Energy Use in Crop Production.We use 2002–2004 U.S. Depart-ment of Agriculture data on fertilizer, soil treatment, andpesticide application rates for corn (Table 1) and soybean (Table2) farming. Our estimates of the energy needed to produce eachof these agrichemical inputs are derived from recent studies(2–7). We also estimate per-hectare (ha) energy use for oper-ating agricultural equipment, for manufacturing this equipmentand constructing buildings used directly in crop production(Table 3), and for producing the hybrid (corn) or varietal(soybeans) seed planted. We transform these estimates of per-hectare energy use into per-biofuel-liter energy use based oncrop to biofuel conversion efficiencies of 3,632 litersha for corngrain ethanol and 544 litersha for soybean biodiesel. Becausethis island industry cannot operate without laborers, we alsoestimate the per-biofuel-liter energy use to sustain farm house-holds (Table 4).Energy Use in Converting Crops to Biofuels.We estimate the energyused to build the facilities used to convert crops to biofuels(Table 6), transport crops to these facilities, power these facil-ities, and transport biofuels to their point of end use (Table 5). As with farm labor, we estimate the energy used by householdsof industry laborers (Table 4) Energy Yield from Biofuel Production.The energy output of biofuelproduction includes the combustible energy of biofuels them-selves and energy equivalent values for coproducts that typicallyhave uses other than as energy commodities (Table 5). We assigncoproduct credits as follows. For DDGS and glycerol we use an‘‘economic displacement’’ method whereby we calculate theenergy required to generate the products for which each servesas a substitute in the marketplace (i.e., corn and soybean mealfor DDGS and synthetic glycerol for soybean-derived glycerol).For soybean meal, which does not have an adequate substitutein the marketplace based on both its availability and proteinquality, we estimate its coproduct energy credit by a ‘‘massallocation’’ method as the fraction of energy, based on therelative weight of the soybean meal to the entire soybean weightprocessed, used to grow soybeans and produce soybean meal andoil. We also apply alternative methods of calculating coproductcredits including issuing energy values based on caloric contentand market value (Table 9).We determine the NEB of a biofuel by subtracting the valueof all fossil energy inputs used in producing the biofuel from theenergy value of the biofuel and its coproducts. Similarly, wecalculate the NEB ratio by dividing the sum of these outputs overthat of the inputs.Environmental Effects.When measuring the life-cycle environ-mental impacts of each biofuel, we expand the island industrymodel to include total net emissions from biofuel combustion aswell as production. Given the NEB of each biofuel and currentfertilizer and pesticide application rates, we calculate for eachbiofuel the amount of each agricultural input applied per unit ofenergy gained by producing the biofuel (Table 10). For ourestimates of GHG savings in producing and combusting eachbiofuel in lieu of a fossil fuel, we first calculate the life-cycleGHG savings from displacing the fossil fuel (i.e., from the energygained in producing the biofuel) and then add to this amount thenet GHG emissions released on the farm