COUPLED EFFECT OF COVER CROPPING AND IN-FIELD CONSERVATION ON WATERSHED SCALE NUTRIENT LOADS IN CENTRAL ILLINOIS

Agricultural nutrient loss through water runoff from the Upper Mississippi (UM) River Basin is one of the major contributing sources to the Gulf of Mexico hypoxic dead zone. Being one of the states located in the UM River Basin, Illinois is collaborating with regulating agencies to establish comprehensive strategies at reducing nonpoint nutrient loss from the state’s agricultural lands.

To investigate cover crops’ role at reducing net nutrient loss from Illinois’ agricultural lands, we designed a paired watershed study started in 2016 in Central Illinois where over 80% of landcover is farmland. Previous studies of cover crops have shown their effectiveness in small-scale plots, but how this scale up to the watershed magnitude is still unknown. This experiment also aims to examine if factors such as cash crop rotation, precipitation pattern, and cover crop varieties may influence nutrient loss.

One watershed serves as a reference with no cover cropping (312 ha.) while the other (445 ha.) utilizes cover crops during off season (variety determined by collaborating producers). To understand the change in nutrient runoff, drainage tile interceptors equipped with automated water-samplers were installed at both watersheds to collect tile water samples continuously from each location. Meteorological data, temperature, and precipitation data were also monitored. Tile water samples were analyzed using EPA-approved water quality analyses. High frequency, 15 minutes interval, nutrient load estimates were calculated at each site.

Preliminary results suggest the nutrient loads in the reference watershed increased over the last three years while the load in the cover cropped watershed decreased after 2016. Nutrient loss was higher in spring compared to summer due to increased discharge. Years with more corn coverage had increased nitrate loss compared to soybeans in each watershed, likely due to increased N-fertilizer input in corn fields. Early results indicate cover crop had a positive effect at reducing nutrient loss on a watershed scale, further observation from this study is needed to ascertain if such loss is largely attributed to cover crops or other in-field conservation techniques.