Speciation and sorption of phosphorus in agricultural soil profiles of redoximorphic character

AbstractControlled drainage is considered as a soil management tool to improve water supply to crops and reduce nutrient losses from fields; however, its closure may affect phosphorus (P) mobilization in soil. To assess the P mobilization potential, three soil profiles with redoximorphic features were selected along a slight hill in Northern Germany. Soil samples from three depths of each profile were characterized for basic properties, total element content, oxalate- and dithionite-extractable pedogenic Al, Fe and Mn (hydr)oxides, P pools (sequential extraction), P species [PK-edge X-ray absorption near-edge structure (XANES) spectroscopy] and P sorption behavior. In topsoil (~  10 cm depth), labile P (H2O-P  + resin-P + NaHCO3-P) accounted for 26 –32% of total P (Pt). PhosphorusK-edge XANES revealed that up to 49% of Pt was bound to Al and/or Fe (hydr)oxides, but sequential fractionation indicated that  >  30% of this P was occluded within sesquioxide aggregates. A low binding capacity for P was demonstrated by P sorption capacity and lowKf coefficients (20 –33 \({\text{mg}}^{{1 - n_{\text{f}} }} \,{\text{L}}^{{n_{\text{f}} }} \,{\text{kg}}^{ - 1}\)) of the Freundlich equation. In the subsoil layers (~  30 and ~ 65 cm depth), higher proportions of Al- and Fe-bound P along with other characteristics suggested that all profiles might be prone to P mobilization/leaching risk under reducing conditions even if the degree of P saturation (DPS) of a p...
Source: Environmental Geochemistry and Health - Category: Environmental Health Source Type: research