Web exclusive posted August 28, 2008 at 12:43 p.m. CST

Sweet potatoes produce two to three times as many carbohydrates than corn in Maryland and Alabama, according to researchers at USDA's Agricultural Research Service who studied the potential to use sweet potatoes as a feedstock for producing ethanol. Tropical cassava, a woody shrub that is cultivated annually in tropical and subtropical regions for its edible starchy tuberous root, showed high carbohydrate content in Alabama.

Sweet potato carbohydrate yields approach the lower limits of those produced by sugarcane, the highest-yielding ethanol crop. Another advantage for sweet potatoes and cassava is that they require less fertilizer and pesticide than corn, according to lead researcher Lew Ziska, a plant physiologist at the ARS Crops Systems and Global Change Laboratory in Beltsville, Md. The downside of the two crops is the high labor requirements for planting and harvesting.

For sweet potatoes, carbohydrate production was 4.2 tons per acre in Alabama and 5.7 tons per acre in Maryland. Carbohydrate production for cassava in Alabama was 4.4 tons per acre, compared to 1.2 tons per acre in Maryland. For corn, carbohydrate production was 1.5 tons per acre in Alabama and 2.5 tons per acre in Maryland. Carbohydrate content in corn is approximately 60 percent to 65 percent of the total yield. In Alabama, the corn yields were 80 bushels per acre and in Maryland 102 bushels per acre. Ziska said the national average corn yield for the same year was 151 bushels per acre.

The researchers say overall, the data indicated it would be worthwhile to start pilot programs to study growing cassava and sweet potato for ethanol, especially on marginal lands. However, further studies are needed to gather data on fertilizer, water, pesticides and estimates of energy efficiency. The additional research could develop new feedstock sources for biofuels.

Ethanol Producer Magazine reported on sweet potato's potential as an ethanol feedstock in its March 2008 issue.