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Simulation models are useful tools to quantify the effects of best management practices (BMPs). After SWAT (Soil and Water Assessment Tool) adaptation and calibration for intensive irrigated watershed, it has been used to evaluate the impact of several (BMPs) on water yield (WYLD), total suspended sediment (TSS), organic P (ORG_P), soluble P (SOL_P), and total P (TP) at the outlet of the Del Reguero stream watershed (Spain). Economic impacts of the BMPs on crop gross margin were also evaluated. In total, 6 individual scenarios and 14 combinations of various management practices including tillage (conservation and no-tillage), fertilizer (incorporated, recommended, and zero), and irrigation (adjusted to crop needs) were been tested. Results indicate that the best individuals BMPs (adjusted irrigation water use BMP) reduced WYLD to 31.4%, TSS loads 33.5%, and TP loads to 12.8%, in comparison of the initial conditions. When individual BMPs were combined, the percentage reductions of losses were increased. The BMPs combination between optimum irrigation application, conservation tillage and reduced P fertilizer dose was the best analysed one with a TP loads reduction about 22.6%. For corn and alfalfa, the best BMP scenario was the combination between conservation tillage and reduced P fertilizer dose, reaching an increase of gross margin by 309 ha-1and 188 ha-1, respectively. While for sunflower and barley, the best scenario was the combination between irrigation adjustment, conservation tillage and reduced P fertilizer dose. The increase of gross margin under this BMP was about 171 ha-1and 307 ha-1, respectively.