Perennial Grasses for Energy and Conservation: Evaluating Some Ecological, Agricultural, and Economic IssuesMark Downing1, Marie Walsh 1Energy Division and Biofuels Feedstock Development Program, 2Energy Division, and 3Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6422. Sponsored by the Biofuels Systems Division, U.S. Dept. of Energy, under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corp. (Corresponding author: MD) From Environmental Enhancement Through Agriculture: Proceedings of a Conference, Boston, Massachusetts, November 15-17, 1995, Center for Agriculture, Food and Environment, Tufts University, Medford, MA. |
IntroductionPerennial prairie grasses offer many advantages to the developing biofuels industry. High-yielding varieties of native prairie grasses such as switchgrass (Panicum virgatum) have low nutrient demand, a diverse geographical growing range and high net energy yields, and offer important soil and water conservation benefits. These crops can supplement annual row crops such as corn in the developing alternative fuels market. However, displacement of row crops by perennial grasses will have major agricultural, economic, social and cross-market implications. To analyze the implications of using lignocellulosic materials to produce ethanol or other fuels, we discuss four related topics: 1) the U.S. energy markets and the niche that biofuels may fill; 2) the contribution of agriculture; 3) economic barriers and the role of technology in reducing them; and 4) the environmental effects of biomass fuels. The need to integrate these considerations is the reason that the eventual benefits of producing liquid fuels from biomass are so complex and often misunderstood. We first outline the U.S. energy situation and the opportunity for producing ethanol from lignocellulosic crops. However, this opportunity is affected by the heavy subsidies currently given for converting corn grain to ethanol. Technological development and advanced engineering could produce vast quantities of ethanol cheaply in a fixed market. Another consideration is that significant environmental issues recently have become important in the debates over producing energy crops. Environmental concerns also have been voiced with respect to current agricultural production, but not with the same intensity. |
The Energy Situation in the United StatesThe need for alternative fuels Transportation fuels in this country have been dominated by oil for nearly 100 years. The supply of oil is finite and its extraction and use are environmentally damaging. Energy price shocks have had dislocating effects. Eventually, we will need alternatives to current transportation fuels, although we do not know exactly when. A longer-term perspective is important in developing bioenergy systems. Most current development in this area has been catalyzed by environmental mandates from the U.S. Environmental Protection Agency (EPA) and by supply and demand shocks in the oil market. Fuel cells and methanol for internal combustion engines are two alternatives to gasoline. Fuel cells that generate electricity from hydrogen or methanol are still being developed. Energy from fuel cells is currently seen as more expensive than gasoline. To operate fuel cells on methanol contributes to the greenhouse effect. To operate them on hydrogen requires remote generation of hydrogen. For internal combustion engines, methanol is less expensive than gasoline, but it must be produced from natural gas and therefore does not reduce the greenhouse effect (Foody, 1988). Ethanol is another alternative to fossil fuels for powering internal combustion engines, and is the focus of this paper. Ethanol can be blended at 10% with 90% gasoline or used neat (100% ethanol). It currently is used to enhance octane levels in gasoline and as a cosolvent for other fuel additives. Its ability to substitute for other additives that have harmful emissions eventually may add economic value beyond its value simply as a gasoline additive. The increased use of renewable fuels offers the United States a strategy for significantly reducing its dependence on imported oil (Lynd et al., 1991; Robertson and Shapouri, 1993). Several renewable feedstocks can be used to produce ethanol while providing diverse benefits to the national agricultural economy: sugar, grains, wood, agricultural residues, herbaceous crops (such as sorghum and switchgrass), municipal wastes, and paper. Currently, U.S. ethanol production is 1426 million gallons per year, of
which 1235 million gallons is produced from corn ( Net energy projections The capacity of energy crops to offset imported energy will depend on their energy yield net of the energy used to grow, harvest and convert them. Extensive studies have found a conversion efficiency of nearly 5: 1 (units of energy out per unit in). Switchgrass requires less energy to produce than does corn. One acre of corn grain contains 50 million BTU and requires 7.6 million BTU to produce, for an energy output/input ratio of 6.6. When the corn stover is included, the energy efficiency ratio improves to 8.8. In comparison, switchgrass will produce 20.6 times the energy required to
produce it if it is transported directly to the ethanol plant. The higher ratio
for switchgrass occurs largely because it is a perennial (remaining in
production for ten years or more before replanting) and because of its lower
chemical and fertilizer requirements. These calculations used chemical and
fertilizer application rates from U.S. Department of Agriculture ( |
Agricultural Benefit and Agronomic Potential After it screened numerous annual and perennial species ( Perennial grasses were an ecological cornerstone of the early American
prairie because of their forage quality and soil stabilizing attributes ( |
EconomicsThe BFDP staff, economists at Oak Ridge National Laboratory, and others have extensively researched the economics of switchgrass production and its potential in the United States. Production budgets are now being empirically verified as DOE begins to fund large plantings of switchgrass for energy. Expansion of ethanol production from its current level of 0.8 billion gallons per year to one that will significantly reduce dependence on foreign oil imports is anticipated to increase agricultural production and productivity and provide additional income for farmers. Thus it will have implications for production of several crops. Under the assumption that increased ethanol production will be achieved using corn, USDA's Economic Research Service estimated agricultural impacts for two scenarios: an increase to 2 billion gallons by 1995; and an increase to 5 billion gallons by 2000. In the first scenario, corn area increases by 1.1 million ha and net farm income by $153 million; in the second, corn increases by 3.8 million ha and net farm income by $1.6 billion. Only the second scenario is projected to affect other agricultural production significantly, including a loss of $550 million in livestock production because of higher feed costs from the increased competition for corn. There will be important regional differences in the gains and losses from meeting additional bioenergy needs solely with corn. The main economic gains will be in the major corn producing regions: the Corn Belt, the Lake States, and parts of the Great Plains. Cattle production losses will be spread more evenly across all cattle producing states. Thus, despite a national agricultural gain, the southeastern and mid-Atlantic states will experience a net economic loss that will be augmented by a loss of approximately 240,000 ha of soybean and cotton because of shifts in grain production. In contrast, a shift to perennial grasses could be achieved using land with a much broader quality range. This would have little effect on other crops and would spread the benefits more evenly across the country. The South, which currently has a depressed agricultural economy, so far has the highest yields of warm-season perennial grasses and would be among the most suitable areas for biofuel production. |
