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A phosphorus sorption index and its use to estimate leaching of dissolved phosphorus from agricultural soils in Ontario

Wang, Y. T., Zhang, T. Q., O’Halloran, P., Tan, C. S. and Hu, Q. C. 2016. A phosphorus sorption index and its use to estimate leaching of dissolved phosphorus from agricultural soils in Ontario. Geoderma 274: 79-87.

Abstract

Compared with soil testing phosphorus (STP), such as Olsen P, the degree of P saturation (DPS) generally improves the risk prediction for soil P loss. This study was conducted to assess various P sorption indices (PSI) to indicate P sorption maximum (Qmax) of soils, and their derived DPS indices as indicators of dissolved reactive P (DRP) concentration in soil leachate. A total of 236 intact soil columns were collected for leaching experiments from six major soil series in Ontario. By conducting the single-point isotherm, PSI-a of a given soil was determined as theamount of P sorbed by the soil during 24-h shaking in the 60mgP L−1 solution, PSI-b as the quotient of PSI-a/log C,where C is the solution P concentration after 24-h shaking, and PSI-c as the sumof PSI-a and Olsen P concentration. Among the tested PSIs, PSI-c gave the best prediction of Qmax. Compared to Olsen P, soil DPS-1 (i.e. the quotient of Olsen P/PSI-c) improved the prediction of leachate DRP concentration. Moreover, soil pH did not impact the relationship of DPS-1 vs. soluble soil P loss. Based on the results fromconditional probability analyses, Ontario soils were grouped into no risk, lowrisk, mediumrisk, and high risk categories. Considering that Olsen P is the current agronomic STP in Ontario and PSI-c can be quickly determined, soil DPS-1 can be used to identify leaching P loss and/or combinedwith site hydrology and P management practices for amore comprehensive soil P loss assessment.

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