Environmental Engineering Reference
In-Depth Information
desired attributes of trees used as live stakes include an open canopy, many
branches, deep tap-root system, leguminous, wind resistance, and evergreen
growth habit. Trees with straight stems and a compact canopy are also used.
The live stakes are pruned leaving the optimum canopy and number of branches
for effective support of the yam vines. Some trees are also coppiced as a way of
managing the shade imposed on the yams. Where the live stake is located far from
the yam mounds, leader stakes are used to link the vines to the live stakes. During
staking, emerged vines are trained on the leader stakes when they are 50 cm to
over 120 cm long with a mode of 60-100 cm. Staking may be done earlier when
vines are around 30 cm long or later at over 120 cm long.
Harvesting
Water yams produce edible tubers five to six months after planting. Some tubers
are harvested between six and eight months after planting. The bulk of the crop
is harvested at between nine and 12 months after planting. In a few instances,
harvesting may be delayed a little beyond 12 months when all the leaves are
completely dried. Harvesting procedures are similar to those of the bush yam.
Some water yams tend to have more shallow tubers making them easier to har-
vest. In some varieties such as
afasew nanka
and
alamoa poto
the tubers tend to
pop out of the soil as they mature, making them easy to harvest. The tubers of
these are continuously earthed up to prevent their exposure until harvesting. This
practice preserves the cooking quality. The length of harvested tubers varies
between 10 and 40 cm. Some cultivars have tubers exceeding 40 cm in length.
For instance,
alamoa gaga
and
osoaba
have tubers measuring 90-118 cm in
length.
Storage
Tubers may be harvested from the field as required. However, most water yams
are harvested once. The tubers are stored in barns, on platforms, or stored covered
under trees. Water yams store very well and may be kept in storage for over one
year. The palatability of the tubers improves with storage as the tubers become
less watery.
Maintenance
Farmers maintain their water yam germplasm by yearly planting. Also purchases of
planting materials from the market ensure that the cultivars at a risk of extinction
are replaced. The plants also regenerate from pieces of tubers left in the field after
harvest. In bulbils-bearing or seed-producing varieties, the bulbils or seeds that drop
from the vines produce volunteer plants and serve as organs of perenniation.
Special attributes and uses
Water yams are known for their ease of sprouting. They are cherished for their
relatively long shelf life, palatability, and food security value. A few farmers also
