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.
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<.
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
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.
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
1. Barn storage or under front storage
2. It can also be stored under ground.