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.
|
Cassava Crop Production Methods:
 The
first system is one
in which the family 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 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.
|
|
