10-01-07 Biofuel from a mix of native prairie grass would yield more energy than ethanol from corn or switchgrass and would do more to combat global warming.
A recent study in the journal Science found that a diverse mixture of grasses can produce more raw material than a single-species planting of, for example, switchgrass. The University of Minnesota research compared several such plantings on poor-quality soil without fertilizer.

If turned into ethanol, the grass mixture would theoretically yield a higher ratio of energy output to input than corn-based ethanol. With improved technology, it also could slow global warming by capturing carbon dioxide.
“This is what really surprised us,” said ecologist David Tilman, who led the study. “There is more carbon stored year after year in the soil than the total amount of fossil carbon that is produced into the atmosphere.”

There still are numerous hurdles to bringing the technology to market, and some experts say it might not be practical. But if successful, the authors say it could be part of a solution to the nation’s energy problems.
In last year’s State of the Union address, President Bush called for a program to make fuel from cellulose, the fibrous structural material found in all plants. One feedstock he mentioned by name was switchgrass.

But during the past couple decades, ecologists have found convincing evidence that diverse mixtures of species are usually more productive than one species can be on its own. Tilman is a pioneer in demonstrating this positive effect of biodiversity in grasslands.
To study energy production, Tilman and his colleagues used data from these biodiversity experiments -- performed at the Cedar Creek Natural History Area, north of Minneapolis. They also gathered data on carbon storage from old soil samples. The results show that diverse mixtures average more than triple the productivity of grass monocultures.

Growing these mixtures for several years also removes about 1,750 pounds of carbon dioxide from the atmosphere per acre. Planting, harvesting and transporting the material only releases about 400 pounds of carbon dioxide per year, Tilman said.
Carbon dioxide is the main greenhouse gas implicated in global climate change. William Gibbons, a South Dakota State University microbiologist, said diverse grass mixtures “are the climax plant community of the Great Plains. Thus, native grasses would be the most productive biomass crop for us to produce.”

But practical obstacles remain.
Stands of native grass are common in South Dakota, often as part of the Conservation Reserve Program for former cropland. Some of that is a mixture of species, but some landowners say stands of pure switchgrass are better pheasant habitat.
“No doubt, switchgrass, that’s No. 1, and I think if they started something with ethanol with this switchgrass, it’d be a great deal,” said Bob Farrell of Mitchell, an avid hunter who has planted grass on his land near White Lake.

Tilman says it probably would not make economicsense to transport grass more than 50 miles from the field to the processing plant. And once it gets to the plant, the mix of grasses could present problems, said Burton English, an agricultural economist at the University of Tennessee.
“It depends on the conversion technology,” he said. “If you’re doing a fermentation system, then you may have some difficulties. You may have a less efficient plant when you take multiple feedstocks versus a single monoculture feedstock.”