Yam (Dioscorea spp.) Production

Land preparation

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. Manual preparation involves slashing and burning of debris. Mechanical preparation involves slashing of the land area, ploughing and harrowing. If maximum tillage is practiced, then incorporate organic matter into the soil to ensure adequate drainage, aeration, nutrition and room for tuber growth. 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.

Planting materials

There are four ways of propagating yams:

• Tubers: This is the most important method of propagation in the field. The planting material is called a “sett” and the size of each sett should be between 400 grams to 500 grams. Pre-germinate setts in moist sawdust or coconut husk.
• Seeds: True seeds found on vines e.g. Cush- cush.
• Cuttings: Basal vine cuttings are best. Use 6 cm-8 cm pieces, dip in a rooting hormone and place in a propagating bin.
• Tissue culture: This is used to produce “clean” plantlets i.e. free from diseases.

Note that, there are three types of setts that can be obtained from a whole tuber:

• Head setts
• Middle setts
• Tail setts

The head portion of yam tuber sprouts 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. Therefore, it is better to use the whole tuber rather than sets, due to the following reason:

 

• It ability to sprout fast
• Produce tuber with higher average weight than the set
• The whole tuber on like the yam set do not have a cut surface and therefore less prone to rot.
• Whole tuber produce higher tuber harvest multiplication ration than set.

Dept of planting should be 9 – 12cm with the uncut surface down ward germination start 30 – 60days after planting depending on rainfall.

 

Variety

Discorea rotundata (white yam)

Discorea alata (water yam)

Discorea cayenensis (Yellow yam)

Discorea dumentorum (Trifoliate Yam)

Discorea bulbifera (Aerial yam)

Discorea esculenta (Chinese yam

 

Climatic and soil requirements:

• Soil type:

The best soils for growing yams are the sandy clay loams. However, yams can be cultivated on most soil types once the yam holes are properly dug and filled with organic material. Organic matter improves soil structure, acts as a slow release fertilizer and allows for optimal growth of the tubers. Adequate drainage, proper aeration, a friable soil and sufficient moisture (not waterlogged) are other critical requirements for yam growth.

• pH: 4.5-6.5
• Shade:

Yams are sensitive to shade leading to low yields and should be grown under full sunlight.

• Temperature:

Yams strive under warm – sunny conditions at temperature of between 25^oc – 30^oc and does not tolerate freezing environment thus yam is restricted to the tropics. 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/annum.

Planting methods

There are four main methods of planting yams:

• Ridges: Form ridges 1m apart and 25-40 cm high. Fill furrows with rotted organic matter then plants the yam setts.
• Heaps or Mounds: Heap soil into a small mound and add organic matter evenly before planting.
• Holes: Dig hole 45cm x 45cm x 45 cm and fill with rotted organic and sharp sand in the following ratio- 1:2. Plant one yam set in hole.
• Flat: Minimum tillage is done and vines are allowed to grow flat on the ground without making ridges or heaps.

Crop management

Mulching: covering of ridges or mounds with dried grasses is essential during dry season to help conserve moisture thereby providing optimum condition for growth.

Staking

This is provision of support structure so as to enable yam vines expose their massive canopy to maximum sunlight throughout its growth.

• Individual staking: One stake per plant e.g. bamboo stakes.
• Pyramidal staking: The support structures are slanted to form a peak.
• Trellising: String wire between two strong posts and each stem is trailed along a string towards the wire support.

Weed control

The yam field should be kept weed free the first four months. Farmers have two options for weed control which is the use of traditional method and the use of herbicides. Three to four hand weeding carried out at 3, 8, 12 and 16 weeks after planting have been found effective for the control of weeds in both ware yams and yam production. The critical period of weed interference for seed yams using the minisett technique is 12- 16 weeks after planting, while that of ware yams is between 4 and 16 weeks after planting. Use a contact herbicide in the furrows during growth and manually remove weeds from around the plant. Selective herbicides can be used to control grass weeds and manual methods can be used to control broad-leaved weeds.

 

Fertilizing

Soil test should be done to determine fertilizer types and rates and also any limestone requirements.

• Two months after emergence apply 85 gm–114 gm of 16:8:24 NPK fertilizers placed 15 cm – 20 cm away from the base of the plant.
• Six months after planting, a similar amount of potash fertilizer e.g. Muriate of Potash is recommended to encourage optimum tuber bulking.

Best yields are achieved using high levels of organic manures and high levels of potash.

 

Pest and diseases management

The major disease problem is anthracnose (Colletotrichum gloeosporioides).

Anthracnose is normally seen as small, black spots between the leaf veins. This disease can be significantly managed using a number of cultural practices with a combination of timely chemical control:

• Soak the planting material and wet planting holes with recommended copper fungicides prior to planting and after planting respectively.
• Vines are sprayed upon shoot emergence.
• Alternate fungicides to prevent the build up to chemical resistance.
• Ensure adequate levels of nutrients.
• Sanitize the field by raking and removing fallen leaves prior to cultivation to reduce the source of the inoculum (spores of the fungus).
• Practice crop rotation.
• Inter-crop with maize.
• Use windbreaks on the windward side of the crop.
• Inspect the field continuously and rogue out infected plants, especially at the windward side of the field.

 

Harvesting

Natural dieback of Yam vines and yellowing of leaves signifies senescence. Yam matures between 9-10 months after planting. After removing the vines, lift the tubers using hand forks taking care to do as little damage to the tubers. The early crop matures at the end of July, main crop from the month of October to January.

 

Problem of yam production

Scarcity and bulk of planting material: The planting materials are bulky and scares

It is labour intensive

Short shelf live and only limited to dormancy period of 4 months after harvesting

 

Storage

Barn storage or under front storage

It can also be stored under-ground.