Phosphorus Transformations from Reclaimed Wastewater to Irrigated Soil: A P-31 NMR Study

摘要

Irrigation of soils with reclaimed wastewater (RW) is a common practice in arid regions, but may pose an environmental threat if labile phosphorus (P) forms accumulate at the soil surface. Soil P lability can be affected by P forms in the applied RW and by P composition and distribution in the soil. Solution P-31 nuclear magnetic resonance (NMR) spectroscopy was employed to identify P forms in RW solutions, in whole soil extracts and in fractionated soil P pools in agricultural soils (maize crop, Acre, Israel) irrigated with the examined RW or with freshwater (FW) and a chemical fertilizer. The RW was rich with total P (P-T) and molybdate-reactive P (MRP), consistent with high concentrations of MRP in the RW-irrigated soil. Identified compounds and compound classes in the RW and in the soils include orthophosphate, polyphosphate, orthophosphate monoesters, and orthophosphate diesters. However, there was a shift in P compound classes from the RW to the RW-irrigated soil; although the water sources were different, P forms in the soils of the different treatments were similar. The possible factors that might control this change are discussed, including biological and geochemical P recycling and crop inputs.