YAM UNIT
Yam
(Dioscrora spp) are among the most valued
tuber crops in the tropics – West Africa is one among the three largest yam
production region in the world and Nigeria is the largest production of yam in
the world. Most of the yams grown in Nigeria are from small farm land. The
various spp of yam are as follows:
1.
Discorea
rotundala (white yam)
2.
Discorea
Alata (water yam)
3.
Discorea
Cayenensis (Yellow yam)
4.
Discorea
Dumentorum (Trifoliate Yam)
5.
Discorea
bulbifera (Aerial yam)
6.
Discorea
esculenta (Chinese yam)
Yam
is a plant consisting of a corm, from which stem, tuber and root emerge
annceally during the growing season yam have a week fibrous root. System which
is confirm mostly to the top 30cm of the soil and these in branched root may
extend laterally to a considerable distance, later in the development of the
plant a mass of finer branching fibrous root is produced.
TUBER
Yam
tuber is a stem tuber detailed morphogenetic studies indicated that it arises
from the meristematic activities of cells in the hypocotyls region of the
plant. The tubers are attached to a main root and stem of the plant. The corn
is formed numediately offer sprouting. The corn is woody and possesses dormant
buds. Serves as the central point of the root, stem and tuber of the plant; the
part of the tuber nearest to the corn is the head while the most distance plant
is the fail, a yew thin root may occur in the tuber surface and devoid of buds.
(the tubers do not contain buds). Yam tuber shapes and sizes varies from
species to species. Most commercial yams are cylindrical in shape
STEM: The yam stem
(vine) have a twisting round structure because they are unable to support there
own weight and so they climb by twisting. The direction of twisting around the
support depends on the yam species.
Discorea rolundata; discorea cayenensis and
discorea alata twist in anti clock wise direction that is going up ward which
discorea dumentorun, discorea bulbifera and discorea esculenta twist in clock
wise direction going upward.
·
Majority
of the species bear simple net veined leaves and more or less heart shape
devious of hair.
·
The
leaves are generally green although the leaves of some cultigens of water yam
are purplish especially when young.
·
Leaves
arrangement on the stem is either opposite or alternate.
FLOWERING OF YAM
Yam
really flowers and when they do, they are deacons (male & female plant in
one plant).
Production
of male and female flower separate on different have been reported the basic
number of chromosome is 10.
·
Discorea
rotundata (white yam)
o
These
species has narrow, pote, green oppositely arranged, which tend to be
triangular in shape.
·
Discorea
Alata (water yam)
·
These
species normally yield more heavily than d. rotundata and d. cayanensis and can
do beta in poor soil. Contains a higher proportion of H2O than either the white or yellow yam. The tuber may be
white, yellow, brown or almost red in colour. The leaves are distinctively
different from the others. Been heart shaped, long brown and winged shape. The
stem climb round the shape.
·
Discorea
cayansis lan (yellow yam)
·
Tuber
of these species has yellow colour when pealed. This is the main different
between the yellow yam and the white yam. It does store for long when compared
to the while (has shorter shelve life).
AREA OF YAM
PRODUCTION IN NIGERIA
The
major yam producing areas in Nigeria; in clued the middle belt. (Benne, Kabba,
Ilorion, Niger, Nassarawa) Eastern part of Nigeria (Owerri, Onitsha, Port
Harcourt, Umuahia) Western pest (Ondo, Oyo, Ibadan) Mid West (beine and delta
areas) yam is well distributed in the humid tropics of West Africa were they
are valued as an important source of food.
ECOLOGY OF YAM
Yams
strive under warm – sunny conditions at temperature of between 25oc – 30oc and does not tolerate freezing environment thus yam
is restricted to the tropics. A family large amount of H2o is required for satisfactory growth during the growth
season. Such that most yam producing area are in the region were the annual
rainfall is 1200mm or more and also evenly distributed in districts were the
rainfall is as high 300mm/Anum. Since they require 6 – 9 months to mature in
the field, it is essential that the raining season last at least as long unless
supplementary irrigation are provided.
The
growth of yam is affected by day length. As short length between 10 – 11 hours,
promote tuber formation, while day longer than 12 hours promote vine growth low
light intensity or shade during growing season tends to reduce yam yields
severely and so yam should be supplied with a means of support to climb begin a
month after emergent in the forest zone.
