N2O emissions and global warming potential as affected by water management and rice cultivar on an Alfisol in Arkansas, USA

The objectives of this study were to evaluate the effects of water management practice (full-season-flood and intermittent-flood) and cultivar (pure-line and hybrid) on nitrous oxide (N2O) fluxes, season-long N2O emissions, and the global warming potential (GWP). Rice was grown in each treatment on a silt-loam soil in the direct-seeded, delayed-flood production system in eastern Arkansas. Gas samples were collected from 30-cm-diameter enclosed chambers at 20-min intervals for 1 h approximately weekly between the establishment of the delayed flood (i.e., 4-5 leaf stage) and several days after end-of-season flood release. Nitrous oxide fluxes differed over time (P = 0.07) throughout the 2016 rice growing season, while N2O emissions ranged from 0.38 to 0.84 kg N2O-N ha−1 season−1 from the full-season-flood/hybrid and intermittent-flood/hybrid treatment combinations, but neither water management nor cultivar affected (P > 0.1) N2O fluxes or season-long emissions. Hybrid rice (XL753; 2272 kg CO2 eq. ha−1 season−1) had lower (P < 0.01) GWP than the pure-line rice (LaKast; 4473 kg CO2 eq. ha−1 season−1), while the intermittent-flood/hybrid combination (2046 kg CO2 eq. ha−1 season−1) had the numerically lowest GWP compared to the other three treatment combinations; however, N2O emission accounted for <20% of GWP for any treatment combination. Despite low emissions magnitudes and the lack of significant water management or cultivar effects from this study, it is still critical to comprehensively quantify and evaluate various effects on N2O emissions from rice under different agronomic and environmental combinations to determine if changes to common, conventional production practices (i.e., altered water management) will have detrimental effects on the environment.