Marie E. Walsh

Energy and Environmental Aspects of Using Corn Stover for Fuel Ethanol

Summary Corn 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 biocon-version 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 todays corn-starch-derived 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 CO2, N2O, and CH4) 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.

Evaluating environmental consequences of producing herbaceous crops for bioenergy.

Abstract 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 Energys Bioenegy Feedstock Development Program (BFDP), has chosen to focus its primary herbaceous crops research emphasis on a perennial grass species, switchgrass ( Panicum virgatum) . The choice of switchgrass as a model bioenergy species was based on its high yields, high nutrient use efficiency and wide geographic distribution. Another important consideration was its positive environmental attributes. The latter include its positive effects on soil quality and stability, its cover value for wildlife, and relatively low 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 addition potential reductions in CO 2 emissions, tied to the energetic efficiency of producing transportation fuels and replacing non-renewable petrochemical fuels with ethanol derived from grasses are very promising. Calculated carbon sequestration rates may exceed those of annual crops by as much as 20–30 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 improved understanding of the long term changes in soil quality associated with annual removal of high yields of herbaceous energy crops.

U.S. bioenergy crop economic analyses: status and needs

Abstract U.S. bioenergy crop production cost, supply curve, and transportation cost studies are summarized and compared. Production cost estimates range from

Methodology for Estimating Removable Quantities of Agricultural Residues for Bioenergy and Bioproduct Use

A methodology was developed to estimate quantities of crop residues that can be removed while maintaining rain or wind erosion at less than or equal to the tolerable soil-loss level. Six corn and wheat rotations in the 10 largest corn-producing states were analyzed. Residue removal rates for each rotation were evaluated for conventional, mulch/reduced, and no-till field operations. The analyses indicated that potential removable maximum quantities range from nearly 5.5 million dry metric t/yr for a continuous corn rotation using conventional till in Kansas to more than 97 million dry metric t/yr for a corn-wheat rotation using no-till in Illinois.

Economic Competitiveness of Bioenergy Production and Effects on Agriculture of the Southern Region

The economic competitiveness of biobased industries is discussed by comparing the South relative to other regions of the United States and biomass as a feedstock source relative to fossil fuels such as coal and petroleum. An estimate of the biomass resource base is provided. Estimated changes in the agricultural sector over time resulting from the development of a large-scale biobased industry are reported, and a study on the potential to produce electricity from biomass compared with coal in the southern United States is reviewed. A biobased industry can increase net farm income and enhance economics development and job creation.

The economics of biomass production in the United States

Biomass crops (e.g. poplar, willow, switchgrass) could become important feedstocks for power, liquid fuel, and chemical production. This paper presents estimates of the potential production of biomass in the US under a range of assumptions. Estimates of potential biomass crop yields and production costs from the Department of Energy`s (DOE) Oak Ridge National Laboratories (ORNL) are combined with measures of land rents from USDA`s Conservation Reserve Program (CRP), to estimate a competitive supply of biomass wood and grass crops. Estimates are made for one potential biomass use--electric power production--where future costs of electricity production from competing fossil fuels set the demand price. The paper outlines the methodology used and limitations of the analysis.

Method to estimate bioenergy crop feedstock supply curves

Abstract This paper describes a partial equilibrium method that has been used to estimate national bioenergy crop supply curves in the US. The method requires information about the number of hectares (acres) suitable for bioenergy crop production by land type and region, bioenergy crop yields and production costs for the corresponding land types and regions, and the profitability of the land in alternative uses. We describe how this information can be integrated to create supply curves and discuss the limitations and weaknesses of the approach.

A framework to assess regional environmental impacts of dedicated energy crop production.

Numerous studies have evaluated air quality and greenhouse gas mitigation benefits of biomass energy systems, but the potential environmental impacts associated with large-scale changes in land-use patterns needed to produce energy crops have not been quantified. This paper presents a framework to assess the potential soil, water, and biodiversity impacts that may result from the large-scale production of dedicated energy crops. The framework incorporates producer economic decision models with environmental models to assess changes in land use patterns and to quantify the consequent environmental impacts. Economic and policy issues that will affect decisions to produce energy crops are discussed. The framework is used to evaluate erosion and chemical runoff in two Tennessee regions. The analysis shows that production of dedicated energy crops in place of conventional crops will significantly reduce erosion and chemical runoff.

Agricultural Impacts of Biofuels Production

Analysis of the potential to supply 25% of projected 2025 U.S. transportation fuels indicates sufficient biomass resources are available to meet increased demand while simultaneously meeting food, feed, and export needs. Corn and soybeans continue to be important feedstocks for ethanol and biodiesel production, but cellulose feedstocks (agricultural crop residues, energy crops such as switchgrass, and forestry residues) will play a major role. Farm income increases, mostly because of higher crop prices. Increased crop prices increase the cost of producing biofuels.

Economic Impacts of Carbon Taxes and Biomass Feedstock Usage in Southeastern United States Coal Utilities

The Southeastern United States depends on coal to supply 60% of its electricity needs. The region leads in CO2 emissions and ranks second in emissions of SO2 and NO2. Compared with coal, biomass feedstocks have lower emission levels of sulfur or sulfur compounds and can potentially reduce nitrogen oxide emissions. This study examines the economic impacts of cofiring level scenarios. Economic impacts are estimated for producing, collecting, and transporting feedstock; retrofitting coal-fired utilities for burning feedstock; operating cofired utilities; and coal displaced from burning the feedstock.