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Agriculture
Sorghum is always grown from seed. It is often planted in rotation, and grown primarily as a rain-fed crop. Sorghum is a short-day plant, and is adapted to a wide range of ecological conditions. Its optimum growth temperature is 30°C, and it cannot survive frosts. Because sorghum is drought-resistant, plants can remain dormant during periods of drought and resume growth when conditions improve; conversely, they cannot tolerate waterlogging. In some countries, like Sudan, plants can be grown under irrigation. Sorghum will grow well on heavy soils, especially the deep-cracking valley bottom and black-cotton soils of the tropics. In Sukumaland, Tanzania, it grows best on the clay mbuga soils of the hillsides. If cultivated with other crops, sorghum can depress their yield because the high sugar content of its roots depletes nitrate availability in the soil. Planting is determined by the time taken to maturity, which varies according to climatic conditions. In hot climates, maturity is reached with the first onset of rains.
Seedlings appear within seven days, and flowering is spread over a period of 6-15 days. Pollination may occur from the same plant, or by wind.
germination varies, with some seed remaining dormant for a month after harvesting. Thinning and weeding is generally manual, but sorghum can tolerate weeds more than most other crops.
During harvest, whole plants are cut down and their heads are removed or cut from the standing plants. Combine harvesting has been developed in the USA, and the technique is exported with the machines.
Grain yields are currently believed to be (in kg/ha): Africa, about 900; South-East Asia, about 700; USA, nearly 4000. The huge discrepancy is due to the small area grown in the USA - less than 4 million ha - that is grown in rotation, fertilised and chemically protected like other cereals; while in South-East Asia and Africa, over 15 million ha are largely sown by individuals for their own subsistence.
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