In experiments, sweet potatoes grown in Maryland and Alabama yielded two to three times as much carbohydrate for fuel ethanol production as field corn grown in those states, Agricultural Research Service (ARS) scientists report. The same was true of tropical cassava in Alabama.
The sweet potato carbohydrate yields approached the lower limits of those produced by sugarcane, the highest-yielding ethanol crop. Another advantage for sweet potatoes and cassava is that they require much less fertilizer and pesticide than corn.
Lew Ziska, a plant physiologist at the ARS Crop Systems and Global Change Laboratory in Beltsville, Md., and colleagues at Beltsville and at the ARS National Soil Dynamics Laboratory in Auburn, Ala., performed the study. The research is unique in comparing the root crops to corn, and in growing all three crops simultaneously in two different regions of the country.
The tests of corn, cassava and sweet potato were in the field at Beltsville, and in large soil bins at Auburn.
For the sweet potatoes, carbohydrate production was 4.2 tons an acre in Alabama and 5.7 tons an acre in Maryland. Carbohydrate production for cassava in Alabama was 4.4 tons an acre, compared to 1.2 tons an acre in Maryland. For corn, carbohydrate production was 1.5 tons an acre in Alabama and 2.5 tons an acre in Maryland.
The disadvantages to cassava and sweet potato are higher start-up costs, particularly because of increased labor at planting and harvesting times. If economical harvesting and processing techniques could be developed, the data suggests that sweet potato in Maryland and sweet potato and cassava in Alabama have greater potential than corn as ethanol sources.
Further studies are needed to get data on inputs of fertilizer, water, pesticides and estimates of energy efficiency. Overall, the data indicate it would be worthwhile to start pilot programs to study growing cassava and sweet potato for ethanol, especially on marginal lands.
The additional research could help develop new biofuel sources without diverting field corn supplies from food and feed use to fuel.