Location: Hydrology and Remote Sensing Laboratory
Title: Assessing effectiveness of winter cover crops to improve water quality Authors
Submitted to: Hydrology and Earth System Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 28, 2013
Publication Date: November 21, 2013
Citation: Lee, S., In Young, Y., Sadeghi, A.M., McCarty, G.W., Hively, D.W. 2013. Assessing effectiveness of winter cover crops to improve water quality. Journal of Hydrology and Earth System Sciences. 10:14229-14263. Interpretive Summary: Winter cover crops is one of the most common Best Management Practices (BMPs) being used to correct water quality problems. This BMP has recently grown extensively, in the State of Maryland and in 2012, Maryland Department of Agriculture (MDA) had invested nearly $18M as cost-sharing program to improve water quality of the Chesapeake Bay watershed. Therefore, there is a need for a reliable management tool or model to assess the success of this program at the state level. As part of the USDA conservation program, we have used the largest sub basin within the Choptank watersd within the Bay, called German Branch (GB) to calibrate and validate the Soil and and Water Assessment Tool (or SWAT model) in the GB watershed for both stream flows and nitrate. We performed scenarios of increased in cover crop implementations on croplands from 20% to 80% with increment of 20% in GB, using the validated SWAT model. Results showed the highest nitrate reduction with winter rye, early planting of nearly 60% and the lowest nitrate reduction of 12% for winter wheat, late planting. Overall, model simulation results showed that cover crops, as BMP, has the potential for significant reductions in nitrate loads from agricultural croplands in the waterways of the Chesapeake Bay watershed.
Technical Abstract: Winter cover crops are an important conservation practice with potential to improve water quality by reducing excess nitrogen (N), remaining during the winter/early spring in soil, from leaching, runoff, and sediment loss into surface waters after harvest of summer crops. Throughout the Chesapeake Bay watershed, cover crop use has been greatly emphasized and currently, federal and state cost-share programs are available for farmers to compensate for the costs of planting winter cover crops. However, the impacts of cover crop N uptake efficiencies at the landscape scale are little known, and more work is needed to evaluate how they affect the water budget and nutrient cycling at that scale. The objective of this study was to assess the effectiveness of the cover crop program at landscape scale, using watershed simulation model, Soil and Water Assessment Tool (or SWAT). The study is being undertaken in German Branch (GB), a sub-basin within the larger Choptank River Watershed. The SWAT model was carefully calibrated and validated using field observation from 1992-1995. A number of scenarios were developed to obtain the baseline information for nutrient losses under current condition, and to investigate how water budget, N uptake, and N leaching was affected by different planting dates, species, and amount of cover crop coverage. In addition, we conducted a geospatial analysis to identify critical areas for high N loading within the GB sub-basin. This provides important information for decision making to prioritize best management practices.