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Erosion can be prevented:
· by stopping the water from flowing away.
Quickly running water carries earth away. It is dirty water,
mixed with earth
If the flow of water is stopped, the earth mixed with the
water settles on the ground.
The water becomes cleaner. The earth is not
lost.
In order to stop the flow of water and keep the earth, we use:
· contour line ridges,
· ditches,
· barrier
strips,
· strip cropping.
· by covering the soil.
Water that falls on bare soil carries away the soil.
Water
that falls on soil covered by plants damages the soil less.
The plants that
cover the soil reduce erosion.
To cover the soil, use mulches and sow cover
crops.
Brush fires leave the soil bare and without plants. They destroy
organic matter. The soil structure becomes bad.
Brush fires are bad for the
soil.
Water flows very fast on sloping land. It flows strongly and
carries away earth.
When ridges are made in the direction of the slope, or if
you plough in the direction of the slope, the water flows faster and faster
between the ridges.
It carries away a lot of earth.
Look at this drawing:
Figure
The lines are in the direction of the slope.
The water flows
very fast. Earth is carried away.
When ridges are made across the slope,
water cannot go fast. It is stopped by the ridges. Earth is not carried away.
Look at this drawing:
Figure
These lines are across the slope. Water and earth are held
up.
When you make ridges across the slope,
When you plough across the
slope,
You are working on the contour line.
A contour line is a line
across the slope running always at the same height!
Making ridges along the
contour lines helps to control erosion.
The water cannot flow fast
The
water is held by the ridges.
Direction of
slope
The tools
The water level
We need:
· a board 80 centimetres by 50
centimetres;
· an empty medicinal
ampoule;
· 1.80 metres of plastic tube of the
same size as the ampoule (the dispensary may have it).
Half fill the tubing with water mixed with a little ink.
Join
the two ends of the tube with the ampoule, which should be open at each end.
Medicinal ampoule
Fix the tube on the board as shown in the drawing, putting the
ampoule at the top.
Protect the tube by strips of wood, except in the places
shown in the drawing.
Nail the board to a stake 1.40 metres high.
· The sighting mark
Get a board 30 centimetres by 30 centimetres. Nail the board to a stake 1.40 metres high. Paint two squares on the board as shown in the drawing. This is our sighting mark.
· Stakes
Get ten stakes 1 metre high.
MARKING THE LINES
Two people are needed, the man in charge and his helper.
The
man in charge takes the water level.
His helper takes the sighting board and
the stakes.
Marking the lines
The man in charge goes to the top of the field. His helper goes to the same height at a distance of 15 metres or paces. The sighting mark and the level are held quite straight.
As shown in the drawing, the man in charge tries to get in the same line of sight the levels of the water in the tube and the centre of the sighting mark.
He takes a sight.
The man in charge does not move from his place. He signs to his helper to go up or down the slope. When he has got a good sight, the helper fixes a stake in place of the sighting mark.
Signing to helper
The helper goes 15 metres or 15 paces away from the stake he has
just fixed in the ground. He is now 30 metres from the man in charge.
The man
in charge takes a new sight. His helper marks the spot with another
stake.
The helper again goes 15 metres away. The man in charge takes another
sight.
The helper gets to the end of the field. All the stakes are at the
same level.
The man in charge marks a ridge joining all the stakes.
This ridge marks the contour line.
To make a line 30
centimetres lower, the man in charge puts his level on the line he has just
marked.
His helper puts a block 30 centimetres high under the sighting
mark.
The man in charge takes a sight.
He finds the beginning of a contour
line that is 30 centimetres lower.
He looks for points on the new line.
Setting a new line 30 cm below
Then he marks a third line, and a fourth line.
· On a slope the soil can be even better protected by making barrier strips.
A strip of uncultivated land is left. Grass grows on this strip;
it stops the flow of water and the earth is not carried away.
Barrier strips
must also be made on the contour lines, across the slope.
A barrier strip
should be at least 2 metres wide.
To better stop the flow of water tall
grasses can be planted. Even trees can be planted.
· If the slope is slight, barrier strips are made 30 to 40 metres apart.
If the slope is a little steeper, barrier strips are made 10 to 20 metres apart.
Slopes
· If the slope is very steep, and if the water flows very fast, it is difficult to stop the water with ridges or barrier strips.
· Ditches 30 centimetres deep are dug along the contour lines.
The earth from the ditch is piled up along the lower edge of the ditch and forms a big ridge, The water is stopped by the ditch and the ridge.
· No crops are grown on this big ridge.
Grass is allowed to grow on it; the roots prevent water from
carrying away the ridge
The ditches are made 20 to 30 metres apart.
Crops
are grown on the strips of land between the ditches.
Crops are grown on the strips of
land between the ditches
Ditches control erosion very well, but they must be cleaned out from time to time.
