Phosphorus Sorption Parameters of Soils and Their Relationships with Soil Test Phosphorus.

Wang, Y.T., O'Halloran, I.P., Zhang, T.Q., Hu, Q.C., and Tan, C.S. (2015). "Phosphorus Sorption Parameters of Soils and Their Relationships with Soil Test Phosphorus.", Soil Science Society of America Journal, 79(2), pp. 672-680. doi : 10.2136/sssaj2014.07.0307  Access to full text

Abstract

Understanding phosphorus (P) sorption characteristics of soils and their relationships with soil test P (STP) may aid the prediction of runoff soluble P concentration. This study was conducted to provide such information for soils in Ontario, Canada. A total of 60 surface soil samples were collected from six major soil series in Ontario. Phosphorous sorption behaviors were characterized by a modified Langmuir equation and summarized by four sorption parameters: P sorption maximum (Qmax), P sorption strength (PSS), equilibrium P concentration at zero net sorption (EPC0), and initially sorbed P (Q0). Soil PSS, EPC0, and Q0 could be predicted by saturated iron-oxide strip P, Olsen P, water extractable P, and Mehlich-3 P, with PSS following a power function (r2 = 0.93–0.95), EPC0 following a quadratic function (r2 = 0.42–0.82), and Q0 following a linear function (r2 = 0.57–0.79). We identified a critical PSS value (i.e., 0.39 L mg-1, corresponding to 30 mg Olsen P kg-1) above which soils had low surface runoff DRP and EPC0 concentration (<0.1 mg L-1). The relationship between Olsen P and EPC0 confirmed that the soil with Olsen P < 30 mg kg-1 would lead to EPC0 concentration < 0.1mg L-1. The findings suggest that soils with Olsen P > 30 mg P kg-1 may cause significant runoff soluble P loss, and thus necessary mitigation measures may need to be adopted on confirmation with assessment of a site P index that integrates source factors with the transport factors (e.g., soil hydrological conductivity, slope, precipitation, and distance from the water source).

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