While cellulosic biofuels derived from grasses, crop residues and inedible plant parts have real potential to be more efficient and environmentally friendly than grain-based biofuels like corn ethanol, more research and science-based policies are needed to reap these benefits, says an international group of experts.
In an article published Oct. 3 in the journal Science, Purdue University Agricultural Economist Otto Doering and a team of 22 other scientists write that there is an urgent need for more comprehensive and collaborative research. This will help next-generation fuels avoid the pitfalls of grain-based biofuels, which include increased nutrient runoff and clearing of new land to recoup lost food production, Doering says.
"It's important that we begin thinking about how to deal with the unintended consequences of cellulosic biofuels as early as possible in order to ensure that they can be produced sustainably," he says.
The Renewable Fuel Standard within last year's energy bill guarantees cellulosic biofuels a relatively bright future, mandating that American companies purchase 21 billion gallons of cellulosic ethanol by 2022. But many questions remain unanswered, like how to comprehensively measure the impact of biofuels. To date, measures often reflect a single dimension rather than considering the system as a whole.
"There are a broad array of concerns," Doering says. "We need to consider biofuel's likely impact on water use and availability along with water quality, especially nutrient runoff. Greenhouse gas emissions must also be considered, as well as effects on soils and the landscape."
Rising demand for corn grain ethanol has gone hand-in-hand with increased water use and, oftentimes, increased nutrient runoff, Doering says. There also is mixed evidence that corn grain ethanol reduces greenhouse gas emissions. The intensive corn cultivation encouraged by high ethanol demand can degrade soil and water quality, he says.
Doering, recently appointed to the Environmental Protection Agency's Scientific Advisory Board, says more work is needed to develop and successfully apply best management practices to minimize nutrient, chemical and water use while limiting greenhouse gas emissions.
It's important to remember, he says, that existing best management practices can help soften the impact of increased corn production and intensified agriculture. Such practices include no-till farming methods, planting of cover crops, diversity-oriented crop rotation and inclusion of uncultivated fallow land into the landscape. All these practices help retain soil nutrients and offer benefits like wildlife habitat and natural pest suppression.
Cellulose, a complex carbohydrate present in all plant tissues, is more abundant in plants than starch. Humans also are unable to digest cellulose. This means cellulosic feedstocks are less likely to displace acreage devoted to food crops.
"The paper is really a plea to think carefully before jumping into cellulosics," Doering says. "We want to avoid making mistakes we're likely to later regret."
Michigan State University Researcher G. Philip Robertson was lead author of the Science article. Authors hail from universities and institutions from two countries and 16 states.
"Business as usual writ larger is not an environmentally welcome outcome," the authors conclude.