Oklahoma State University


Sorghum as a Biofuel Crop

Sorghum (Sorghum bicolor (L.) Moench), is a plant species in the grass family Poaceae and is primarily cultivated for grain for human consumption and for animal feed. The species originated in sub-Saharan Africa and can grow in arid soils and withstand prolonged droughts.  Sorghum includes grain, grassy, and forage types, as well as weed relatives.  The grain types grow to heights of two to six feet; grassy sorghums are normally about five to seven feet tall; and forage and sweet sorghums reach heights of eight to fifteen feet.  Typically sorghum is grown as an annual, but some cultivars are grown as perennials in areas where winters are mild.

Like corn sorghum could be used potentially in three different ways to produce energy.  Ethanol can be produced from sorghum grain in a process similar to corn grain, from forage sorghum stalks similar to switchgrass or corn stover, or from sugars in the stalks of sweet sorghum similar to tropical corn or sugar beet.

In addition to its use as a biofuel crop, generally sorghum is used in the same ways as corn and its quality is considered to be almost equal to corn.  Sorghum’s main advantage over many other species is its ability to be productive under drought stress and high temperatures.  Under dry conditions sorghum yields are reduced but not to the extent of corn.  A complete crop failure is rare.

It is more likely that the sweet sorghums will become an important biofuel crop than grain sorghum or grass sorghums.  Grain sorghum would compete directly with corn and grass sorghum would compete with switchgrass and other crops in the cellulosic conversion of stems to ethanol.  Juice can be squeezed from stems of sweet sorghum relatively easily and the sweet juice converted to ethanol with a minimal amount of expense in transportation.  The stem material after juice has been removed can be used in cellulosic conversions or burned as is proposed for many other crop species.

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