The Virtues of Switchgrass as an Alternative Fuel
When European settlers emerged from eastern forests onto the prairies, they encountered what at first seemed like an alien and hostile landscape: a veritable sea of tall grasses, with almost no wood for building homes and fences. But before too long, many of them came to see the wide-open spaces and fertile soil as a potential agricultural Garden of Eden—if only a way could be found to plow up the thick sod.
For thousands of years since the most recent ice age, the root systems of the tall grasses had been fingering ever outward, creating the prairie equivalent of root-bound houseplants. The result was some of the richest soils in the world, packed with organic matter and carbon. But the sod was so sticky and dense that even a team of oxen had difficulty dragging a plow through it. It was an exquisite irony: The very thing that made the soils so ready for agriculture—their extraordinary fecundity—actually prevented it.
Until 1837, that is, when John Deere invented a steel plow that could cut through the sod like a hot knife through butter. What followed, of course, was the transformation of a sea of grass into an ocean of corn and soybeans. Today the tallgrass prairie has been reduced to less than 1 percent of its original range, making it one of the rarest ecosystems in the world. And according to David Tilman, an ecologist at the University of Minnesota, farming those soils has caused them to lose up to half of the enriching carbon they once had—to the atmosphere in the form of heat-trapping carbon dioxide.
But now descendants of the sod-busting pioneers may be poised to help at least one native tallgrass species, switchgrass, stage a comeback. And not as feed for livestock but as something far more valuable in this age of expensive oil and global warming: ethanol for use as a renewable “biofuel.”
If all goes well (no trivial if), within five years or so farmers may begin replacing corn and other crops now grown on degraded land, or on land only marginally suitable for agriculture (because of its vulnerability to erosion and other factors), with cultivated fields of switchgrass. If recent research by Tilman and others pays off, we may eventually see farmers replanting not just with switchgrass but with a diverse array of grasses and other plants, re-creating something akin to the native prairies first encountered by the pioneers on their way west. The goal: replacing gasoline with ethanol that would reduce global warming while also helping struggling farm economies, restoring soil fertility, and improving habitat for imperiled grassland birds and other species.
Steve Fransen, a Washington State University (WSU) forage agronomist, is one of the researchers working to make this vision a reality. On a warm July morning beneath southeastern Washington’s Horse Heaven Hills, he stoops beside a lush three-acre plot of head-high switchgrass. Parting the thick growth, he fingers dozens of green blades growing from a single plant. “You can see here why switchgrass produces much more biomass than corn”—a key attribute that could help this tallgrass prairie species supplant corn as a raw material for producing ethanol, a form of biofuel. Fransen is experimenting with ways to cultivate switchgrass 1,000 miles west of its native Midwestern home, with help from a little irrigation. The soils here in the Yakima River valley are drier—so dry, in fact, that it takes two years for the earth up in Horse Heaven to accumulate enough moisture for wheat to be grown successfully. So if switchgrass can make it here, it can make it anywhere.
“We’re making real progress,” Fransen tells me as we walk among the plots at WSU’s Irrigated Agriculture Research and Extension Center in Prosser. “When we harvest this grass in a day or so, I think we’ll get a yield of five tons per acre.” With a second harvest in the fall, the annual yield should be 10 tons per acre. That much biomass translates into more than 1,000 gallons of ethanol—enough fuel to keep a hulking Hummer H2 rolling for 16,000 miles.
But it won’t mean much unless farmers choose to cultivate switchgrass, says Fransen’s collaborator, Hal Collins. A self-described “dirt guy” who refers to soil microbes as “my buddies,” Collins is a microbiologist and soils specialist with the USDA’s Agricultural Research Service. “You can’t just tell farmers to grow this stuff,” he says. “But they will grow it if they decide they can make money and it will stick around. We’re demonstrating in our fields right now that yes, you can grow it, and here’s how you do it.”
Along with its impressive biomass yield, switchgrass embodies other valuable qualities. It can grow in varied environments and requires less fertilizer than row crops like corn (and, in some environments, little or no fertilizer at all). What’s more, because it is a densely rooted perennial, it stabilizes the soil against erosion, preventing runoff into waterways. Best of all, the “cellulosic” ethanol made from switchgrass, along with many other inedible plant fibers, can do much more to reduce global warming by displacing fossil fuels than ethanol made from corn—possibly even cutting 80 percent of U.S. greenhouse-gas emissions from transportation by the year 2050, according to a report by the Natural Resources Defense Council.
