UNL researchers optimize sweet sorghum for bioenergy feedstock

By Erin Voegele | April 08, 2011

Researchers at the University of Nebraska-Lincoln have made impressive strides in their work to optimize sweet sorghum for use as a bioenergy feedstock. According to UNL associate professor Ismail Dweikat, at least two hybrid strains of the crop developed by his team will be entering the market next year. In addition, work is continuing to develop cold-tolerant and nitrogen-efficient strains of sweet sorghum.

The two hybrids that will be entering the market next year feature higher sugar content levels than sugarcane, Dweikat said. “Sugarcane has about 14 to 16 briks, which is the measure of the soluble solid in the juice,” he said. “Our hybrid that we are going to release has about 19 to 21 briks.” The high sugar content of the hybrid has obvious benefits for first-generation biofuels production. However, the residual biomass of the crop could also be an excellent feedstock for cellulosic biofuel production, he added, noting that there is also potential to use the crop as a feedstock for heat and power generation.

Dweikat and his team are also working to develop additional varieties of sweet sorghum. A project funded with grants from the U.S. DOE and the National Sorghum Checkoff aims to develop varieties of the crop that are more cold-tolerant and use soil nitrogen more efficiently.

According to Dweikat, current varieties of sweet sorghum required soil temperatures of 65 to 75 degrees Fahrenheit to germinate. “What we are trying to do is select for lines and varieties of sweet sorghum that are able to be planted [earlier in the season], the same time as you plant your corn,” he said. “The other objective we have it to try to enhance the nitrogen efficiency in both grain sorghum and sweet sorghum. Farmers add nitrogen to the soil and [plants] uptake less than 50 percent of it. The rest is just washed down to our streams and our oceans. We are trying to minimize the input of nitrogen so we could reduce the environmental pollution and also cut down on the cost [of nitrogen].”

Nearly 25 acres of research plots have already been planted with sweet sorghum as part of the research. “Most of these plots are rain fed and we do not apply any nitrogen to them because we have them in rotation with soybeans,” Dweikat said.

There are several reasons why sweet sorghum is an attractive biofuel feedstock, he continued. It is very drought-tolerant, can be grown on marginal land and requires very little nitrogen when compared to corn. In addition, Dweikat noted that most of the sweet sorghum already grown in the U.S. is rain fed, which not only saves water but also energy associated with irrigation.  

Dweikat is also conducting research on a crop called millet, which could serve as a cellulosic feedstock. “It produces high biomass and would be an ideal crop for cellulosic-based ethanol because it requires very low input and is drought-tolerant, and can be grown on marginal land,” he said.

Dweikat is scheduled to speak about his research at the International Biomass Conference & Expo in May. His presentation, “Sweet Sorghum: The Sugarcane of the Midwest,” will be featured during the event’s Aligning Energy Crop Production with Desired Energy Product Outcomes panel. The panel will also feature presentations by Saritha Peruri of Ceres Inc., Richard Carlton of CST Growth LLC and David Allen of White Technology LLC.