Switchgrass Intercropped with Alfalfa Results in Significant Reductions in Nitrogen Applications, Energy Savings, and Reductions in Nitrous Oxide Emissions.

Biofuels have been projected as a technology to reduce fossil fuel consumption and greenhouse gas emissions. Our research objectives were to measure N₂O emissions from switchgrass plantings and perform a life cycle assessment of total savings of greenhouse gases by using switchgrass derived ethanol vs gasoline. We measured the N₂O gas emissions at a site in Eastern Washington near Prosser. Treatments included no fertilizer, agronomic rate of chemical fertilizer and intercropping of switchgrass with alfalfa. Static chamber gas samples for N₂O were taken roughly at monthly intervals to calculate an N₂O flux. N₂O fluxes were greater when the soils were wet (immediately after irrigation) versus dry (before irrigation). The overall seasonal N₂O flux was estimated by considering the number of dry and wet cycles that the soil goes through during the season. Dry matter biomass yields in the intercropped plot were 37% higher than control plots and 32% lower than the fertilized plots. Intercropping with 70:30 (switchgrass: alfalfa combination) produced higher yields and lower N₂O emissions. We will present a life cycle assessment for cellulosic ethanol production and greenhouse gas reductions using switchgrass alone and switchgrass intercropped with alfalfa.