Linda Benedict | 5/12/2015 8:12:58 PM
Donal F. Day
In 2011, the LSU AgCenter embarked upon a five-year initiative, funded through the U.S. Department of Agriculture, to develop crops that can be used for biofuel production across the southern United States, thus offering an opportunity to improve local farm incomes, create manufacturing jobs and supply significant quantities of feedstocks for the next generation biofuel industries. The major constraints on the chosen crops are the ability to tolerate the wide variety of climatic conditions that exist between north and south Louisiana and the need for staggered harvest schedules so crops can be delivered continuously to processing facilities over a major portion of a year.
To take advantage of Louisiana’s experience in sugarcane production and processing, two crops similar in structure to sugarcane and containing fermentable sugars – energycane and sweet sorghum – were chosen for development. Energycane is a variant of sugarcane high in fiber and low in sugar-containing juice. Sweet sorghum, a relative of grain sorghum that produces less seed, also contains a sugar juice. Both crops can be harvested and processed in a manner similar to sugarcane. The fermentable sugars in these juices could support rapid development for biofuel or any fermentation-based bioproducts industry, with lignocellulosic sugars phasing in as conversion technologies develop. The two chosen crops appear to be productive on marginal or underutilized land and would not affect current crop production.
Energycane will produce 20 dry tons per acre of biomass and 24 tons of juice per acre. The juice contains about 4,700 pounds of sugars per acre, primarily sucrose. The composition of sugars in the juice is identical to that of sugarcane juice. The biomass component again looks like sugarcane in composition. The major difference from commercial sugarcane is in the biomass-to-juice ratio, with energycane producing significantly more biomass and less juice than commercial sugarcane. This crop grows significantly faster than commercial sugarcane. Because of fast growth, it outcompetes weeds for water and light, negating the need for herbicide treatment. Most importantly, this crop survives winters in north Louisiana.
Sweet sorghum is in many ways the opposite of energycane. It produces more juice and less biomass. The juice contains sucrose, glucose and fructose. The yields per acre are less than energycane, 5-10 dry tons of biomass per acre and 3.6-36 tons of juice per acre, containing between 600 to 6,000 pounds of sugar per acre. Unlike energycane, it is an annual with a short growing season, 90-120 days, depending on the variety, allowing rotation with a nitrogen-fixing crop, such as clover, to minimize fertilizer requirements. The harvest cycle covers a part of the year when energycane is not available.
Post-harvest processing of these crops using sugarcane processing technology produces biomass and sugar syrups that are storable and contain high contents of fermentables. The biomass is suitable for power generation and could be converted to fermentable sugars using technologies that have been developed for converting corn biomass, called stover, to fermentable sugars. The value of these syrup sugars should be competitive with the value of sugars in sugarcane molasses. The breeding programs at the LSU AgCenter and the USDA Agricultural Research Service-Sugarcane Research Unit in Houma are producing improved varieties of energycane that give higher yields and show improved cold resistance. Commercial varieties of sweet sorghum are already available.
Markets have yet to be established for products from these crops. The syrups should fit well into the molasses markets, but there is not yet an established market for the biomass. Growth of industries that can use these crops will provide a path for financial growth for underdeveloped agricultural regions in Louisiana.
Donal F. Day is a professor and researcher at the Audubon Sugar Institute in St. Gabriel.
(This article was published in the spring 2015 issue of Louisiana Agriculture Magazine.)