Can Nitrogen Fertilizer Applied to Corn Affect N2O Emissions the Following Year from a Corn-Soybean Rotation in the US Midwest?.

Agricultural management strategies are needed to reduce N₂O emissions from croplands. However, most research has focused on corn due to large N fertilizer inputs that promote N₂O emission. Corn is commonly rotated with other crops that receive little or no N fertilizer, yet little information exists on the potential for N fertilizer applications to corn to affect N₂O emissions during subsequent crops. To determine how N fertilizer application to corn affects N₂O emissions during the subsequent crop in rotation, we conducted a three year study (2011, 2012, and 2013) of N₂O emissions from a corn-soybean rotation at Boone, Iowa with three N fertilizer rates applied to corn (0 kg N ha^-1, a recommended rate of 135 kg N ha^-1, and an excessive rate of 225 kg N ha^-1). Soybean received no N fertilizer. We further investigated the potential for a winter cereal rye cover crop to affect N₂O emissions from both crops. In both crops, cover crop effects on N₂O emissions and NO₃ concentrations were not consistent across years or N fertilizer treatments. Across all years and irrespective of cover crops, an increase in N fertilizer rate from the recommended to excessive rate resulted in a 16% increase in mean N₂O emission rate from corn. In two of three years, mean N₂O emission rates from the soybean crop were not affected by the N rate applied to the corn. However, in 2013 following the drought year 2012, mean N₂O emission rates from the recommended and excessive rates were 35% and 70% greater than the zero N rate. These results suggest that cover crops do not consistently reduce N₂O emissions in either the corn or soybean phase of the rotation, and climate patterns interact with N fertilizer rate to affect N₂O emissions from crops that follow corn.