Feedstocks for Biofuels

by John McClelland, Agricultural Economist. Office of Energy, USDA, Washington, DC, and John Farrell, Physical Scientist, Office of Alternative Fuels, U.S. Department of Energy, Washington, DC.

Dave Tolsted, a Forest Service forestry research technician, samples hybrid poplar chips at the Harshaw Forestry Research Farm, North Central Forest Experiment Station, Rhinelander, WI. One of the potential uses for the wood chips is fuel. The development of new tree species can make it possible to produce significant quantities of liquid fuels from their cellulose and hemicellulose.

Bob Nichols/USDA 92BWO733-34A

The term "biofuels" defines a broad range of materials that are biological in nature and used to produce energy Biofuels include wood for burning, ethanol, and diesel substitutes we will call biodiesel.

Many different types of plant and animal products can be used to produce liquid biofuels for the U.S. transportation sector. Raw materials used to produce liquid fuels are referred to as biofuels feedstocks. In this chapter, we will identify some of the most promising feedstocks, discuss the potential for growing them on a widespread basis in the United States, investigate the economics of biofuels feedstock production, and look at future opportunities for farmers to get involved in the biofuels industry.

In 1991, the United States used almost 120 billion gallons of gasoline and 25 billion gallons of diesel fuel for transportation. The petroleum we use in the transportation sector accounts for about 60 percent of oil we use, and the U.S. transportation sector is 97 percent dependent on petroleum. In 1990, the United States imported an average of 7.2 million barrels of oil per day. Our production of motor gasoline on an average day in 1990 was also 7.2 million barrels, which means that we use all of our imported oil plus some of our domestically produced crude oil to meet daily gasoline demand. The average price of imported crude oil in 1990 was slightly less than $22 per barrel. Our daily oil imports add $158 million to the U.S. balance of trade deficit. About one-third of our imported oil comes from the Middle East and another one-third comes from Latin America and Africa. These factors make oil supplies vulnerable and prices uncertain. Within the past 20 years, the United States has sustained three major oil price shocks.

One solution to the problems posed by our oil supply situation is "homegrown energy." While this sounds good, in practice home-grown energy is a tremendously complex undertaking that will require a lot of work and experimenting. Fortunately, USDA and the U.S. Department of Energy (DOE) have been devoting considerable resources to develop existing and new crops that can be grown and processed into liquid fuels to replace gasoline and diesel.

Corn

Corn has been the primary feedstock for producing fuel ethanol for more than 15 years. During that period, we have had good supplies of corn with yearly average production in excess of 7 billion bushels. This year, USDA expects farmers to plant nearly 80 million acres of corn, and if yields are good we can expect the 1992 crop to exceed 8 billion bushels.

Corn has several advantages as a biofuels feedstock. Corn is a major agricultural crop. We already know how to grow it, haul it, handle it, and process it. Within the last 50 years, we have made great strides in all of these areas; our yields have increased from about 40 bushels per acre in 1950 to more than 118 bushels per acre in 1990. New processing technologies have made it possible to process corn into starch products such as sweeteners and ethanol, thus expanding the market for corn beyond its conventional use as an animal feed. In 1991 we had about 5 million acres idled in the annual Acreage Reduction Program for corn, and nearly 4 million acres of corn land in the long-term Conservation Reserve Program. In addition, farmers elected to place in conserving use another 2.6 million acres of corn land. This means that if there is significant expansion in corn utilization, we have ample land on which to expand production.

Cellulosic Feedstocks

While the corn-based ethanol industry has grown to nearly 1 billion gallons of annual production over the last 15 years, it is unlikely that corn-based ethanol can supply all of our liquid fuel needs. Therefore, it is important that we look for other sources of agricultural biomass from which renewable biofuels can be produced at a reasonable cost with available resources. Cellulosic energy crops are probably the best alternative for producing ethanol. Conversion of cellulose into ethanol will be discussed in chapter 33, but before conversion can take place, we need to be able to produce ample supplies of feedstock. Crops that produce large amounts of cellulose can be categorized into two groups, herbaceous species and woody species.

Herbaceous Crops. Herbaceous energy crops have more variety and greater versatility then woody energy crops. Some are annual crops such as sweet sorghum or rye, while others are perennials such as switchgrass or reed canarygrass. Depending on conditions, herbaceous energy crops can be either grown in monoculture or interseeded with more than one species in a stand. They can also be double-cropped with other energy crops or with conventional agricultural crops.

A number of grasses and legumes are being evaluated for their potential as energy crops in the DOE Herbaceous Energy Crop Program. Grasses include bahiagrass, bermudagrass, eastern gamagrass, Johnsongrass, napiergrass, reed canarygrass, rye, sudangrass, switchgrass, tall fescue, timothy, and weeping lovegrass. Legumes being investigated include alfalfa, birdsfoot trefoil, crownvetch, flatpea, clover, and sericae lespedeza. Field testing is taking place at a number of sites around the country; we will discuss a small sample of these results.

Trials done by Auburn University at four Alabama Agricultural Experiment Station sites examined the performance of bahiagrass, bermudagrass, energy cane, Johnsongrass, napiergrass, sericea lespedeza, switch-grass, sweet sorghum, and weeping lovegrass. Drought in the area during the trial period caused some species to fail to establish. When double cropped with rye, combined yields ranged between about 3 dry tons per acre for bermudagrass at the Sand Mountain Station to slightly more than 7 dry tons per acre for sweet sorghum in the Upper Coastal Plain. Switchgrass was a consistent performer at all locations, with yields ranging from 3.25 dry tons per acre at Sand Mountain to 4.7 dry tons per acre in the Upper Coastal Plains.

The Forest Service is researching species of trees, such as hybrid poplar, that are suitable for conversion to ethanol. To be effective, the trees must produce large quantities of wood in a short growing period. Such species are known as short-rotation woody species, because they are grown and harvested within 3 to 8 years. Bob Nichols/USDA 92BWO733-20A