Soil Science Society of America Journal Soil Sci. Soc. Am. J. 80:428–437 doi:10.2136/sssaj2015.05.0182 Supplemental material available online. Received 11 May 2015. Accepted 28 Oct. 2015. *Corresponding author (bkr2@cornell.edu). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All Rights reserved. Spring-Thaw Nitrous Oxide Emissions from Reed Canarygrass on Wetness-Prone Marginal Soil in New York State Soil & Water Management & Conservation In temperate climates, a signifcant fraction of annual emissions of N 2 O 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 N 2 O emissions and to identify feld-scale drivers that infu- ence emissions. Using static chambers, we monitored mid-afternoon N 2 O fuxes during the 2013 spring thaw from 27 March to 7 April, observing fal- low grassland and second-year reed canarygrass (Phalaris arundinaceae L., ‘Bellevue’) across a short topographical gradient. Soil temperature, soil mois- ture, and residual aboveground biomass were also observed, as were hourly air temperature and precipitation. Fluxes of N 2 O were generally low (−9.8 to 21.3 mg N 2 O-N m −2 h −1 ) except for one observation of 77.6 mg N 2 O-N m −2 h −1 . Hot-moment analysis, non-parametric statistical tests, and ANOVA results showed that downslope positions converted to managed and fertil- ized grass had signifcantly higher N 2 O emissions than the fallow and upslope positions. We found that these downslope managed grass sites had mean soil moisture of 75.0% water-flled pore space and less insulating residu- al 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 N 2 O emissions in wet- ness-prone areas. Abbreviations: FG, unconverted fallow grassland; MG, managed reed canarygrass; WFPS, water-flled pore space. E mission of the greenhouse gas N 2 O is an important parameter in climate change prediction. Nitrous oxide has an estimated 100-yr global warming potential 298 times that of CO 2 (Forster et al., 2007). It also degrades the Earth’s stratospheric ozone layer (Conrad, 1996) and is recognized as the primary current anthropogenic threat in this regard (Ravishankara, 2009). Because agri- culturally managed soils contribute 60% of global anthropogenic N 2 O emissions (Smith et al., 2007), agriculture and climate change are intimately linked. Globally, N 2 O emissions are expected to rise due to increased fertilizer and animal manure production (Smith et al., 2007) and conversion of uncultivated land for food and energy production. Expanded production of bioenergy crops is one cause of land conversion (Stoof et al., 2014). While redirection of first-generation crops (corn [Zea mays L.] and soybean [Glycine max (L.) Merr.]) grown on prime cropland from feed and food uses to bioenergy does not affect the per-hectare balance of N 2 O fluxes, etha- nol demand-driven price increases for corn have resulted in the recent withdrawal from the Conservation Reserve Program of millions of hectares of lower quality Cedric W. Mason Dep. of Biological and Environmental Engineering Riley Robb Hall Cornell Univ. Ithaca, NY 14853 Cathelijne R. Stoof Dep. of Biological and Environmental Engineering Riley Robb Hall Cornell Univ. Ithaca, NY 14853 and Soil Geography and Landscape Group Wageningen Univ. PO Box 47 6700 AA Wageningen The Netherlands Brian K. Richards* Dep. of Biological and Environmental Engineering Riley Robb Hall Cornell Univ. Ithaca, NY 14853 David G. Rossiter School of Integrative Plant Sciences Section of Soil and Crop Sciences Emerson Hall Cornell Univ. Ithaca, NY 14853 Tammo S. Steenhuis Dep. of Biological and Environmental Engineering Riley Robb Hall Cornell Univ. Ithaca, NY 14853 Core Ideas • We monitored N 2 O fuxes from grasses on seasonally wet soil during spring thaw. • We used three different statistical approaches to analyze trends in the fuxes. • N 2 O emissions were elevated in wet areas recently converted to reed canarygrass. Published February 19, 2016