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Today i will be discussing Yam and its propagation, using Nigeria as a case study.

Yam

Site Selection and Soil Management

Select a good fertile well drained soil. The level of inherent fertility will determine the growth development and yield of tuber yam.

Field Measurement

Field measurement is very important because its accuracy guides farmers to know their farm sizes for vital decision on farm operations including the right amount of inputs needed and the anticipated yields from the farms. The use of (Geographical positioning System, GPS) hands receiver has simplified the rigor of land measurement. Land area can be easily measured using GPS receiver while transecting the perimeter of the land. For field measurement using GPS, refer to GPS manual.

Land Preparation

In atypical rain forest zone cut down the trees and shrubs, and remove them from the farm or burn. For a field that has been cultivated previously, plough and harrow before mounds are made. However, plough should be made deep since yams need a deep loose soil. Construct ridges one meter or 75 cm apart. In the case of sloping or rolling fields, construct ridges to follow the contour to minimize soil erosion.

Variety and seed selection

Yams are grown by planting pieces of tuber, or small whole tubers ( seed yams') saved from the previous season. Small-scale farmers, the majority of producers, often intercrop yams with cereals and vegetables The most common varieties of yam are: White yam (Dioscorea rotundata Poir). Yellow yam (Dioscorea cayenensis Lam.). Water yam (Dioscorea alataL.),Bitter yam (Dioscorea dumetorum).
There are major two planting period: early planting (Month of May) and late planting (Month of October/November.

There are four main methods of planting yams:

1. RIDGES: Form ridges 1m apart and 25-40 cm high. Fill furrows with rotted organic matter then plants the yam setts (seed Planting Material).
2. MOUNDS: Heap soil into a small mound and add organic matter evenly before planting.
3. 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 sett in hole.
4. FLATS: Minimum tillage is done and vines are allowed to grow flat on the ground without a trellis.

There are other two local methods of planting yams that are practiced using minimum land preparation and crop care:

i . RIVER BANKS METHOD: The land is not tilled. Holes are dug using a cutlass and setts placed in each hole.

ii. FOREST METHOD: Mounds are prepared using rotted trees, fallen leaves etc. Setts are then planted in the mounds.

There are four ways of propagating yams:

1. 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 coir.
2. Seeds: True seeds found on vines e.g. Cush- cush.
3. Cuttings: Basal vine cuttings are best. Use 6 cm-8 cm pieces, dip in a rooting hormone and place in a propagating bin.
4. Tissue culture: Used to produce "clean" plantlets i.e. free from diseases.

There are three types of setts that can be obtained from a whole tuber:
1.Head setts: These are the best yam setts to plant because of the presence of the primary nodal complex (eye) which gives rise to the new plants.

1. Middle setts.
2. Tail setts.
   Whole tubers can also be planted. Dust all planting setts, especially those with an exposed cut surface, with a fungicide and anhydrous lime at storage and before planting. Dusting encourages wounds to heal and prevents the entry of pathogenic organisms that potentially could cause spoilage to the stored planting material.

Soil management

Intercropping of yam with legume crop and cover crop help to improve soil fertility, reduce soil erosion and reduce weed aggressiveness.

Integrated soil fertility management

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

1. Two months after sprout emergence apply 85 gm 114 gm of 16:8:24 NPK fertilizer placed 15 cm - 20 cm away from the base of the plant.
2. 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.

Water management

Although yams are relatively drought-resistant, they require ample moisture throughout their growing period, particularly from 14 to 20 weeks after planting when tuber bulking occurs rapidly. Irrigation should be provided in areas where the dry season is longer than 3 or 4 months and falls within the growing period of the plants.

Weed Management

Prompt weed management is crucial for yam production. Control weeds for the first 6-8 weeks after planting promplty. Use a contact herbicide in the furrows during growth and manually remove weeds from around the plant. Selective herbicides can be used to control weeds. Two to three Traditionally hoe-weeding/slashing is encouraged. The frequency of weeding will depend on prevalent of weeds which is also related to the ecology, rainfall pattern and the methods of land preparation. Intercropping with other crops will reduce the aggressiveness of weeds in yam. For chemical control of weeds in yam use the following chemicals
Fluometuron at 2.0 kg ai/ha
Diuron at 3.0 kg ai/ha
Chlorambenat 1.5-3kg ai/ha .
Formulated mixture of flumeturon + metolachlor (2 + 2 kg a.i/ha)
Metobromuron and metolachlor (2 + 2 kg a.i /ha)
Fluometuron and Pendimethalin( 2 + 2 kg a.i /ha)
Primextra (2 3 kg a.i /ha)

Safety Use And Handling Of Pesticides

Whenever pesticide is to be used in farms certain precautions must be followed to ensure its safe use. Even after use, the empty containers must be disposed very well by burying them. This precaution is very critical because misuse of pesticide could be harmful both to the crop and the person applying the pesticide. For this reason, instructions as stated on the label of the pesticide must be followed while only trained personnel should apply pesticide at recommended rate. The personnel should also wear protective clothing during application of pesticide.

Pests Diseases and their control

The major pests that affect yams include insects such as leaf and tuber beetles, mealy bugs, and scales; parasitic nematodes; fungi causing anthracnose, leaf spot, leaf blight, and tuber rot; and viruses, especially the yam mosaic virus (YMV). The major disease problem is anthracnose (Colletotrichum gloeosporioides Penz.). Anthracnose is normally seen as small, black spots between the leaf veins. Some infections can coalesce to form massive blighted lesions. This disease can be significantly managed using a number of cultural practices with a combination of timely chemical controls as listed hereunder:

1. Soak the planting material with recommended copper fungicides prior to planting and drench the planting holes with the fungicide after planting.
2. Spray the vines upon shoot emergence.
3. Alternate fungicides to prevent the build up to chemical resistance.
4. Encourage healthy plants by ensuring adequate levels of nutrients.
5. Sanitize the field by raking and removing fallen leaves prior to cultivation to reduce the source of the inoculum (spores of the fungus).
6. Practice crop rotation.
7. Inter-crop with corn. The corn crop helps to move the spores up and away from the yam leaves reducing the infection rate.
8. Use windbreaks on the windward side of the crop.
9. Inspect the field continuously and rogue out infected plants, especially at the windward side of the field.

Crop Maturity, Harvesting and Storage

In Nigeria tubers planted between February and April, depending on whether in humid forest or on the savanna, are harvested 180 to 270 days later. Harvest carefully to minimize damage to tubers which could lead to rot and a decrease in market value. Harvested tubers normally stay dormant (do not develop sprouts) for 30 to 120 days depending on environmental conditions, the date of harvest, and the species. This means that only one crop cycle is possible per year. Amongst the major roots and tubers, yam is considered to be the least perishable. It is generally stored fresh, the storage of dehydrated yam chips being relatively limited. Successful storage of yams requires, the use healthy tubers, proper curing, if possible combined with fungicide treatment, adequate ventilation to remove the heat generated by respiration of the tubers, regular inspection during storage and removal of rotting tubers and any sprouts that develop and protection from direct sunlight and rain.


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