Submitted to: Journal of Environmental Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2006
Publication Date: 9/13/2006
Citation: Gowda, P., Mulla, D.J. 2006. Modeling alternative agricultural management practices for High Island Creek watershed in South-Central Minnesota. Journal of Environmental Hydrology. 14(13):1-15.
Interpretive Summary: High sediment and nutrient loadings in the Upper Mississippi River System are associated with tributaries from agricultural areas in the states of Minnesota, Indiana, Iowa, and Illinois where a high percentage of agricultural land is in row crops which are managed with subsurface tile drainage systems. Watershed-scale monitoring studies to quantify the impacts of alternative agricultural management practices on water quality are difficult to carry out because many farmers must simultaneously be convinced to adopt new practices. It is also difficult to evaluate the impact of more than one or two farming practices in watershed scale studies due to the difficulty in monitoring water quality impacts of each practice independently. Water quality simulation models can help fill this knowledge gap in a time and cost-effective manner. We used a mechanistic model to evaluate possible reductions in sediment, nitrate, and phosphorus losses with several alternative agricultural management practices in an agricultural watershed located in south-central Minnesota. Calibrated model results were in excellent agreement with observed data. Predicted results indicated that significant reductions in annual sediment and phosphorus loadings can be achieved by adopting conservation tillage on all row cropped land and adopt injection as a method for animal manure application. Also, significant reductions in annual nitrate losses can be achieved by switching the timing of application from fall to spring and by reducing the rate of nitrogen fertilizer application. These findings are of great interest to farmers and policy makers seeking to reduce agricultural impacts on water quality while maintaining farming profits.
Technical Abstract: Nonpoint source pollution from row crop land is a widespread problem in North America. Concerns include sediment, nitrate and phosphorus loadings to water bodies from row cropped lands. In this study, a spatial-process based water quality model was calibrated (2001-2002) for flow, sediment, nitrate and phosphorus losses from the High Island Creek, a 3856 ha agricultural watershed located in south-central Minnesota. The calibrated model was used to evaluate alternative tillage and fertilizer management practices such as adoption of conservation tillage practices, rate, timing and method of N– and P-fertilizer applications, and method of manure application. Statistical comparison of calibration results with observed data indicated excellent agreement with r2 of 0.95, 0.96, 0.87, and 0.97 for flow, sediment, nitrate and phosphorus losses, respectively. The model simulated a 37.5% reduction in annual sediment losses can be achieved by adopting conservation tillage on all row cropped land in the watershed. Reductions in annual nitrate losses can be achieved by switching the timing of application from fall to spring and by reducing the rate of nitrogen fertilizer application. A 41% reduction in annual phosphorus losses can be achieved if all farmers adopt injection as a method for animal manure application.