Tuesday, November 6, 2007 - 2:45 PM
207-6

Evaluation of the Georgia P Index Using On-farm, Field-scale Data.

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

In order to better manage agricultural P, most states in the USA have adopted a “P indexing” approach which ranks fields according to potential vulnerability for losses of P.  In Georgia, the Georgia P Index was developed to estimate the risk of bioavailable P loss from agricultural land to surface waters considering sources of P, transport mechanisms, and management practices.  Given the limited nature of available data on runoff P from varying agricultural management practices, data collected on-farm at the field-scale will be useful in further calibrating and improving the Georgia P Index.  As such, eighteen farm fields, managed as pasture, hay, or field crop systems were outfitted with small in-field runoff collectors (SIRCs) and runoff P, soil test P (STP), and management practices monitored from 1999 to 2006.  Nutrient treatment of fields varied from those rich in P (broiler litter or dairy slurry) to those without P amendments (inorganic N or unfertilized).  Data relating to nutrient applications, soil properties, STP, and cropping management were used as input values to determine a P Index value indicating the risk of P export from each field.  These values were regressed against observed values of P export in order to determine the precision of the Georgia P Index under varying management practices and soil conditions.  Preliminary results indicated that levels of P export from fields corresponded well to risk ratings calculated by the Georgia P Index.

Back to Management Effects on Soil Carbon and Phosphorus
Back to S06 Soil & Water Management & Conservation

Back to The ASA-CSSA-SSSA International Annual Meetings (November 4-8, 2007)