Sorghum (Sorghum bicolor) appears to have been domesticated in Ethiopia about 5000 years ago. Present world production is about 58 million tons grain from 42.6 million ha. (FAOSTAT, 2001).
Sorghum has a number of features which make it a drought-resistant crop. It is extensively grown under rainfed conditions for grain and forage production. In dry areas with low and/or erratic rainfall the crop can respond very favourably to supplemental irrigation. However, considerable differences exist amongst varieties in their response to irrigation and those that are considered very drought-resistant respond slightly while others produce high yields under irrigation but are poor yielding when water is limiting. Temperature is an important factor in variety selection. Optimum temperatures for high producing varieties are over 25°C but some varieties are adapted to lower temperatures and produce acceptable yields. When mean daily temperatures during the growing season are greater than 20°C, early grain varieties take 90 to 110 days and medium varieties 110 to 140 days to mature. When mean daily temperatures are below 20°C, there is an extension of about 10 to 20 days in the growing period for each 0.5°C decrease in temperature, depending on variety, and at 15°C a sorghum grain crop would take 250 to 300 days to mature. With mean daily temperatures in the range of 10 to 15°C, the sorghum crop can only be grown as a forage crop because of the problems with seed set and grain maturity under cool conditions. Low temperatures (<15°C) during flowering and yield formation, and high temperatures (>35°C) lead to poor seed set, problems with ripening and reduced yields.
For optimum light interception the density index (plants per ha s row spacing) is about 3000 when adequate water and fertilizers are available (100 000 to 150 000 plants per ha). In areas where water (rainfall + irrigation) is in short supply, the greater the shortage, the greater is the advantage of wider spacing. Sorghum is a. short-day plant but day-neutral varieties exist.
The crop does well on most soils but better so in light to medium textured soils. The soil should preferably be well-aerated and well-drained. Sorghum is relatively tolerant to short periods of waterlogging. The fertilizer requirements are up to 180kg/ha N, 20 to 45 kg/ha P and 35 to 80 kg/ha K.
Sorghum is moderately tolerant to soil salinity. Yield decrease due to soil salinity under irrigation is: 0% at ECe 4 mmhos/cm, 10% at 5.1, 25% at 7.2, 50% at 11 and 100% at ECe 18 mmhos/cm.
The graph below depicts the crop stages of sorghum, and the table summarises the main crop coefficients used for water management.

| Stages of Development | Plant date | Region |
---|
Crop characteristic | Initial | Crop Development | Mid- season | Late | Total | | |
Sorghum-grain |
Stage length, days | 20 20 | 35 35 | 40 45 | 30 30 | 130 145 | May/June March/April | USA, Pakis., Med. Arid Region |
Depletion Coefficient, p | 0.6 | >> | 0.5 | 0.8 | 0.55 | | |
Root Depth, m | 0.30 | >> | >> | 1.4 | – | | |
Crop Coefficient, Kc | 0.7 | >> | 1.0-1.15 | 0.55 | – | | |
Yield Response Factor, Ky | 0.2 | 0.55 | 45 | 0.2 | 0.9 | | |
Sorghum-sweet |
Stage length, days | 20 20 | 35 35 | 40 45 | 30 30 | 130 145 | May/June March/April | USA, Pakis., Med. Arid Region |
Depletion Coefficient, p | – | – | – | – | 0.5 | | |
Root Depth, m | – | – | – | – | 1.0-2.0 | | |
Crop Coefficient, Kc | 0.7 | >> | 1.2 | 1.05 | – | | |
Yield Response Factor, Ky | – | – | – | – | – | |