From corn waste to bio-fuel.

What's the big deal about ethanol, anyway? Made primarily from corn kernels, it's mostly used as a gasoline additive that boosts oxygen content and reduces air pollution, but it has the potential to replace gasoline in passenger vehicles. Already, auto manufacturers are turning out "flex-fuel" vehicles that can run on either gasoline or a blend containing 85 percent ethanol. (Environmentalists have criticized the ethanol subsidy program as a political giveaway to farm states, since many "flex-fuel" vehicles rarely run on hard-to-find ethanol.)

While ethanol is cleaner and more efficient to produce than gas, the land and fertilizers used to grow the corn, the runoff from the fields, and the energy used to plant and harvest the crop have many environmentalists giving this alternative fuel the cold shoulder.

But some supporters argue that needn't be the case. The ethanol source of the future, some experts say, is not the corn kernel but the stover--the stalk, cob and other portions of the plant that are currently fed to livestock, burned or left lying on the field--as well as wheat residue, rice straw and fast-growing "energy crops" such as switchgrass or poplar trees. Such cellulosic ethanol, as it is called, "is dramatically more efficient than corn ethanol," says David Friedman, research director of the Union of Concerned Scientists' Clean Vehicles Program.

Already cellulosic ethanol is being produced in small quantities throughout the country, using everything from brewery waste to cheese whey. A Canadian company, Iogen Corporation, is processing up to 50 dry tons of wheat straw into ethanol every week and selling it commercially in the Ottawa area.

The Iogen plant has a capacity of only about a million gallons a year. In 2004, U.S. ethanol producers made about 3.4 billion gallons of the fuel, mostly from corn, according to the Renewable Fuels Association (RFA), an ethanol lobbying group. "Right now cellulosic is an inefficient technology," says RFA spokesperson Monte Shaw. "Funding into additional research is needed."

John Sheehan of the National Renewable Energy Laboratory (NREL) National Bioenergy Center says that farmers often leave corn stover on the land to enrich and protect the soil. To collect it sustainably, farmers would have to invest in equipment for whole-plant harvesting. Sheehan says farmers would also need to adopt no-till practices.

Cellulosic supporters note that the U.S. gasoline habit, at 375 million gallons per day according to the Department of Energy, cannot be replaced with agricultural wastes alone. Another potential source being looked at is switchgrass, a native prairie grass that doesn't need much fertilizer, is drought resistant and grows well in our climate, according to Nathaniel Greene, a senior policy analyst at the Natural Resources Defense Council.

Environmentalists agree ethanol has a place at the table. "But are we ever going to evolve beyond corn ethanol?" Greene asks. "If not, we won't be able to make a big dent in oil consumption." CONTACT: Iogen, [phone], www.io gen.ca; NREL, [phone], www. nrel.gov; RFA, [phone], www. ethanolrfa.org; UCS, [phone], www.ucsusa.org.