Modeling Nitrous Oxide Emissions in Bioenergy Cropping Systems Using DNDC.

The 2007 Energy Independence Security Act mandates the production of 60 billion liters per year of cellulosic biofuel by 2022, which will be required to have life cycle assessment greenhouse gas (GHG) emissions at least 60% below those of gasoline/diesel. Emissions of nitrous oxide (N₂O) could have a major impact on the GHG balance of biofuels. The multiple environmental and management factors driving N₂O emissions make process-based models, like the DeNitrification DeComposition (DNDC) model, necessary to quantify these processes over large spatial and temporal scales. However, few studies have used DNDC to simulate N₂O in bioenergy cropping systems. Therefore, the objectives of this study were to 1) use DNDC to model dedicated bioenergy crop growth in Manhattan, KS and 2) evaluate the ability of DNDC to predict N₂O emissions under different bioenergy crops. DNDC crop parameters and field observations from the literature were used to develop initial crop parameters for corn, photoperiod-sensitive sorghum, switchgrass and miscanthus. DNDC was used to simulate biomass production of these crops and was compared to measured data from a 7 year field trail in Manhattan, KS. DNDC was then used to model N₂O emissions which were compared to field observations. Yield was poorly simulated by DNDC, with negative Nash-Sutcliffe model efficiency coefficients (ME) for all crops except switchgrass. Daily fluxes of N₂O were successfully simulated in switchgrass only (ME = 0.43). Simulated annual N₂O emissions were significantly different from measured estimates in 7 out of 16 crop-years. These preliminary findings suggest that calibration of crop and soil parameters is required to improve yield and N₂O simulations in DNDC for the crops in this study.