ARS | Publication request: Development of a quantitative pasture phosphorus management tool using the SWAT model

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 22, 2008
Publication Date: April 1, 2009
Citation: White, M.J., Storm, D.E., Smolen, M.D., Zhang, H. 2009. Development of a quantitative pasture phosphorus management tool using the SWAT model. Journal of the American Water Resources Association. 45(2):397-406.

Interpretive Summary: Assessment tools to evaluate phosphorus loss from agricultural lands allow conservation planners to evaluate the impact of management decisions on water quality. Available tools to predict phosphorus loss from agricultural fields are either: (1) qualitative indices with limited applicability to address offsite water quality standards, or (2) models which are prohibitively complex for application by most conservation planners. The purpose of this research was to develop a simple interface for a comprehensive hydrologic/water quality model to allow its usage by farmers and conservation planners. The Pasture Phosphorus Management (PPM) Calculator was developed to predict average annual P losses from pastures under a variety of field conditions and management options. PPM Calculator is a vastly simplified interface for the Soil and Water Assessment Tool (SWAT) model that requires no knowledge of SWAT by the user. PPM Calculator was validated using 33 months of data on four pasture fields in northwestern Arkansas. This tool has been extensively applied in the Lake Eucha/Spavinaw Basin in northeastern Oklahoma and northwestern Arkansas. PPM Calculator allows conservation planners to take advantage of the predictive capacity of a comprehensive hydrologic water quality model typically reserved for use by hydrologists and engineers. This research demonstrates the applicability of existing water quality models in the development of user friendly P management tools.

Technical Abstract: The Pasture Phosphorus Management (PPM) Calculator allows conservation planners to predict phosphorus loss from pastures in eastern Oklahoma. The computer based tool is a vastly simplified interface for the popular, yet complicated Soil and Water Assessment Tool (SWAT). PPM Calculator allows users with little or no training to predict actual edge of field phosphorus losses. These data may be especially useful in watersheds with numeric water quality standards. This tool was validated using measured field data and successfully applied to hundreds of pastures in eastern Oklahoma. PPM Calculator demonstrates that existing models like SWAT can be the engine behind user friendly conservation planning tools.