INVESTIGATING HOW TO SUSTAIN BOTH FARM AND WATERSHED BY TRACKING NUTRIENT LOSS FROM TILE-DRAINED AGRICULTURE

Traditional agricultural practices within the Mississippi River watershed contribute to excess nutrients received by the Gulf of Mexico. These excess nutrients have degradative effects on the Gulf of Mexico ecosystem. Agricultural practices in Illinois are not responsive to common best management practices because the fields are drained by a subsurface network of perforated piping allowing the land to remain well drained for good crop growth. However, tile drains also speed up nutrient loss by interrupting the natural filtration of water through soil. This type of loss can be reduced by implementing cover crop practices. Cover crops are non-cash crops grown during fall, winter, and spring to retain nutrients that are released via decomposition. The quantitative impact of this practice on nutrient loss has not been substantially studied. We aim to quantify the impact of cover crops on nutrient loss in two 1000-acre Illinois watersheds whose landcover is predominantly agriculture. In the first year of this study, nutrient data were collected from both watersheds which had no cover crops in place to see if the two watersheds were in fact comparable. Bi-weekly grab samples and water velocity data were collected from one creek and agricultural tile drain outlets within each watershed over the last year. Grab samples were analyzed for total phosphorus, dissolved reactive phosphorus, ammonia nitrogen and nitrate nitrogen (NO3-N) on a Flow Injection Analyzer and for chloride on an Ion Chromatograph. The NO3-N concentrations ranged from a low of 5.76 mg/l in April stream water to a high of 22.2mg/l in June tile water. All study sites across both watersheds showed similar patterns in nutrient concentrations. Tile drain outlet samples had on average 51% higher concentrations of NO3-N than that of the creeks, but the concentrations rose and fell over time in parallel with each other. As the study progresses, one watershed will undergo significant cover cropping. We will continue to collect nutrient data and draw conclusions about the quantitative impact that cover crops have on nutrient loss reduction. This data can then be extrapolated across the entire Mississippi River watershed, giving us an idea of what types of practices need to be implemented and at what scale in order to reduce and/or reverse the degradation of the Gulf of Mexico.