The Virtues of Switchgrass as an Alternative Fuel
The DOE calculates that 1.3 billion dry tons of inedible plant materials could be grown and gathered in the United States without harm to the environment or the food economy. (That’s three and a half times more than all the corn grown in the country in a year.) And 1.3 billion dry tons of biomass, according to the DOE, would yield at least 60 billion gallons of cellulosic ethanol a year—enough to displace 30 percent of the nation’s 2004 gasoline consumption. With investments in research and development, the DOE believes reaching that target is achievable by 2030. In this scenario, cellulosic ethanol is clearly no panacea. “There is no one known technology that will solve our problems,” Tilman notes. “But there are a series of technologies that can.” And some see cellulosic ethanol as a bridge to a more sustainable alternative fuel, such as hydrogen produced with solar energy.
A report from the Natural Resources Defense Council, with contributions from major universities and the Oak Ridge National Laboratory, suggests that biofuels overall, combined with significantly improved energy efficiency and better urban planning, could be much more than a bridge: They could help eliminate the demand for gasoline in the United States by 2050. Along the way biofuels could provide farmers with profits of more than $5 billion per year, while reducing U.S. greenhouse-gas emissions by 1.7 billion tons annually—an amount equal to 22 percent of the nation’s entire emissions in 2002.
Under the Horse Heaven Hills, the nearly six-foot-high blades of switchgrass are whispering as a hot breeze drifts through the test plots. But true to form, Hal Collins of the Agricultural Research Service is focused on the soil—or, more precisely, the roots, and how even they can help reduce global warming.
“Switchgrass can root to depths of 8 to 10 feet, depending on the soil type,” he says. The plant draws carbon dioxide from the atmosphere to produce those roots. “That means they store something like 1,000 pounds of carbon per acre in the soil. So these types of crops can sequester a tremendous amount of carbon.”
Dead and decomposing root material also adds organic matter to the soil. Combine the carbon with all that rich organic stuff and you get another environmental benefit: Prairie grasses like switchgrass aid marginal soils. “Studies show that switchgrass builds soil, improves soil structure, and aids infiltration of water,” Collins says. The soil here consists of 0.4 percent organic matter, compared with 20 times that much in the Midwestern corn belt. Of course, switchgrass won’t be transforming southeastern Washington’s dry, sandy soils into rich Midwestern loam. But when you’re starting so low, says Collins, every little bit helps.
Growing and collecting switchgrass and other plant materials to produce cellulosic ethanol could have a range of other environmental benefits. In ongoing research in Minnesota, for example, scientists are finding that switchgrass, as well as hybrid poplar and other trees, can curb pollution when they replace traditional crops in flood-prone riparian areas, thanks to the extensive root systems of perennial grasses and trees. “Every study has shown that by the second or third year of cultivating a perennial such as switchgrass, you very significantly reduce runoff of pesticides and nutrients compared with annual crops like corn,” says Lynn Wright, a former researcher at the Oak Ridge National Laboratory and now a consultant working on biofuels issues.
Bioenergy crops will also affect habitat and biodiversity. Whether those effects will be positive or negative will depend on what is displaced, Wright says. For example, at least two studies show that while the numbers and species diversity of birds in poplar tree plantations are lower than in wooded wildlands, they are higher than on pasture and hay fields and lands devoted to row crops such as corn and soybeans. In fact, research by scientists at the Oak Ridge lab and elsewhere suggests that if bioenergy tree plantations are grown and harvested properly, they could help support neotropical migrants—the songbirds that make up about 50 percent of North American species. These migrants from Mexico, Central and South America, and the Caribbean have been in steep decline during the past few decades because of the fragmentation of their habitat and the loss of breeding territories. The Oak Ridge research shows that in the Southeast, species such as the common yellowthroat, the indigo bunting, and the ovenbird frequent plantations of sweet gum and sycamore. Wright agrees with her fellow researchers that even though tree plantations do not match natural woodlands, they can still support a diverse array of bird species, including ones that are of special concern.