2
Biomass Resources for Liquid Transportation Fuels

America’s transportation systems will undergo major and multifaceted transformations as the nation addresses human-driven climate change, the availability and cost of liquid transportation fuels, and the need for energy security. Plant biomass has the potential to play an important role in America’s energy future. Plants convert solar energy to chemical energy naturally for their growth and development through the process of photosynthesis. Plant biomass can be produced sustainably and converted into liquid transportation fuels via biochemical conversion (Chapter 3) or thermochemical conversion (Chapter 4). Liquid transportation fuels derived from biomass feedstock are often referred to as biofuels. The amount of biomass that can be produced in an area depends on the local availability of sunlight, water, and other resources. In principle, biofuels are attractive alternatives to gasoline because they are made from renewable feedstocks and can decrease the net release of greenhouse gases by the transportation sector. Although those benefits are important, they must be viewed in the context of other societal needs that are also met by the nation’s land base, especially needs for food, feed, fiber, potable water, carbon storage in ecosystems, and preservation of native habitats and biodiversity. Responsible development of feedstocks for biofuels and expansion of biofuel use in the transportation sector would be economically, environmentally, and socially sustainable. This chapter addresses the questions raised in the statement of task regarding the following:

  • The quantities of biomass that could potentially be produced and collected in a sustainable manner for use as feedstocks for liquid transportation fuels.



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2 Biomass Resources for Liquid Transportation Fuels A merica’s transportation systems will undergo major and multifaceted transformations as the nation addresses human-driven climate change, the availability and cost of liquid transportation fuels, and the need for energy security. Plant biomass has the potential to play an important role in America’s energy future. Plants convert solar energy to chemical energy natu- rally for their growth and development through the process of photosynthesis. Plant biomass can be produced sustainably and converted into liquid transporta- tion fuels via biochemical conversion (Chapter 3) or thermochemical conversion (Chapter 4). Liquid transportation fuels derived from biomass feedstock are often referred to as biofuels. The amount of biomass that can be produced in an area depends on the local availability of sunlight, water, and other resources. In prin- ciple, biofuels are attractive alternatives to gasoline because they are made from renewable feedstocks and can decrease the net release of greenhouse gases by the transportation sector. Although those benefits are important, they must be viewed in the context of other societal needs that are also met by the nation’s land base, especially needs for food, feed, fiber, potable water, carbon storage in ecosystems, and preservation of native habitats and biodiversity. Responsible development of feedstocks for biofuels and expansion of biofuel use in the transportation sector would be economically, environmentally, and socially sustainable. This chapter addresses the questions raised in the statement of task regarding the following: • The quantities of biomass that could potentially be produced and col- lected in a sustainable manner for use as feedstocks for liquid transpor- tation fuels. 

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 Liquid Transportation Fuels from Coal and Biomass • The input and costs involved in growing and harvesting the crops or in collecting the feedstock and delivering it to a biorefinery for production of liquid transportation fuels. • The land-use, agricultural, price, greenhouse gas, and other environ- mental implications of biomass production for liquid fuels. • Research and development (R&D) needed to advance production of biomass feedstock for transportation fuels. The chapter examines the quantities of different types of biomass that can be harvested or produced while minimizing competition between food and fuel and minimizing adverse environmental effects. It also assesses the total costs of various feedstocks that will be delivered to a processing plant for conversion to biofuel. The panel considered societal needs on the basis of recent analyses that have explored tradeoffs between using land for biofuel production and using it for food, feed, fiber, and other ecological services that land resources provide. CURRENT BIOMASS PRODUCTION FOR BIOFUELS Biofuel produced in the United States is overwhelmingly dominated by ethanol made from corn grain; biodiesel derived from soybean oil makes up most of the remainder. In the 2007 crop year (from September 2, 2007, to August 31, 2008), 3.0 billion bushels of corn, or 23 percent of the year’s harvest, was used to pro- duce 8.2 billion gallons of ethanol (NCGA, 2008). Around 450 million gallons of biodiesel were also produced, about 90 percent of which was derived from the oil extracted from 275 million bushels of soybean, 17 percent of the year’s harvest (USDA-NASS, 2008a; NBB, 2008). On an energy-equivalent basis (in British ther- mal units), corn grain ethanol and soybean biodiesel together made up 2.1 percent of the liquid transportation fuel used in the United States in 2007 (EIA, 2008). The social, economic, and environmental effects of domestic biofuels have been mixed. Diverting corn, soybean oil, or other food crops to biofuel produc- tion could induce competition among food, feed, and fuel, but increases in crop price have helped to revive rural economies. From the perspective of farmers and small rural communities, development of ethanol plants has created greater local demand and higher prices for corn grain (and for soybean through parallel efforts associated with production of biodiesel). Local investment in and con- trol of these plants have also provided well-paying employment opportunities

