Oil and latex-Producing Crops And It Examples


Due to the rapidly increasing demands for vegetable oils for both industrial needs and domestic consumption, the crops which produce edible oils are being planted on an increasing scale in most parts of the tropics and the production of palm oil in West Africa is still increasing to meet these demands.
Among the most important crops are: coconut, oil palm; rubber; sesame; sunflower and the shea butter tree. 

The cultivation of this crop is limited to coastal areas with sandy or alluvial soils since this crop has a high temperature requirement and is tolerant to high levels of soil water. This crop rarely grows well at elevations of more than 800m. Seeds are sown in sandy nursery beds with about one third of the husk exposed above the sand. Irrigation in the dry season promotes germination and the seedlings are transplanted to prepared planting holes well provided with organic material when the main shoot is about 140-150 cm long. Planting should preferably be carried out during the early rains.

Weeds should be kept in check and fertilisers applied if available, potassium has been found to favour growth. Pests can be controlled by baiting or spraying while the plants are relatively small, but for large trees, this may not be economic. Diseases are rarely serious. Dwarf selections normally bear their first fruit much earlier than the more traditionally grown tall forms, but the quantity of oil produced per nut is often lower.

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Oil Palm
Palm oil is one of the main foods of West Africa, the oil palm is also an important export or cash crop. It requires a moderately high rainfall but will withstand a fairly long dry season which normally coincides with the harvesting period.

Many new hybrids and selections have been produced by Research Stations in recent years and these have contributed a great deal towards an increase in production of both domestic palm oil and palm kernels for export. Oil palms grow well in deep alluvial or sandy clay loams but are tolerant of a wide range of soil conditions. Their main requirement is for a stable high temperature with fairly high humidity and a good measure of soil moisture and these conditions are found mainly at elevations of less than 800 m, on flat land or shallow valleys.

Seeds will only germinate satisfactorily if given high temperatures in moist conditions, due to a dormancy factor. These conditions are provided by soaking and washing the seeds daily for about a week and then placing them in plastic bags, in a temperature of 40°C for 11-12 weeks, in special seed germinators. The germinating nuts are then transferred to containers in nursery conditions and are transplanted to the field after about 18-20 weeks.
The use of polyethylene pots for the nursery stages of growth is now becoming more usual and this considerably reduces the labour involved in handling and transplanting the seedlings. It also reduces the amount of root disturbance and damage which occurs during the transplanting operation.
The transplanting holes should be well prepared in advance, the most suitable period for transplanting is at the beginning of the rains. Mulching is generally recommended and the plants may require irrigation during dry periods until well established.

Routine cultural operations include weed control and the application of fertilisers, particularly those containing potassium, once the plants are established.
Wire collars may be required in some areas to prevent rodent damage. Pests and diseases may be controlled by spraying and deficiency diseases such as orange leaf spot reduced by applying potassium. Orange frond, due to a lack of magnesium, can be treated by applying magnesium sulphate. Blast, a disease of young seedlings, may be partially controlled by regular irrigation during dry periods.

Several methods are used for extracting the mesocarp or palm oil, the most widely used small scale press is the hydraulic hand press. Sterilising is mainly carried out in oil drums, heated by a fire, and digestion or maceration of the fruit is carried out in concrete tanks or large mortars.

Although the main West Africa is Liberia, many other countries are increasing production since natural rubber is maintaining an important place in the world markets.

Rubber trees are relatively tolerant to soil conditions although they grow well on deep soils which are well drained and have a good level of fertility. High and fairly stable temperatures, with medium to high rain producing centre of rubber in fall which is well distributed are the most suitable conditions for growth and rubber therefore is rarely grown economically at elevations of more than 400m.

The two methods used in the propagation of rubber are by seeds and budding. Seeds, preferably obtained from selected high yielding 'clonal' parents, are sown in nursery beds or preferably in polyethylene containers, similar to those uscd for oil palm. The seedlings are transplanted to the field when 2.5-3.0 m in height at a density of about 600 per hectare. They are later thinned to a density of about 350 per hectare.

Seedlings required for budding are produced from seeds selected from parents with vigorous root development; these seeds are sown in the nursery, usually in double rows, spaced at about 60 cm apart.
Budding is carried out when the seedlings are about 12 months old, when the diameter of the stem is about 2.5 cm. The method of budding is a modification of the patch budding technique, whereby the piece of bark which is cut from the stock is not detached from the stem but is left attached as a flap. This is tied back in position over the bud, after insertion. This technique is sometimes referred to as 'veneer' budding.
When the cambial layers have united, after about 21 days, the stock above the developing bud is carefully severed, leaving a sloping cut. Scions for budding are normally obtained from trees which are cut back annually to provide a budwood supply. Many new cultivars of rubber have become available in recent years, some are very high yielding and others have resistance to some diseases. For exposed positions cultivars are available which have a dense, short branching system so that wind damage is reduced.
Budded plants are staked and unwanted stock sideshoots removed before they are transplanted to permanent positions at a spacing of about 370-450 per hectare; they are later thinned to about 280-350 after
about 10 years.
Routine maintenance operations include clean weeding or ring weeding around the base of the trees, cover crops are recommended for establishment between the tree rows. Paraquat and simazine herbicides may be used, on a commercial scale, for keeping the tree bases free of weed growth.
Tapping begins when the trees are 6-7 years of age, the first tapping panel being opened at a distance of about 50 cm from the base of the tree. The angle of the cut, from the horizontal, should be 221 for seedlings and 30 for budded trees. Tapping is carried out during the early morning, on alternate days; the trees are not usually tapped during the dry season. Stimulation of the latex flow may be obtained by using chemicals such as 2, 4-D or 2, 4-5T which are other wise used as herbicides. Latex is collected in metal or earthenware cups and coagulation is prevented by adding ammonia. The operations of testing for density and coagulation with formic or acetic acid are followed by rolling and drying to produce sheet rubber.

Some diseases of rubber, such as 'Collar crack' or 'Bootlace fungus' can cause serious losses and infected trees should be completely removed and burned. Root rot fungi are also serious and may be prevented by ensuring that the soil is well drained and maintaining a good standard of husbandry; infected trees should be uprooted and burned.

Sesame, Benniseed Or Sim-Sim
This is a cash crop which is being increasingly grown for export as a valuable oil crop used in the manufacture of margarine and salad oil; it is also a valuable cooking oil.
Benniseed is tolerant to a wide range of
soil conditions and is rarely given the cultural treatments which lead to maximum yields. It is sown broadcast, at the beginning of the rains, and should be weeded and thinned to give satisfactory yields. Plants may attain a height of 2 m. Several cultivars are grown, flower colour varies and may be white or pink, the most popular types have white seeds which contain from 45-50% of edible oil.

Plants are harvested by cutting them at the base, they are tied in bundles and either stacked or dried on cloth or canvas since the seed capsules split readily when ripe.

This crop is not widely grown in West Africa, but it is Tikely to increase in popularity as the world demand for oil seeds increases. It is used also, on a limited scale, as a fresh fodder or silage crop. Many high yielding cultivars are now available but, for maximum yields, these require relatively fertile soils with a good organic content. Seeds are sown broadcast and thinned later to a single plant. Plants may attain a height of up to 3 m and are either harvested as whole plants for livestock feed or the heads left until the seeds are mature.

Shea Nut
Also known as the shea butter nut, this tree is indigenous to parts of West Africa, particularly northern Nigeria, and the fruits are harvested from trees growing in the wild state. The outer fleshy portion is eaten and the kernel used for oil extraction after the nuts have been cracked.


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