Integrated regional modeling assessment of the environmental and economic potential of perennial grass bioenergy feedstocks

Perennial grasses have been proposed as viable bioenergy crops because of their potential to yield harvestable biomass on marginal lands without displacing food and contribute to greenhouse gas (GHG) reduction by storing carbon in soil. Switchgrass, miscanthus, and restored native prairie are among the crops being considered in the corn and agricultural regions of the eastern United States. In this study, we used an extensive dataset of site observations for each of these crops to evaluate and improve a combined ecosystem and economic modeling framework about how both yield and GHG fluxes would respond to different land use strategies. Using this model-data integration approach, we found 30-75% improvement in our predictions over previous studies and good model-data agreement of harvested yields and soil carbon stocks (r2 > 0.62 for all crops). We found that growing perennial grasses would result in average onsite GHG reductions of 0.5-2.0 Mg CO2e ha-1 yr-1compared to a corn-soy baseline, not including fossil fuel offsets. If grown on marginal lands, average onsite GHG reductions remain significant at 0.3-1.0 Mg CO2e ha-1 yr-1. After conversion to bioenergy and complete life cycle assessment, offsite GHG savings can increase by up to 150%, providing a dry biomass supply of 11-22 Mg ha-1 yr-1 for energy use. Preliminary model results of the abatement cost range between 62- 250 per ton of CO2e abated. While a carbon tax would provide an incentive, we find that it would need to be larger than the abatement cost to induce production of cellulosic biofuels.