Impact of Nitrogen Rate on Nitrous Oxide Emissions and Life Cycle Greenhouse Gas Emissions in Switchgrass-based Cellulosic Ethanol

The 2007 Energy Independence Security Act mandates the production of 16 billion gallons per year of cellulosic biofuel by 2022. These biofuels will be required to have life cycle assessment (LCA) greenhouse gas (GHG) emissions 60% below gasoline. Switchgrass is one potential feedstock for the production of cellulosic ethanol in Kansas. Emissions of the GHG nitrous oxide (N2O) from soils treated with nitrogen (N) fertilizer could negatively impact the GHG balance of biofuels. The objectives of this study were to 1) characterize the yield and N2O emissions from switchgrass receiving different rates of N fertilizer and 2) determine the impact of these emissions on the LCA GHG emissions of switchgrass-based ethanol. In 2012 and 2013, 0 – 200 kg of N were applied to switchgrass plots in Manhattan, KS. Annual N2O emissions were measured from soils in the plots using static chambers. Measured yields and N2O emissions were used as inputs in the GREET LCA model to estimate the life cycle GHG emissions of switchgrass-based ethanol. There was a quadratic relationship between N rate and yield. In 2012, N2O emissions increased exponentially with increasing N rate. In 2013 N2O increased linearly with increasing N. Increasing N rates caused substantial increases in the LCA GHG emissions of switchgrass-based cellulosic ethanol. Much of the increase was due to increased N2O emissions, which accounted for 67% and 44% of total LCA GHG emissions in switchgrass receiving 150 kg N ha-1 in 2012 and 2013, respectively. LCA GHG emissions of ethanol were lower than emissions from gasoline at all N rates. Increased N rates increased yield but also substantially increased N2O emissions and the GHG balance of ethanol, indicating that trade-offs may exist in managing nitrogen to maximize agronomic productivity and to reduce nitrogen losses as N2O. Stalk rots are among the most detrimental diseases of sorghum worldwide. Grain yield reduction and plant lodging due to these diseases are major sources of concern in using sorghum as a feedstock for bioethanol production. The objective of this study was to test the effects of Fusarium stalk rot and charcoal rot on sorghum grain yield and total soluble solids (TSS) of stem juice, when plants were inoculated at two growth stages. Four sorghum genotypes were tested in the greenhouse and field against three Fusarium spp. (F. thapsinum, F. proliferatum, F. andiyazi) and Macrophomina phaseolina at GS1 (30 d after emergence) and GS3 (14 d after flowering). …