· If the slope is even steeper, it is impossible to grow crops on the slope.
But little walls of earth or stone can be built.
These walls
are built across the slope.
Earth is put behind the little walls.
In this
way terraces are made. Crops are grown on the terraces.
Crops are grown on the terraces
A ditch is made at the foot of the wall.
The ditch takes the
water that runs down from the terrace.
In some African countries there is a
lot of terrace farming, for example:
· among the Dogons in
Mali;
· among the people of the highlands of
northern Cameroon;
· among the hill people of
Rwanda and
Burundi.
Heavy rains, dry wind and sun all ruin the soil (see pages 5 to
6).
Plants protect the soil against rain, wind and sun.
· Plants that cover the soil prevent erosion.
The rain drops do not fall on the soil.
They fall on the
leaves.
Then they run gently on to the soil and do not carry away earth.
Raindrops are stopped by the leaf
Plants break the force of the wind, and make it less
strong.
Herbage protects the soil. The wind does not blow away the soil in
dust.
The sun does not shine straight on to the soil. Plants with their
leaves cast shade. The earth remains damp. Humus is not
destroyed.
· You can cover the soil with:
straw cut herbage; leaves, stems of millet, maize, etc.
This
cover of dead plants is called a mulch.
· A mulch is useful because:
It protects the soil against water and wind that carry away earth. It protects the soil against the sun which dries the earth. The soil stays damp. It prevents weeds from growing
· After mulching
the straw etc. rots and makes humus. The soil is made richer.
· Mulching is used to protect the soil of gardens, and in growing bananas.
Mulches are also spread round certain fruit trees, such as
mango, papaw and orange.
For palms and coconuts the residues of fruit
clusters and coconut fibre are used for mulching.
· When you clear a field, do not burn the herbage and the small trees. Leave them on the soil so that the leaves and cut trees cover the soil.
· Cover crops are the plants which are sown or planted to cover the soil in certain plantations.
When you let soil rest by leaving it fallow after three or four years of crop production, you can sow cover crops which protect the soil from erosion.
In tree plantations, such as palms, coffee, cocoa, rubber, you must sow a cover crop between the lines of trees, for example, Pueraria.
When the cover crops grow too big, cut them down. Prevent them from climbing up the trees.
· Choose the right cover crops.
A good cover crop must grow quickly and last a long time.
Some cover crops can be used for feeding animals, for example, Stylosanthes and Pueraria.
The agricultural extension service will tell you which is the best cover crop for your plantation.
· The cover crop also improves the soil by giving it organic matter (see Booklet No. 2, page 23).
BRUSH FlRES
During the dry season, many plants die and lie on the
soil.
They are burned in a brush fire.
Why are brush fires made?
· To clear the land.
Fire cleans the field and makes work easier.
· For hunting.
Animals are afraid of the fire and take flight.
They are
caught and eaten.
· To make the grass grow again.
Cattle do not want to eat dry grass.
After the fire, green
grass grows, and cattle eat it.
· To protect the following crop (see Booklet No. 2, page 28).
Many little animals, such as agoutis, rats and insects spoil
crops.
The fire kills them.
They won't attack the following crop.
The
fire also burns up diseased plants.
They won't pass the disease to the
following crop.
· To walk more easily in the bush.
The fire burns tall grasses.
It is easier to get
about.
Fire destroys organic matter.
Plants burned by the fire do not yield any humus.
After the
fire there is nothing left but ashes.
Wind and rain can carry them
away.
Humus enriches the soil and improves its structure.
Ashes enrich the
soil but do not improve its structure.
Fire leaves the soil bare.
Grass cannot grow again on soil burned at the end of the dry
season; the soil is too dry.
The first rains are often very heavy.
They
fall on bare soil.
They easily carry it away after a brush fire.
Fire destroys good plants.
After the fire a lot of plants die.
Often the good plants die
more easily than the bad ones.
Each year bad plants take the place of good
plants.
In this way savanna takes the place of forest.
Fire is dangerous.
Often whole plantations are destroyed, for instance coffee
trees, or oil palms.
Often houses and barns are burned, sometimes the whole
village.
In Africa many soils have often become poor because of fire.
The brush fire is bad.
If we want to stop making it, we must:
· destroy insects, small animals
and diseases by using chemical products
·
bury weeds by ploughing.
· feed animals
during the dry season with hay
But farmers do not always have the machines and the chemical products Many of them must still make fires However, they can prevent the fire being too bad.
If the fire is lit at the beginning of the dry season, the fire is not so fierce and not everything is burned The grass has time to grow again
Then the soil will not be bare at the beginning of the rainy season.
When a farmer cannot get the good results of fire by other means, he should make brush fires at the beginning of the dry season.
When you clear a field, the first harvests are good.
But
after four or five years the harvest is less good; the plants have taken the
mineral salts from the soil and the soil becomes poor.