Corn ethanol is currently the undisputed U.S. champion of biofuels. But it is cellulosic ethanol that is the great hope of the coming era of truly green, renewable fuel, because making ethanol from the sugars locked in plant fibers, as opposed to corn kernels, has many advantages. For one, the raw materials are much cheaper and more abundant. In addition to switchgrass, these fibers include other grasses, wood from tree plantations, residue from logging operations, and the leftovers after the harvesting of wheat and corn. Another advantage is that unlike corn, which requires tilling and replanting every year, perennial grasses like switchgrass can be harvested for a minimum of five to ten years without the need to reseed. And the environmental benefits are far greater.
“The sustainable resource transition is one of the big challenges of our age,” says Lee Lynd, a Dartmouth College engineering researcher who is helping pioneer new technologies for making cellulosic ethanol. “Historians will look back to see how well we saw the icebergs ahead of us, and whether we changed course. I think we can navigate successfully, and I strongly believe that cellulosic ethanol made from materials like switchgrass can help us do it.”
Ironically, the corn ethanol industry may be laying the groundwork by helping to establish infrastructure and expand the number of “flex-fuel” vehicles on the road that can run on a mixture of ethanol and gasoline. And that industry is booming. With a push from the National Energy Policy Act of 2005, ethanol production soared to 4.86 billion gallons in 2006, a 24 percent increase over 2005. One hundred and fourteen ethanol distilleries were already in place at the end of the year, with an additional 78 under construction.
Still, corn ethanol alone can take us only so far. The increasing diversion of grain to ethanol distilleries is already pushing corn prices higher. Demand from ethanol distilleries has caused the price of corn to soar so high that the cost of tortillas in Mexico has doubled, prompting thousands of poor people to take to the streets in protest.
“Since almost everything we eat can be converted into fuel for automobiles, including wheat, corn, rice, soybeans, and sugarcane, the line between the food and energy economies is disappearing,” writes agricultural economist Lester Brown in a report by the Earth Policy Institute. As that line disappears, corn ethanol’s limitations become clearer. Consider that filling a 25-gallon SUV gas tank with corn ethanol requires enough grain to feed one person for an entire year.
In 2006, 20 percent of U.S. corn went to making ethanol—up from 14 percent the year before. Yet that ethanol displaced just 3.5 percent of U.S. gasoline use. Furthermore, according to recent research described by the University of Minnesota’s Dave Tilman and his colleagues in the Proceedings of the National Academy of Sciences, dedicating the entire U.S. corn crop to ethanol production would meet just 12 percent of gasoline demand.
Collins says this raises a moral question: “Should we be growing energy or should we be growing food?”
With corn ethanol, there are even doubts about just how much energy we’re growing. Corn lives on solar energy, but fertilizing, harvesting, transporting, and distilling ethanol require lots of fossil energy. Some research suggests that the fossil energy used to produce corn ethanol actually exceeds the energy it provides. Most research, however, shows a positive, if modest, energy balance—25 percent more energy out than in, according to Tilman’s 2006 report in the National Academy of Sciences journal. Here cellulosic ethanol has a huge advantage: It may yield at least four times as much energy than is required to produce it.
So even as corn ethanol production ramps up, the United States ultimately is headed toward other alternatives, and not just cellulosic ethanol. One that’s coming on fast is biodiesel, made from soybeans and other oil crops. Still, even if 100 percent of the nation’s soy crop were dedicated to making biodiesel, it would meet just 6 percent of diesel demand.
With this in mind, the U.S. Department of Energy (DOE) is placing most of its biofuels bets on cellulosic ethanol. That research funding is seen as essential to drive down costs and get a commercial industry up and running. The DOE’s goal is for cellulosic ethanol to be cost-competitive by 2012. Last February the agency announced that it would invest up to $385 million for six biorefineries that would produce more than 130 million gallons a year. And in June the DOE said it would spend up to $375 million to create three new bioenergy research centers intended to boost research and development into cellulosic ethanol. Meanwhile, Iogen Corp. is already producing cellulosic ethanol at a demonstration plant in Canada, and the first U.S. commercial facility is being planned for Iowa.
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.
