Sweet potatoes can yield two to three times as
much fuel ethanol as field corn, approaching the amount that sugarcane can
produce. Photo courtesy of the Louisiana Sweet Potato Commission.
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Sweet Potato Out-Yields Corn in Ethanol Production Study
By Don Comis
August 20 , 2008
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.
ARS is a scientific research agency within the
U.S. Department of Agriculture.