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Biomass Resources for Liquid Transportation Fuels  that reinvigorated many small midwestern communities, but some argue that the number of jobs added to the local economy is overestimated (Low and Isserman, 2009). For farmers, the increase in corn grain prices, which averaged $2.36 ± 0.40 per bushel of grain (25 kg) in 1973–2005 but $3.04 and $4.00 per bushel in 2006 and 2007 (USDA-NASS, 2008a), was of great importance. The increased prices were results of an increased global demand for corn as animal feed and for grain ethanol production. Higher commodity prices have also led to markedly higher values of fertile farmland, and have adversely affected low- income consumers in the United States and abroad and the drawing of land out of the U.S. Conservation Reserve Program (CRP). On a global scale, high com- modity prices are expected to accelerate clearing of rain forest and savanna. There is growing concern about the use of grain for fuel instead of food. Other environmental concerns, especially the loss of nitrogen by leaching (Donner and Kucharik, 2008), have also been pointed out. Corn and soybean are renewable biofuel feedstocks, but large amounts of fertilizer and pesticide are often needed to grow them (Hill et al., 2006). The resulting greenhouse gas and other pollutant effects of those practices can be harmful to human health and the environment. Corn grain ethanol and soybean biodiesel are viewed by some as interme- diate fuels in the transition from oil to advanced biofuels made from cellulosic biomass. As a biofuel feedstock, cellulosic biomass has numerous advantages over food and feed crops, including its availability from sources that do not compete with food and feed production. Biomass can be reclaimed from municipal solid- waste streams and from residual products of some forestry and farming opera- tions. It can also be grown on idle or abandoned cropland, on which food or feed production is already minimal. Growing cellulosic biomass can require less fossil fuel, fertilizer, and pesticide inputs than growing corn and soybean (Tilman et al., 2006), especially if legumes (nitrogen-fixing plants) are included in the mix (NRC, 1989). In addition, cellulosic biomass can serve not only as a feedstock for biofuel production but also as a source of the heat and power required for biorefineries and thus displace fossil fuels and fossil-fuel-derived electric power (Morey et al., 2005). Therefore, this chapter focuses on the biomass resources available for cel- lulosic biofuel production. Sustainable Production of Biomass for Conversion to Biofuels Globally, about 12 billion acres of land are used for agriculture, about 4 bil- lion of which are cultivated and the remainder used for grazing. Any substantial

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 Liquid Transportation Fuels from Coal and Biomass expansion of agriculture to accommodate dedicated biofuel crops via the direct conversion of natural ecosystems—such as native rain forests, savannas, and grasslands—into cropland could threaten those ecosystems and reduce their bio- diversity. Biofuels can also indirectly cause land to be cleared when fertile agricul- tural soils or food crops are used for biofuels. Such indirect land clearing provides land used to grow “replacement” food crops. Moreover, intact ecosystems are major storehouses of carbon: terrestrial vegetation stores as much carbon as the atmosphere does, and terrestrial soils store twice as much (Schlesinger, 1997). Dry biomass—whether wood of trees, hay, or corn stover—contains about 45 percent carbon. On combustion or decomposition, every ton of dry biomass contributes about 1.5 tons of carbon dioxide (CO2) to the atmosphere. In many cases, conver- sion of intact ecosystems to grain or fuel-crop production could incur losses of biomass and soil carbon to the atmosphere as CO2 that greatly exceeds the green- house gas savings associated with biofuel production on such lands for many years (Box 2.1) (Fargione et al., 2008; Searchinger et al., 2008). Biofuels offer opportunities for greenhouse gas reductions, but large amounts of cellulosic biomass will be needed. Sustainably produced biomass would be derived from various agricultural or forestry residues, from current waste streams, or from dedicated fuel crops grown on agricultural reserve land or on land so degraded that it is no longer cost-effective for commodity production (Tilman et al., 2006). The United Nations Environment Programme and other sources estimate that globally there are about 400–500 million hectares of such land (Campbell et al., 2008; Field et al., 2008). Collecting agricultural residues and producing biofuel crops both have environmental benefits and costs. Removing biomass and crop residues, such as corn stover, could increase soil erosion by wind and water and deplete soil car- bon reserves, ultimately affecting water entry, retention, runoff, nutrient cycling, productivity, and other critical functions. Depending on the crop, soil type, and terrain, various amounts of biomass or crop residues need to be left on a field to mitigate soil erosion and sustain soil carbon and nitrogen (Wilhelm et al., 2007). The proportion of biomass that has to be left on the soil surface to prevent ero- sion is higher for annual crops than for perennial crops because of the tillage gen- erally used to establish a new crop each year. Perennial crops, especially grasses, have dense long-lived root systems that can maintain soil resources. When ecosystems are cleared of perennial vegetation and converted to annual row crops, soil carbon stores tend to decline by 30–50 percent until a new equilib- rium is reached (Davidson and Ackerman, 1993). Removal of plant residues, such

