Nitrous Oxide Emissions At Varying N Rates From Rainfed and Irrigated Row Crops in the US Midwest.

Global N₂O emissions from agriculture are estimated to be ~2.8 Pg CO₂e yr^-1 accounting for 60% of total anthropogenic emissions. N₂O is the largest contributor to the GHG burden of cropping systems in the US, with annual estimated emissions of ~0.5 Tg primarily due to N fertilizer inputs and other soil management activities. Currently, approximately 23 million acres of corn, soybean and wheat are irrigated annually in the U.S. Here we compare N₂O emissions and yields (corn, soybean and wheat) from a long-term resource gradient experiment situated at the Kellogg Biological Station in SW Michigan, that investigates nitrogen (nine rates between 0 and 246 kg N ha^-1) and water (irrigated and rainfed) constraints and interactions on crop yield and GHG emissions.

Initial results show that the N₂O response curve to increasing N rate in irrigated corn may be different to that in rainfed corn. Cumulative N₂O emissions over the growing season were doubled (0.69 to 1.34 kg N₂O-N ha^-1) by an increase in N rate from 67 to 246 kg N ha^-1 in the irrigated treatment, but increased by a factor of approximately eight (0.36 to 2.70 N₂O-N ha^-1) in the rainfed system. However, average daily emissions during the growing season across all N rates were similar (5.0 and 4.9 g N₂O-N ha^-1 day^-1 for the irrigated and rainfed systems respectively).

Data will be presented for a three year corn-soybean-wheat rotation, and trade–offs between N₂O emissions, N fertilizer rate, crop yield and irrigation practice will be evaluated from a local and regional environmental and economic standpoint.