Nitrous Oxide Emissions From Cover Crop Systems in the US Midwest Under Conventional and Organic Management.

N₂O is the largest contributor to the GHG burden of cropping systems in the US, with annual estimated emissions of ~500 Pg primarily due to N fertilizer inputs and other soil management activities. In the US Midwest, the practice of including winter cover crops in corn-based row-crop systems is not widely adopted but rising, with cereal grains, legumes, forage grasses and Brassicas planted. The beneficial impacts of cover crops on agro-ecosystem functioning that include reduced soil erosion, increased SOM, and weed suppression are well known. However, only a few studies have investigated the effect of cover crops and their residue quality (e.g., C:N ratio, lignin content) on N mineralization-immobilization patterns, and none have looked simultaneously at long-term N₂O emissions in systems with various cover crop species under conventional and certified organic management. Quantifying N₂O emissions under varying management is important for improving the accuracy of inventories of agricultural GHG emissions in the US and will help evaluate the potential of new market based incentives such as carbon credits to help farmers transition to organic certification.

Here we present preliminary N₂O emissions and soil N data from a corn-soybean-winter wheat rotation with varying cover crops (annual ryegrass, oilseed radish, red clover) under conventional and certified organic management at two independent sites at the Kellogg Biological Station in SW Michigan. The impacts of variation of N fertilizer formulation, tillage, crop type, and termination practice within and between the sites will be evaluated.