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Biomass Resources for Liquid Transportation Fuels  as corn stover or wheat or rice straw, without such offsetting practices as grow- ing cover crops or decreasing tillage intensity, could reduce soil carbon to a lower equilibrium. A portion of the crop residue is needed for erosion and nutrient man- agement and to sustain soil organic carbon, which is the carbon fraction associ- ated with all types of organic matter, including plant and animal litter, microbial biomass, water-soluble organic compounds, and stabilized or recalcitrant organic matter (Stevenson, 1994; Johnson et al., 2006a). Removing plant residues for any purpose would decrease the annual carbon input, gradually diminish soil organic carbon (Figure 2.1), and threaten the soil’s production capacity (Johnson et al., 2006a). Therefore, a “systems” approach1 is required for sustainable biomass pro- duction to ensure that its production has a low impact on global food, feed, and fiber production and that addressing the biofuel problem does not aggravate other critical challenges, including soil, water, and air quality; carbon sequestration; greenhouse gas emissions; rural development; and wildlife habitat. A Landscape Vision of Feedstock Production The rapidly emerging technologies to develop and use lignocellulosic materials for production of bioenergy and bioproducts might offer an opportunity to reduce the environmental footprint of the transportation sector and improve the envi- ronmental sustainability of agriculture. For example, periodically mown peren- nial biomass crops could be used to reduce some of the agricultural production “externalities” if they are planted as buffer strips and in locations that would help to reduce soil erosion, improve water quality, sequester carbon, and provide wild- life habitat (Tilman et al., 2006; Doornbosch and Steenblik, 2007; Ernsting and Boswell, 2007; Fargione et al., 2008; Searchinger et al., 2008). Implementation of a landscape approach for producing biofuel feedstocks while addressing some of the externalities associated with agriculture could be made more feasible by precision agriculture (Giles and Slaughter, 1997; Tian et al., 1999; Ferguson et al., 2002; Khosla et al., 2002; Robert, 2002) and other changes (Zhang et al., 2002; Berry et al., 2003; Dinnes, 2004). Examples of how water- shed-scale or landscape-scale management could potentially address those multiple 1A “systems approach” to agriculture is a holistic or integrated framework that recognizes the connectivity of multiple processes that occur on the farm and in the ecosystem and that reach across spatial, temporal, and trophic dimensions and scales. The systems approach examines the connections and interactions between the different components that make up a system so that the relative effects of change on each component can be understood.

