This study estimated the potential emissions of greenhouse gases (GHG) from bioenergy ecosystems with a biogeochemical model AgTEM, assuming maize ( Zea mays L.), switchgrass ( Panicum virgatum L.), and Miscanthus ( Miscanthus * giganteus) will be grown on the current maize-producing areas in the conterminous United States. We found that the maize ecosystem acts as a mild net carbon source while cellulosic ecosystems (i.e., switchgrass and Miscanthus) act as mild sinks. Nitrogen fertilizer use is an important factor affecting biomass production and N 2O emissions, especially in the maize ecosystem. To maintain high biomass productivity, the maize ecosystem emits much more GHG, including CO 2 and N 2O, than switchgrass and Miscanthus ecosystems, when high-rate nitrogen fertilizers are applied. For maize, the global warming potential (GWP) amounts to 1-2 Mg CO 2eq ha -1 yr -1, with a dominant contribution of over 90% from N 2O emissions. Cellulosic crops contribute to the GWP of less than 0.3 Mg CO 2eq ha -1 yr -1. Among all three bioenergy crops, Miscanthus is the most biofuel productive and the least GHG intensive at a given cropland. Regional model simulations suggested that substituting Miscanthus for maize to produce biofuel could potentially save land and reduce GHG emissions.
