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Part three: Technical section
1. THE AGROFORESTRY PROJECT (PAF)
HOW STONE BUNDS ARE BUILT
1. Eroded or abandoned land is selected for treatment.
2. Contours for the bunds are surveyed using a water tube level starting at the top of the field and working downwards.
3. Lines are marked on the ground with a hoe.
4. A shallow foundation trench is dug for each bund.
5. Construction begins with large stones in the rear of the trench (downslope side).
FIG 1: CONTOUR STONE BUNDS
6. Smaller stones are used to build the rest of the bund. The stones must be packed carefully, especially at the bottom.
7. Earth from the trench is piled up in front of the bund.
8. If the land treated is an abandoned plot, the stone bunds are left for a year to catch sediment. Cultivation begins only in the second season.
9. Andropogon grasses and tree seedlings are planted alongside the bund during the rains.
15-30 metres apart
FIG 3: ZAI
ZAI - (PLANTING PITS)
zai are deep planting pits, which help crop growth
they are dug before the rainy season
compost or manure is placed in the zai to improve fertility
zai fill up with rainwater runoff during the rains
Where stone bunds and zai can be used:
suitable for all dry areas
soils do not need to be deep
best water harvesting effect on slopes below 2%
must be a good local supply of stone!
90 cm apart
HOW TO MAKE A COMPOST PIT
1. A mud wall of not more than 50 cm high is built around a pit about 75 cm deep. The area enclosed should be 3 metres x 6 metres.
FIG 4: COMPOST PIT
2. A layer of thin branches or stalks of cereals is placed at the bottom of the pit to for allow circulation of air, which is necessary for good composting.
3. The pit is built up with waste materials, for example:
- stalks (well chopped)/leaves from harvested plants
- kitchen waste
- household sweepings
4. Some old, well rotted compost and manure should be added to help the composting process to get going.
5. The pit must be kept moist by watering, and must be turned occasionally.
6. When the compost is well rotted (black and crumbly) it is ready for use - in zai for example. One pit makes enough for a handful or two of compost in the zai of 2-3 hectares.
7. Usually each pit is filled and emptied for use once each year.
HOW PERMEABLE ROCK DAMS ARE BUILT
1. The site for the permeable rock dam is identified by the village committee.
2. The most suitable sites are where gullies are beginning to form in the middle of productive land.
3. Where possible a series of permeable rock dams should begin at the top of a valley.
4. Sites immediately above gully heads should be avoided - because the permeable rock dams may be undercut.
5. If the gully which the dam crosses is less than one metre deep, no spillway is required.
6. Where a spillway is needed - to allow passage of heavy flows - it can be made from gabion baskets (wire cages filled with stone), where available.
7. Using a water tube level, the alignment of the main "wings" of the dam is marked out. The wings approximately follow the contour, and therefore they curve back down the valley.
8. A shallow foundation is dug in places where the soils are easily eroded. The trench is filled with small stones/gravel. The main dam wall is constructed carefully, using large flat stones as the casing, with smaller stones packed inside.
FIG 5: PERMEABLE ROCK DAMS
9. The wall is constructed evenly along its length to lessen the damage if an early flood occurs. The top is surveyed with the water tube level to make sure it is level.
FIG 6: CONSTRUCTION OF PERMEABLE DAM
Where Permeable Rock Dams can be used:
Suitable in dry areas with less than 700 mm rainfall
Where gullies are forming in productive land
Slopes should be less than 2%
Good supply of stone and transport are essential
50-200m apart (ideally the top of one should be level
with the bottom of the one ups-slope but in practice,
this is not usually possible)
required (for a dam 600m long): 300-600 cubic metres
(depending on height)
USE OF THE WATER TUBE LEVEL FOR SURVEYING
FIG 7: USE OF WATER TUBE LEVEL
The water tube level is a simple surveying instrument which is used for laying out contours in fields. It is easy to understand, and farmers can quickly learn how to operate it for themselves.
It consists of:
- 10-20m of clear plastic piping, with inside diameter 610 mm
- two poles of 1.5 -2.0 metres length
- four rubber straps (from inner tube) to attach pipe to poles
- one to two litres of water
The water tube level is assembled by uncoiling the tube and then filling it with water by siphoning (sucking one end of the tube with the other end dipped in water). Each end of the tube is then tied to one pole.
The poles are held side by side and the levels of water marked on the poles.
Laying out a Contour with the Water Tube Level
1. The team begins at the top of the field, and continues downslope. Two operators are necessary to hold the poles, and a third is required to trace the line on the ground with a hoe.
2. One operator ("A") remains stationary holding one pole, while the other, ("B") moves up and down the slope with the other pole until the level of water in each tube matches the "level" mark. The two points are now on the contour.
3. The person with the hoe marks the ground between the poles.
4. Operator "A" now picks up his/her pole and moves to the other side of "B" who remains stationary. It is now "A" s turn to find the correct spot.
5. This procedure is carried on until the end of the field is reached. The distance to the next contour line is paced out, and surveying continues.