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 Liquid Transportation Fuels from Coal and Biomass BOX 2.1 Effects of Land-Use Change on Greenhouse Gas Emissions Recent studies have focused on the life-cycle greenhouse gas emissions from differ- ent biofuels compared with gasoline or diesel. Despite some important disagreement, the prevailing view is that corn grain ethanol emitted less greenhouse gas than did gasoline, that biofuels from sugarcane provided an even greater benefit, and that cellulosic ethanol, once commercialized, would further increase the benefit (Farrell et al., 2006; Hill et al., 2006; Wang et al., 2007). Some earlier studies recognized that carbon sequestration achieved by changing practices to reduce carbon on a landscape could be offset by increased carbon releas- es on other landscapes, which would result in a smaller net decrease or even a net increase in total carbon emission (Murray et al., 2004; IPCC, 2006). However, emissions from change in land use were not explicitly included in the comparative analyses of different biofuels in the life-cycle assessment. If land is cleared and used to grow plants for biofuels, much of the carbon stored in the biomass and some of that in the soil is released as CO2. A more complete life-cycle analysis than the earlier biofuel analyses would deduct the carbon lost into the atmosphere from land-clearing and no longer being stored in an ecosystem. That approach is being implemented by the U.S. Environmental Protection Agency under the 2007 renewable fuels standard man- dated in the Energy Independence and Security Act (EISA). Fargione et al. (2008) determined the greenhouse gas carbon released in convert- ing forest or grassland to biofuel production, which they called the “carbon debt,” and the years of biofuel production required to “pay back” the debt. They argued that the carbon debt would arise from land where upland and lowland forest in Southeast Asia was converted to produce palm oil, where various forms of cerrado forest in Brazil were converted for production of biodiesel fuel, and where CRP grass- lands were converted to corn for ethanol—scenarios with payback periods of 48 years (the CRP) to more than 400 years (lowland palm oil). If land converted to biofuel production had been sequestering carbon, as would occur with regrowing forests and conservation grasslands, it is also necessary to con- sider the greenhouse gas effects of forgoing the benefits that would have occurred on the same land if it had not been used for biofuel production. Similarly, in a global agricultural system, if land used for food production is converted to biofuel produc- tion, some portion of the decrease in food production will be replaced by cultivation elsewhere and to a substantial extent through the conversion of noncropland to cropland (Searchinger et al., 2008). This indirect cause of converting forest and grass- land to cropland also creates a carbon debt that needs to be accounted for in order to evaluate effects on greenhouse gases fully. Searchinger et al. (2008) used the international model developed by the Center for Agricultural and Rural Development at Iowa State University and the Food and Agricultural Policy Research Institute at Iowa State University and the University of Missouri–Columbia to estimate emissions from such indirect land-use changes. They found that each acre of corn diverted to ethanol in the United States would result in roughly 0.8 acre of new cropland worldwide. They concluded that U.S. corn grain ethanol increased greenhouse gas emissions over 30 years by 93 percent relative to

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Biomass Resources for Liquid Transportation Fuels  gasoline and that it would take 167 years to pay back the carbon debt. Ethanol made from switchgrass grown on former corn land increased emissions over 30 years by 50 percent relative to gasoline. Estimating effects of land-use change on greenhouse gas emissions requires a worldwide agricultural land-use model, a basis of estimating which ecosystems will contribute to new cropland, and a basis of estimating carbon release per hectare. Each step contains uncertainties. The path through which land conversion takes place is complicated, requiring consideration of animal-feed by-products of biofuel pro- duction, crop-switching, reduction in food demand as a result of higher prices, likely regions of expansion, different yields in different countries, and alternative means of increasing production (for example, increased fertilizer use, drainage, or irrigation). All those factors interact and require at least a partial-equilibrium model for analysis. Because of the complexity, the exact magnitude of indirect carbon debt is difficult to determine with great certainty. Nevertheless, the analyses of Searchinger et al. (2008) show that conversion of fertile farmlands to biofuel production is likely to have caused substantial indirect greenhouse gas release via land conversion to pasture or row crops and that indirect effects cannot be ignored in determining the full life-cycle greenhouse gas effects of biofuels. The best way to minimize such indirect effects is to avoid using for biofuel production those fertile lands that are well suited for food and feed production. One way to deal with indirect land-use conversion, followed by the EISA, is to require calculation of indirect land-use change for each source or type of biofuel and to mandate only the biofuels that achieve specified reductions in greenhouse gas emissions relative to those from gasoline. The requirement has the obvious benefit of encouraging only biofuels that, on balance, reduce greenhouse gas emissions. One limitation of the approach is the failure to consider effects on food production and prices or other environmental effects of agricultural expansion, including loss of biodiversity and other ecosystem services. An alternative approach that takes into account both food and carbon limitations would mandate or provide incentives only for biofuels that present little risk of substantial emissions from land-use change. Such a policy would emphasize biofuel production from waste products or from feed- stocks grown on marginal land (that is, areas that sequester little carbon or produce little food but can produce biomass for biofuels). Such a policy would be designed to avoid greenhouse gases, biofuel-food competition, and other potential environmen- tal effects of agricultural expansion on water quality or quantity and biodiversity. It would also avoid the difficulty of estimating greenhouse gas emissions from indirect land-use conversions accurately. In summary, the greenhouse gas benefit of biofuels compared with petroleum- based fuels depends not only on direct greenhouse gas emissions from biofuels during their life cycle (that is, from the growth of biomass to the production and burning of the biofuels) but also on any indirect emissions that might be incurred by changes in land use. The appropriate quantification of indirect greenhouse gas emis- sions is being debated. Policies could play an important role in ensuring that the bio- fuels produced provide environmental benefits.

