Biomass Yields and Soil Greenhouse Gas Fluxes for Biofuel Cropping Systems in the Central USA.

The Energy Independence and Security Act of 2007 includes biofuel production requirements and greenhouse gas (GHG) mitigation targets. To meet these goals, land currently used for other purposes will be converted to biofuel cropping. However, the capacity of different lands to produce biofuels and the GHG emissions associated with biofuel production systems are highly uncertain. To assess the feasibility of different biofuel cropping systems to supply sufficient quantities of biomass feedstock and minimize GHG emissions, we conducted regional simulations using the DAYCENT ecosystem model. DAYCENT uses soils, weather, and land use data to simulate plant growth, soil GHG fluxes, NO₃ leaching, and other variables. The ability of DAYCENT to simulate biofuel crop yields, soil C levels, and N₂O emissions was validated using field data from switchgrass, miscanthus, and corn plots in different parts of the US along climate and soil fertility gradients. Regional simulations were then conducted for these 3 biofuel crops where current and previous land use and soil suitability were varied. Our analyses suggest that miscanthus and switchgrass cropping can produce large amounts of biomass, increase soil C, and minimize N₂O emissions. Corn cropping has higher soil N₂O emissions but these can be reduced by using nitrification inhibitors. Conservation Reserve Program (CRP) and pasture lands converted to corn cropping are likely to lose soil C under conventional tillage but soil C can be maintained with reduced tillage intensity. Improved N and tillage management and judicious use of marginal lands can help the US meet its biofuel production goals and also reduce GHG emissions and maintain or enhance soil and water quality.