Sorghum

Sorghum is an erect cereal plant that grows to a height of 0.5m-4.5m depending on the type of cultivar. Sorghum belongs to the sub family of Panicoideae and tribe andropogoneae.

Two sub-species of sorghum are generally recognized thus sorghum bicolor which represents all the cultivated forms and wild sorghums, and grass sorghums which are either perennial weeds or grown as forage.

Sorghum is the 5th important cereal after wheat, rice and maize. It's a staple food crop for arid and semiarid areas of the world. Sorghum is also commonly referred to as kafir corn, milo, sorgos, durra and guinea millet.

According to Purseglove (1988) there are 5 different types of sorghum:

1. Grain sorghum which is grown for grain
2. Sorgos grown mainly for fodder, hay and silage
3. Grass Sorghum is wild sorghum e.g. Sudan grass
4. Broom corn sorghum used for making brooms
5. Waxy Sorghum has waxy endosperm and is used for starch manufacture

The origin of sorghum is generally believed to be around the present day Ethiopia. Many authors now regard Ethiopian highlands as a primary center of domestication.

From Ethiopia sorghum was taken to West Africa across the Sudan from where it was first grown among the Mande people of the upper Niger.

Also from Ethiopia, sorghum was taken to east Africa from where it was distributed among the Nilotic and Bantu people.

Sorghum was taken from East Africa to India during the first millennium from where it was taken to China in the early Christian era. Sorghum races in India are closely related to those in northeast Africa.

From West Africa, sorghum was distributed to USA and other parts of the world through slave trade around mid 19th Century. Before 1900 full-scale cultivation of sorghum had started in the southern great plains of the USA.

Ecological conditions

Sorghum can grow in a wide range of ecological conditions and can still yield well even under unfavorable conditions of drought stress and high temperatures. It is generally grown between 40 degrees North and 40 degrees South of the equator, in warm and hot countries characteristic of the semiarid environment. Sorghum is usually grown in areas that are too hot and dry for maize.

Drought tolerance

The ability of sorghum to grow in drier environments is due to a number of physiological and morphological characteristics;

1. Produces many roots compared to other cereals
2. Has reduced leaf area thus reducing water loss through transpiration
3. Can remain dormant during drought and resume growth when conditions are favorable
4. Above ground parts of plant grow only after the root system is well established
5. The leaves have a waxy coating and have the ability to roll in during drought thus effectively reducing transpiration
6. Competes favorably with most weeds
7. Has higher net photosynthesis compared to other cereals

Soils

Sorghum also tolerates a wide range of soil conditions. It does well both in fertile valley bottom soils as well as in nutrient poor soils. However, under dry land conditions, dry soils retard uptake of nutrients.

Also, soil water, soil physical resistance and soil porosity affect growth and distribution of sorghum roots.

Photoperiod

Sorghum is a short day plant and different cultivars vary in their sensitivity to the photoperiod. Sensitivity to the photoperiod is a genetically controlled character, which can be bred or selected for.

In West Africa, informal selection by farmers for day length sensitivity in sorghum resulted in crops that mature as the available water is exhausted in the early part of the dry season.

This ensures that the crop fully utilizes the growing season while avoiding diseases associated with high humidity during grain maturation.

»  Photoperiod sensitivity - Why extended rains In the Sahel have only
   marginal effects on yields of most sorghum and many millet varieties

»  ¹Reger, Naturhistorische Gesellschaft Nrnberg
»  ²Sorghum: Origin, History, Technology, and Production; 2000; Edited by C.
     Wayne Smith and Richard A. Frederiksen; Wiley Series In Crop Science
»  ³University of New Mexico, Sorghum, Sorghum bicolor
»  ⁴Lost Crops of Africa: Volume I: Grains. 1996. Board on Science and
     Technology for International Development, National Research Council. p 127-
     214.
»  ⁵CAB International, Crop Protection