Establishing an swcsystem
Soil erosion, which leads to low crop yield, is caused by the
washing down of the soil from the slope. Erosion can be checked by putting up
physical structures and live barriers across the farm conserving both the soil
and the water.
1. Mark contour lines using an
A-frame beginning from
2. Make the contour canals and place
the dug-out soil above the canal.
3. Plant soil stabilizers (grass
species) and N-fixing trees at the upper side of the canal.
4. Make a drainage canal that would
run across the contour canals.
5. Build check dams along the
drainage canal.
6. Dig soil traps soil within the
contour or drainage canals
PHYSICAL STRUCTURES IN A SOIL AND WATER CONSERVATION SYSTEM
1. Contour canal. Contour canals are constructed on farmlands
where the soil is deep. They hold water longer and allow it to seep slowly into
the ground, thus increasing soil moisture and draining excess water away from
the field.
Contour cycle
2. Contour bunds
In the process of digging a contour canal, place the soil on the
upper edge of the canal until a mound or bund is formed. (Note The soil dug out
from the cane/may also be placed on the lower edge of the canal).
Contoue bund
Tamp the soil until the mound becomes firm.
The contour bund checks the rapid downward flow of water during
heavy rains and the topsoil that goes with it.
3. Bench terrace. Bench terraces can be dug at the hillside. The
steeper the hillside' the smaller the terraces. It is recommended that the
topsoil be removed first, the terraces constructed and then the topsoil placed
evenly on the terrace. The riser should slope gently to reduce erosion. A
contour canal is dug at the base of the riser and a small mound of soil is
constructed at the edge of the terrace to prevent soil loss.
Midport
Locate midpoints between two contour lines
Along the lower contour line, cut from the hillside a 50cm
bench.
Excavate the soil above the midpoint, first in big chunks then,
in finer particles.
Pile the big chunks of soil on the 50-cm bench to form a mound,
the height of which should be level with the midpoint. This will become the
riser, which should be sloping, not vertical.
Construct a contour canal below the riser.
Midport
4. Contour hedgerow. The simplest soil erosion control structure
for a hillside is a contour hedgerow.
Plant the contour bunds with multipurpose shrubs/trees in a
triangular form Planting napier grass on the hedgerow is not recommended because
they compete with other crops for soil nutrients.
Plant napier grass or creepers on the riser to stabilize it
Grass
5. Check dam. This is a simple structure that can stop gully
erosion by slowing down water flow.
In the drainage system, drive stakes into the ground,
perpendicular to the water flow. Gliricidia makes an ideal "live" peg if it is
available. The cuttings will grow and form a permanent living barrier.
Weave split bamboo strips between the pegs and place bush or
stones against the dam's upper side. Periodically, clean the area above the dam.
Begin constructing dams from the top portion of the drainage
canal. The steeper the slope, the closer together the dams should be.
Fence
6. Soil trap. The purpose of this structure is to catch soil
carried by water in a canal or gully. The pit should at least be 0.8 m deep
× 1.0 m long × 0.5 m wide in a drainage canal. Clean the pit
periodically and spread the soil on the farm Soil traps should be placed about 1
m above the dam.
Soil trap
In fames where zero or minimum tillage is practiced (rocky or
heavy limestone areas, steep slopes or where there are plenty of tree roots as a
result of bush farming), digging of contour canals may prove to be difficult.
Other alternative structures can be built.
1. Drainage/diversion canal. This canal will catch water coming
from above the farm and throw it off to a nearby gully. The size of the canal
should be enough to accomodate the volume of the water.
Dig from the uppemmost portion of the farm, sloping gradually
across the farm at about one percent grade.
Place the excavated soil on the lower portion of the canal to
form a mound or bund.
Rockwalls
2. Rockwalls. in areas where rocks are abundant, rockwalls are
appropriate.
Along the contour line and above the contour stakes, cut the
hillside. This is the base to hold the stones.
Pile the stones, putting the bigger ones on the base.
If enough stones are available on the farm make the height of
the rockwall level with the midpoint (of the contour lines).
Plant hedgerows of multipurpose trees at the base of the rocks.
These will stabilize the rockwall and will also serve as a forage source.
Rocks
