Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2008
Publication Date: 5/1/2010
Citation: Tuppad, P., Santhi, C., Wang, X., Williams, J.R., Srinivasan, R., Gowda, P. 2010. Simulation of conservation practices using the APEX model. Applied Engineering in Agriculture. 26(5):778-779. Interpretive Summary: Regulating agencies in the United States are investing substantial amounts for implementing various kinds of conservation practices and programs. Quantitative benefits of those programs and practices are necessary for future planning and resource allocation. However, long-term monitoring data needed for quantifying the benefits are not available. In this study, we demonstrated an approach to assess the impacts of conservation practices on water quality and quantity at both field and watershed levels. Results indicated that the proposed approach has the potential to be used for supporting projects such as the Conservation Effects Assessment Project that focused on the effects on conservation practices on water quality.
Technical Abstract: Information on agricultural Best Management Practices (BMPs) and their effectiveness in controlling agricultural non-point source pollution is crucial in developing Clean Water Act programs such as the Total Maximum Daily Loads for impaired watersheds. A modeling study was conducted to evaluate various BMPs including pasture planting, nutrient management, brush management, clearing and range planting, prescribed grazing, critical area planting, conservation cropping, contour farming, terrace, ponds, grade stabilization structures, and grassed waterways implemented in a 280 square kilometers Mill Creek Watershed in north-central Texas. The main objective of this study was to assess the long-term impacts of BMPs, at both field and sub-watershed levels, on surface runoff, sediment, and nutrient losses using the Agricultural Policy/Environmental extender (APEX) model. Considering all BMPs, the average annual reductions in runoff, sediment, total nitrogen (TN), and total phosphorus (TP) at the field level ranged from 0 to 52%, 36% to 99%, 0 to 96%, and 15% to 92%, respectively. This reflects the variability in topography, soils, land-use, climate, and relative magnitude of these constituents entering the field from upstream contributing area. However, at the sub-watershed level, the reductions only ranged from 2.9% to 6.5% in runoff, 6.3% to 14.8% for sediment, 11% to 15.1% for TN, and 6.3% to 8.6% for TP. The impacts of BMPs on water quality varied depending on the type of practice and its location in the landscape. This study also showed that the reduction in sediment at the watershed outlet was proportional to the area treated with BMPs.