Estimating Dissolved Reactive Phosphorus Concentration in Surface Runoff Water from Major Ontario Soils

Phosphorus (P) loss from agricultural land in-surface runoff can contribute to eutrophication of surface water. This study was conducted to evaluate a range of environmental and agronomic soil P tests as indicators of potential soil surface runoff dissolved reactive P (DRP) losses from Ontario soils. The Soil samples (0 to 20-cm depth) were collected from six soil series in Ontario, with 10 sites each to provide a wide range of soil test P (STP) values. Rainfall simulation studies were conducted following the USEPA National P Research Project protocol. The average DRP concentration (DRP30) in runoff water collected over 30 min after the start of runoff increased (p < 0.001) in either a linear or curvilinear manner with increases in level of various STPs and estimates of degree of soil P saturation (DPS). Among the 16 measurements of STPs and DPSs assessed, DPSM3-2 (Mehlich-3 P/[Mehlich-3 Al + Fe]) (r(2) = 0.90), DPSM3-3 (Mehlich-3 P/Mehlich-3 Al) (r(2) = 0.89) and water-extractable P (WEP) (r(2) = 0.89) had the strongest overall relationship with runoff DRP30 across all six series. The DPS30 loss. However, DPSM3-3 was preferred as its prediction of DRP30 was soil pH insensitive and simpler in analytical procedure, if a DPS approach is adopted.