If cultivated properly, switchgrass may also improve habitat. In a 1997 study, for example, a team of researchers in Wisconsin observed 17 bird species inhabiting both harvested and unharvested fields of switchgrass in the southwestern part of the state. Ten of the 17 were grassland birds considered to be “species of management concern” for reasons ranging from declining numbers to vanishing grassland habitat. Among them were shortgrass species, including the western meadowlark and the grasshopper sparrow; mid-grass birds, such as the eastern meadowlark and the dickcissel; and tallgrass species, including the Henslow’s sparrow and the sedge wren.
“There was actually a greater diversity and a higher number of birds in the harvested switchgrass than in the unharvested plots,” says Laura Paine, now with the Wisconsin Department of Agriculture. She concludes that farmers could grow switchgrass for profit while also providing habitat benefits for imperiled grassland bird species. “That’s a win–win situation,” she says.
But others are not so sure of the benefits of switchgrass monocultures. Michael Palmer, an ecologist at Oklahoma State University, concedes that switchgrass is better for the environment than corn. “But here’s a plant that typically occurs with anywhere from 60 to 100 other species. If we start having these massive monocultures of switchgrass, it’s an invitation to all sorts of diseases, and that’s a prediction for massive crop failures.”
Additionally, some ornithologists, including Greg Butcher, Audubon’s director of bird conservation, contend that a mixed prairie landscape would be vastly better for biodiversity. “Switchgrass by itself is not good habitat for birds,” he says. “Birds need grasslands for a variety of reasons. Different plants produce food for birds at different times and attract insects, some of which are eaten by birds, at different times. All this means diverse grasslands will attract more species of birds than a monoculture will.“
Help could come from research conducted by the University of Minnesota’s David Tilman and colleagues. They’ve found that if degraded agricultural lands were planted with a diverse mixture of prairie species, including western wheatgrass, big bluestem, and little bluestem; vascular plants such as sundial lupine and rounded-headed bush clover; and forbs such as rigid goldenrod and tall blazing star, the energy yield could exceed that from switchgrass alone by more than 200 percent. “Our research shows that biofuels made from a diverse mix of prairie plants can eliminate about 15 to 25 percent of the global warming problem the world faces,” Tilman says. At the same time, these cultivated prairies would feature greater biodiversity, providing even better habitat for many animals.
Tilman’s research may herald a new direction in biofuels research. Collins, for example, has already planted a diverse array of prairie grasses in experimental plots to study how they will do—a “polyculture,” as opposed to a monoculture. But even Tilman admits that it’s too soon to say whether farmers can make a go of it economically. “I see two competing ideas, and I don’t know which one will win,” he says. It’s even possible that switchgrass monocultures will work in some environments and polycultures in others.
Currently, however, federal research into finding suitable tallgrass crops for making cellulosic ethanol is concentrated primarily on switchgrass.
Regardless, Mark Downing, an agricultural economist and senior scientist at the Oak Ridge National Laboratory, believes we’ve already crossed a key threshold. “I’ve never seen such a focus on the environment and sustainability,” he says—including within the Bush administration. “The Secretary of Energy is breathing down my neck to make some progress before Bush leaves office. The issue now is, how are we going to do this? Because of concern about global warming and environmental sustainability, we’ve decided that biofuels are important. Now we can really get down to the brass tacks of figuring out how to do it.”
If the effort can be sustained over the next five to ten years, the prairie grasses that created America’s breadbasket may well lead the country toward a more sustainable future. “This is one of my dreams,” says Tilman, “to see this happen.”
As scientists and engineers look to replace fossil fuels and fight global warming with renewable energy sources made from vegetation, Audubon and other environmental groups are sounding a note of caution. Creating energy from cellulosic biomass such as switchgrass, trees, and other plant materials holds great promise, but carries its own costs. Here are some guidelines.
• No farm or energy subsidies should be given for biofuel crops grown on land that was converted from native habitat or forest.
• There should be support for research into a broad range of technologies and vegetation for biofuels.
• Larger incentives should be paid for growing native species and polyculture crops.
• A minimum 10-inch stubble should remain after grass crops are harvested to ensure some cover for wildlife.
• Soil conservation plans should be required, including buffer zones to protect water resources.
• The extraction of biomass from forests should be done sustainably to maintain fish and wildlife habitat and soil and water quality.
• The harvesting of biomass should be done after ground-nesting bird eggs have hatched and chicks have fledged.
• Woody biomass should not be taken from old-growth forests, national monuments, roadless areas, or national wildlife refuges.
This story originally ran in the September-October 2007 issue as "Grass Is Greener."