By Jan Suszkiw

Corn and soybeans may be the current "go-to" crops for producing ethanol and biodiesel, respectively. But two other crops—switchgrass and hybrid poplar—could steal the show in the future when it comes to curbing greenhouse gases, according to Agricultural Research Service (ARS) and collaborating scientists.

In a study published in a recent issue of Ecological Applications, ARS scientist Paul Adler and colleagues compared the net production of carbon dioxide and two other greenhouse gases associated with producing biofuels from several different bioenergy crops.

In short, it takes energy to produce energy, notes Adler, who's in the ARS Pasture Systems and Watershed Management Research Unit, University Park, Pa. For example, operating a tractor to plow, plant, fertilize and harvest all require gasoline or diesel fuel. This, in turn, releases carbon dioxide and other greenhouse gases tied to global climate change.

The good news? Bioenergy crops offset their greenhouse-gas contributions in three key ways: by removing carbon dioxide from the air and storing it in crop roots and soil as organic carbon; by producing coproducts like protein for animal feed, which saves on energy to make feed by other means; and by displacement, whereby replacing a fossil fuel with a biobased one "recycles" rather than adds more carbon dioxide to the atmosphere.

Together with ARS scientist Stephen Del Grosso of Fort Collins, Colo., and William Parton of Colorado State University, Adler predicted a 40 percent reduction of greenhouse gas emissions if ethanol and biodiesel from corn-soybean rotations were used instead of gasoline and diesel. This reduction was about two times greater than using ethanol produced from corn grain alone. However, the team predicted that using switchgrass and hybrid poplar would produce nearly a three-fold greater reduction in greenhouse gas emissions compared to corn-soybean rotations.

This research shows that biofuels do indeed have potential to remove greenhouse gases from the atmosphere while helping reduce U.S. reliance on foreign oil, according to Adler.