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

Abstract

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 31P 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 (PT) 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.