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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #212501
Title: Precision feeding and forage management effects on phosphorus loss modeled at a watershed scale

Author
item GHEBREMICHAEL, LULA - PENN STATE UNIV
item Veith, Tameria - Tamie
item HAMLETT, J - PENN STATE UNIV
item Gburek, William

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2008
Publication Date: 9/1/2008
Citation: Ghebremichael, L.T., Veith, T.L., Hamlett, J.M., Gburek, W. 2008. Precision feeding and forage management effects on phosphorus loss modeled at a watershed scale. Journal of Soil and Water Conservation. 63(5):28-291.

Interpretive Summary: Major concerns remain regarding continuing phosphorus (P) inputs to the Cannonsville reservoir, a major water supply source for New York City. Also, P continues to build up in the soil because farm P imports (as feed and fertilizer) exceed P exports (in milk, manure, and other products). Using detailed farm data, P losses before and after implementation of farm-level precision feed management (PFM) strategies were simulated using a watershed water quality model (Soil and Water Assessment Tool-SWAT) on a single-farm watershed located within the Cannonsville Reservoir Watershed. The PFM strategies more precisely balance dairy cattle dietary P and improve on-farm forage production and utilization in the animal diet in an effort to reduce manure P concentration, importation of feed nutrients, P imbalance problems, and soil-P build-up while maintaining farm profitability. Overall, the PFM strategies, in addition to their primary objectives of economic benefits and reducing P imbalance problems, were found to have potential for reducing soil-P build-up and P losses both at field and watershed levels. Such model-based representation and evaluation of farm plans at a watershed level helps integrate farm management plans (the smallest management unit) into a watershed plan. Also, it is a helpful tool in assessing comprehensive and economically viable solutions to the permanent reduction of P losses from dairy agriculture to the Cannonsville Reservoir.

Technical Abstract: This study extrapolated benefits of farm-level precision feed management (PFM) strategies to a watershed scale by evaluating effects of several PFM variations in controlling phosphorus (P) losses and reducing soil-P build-up at field and watershed scales. The PFM strategies more precisely balance dairy cattle dietary P and improve on-farm forage production and utilization in the animal diet in an effort to reduce manure P concentration, importation of feed nutrients, P imbalance problems, and soil-P build-up while maintaining farm profitability. The Soil and Water Assessment Tool (SWAT) was used for this study. SWAT simulation of manure application to cropland with reduced P concentration integrated with increased productivity of grass-forage resulted in particulate phosphorus (PP) and soluble phosphorus (SolP) losses reductions of 22% and 12%, respectively. Predicted average PP and SolP losses reductions at the watershed outlet were 16% and 13%, respectively, compared to the baseline. Model results also demonstrated an appreciable decrease in field-level soil-P during the growing season, indicating increased soil-P removal by the improved grass-forage. For the growing season, reductions for predicted active and labile P pools compared to the baseline were 11 mg/kg and 5 mg/kg, respectively. Compared to the baseline condition, the reduction in field-level soil P was equivalent to 8% and 7%, for labile and active P pools, respectively. Overall, the PFM strategies, in addition to their primary objectives of economic benefits and reducing P imbalance problems, were found to have potential for reducing soil-P build-up and P losses both at field and watershed levels. Performing model-based environmental evaluation of farm management strategies done at watershed level helps to integrate farm management plans (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.