Testing the Texas Best Management Practice Evaluation Tool to Inform the Phosphorus Index.

The United States Environmental Protection Agency recognizes agricultural nonpoint-source pollution as the primary source of stream and lake contamination in the United States. Phosphorous (P) Indices, regulatory tools for budgeting P loss, have not been sufficiently tested against field-scale P loss measurements. The Texas Best Management Practice Evaluation Tool (TBET), a much simplified interface for the Soil and Water Assessment Tool, was developed to predict field-scale mean annual runoff, sediment, nitrogen, and P losses in Texas under a variety of management and conservation practices. Nine hydrologic parameters not expected to be known by potential field users of TBET were determined using calibration in representative watersheds within Texas. We will test whether these calibrated parameters produce satisfactory model predictions in states other than Texas. First, we will use TBET and each respective state P Index to predict mean annual runoff and P loss from 17 benchmark agricultural fields in Arkansas, Georgia and North Carolina. The sites range in size from 0.07 to 2 acres and have various soils, crop system and fertilization regimes. TBET and P Index predictions will then be compared against observations from the benchmark fields. Lastly, predictions from the benchmark sites will be tested against model results from Texas and Oklahoma fields to assess whether model performance in other physiographic regions is significantly different from the region where TBET calibration occurred.