Accounting for the Risks of P Losses Through Tile Drains In a P Index.

In areas where subsurface drainage is a common part of crop production systems, a significant portion of the total P losses to surface water can occur through the subsurface drainage system.  At present, however, P indexes either ignore this transport pathway completely or have only a rudimentary indicator of enhanced risk.  The authors will propose a method to estimate the relative risk of P movement through subsurface drains and by surface runoff, depending on the individual field characteristics.