The chemical nature of soil phosphorus in response to long-term fertilization practices: Implications for sustainable phosphorus management

Developing sustainable phosphorus (P) management strategies is a worldwide challenge in the face of growing food demand, dwindling rock phosphate resources, and deteriorating environmental quality. This requires improved knowledge on the effect of current fertilization practices on long-term P accumulation, bioavailability and mobility, which are functions of the chemical nature of soil P. Using state-of-the-art techniques such as solution 31P-NMR and P K-edge XANES spectroscopy, combined with sequential fractionation, this study investigated the chemical speciation and transformation of P in soils under three fertilization treatments (no fertilization, CK; chemical nitrogen (N), P and potassium (K) fertilization, NPK; and partial substitution of chemical fertilizer with sheep manure, NPKM) from a long-term experiment in China initiated in 1990. Compared to the NPK soil, total P and organic P (Po) concentrations were lower in the NPKM soil in the sampling years of 2000 and 2015, suggesting reduced P accumulation under the NPKM treatment. The NaHCO3-extracted P, considered the most readily plant-available P fraction, significantly increased in the NPKM soil relative to the NPK soil in 2000. The P-XANES results revealed the formation of the magnesium (Mg)–P compound newberyite, which probably contributed to soil P availability with NPKM application. Moreover, P-NMR analysis showed higher deoxyribonucleic acid content and ratio of orthophosphate diesters to monoesters in the NPKM soil relative to the NPK soil, which implied the stronger soil Po lability with NPKM fertilization. This study provides new insights on the significant role of NPKM treatment in optimizing soil P fertilization regimes, which benefits sustainable crop production.