Agronomic Management Impacts on Carbon Dioxide and Nitrous Oxide Emissions over Four Years of Bioenergy Sorghum Production.

Bioenergy sorghum (Sorghum bicolor L.) is a promising biomass feedstock for future advanced biofuels production. However, little is known of the impacts of sorghum production on emissions of CO₂ and N₂O from soil. The goal of this study was to determine effects of N fertilization (0 vs. 280 kg urea-N ha^-1), residue management (0 vs. 50% of sorghum biomass returned), and crop sequence [corn (Zea mays L.)-sorghum vs. sorghum-sorghum] on CO₂ and N₂O emissions from bioenergy production scenarios in central Texas. Gas measurements were taken throughout each year utilizing chamber-based techniques integrated with a photoacoustic analyzer from 2010 to 2012 and a mobile-FTIR gas analyzer thereafter. Analysis was performed to determine treatment effects on gas flux rates from every sampling event from 2010 to 2014. Gas fluxes of CO₂ and N₂O peaked during the growing seasons and generally followed significant precipitation or irrigation events. Crop sequence most frequently impacted emissions of CO₂ followed by residue management and N fertilization. The effect of N fertilization on CO₂ emissions was most often observed early in the growing season, while crop sequence and residue management were observed throughout the year. Nitrogen fertilization most frequently impacted N₂O emissions followed by crop sequence and residue management. The impact of treatments on N₂O emissions only occurred during the growing season, with few measurable fluxes observed during fallow seasons. This research identified important trends in CO₂ and N₂O emissions from bioenergy sorghum production and will enhance future research efforts.