Simulating management effects on phosphorus loss from farming systems

A process-level soil phosphorus (P) model including surface and subsurface components was incorporated into the Integrated Farm System Model (IFSM). Model evaluation indicated that sediment losses were adequately estimated compared to observed data for a corn production system in Texas. In a further evaluation, sediment losses simulated for a wide range in cropping systems and tillage practices were similar to those predicted by the current state-of-the art erosion estimation model (WEPP). Total P losses were accurately predicted when manure P was applied at suitable rates of less than 250 kg P ha ^-1, but at higher application rates overestimation of P loss was found. Compared to observed data, soluble P loss was underestimated and sediment P loss was overestimated, but this was primarily due to a difference in the differentiation between soluble and sediment P between the modeling and experimental studies. To illustrate the use of the model, IFSM simulations were performed to evaluate the effects of manure handling and tillage systems on P loss from farms in Pennsylvania. For a 100-cow dairy farm, a manure handling strategy that used a 6-month storage and application by injection decreased total P loss by 19% compared to daily surface application, but annual farm net return was decreased by $57/cow. Compared to conventional tillage with a moldboard plow, use of conservation tillage and no-till systems reduced total P loss by 46% and 57%, respectively, with small increases in farm profitability. Reduced tillage increased soluble P loss, suggesting that conservation and no-till systems should be combined with practices such as manure injection to reduce all forms of P loss. The enhanced IFSM containing the soil P model provides a tool for whole-farm analysis of management effects on P loss along with other environmental and economic considerations.