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0 Liquid Transportation Fuels from Coal and Biomass Cultivation Stover Harvest Projected with cover crops Soil Organic Matter intercropping, or other Precultivation carbon input sources steady state Projected with no-till With no management change Management Change Time FIGURE 2.1 Conceptual diagram of how agriculture has affected soil organic matter and what may occur after various strategies for crop-residue removal. concerns while supplying the necessary volume of biofuel feedstocks are presented ALTF 2-1 in Appendix E. BIOMASS RESOURCES The following is an assessment of biomass resources for liquid fuel production using technologies available and management practices known in 2008 and pro- jected to be available in 2020. It is predicated on two fundamental principles: (1) that biomass production for liquid fuels should not compete for land on which an existing crop is produced for food, feed, or fiber or compete for pasture land that will be needed to feed a growing and increasingly affluent population, even with yield increases, and (2) that the environmental impact on land used for bio- mass production should be no worse than that of its previous use and provide greater benefits wherever possible (for example, reducing fuel loads in fire-prone areas, managing volumes of urban waste, and increasing soil carbon sequestra- tion in restoration of native grassland ecosystems). Although many other possible visions of biomass availability that do not hold as closely to those two principles are possible, the panel chose to conduct its assessment with those two in mind.2 2These criteria are consistent with those of Johnson et al. (2006a,b), who concluded that (1) biomass feedstocks should come first from wastes that would otherwise go to landfills, (2) agricultural residues should be harvested only when the needs for protecting soil from wind and water erosion and loss of soil organic carbon have been met, (3) dedicated fuel crops should

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Biomass Resources for Liquid Transportation Fuels  Among the biomass sources considered are corn stover, straw from wheat and seed grasses (for example, bluegrass and fescue), traditional hay crops (for example, alfalfa and clover), normal and high-yielding fuel crops, woody residues, animal manure, and municipal solid waste. Advantages of and concerns about each of these feedstocks are described below. The resource amounts that could be made available by using technologies and management practices of 2008 and the resource amounts projected to be available by 2020 are also described. Corn Stover In 2007, 13.1 billion bushels of corn grain was harvested in the United States from 86.5 million acres of cropland. Assuming a 1:1 ratio of dry weight of corn grain to stover (Johnson et al., 2006a), the amount of stover produced was esti- mated to be 370 million tons. Not all the corn stover can be used to produce biofuel, however, because this crop residue is also a “resource” that farmers use to mitigate wind and water erosion and to maintain soil organic matter. The amount of stover that needs to be left on the land for those purposes depends on the tillage practice being used as soil is being prepared for planting by plowing, ripping, or turning (Johnson et al., 2006a; Wilhelm et al., 2007). Perlack et al. (2005) estimated that no-tillage requires 0.35–0.5 ton of stover per acre to protect against wind and water erosion, but that amount of crop residue is not sufficient to control soil erosion if more aggressive tillage is used (Figure 2.2) and is not suf- ficient to sustain soil organic matter (soil carbon). To maintain soil organic matter, 2.3–5.6 tons/acre needs to be left in the field, depending on crop rotation and tillage practice (Wilhelm et al., 2007). Maintaining soil organic matter is crucial for sustaining soil structure, water entry and retention, nutrient cycling, biological activity, and other critical soil processes. Erosion control and maintenance of soil organic matter are critical factors to be considered in the estimation of the sustainable amount of corn stover that could be harvested to produce biofuel. The national average corn-grain produc- tion in 2008 was 151 bushels/acre (USDA-NASS, 2008b). If erosion is to be controlled and soil organic matter maintained, the potential harvestable corn stover even with no-tillage practices is reduced from 3.58 tons/acre to 0.06–1.25 tons/acre depending on the crop rotation (Figure 2.2). If more intensive tillage be developed regionally to meet local needs, and (4) management strategies must ensure that soils do not lose their ability to provide food, feed, fiber, and fuel.

