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

Speciation and sorption of phosphorus in agricultural soil profiles of redoximorphic character (2020)

Baumann K., Shaheen S., Hu Y., Gros P., Heilmann E., Morshedizad M., Wang J., Wang S., Rinklebe J., Leinweber P.

Environmental Geochemistry and Health, 42 (10), 3231-3246

Abstract

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 Ptwas 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 lowKfcoefficients (20–33 $${\text{mg}}^{{1 - n_{\text{f}} }} \,{\text{L}}^{{n_{\text{f}} }} \,{\text{kg}}^{ - 1}$$mg1-nfLnfkg-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 profile under oxic conditions was < 25%. The results suggest that a closure of the controlled drainage may pose a risk of increased P mobilization, but this needs to be compared with the risk of uncontrolled drainage and P losses to avoid P leaching into the aquatic ecosystem.

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