By Isaiah Turkighr
Yam is a starchy root vegetable that belongs to the Dioscorea genus. It is commonly grown in tropical and subtropical regions, especially in Africa, Asia, the Caribbean, and Latin America.
PRE-PLANTING :
Soil preparation
- Clear the bush and remove large tree stumps. Allow the scattered remains to decay and then work it into
the soil.
Land preparation can be done manually or with tractor-drawn implements. The soil at planting time should be
loose and well-worked. - Plough, harrow, and ridge the land, or form mounds with hoes.
The size of the mounds depends on the size of tubers desired at harvest. Yam seed tubers can also be planted
on flat ground. Seed preparation and planting: Cut large yam tubers into appropriate sizes.
Yam sets can be from 30 to 300 g depending on desired tuber sizes at harvest. Yams can also be planted as
whole seed tubers.
After being cut, the yam cuttings need treatment with a mixture
of a suitable broad spectrum fungicide (e.g., Z-Force:
active ingredient is mancozeb 80% WP) and insecticide(e.g., ActForce gold: active
ingredient is chlorpyrifos
48% EC) to prevent rots
and damage by pests
after planting. There are
many types of chemical
products available that
could be used. It is essential to read all instructions carefully
on the appropriate handling and disposal of chemicals
to safeguard human and animal health, as well as the
environment. The mixture could be in liquid or powder
form. If it is a liquid, a perforated basket or net bag is used
to immerse the seedling in
the solution for 5-10 minutes; if it is a powder,
the seed yam cutting should be
placed in a plastic bag or
bucket with a lid and shaken
carefully until they are well
coated.
In the absence of
commercial chemical
treatment, wood ash with a high content of Potassium is
used as a solution or dust.
Planting Yam Setts(cuttings):
Plant yam sets 10 cm deep in soil to avoid exposure to sun.
Spacing of yams depends on the set size. The normally recommended spacing of yams for commercial yam
production is 1 m × 1 m between rows and stands, respectively (10,000 stands/ha). Use narrower spacing
(1 m × 0.25 m) for smaller sets (e.g., 30 g).
Mulch yam mounds and ridges to prevent Sun penetration.
Transplanting yam seed cuttings:
Yam seed cuttings should be handled carefully to avoid damage
to young sprouts. Transplanting is best done when
sprouts are still short and have not elongated into vines
or produced broad leaves. It should also be done when
rains are well established. To reduce transplanting shock,
Yam seed cuttings should be planted as soon as possible after they
leave the nursery bed. If for some reason, such as a protracted
period of drought, the yam seed have to overstay in the
nursery and develop excessively long vines with many
leaves, the leaves should be reduced before planting.
Intercropping yam seed cuttings:
Yam seed cuttings can be intercropped with maize; both crops are
planted at the same place. A single maize seed can be
planted at a spacing of 1 × 2 m between the yam seeds
on the ridge or at a spacing of 1 × 1 m by the side of
the ridge. The maize plants eventually provide
support to the yam plants. Plants from yam seeds of water
yam grow more aggressively so only maize varieties
with sturdy stalks will be able to support the weight of
the foliage. Other crops found in mixtures with seed yam
include cassava, vegetables, cocoyam, sorghum, millet,
groundnut, melon, and beans.
In mixtures, yam is often planted before the other
crops.
Staking : In regions where yam is staked, plants from seed yam cutting should also be staked. Since the plant foliage(leaves) is
smaller than that of ware yam, smaller stakes of 1-2 m will
be adequate. Small sticks, split bamboos, or maize stalks
can be used as staking material. Depending on the size,
a stake can be placed against individual plants or several
plants directed to a stake using strings; this is pyramidal
staking ( Picture of it ). Where stakes are not readily available,
trellising can be done.
While both staking and trellising are gardening techniques used to support plants, the key difference is that staking typically uses a single upright stake to support a single plant, while trellising provides a more complex lattice-like structure for climbing plants to grow on and can support multiple plants simultaneously; essentially, staking offers basic support, whereas trellising provides a guided pathway for climbing growth. (Picture of trellis).
