Yam, Dioscorea spp,
is grown for their edible tubers. It was believed to have originated in parts
of Africa (West Africa) and Asia.
In West Africa, Nigeria produces the greatest quantity of
yam. The crop is commonly cultivated in parts of the Eastern Nigeria and other
areas such as Agbon, Benin, Asaba, Oyo, Zaria, Kwara, Plateau, Niger, Kaduna,
Benue and Cross River State.
In Ghana, large quantities of yam is grown in Northern part
of Ashanti.
Varieties
White yam (Dioscorea
rotundata)
Water yam or purple yam (Dioscorea
alata)
Yellow yam (Dioscorea
cayenensis)
Air-potato yam/Aerial yam (Dioscorea bulbifera)
Asiatic or Lesser yam (Dioscorea
esculenta)
Bitter yam (Dioscorea dumetorum)
Chinese Yam (Dioscorea
opposita)
Potato yam (Dioscorea
babatas)
Chinese yam (Dioscorea
polystachya)
Indian yam or Cush-cush yam (Dioscorea trifida)
Japanese mountain yam (Dioscorea
japonica)
Method of Propagation
Yams are propagated by:
(1)
Tubers (seed yam) which are either planted whole
or cut into smaller pieces called setts.
(2)
Seeds but this is mainly done for breeding
purposes.
(3)
Vine cutting and tissue culture.
Climate and Soil Requirement
The temperature of 20 – 30oC is ideal and an
annual rainfall of 1100 – 2200mm equally distributed throughout 8 – 10 months
is ideal. Ideal soil pH is between 5.5 and 6.5.
Yam is planted when day length is more than 12 hours.
A high level of soil moisture is necessary for excellent
tuberization. Yam requires a loose, free drainage and fertile sandy soil.
The shape of the tuber is influenced by the depth and
softness of the soil.
Land Preparation
The land is cleared of existing vegetation. The herbaceous
parts are ploughed into the soil while the rest is discarded.
The seed bed used may be holes dug in the ground, mounts,
heaps or ridges depending on the soil type.
Planting
In riverine areas, planting is done in October to December
to enable the yams mature before the area gets waterlogged in July or August
the following year.
In the hinter land, planting is between March and June, if
the crops are to be rain-fed.
For seed rate: 3
– 4 tons per ha are used. For ware yam
production (large yams sold in the market for consumption), seed yams or
sett weighing 1kg are used while
for seed yam production, setts weighing
about 0.4kg are used.
Spacing: Spacing depends
on the nature of the soil as well as the purpose for which the crop is grown
For sole cropping, 1m x 1m spacing is ideal whereas, if the
yam is intercropped with other crops like maize, a spacing of 1.5m x 1.5m is
recommended.
Closer spacing generally produces higher yields per ha but
smaller tubers are produced.
Planting is done at an angle of 45OC in a
slanting position.
Planting depth:
15cm especially for those planted very early before the rainy season.
Mulching:
Continuous mulching of the entire ridge top is better than capping (using of
the mulching material to cover the area in which the yam sett is placed). This
helps to keep the soil cool around the planted sett.
Staking
This is done to hold the yam vines to ensure a good yield.
Staking materials include branch or stem of plants, bamboo, palm frond as well as some strong
grass stem.
Yam vines should be staked with stakes of about 2m long. If
the yams are big enough, they’d be supported with long sticks of about 5m.
This helps the stake to stand upright and also spread the
yam leaves enough for them to receive sunlight energy.
The vines are tied up the stakes in an anti-clockwise direction
except for few species e.g D. bulbifera and
D. domentorum which climb in a
clockwise direction.
Early planted yams begin to germinate 20 – 60 days after
planting. If after 60 days, the planted yams did not germinate, a replacement
may be necessary.
Organic Fertilizer Application
Compost or farmyard manure is used, it is better added at
the time of planting. About 20 – 25 metric tons of manure per hectare of land
is adequate.
Yam is a heavy feeder and therefore require a lot of
nutrient for optimal yield. This is why farmers always grow yam first in a
newly open land i. e land that have been
laid fallow for more than 4 years.
The organic fertilizers are used to supplement less fertile
soils, 60g per plant about 2-3 months after planting.
Where the soil pH is
less than 5, liming is done during tilling to reduce the soil acidity.
Also, vermicompost, produced by chemical disintegration of organic matter by earthworms, is an ideal blend of plant nutrients with worm enzyme and probiotics to boost the crop performance. It contains higher amount of nutrients, hormones and enzymes and has stimulatory effect on plant growth.
Weeding
One of the causes of poor farm harvest is weed. Yam cannot
withstand the effect of weed.
Yam farm should be regularly weeded at least 2-3 times
before harvest.
During weeding, build up the ridge from the soil in the
furrow from bottom to top. This will prevent the ridge from being reduced in
size by erosion during the rainy season. This practice is called earthen-up.
Pest and Disease Management
Ø
Plant yam varieties that are resistant to
anthracnose.
Ø
Use disease free tubers or setts for planting.
Ø
Keep the farm free of weeds.
Ø
Termites attack is controlled with neem leaves
and oil.
Ø
Destroy crop debris on the farm.
Ø
Treat tubers with hot water for 40 minutes at 55OC
before sowing and after harvest so as to reduce disease while in the field and
after harvest.
Ø
Coat tubers with wood ash to prevent nematode
infestation.
Ø
Practice crop rotation with groundnut, sorghum,
maize or chili pepper.
Ø
Neem oil insecticide is applied to kill all
stages of mealy bug infestation.
Harvesting
Harvest the yams when the leaves starts turning yellow.
Dig the soil around the tubers to avoid damaging the tubers.
Harvesting is best done on a dry or sunny day to avoid tuber
rot.