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Title:   Author  item
                                            Adler, Paulitem
                                            DELGROSSO, S - COLORADO STATE UNIVitem
                                            PARTON, W - COLORADO STATE UNIV
  Submitted to: Ecological Applications
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 7/10/2006
                                    Publication  Date: 4/20/2007
                                    Citation: Adler, P.R., Delgrosso, S.J., Parton, W.J. 2007. Life cycle assessment of net greenhouse gas flux for bioenergy cropping systems. Ecological Applications. 17(3):675-691.Interpretive Summary: The use of fossil fuels has increased the concentration of greenhouse gases (GHGs). Biofuels can be produced from plants thereby minimizing the release of GHGs from energy consumption by recycling carbon dioxide. However, bioenergy cropping systems vary in contribution to the global warming potential due to the crop yield and resulting quantity of fossil fuels displaced, quantity and quality of carbon added to the soil, plant to enegry conversion efficiency, GHG emissions associated with crop production, N use efficiency, and inputs required for crop production and operation of farm machinery. We used the DAYCENT simulation model to assess the net greenhouse gas (GHG) emissions of bioenergy cropping systems (corn, soybeans, alfalfa, switchgrass, and hybrid poplar) in Pennsylvania for inclusion in a full C cycle analysis.  The largest source of reduction in GHGs with biofuel production came from fossil fuels that could now be replaced by use of biofuel. Carbon storage in the soil was the second largest source of GHG reduction. The greatest source of GHGs was nitrous oxide fluxes from the soil, followed by fossil fuel use for farm machinery and production of nitrogen fertilizer. When displacement of fossil fuel was not considered in the analysis and carbon storage in the soil was assumed to have reached its maximum capacity, switchgrass and hybrid poplar were the only cropping systems to remain a sink for GHGs. Use of switchgrass and hybrid poplar for production of biofuels has the potential to be GHG neutral and may reduce GHGs.
                                Technical Abstract: Reducing the net global warming potential (GWP) of energy use is a major factor driving interest in biofuels. Bioenergy cropping systems vary in contribution to the GWP due to the crop yield and resulting quantity of fossil fuels displaced, quantity and quality of C added to the soil, feedstock conversion efficiency, N2O emissions, N use efficiency, and inputs required for crop production and operation of farm machinery. The objective of the study was to assess the net greenhouse gas (GHG) emissions of bioenergy cropping systems (corn, soybeans, alfalfa, switchgrass, and hybrid poplar) in Pennsylvania for inclusion in a full C cycle analysis using the DAYCENT model. The quantity of displaced fossil fuel was the largest GHG sink. Soil C sequestration was the second largest GHG sink. Although crops with higher soil C inputs, such as switchgrass and hybrid poplar, will have higher equilibrium soil C levels, the change in system C will approach zero in the long term. N2O emissions were the largest GHG source. When the credit for the amount of fossil fuel displaced was not taken and soil C storage was assumed to have reached its maximum capacity, switchgrass and hybrid poplar were the only cropping systems to remain a sink for GHGs. Therefore, use of switchgrass and hybrid poplar for production of biofuels has the potential to be GHG neutral and may reduce GHGs.


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