Reduced Tile Nitrate Loads with Cover Crops Following Corn in East-Central Illinois.

Agricultural production in the flat, poorly-drained Mollisols of central Illinois relies on tile drainage to quickly remove excess water from fields; however, tile water is a major source of nitrate from fields to streams. Cover crops have been shown to decrease soil nitrate concentrations, especially following corn production, and have been proposed as a primary means of reducing tile nitrate losses in the Illinois Nutrient Loss Reduction Strategy. Using the paired watershed approach, we measured tile nitrate concentrations and loads in paired tile systems managed under the same production system, but with and without a cover crop. Following a severe drought which greatly impaired corn yield and N uptake in 2012, soil nitrate concentrations remained high throughout the growing season. On September 8, we aerially seeded a mixture of annual ryegrass and radish into standing corn. A warm and wet fall season allowed for excellent cover crop growth, producing approximately 2 Mg/ha of above ground biomass containing 60 kg N/ha. This sequestration of N by the cover crop reduced the tile nitrate load by 30% during the following winter and spring drainage season. In a field with a history of seed corn production and high tile nitrate concentrations, we again used the paired watershed approach and planted cereal rye after corn on one of two tile systems in October of 2014. Above ground biomass for cereal rye in April of 2015 was 1.3 Mg/ha with approximately 40 kg N/ha. Tile nitrate concentrations between the two tiles were nearly identical throughout the drainage season until the occurrence of heavy rainfall and high tile flow in May of 2015. Nitrate concentrations from the tile system with cereal rye were then about 20% less than from the tile system without a cover crop. These data show on a field scale that cover crops grown after corn can reduce tile nitrate concentrations and loads during the subsequent drainage season.