Crop production: Sorghum can play a stabilising role


By Digital team | 4 September 2018
staple; CGIAR; zinc; sorghum
Photo: Charl van Rooyen

Here are some production tips for grain sorghum.

  • Grain sorghum must be planted shallow, especially on heavy soils.
  • Place the seed in moist soil, otherwise germination could be retarded.
  • The planting depth varies between 3 cm and 5 cm.
  • After planting, the soil crust must be broken up to enable the young seedlings to emerge.

SOIL REQUIREMENTS

Grain sorghum can be grown more successfully than maize on less fertile soils, shallow soils, heavy turf soils and soils inclined to water-logging.

It can also withstand some salinity. On the other hand, grain sorghum is more sensitive to aluminium toxicity than maize.

It should also not be planted on soils with an acid saturation of more than 15%, while soils heavily infested with witchweed should be avoided.

The best results are obtained on deep, well-drained, fertile sandy-clay loam soils with a pH of 4.5 – 7.5. In good seasons heavy soils produce the best yields, but during times of stress sandier soils are better.

However, during a normal drought grain sorghum will still produce satisfactory yields on soils with a clay content of more than 50%, unlike maize.

CLIMATIC CONDITIONS

Grain sorghum requires a summer rainfall of 400 mm to 700 mm and higher. However, this crop is known for its superior drought-resistance. After good rains it recovers rapidly.

Grain sorghum is more sensitive than maize to low soil temperatures. Germination is slow at soil temperatures below 18ºC.

High humidity may affect seed set. Most cultivars require between 130 and 140 frost-free days during the growing season. Plant maturation should be achieved before the first frost occurs.

The ideal temperature for plant development is 25°C to 30ºC, with a minimum of 15ºC. Sufficient sunlight will favour yields, but at flowering extremely high temperatures may be harmful. Just before the emergence of the ear, the sorghum plant is sensitive to low temperatures (which will reduce yields).

Good news for the cooler regions is that great advances have been made in the development of hybrids that tolerate the cold well.

SOIL PREPARATION

Soil preparation is similar to that of maize, but because the seeds are smaller, the seedbed, particularly on clay soils, must be finer to ensure good germination.

Good soil preparation could increase yields by 25% to 30%. On soils that are susceptible to wind erosion, furrows must be drawn or strip cultivation must be practised.

CULTIVARS

From time to time existing cultivars are replaced by new, improved cultivars.

It is therefore advisable that you consult a seed company for information about the latest developments and for recommendations for each production area.

BEST PLANTING DATE

By taking long-term climatic conditions into consideration, you can choose a planting date. Potentially cooler conditions during planting and later during flowering should be avoided as far as possible.

Risk can also be reduced by adopting a reasonably longer planting period, and also by planting hybrids with varying maturities.

In South Africa planting usually takes place in late October and November, but it should happen as early as possible in the eastern areas.

In the warm production areas, grain sorghum could still be grown successfully as late as January, depending on the climatic conditions and the growing season of the cultivar. In the western areas, the best planting time is around mid-November.

PLANT POPULATION

Grain sorghum is less sensitive to plant population than most other dryland crops.

At low plant populations the crop effectively compensates by producing ear-bearing suckers with the result that major differences in the ultimate ear counts between lower and higher populations seldom occur.

Very low population (less than 90 000 plants/ha) must however be avoided, as a poor canopy may lead to weed problems. Plant populations of 100 000 to 160 000 plants/ha are recommended. The higher population applies especially where weed competition may be severe.

FERTILISATION

The nutrient requirements of grain sorghum are similar to those of maize, but grain sorghum can use soil nutrients more efficiently than maize.

As in the case of maize, the fertilisation programme must be based on the projected yield and reliable soil analysis.

WEED CONTROL

The sorghum plant grows very slowly in the early stages and as a result it could easily be suffocated by weeds. It is important that weeds are effectively controlled. A well-prepared seedbed mostly prevents weeds from becoming a problem after planting.

Various chemical herbicides produce effective weed control in grain sorghum. It is extremely important that the manufacturer’s instructions regarding the use of herbicides are carefully followed, as grain sorghum is very sensitive to herbicides such as 2.4 D and Atrazine under certain conditions.

Also read: Do not neglect weed control

DISEASES

The disease that is possibly of greatest economic concern to the farmer is ergot, which is more prevalent in the higher rainfall and cooler production areas. Cool, wet conditions favour the development of this disease.

YIELDS

Grain sorghum compares very well with maize in all production regions. Depending on the soil quality, yields of 2.5 t/ha to 8 t/ha can be achieved. Under irrigation, like maize, yields of 8 t/h to 12.5 t/ha are possible.
Source: Pannar

  • This article was written by Jacques Claassen and first appeared in Farming SA.