Some bioenergy crops are greener than others

Compared with rows of maize, tufts of switchgrass grown for biofuel have hidden perks, a new study finds. The benefits over maize include increased biodiversity, removal of more greenhouse gases from the atmosphere and boosted pest control.

The U.S. government encourages production of bioenergy crops, and maize, or corn, is the most commonly grown. But farmers might consider switchgrass or other prairie grasses instead if they knew of the crops’ strengths, says lead author Douglas Landis, an ecologist at Michigan State University in East Lansing.

Landis wanted to evaluate the benefits of growing bioenergy crops on marginal lands, sections of farmland that are suboptimal for growing food. He and his colleagues repeatedly visited more than 100 marginal fields growing maize, switchgrass or mixed prairie plants in Wisconsin and Michigan. At each site, the researchers evaluated biodiversity, looking at microbe, insect and bird populations. They also measured the “ecosystem services” that each field provided, including the rate of flower pollination, consumption of the greenhouse gas methane by soil microbes and suppression of insect pests.

Fields of maize produced more starter material for making biofuel. But fields of switchgrass and mixed prairie — planted mixtures of perennial grasses and flowering plants — enhanced biodiversity and improved ecosystem services, Landis and colleagues report January 13 in the Proceedings of the National Academy of Sciences. For instance, compared with maize fields, at switchgrass plots, methane consumption jumped by an order of magnitude and bird sightings doubled. The researchers also found that fields neighboring grassland plots had fewer pests and more flower pollination. One reason for the differences, Landis explains, may be that perennial grass fields don’t need to be replanted annually. Thus, they can accumulate more biodiversity and ecosystem services over time.

Though researchers knew that switchgrass and other perennial grasses have certain advantages over maize, the study is the first to look at multiple ecosystem services and animal populations at the same time, says Silvia Secchi, an agribusiness economist at Southern Illinois University in Carbondale. “Typically people look at one ecosystem service at a time,” she says.

For this reason, Secchi says that land managers outside the Upper Midwest should do studies like this one to determine which bioenergy crops may best suit local ecosystems. “They’re showing a methodology,” she says.

Though the study is complete for the Upper Midwest, many farmers may still be hesistant to switch to switchgrass because they are accustomed to growing maize for food and for fuel, says economist Gregory Parkhurst of Weber State University in Ogden, Utah. And to get the maximum ecosystem benefits, neighboring farmers should coordinate efforts, which may add another hurdle.  

The ecosystem improvements don’t all help the farmer, he says. “So the incentives have to be right.”