitioning coefficient was determined to assess the soil Pi sorption capacity. Kd decreased from the andosol (median: 3231 L/kg) to the arenosol (median: 103 L/kg), suggesting a decrease in Pi sorption with the soil evolution. In addition, Kd decreased with increasing pH for all soil types and with increasing content of organic carbon for the arenosol, showing that Pi sorption capacity changed with the changes in soil properties induced by fertilizer application. Pi‐DGT (from <0.01 to 0.27 mg/L) and Pi‐water (from <0.1 to 40.7 mg/kg) changed with the soil type and fertilizer application rate. Our study suggests that advice for P fertilizer management should integrate the effects of repeated fertilizer application on soil pH and organic carbon content, which change soil P availability.