SWAT Literature Database for Peer-Reviewed Journal Articles

Title:Precision feeding and forage management effects on phosphorus loss modeled at a watershed scale 
Authors:Ghebremichael, L.T., T.L. Veith, J.M. Hamlett, and W.J. Gburek 
Journal:Journal of Soil and Water Conservation 
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URL (non-DOI journals): 
Broad Application Category:hydrologic & pollutant 
Primary Application Category:BMP assessment 
Secondary Application Category:nutrient cycling and transport 
Watershed Description:163 ha Cannonsville Reservoir Watershed, Delaware County, New York 
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Validation Summary: 
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Abstract:Delaware County and the Cornell Cooperative Extension of Delaware County of New York State have initiated a farm-scale precision feed management (PFM) program to reduce soil-phosphorus build-up and phosphorus (P) losses to the Cannonsville Reservoir, a major supply source of New York City drinking water. The PFM program includes strategies that more precisely balance dairy cattle dietary P requirements with actual P intake and that improve on-farm forage production and utilization in the animal diet. The goal of the PFM program is to reduce manure P concentration, feed nutrients importation, P imbalance problems, and soil-P build-up while maintaining farm profitability. In this study, several PFM strategies were evaluated with respect to controlling P losses and soil-P build-up at both field and watershed scales using the Soil and Water Assessment Tool (SWAT) model. Using the SWAT model, manure with reduced P concentration was applied to cropland while grass-forage crop productivity was increased through N fertilizer application. The SWAT model simulation revealed decreased particulate phosphorus and soluble phosphorus losses by 22% and 13%, respectively. Predicted reductions of average particulate phosphorus and soluble phosphorus losses at the watershed outlet were 16% and 13% respectively, over a three-year period, compared to the baseline (conditions before changes were implemented). Model results also demonstrated an appreciable decrease in field-level soil-P during the growing season, indicating increased soil-P uptake by the improved grass-forage. For the growing season, reductions for predicted active and labile P pools were 11 and 5 mg kg–1 (0.02 and 0.01 lb tn–1), respectively, compared to the baseline. The corresponding reductions in field-level soil P were equivalent to 8% and 7% for labile and active P pools, respectively. Overall, the PFM strategies were found to have a potential for reducing soil-P build-up and P losses both at field and watershed levels. Performing a model-based environmental evaluation of farm management strategies at a watershed level helps to integrate farm management planning (the smallest management unit) into watershed level planning. Also, evaluating farm management strategies at a watershed scale provides valuable and comprehensive information for assessing the potential for long-term, cost-effective, and permanent reduction of P loss from dairy agriculture to the Cannonsville Reservoir. 
Keywords:phosphorus loss, precision feed management, simulation, soil phosphorus, Soil and Water Assessment Tool (SWAT)