Nitrous Oxide Emissions from Annual and Perennial Biofuel Cropping Systems

Core Ideas A majority (40–80%) of N 2 O was emitted in the first 10 wk of the growing season. No consistent significant differences were found in N 2 O emissions among crops. Most N 2 O was emitted during large events of short duration after substantial rainfall.Burning of fossil fuels in the transportation sector accounts for 28% of US greenhouse gas (GHG) emissions. Substitution of cellulosic biofuel in place of conventional gasoline or diesel could reduce GHG emissions from transportation; however, the effectiveness of cellulosic biofuel in reducing emissions depends on emissions during the growth of biofuel crops. The objectives of this study were (i) to measure N 2 O emissions of potential cellulosic biofuel cropping systems, and (ii) to characterize the temporal variations in N 2 O emissions in these cropping systems. Annual N 2 O emissions were measured in corn ( Zea mays L.)–soybean [ Glycine max (L.) Merr.] and photoperiod‐sensitive sorghum [ Sorghum bicolor (L.) Moench ]–soybean rotations as well as in switchgrass ( Panicum virgatum L.) and miscanthus ( Miscanthus sacchariflorus ) from 2011–2013 in Manhattan, KS, using static chambers. No consistent significant differences were found in N 2 O emissions among crop species, though miscanthus tended to have the least emissions. Most N 2 O was emitted during large events of short duration (1–3 d) that occurred after substantial rainfall events with high soil NO 3 − . In 2011 and 2012, most N 2 O was emitted during the growing season. In 2013, 30–50% of the N 2 O emissions were emitted after September which was attributed to freeze–thaw cycles.