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Cassava in Gambia
 
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The Cassava plant (Manihot esculenta)
The crop is known in the New World as manioc or yucca it is a herbaceous shrub or mini tree which grows up to 4 metres high with thin hand-like leaves. It was introduced to Gambia by the Portuguese between the 17th and 18th centuries.  It is one of the highest starch yielding plants grown in Gambia and on average Gambians consumption levels is about 100kg per person per annum in 2002 (FAO).  This tuber is poisonous unless processed in a certain way, so it is best to seek advice before attempting to make your own nyambe nyebe! (beans & cassavas in palm oil). The root of the cassava plant, a large thick-skinned tuber like the potato when boiled, that is eaten in many tropical countries and is the source of tapioca.

Toxicity Levels:
The crop's tubers must be processed very carefully as they include a glucoside, linimarin, which is acted upon by an enzyme to liberate prussic acid. The peeled roots contain much less prussic acid than unpeeled roots because most of the prussic acid is in the skin.

There are 2 main varieties:
1. Bitter varieties with roots containing 0.02-0.03% prussic acid.

2. Sweet varieties with roots containing less than 0.01% prussic acid. These can be used raw for feeding.

The prussic acid content depends not only on the variety, but also, and possibly even more, on soil conditions. Usually the bitter varieties have longer and thicker roots than the sweet varieties, but there is no simple safe method to judge the level of prussic acid in the roots.

The toxic elements can also be removed by cooking or by drying slices of the roots for about two weeks. Cassava root meal is not attacked by insects; the same is true, of feed concentrates to which 15% cassava root meal has been added.

Uses of Cassava:
Both fresh and dried cassava roots and peels are consumed by ruminants such as cows and goats in different forms (sliced, chopped, ground). Dried cassava roots have given satisfactory, results as the principal energy source for dairy cattle, intensive beef fattening and lamb growth. Cassava can replace almost all of the grain in the diets with little reduction in performance. Inclusion levels of up to 65%, preferably pelleted, do not seem to affect health, carcass quality or overall performance when the diets are carefully balanced. Palatability can be enhanced by the addition of molasses if pelleting is not possible. The whole cassava plant (including root and aerial part) can be chopped and ensiled in simple pit silos for dry-season feeding at the village level. Simple equipment is required both for harvest and preparation of the silage. The silage is fairly well balanced for ruminants.

Complete replacement of grain by cassava root meal in layer feed has yielded similar egg production.

Leaves:
It is possible to obtain from cassava more than 6 tons of crude protein per hectare a year with the proper agronomic practices directed toward foliage harvesting. Cassava leaf and stem meal has been used at the 35% level in dairy cow concentrates to advantage. Cassava bushes can be harvested as forage when they are three to four months old. They are cut about 40 cm from the ground and chopped in small pieces by hand or in a stationary forage chopper. The forage has been used to provide by-pass protein to ruminants fed urea and molasses. The intake of cassava forage was about 5 kg per day, and about two months of adaptation was required before full production was obtained. In poultry rations the replacement of as little as 5% of the lucerne meal with cassava leaf meal significantly reduced broiler weight gains; however, the inclusion of methionine and vegetable oil additives in rations consisting of up to 20% cassava leaf meal practically eliminated the depression in response.

Pomace:
Often called cassava meal, pomace is the residue from the extraction of starch from cassava roots. Cassava roots yield approximately equal amounts of starch and pomace, which have less feed value than cassava root meal but can be included in rations for cattle. Starch and pomace are extensively used for pigs in Southeast Asia, where they are regarded as a valuable feed. Up to 10% has been used in poultry rations via suppliers.

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Cassava Crop Production Methods:
The first system is one in which the farming family's household is the major source of labour used for food crop and livestock production.

In this crop system, cassava is commonly intercropped (the practice of growing 2 or more crops on the same field) with early maturing annuals such as maize, and vegetables like okra, and bitter leaf. The crops intercropped with cassava in different parts of Africa very with regions of growth and food preferences.

In The Gambia, rice is the dominant intercrop. Protected trees, and perennials such as bananas and plantains, are also regularly grown in patches or as individual areas in cassava fields. While cassava and related crops are the main food crops, trees provide building materials and firewood.

Cassava leaves are cooked and eaten by people and also fed to livestock, or used as poultry feed. These animals provide the household with meat and eggs for consumption and as a cash crop. Animal wastes are used for soil fertilisation.

Cassava is highly compatible for use in intercropping with these annual crops because of its lengthy early growth, especially between planting and 6 to 8 weeks of growth. The annuals which grow faster during the initial growth phases rarely compete adversely with cassava and have been shown to smother weeds.

In times of war, drought or low national incomes, cassava consumption increases relative to alternative food staples such as rice, maize, yam, and wheat. This is why it is sometimes known as a crisis crop.

Cassava in certain forms is a low income consumers' staple. Although an individual may not increase the quantity of cassava consumed in a year, as national income declines, annual average cassava consumption per person increases because more people begin to substitute cassava for more expensive alternative food staples.

A Gambian farmer's capacity to react to falling fallow periods due to demographic, market, agricultural pests such as the cassava mealy bug or Phanacoccus manihoti, diseases and other pressures by replacing more susceptible crops with cassava is limited by its long cropping cycle. Cassava can be harvested from 6 months after planting, but most available local varieties do not achieve maximum yield before 22 months. Shortening fallow periods require varieties selected for efficient nutrient absorption and for better ability to be intercropped with beans or other soil fertility preservation techniques.


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