Evaluating the least cost selection of agricultural management practices in the Five-Mile Creek area of Fort Cobb watershed

One of the main causes of water quality impairment in the United States is human induced Non-Point Source (NPS) pollution through intensive agriculture. The Fort Cobb Reservoir (FCR) watershed located in southwestern Oklahoma, United States is a rural agricultural catchment with known issues of NPS pollution including suspended solids, siltation, nutrients, and pesticides. The FCR watershed with an area of 813 km2 includes one major lake fed by four tributaries. Despite efforts and research to improve water quality in the FCR watershed through the implementation of varieties of Best Management Practices (BMPs) for decades, there are still problems of sediment and phosphorous loads in this catchment, which demonstrates the need for research. Since the cost of implementing some BMPs can be expensive, the cost effective selection and location of BMPs can aid in increasing both the efficiency of public funds and the total income of farmers. The major goal of this study was to identify optimal selection and location of livestock-crop-BMPs including crop types, production methods, and agricultural management practices that could further reduce sediment and phosphorous loss from the agricultural fields in Five-Mile Creek (FMC) sub-watershed of FCR watershed at the least-cost to producers and the public in both the dry and irrigated areas with consideration of existing BMPs. For this, a hydrological model of the study area was developed using the Soil and Water Assessment Tool (SWAT). The model was calibrated and validated satisfactorily for streamflow, crop yield, sediment, and phosphorous. The verified model was used to simulate 22 crop-BMP combinations over the 1989-2016 period. A Linear Programming (LP) model was used to determine the crop-BMP choice that would maximize income and minimize public cost while abating sediment and phosphorous under two different scenarios: market solution (maximize revenue with no constraints on sediment and phosphorous production) and tax solution (discourage sediment and phosphorous production through incentive programs).The model was capable of providing precise information for stakeholders to prioritize ecologically sound and economically feasible BMPs that are capable of mitigating human induced impacts at the watershed scale based on soil texture, land slope and dryland and irrigated areas