Properties: Sweet sorghum is grown worldwide on about 44 million hectares in almost one hundred different countries. It is therefore the fifth most important cereal crop in the world. The major producers are the United States, India, Nigeria, China, Mexico, Sudan and Argentina.
Sweet sorghum is a highly competitive crop and can dominate over many weeds and other plants. Sweet sorghum is a drought resistant plant that needs only about 175 cubic meters of water per crop to thrive. This is not even one quarter of the average water requirement of sugarcane crop. Tillers and heads are produced over a longer time period and therefore short periods of drought do not seriously harm pollination and fertilisation. In a longer drought, sweet sorghum produces fewer and smaller heads. The waxy coating of sorgum foliage makes them resist drying and they lose a smaller percentage of their water content than, for instance, corn leaves.
The planting season of sweet sorghum, at 100-115 days, is relatively short. The average yield for this period of time is varying between 95-125 tons. Sweet sorghum has a very high sugar content, varying from 15 to over 20 percent. Maximum yields are achived at average temperatures of at least 80°F. Photosynthesis is best at day-time temperatures higher than 90°F. During planting time the sorghum seed needs soil temperatures of 60-65°F.
Ethanol is produced from the sweet juice available in the stalk of the crop plant. The grains can still be used for food and feed purposes. Sweet sorghum has a higher vitamin and protein content than honey and can be used for the production of syrup, flour, and a popcorn-like product called pop sorghum kernels. Sweet sorghum is cheaper to produce than other comparable grains. In India for example, its cost of cultivation is about one-third that of sugarcane.
Even though its sugar is more nutritious and easier to grow than that produced from sugar cane, its primary drawback as a sweetener is the difficulty of converting sweet sorghum sugar into sugar crystals. It is for this reason that sweet sorghum has never thrived as a primary food sugar crop. This issue presents no problem for biofuel production--in fact, due to the biologically simplier structure of the sugars in sweet sorghum its sugar is easier to convert to ethanol than most other sugar crops.
In recent years with tests in India, Europe, Asia, the USA, and now in Australia, Sweet Sorghum has been discovered to be a nearly ideal biofuel crop, with all of the advantages of sugar cane (and more of its own) and almost none of its disadvantages.
Food: Sweet sorghum, similar to grain sorghum grows a high value grain cob that can be sold for human consumption and animal feed.
Fuel: Juice from the cane stem can easily be converted to ethanol by sugar fermentation in a similar process to sugar cane juice.
Future: Sweet sorghum bagasse (cane fibre remained after sugar juice pressing) can be used in many green technology applications and is especially suited to emerging technologies such as cellulosic ethanol conversion.
Hundreds of varieties of sweet sorghum have been bred over the years and varieties can be selected by growers to tailor the output characteristics for any number of requirements such as climate, soil and water availability, height, fibre content, amongst many others.
In essence, sweet sorghum is an almost ideal biofuel crop and this assertion is supported by volumes of academic research the world over. Perhaps its only disadvantage is that it can produce only 1-2 crops per year in colder climates as compared to 3-4 crops per year in sub-tropical and tropical regions.
For detailed academic information supporting sweet sorghum’s claims to its suitability as an idea biofuel, please contact AgriFuels.
Some of the economic and energy contributions of the by-products mentioned earlier are negated by the environmental pollution costs associated with ethanol production using corn as input feedstock. These are estimated to be more than 6c / per l of ethanol produced (Pimentel, 2003). U.S. corn production causes more total soil erosion that any other U.S. crop (Pimentel and others, 1995; NAS, 2003). In addition, corn production uses more herbicides and insecticides than any other crop produced in the U.S. thereby causing more water pollution.
Further, corn production uses more nitrogen fertilizer than any crop produced and therefore is a major contributor to groundwater and river water pollution (NAS, 2003). In some Western U.S. irrigated corn acreage, for instance, in some regions of Arizona, groundwater is being pumped 10 times faster than the natural recharge of the aquifers (Pimentel and others, 2004b). All these factors suggest that the environmental system in which U.S. corn is being produced is being rapidly degraded. Further, it substantiates the conclusion that the U.S. corn production system is not environmentally sustainable now or for the future, unless major changes are made in the cultivation of this major food/feed crop. Corn is raw material for ethanol production, but cannot be considered to provide a renewable energy source. Major air and water pollution problems also are associated with the production of ethanol in the chemical plant. The EPA (2002) has issued warnings to corn ethanol plants to reduce their air pollution emissions or be shut down. Another pollution problem is the large amounts of wastewater that each corn ethanol plant produces. As mentioned, for each liter of ethanol produced using corn, about 13 l of wastewater are produced. This wastewater has a biological oxygen demand (BOD) of 18,000–37,000 mg/l depending on the type of plant (Kuby,Markoja, and Nackford, 1984). The cost of processing this sewage in terms of energy (4 kcal/kg of BOD) was included in the cost of producing ethanol.
