SIOUX FALLS, S.D. - Corn is the seasoned veteran of the ethanol industry, but promising prospects including wood chips and prairie grass - including switchgrass, made famous by President Bush - could soon be in the alternative energy lineup.

While corn gets the headlines, companies are exploring a host of other potential fuel sources including sorghum stubble, citrus peel, timber scraps and even landfill trash.

Experts say it will be years before companies decide if those sources can be commercially viable, but the research is well under way.

And some refinery production could be as little as two years away.

Ottawa-based Iogen Corp. has been producing ethanol from wheat, oat and barley straw for several years at its demonstration plant in Canada, and it plans to build a commercial-size version in Shelley, Idaho.

When it comes to things like switchgrass - mentioned prominently by Bush this year and last - success will depend on farmers learning how to grow new crops, said Anna Rath, director of business development for Ceres Inc., a biotechnology company in Thousand Oaks, Calif.

Crop-breeding technology developed over the past 70 years has increased corn yields more than fivefold, Rath said, and Ceres wants to be on the forefront of developing energy crops.

So-called cellulosic ethanol is basically fuel made from plants or plant waste - something other than a corn kernel.

Making fuel from this biomass is well-established, but it costs about twice as much as cooking up corn-based fuel, government researchers say.

Earlier this year, the Energy Department awarded $385 million to six companies hoping to build the nation's first big biomass-to-fuel plants.

The investment is part of the Bush administration's goal of making cellulosic ethanol competitive by 2012.