ARS | Publication request: Comparative Biogeochemical Cycles of Bioenergy Crops Reveal Nitrogen-Fixation and Low GHG Emissions in a Miscanthus x giganteus Agro-ecosystem

Submitted to: Ecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 30, 2009
Publication Date: January 4, 2010
Citation: Davis, S.C., Parton, W.J., Dohleman, F.G., Gottel, N.R., Smith, C.M., Del Grosso, S.J., Kent, A.D., Delucia, E.H. 2010. Comparative Biogeochemical Cycles of Bioenergy Crops Reveal Nitrogen-Fixation and Low GHG Emissions in a Miscanthus x giganteus Agro-ecosystem. Ecosystems 13: 144-156.

Interpretive Summary: Although most biofuel currently used in the US is made from corn, grasses such as switchgrass and miscanthus have potential to supply our energy needs in the future. We evaluated the greenhouse gas mitigation potential of different biofuel crops using the DayCent ecosystem mxodel and field measurements. Miscanthus had the lowest emissions per unit of product because it grows very fast and no nitrogen fertilizer was required. We suggest that biological nitrogen fixation is necessary to maintain the high growth rates observed in field trials of miscanthus. Observations of nitrogen fixing bacteria isolated from miscanthus roots support this suggestion. Our results are part of a large-scale field study of biofuel crop alternatives for the Midwestern US. Miscanthus has the potential to restore soil carbon to the depleted soils of the Midwest, reduce atmospheric greenhouse gasses, and improve water quality. Growing miscanthus as a biofuel could reduce greenhouse gas emissions compared to growing other biofuel crops, particularly corn, because corn requires high nitrogen additions. Miscanthus cropping also would improve water quality because little, if any, nitrogen fertilizer additions are required, so less nitrogen leaches into waterways

Technical Abstract: We evaluated the relative greenhouse gas mitigation potential of plant species considered as biofuel feedstock crops by simulating the biogeochemical processes associated with Miscanthus x giganteus, Panicum virgatum, Zea mays, and a mixed prairie community. DayCent model simulations for Miscanthus were parameterized with data from previous literature and trial plots established in Urbana, Illinois in 2002. Comparisons of Miscanthus with previously validated parameters for the other three biofuel feedstock crops lead to hypotheses about biogeochemical N transformations that are required for the high observed Miscanthus crop yields. We tested Miscanthus microbial isolates for N-fixing activity and now have evidence to support the hypothesis that N-fixation contributes to the nitrogen demand of this highly productive perennial grass. Our results are a priori of a large-scale replicated field study of biofuel crop alternatives for the Midwestern US. Miscanthus x giganteus has the potential to restore soil C to the agriculturally exploited soils of the Midwest, reduce atmospheric greenhouse gasses, and improve water quality because it has a self-sustainable nitrogen budget. Using Miscanthus as a biofuel could reduce greenhouse gas emissions associated with fossil fuel burning; this reduction would far exceed that of other biofuel crop options.