Yam
prefers deep rich permeable and loose texture soil for tuber development and
expansion. Heavy clay soil tend to be water logged resulting tuber not and
difficult harvesting and it should there be avoided in yam. Stony or graveling
soil should be avoided in yam production because yam growing through such soil
could be distinct. The optimum soil pH for satisfactory yield is 5.5 with
essential no exchangeable aluminum <A/3+>present<.
CULTURAL PRACTICES
AGRONOMY OF YAM
PRODUCTION
1.
Planting
date: early planting is done in November, when the soil is still moist.
i.
Late
planting is done in February to April for good yam production planting at high
stand density can be carried out in May.
2.
Land
preparation: Land clearing for yam cultivation in traditional agriculture is
done essential with hand tools, in such instance, clearing is selectively done
and several upright trees are deliberately left standing to serve as stake.
3.
Seed
bed preparation and planting material: tuber requires a permeable soil in which
the tuber can grow with little hindrance, many tuber crops grow initially from
root or strollen. That penetrates the soil and later begins to enlarge to form
tubers. As in cassava and potatoes and the case of any stolen formation, in
that case it is the meditation part that gives rise to the tuber that
accomplish penetration through the soil on the bases of the type of tillage.
Four generally
method of planting yam exist
1.
Planting
on heap/mounds
2.
Ridges
3.
Holes
4.
Flat
Four categories
of propagation yam
1.
Reproduction
seeds
2.
Vine
cutting
3.
Tissue
cutting <Micro Propagation>
4.
Tuber
materials
The propagation through tuber material
can be achieved through small whole tuber <seed yam> as well as pieces
<yam setts>
Planting with tuber material produces
genetically uniform materials.
It
is better to use the whole tuber rather than sets, due to the following reason
1.
It
ability to sprout fast
2.
Produce
tuber with higher average weight than the set
3.
The
whole tuber on like the yam set do not have a cut surface and therefore less
prone to rot
4.
Whole
tuber produce higher tuber harvest multiplication ration than set.
MR
= weight
of harvested tuber
Weight
of the planting material
5.
Mechanical
planting can be conducted easily with whole tuber.
Yam set may be derived from the head,
middle or tail region of tuber, depends on the rapidity with which it sprout
and prone it is not after planting.
The
head portion of yam tuber sprat more easily than the middle and tail portion,
as the head has more buds and is less prone to rot than the middle and tail
portion. The head produce higher tuber yield than the middle and tail portion.
The
most frequently used type of tuber for proportion, usually weigh been 150g –
300g as rule the larger the weight of the yam set used, the tuber yield
obtained from the resulting plant.
Dept of planting should be 9 – 12cm
with the uncut surface down ward germination start 30 – 60days after planting
depending on rainfall.
CROP MANAGEMENT
1.
MULCHING: covering of
ridges with grasses of leaf is essential on dry month. Mulching reduces soil
temperature as well as conserve soil moisture thereby providing ultrinum condition
for growth.
2.
STAKING: This is
essential for good yield when the yam vines are about in tall, they should be
provided with stakes which they stain about. There should be done about a month
after emergent.
3.
WEED CONTROL: Weeding is a major
operation after staking. Weeding most be done carefully if hoes are used in
other met to injune the shallow yam root chemical weed control can also be done
using per – emergent herbicides of different 1.okg (A.) /ha followed be
supplementary hoe weeding at about 800kg after planting.
4.
FERTILIZER
APPLICATION:
N.P.K application rate of 20 -30kg this is widely used (Law – Ogborno and Remission
2009) organic manure is also
beneficiary if available. It is best to apply fertilizer one month after emergent.
5.
HARVESTING: The early crop
manure at the end of July, main crop from the month of October to January.
There
are two type of harvesting
A.
Single Harvesting: Here the farmer
wait until after the leaves have dried up and harvest once
B.
Double Harvesting: Each crop is harvests twice
the first is harvest 4 – 5 month and that time you remove the edible yam and
after you remove the seed yam after the leaves dries up.
ADVANTAGES OF
DOUBLE HARVESTING
1.
Farmers
get both whole yam and seed yam.
2.
It
moves farmers to harvest earlier.
ADVANTAGES OF
SINGLE HARVESTING
1.
It
saves labor
2.
It
stores better than double harvest
PROBLEM OF YAM
PRODUCTION
1.
Planting
Material: The planting materials are bulky and scares
2.
Production
operation are labour intensive
3.
In
storage, the shelf live is short and
only limited to dormancy period of 4 months after harvesting
STORAGE
1.
Barn
storage or under front storage
2.
It
can also be stored under ground.