Miscanthus bests switchgrass, researchers find

Europe may have placed the better bet. But when it comes to the biofuel feedstock Miscanthus, some scientists are sounding warnings.

Researchers at the University of Illinois at Urbana-Champaign have presented research from a two year study that shows the grass Miscanthus—experimented with widely in Europe since the 1980s as a potential feedstock for biofuel—beats North America's switchgrass.

At the annual meeting of the American Society of Plant Biologists in Chicago this week, researchers showed data illustrating that Miscanthus was twice as productive as switchgrass.

The group made direct comparisons of the biomass productivity of two C4 perennial grasses: switchgrass Panicum virgatum and Miscanthus x giganteus.

Results showed Miscanthus' efficiency of conversion of sunlight into biomass was amongst the highest ever recorded.

The team, led by Frank Dohleman of the University of Illinois at Urbana-Champaign's Plant Biology department, theorized that Miscanthus produces more usable biomass than switchgrass for three main reasons:

• Miscanthus can gain greater amounts of photosynthetic carbon per unit of leaf area
• Miscanthus has a greater leaf area, and
• Miscanthus has a longer growing season

The team measured the amount of gas exchanged on the upper canopy of Miscanthus leaves from pre-dawn to post-dusk on 20 dates in the 2005 and 2006 growing seasons.

The averages from two years’ data showed that Miscanthus gained 33 percent more carbon than switchgrass.

Measurements also found the Miscanthus leaf area was 45 percent greater than switchgrass, and that Miscanthus plants grew an average of eleven days longer.

The extended growing season and accompanying lower temperatures proved to further boost the photosynthetic activity of the grass.

Miscanthus, sometimes called "Elephant Grass," can grow to heights of more than 3.5m in one growth season. Its dry weight annual yield can reach 25t/ha (10t/acre).

It's native to subtropical and tropical regions of Africa and southern Asia. And that's potentially a problem, say some.

Robert N. Wiedenmann, professor of entomology at the University of Arkansas, called for care in Miscanthus research in an article in last September's issue of Science.

"Most of the traits that are touted as great for biofuel crops—no known pests or diseases, rapid growth, high water-use efficiency—are red flags for invasion biologists," Wiedenmann wrote.

Seemingly benign crops have become invasive species when brought into new environments, he noted.

Wiedenmann and his colleagues cited the case of Sorghum halepense, otherwise known as Johnson grass. Johnson grass was introduced in the U.S. as a forage grass and rapidly became an invasive weed in many states, causing up to $30 million annually in losses for cotton and soybean crops in just three states.

And Miscanthus, Wiedenmann said, is "Johnson grass on steroids."

"Plants like these, particularly grasses, have great potential from an energy standpoint, but the benefits need to be balanced with the costs," he said.

The University of Illinois at Urbana-Champaign is participating with the University of California at Berkeley and the Lawrence Berkeley National Laboratory in a $500-million Energy Biosciences Institute (EBI) funded by BP (see BP funds biofuel research with $500M.)

As part of the EBI, some 340 acres of farmland at the Urbana campus are to be devoted to the study and production of feedstock for biofuel production.

Researchers will explore the potential of using corn crop residues, switchgrass, Miscanthus and other herbaceous perennials as fuel sources.