Last update: April 4, 2012 08:37:08 AM E-mail Print



J. D. Aucamp

Wheat is cultivated to a greater or lesser extent on most farms in the Karoo Region. The popularity of wheat can be attributed to the fact that it can be used as a cash or grazing crop. It also fits in well as a rotation crop with lucerne, not only because it is able to utilize the accumulated nitrogen but also because more irrigation water is available during winter.

In many cases the poor yield or small amount of grazing material obtained from wheat can be ascribed to the fact that farmers are not sufficiently acquainted with the basic growth pattern of the wheat plant.

Wheat is an annual plant of which there are basically two seasonal types, viz. the so-called winter wheat and spring wheat. The difference between the two types is chiefly in respect of time of sowing and growing period. The winter wheat requires a relatively long growing period and are therefore sown during early winter (May to middle July), while the spring wheat have a relatively short growing period and are thus sown later (middle July to end August). This dividing line is becoming more prominent with the development of the so-called short straw cultivars, especially in the colder areas where late frosts are a problem.

The wheat plant has a branched, fibrous root system. At germination three embryonic roots usually develop but up to eight of these roots can be formed. These embryonic roots (primary roots) can either remain during the whole life of the plant or die during the growing period. The adventitious roots (secondary roots) develop from nodes approximately 2-5 cm below the soil surface irrespective of the depth of planting. The adventitious roots usually first grow horizontally and then downwards.

The roots of a mature plant can reach a distance of 1 metre horizontally and can penetrate to a depth of 2 metres. The depth is influenced to a large extent by the condition of the soil and available moisture. Usually the first 60-100 cm depth of soil is filled with a mass of roots.

The wheat plant has a typical grass culm, which usually consists of six internodes. The shortest internode is near the soil surface and the internodes gradually become longer towards the top of the plant. Only one culm develops at germination. Side shoots are formed from buds on the crown at a later stage. The formation of these side shoots is known as the tillering or shooting stage of wheat. During this stage (sometimes also known as the grassy stage), defoliation or grazing can take place without harm to the plant.

During this stage the initiation or forming of the ear also takes place and it is therefore essential that the plant must have sufficient moisture and nutrients available. If the wheat is to be grazed, regrowth also depends on the availability of moisture and nutrients.

Initially these side shoots remain short, but later a lengthening of the internodes takes place and the plants grow more erect. This is known as the piping stage during which grazing must not be allowed because the ear is pushed up and is grazed off, thus lowering or destroying the eventual yield.

The wheat plant has a typical grass leaf, which in wheat is usually narrower than those of oats and barley and are of a lighter green colour. The flower of the wheat plant is a spike (ear), which is formed on the tip of the culm. There are usually 15 to 20 fertile spikelets on a spike, but environmental conditions, especially in the early stages of development, largely determine the number of spikelets. Usually one or more of the lower spikelets are sterile. The number of sterile spikelets varies in different cultivars. Drought during the piping and flowering stages increases the number of the sterile spikelets while frost in particular results in sterile spikelets on the tip of the spike. The number of flowers borne on the spikelet varies from 2 to 9 of which 2 to 3 are usually fertile and develop into grains.

A wheat spike usually remains in flower for 2 to 3 days under favourable conditions, but may flower for as long as 8 days under moist, overcast conditions. Although the ear remains in flower for such a short period, it is susceptible to frost and low temperatures for a much longer period. Cases are known where the ear was completely killed by frost even during the piping stage or well after flowering was completed.

The occurrence of frost must therefore be taken into account when deciding on the cultivar and date of sowing. The winter wheat types such as Red Epyptian, Scheepers 69, Sterling, etc. can thus be sown much earlier because they stay longer in the vegetative stage and do not come into flower as quickly as the early cultivars (Zambesi, T4, etc.)



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