Growing perennial grasses on the least productive farmland now used for corn ethanol production in the U.S. would result in higher overall corn yields, more ethanol output per acre and better groundwater quality. So say University of Illinois researchers in a new study. The switch would also slash emissions of two greenhouse gases: carbon dioxide and nitrous oxide.
The study used a computer model of plant growth and soil chemistry to compare the ecological effects of growing corn, miscanthus and switchgrass. The researchers found that switching 30% of the least productive corn acres to miscanthus offered the most ecological advantages.
"If cellulosic feedstocks (such as miscanthus) were planted on cropland that is currently used for ethanol production in the U.S., we could achieve more ethanol and grain for food, while reducing nitrogen leaching and greenhouse gas emissions," the researchers wrote in their report, published in Frontiers in Ecology and the Environment.
"Globally, agriculture contributes about 14% of the greenhouse gases that are causing global warming to the atmosphere," says University of Illinois plant biology and Energy Biosciences Institute (EBI) professor Evan DeLucia, who led the study with EBI feedstock analyst Sarah Davis. "The whole Midwest has been, since the advent of modern agriculture, a source of greenhouse gases to the atmosphere.
"According to our model, just by making this replacement you convert that whole area from a source of greenhouse gases to the atmosphere to a sink for greenhouse gases from the atmosphere."
Miscanthus grows in thick stands up to 13’ tall in test plots in Illinois. It does well on marginal land without being fertilized, so using it as a biofuel feedstock instead of corn would eliminate a major source of air and water pollution, says Davis. Nitrous oxide, a byproduct of the fertilizers used on cornfields, "is actually a more potent greenhouse gas than carbon dioxide.
"Both switchgrass and miscanthus are perennial grasses, which means that you don't have to till every year, you don't have to plant every year, so there's much less soil disturbance happening than with corn," says Davis. "And because the root system remains in place year after year, there's more carbon going into the soil."
Several hurdles remain before the transition from corn to cellulosic ethanol production can occur on a commercial scale, say the researchers. Converting the sugars in corn to ethanol is easier than releasing the energy locked in plant stems and leaves.
"We know that these grasses are enormously productive; we know the agronomy works; we know the ecology works," says DeLucia. "So the next step is to break down the economic barriers by making an efficient conversion chain from lignocellulosics to ethanol."