Risk of phosphorus leaching from phosphorus-enriched soils in the Dianchi catchment, Southwestern China.

As an important pathway for phosphorus (P) transport from soil to water body, P leaching has aroused attention. This study aimed to investigate the degree of risk and forms of P leaching from P-enriched soils. Surface soils were collected from forest land (FL) and open agricultural land (OAL) in typical P-enriched area of the Dianchi catchment, China. Based on analysis of soil P and water-soluble P using chemical methods and (31)P-NMR analysis, combined with a soil column leaching experiment, P forms and risk of P leaching were identified. CaCl2-extractable water-soluble organic P (CaCl2-Po), inorganic P (CaCl2-Pi), and total P (CaCl2-P) extracted using 0.01-M CaCl2 solution were found to be useful for predicting potential organic and inorganic P leaching, given a linear, positive correlation between CaCl2-P, CaCl2-Pi, and CaCl2-Po in soils and accumulated amounts of corresponding P forms in soil leachates. The majority of investigated FL was at or above the change points of 46, 46, and 42 mg AP kg(-1) for CaCl2-Pi, CaCl2-Po, and CaCl2-P, respectively, and thus at a risk of P leaching. Organic and inorganic P leaching was present in nearly all investigated OAL. CaCl2-Po accounted for 66.0 % of CaCl2-P in FL and 56.1 % in OAL. Signals of (31)P-NMR spectra were mainly attributable to orthophosphate, orthophosphate monoesters, and orthophosphate diesters in FL and OAL soils. It is important to consider P loss due to leaching of inorganic and organic P in P-enriched areas.