Nebraska Sweet Sorghum
It looks like split-pea soup and tastes like sugar water with a vague vegetative twist. But never mind.
Ishmail Dweikat and John Rajewski don’t have their collective eye on Gatorade as the primary competition for the juice from the 12-foot long, one inch-thick stalks of sweet sorghum they’re harvesting from a University of Nebraska test plot.
Dweikat, leader of sweet sorghum research at UNL, and Rajewski, field manager and plant breeder, are more interested in using these plants rustling in the East Campus breeze as the raw material for future ethanol production.
“If you want a reliable source for ethanol,” Dweikat said, “corn would not be the one.”
Sweet sorghum’s advantages over Nebraska corn are many, he said.
It doesn’t need to be irrigated and goes into dormancy during drought periods. The ratio of energy consumed to energy produced is much higher than corn, and an acre of sweet sorghum can produce as much as 800 gallons of ethanol.
Corn’s ethanol yield is closer to 250 gallons per acre.
Despite what the UNL researchers see as sweet sorghum’s considerable promise, corn growers serving the ethanol market don’t need to leap out of the way just yet.
It will take another year or two to develop the right hybrid, Dweikat said. Harvesting equipment that can crush the juice out of the stalks as it moves through the field is also a work in progress.
“Back in the 1900s, sweet sorghum was used as a source of molasses,” he said.
In a new century, possibilities for what can happen with a plant traceable mostly to Africa are headed in an energy direction.
Can the crop be a major source of renewable fuel?
“It’s very likely it will be if we can get the mechanics worked out for it,” said Rajewski.
Dweikat said Texas and Oklahoma, neither of which is a major producer of corn, are further along in building distilleries to boil the water out of sorghum juice and convert what’s left to motor fuel.
But tall stands of sweet sorghum, which carry seed clusters at the very top, can be grown anywhere corn and grain sorghum can be grown.
In Nebraska, home to gusty winds early and late in the growing season, an adaptation is in the works.
“We’re trying to breed for tall, big stalks without seed,” Dweikat said. “If there’s nothing heavy on the top, it has a much better chance of standing the wind.”
Signs of success at UNL are not exactly taking the ethanol industry by storm. Preliminary checks with the ethanol establishment in other states failed to turn up anybody gushing with enthusiasm.
Brian Jennings, based in Sioux Falls, S.D., with the American Coalition for Ethanol, is among the less than overwhelmed. He sees corn and cellulosic ethanol made from the rest of the corn plant as dominant factors.
“I think corn will remain the centerpiece for years to come,” Jennings said, “and then we will see corn stover and corn fiber and other things like that kick off very soon.”
If sweet sorghum is a better choice, “that would be news to me.”
James Covey, ethanol advocate and state legislator from Custer City, Okla., said his state is moving toward building its first ethanol plant, but will use the same grain supply to make the finished product as plants elsewhere.
Sweet sorghum, said Covey, is “a different breed of pup.”
Dweikat and Rajewski are undeterred and lay out a future in which Nebraska farmers distill their own juice and store it in rubber bladders until it can be picked up by cooperatives and hauled off to make ethanol.
“Of course, economics drives everything,” Rajewski said, “economics and water availability. So we’ll see how that goes.”
The sweet sorghum research is being conducted on dryland plots at UNL’s High Plains Ag Lab near Sidney and at other Nebraska locations. UNL is looking at some alternative ethanol-producing crops for farmers who rely on dryland or limited-irrigation production, according to Drew Lyon, extension dryland crops specialist at the Panhandle Center. Growing dryland corn is risky in the Nebraska Panhandle. Sweet sorghum may be a crop that dryland farmers can grow more consistently and profitably.
In 2007, field studies were conducted at Sidney, North Platte, and Clay Center to determine theoretical ethanol yield from sweet sorghum, corn, and grain sorghum. This work was done by Lyon, in cooperation with other UNL experts, Ismail Dweikat of Lincoln, Charles Wortmann, extension, from Lincoln, and Bob Klein, extension cropping systems specialist at the West Central REC in North Platte.
Preliminary findings indicate that, compared to corn and grain sorghum, sweet sorghum does not produce more ethanol yield per acre, but does produce greater net energy. This results in a net reduction in CO2 emission compared to corn or grain sorghum, and much more energy produced per energy invested. Approximately 250% more energy is produced than invested for sweet sorghum, compared to 50% more produced than invested for corn or grain sorghum. Sweet sorghum produces more net energy because it produces sugar, rather than starch. According to Lyon, less energy is needed to make ethanol from sugar than from starch. Sweet sorghum may require less nitrogen fertilizer input than corn, and may be more water-use efficient than corn.
Some potential problems with sweet sorghum include harvest challenges — for example, what to do with all the biomass and where and how to extract the sugar. The plants are very tall, and seed production is low. Questions also remain about how to feed sugar into a corn ethanol stream.
