Agronomic and environmental soil phosphorus tests for predicting potential phosphorus loss from Ontario soils

Abstract

There has been an increased research interest towards developing appropriate environmental soil P tests for identifying soils sufficiently high in P to be of concern to water quality. The objectives of this study were to evaluate the relationships between various soil test P (STP) measures, and to assess the suitability of these STPs and derived indices of degree of P saturation (DPS) as indicators of soluble P losses (assessed as water extractable P (WEP)) from Ontario soils. A total of 391 surface (0–20cm) soil samples were collected across the province to represent the diverse physical and chemical properties of agricultural soils in Ontario. Significant relationships were generally found between the tested STPs. Among all measured STPs and DPSs, soil Fe-oxide coated filter paper strip P (FeO-P) and DPSOl (Olsen-P/(Olsen-P+PSI)) had the strongest non-linear relationships with soil WEP concentration (r2 values of 0.88 and 0.82, respectively), suggesting these measures may be useful as indicators of soil P losses for Ontario soils. The soil WEP concentrations were significantly correlated to P extractable by the Olsen and the Mehlich-3 methods (r2=0.72 for both extractants). In addition, DPSM3-2 (Mehlich-3 P)/(Mehlich-3 Al+Mehlich-3 Fe) and DPSM3-3 [Mehlich-3 P/(Mehlich-3 Al)] were highly promising indicators of soil P losses for agricultural soils in Ontario.