Nitrous Oxide Emissions As Affected By Drainage Design and Management in Corn Based Cropping Systems.

Subsurface drainage is required to optimize crop production in the Midwest USA. The effect of subsurface drainage on nitrate losses is well documented. However, there is little information about the effect on nitrous oxide (N₂O) emissions. The objectives of this study were to evaluate the response of subsurface drainage on N₂O emissions. To understand the effect of drainage on soil N₂O emissions, we measured in situ N₂O fluxes across two seasons (2013 and 2014) in controlled drainage (18 m drainage spacing, 1.2 m depth, and controlled structure to manage the water table), conventional drainage (18 m drainage spacing, 1.2 m depth), shallow drainage (12.2 m drainage spacing, 0.75 m depth) and no-drainage plots in a continuous corn at the Iowa State University Southeast research farm in Crawfordsville, Iowa. In situ N₂O fluxes did not show a clear pattern across drainage plots in both years. However, these fluxes showed temporal variability across drainage plots during warm summer months (May-July) in both years. Due to the high variability in in situ fluxes, we used a laboratory approach to determine the potential effect of subsurface drainage on N₂O fluxes. For this work, we used soils from the Iowa site and a southeast Indiana site with poorly-drained (40 m drainage spacing) and highly-drained (5 m drainage spacing) plots in a corn-soybean rotation. In the laboratory, denitrification enzyme activity (DEA) was significantly higher in less-drained compared to more drained plots at both Iowa and Indiana sites. The difference in DEA was coincident with higher total carbon concentrations in soils from less-drained sites. These results suggest drainage may have an effect on N₂O emissions, but our field data indicate that understanding this effect will be difficult.