Del, Grosso Stephen (USDA-ARS, Natural Resources Research Center, 2150 Centre Ave, Fort Collins, CO, 80526-8119; Phone: 970-492-7281; Fax: 970-492-7213; Email: delgro@nrel.colostate.edu)

DAYCENT National Scale Simulations of N2O Emissions from Cropped Soils in the USA

S.J. Del Grosso *, W.J. Parton, A.R. Mosier, M.K. Walsh, D.S. Ojima, P.E. Thornton

Until recently, IPCC emission factor methodology, based on simple empirical relationships, has been used to estimate N and C fluxes for regional and national inventories. However, the 2005 EPA greenhouse gas inventory includes estimates of N₂O emissions from cultivated soils derived from simulations using DAYCENT, a process based biogeochemical model. DAYCENT simulated direct soil N₂O emissions, as well as indirect N₂O emissions from NO₃ leaching and N volatilization. Corn, soy, wheat, alfalfa hay, non-alfalfa hay, cotton, and sorghum were simulated at county level resolution. IPCC emission factor methodology was used to estimate emissions for the ~10% of cropped land not simulated by DAYCENT. N₂O emissions from simulations of presettlement native vegetation were subtracted from cropped soil N₂O to isolate anthropogenic emissions. Meteorological data required to drive DAYCENT were acquired from DAYMET, an algorithm that uses weather station data and accounts for topography to predict daily temperature and precipitation at 1 square km resolution. Soils data were acquired from STATSGO. Weather data and dominant soil texture class that lie closest to the geographical center of the largest cluster of cropped land in each county were used to drive DAYCENT. Land management information was implemented at the agricultural region level as defined by the Agricultural Sector Model. Maps of model simulated county level crop yields were compared with yields estimated by NASS for quality control. Combining results from DAYCENT simulations of major crops and IPCC methodology for remaining crop land yielded estimates of ~100 and ~70 Tg CO₂ equivalents for direct and indirect, respectively, mean annual anthropogenic N₂O emissions for 1990-2003.