Environmental Engineering Reference
In-Depth Information
Sources and types of planting material
Most cultivars are passed on as heirloom cultivars within the farm family.
Farmers also purchase additional planting materials from the market or add to
their collections by exchanging planting materials with their peers. Large tuber
heads or small tubers weighing between 400 and 500 g are planted. Where
planting material is limited, tuber sections, 200-500 g, are also used.
Planting
Planting holes, about 30-50 cm in diameter and 40 cm deep, are dug, usually
between 100 and 200 cm away from the permanent tree stakes. The holes are refilled
with a mixture of topsoil and leaf litter, leaf mound, or decomposed cocoa husk. The
sett is placed 10 cm deep, slanted with the head section up. Where cuttings are used
the planting material is placed in the hole with the skin or periderm section down-
ward, covered with topsoil, and capped with leaf litter. In areas with deep friable
soils, the bush yams are planted in the holes on the flat or mounded. Where the soils
are not deep, mounding is more frequently practised. The size of mounds ranges
between 50 and 100 cm in diameter and between 15 and 20 cm in height. Mounding
is frequently done after the yam has started sprouting.
Staking
Bush yams are exclusively grown on stakes. Plantation crops such as oilpalm, or
cocoa serve as live stakes. However, certain trees with deep tap-root systems, fewer
lateral roots, or which root easily are commonly used as stakes. These include
Newbouldia laevis
,
Zanthoxylum xanthozyloides
,
Horrlarhena floribunda
,
Nesogordonia papaverfera
,
Ficus exasperata
,
Spondias mombin
,
and Mallotus
oppositfolium
. Farmers manage the live stakes by root pruning, coppicing, or prun-
ing off some branches at the beginning of the planting season. Young vines, about
60-100 cm long, are trained to leader stakes that are placed 20-30 cm from the
planting hole and leaned on to the permanent stake. The leader stakes may be bam-
boos, rachis of palm fronds, sticks, water sprouts from trees, or simply old vines
from previous years' growth that serve as trellises.
Harvesting
Bush yams are ready for harvest between July and September (seven to eight months
after planting). Milking or pricking usually commences at the end of July. It involves
careful removal of the soil from the mound or planting hole to expose the tubers. The
ware yam is detached with the aid of a cutlass leaving only the corky section of the
head (corm) and its propping roots intact. The corky head may be covered immedi-
ately or left uncovered until fresh tubers are initiated from the corm (Plate 9).
Full-term tubers are harvested after nine months. To harvest the full-term
tuber, the soil is carefully loosened a little at a time with the aid of a cutlass. The
loose soil is removed by hand to expose the top section of the tuber. The process
is continued until the entire tuber is freed (Plate 5). Where tubers are very long
