Tuesday, November 14, 2006

Impact of Agricultural Management Practices and Soil Test P on P Export in Runoff.

David M. Butler1, Dorcas Franklin2, Miguel Cabrera1, Mark Risse1, and Jean Steiner2. (1) Univ of Georgia, Dept of Crop and Soil Sciences, 3111 Miller Plant Sciences Building, Athens, GA 30602, (2) USDA-ARS, 1420 Experiment Station Road, Watkinsville, GA 30677

A greater understanding of the role of soil test P (STP) and management practices on P export from farm fields can enhance agricultural sustainability and water quality.  Eighteen farm fields, managed as pasture, hay, or field crop systems were outfitted with small in-field runoff collectors (SIRCs) and runoff was monitored from 1999 to 2003.  Nutrient management practices were either rich in P (broiler litter or dairy slurry) or without P amendments (inorganic N or unfertilized).  Mean concentrations of dissolved reactive P (DRP) were greater under pasture management (3.52 mg P L-1) than hay management (2.07 mg P L-1) for all nutrient treatments, despite lower mean STP levels under pasture management (150 mg P kg-1 vs. 218 mg P kg-1).  Mean DRP export from field crop systems was generally intermediate and not significantly different from either pasture or hay systems.  Mean export of total P followed similar trends. The on-farm, field-scale data from this study may be most useful for adjusting and improving models of agricultural P export used by farmers and professionals to conserve nutrients and protect environmental quality.