Comparison of Southern P Indices to Water Quality Data.

USDA-NRCS revised their 590 Nutrient Management Conservation Standard in 2012 with the intent of normalizing P-Index values across state lines.  The Southern Region (AL, AR, FL, GA, KY, LA, MS, NC, OK, SC, TN, and TX) has a collaborative project, Refine and Regionalize Southern Phosphorous Assessment Tools Based on Validation and State Priorities, to explore current model (APEX, APLE, and TBET) functionality as a potential P Index.  In addition, it is expected that P losses from agricultural fields derived from experimental datasets (AR, GA, MS, NC, OK, and TX) be compared to each southern state’s P Index. There is a lack of consistency of state P Indices when used on the same data set, as States tended to develop their Indices independently of their neighbors.  Also, P leaching, a major pathway of P transport in sandy soils in Florida and Coastal Plains area of the southeast, have not been included.  Further, there has been a general reluctance by various stakeholders to relate Index risk, amounts of P runoff, and receiving water quality impairment. These data will be presented to demonstrate the problems with assigning risk.