Spring‐Thaw Nitrous Oxide Emissions from Reed Canarygrass on Wetness‐Prone Marginal Soil in New York State

Core Ideas We monitored N2O fluxes from grasses on seasonally wet soil during spring thaw. We used three different statistical approaches to analyze trends in the fluxes. N2O emissions were elevated in wet areas recently converted to reed canarygrass. In temperate climates, a significant fraction of annual emissions of N2O from agricultural land can occur during soil thaw in late winter and early spring. The objective of this study was to determine the impact of land use change from long‐term fallow grassland to managed perennial grass crops on these thaw‐related N2O emissions and to identify field‐scale drivers that influence emissions. Using static chambers, we monitored mid‐afternoon N2O fluxes during the 2013 spring thaw from 27 March to 7 April, observing fallow grassland and second‐year reed canarygrass (Phalaris arundinaceae L., ‘Bellevue’) across a short topographical gradient. Soil temperature, soil moisture, and residual aboveground biomass were also observed, as were hourly air temperature and precipitation. Fluxes of N2O were generally low (−9.8 to 21.3 μg N2O‐N m−2 h−1) except for one observation of 77.6 μg N2O‐N m−2 h−1. Hot‐moment analysis, non‐parametric statistical tests, and ANOVA results showed that downslope positions converted to managed and fertilized grass had significantly higher N2O emissions than the fallow and upslope positions. We found that these downslope managed grass sites had mean soil moisture of 75.0% water‐filled pore space and less insulating residual aboveground biomass than the fallow grassland. Our results suggest that converting fallow grassland to managed perennial grass cropping systems for bioenergy or other uses could increase spring‐thaw N2O emissions in wetness‐prone areas.