Print PageCurrent US energy policy aims to foster national energy independence and environmental stewardship by stimulating liquid biofuel production. Cellulosic biomass sources under consideration for ethanol production include agricultural residues and dedicated cellulosic biomass crops. Clearly both profitable biomass supply and environmental outcomes will depend on environmental setting, and can be effectively modeled at watershed scale.
This paper aims to address four research questions 1) Under what price conditions would biomass production become attractive to profit-oriented farmers? 2) What is the sequence of crop production systems and associated land uses as biomass price and supply increases? 3) What are the environmental consequences of the changing crop production systems as biomass production increases? and 4) How are these results altered by provisions of the Biomass Conversion Assistance Program (BCAP) in the 2008 farm bill?
Profit-maximizing cropping system choices are simulated in two steps. First, the EPIC (Environmental Quality Integrated Climate) model simulates mean crop yields, greenhouse gas fluxes, soil erosion and water-borne nutrient losses for 74 crop systems, defined by crop rotation, mineral fertilization, tillage and level of biomass removal. Separate 24-year simulations are conducted for two land quality classes in each of 37 sub-watersheds of southwestern Michigan. Second, a mathematical optimization model simulates cropping systems choices by a profit-maximizing representative farmer in a manner that captures the opportunity cost of replacing current crops by cellulosic biomass crops. The model draws upon biophysical crop input-output coefficients, price and cost data, and spatial transportation costs.
Results/Conclusions
Biomass supply response results show that crop residues are the first types of biomass to be supplied. Corn stover and wheat straw supply start at delivered biomass-to-corn price ratios of 0.14 and 0.18. Perennial bioenergy crops become profitable when the biomass-to-corn price ratio reaches 0.31 for switchgrass, 0.78 for grass mixes and 1.02 for miscanthus giganteus. The BCAP sharply reduces the minimum biomass-to-corn price ratio at which miscanthus would become profitable to supply. Compared to conventional crop production practices in the area, removal of cellulosic residues from corn and wheat triggers increased fertilizer use, boosting greenhouse gas emissions and reducing water quality through increased nutrient loss. By contrast, perennial cellulosic biomass crops reduce greenhouse gas emissions and improve water quality.