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 Liquid Transportation Fuels from Coal and Biomass 8 Stover to Retain (Tons per Acre) Soil organic 6 Water 5.58 Wind 4 3.56 3.52 3.38 2.34 2 1.39 1.22 0.77 0.43 0.29 0.06 0.15 0 Moldboard No-tillage or Moldboard No-tillage or Plow Conservation Tillage Plow Conservation Tillage Continuous Corn Corn–Soybean FIGURE 2.2 Tillage and crop-rotation effects on the amount of corn stover required to protect soil resources against wind or water erosion and to sustain soil carbon (organic matter) levels. Source: Adapted from Wilhelm et al., 2007. ALTF 2-2 equivalent to moldboard plowing is used, as is the case for about 17 percent of U.S. corn cropland, all the corn stover in the corn–soybean rotation is required for maintenance of soil organic matter, and only 0.2 ton/acre would be available as a feedstock if corn is grown continuously. Using the higher harvestable value3 of 1.25 tons/acre and recognizing that only 70 percent of the available cropland area at most would be planted continuously in corn because of disease, insects, and other factors, the maximum sustainable amount of corn stover available as biofuel feedstock in 2007 would have been 75.7 million tons. That value, rounded to the nearest million tons, was used for the panel’s baseline estimate for the amount of corn stover that could be harvested sustainably. The panel’s projection of 112 million tons available by 2020 was calculated in a similar manner and allowed for increased yield as a result of genetic improvement and improved management. (See Appendix F for details of those estimates.) 3The panel used the high harvestable value because it took a conservative approach to esti- mating the amount of stover that has to be left in the field to maintain soil.

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Biomass Resources for Liquid Transportation Fuels  Wheat Straw and Seed-Grass Straw Wheat straw and grass straw can be biofuel feedstocks as the technology to con- vert them to liquid fuels develops. Banowetz et al. (2008) estimate that the Pacific Northwest states of Idaho, Oregon, and Washington could provide at least 6.5 million tons of crop residues with the wheat straw and grass straw yields in 2007 after the appropriate amount of wheat straw and grass straw are left on the field to protect soil resources. However, those straws are often distributed across the landscape at an average available density of about 1 ton/acre, so transporting them to centralized biomass-processing plants would probably increase transpor- tation costs and transportation-dependent greenhouse gas releases. One approach for overcoming those limitations would be to establish localized preprocessing and densification centers. Similar estimates by Nelson (2002) for Kansas, Texas, Ohio, Illinois, and Missouri projected the availability of another 8.8 million tons of wheat straw for harvest from the Great Plains each year. The panel estimated that 15 million dry tons of wheat and grass straws per year could be available for fuel production on the basis of earlier studies. It assumed a 20 percent increase in available wheat and grass straws by 2020. Hay U.S. hay production ranged from about 50 million tons in 1999 to about 142 million tons in 2006 (USDA-NASS, 2008b). The average yield in 2007 was 2.4 tons/acre. Most hay is consumed as animal feed, but as with corn grain, aver- age yields are often lower than many good producers achieve. On the basis of the 30-year record of increases in hay yields, the panel estimated that 10 percent of the average production for 2003–2007 (15 million tons) could be available for biofuel production without substantially affecting the hay price and supply. The portion of the hay crop used as biofuel feedstock was assumed to have very low nutritional quality for animal production because of excessive weathering. The low-quality hay would be marketed only in areas where biofuel plants provided an alternative marketing option to local farmers. The assumed supply of hay for use as a biofuel feedstock is small because hay production is dispersed, bulky, and expensive to transport. As with wheat and grass straws, the panel’s projection of available hay for biofuels in 2020 was based on a 20 percent yield increase as a result of better genetics and management practices.

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