Sorghum bicolor (L.) Moench

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Graminae

Synonyms

S. vulgare Pers.; Andropogon sorghum (L.) Brot.

Common names

Sorghum (United States, Australia), durra (Africa), jowar (India), bachanta (Ethiopia).

Description

Annual or short-term perennial, culms up to 4 m or more high, sweet except in grain types; panicle 8-40 cm long, loose or contracted; sessile spikelets 4- 6 mm long. Var. bicolor (Pers. ) Snowden: panicle loose and open, the upper branches slender and often drooping. Mature glumes of sessiIe spikelets either red or reddish brown, or straw coloured or yellowish, sometimes flushed with dark red or reddish brown; grain predominantly red or reddish brown. There are no creeping rhizomes and the mature sessile spikelets are persistent, less than twice as long as wide, not ridged in the middle, 3-4.5 mm wide (Chippendall, 1955). The bicolor sorghums are characterized by long, clasping glumes at least three-fourths as long as the broadly elliptical grain (de Wet, Harlan & Kurmarohita, 1972).

Distribution

It probably originated in Ethiopia and has spread to other parts of Africa, India, Southeast Asia, Australia and the United States.

Season of growth

Spring and summer through autumn until frosting.

Altitude range

Sea-level to 1 000 m.

Rainfall requirements

Mostly in an annual rainfall range of 400-750 mm. It is grown in areas which are too dry for maize.

Drought tolerance

The great advantage of sorghum is that it can become dormant under adverse conditions and can resume growth after relatively severe drought. Shoot removal lowers its capacity to withstand drought. Early drought stops growth before floral initiation and the plant remains vegetative; it will resume leaf production and flower when conditions again become favourable for growth. Late drought stops leaf development but not floral initiation (Wilson & Whiteman, 1965; Whiteman & Wilson, 1965).0

Soil requirements

It has adapted to a wide range of soils, from the deep sands of the Goz to the heavy black cracking clays of the Gedaref, Sudan. Varieties to suit each have been selected. Good drainage, however, is necessary. Its deep rooting can extract water from low sources, though not as deep as Pennisetum americanum (pearl millet). Its soil pH range lies between pH 5 and 8.5.

Ability to spread naturally

Very low, except for loose seed.

Land preparation for establishment

Sorghum requires full seed-bed preparation for good performance.

Sowing methods

In developing countries the seed is often planted by hand hoe and covered, the spacing depending on expected rainfall. Small hand drills are available as a first step in mechanization; sophisticated grain and fertilizer drills for precision placement are used in advanced agriculture.

Sowing depth and cover

Sorghum seed is usually sown at 4-5 cm depth.

Sowing time and rate

Spring to summer after rain (soil temperature should be above 18.5C) at 2-12 kg/ha, depending on soil-moisture expectancy and density of stand required, the heavier seeding being for forage production. Grain production in the 675-750 mm rainfall areas calls for 7-8 kg/ha of seed.

Number of seeds per kg.

28 600 to 61 000 in the United States.

Seed treatment before planting

All Sorghum spp. seed should be dusted with a combined fungicidal/insecticidal dust before planting.

Seedling vigour

Good.

Vigour of growth and growth rhythm

Most sorghum plants take 90-120 days to mature. The boot stage is reached in 50-60 days, flowering in 60-70 days, with full grain maturity in 120 days.

Response to defoliation

Sweet forage sorghum will stand a series of grazings where soil moisture and the temperature remain adequate, new branches and tillers being produced. Stalks may become thick and fibrous in the fodder types, and the forage or grass sorghums, such as Sudan grass, make better grazing.

Grazing management

In Queensland, Australia, the fodder sorghums are used mainly for silage production and the grain sorghums for grain. The fodder sorghums, however, are also used for autumn grazing by dairy and beef cattle to fill in a feed shortage between summer and winter grazing crops. The grain sorghums are valuable for grazing after the grain has been harvested and the crop residues (stubble, dropped seed-heads and regrowth, plus weeds) provide good autumn and winter roughage.

Response to fire

There is little trouble with fire, as the crop is generally fully utilized. The stubble can be burnt off to make way for cultivation for a new crop, but stubble retention can help prevent soil erosion and, if ploughed in, improves the organic status of the soil, especially if assisted by added nitrogen.

