Kudzu Gets Kudos as a Potential Biofuel

June 16, 2008 -- As concerns rise over corn ethanol creating competition between food and fuels, ethanol made from one of the country's most invasive plants -- kudzu -- could be part of the solution, according to Rowan Sage of the University of Toronto and colleagues at the U.S. Department of Agriculture.

The kudzu vine, also known as "the plant that ate the South," was brought from eastern Asia in 1876 and can grow more than 6.5 feet a week. Its starchy roots plunge deep into the soil, and just a fragment of the plant remaining in the ground is enough to allow it to come back next season.

"Kudzu is just a large amount of carbohydrate sitting below ground waiting for anyone to come along and dig it up," Sage said. "The question is, is it worthwhile to dig it up?"

His team gathered samples of kudzu from different locations in the south at different times of year and measured the amount of carbohydrate -- which can be converted into ethanol by yeast -- present in leaves, vines and roots.

The roots were by far the largest source of carbohydrate in the plant: up to 68 percent carbohydrate by dry weight, compared to a few percent in leaves and vines.

The researchers estimate that kudzu could produce 2.2 to 5.3 tons of carbohydrate per acre in much of the South, or about 270 gallons per acre of ethanol, which is comparable to the yield for corn of 210 to 320 gallons per acre. They recently published their findings in Biomass and Bioenergy.

Crucial to making the plan work would be figuring out whether kudzu could be economically harvested, especially the roots, which can be thick and grow more than six feet deep. To balance this expense, Sage said, the plant requires zero planting, fertilizer or irrigation costs.

Even if equipment could harvest the roots, a large fraction of kudzu vines blanket steep hillsides and would be difficult to access. The team estimated that about one-third of kudzu plants would be harvestable. If so, they calculate that kudzu could offer about 8 percent of the 2006 U.S. bioethanol supply.