The P Index is used by nutrient management planners to determine the risk of P runoff losses for each field on a farm. In general, the P Index helps planners identify fields that have both a build-up of P (i.e. "Source" potential) and a high potential for P loss (i.e. "Transport" potential). Click on the diagram, below.
It is estimated that 90% of P losses from farms comes from less than 20% of the farm's landbase. Where are theses critical areas for P losses in our example watershed, below? Click on arrow in the image below to see the integration of source potential and transport risk.