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

摘要

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 (Q(max)) 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 the amount of P sorbed by the soil during 24-h shaking in the 60 mg P 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 sum of PSI-a and Olsen P concentration. Among the tested PSIs, PSI-c gave the best prediction of Q(max). 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 from conditional probability analyses, Ontario soils were grouped into no risk, low risk, medium risk, 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 combined with site hydrology and P management practices for a more comprehensive soil P loss assessment. (C) 2016 Elsevier B.V. All rights reserved.