6. The true contour can now be "smoothed" by eye to make ploughing easier.
Important Points to Remember:
1. MACHAKOS DISTRICT - NSWCP
HOW A FARM IS CONSERVED USING FANYA-JUU TERRACES
1. The farm is surveyed by a technician to see if a cutoff drain is required above the fields.
2. A cutoff drain is laid out along the contour. All the runoff from outside the farm is held and infiltrates.
3. The soil dug out from the cutoff drain is heaped downslope.
4. Contours are then surveyed with a line level.
5. Soil is loosened with hoes or mattocks along the line of the contour and then thrown upslope to make the bund. A small step is left between the trench and the bund so that soil is not washed straight back in when it rains.
FIG 8: CONSTRUCTION OF FANYA-JUU TERRACE
6. Grass is planted on top of the bund to stabilise it. "Bane grass" is one of the best varieties for Kenya. Bananas or other trees may be planted in the trench.
FIG 9: DEVELOPMENT OF FANYA-JUU TERRACES
7. Ploughing, weeding and natural soil movement cause the land between the terrace banks to level off into benches after a few years.
FIG 10: FANYA-JUU TERRACES
Where fanya-juu terraces can be used
in marginal/wetter zones (700 mm rainfall and above)
soils should be deep
suitable for slopes from less than 5% to 50%
1.25 m wide at top and 1.0 metre wide at bottom
of terrace banks: usually between 5 and 20 metres
apart, (depends on the slope of the land - the steeper
the land, the closer the terrace banks)
OTHER CONSERVATION TECHNIQUES USED IN MACHAKOS
"Conservation farming" means reducing erosion by good crop husbandry. This includes:
strip cropping (alternating strips of different crops)
use of farm yard manure and fertilisers.
FIG 11: CONTOUR PLOUGHING
Grass strips are a cheap alternative to fanya-juu terracing. A grass like "Makarikari" (Panicum coloratum) is planted in dense strips, up to a metre wide, along the contour. The grass slows down runoff and silt builds up in front of the strip. Benches are formed, though this takes a long time to occur.
Gully control is expensive and therefore not usually a priority, except where gullies threaten good I land, roads or buildings. Gullies are stabilised by the use of a variety of materials, including brush-wood held in place by stakes of wood from trees which sprout from cuttings (eg Commiphora spp.).
2. LOKITAUNG PASTORAL DEVELOPMENT PROJECT
HOW A RAINWATER HARVESTING GARDEN IS MADE
FAG 12: RAINWATER HARVESTING GARDEN
1. A suitable site for the garden is chosen - this is where a small gully brings rainwater runoff to the plot.
2. Starting from the centre of the plot, a line level is used to survey the land before levelling (see next section).
3. The position of the "bottom" bund and the side bunds are pegged out after discussions between plot owner and technician.
4. The outline of the bund's cross section is marked with stakes and string to guide construction.
5. Oxen scoops are used to level the plot and to collect soil for construction.
6. Soil is carried in basins, and layer by layer the bunds are compacted by foot.
7. The line level is again used to make sure the top of the bund is level around the whole plot, and that the tips of the side bunds are on the same contour.
8. The tips of the side bunds are then protected from erosion by covering with loose stone.
9. Where too much runoff from the catchment is a problem, a diversion ditch is made to prevent runoff entering the field.
Where a Rainwater Harvesting Garden can be used:
only suitable for the driest areas (less than 400 mm rainfall)
deep soils necessary
soil should not be a "cracking clay"
slopes less than 2%
size: 0.5 - 2.0 hectares
required: 250-500 person-days/hectare (when oxen
USE OF THE LINE LEVEL FOR SURVEYING
The line level is a simple instrument which is used for laying out contours and for other simple surveying tasks. It is quick to operate, accurate and easy to transport.
A line level consists of two poles which may be short (as in Turkana) or the height of a person (as in Machakos). A notch is made in each pole at exactly the same height and one end of a length of string (usually 8 metres) is tied to each notch.
The centre of the string is marked and a builder's spirit level is hung on the string at this point.
When the bubble is in the middle of the spirit level, the two poles are on ground of equal elevation - that is, the two points are "level" or "on the contour".
How to Lay Out a Contour
1. Each pole is held by an operator and the line level read by a third person. The first pole is held by operator "A" who remains stationary. Operator "B" then moves up and down the slope until the level reads dead centre.
2. The two positions are marked, and while "A" moves to "B's" old position, "B" moves onwards and the process continues until the length of contour required has been completed.
3. The true contour is then "smoothed" by eye to give a better shape for ploughing.
How to Survey Land for Levelling
1. The centre of the field is used as the starting point. A flat stone is placed in a hole with one side level with the ground surface. This is the "bench mark".
2. Operator "A" places his/her pole on this stone. "B" stands downslope with his/her pole on top of a wooden peg. The peg is driven into the ground until a level is found. The top of the peg will be above ground surface. "A" then moves the pole to this peg, and "B" continues down the field and places his/her pole on another peg.
3. The process is similar for the upslope part of the field, except that the pegs are driven below ground to find the level.
4. During the land levelling process, soil is scraped away from around the upslope pegs, and deposited around the downslope pegs. This continues until the tops of all the pegs are at the new surface level.
FIG 13: USE OF LINE LEVEL
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