Cover Crop Adoption and Performance on a Watershed Scale: Potential Impacts on Water Quality.

The Illinois Nutrient Loss Reduction Strategy has identified cover cropping as the most effective and economical strategy for reducing nitrogen (N) loss from agricultural fields. Plot and field scale research has established that the inclusion of cover crops into traditional row crop systems reduces N loading via subsurface drainage. However, there is a dearth of research that evaluates the adoption and effectiveness of cover crops to impact N loss through subsurface drainage at a watershed scale. Therefore, the objectives of this study are to: (i) Identify critical variables that influence cover crop biomass production and N uptake at a watershed scale and to (ii) determine the impact of watershed scale mass cover crop adoption on N loading to surface water. To achieve these objectives, two paired sub-watersheds of the Lake Bloomington Watershed were delineated near Towanda, IL. Collaborating operators planted daikon radish/oats (Raphanus sativus L./Avena sativa L.) before corn (Zea mays L.) and daikon radish/ cereal rye (Secale cereal L./Raphanus sativus L) before soybeans (Glycine max L.). The data revealed that the average cover crop biomass was 1495 kg ha^-1 and that the cereal rye/radish mix resulted in 2.76 times greater N uptake relative to the radish/oats mixture. The cereal rye/radish mixture resulted in a greater concentration of soil NH₄-N in the agronomic depth of soil relative to the radish/oats mixture that contained a greater soil NO₃-N concentration in the spring. Monitoring the tile water of each watershed revealed that NO₃-N concentrations were more likely to be lower than the EPA drinking water standard for a cover crop treated watershed. Results from this study indicated the potential of cover crops to impact spring soil inorganic N speciation and water quality on a watershed scale.