The soil must not be
used again.
The soil must be allowed to rest.
This rest for the soil is
called a fallow.
On soil that is left fallow, grass and other herbage
grows.
The plants protect the soil against erosion.
The plants die.
The
organic matter from the plants (see Booklet No. 2, page 23) enriches the soil
with humus.
The soil becomes rich again.
To get a better fallow:
· Sow plants.
These plants grow more quickly than grasses, and cover the soil
better.
They make more organic matter.
For example, Stylosanthes and
Crotalaria are good fallow plants.
· Do not bum plants growing on the fallow.
· The fallow can be used for feeding animals.
But the animals must not eat all the plants.
Because then the
soil will no longer be
protected.
· If the same crop is grown on the same field every year the harvests get much smaller, and the soil becomes poor.
· if the crop is changed on the same field every year, the harvest can stay good, and the soil does not become poor. This is called crop rotation.
An example of crop rotation from the Baoule country,
|
Ivory Coast: |
first year: |
yams |
| |
Second year: |
maize or rice |
| |
Third year: |
cotton |
| |
Fourth year: |
fallow |
· In traditional farming, the same crop is grown on the same field for several years.
The crop takes all the mineral salts.
The soil becomes very
poor.
The soil structure (see Booklet No. 4, page 24) becomes bad.
Erosion
carries away soil. Sometimes even the village has to be moved.
Crop rotation means growing a different crop each year on the same field.
REASONS FOR CROP ROTATION
· To make better use of all parts of the soil.
For example:
The first year / grow cotton.
Cotton has a
tap- root {see Booklet No. 1, pa
Cotton gets its food deep down.
The
second year I grow rice.
Rice has fibrous roots {see Booklet No. 1,
pag
Rice gets its food on the surface.
Thus all parts of the soil are
used.
· To make better use of all the mineral salts in the soil.
For example:
The first year / grow cotton.
Cotton uses
chiefly one mineral salt phosphoric acid.
If I grow cotton for two years
running on the same field, the cotton will lack phosphoric acid.
The second
year I grow rice.
Rice uses chiefly another mineral salt, one containing
nitrogen.
A farmer who grows cotton and then rice makes better use of all the
mineral salts in the soil.
· To control insects and diseases.
For example:
When you grow cotton, the insect pests and
diseases of cotton increas
If you grow cotton again the next year, the pests
and diseases which have remained in the field do a lot of harm to the
cotton.
If you grow rice after cotton, the pests and diseases of cotton do no
harm to the rice, and disappear.
· An example of crop rotation in the Central African Republic:
|
First year: |
groundouts |
|
Second year: |
cotton. |
|
Third year: |
rice |
|
fourth year: |
cassava |
|
Fifth year: |
fallow |
|
Sixth year: |
fallow |
|
Seventh year: |
fallow |
Thus four years of crops are followed by three years of
fallow.
Fodder crops can be sown on the fallow, and so the animals can be
fed.
This is a seven- year rotation; every seven years the same crops are
grown.
HOW TO CHOOSE A CROP ROTATION
Before choosing a rotation you must think carefully.
· You must choose crops that will feed the family all the year.
· You must choose crops that will bring in money (industrial or cash crops).
· You must choose crops that can be grown one after the other without making the soil poor. They must be plants that have different roots, plants that do not use the same mineral salts.
· A crop rotation enables you to keep the soil rich. cut down the length of fallow, farm the same fields.
· Every year the farmer needs several different crops.
For example: millet or cassava to eat, cotton or maize to sell, grass for his animals.
· So every year he must grow different crops on different fields. He must allocate his land according to crop use.
Examples of land- use allocation:
Mamadou has six fields. He
does not grow millet on all his fields. On field 1, he plants cotton. On field 2
he sows rice. On field 3 he sows groundnuts. On field 4 he sows millet. Fields 5
and 6 he leaves fallow.
Fields 1- 6
Mamadou has made a good land- use a/location. He has crops to eat {millet and rice}. He has crops to sell (cotton, groundouts, riced. He has two fields of fallow to feed his animals and to let the soil rest.
REASONS FOR LAND - USE ALLOCATION
· To organize your work better.
Sowing, hoeing, cultivating, applying pesticides and harvesting of different crops do not always have to be done at the same time.
For instance, it is easier to grow during the same season one hectare of millet and one hectare of groundnuts, than to grow two hectares of millet.
If you grow only one crop, you have to do all the work at the same time.
With a good land- use allocation you always have enough time to do all your jobs well: ploughing, sowing, cultivating and harvesting.
· To provide a safeguard.
If you grow only one crop, and if a tornado, drought or animals destroy this crop, you have nothing left.
If you grow only one crop and this crop fetches a poor price, you earn no money.
By growing several crops you can always have both food and money.
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