The cumulative energy and global warming impacts associated with producing corn, soybeans, alfalfa, and switchgrass and transporting these crops to a central crop processing facility (called a " biorefinery ") are estimated. The agricultural inputs for each crop are collected from seven states in the United States: Illinois, Indiana, Iowa, Michigan, Minnesota, Ohio, and Wisconsin. The cumulative energy requirement for producing and transporting these crops is 1.99 to 2.66 megajoules/kilo-gram (MJ/kg) for corn, 1.98 to 2.04 MJ/kg for soybeans, 1.24 MJ/kg for alfalfa, and 0.97 to 1.34 MJ/kg for switchgrass. The global warming impact associated with producing biomass is 246 to 286 grams (g) CO 2 equivalent/kg for corn, 159 to 163 g CO 2 equivalent/kg for soybeans, 89 g CO 2 equivalent/ kg for alfalfa, and 124 to 147 g CO 2 equivalent/kg for switch-grass. The detailed agricultural data are used to assess previous controversies over the energy balance of bioethanol and, in light of the ongoing debates on this topic, provide a needed foundation for future life-cycle assessments.
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