ARS | Publication request: Manure nutrient management effects in the Leon River Watershed

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 17, 2011
Publication Date: May 1, 2012
Citation: Rossi, C.G., Dybala, T.J., Amonett, C., Arnold, J.G., Marek, T. 2012. Manure nutrient management effects in the Leon River Watershed. Journal of Soil and Water Conservation. 67(3):147-157.

Interpretive Summary: The Leon River watershed has been studied by the United States Department of Agriculture. Since its neighbor to the northeast, the Bosque River watershed, has been documented for its water quality impairments, six realistic manure management scenarios were selected to determine if sediment and nutrient loads could be reduced with alternative management practices. The manure management scenarios include varying the manure application rates and timing based on number of cows and manure-haul distance from the manure-producing dairy. The Soil and Water Assessment Tool (SWAT) model simulations were evaluated over a period of thirty years. Reductions in total nitrogen and total phosphorus loads were greater than sediment loads due to the existing sediment retention structures in place. With additional management, nutrient loads can be greatly reduced.

Technical Abstract: The Leon River Watershed (LRW) in central Texas is a Benchmark and Special Emphasis watershed within the Conservation Effects Assessment Project (CEAP) located in central Texas. Model simulations from 1977 through 2006 were used to evaluate six manure nutrient management scenarios that reflect realistic strategies that could be employed to reduce nutrient and sediment loadings in the LRW. Due to the presence of several dairies, and a relatively large number of cows, within this watershed special attention is necessary to determine beneficial adjustments that can be made to protect water quality. The nutrient management scenarios analyzed reduced total N and total P loading in nearly all of the subbasins. Total N and total loading was also reduced at the watershed scale; sediment load reduction was minor due to effective management measures already existing within the LRW. The percentage change in TN and TP loadings varied from an increase of 3 percent to a decrease of 11 percent and increase of 5 percent to a decrease of 12 percent, respectively. The percentage change in sediment loadings varied from an increase of 22 percent to a decrease of 12 percent per subbasin. Model simulations conducted over a 30-year period for six manure management scenarios indicated that both total N and total P can be significantly reduced by employing additional nutrient strategies. This is the case whether the nutrients are removed from the immediate vicinity of the dairy or are transported outside of the watershed.