Nitrous Oxide Emissions from Midwest Row-Crops: Comparing Presence and Absence of Winter Cover Crops within and Between Conventional and Organic Management Systems.

N₂O is the largest contributor to the GHG 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.

The beneficial impacts of cover crops that include reduced soil erosion, increased SOM, and weed suppression, are well known. However, very few studies have investigated the effect of cover crops on N₂O emissions. Quantifying N₂O emissions from cover crop systems under varying management is important for improving the accuracy of inventories of agricultural GHG emissions, evaluating the potential of cover crops as a GHG mitigation strategy, and assessing the potential of incentive programs and environmental markets to help farmers transition to more environmentally sustainable management practices.

Here, we will present three years of N₂O emissions data from a corn-soybean-winter wheat rotation, either with or without cover crops, and either under conventional (CON) or certified organic (ORG) management, situated at the Kellogg Biological Station in SW Michigan. Results will explore the effects of overall management (CON vs. ORG), cover crop presence or absence, type (grass, legume, Brassica), residue quality (C:N, and lignin content), and termination time (early vs. late), and N fertilizer type (synthetic vs. poultry manure) on emissions of N₂O.

Initial results from the establishment year and 1^st year of cover crop inclusion show that: 1) emissions of N₂O averaged across all ORG management treatments were more than two times higher than emissions of N₂O averaged across all CON treatments; 2) emissions of N₂O averaged across all cover crop treatments were higher than emissions of N₂O averaged across corresponding no cover crop treatments under CON, but not ORG management; 3) emissions of N₂O from grass and legume cover crop, but not Brassica cover crop containing treatments were higher than emissions from their no cover crop counterparts under CON management, and; 4) average N₂O emissions from the cash crops were highest in corn, when compared to wheat and soybean under CON and ORG management.