Sweet Fuel

Sweet sorghum is great for moonshine and might be a promising Missouri-made biofuel

During World War II, when sugar was rationed, bootleggers used the juice of sweet sorghum to make moonshine. Now researchers at the University of Missouri Delta Research Center are studying ways to boost the plant’s potential to brew not booze, but biofuel.

The corn-like grass, which can grow to 12 feet, shows promise as a source of ethanol, said Gene Stevens, MU College of Agriculture, Food and Natural Resources extension associate professor.  He is evaluating initial research results on ways to genetically adapt a plant that is not normally productive in Missouri to create something that could serve as a homegrown source of alternative fuel.

“Sweet sorghum is a first cousin to sugar cane and usually grown in tropical areas,” Stevens said.  “As we have seen in Brazil, both crops can yield as much ethanol as corn can.”

Sweet sorghum can and does grow in temperate zones such as Missouri, but often struggles or dies from cold temperatures when it is planted before early May. “Most varieties of this native African plant do not grow fast enough in the American Midwest to make it a better ethanol producer than corn,” Stevens said.  “By genetically blending sweet sorghum with other grass species such as sudangrass, we think that can create a hybrid that is more cold-tolerant and yield a profitable crop in Midwestern states.”

“In Africa, we can grow sweet sorghum twice a year, but here in America you can grow it just once a season,” said Roland Holou, MU graduate student working with Stevens and who is originally from the African nation of Benin.  “A big benefit that we have in Africa is that we can get two yields through Ratoon cropping.”  Ratoon cropping is often used in sugar cane production with the lower part of the cane and stalk left uncut during the first harvest.  For the second crop, new shoots grow from the original roots, saving farmers the cost of preparing the soil and planting new seeds.

Stevens planted five sweet sorghum varieties on about 10 acres at the Delta Research Center in Portageville, Mo. at different seasonal timings to test which has more natural cold-tolerance. Once the plants mature, Holou measures the sugar content in their stems. The best-performing varieties may be candidates for efforts to genetically engineer a crop better suited to Missouri.

“If we can take genes from the cold-tolerant variety and put them into a variety that produces more sugar, we’ll get the best of both worlds,” Stevens said.

“If we can harvest earlier, it will grow back again and we could get two harvests instead of one, making sweet sorghum a more viable fuel crop which would benefit both farming and conservation, he continued.”

Sweet sorghum as a fuel has several potential ecological benefits

Sweet sorghum as a fuel has several potential ecological benefits, Stevens said.  It consumes less nitrogen and water in the growing process, and returns more nutrients to the soil.  It needs less energy in the ethanol production process, he said.

Less nitrogen fertilizer put onto the plants during growth would reduce runoff into streams, Holou said. “The plant is also carbon-neutral.  It removes almost the same amount of carbon dioxide from the atmosphere while growing that is emitted during ethanol production.”

Stevens said that tests so far show that sweet sorghum grown in high-quality silt loam soil plots produced stalks that contained enough sucrose and glucose to produce 600 gallons of biofuel per acre when fermented properly.  Corn plots in the same study produced almost exactly the same amount of ethanol, but required approximately three times the amount of fertilizer.

On poor quality sandy and heavy clay soils, however, sweet sorghum easily out produced corn as a maker of biofuel.  “This indicates to me that we may be better off planting corn for food and feed on our most productive silt loam soils and growing sweet sorghum for ethanol in fields with marginal soils,” Stevens said.

“Sweet sorghum can be grown in areas where corn doesn’t grow very well right now,” Stevens said. “It’s another crop option that’s versatile and will keep performing in situations where corn won’t.”

Great news.  But let’s not tell the bootleggers.