Dry-matter and green-matter yields

Sweet sorghums yield 25 000-75 000 kg/ha green matter, according to soil fertility and rainfall. Grain sorghums yield 300-2 000 kg/ha of grain in India and Africa under rain-fed conditions, and irrigated hybrid sorghums in the United States produce 4 500-6 500 kg/ha of gram.

Suitability for hay and silage

Sorghum is made into a coarse hay in some countries and stored for later feeding. Frequently the grain is first harvested and the "stover" used for fodder, for example for work oxen in India, and for building, such as African rondels. Good hay was made in the Burdekin area of Queensland from 50-day growth of 'Zulu' forage sorghum which contained 16.2 percent crude protein in the dry matter (Thurbon, Byford & Winks, 1970). Sorghum is one of the best crops for silage because of its high yields, the sugar content and juiciness of its stalk and its adaptability to areas receiving too little rain to ensure crops of maize. The ensilage of sorghum also usually effectively stops stock losses from prussic acid poisoning.

Value as a standover or deferred feed

It is quite a useful crop for standover and deferred feed, especially in frost-free areas, as it will continue to tiller and give a new green leaf for grazing while there is any moisture available in the soil.

Toxicity

In common with other Sorghum spp., it can contain lethal amounts of prussic acid (see S. almum for details).

Seed yield

The grain sorghums yield 300-2 000 kg grain per hectare in India and Africa under rain-fed conditions, and 4 500-6 500 kg/ha under irrigation for hybrid types in the United States and Australia.

Cultivars

There are numerous cultivars in use throughout the world and enquiries about the best cultivars and varieties for specific conditions should be made to agronomists within each country. Cultivars from the United States have been widely used in Australia, and Australian hybrids have also been produced to suit local conditions. Some Australian cultivars (Barnard, 1972) include the following:

  • 'Saccaline' 

    probably introduced from the United States to Australia, but thought to have originated in Natal. A tall, erect annual with five to six culms per plant; pith solid, juicy and sweet. Seeds reddish-brown, elliptical, approximately 39 000 per kg. Foliage abundant but dries off rather early and the crop presents a somewhat stemmy appearance compared with cv. Sugar drip or cv. White African. Late maturing, flowering in 80 days in latitude 27-30S and 65 days in latitude 23-24S, in Australia. It produces heavy fodder yields (50 000-70 000 kg/ha green matter), palatable to maturity; it makes excellent silage.

  • 'Sumac' 

    introduced to Australia from the United States, which in turn acquired it from Africa. Slightly shorter than 'Saccaline' with a short, compact panicle and plump, reddish-brown seeds. Its maturity date approximates that of cv. 'Saccaline'. Because of its lower height, it is a little easier to harvest for silage than 'Saccaline'.

  • 'Sugardrip' 

    introduced to Australia from the United States. Similar to, but leafier than, 'Saccaline'. Stems are juicy and very sweet. Seeds are brown and small, rounded on top and pointed at the base (rather than elliptical, as in 'Saccaline'). It is late maturing, five to seven days behind 'Saccaline' in flowering. It stands well and does not lodge as readily as 'Saccaline' and 'Sumac'.

    • 'White African'

    introduced to Australia from the United States, but originally from Natal. Thicker, taller and with stronger stems than 'Saccaline', it tillers less, and its leaves are more widely spaced. Seeds white, approximately 40 000 per kilogram. Germination tends to be low. Late maturing, resists lodging, more resistant to leaf diseases than other cultivars. It carries well into the winter, but its juice is not so sweet. Very good for silage.

    • 'Early Orange'

    developed at Grafton Agricultural Research Station from a variety called 'Kansas Orange' in the United States. Similar to cv. Saccaline, with stalk a little stronger (but not as strong as 'White African' or 'Tracy'). Panicles medium compact; seeds orange-brown, ellipsoid, approximately 40 000 per kilogram. Early- maturing type, suitable for late sowing. Has a higher sugar content in its juice than 'Saccaline'.

