INTRODUCTION
Cocoyams
are herbaceous perennial plants belonging to the family Araceae and are grown
primarily for their edible roots, although all parts of the plant are edible.
Cocoyams that are cultivated as food crops belong to either the genus Colocasia
or the genus Xanthosoma and are generally composed of a large spherical corm
(swollen underground storage stem), from which a few large leaves emerge. The
petioles of the leaves (leaf stems) stand erect and can reach lengths in excess
of 1 m (3.3 ft). The leaf blades are large and heart-shaped and can
reach 50 cm (15.8 in) in length. The corm produces lateral buds that
give rise to side-corms (cormels, suckers) or stolons (long runners, creeping
rhizomes) depending on the species and variety. Cocoyams commonly reach in
excess of 1 m (3.3 ft) in height and although they are perennials,
they are often grown as annuals, harvested after one season. Colocasia species
may also be referred to as taro, old cocoyam, arrowroot, eddoe, macabo or
dasheen and originates from the region of Southeast Asia. Xanthosoma species
may be referred to as tannia, yautia, new cocoyam or Chinese taro and
originates from Central and South America.
Cocoyams are plants of the tropical
rain forest and although in their natural habitat they grow under the forest
canopy, under cultivation they are usually sown with full exposure to sunlight
(Giacometti and Leon, 1994). Since
cocoyam tolerates shade, the crop is frequently grown in intercropping systems
together with perennial crops such as banana, coffee, coconut, rubber, oil palm
and cocoa (Wilson, 1984a). The corm and cormels of
cocoyam which are the major economic part contains about 15 to 39%
carbohydrates, 2 to 3% protein and 70 to 77% water. The young leaves contain 2%
protein and are also rich in vitamin C,
thiamine, riboflavin, niacin, calcium, phosphorus and iron (Ndon et al., 2003). It has a
nutritional value comparable to potato but easier to digest (Sefa-Dedeh and Sackey, 2002).
In Ghana the cormel is used as
substitute for yams and plantain for the preparation of various dishes
especially in the dry season. The young leaves are also widely used as spinach
in the preparation of stews or sauces. In a socioeconomic survey conducted by Quaye et al. (2010), they found
out that majority of the farmers in Ghana cultivated cocoyam for both the
cormel and leaf, but very few of them cultivated it purposely for the cormels.
The crop which is mainly grown in the forest areas of Ghana is threatened with
environmental problems such as deforestation. Decreasing rainfall and poor
soils have also been identified as some of the causes of the decline in cocoyam
production in the country (Sagoe, 2006). The crop is generally grown
by small-scale farmers with no intensive management such as fertilization and
the use of improved varieties for commercial cormel and cocoyam leaf
production. Production and the area planted to the cocoyam are on the decline
since 2001 to 2006. The mean annual growth rates for area planted and
production during the period were 0.2 and 0.3%, respectively (Ministry of Food and Agriculture, 2010).
Cocoyam plant development consists of
three major stages namely plant establishment (from planting to about 2 months
after planting), rapid vegetative growth (2-5 months) and a third stage (after
5 or 6 months) characterized by tuber development and maturation (Adiobo et al., 2011). The leaves and
cormels which play major roles in the diet of Ghanaians need proper development
to sustain the plant. Adoption of technical innovation by farmers demands
precise and detailed information on cost and return so that farmers can choose
the right combination of resources or enterprises. (Das et al., 2010). It became
necessary therefore to find out the right time to start harvesting cocoyam
leaves and at what frequency for optimum economic gains. The objectives of this
investigation was to assess the effect of leaf harvesting on growth,
development and cormel yield of cocoyam and to determine the appropriate age or
stage of crop and frequency of leaf harvest for maximum economic returns.
Cocoyam have more calories than
potatoes. 100 g provides 112 calories. Their calorie mainly comes from complex
carbohydrates known as amylose and amylopectin. However, the roots are very low
in fats and protein than in cereals and pulses. Their protein levels can be
comparable to that of other tropical food sources like yam, cassava, potato,
banana, etc.
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