Site-Specific Evaluation Tool for Phosphorus Risk Assessment.

The possible introduction of a Phosphorus Risk Assessment Tool that would be applicable across similar field conditions from state-to-state prompted an evaluation of a better tool than the suggested P saturation indicator. The new tool is site-specific and needs no further evaluation parameters than needed for P saturation ratio (PSR) calculations, i.e. P, Fe and Al in a solution of oxalate, Mehlich 1 or Mehlich 3. The choice of the actual extraction solution can be made depending on the soil test solution used at a given location. Mehlich 3 may be the most practical as a standard solution as it is a soil test used across several states. This tool, the soil P storage capacity (SPSC), is calculated as SPSC = (threshold PSR – soil PSR) * (molar Fe+Al) * 31 mg/kg would be useful while designing best management practices (BMPs) on a field-to-field basis. The threshold PSR will be that value that is determined as a P saturation indicator. We will provide typical uses of SPSC for designing BMPs at a given site.