SummaryCorn stover is the residue that is left behind after corn grain harvest. We have constructed a life-cycle model that describes collecting corn stover in the state of Iowa, in the Midwest of the United States, for the production and use of a fuel mixture consisting of 85% ethanol/15% gasoline (known as "E85") in a flexible-fuel light-duty vehicle. The model incorporates results from individual models for soil carbon dynamics, soil erosion, agronomics of stover collection and transport, and bioconversion of stover to ethanol.Limitations in available data forced us to focus on a scenario that assumes all farmers in the state of Iowa switch from their current cropping and tilling practices to continuous production of corn and "no-till" practices. Under these conditions, which maximize the amount of collectible stover, Iowa alone could produce almost 8 billion liters per year of pure stover-derived ethanol (E100) at prices competitive with today's corn-starchderived fuel ethanol. Soil organic matter, an important indicator of soil health, drops slightly in the early years of stover collection but remains stable over the 90-year time frame studied. Soil erosion is controlled at levels within tolerable soil-loss limits established for each county in Iowa by the U.S. Department of Agriculture.We find that, for each kilometer fueled by the ethanol portion of E85, the vehicle uses 95% less petroleum compared to a kilometer driven in the same vehicle on gasoline. Total fossil energy use (coal, oil, and natural gas) and greenhouse gas emissions (fossil CO 2 , N 2 O, and CH 4 ) on a life-cycle basis are 102% and 113% lower, respectively. Air quality impacts are mixed, with emissions of CO, NOx, and SOx increasing, whereas hydrocarbon ozone precursors are reduced.This model can serve as a platform for future discussion and analysis of possible scenarios for the sustainable production of transportation fuels from corn stover and other agricultural residues.

The environmental costs and benefits of producing bioenergy crops can be measured both in terms of the relative effects on soil, water, and wildlife habitat quality of replacing alternate cropping systems with the designated bioenergy system, and in terms of the quality and amount of energy that is produced per unit of energy expended. While many forms of herbaceous and woody energy crops will likely contribute to future biofuels systems, The Department of Energy's Biofuels Feedstock Development Program ( B F D P ) , has chosen to focus its primary herbaceous crops research emphasis on a perennial grass species, switchgrass (Panicum virsatum) , as a bioenergy candidate. This choice was based on its high yields, high nutrient use efficiency, and wide geographic distribution, and also on its positive environmental attributes. The latter include its positive effects on soil quality and stability, its cover value for wildlife, and the lower inputs of energy, water, and agrochemicals required per unit of energy produced. A comparison of the energy budgets for corn, which is the primary current source of bioethanol, and switchgrass reveals that the efficiency of energy production for a perennial grass system can exceed that for an energy intensive annual row crop by as much as 15 times. In additions reductions in CO, emissions, tied to the energetic efficiency of producing transportation fuels and replacing non-renewable petrochemical fuels, are very efficient with grasses. Calculated carbon sequestration rates may exceed those of annual crops by as much as [20][21][22][23][24][25][26][27][28][29][30] times, due in part to carbon storage in the soil. These differences have major implications for both the rate and efficiency with which fossil energy sources can be replaced with cleaner burning biofuels. Current research is emphasizing quantification of changes in soil nutrients and soil organic matter to provide understanding of the long term changes in soil quality associated with annual removal of high yields of herbaceous energy crops.

Increasing demand for the production of energy from renewable sources has fueled a search for alternatives to supplement those currently in production. One such alternative is switchgrass, a perennial grass native to North America that appears to have considerable potential as a biomass feedstock for energy production. While the properties of switchgrass as a biomass feedstock have been intensively studied, the potential market for switchgrass has received much less attention. A survey of Tennessee farmers was conducted to improve our understanding of those who might be willing to supply switchgrass to an emerging energy market. The results of this survey provide information on the willingness of Tennessee's agricultural producers to grow switchgrass as an energy crop and the acreage that these producers would be willing to convert to switchgrass production. The majority of respondents had not heard of growing switchgrass for energy production and roughly half were unsure as to whether they would be willing to grow switchgrass. For those with an opinion about whether they would grow switchgrass, a two limit Tobit model of acreage share was used to ascertain the effects of various farm and producer characteristics on the share of acreage they would be willing to convert to switchgrass.

The quantities of mill residues generated at primary wood mills (i.e., mills producing lumber, pulp, veneers, other composite wood fiber materials) in the U.S. are obtained from the data compiled by the USDA Forest Service for the 1997 Resource Policy Act (RPA) Assessment (USDA, 1998a). Mill residues are classified by type and include bark; coarse residues (chunks and slabs); and fine residues (shavings and sawdust). Data is available for quantities of residues generated by residue type and on uses of residues by residue type and use category (i.e., not used, fuel, pulp, composite wood materials, etc.). Data is available at the county, state, subregion, and regional level. In cases where a county has fewer than three mills, data from multiple counties are combined to maintain the confidentiality of the data provided by