By Kristen Johnson
The Department of Energy (DOE) has set the goal of making cellulosic ethanol cost-competitive by 2012, and by 2030, it aims to make biofuels displace 30% of the country’s projected gasoline use. Some of the primary types of feedstocks being considered to meet these goals are crop residues, perennial woody crops, and perennial grasses. Perennial grasses have been a particular focus, with switchgrass receiving the most attention. Switchgrass, a native tall-grass prairie species, is considered most promising because of its high yields, low inputs, and ability to adapt to a variety of conditions. But an important question concerning the sustainability of this feedstock is: where should this perennial grass be grown?
The Department of Energy (DOE) has set the goal of making cellulosic ethanol cost-competitive by 2012, and by 2030, it aims to make biofuels displace 30% of the country’s projected gasoline use (USDOE, 2007). Some of the primary types of feedstocks being considered to meet these goals are crop residues, perennial woody crops, and perennial grasses. Perennial grasses have been a particular focus, with switchgrass receiving the most attention. Switchgrass, a native tall-grass prairie species, is considered most promising because of its high yields, low inputs, and ability to adapt to a variety of conditions (USDOE website). But an important question concerning the sustainability of this feedstock is: where should these perennial grasses be grown? This article summarizes two types of land on which perennial grass for cellulosic ethanol could be grown—land used for row crops and Conservation Reserve Program (CRP) land. It also discusses ways in which converting this land to biomass production could either be a benefit or detriment to habitat, carbon mitigation, and environmental quality. While not comprehensive, these are the types of issues that must be considered for sustainable adoption of cellulosic ethanol. Furthermore, these two options represent many of the trade-offs involved in choosing where to grow grassy biomass.
Row Crops to Perennial Grasses
Land currently used to grow row crops would provide one source of land for perennial grass production. The primary concern associated with this conversion is that less cropland would be available for food production, leading to diminished food supplies and increased food prices (Carey 2005). However, this competition could be mitigated if switchgrass is grown on land currently used to grow corn for ethanol. It is estimated that about 20% of harvested corn goes into ethanol production (Yates, 2008). Based on this percentage and the amount of corn acreage grown in 2008, approximately 16.5 million acres would open up for switchgrass production if corn ethanol were replaced.
Replacing corn acreage with switchgrass carries with it numerous environmental benefits. Switchgrass would require substantially less agrichemical inputs than corn—less nitrogen, phosphorous, and pesticides. Furthermore, several studies have shown that the carbon sequestration capacity of switchgrass is significantly higher than corn. Table 1 compares the soil erosion, fertilizer needs, and habitat suitability of corn and switchgrass. Using the values in table 1, converting 16.5 million acres of corn to switchgrass production would decrease soil erosion by approximately 7.3 tons of soil per year and would decrease nitrogen use by about 567 million kilograms per year.
Switchgrass also has the potential to provide dramatic benefits to wildlife when grown in place of row crops. In general, row crops are extremely poor habitat; the fields lack protective cover and leave wildlife more vulnerable to predation, and harvesting practices destroy nests and young. Switchgrass, while not as beneficial as a diverse mix of native grasses, can be provide more suitable habitat. For maximum benefit to wildlife, switchgrass should be harvested once a year in the fall, after nesting and rearing take place during the spring and summer, and should not be cut shorter than 12 inches (Harper, 2008; Ringelman, 2008). Additional harvesting practices can also be implemented, although some of these entail harvesting less acreage, which could decrease overall yields and may be less economically attractive to landowners (Harper, 2008).
While there are numerous environmental benefits to replacing corn ethanol with grassy biomass, current federal policies, particularly the Renewable Fuel Standards (RFS), make this option unlikely even if cellulosic technology were to become commercially viable. The RFS mandates that corn ethanol production will increase steadily and level off at 15 billion gallons a year by 2015. The legislation requires that any cellulosic ethanol production would be above and beyond the 15 billion gallons/yr of corn ethanol (RFA, 2009). Given this reality, growing perennial grasses on sources of land that do not displace corn will likely take precedence.
CRP for Biofuels
Conservation Reserve Program (CRP) land has been commonly mentioned as a possible source of land for the purpose of growing switchgrass (NRDC, 2004; DOE, 2005). CRP is privately own land that is retired from agricultural production for the specified length of a contract. Because this land is not used to grow crops, many argue that using it for biomass will preclude competition between fuel and food. There are currently approximately 30 million acres enrolled in CRP (USDA, 2009), and while studies often refer to this land as idle or unused, this underplays its ecological and environmental importance. Conservation practitioners cite the tremendous success of CRP in protecting grassland, wetlands, and soil and water quality.
