PREDICTING MANAGEMENT EFFECTS ON PHOSPHORUS LOSS FROM FARMING SYSTEMS

Authors: SEDOROVICH, DAWN - PENN STATE UNIV; Rotz, Clarence - Al; Vadas, Peter; Harmel, Daren

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2007
Publication Date: 8/25/2007
Citation: Sedorovich, D.M., Rotz, C.A., Vadas, P.A., Harmel, R.D. 2007. Predicting management effects on phosphorus loss from farming systems. Transactions of the American Society of Agricultural Engineers. 50(4):1443-1453.

Interpretive Summary: The United States Environmental Protection Agency estimates that there are 22,000 impaired surface waters (e.g., lakes, streams, reservoirs) in the country, with 11% of these impairments due to nutrients originating primarily from agriculture. Because phosphorus (P) is a primary control of eutrophication in surface waters, P pollution from agriculture is a major concern. Research on P management is focused on implementing alternative management practices to reduce the amount lost from farms. If these management strategies reduce the profitability of farms though, the practices are unlikely to be implemented. Thus, strategies to reduce P pollution from farms must be evaluated along with other environmental factors and the economics of the farm. Computer models provide a cost-effective and relatively rapid method of analyzing farm management scenarios. One model, the Integrated Farm System Model, simulates the major farm processes including crop growth, herd performance, economics, and nutrient flows. This farm model includes the prediction of volatilization, leaching, and denitrification losses of nitrogen (N), but a weakness has been that the P cycle was not simulated. Thus, this farm model was expanded to include a component that predicts the effects of management on farm-level P loss. The model was used to illustrate that P loss from dairy farms could be reduced up to 50% through the use of conservation tillage practices and improved manure application methods while maintaining or improving farm profit. The expanded farm model provides a tool for evaluating management effects on P and N losses to the environment along with farm economics.

Technical Abstract: A process-level soil phosphorus (P) model including surface and subsurface components was developed and incorporated into the Integrated Farm System Model (IFSM). Preliminary evaluation indicated that the model accurately predicted soluble P losses, but under-predicted total P losses due to under-prediction of erosion. Erosion was under-predicted compared to observed data but was simulated as well as the current state-of-the art erosion prediction model. Simulations with IFSM analyzed the effects of manure handling and tillage systems on P loss from farms. For a free-stall 100 cow dairy, a manure handling strategy that used six-month concrete tank storage and application by injection decreased total P loss by 15% compared to daily surface application but decreased annual farm net return by $47/cow. Use of conservation tillage and no-till systems reduced total P loss by 48% and 51%, respectively, with only small effects on farm profitability. Reduced tillage increased soluble P loss, suggesting that conservation and no-till systems should be combined with systems such as manure injection to reduce all forms of P loss. The enhanced IFSM containing the SOILP model provides a tool for whole-farm analysis of management effects on P loss along with other environmental and economic considerations.