Economic factors affecting commercial feasibility Foody (1988) noted that the technology for producing ethanol from biomass was improving rapidly and that laboratory results were approaching the limits of technical and economic feasibility. Neat ethanol could compete with gasoline in the current marketplace at an oil price of $20 to $30 per barrel. A successful demonstration of economically competitive ethanol production would dramatically change the debate over energy-related environmental problems. Fuel ethanol's primary advantage is environmental, as it burns much more cleanly than gasoline. When derived from lignocellulosic biomass, it is the only liquid transportation fuel that does not contribute to the greenhouse effect (Foody, 1988). Many additional factors will affect its commercial feasibility. Successful
development of enzymatic hydrolysis technology will be crucial. The process for
making ethanol from lignocellulosic biomass involves seven major steps: biomass
production, pretreatment, enzyme production, enzymatic hydrolysis,
fermentation, distillation, and by-product processing. (For more on these
steps, see Foody, 1988.) Since these processes are
interdependent, improving one may decrease the ability to make improvements in
another. Finally, the ability to market by-products and co-products is crucial
to the economic viability of a commercial system ( |
Conservation Reserve Program The Conservation Reserve Program (CRP) was initiated under the Food Security Act of 1985, largely to stabilize and improve soils degraded by overcropping. Almost 15 million ha were idled by this law, primarily in the Great Plains and Southeast. Much of this land was replanted to perennial grasses that were the principal species of the original prairie. Predominant species were big bluestem (Andropogon gerardi Vitman), Indian grass (Sorghastrum nutans [L.] Nash), western wheatgrass (Agropyron smithii Rydb.) and switchgrass. CRP is at a critical point after 10 years of contracting with agricultural producers. Renewal or elimination options are currently being considered in the 1995 Farm Bill. Critics see it as an unnecessary expense with questionable benefits to taxpayers. However, recent consideration of both the resource conservation benefits of CRP and the cost of subsidies if these lands are returned to annual crops, notably wheat, suggests that CRP represents a gain to taxpayers. An alternative to returning these lands to the very practices that made CRP necessary would be to use them for energy crops that can both enhance land quality and provide an economic return to landowners. This possibility is strengthened by the fact that the native perennial grasses planted under the CRP also are excellent for production of liquid fuels. |
Environmental ConsiderationsPerennial grasses grown under CRP conserve the soil and improve its quality. They also provide excellent protective cover and food for wildlife. The significant reduction in soil erosion is their most obvious advantage over row crops such as corn. Soil loss from annual cropping of erodible land can be very high, resulting in the loss of valuable nutrients and the contamination of adjoining areas and wetlands by sediments and chemicals. Typically, soil loss is several orders of magnitude greater with annual crops than with perennial grasses (Shifflet and Darby, 1985), especially during heavy rains. Loss of soil organic matter (SOM) also is greater with annual crops,
because it breaks down faster under tillage and because more SOM-rich topsoil
is removed by erosion (Buckman and Brady, 1960). The
current loss of soil organic matter in the US through annual row cropping is
estimated at 2.7 million t per year (Council for
Agriculture, Science, and Technology, 1992). This loss is important not
only because it equals 7.5 % of the total carbon released to the atmosphere by
combustion of fossil fuels, but because SOM is critical for soil productivity.
The soil's moisture-holding capacity, density, aeration, and ability to supply
and conserve plant nutrients all are improved by SOM ( Recent studies of the changes in SOM during five years of perennial grass production on CRP lands indicate that perennial grasses added C at an annual rate of 1.1 t/ha to the upper 100 cm of CRP soils (Gebhardt et al., in press). These additions replaced 23 % of the soil carbon that was lost during decades of prior tillage. The source of this carbon is the large standing pool of roots, which can equal or exceed annual aboveground production (Anderson and Coleman, 1985) and which turn over rapidly. Preliminary data from research on switchgrass grown for energy indicate that belowground root mass is very high, totaling almost 8 t/ha just in the top 75 cm (Bransby et al., 1994). With Alamo switchgrass (P. virgatum cv. 'Alamo'), over 1 t/ha was found just in the interval 60-75 cm. |
SummaryPerennial grass production for biofuels offers significant advantages for a national energy strategy that considers both environmental and economic issues. The benefits of using a native prairie species such as switchgrass rather than annual crops such as corn include: improved soil quality; reduced soil erosion and associated water pollution; reduced emissions of greenhouse gases; increased efficiency of land and energy use; and a more equitable distribution of economic benefits to farmers. To achieve these benefits in a timely manner will require us to look beyond the short-term and consider not just the supply of municipal wastes, crop residues and other wastes that can serve as feed-stocks for industrial uses; we also should consider growing crops specifically for energy. Our planning should include accelerated commercialization of both ethanol conversion and grass-fired combustion systems. We also should study the options for maintaining landowner participation in a conservation reserve program that achieves conservation objectives with reduced subsidies, and for involvement of landowners in energy crop production. The benefits of these strategies for the economy and environment of the nation are too obvious to ignore. |
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