In this article we will discuss about the climate and soil requirements for sorghum cultivation.
Climate:
Although sorghum is of tropical origin, it has been adopted by breeding for cultivation in temperate regions provided temperatures are sufficiently high. In temperate regions, it is grown during summer, whereas in tropics it can be grown throughout the year. It does not tolerate frost and most sorghum production is concentrated between latitudes 40°N and 40°S. It can adequately recover from drought and can also withstand temporary flooding.
Sorghum is well adopted to semiarid regions with a minimum annual precipitation of 350-400 mm. It is grown in areas that are too hot and dry for growing maize. In India, main sorghum belt receives an annual rainfall ranging from 400-1000 mm, mainly between last week of June to first week of October. Southernmost part of the country receives rains in northeast monsoon also. Sorghum is a drought resistant crop.
Drought resistance is related to morphological and physiological properties including:
1. Slow shoot growth until the root system is well developed.
2. Great root weight and volume and high shoot/root ratio.
3. Larger adventitious root system and lower leaf area than maize.
4. Ability to reduce leaf osmotic potential and maintain turgor during stress.
5. Ability to maintain relatively high leaf water potential under condition of increasing soil moisture stress.
6. Ability to produce large amounts of epicuticluar wax and roll leaves at times of drought to reduce water stress.
Although, sorghum is able to resist drought, it can respond well to irrigation during booting and heading, the critical stages for soil moisture stress.
The minimum temperatures are 7°-10°C for germination and 15°C for growth. Optimum temperatures for growth are 27°-30°C. Sorghum is better able than most grain crops to withstand high temperatures but yields are adversely affected when the mean temperatures exceed 26°C during heading period.
Downes (1972) reported that irrespective of the temperature to which the crop was subjected to in the post panicle initiation stage, sorghum yield due to day and night temperature of 33°/28°C was only 50 per cent of that due to 27°/22°C.
Higher temperature regime delays panicle initiation and additional leaves are laid down. This, in turn, delays flowering, since for flowering to occur the additional leaves must expand to appropriate stage.
Under favourable conditions, delay in flowering would increase yield while under stress conditions early maturity may be desirable. The crop at boot leaf stage is very sensitive to temperature but less sensitive to soil stress than during flowering. Under optimum photoperiod, temperature will be a dominant factor controlling flowering, while with optimum temperature regimes, photoperiod would become very important.
The accumulated growing day degree requirements in excess of 10°C for sorghum are: 145 for seedling establishment, 440 for ear differentiation, 730 up to bud leaf, 880 up to half bloom, 1025 up to dough stage, 170 up to hard kernel stage and 1315 for maturity.
Soils:
Sorghum can grow on wide range of soils. Medium to deep black soils are predominantly suitable for growing sorghum. Rabi sorghum is wholly confined to black soils, while the kharif crop is grown on light soils also. It can be grown with wide range of soil pH from 5.0 to 8.5.
Grain sorghum is considered to be moderately tolerant to salinity. A 10 per cent reduction in grain yield occurs when the EC is 4.8 dS m-1 and 12.0 dS m-1 causes a 50 per cent reduction. Each unit increase in salinity above 6.8 dS m-1 reduced grain yield by 10 per cent. Germination and vegetative growth are less sensitive to salinity. In comparison with other cereals, grain sorghum is more sensitive to salinity than barley but less sensitive than maize.