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Best Management Practices (BMPs) were designated to protect the water quality. However, their effectiveness needs to be evaluated before implementation, especially for a mixed land use watershed. A continuous time and watershed scale model, SWAT, was applied to a small agricultural watershed with mixed land use in the Piedmont region of Maryland to evaluate its hydrologic/water quality responses under several BMPs. Nine years (1994-2002) of hydrologic and water quality data were used to calibrate and validate the model. Simulations were conducted for background conditions where conventional tillage with up and down hill planting was used for row crops. Other simulations were conducted for nonstructural BMPs that ranged from conservation tillage to no-till and with contour and strip cropping. Results indicate that each of these BMPs had significant effect in reducing sediment and nutrient losses compared to background scenario. Reductions in sediment ranged from 18.7% (9-year average) for contour planting with conventional tillage to 41.7% for contour-strip cropping with no-till operation. Similar reductions in nitrate-N (10.1% to 29.2%) and soluble P (23.2% to 34.4%) were also obtained. In addition, within the same BMP having winter crop resulted in significant load reductions. Finally, the effects of filter strip with varied strip widths (3m, 6m, and 12m) are found to be trivial. This study concluded that the most feasible scenario is the BMP combination of contour planting with no-till-winter crop-3m filter strip. Average simulated flow, sediment, and nutrient loads obtained under each BMP was also associated with model uncertainties due to input variability. Data indicated that one should be cautious in using simulation results for making policy decision.