Description
#Sorghum (Sorghum bicolor (L.) Moench) grain is the fifth major staple cereal after wheat, rice, maize and barley. It is cultivated worldwide in warmer climates and is an important food crop in semi-arid tropical areas of Africa, Asia and Central America. Sorghum grain is a small, hard caryopsis covered by glumes. In grain sorghum, panicles are compact and bear 25,000 to 60,000 seeds/kg. Forage sorghum yields 120,000-160,000 seeds/kg. The whole grain can be boiled, roasted, popped or ground to make flour for baking (flat breads) and pastry. Sorghum grain is used for the production of alcoholic beverages, including beer and liquors. Some sorghum varieties are used for dyeing textiles or leathers.
In animal nutrition, grain sorghum is mostly used as an energy source and is a good feedstuff for poultry, pigs and ruminants. The stalks remaining after harvest can be grazed as some varieties stay green for a long period of time. Sorghum may also be grown for fodder, for grazing or cut green to make silage and hay.
Cultivars
Sorghum bicolor comprises several wild, weedy and cultivated annual types (subspecies) that are fully interfertile. Cultivated annual types are subdivided into 7 agronomic groups:
Kafir sorghums, originated from South Africa, with thick, juicy stems, large leaves, and awnless cylindrical-shaped panicles. Seeds are white, pink or red and medium in size.
Milo sorghums, originated from East Africa, have less juicy stems than the Kafir group. Leaf blades are wavy with a yellow midrib. Heads are bearded or awned, compact and oval in shape. Seeds are large, pale pink to cream in colour. Plants tend to be more tolerant to heat and drought than the Kafir group.
Feterita sorghums came from Sudan. Leaves are sparse in number. Stems are slender and dry. Panicles are compact and oval in shape. Seeds are very large for sorghum and chalky white in color.
Durra sorghums are from the Mediterranean Area, the Near East and Middle East. Stems are dry. Panicles are bearded, hairy and may be compact or open. Seeds are large and flattened.
Sballu sorghums from India have tall, slender, dry stems. Heads are loose. Seeds are pearly white in color and late maturing, thus requiring a relatively long growing season.
Koaliang sorghums, typical of those mainly grown in China, Manchuria and Japan, have slender, dry, woody stems with sparse leaves. Panicles are wiry and semi-compact. Seeds are brown and bitter in taste.
Hegari sorghums from Sudan are somewhat similar to Kafirs but have more nearly oval panicles, and plants that tiller profusely. Seeds are chalky white.
In the United States most varieties have been derived from crosses involving Kafir and Milo.
These 7 groups can cross-pollinate to give many hybrids. The germplasm of sorghum is enormous: the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in Patancheru, India, keeps a collection of 36,000 accessions from all the major sorghum-growing areas of the world.
Supply / Distribution
Sorghum is native to East Africa, possibly to Ethiopia and it is thought to have been domesticated around 1000 BC. It is now widespread between 50°N (USA and Russia) and 40°S, and from sea-level up to an altitude of 1000 m. Optimal growth conditions for sorghum are 25-30°C at seedling and 30°C day-temperature during growth, 400-750 mm annual rainfall on deep, well-drained loamy clay with a pH between 5.5 and 7.5.
Sorghum is tolerant to drought because of its root system. It performs better than maize during drought and occupies areas unsuitable for maize in stress-prone semi-arid areas. It is tolerant of salinity and to some extent to waterlogging for a short period. It is sensitive to frost and to sustained flooding. It is susceptible to weeds during its early stages of development. In Africa, Striga hermonthica, a parasitic weed, attaches itself to the roots and is particularly noxious to sorghum.
Processes
The grains have to be processed before being fed to cattle, or else a large proportion of them will be swallowed whole and the waxy bran covering the grain will make digestion difficult. Grinding is the simplest, least expensive method of preparing sorghum grain for cattle; other methods include dry-rolling, steam-rolling, flaking and popping. All methods produce end products with different degrees of digestibility.
Forage management
Yields
Green matter yields are about 20 t/ha, but may reach 75 t/ha under optimal growing conditions. Average yields of grain range from 0.5 to 0.9 t/ha in Africa, 2.3 t/ha in China and 3.6 t/ha in the USA (rainfed sorghum), or 4.5 to 6.5 t/ha from hybrid types under irrigation.
Environmental impact
Grain sorghum can be a high productive crop that requires adequate amounts of NPK fertilizer, with potentially deleterious effects on soils and groundwater. However, under harsh economic conditions, it may be cultivated in rotation with a legume crop benefiting from the nitrogen provided by the legume. After harvest, ploughing in the stubble can improve the organic matter status of the soil and help limit erosion. When sown in 20 cm rows, sorghum gives good protection from soil erosion. As a drought-tolerant species, sorghum improves water use efficiency while supporting relatively high levels of production in dairy cattle.
Nutritional attributes
Grain sorghum is mostly used as a cereal grain energy source and is a good feedstuff for poultry, pigs and ruminants. Its composition is roughly similar to that of maize and it is particularly rich in starch (more than 70% of the dry matter). Crude protein content in sorghum grain ranges from 9 to 13% DM and is slightly higher than that of maize, though much more variable depending on growing conditions. Like maize, it has a low lysine content and its utilization may require amino acid supplementation. Fat content is also slightly lower in sorghum grain than in maize. Sorghum grain is devoid of xanthophylls and 70% of its phosphorus is bound in phytate.
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