McGowan, Andrew R.2015-11-162015-11-162015-12-01http://hdl.handle.net/2097/20510Substitution of cellulosic biofuel in place of gasoline or diesel could reduce greenhouse gas (GHG) emissions from transportation. However, emissions of nitrous oxide (N₂O) and changes in soil organic carbon (SOC) could have a large impact on the GHG balance of cellulosic biofuel, thus there is a need to quantify these responses in cellulosic biofuel crops. The objectives of this study were to: (i) measure changes in yield, SOC and microbial communities in potential cellulosic biofuel cropping systems (ii) measure and characterize the temporal variation in N₂O emissions from these systems (iii) characterize the yield and N₂O response of switchgrass to N fertilizer and to estimate the costs of production. Sweet sorghum, photoperiod-sensitive sorghum, and miscanthus yielded the highest aboveground biomass (20-32 Mg ha⁻¹). The perennial grasses sequestered SOC over 4 yrs, while SOC stocks did not change in the annual crops. Root stocks were 4-8 times higher in the perennial crops, suggesting greater belowground C inputs. Arbuscular mycorrhizal fungi (AMF) abundance and aggregate mean weight diameter were higher in the perennials. No consistent significant differences were found in N₂O emissions between crops, though miscanthus tended to have the lowest emissions. Most N₂O was emitted during large events of short duration (1-3 days) that occurred after high rainfall events with high soil NO₃₋. There was a weak relationship between IPCC Tier 1 N₂O estimates and measured emissions, and the IPCC method tended to underestimate emissions. The response of N₂O to N rate was nonlinear in 2 of 3 years. Fertilizer induced emission factor (EF) increased from 0.7% at 50 kg N ha⁻¹ to 2.6% at 150 kg N ha⁻¹. Switchgrass yields increased with N inputs up to 100-150 kg N ha⁻¹, but the critical N level for maximum yields decreased each year, suggesting N was being applied in excess at higher N rates. Yield-scaled costs of production were minimized at 100 kg N ha-1 ($70.91 Mg⁻¹). Together, these results show that crop selection and fertilizer management can have large impacts on the productivity and soil GHG emissions biofuel cropping systems.en-US© the author. This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).http://rightsstatements.org/vocab/InC/1.0/BiofuelSoil carbonNitrous oxideGreenhouse gasesDissertationAgronomy (0285)Alternative Energy (0363)Soil Sciences (0481)