Long-term fertilization impacts on soil phosphorus forms using XANES and NMR spectroscopy

Abstract

ABSTRACT A 32-year fertilizer experiment was conducted to investigate mineral and organic fertilization impacts on soil P forms by P K-edge X-ray absorption near edge structure and solution 31P nuclear magnetic resonance spectroscopy. The experiment included six treatments: control without fertilization, mineral fertilizers (NPK), pig manure at 30,000 (M1) and 60,000 kg ha–1 (M2), M1 plus NPK, and M2 plus NPK. The predominant P compounds were hydroxyapatite (up to 51.3% of soil total P) and orthophosphate and orthophosphate monoesters (up to 85.7% and 57.0% of soil NaOH-EDTA extractable total P, respectively). Compared with the control, the concentrations and proportions of monocalcium phosphate and orthophosphate increased following mineral fertilizers alone. Manure application, especially high rate manure combined with mineral fertilizers, further increased the concentrations and proportions of monocalcium phosphate and orthophosphate relative to mineral fertilizers alone. Moreover, manure amendment also generally increased the concentrations of other inorganic and organic P compounds. Manure application improve soil P availability by adding high concentrations of bioavailable inorganic P compounds to soil, similar to the addition of mineral fertilizers. This study contributes to the understanding of applied fertilizers and residual soil P dynamics and provides insights for sustainable P management in agricultural ecosystems.