Sweet potato (Ipomoea batatas (L.) Lam.) ranks seventh among crops grown for food, and tenth among all crops grown worldwide (FAO 1986). Besides food production, sweet potato has good potential as a biomass crop for ethanol and methane (Smith and Frank 1984). The accumulated carbohydrate in the roots can be efficiently digested and converted into ethanol or methane gas and used for energy (Smith et al. 1987).