What is contour
trenching?
Contour trenching is an
agricultural technique that is adopted in order to achieve water and soil
conservation and enhance the agriculture productivity.
Contour trenches are
ditches dug along a hillside in such a way that they follow a contour and run
perpendicular to the flow of water. The soil that is excavated from these ditch
are used to form a berm or narrow bank on the downhill edge of the ditch. The
berm is then planted with permanent vegetation, which might be native grasses
or legumes, to stabilize the soil and for the roots and foliage in order to
trap any sediment that would overflow from the trench in heavy rainfall
events.
Purposes of contour
trenching:
- To reduce surface water flow velocity
- Promote infiltration
- Prevent pollutants from draining into water bodies (suspended sediments, nitrogen, phosphorous)
- A step to soil and water conservation
 |
| A Contour Trench |
Technique
To build a proper
contour trench, the trench should accurately follow the contour or the outline
of the hill. The use of A-frame level is very popular in determining the
contour. The contour is marked with stakes for digging after contour level is
found.
How to make A-frame
Level?
Material Required:
·
2 poles about 2 metres long
·
1 shorter pole about 1 metre long
·
Some strings
·
A stone
Procedure
1.
First, you need to tie the poles tightly
together in such a way that it makes the shape of a letter A.
2.
Then hang the stone from the top of
the A-Frame, making sure the stone hangs below the cross bar.
3. Holding the frame upright, mark
with two sticks exactly where the poles touch the ground.
4.
When the stone stops moving, mark
where the string crosses the cross bar.
5. Turn the A-Frame around, placing
the poles in exactly the positions marked by the two sticks. Again mark where
the string crosses the cross bar.
6.
Mark the level mark on the cross
bar - exactly half way between the previous marks. If the first two marks
happen to be on the same place - this is the level mark.
How to use the A-frame
1.
Before using the A-Frame, collect a
number of sticks.
2.
Begin at one side of the field
where the first contour line is wanted. Hold one pole firmly on the ground.
Move the other pole until both poles are on the ground with the string touching
the level mark.
3.
Place a stick into the soil by each
pole. Move the A Frame along, by turning it around (pivoting), keeping pole 1
in exactly the same place. Move pole 2 until the string touches the level mark
and place another stick into the ground by pole 2.
4.
Carry on in this way, pivoting the
A-Frame across the field.
How to make trenches?
1.
After the contours have been marked
the farmers can begin to excavate the trench.
2. To maintain structural rigidity on
the uphill slope of the hill, the shovel should be applied to the contour with
the user faceing downhill, not along the contour, so that the uphill face of
the trench is not structurally compromised.
3.
Place the excavated soil downslope
along the edge of the trench.
4.
Pack excavated soil to create a
berm on the downhill border of the trench.
5.
Plant native grasses, legumes, or
perennials on the berm. These varieties have a root system capable of providing
adequate structure to the berm.
6.
Apply mulch to berms to prevent
erosion while the plants take root.
7. If possible, trenches should be dug
in the dry season so that the rain does not destabilize or wash away the berm
before vegetations can provide stabilization.
Maintaining the
trenches
1. Over their lifetime the trenches
will fill with sediment. Periodically, the sediment should be removed from the
trench and re-applied to the field uphill from the trench.
2.
Removal should take place prior to
tilling of the soil, so it can be incorporated into the soils of the new crop.
3. Farmers should take care not to
accidentally deepen the original depth of the trench during this maintenance
step.
4.
Berms may need repair if the
vegetation is still establishing itself as a stabilizing force.
Advantanges
- · Less runoff
- · Reduces evaporation
- · The water balance is enhanced
- · Helps to meet the water demand of crops
- · Less chances of wind and water erosion
References
MANAGE – National Institute of Agricultural Extension Management, Ministry
Agriculture, Government of India. www.manage.gov.in
Footsteps, Tearfund. Tearfund International Learning Zone. Issue 15 http://tilz.tearfund.org/Publications/
0 comments:
Post a Comment