  • 'Tracy' 

    developed in Mississippi, United States for sugar production; introduced to New South Wales and Queensland. Similar in appearance to 'Saccaline', but leaf growth rather sparse in comparison to its height. Panicle small, erect, and cylindrical. Seed dark reddish brown and duller than those of 'Saccaline'; approximately 40 000 per kilogram. It is late-maturing, flowering two weeks after 'Saccaline' (about the same time as 'White African'). It resists lodging. The stems are palatable and juicy, with a high sugar content; they hold their juiciness into winter. Resistant to leaf diseases.

Diseases

There are numerous diseases of sorghum. Leaf diseases are the most troublesome for forage producers. These are anthracnose caused by Colletotrichum graminicola (which can be overcome by using resistant varieties) and leaf blight caused by Helminthosporium turcicum. Charcoal rot (Macrophomina phaseoli) causes plants to lodge badly. Grain may be affected by covered smut (Sphacelotheca sorghi) in which the seed is replaced by a sac of spores; fungicidal seed dressing before planting corrects this malady. The parasitic weed Striga hermonthica occurs in Africa. Its seeds can only germinate when stimulated by a substance from the host root, and must be not more than 1 cm from it. The radicle attaches itself to the host root by a haustorium which penetrates the vascular system and parasitizes the sorghum below ground for three to six weeks; it then emerges and produces chlorophyll and photosynthates. Flowering commences ten to 20 days after emergence. It can be controlled by using a trap crop of Sudan grass, which is ploughed in after two months' growth.

Main attributes

Sorghum has wide adaptability, is more drought-hardy than maize, makes excellent silage and has a wide range of uses.

Main deficiencies

Its tendency to be toxic.

Optimum temperature for growth

30C.

Frost tolerance

Sorghum is very susceptible to frost, but thick-stemmed, standing, sweet fodder sorghum will retain stem juiciness and sweetness for some time after the leaves are killed.

Latitudinal limits

40N and S.

Response to light

Sorghum requires full harnessing of incoming radiation for high yields of grain and forage, and does not grow well in shade.

Ability to compete with weeds

For grain production inter-row cultivation is frequently used. Where rows are close, weeds are suppressed by the shade of the crop canopy, but thorough seed-bed preparation is needed before planting to ensure a low weed population. Spraying with a pre-emergence weed-killer, e.g. atrazine at 1 kg AI/ha (Singh, Pandey & Shankarnarayan, 1970), completely controlled broad-leaved weeds such as Portulaca and Amaranthus spp. and the grassy weeds Eleusine indica, Echinochloa corona, Brachiaria ramosa and Digitaria ciliaris.

Maximum germination and quality required for sale

70 percent germinable seed, 97.6 percent purity (Queensland).

Pests

From a forage point of view, grasshoppers would appear to be the worst pest, and feral pigs can cause havoc. Grain pests include the sorghum midge, Contarinia sorghicola, whose larvae feed on the developing seeds. Bird damage is also important and in Africa the weaver bird, Quelea quelea, causes major losses. Attempts to prevent damage by using awned varieties of sorghum give some hope of reducing losses. The high tannin content of the sweet sorghum seed is another deterrent, and early harvesting for silage avoids the main problem.

Palatability

The sorghums are all very palatable, especially in the young and flowering stages.

Response to photoperiod

Sorghum is a short-day plant. One variety began head differentiation in 23 days in a ten-hour photoperiod, compared with the norm of 39 days with a day length of 14 hours. Temperature also has an effect; flowering occurs earlier at 22-26C than at 17-20C.

Chemical analysis and digestibility

At harvest the grain sorghum stubble contains 50-70 percent moisture; it can be made into silage. The crude protein content will be about 6-7 percent (3-5 percent if irrigated) in the stubble; silage made from it will have 48-56 percent digestibility or, if dry, 48-50 percent. The material will generally need a mineral supplement of CaP of 1:1 for gestating and lactating cows, plus a vitamin A supplement (Corah, 1979). In Sri Lanka, Andrew (1971) recorded 20 percent dry matter, 3.9 percent digestible crude protein, 61.9 percent total digestible nutrients, 7.8 percent crude protein, 33.2 percent crude fibre, 1.5 percent ether extract, 51.2 percent nitrogen-free extract and 6.3 percent ash.