CRP land could be used for energy crop through two mechanisms: the USDA could implement a program specifically designed to allow biomass harvesting on CRP land, or if the price for this energy crop were high enough, landowners may decide to remove their land from the CRP program and forgo CRP payments for the purpose of biomass production (leading to a decline in CRP enrollment). USDA’s consideration of the former has prompted harsh responses from wildlife conservationists. In a letter to Congress in 2006, more than twenty wildlife organizations argued that biomass production on CRP land would conflict with the program’s purpose, which is “to conserve and improve the soil, water, and wildlife resources…” (IWLA, 2006). Advocates of using CRP land suggest that under a responsible management regime that still protects the most sensitive landscapes, these goals will not be compromised. One study suggests that depending on the management priorities, 33% to 50% of CRP could be used for energy crops (De La Torre Ugarte, 2003).
Table 1 reveals that converting CRP to switchgrass production will likely increase fertilizer use and decrease the habitat suitability of the land. Although erosion amounts are similar for switchgrass and CRP, converting 15 million acres of CRP (about 50% of enrollment) to switchgrass production would increase nitrogen use by about 303 million kilograms per year.
Within the next 10 years, cellulosic ethanol will be an increasingly important source of fuel, given DOE’s commitment to bringing cellulosic ethanol online by 2012 and to increasing its production substantially by 2030. Clearly challenges lie ahead in determining on what type of land switchgrass and other biomass will be grown. As a result of the RFS mandate for continued corn ethanol growth, an increasing supply of land for corn will be necessary. While switchgrass would provide the most environmental benefits by displacing these acres of corn, using retired agricultural land, such as CRP, is more likely to be considered in light of corn ethanol policy.
Carey, J., Carter, A., & Shameen, A. (2005). “Food vs. Fuel.” BusinessWeek. Retrieved April 17, 2009, from http://www.businessweek.com/print/magazine/content/07_06/b4020093.htm?chan=gl
De la Torre Ugarte, D.G., M.E. Walsh, H. Shapouri, and S.P. Slinsky. (Feb. 2003). “The Economic
Impacts of Bioenergy Crop Production on U.S. Agriculture.” U.S. Department of Agriculture,
Office of the Chief Economist, Office of Energy Policy and New Uses, Agricultural Economic Report No. 816
DOE and USDA. (April 2005). “Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of Billion-Ton Annual Supply.” Retrieved April 17, 2009, from http://www1.eere.energy.gov/biomass/pdfs/final_billionton_vision_report2.pdf
Harper, Craig A., and Patrick D. Keyser. “Potential Impacts on Wildlife of Switchgrass Grown for Biofuels.” UT Biofuels Initiative May 2008.
Izaak Walton League of America. (June 2006). Letter to Congress. Retrieved April 17, 2009, from http://www.iwla.org/index.php?id=325
Renewable Fuels Association. (2009). Renewable Fuels Standard. Retrieved April 17, 2009, from http://www.ethanolrfa.org/resource/standard/
Ringelman, Jim. “Biofuels and Ducks: How will the nation’s growing demand for ethanol fuel affect breeding waterfowl?” Ducks Unlimited.
Ritter, Stephen K. “Ethanol from Switch Grass Deemed Feasible.” Chemical & Engineering News 8 Jan. 2008.
University of Nebraska-Lincoln (2008, January 14). Biofuel: Major Net Energy Gain From Switchgrass-based Ethanol. ScienceDaily. Retrieved April 17, 2009, from http://www.sciencedaily.com¬ /releases/2008/01/080109110629.htm
U.S. Department of Energy. (2007). DOE Biomass Program, Biomass Program Brochure. Retrieved Apr. 17, 2009, from http://www1.eere.energy.gov/biomass/pdfs/biomasstobiofuelsbrochure2007.pdf
U.S. Department of Energy. “Biofuels from Switchgrass: Greener Energy Pastures.” Retrieved April 17, 2009, from http://bioenergy.ornl.gov/papers/misc/switgrs.html
Yates, Diana. (Dec.2, 2008).”Replacing Corn with Perennial Grasses Improves Carbon Footprint of Biofuels.” News Bureau, University of Illinois at Urbana-Champaign Retrieved April 17, 2009, from http://news.illinois.edu/NEWS/08/1202soilcarbon.html