“We have a finite amount of oil left in the earth, and we can’t wait around for the earth to make more,” said Kurt Thelen, professor of Plant, Soil, and Microbial Sciences at Michigan State University (MSU). “Eventually, we’re going to have to go to alternative fuels.” Cellulosic biofuels, derived from grasses and wood, could be part of the answer to our energy needs for the future. Researchers at the Great Lakes Bioenergy Research Center (GLBRC), including Thelen and MSU professor Phil Robertson, are investigating the possibilities of sustainable biofuels, which are hoped to be a step toward cleaner energy especially for transportation.

From a global climate change standpoint, these biofuels are a clear winner over oil. The carbon we release into the atmosphere when we burn oil, estimated to be about 200 million years old, is not native to the atmosphere, and accelerates climate change. Sustainably grown biofuels, on the other hand, give us the opportunity to recycle carbon from the atmosphere. Biofuel plants can also sequester some carbon in the soil, which results in a net negative release of carbon.

“We can burn the biofuels so much more cleanly than the way we burn fossil fuels,” said Thelen. In 2016, a record-breaking high of 143.37 billion gallons of petroleumbased gasoline were consumed in the United States, according to the U.S. Energy Information Administration. As gasoline is burned, it produces carbon monoxide, carbon dioxide, nitrogen oxides, and other contributors to air pollution.

“In the near term, biofuels are mostly a gasoline replacement,” said Robertson, who is a distinguished professor of ecosystem science in MSU’s Department of Plant, Soil and Microbial Sciences. “We want to be all-electric in the future, but we need to have a climate-friendly bridging technology until we have the energy grid to support that. Biofuels are the natural choice for that bridging period.”

Going all-electric could be a carbon-free scenario for transportation if the fuel used to produce the electricity were renewable. However, even if we were able to make passenger vehicles electric across the board, there would still be some energy needs that electricity couldn’t match, like airplanes and long-distance transport like trains and trucks. There are also other uses of oils that would need to be accounted for.

“Only about 70 percent of a barrel of oil is actually used for gasoline or other power,” said Robertson. “The other 30 percent goes into products like plastics and paints and other chemical uses, and those are also going to need to be made with renewable sources like cellulosic biomass in order to go carbon-neutral.”

The GLBRC is a collaboration between the University of Wisconsin-Madison and MSU, with field sites at several locations in Wisconsin and Michigan, including one at MSU’s W.K. Kellogg Biological Station, there Robertson conducts the bulk of his research.

This year, the GLBRC was granted next-phase funding from the US Department of Energy. With that funding, GLBRC researchers are taking steps toward highly focused research on four biofuel crops - switchgrass, energy sorghum, poplar trees and restored prairies. These crops are being grown on marginal lands, which are nutrient-limited and aren’t used for growing food. This means that biofuels would be grown without competing for arable land that we need for food production.

“It’s pretty clear that in the future, marginal soils are where biofuels will be relegated, because food is always our top priority,” said Thelen. “We can also look at bringing some of these marginal soils into production in a way that’s going to even improve their ecosystem services, plus give us some economic development in those rural areas where these soils exist.”

Growing biofuels on nutrient-limited lands means that researchers have to get creative in how these plants can sustainably thrive. Part of that is examining what natural processes they might be able to leverage, like nitrogen-fixing bacteria in the rhizosphere that can give plants the nitrogen they need.

“We know the cost of nitrogen fertilizer is often the most expensive input for the farmer,” said Thelen. “It’s also the most expensive in terms of its carbon footprint. It takes a lot of natural gas to make synthetic nitrogen fertilizer, and that has its own emissions problems, so there’s tremendous advantage if you have nitrogen fixation taking place.”

“There’s a lot of work to be done,” said Robertson. “This area of microbiome-assisted plant growth is a novel one that is only now getting to the point where we understand enough about it to think about managing it in the future.”

Robertson, Thelen, and others at the GLBRC reported in a 2017 Science article that the climate benefit of biofuels is even greater than originally anticipated. However, it’s a challenge to pin down how to maximize that benefit, and minimize other tradeoffs.

Future research on biofuels will help to determine an optimal balance of productivity, sustainability, and cost-effectiveness, and a big part of sustainability is the provision of biodiversity and climate benefits. It’s difficult to engineer a win-win-win situation across the board.

“For example, as a landowner I might be happy to give up 10 percent of my productivity to double my impact on conservation,” said Robertson. “But if I have to give up 90 percent of potential productivity in exchange for 10 percent more biodiversity, the economics get dicier. In order to make sound choices we have to know the consequences of different choices."

The future of biofuels, according to Thelen and Robertson, rests on their economic viability and sustainability, and will likely require government policy in order to be implemented effectively.