Tolerance to flooding

Sorghum is intolerant of sustained flooding, but will survive temporary waterlogging.

Fertilizer requirements

These will be determined by soil type and rainfall. A basic dressing of NPK may be required, and the crop usually responds well to additional dressings of nitrogen during growth. A fallowed black clay may not need fertilizer. Rotation with a leguminous crop can give low-cost fertility build-up, for example, gum arabic (Acacia senegal) in the Sudan. Asher and Cowie (1974) showed that the effect of nitrogen deficiency on grain yield is greatest when the deficiency occurs early in the growing season. Low grain protein results when nitrogen deficiency occurs between anthesis and maturity.

Compatibility with other grasses and legumes

It is generally grown as a pure crop in commercial grain production. In village crop areas it may be planted in rows alternating with other food or fibre crops in a rotation to spread labour and improve fertility. For forage and silage it is frequently grown with legumes, such as cowpea, to improve the nutritive value for grazing or stored fodder.

Genetics and reproduction

2n=20 (Fedorov, 1974). They cross-pollinate readily, thus seed-producing crops should be isolated by a distance of about 1 km from others.

Seed production and harvesting

Sorghums usually give high yields of seed. The fodder sorghum grains contain higher tannin than the grain sorghum. This may affect egg production by poultry consuming a sorghum meal mixture; hence, grain sorghum is usually used.

Economics

Sorghum bicolor is one of the major grain crops for human food throughout the drier areas of Africa and India. The fodder varieties are used widely for cut green fodder and silage, and for syrup production. The stalks are used for stover, roughage, thatch and fuel.

Animal production

The grain is used extensively for animal feeding in concentrate rations, with high-protein constituents. After the grain is harvested, the sorghum stubble gives quite useful grazing in winter when other feed may be scarce. Curran (1957) reported a grain yield of 1 609 kg/ha in central Queensland, and afterwards the stubble carried 5.5 sheep per hectare for a whole year. Grazing fodder sorghums in autumn to fill in a feed gap is also a sound practice. Onley and Sillar (1965) obtained an average live-weight gain of 0.86 kg per head per day over a seven- month period in northern Queensland from yearling steers grazing sweet sorghum at the rate of 1 beast/0.8 hectare.
Hintz and Gilliland (1976) showed that cv. Zulu, when sown in early October on the Darling Downs in Queensland, will yield 10 080 kg/ha green matter, of which about 5 000 kg/ha will be available from December to January. Two other grazings will be obtainable before winter, each of about 300 kg/ha. Nitrogen applied at 50 kg/ha with adequate subsequent rain after the first grazing will boost yields. If sown in late December to early January the crop yields about 5 000 kg/ha grazed in March-April with little regrowth. Cultivar Sugardrip, sown in October, will yield 8 400 kg/ha green matter, giving 3 900 kg/ha in December, plus two other grazings each of about 2 400 kg/ha. If sown in mid-January and fed late April to July it will yield about 5 600 kg/ha.

Dormancy

Sorghum seed shows dormancy for the- first month after harvest.

Value for erosion control

Row sorghum gives only reasonable protection from soil erosion but broadcast sorghum or sorghum sown in 20-cm rows gives good protection. Its quick growth is valuable in this regard.

Tolerance to salinity

In some areas of California, accumulation of salt in the soil is sufficiently high to inhibit germination of seed, and young plants are injured. The tolerance of sweet sorghum to salt, however, appears to be relatively high after the plants become well established. The seed can be planted in beds 75-100 cm apart. In this single-row bed the seed is planted in a furrow made with a small plough mounted ahead of the planter shoe. The concentration of salt in the immediate vicinity of the seed is lower here than at the top of a high bed, and germination of seed is not inhibited (Price & Stokes, 1966). Sorghum has a high tolerance of sodium carbonate (Chapko, 1977).

Links:

Links for the genus:

  • Poisonous plants: Short description of S. bicolor, S. halepense and S. sudanese; photographs

Further reading

Hintz & Gilliland, 1976; Martin & Leonard, 1959; Wyllie & Stirling, 1977.