MAINTENANCE:
♣ Weed control :
The seed yam field should be kept free
of weeds as much as possible, especially during the first
8 to 12 weeks when the crop cover is low. Apart from
using up soil nutrients, some weeds harbor pests and
diseases which may affect yam plants. Weeding can be
done manually using the hand-held hoe as practiced by
farmers, or it can be done chemically with herbicides.
After direct planting or transplanting of yam seed cuttings with
small sprouts, pre-emergence herbicides such as Diuron,
Flumeturon, Alachlor, or Premextra can be applied at
recommended rates for the effective control of weeds.
At high plant populations and without staking (commonly
practiced in the savanna region), vines will spread over
the soil and provide some control of weeds from about
12 Weeks After Planting .
Fertilizer application :
In traditional systems most
farmers do not apply fertilizer to yam, but plant the
crop immediately after a fallow so that it benefits from
the organic matter accumulated during the fallow
period;or they engage in crop rotation. Where there is need for fertilizer application, the
recommendation for the location should be followed. NPK
20:10:10 or 15:15:15 at 400-500 kg/ha applied at 8-12
Make holes on both sides of the ridge for single row
planting, and double rows on each side of the ridge for double row planting could serve as
a guide. If pre-sprouted yam seeds are used, fertilizer is
applied earlier at 4-8 Weeks After Planting . The nutrient status of the yam
field can be improved by following a good rotation plan
(rotating with leguminous plants). A good soil management
regime will ensure sustainable production.
HARVESTING :
Seed yam mature in 5 to 8 months after planting or
transplanting. At maturity the leaves turn yellow and
dry off; this is followed by the drying of the vine.
Yam harvest can be carried out twice in it’s harvest season: The first harvest is done between
the fifth and seventh month of growing, when the tuber
which is mostly used for food is carefully cut off below the
coronal roots to avoid damage to the root system. The
roots are then covered with soil and a second harvest of
the same plant is done at the end of the season for use as
seed yam.
The tubers should be dug carefully to avoid cuts and bruises
which serve as entry points for pathogens and increase
respiration during the healing process. Harvesting when
the soil is wet may increase the chances of wounded
tubers developing rots in storage. Immediately after
harvest, seed yam should be removed from direct sunlight
to a shaded place to prevent sun scorch. Tubers do
not store well that are left in the sun for too long or have
cuts. Seriously damaged tubers should be sorted out for
immediate use. Seed yam of each variety should be stored
separately and graded according to size.
STORAGE
After the harvest of yam,there’s every need to store the tubers. Here are 5 Considerations that should be noted in yam storage:
- Proper Temperature and Humidity
Yams should be stored in a cool, well-ventilated place with temperatures between 12°C and 16°C (54°F to 61°F). Extreme temperatures can lead to spoilage; if too cold, yams can develop chilling injuries, and if too warm, they may sprout or rot quickly. Maintaining moderate humidity levels prevents dehydration and fungal growth.
- Adequate Ventilation
Good air circulation is essential to prevent the buildup of moisture and heat, both of which can encourage mold growth and rot. Yams should not be stored in plastic bags or airtight containers, as these can trap moisture. Instead, they should be placed in well-ventilated crates, baskets, or racks.
- Proper Handling and Sorting
Before storage, yams should be carefully inspected for damage. Bruised or cut yams spoil faster and can spread decay to healthy ones. Sorting and storing only undamaged yams will help maintain overall quality. Handling them gently also minimizes bruising, reducing the risk of early spoilage.
- Protection from Direct Sunlight and Moisture
Exposure to direct sunlight can cause yams to dry out or sprout prematurely, while excess moisture creates a breeding ground for mold and rot. A dry, shaded storage area, such as a yam barn or ventilated shed, is ideal for preserving freshness.
- Use of Traditional Storage Methods
In some regions, farmers use traditional methods like yam barns (vertical stacking tied to wooden poles) or storage pits covered with dry leaves to extend shelf life. These methods regulate temperature and humidity naturally, reducing post-harvest losses.
Conclusion
Proper yam storage is essential for minimizing spoilage and maintaining quality. By considering temperature, ventilation, handling, moisture control, and traditional storage techniques, farmers and consumers can ensure a longer shelf life for their yams. Whether for commercial purposes or home use, these storage practices help prevent wastage and ensure a steady food supply.