Introduction:
 The
Cassava plant (Manihot esculenta) 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.
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. |
