The P Index estimates runoff P delivery to surface water under average conditions. Within watersheds, it can be used to identify the fields and pastures  that are contributing the most phosphorus to runoff.  It can also be used to identify appropriate practices for reducing runoff losses.

The use of the P Index for targeting areas witihin a watershed for alternative management was recommended by the Wisconsin Buffer Initiative report.

This approach was tested and shown to be successful in a paired watershed project in Wisconsin’s Driftless Region.