The Influence of Potential Biofuel Cover Crops on Nitrous Oxide (N2O) Emissions from Midwest Row-Crops.

Nitrous oxide (N₂O) is the largest contributor to the greenhouse gas burden of cropping systems in the US, with emissions primarily due to N fertilizer inputs and other soil management activities. The practice of including winter cover crops in corn-based row-crop systems is not widely adopted but is increasing. Perennializing annual crop systems through year-round soil cover can: reduce nutrient run-off and soil erosion; provide a cellulosic biofuel feedstock additional to the primary grain crop; provide climate stabilization through additional soil carbon storage and perhaps N₂O mitigation. There is little N₂O emissions data from cover crop systems. We will present four years of N₂O emissions data from a corn-soybean-winter wheat rotation, either with or without cover crops (Grass, Legume and Brassica), situated at the Kellogg Biological Station in SW Michigan.

Results show that: including potential biofuel cover crops in annual crop systems affected N₂O emissions differently (red clover increased total N₂O emissions, whereas annual ryegrass and oilseed radish had no effect); average daily N₂O emissions from biofuel cover crop treatments decreased in the order Legume > Grass ≥ Brassica; late cover crop termination time decreased N₂O emissions in red clover, but not annual ryegrass; N₂O emissions were highest in corn (vs. wheat and soybean), irrespective of cover crop presence or absence; highest N₂O fluxes occurred following fertilization, soil disturbance (annual crop planting and cover crop termination), and rainfall. Cover crop effects on N₂O emissions vary by species and cash crop: Legumes can increase N₂O emissions, whereas non-legumes have no effect or can depress N₂O emissions in soybean years.