Twenty-three titles have been published in this series, designed as handbooks for intermediate level agricultural education and training. They may be purchased as a set or as individual documents.
1. The way to work. The living plant
2. The plant – the root
3. The plant – the stem
4. The plant – the leaf
5. The plant – the flower
6. The soil – man and the soil
7. The soil – how the soil is made up
8. The soil – the living soil – working the soil
9. The soil – working the soil (continued)
10. The soil – conserving the soil – improving the soil
11. Animal husbandry – introduction
12. Animal husbandry – feeding animals
13. Animal husbandry – looking after animals – how cattle reproduce
14. Animal husbandry – what cattle produce
15. Keeping chickens
16. Food crops
17. Market gardening
18. The oil palm
20. Upland rice
21. Wet paddy or swamp rice
Published by arrangement with the Institut africain pour le développement économique et social
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
© French edition, lnstitut africain pour le développement économique et social (INADES) 1967
© English edition, FAO 1970
The text of this manual is a translation and adaptation of “Le sol – Comment est fait le sol,” published by the Agri-Service-Afrique of the Institut africain pour le développement économique et social (INADES), and forms part of a series of 23 booklets. Grateful acknowledgement is made to the publishers for making available this text, which it is hoped will find widespread use at the intermediate level of agricultural education and training in English-speaking countries.
It should be noted that the original texts were prepared for an African environment and this is naturally reflected in the English version. However, it is expected that many of the manuals of the series — a list of which will be found on the inside front cover — will also be of value for training in many other parts of the world. Adaptations can be made to the text where necessary owing to different climatic and ecological conditions.
Applications for permission to issue this manual in other languages are welcomed. Such applications should be addressed to: Director, Publications Division, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy.
The cover illustrations were prepared by Asun Balzola.
• Conserving the soil
How to control erosion
What is a contour line?
Contour line ridges
Contour line ditches
• Soil cover
How to cover the soil
• Improving the soil
Advantages of rotation
Advantages of land-use allocation
How to apply fertilizers
Why apply fertilizers and manure?
• Conclusion to course on the soil
• Suggested question paper
• Read pages 4 to 8.
This first-week lesson is not very long.
But you must understand that erosion is a very bad thing, and how and why soils are carried away by the rain or wind; and why the contour levels prevent erosion.
• Reread pages 4 to 8.
Read pages 9 to 16.
• We shall see that there are several ways of controlling erosion.
• Where you live, do people make contour line ridges or ditches, barrier strips or terraces?
• Why must mulching be done, or cover crops grown?
• Read pages 17 to 23.
• Fallow and green manures improve the soil.
• Crop growing and animal husbandry must both be practised. Why?
• In the past did people practise rotation of crops or division of fields?
How long did the fallow last?
• Why must there be a change?
• Reread pages 17 to 23.
Read pages 24 to 29.
• Plants find their nourishment in the soil.
When the farmer harvests he takes away what the earth has produced.
He must give back to the soil what the crops have taken out.
• Reread the whole booklet.
• Answer the question paper.
Soils an very quickly become poor in quality. Why?
1. In savanna country the soils are often sandy.
Sandy soils have an unstable structure.
The structure quickly becomes bad.
These soils must be protected.
2. Sun, rain and wind quickly change the soil.
In Africa the rains are often very heavy.
After the rains the heat is very great.
Great heat after heavy rains ruins the soil: the humus is quickly destroyed.
The wind too ruins the soil.
3. So we have to:
protect the soil against erosion;
keep the humus in the soil.
If the soil remains rich, the harvests will be better.
4. Rainwater may carry away cultivable land. This is erosion.
Every drop of heavy rain that falls on the soil takes away a little earth.
5. When the rain falls gently,
it does not flow off,
it goes into the soil.
All the earth becomes wet.
Gentle rain does not carry away earth.
6. When the rain is very heavy,
it does not all go into the soil,
it flows and makes ditches.
If the soil is on a slope, the water flows more quickly and makes deeper ditches.
A lot of earth is carried away.
If there are no plants protecting the soil, if the soil is bare, there is more erosion.
7. The wind can also carry away the earth.
In some very dry regions where the wind is very strong, it carries away the earth.
Bare soils, and soils that have a bad structure, are most easily carried away by the wind.
8. Brush fires
Brush fires leave the soil bare.
They make erosion by wind or rain easier.
9. Erosion on cultivated land is very bad:
it uproots the plants,
it destroys the ridges,
it takes away mineral salts.
Sometimes all the cultivable soil is taken away.
The hardpan is exposed and no more cultivation can
Erosion is not the same everywhere.
It also changes with the crops grown.
For instance, at Adiopodoumé, Ivory Coast,
the weight of earth in kilogrammes (kg) carried away
by the rain in one year has been calculated:
|From I hectare of:||kg carried away|
|bare land||117 000|
|land growing cassava||92 800|
|land under cover crops||42 500|
|land under pineapples||15 100|
|forest land||2 400|
10. By stopping the wafer from flowing away.
Running water quickly 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.
There are various ways of stopping the flow of water and retaining the soil:
• contour line ridges,
• barrier strips,
• strip cropping.
11. By covering the soil
The water that falls on bare soil carries away the soil. The water that falls on soil covered by plants damages the soil less. Plants covering the soil reduce erosion.
To cover the soil, use mulches and sow cover crops.
12. Look at the following drawings.
• These lines follow the direction of the slope. Water flows very fast and carries away soil.
• These lines cut across the slope along the contour lines. Water and soil are held back.
13. A contour line is a line across the slope running always at the same height.
14. When ridges are made in She direction of the slope, water flows faster and faster between the ridges.
It carries away a lot of earth.
When ridges are made along the contour line,
water cannot go so fast,
it is held up by the ridges.
The earth is not carried away.
Making ridges along the contour lines helps to control erosion.
15. If the slope is very steep, and if the water flows very fast, the ridge can be carried away.
What can be done to hold up the water?
Ditches are dug along the contour lines.
The earth dug out from the ditch is piled up along the lower edge of the ditch and forms a strong ridge.
No crops are grown on this strong ridge.
Grass is allowed to grow; the roots prevent the 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.
16. If the slope is not steep, ditches are not used.
Instead, a strip of uncultivated land is left
Grass grows on this strip and checks the flow of water, and the earth in it drops to the ground.
Barrier strips must also be made along the contour lines.
A barrier strip should be about 2 metres wide.
To help stop the flow of water, tall grasses can be planted.
If the slope is very 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.
17. Certain crops prevent erosion.
Other crops make it easier.
Beans make a good soil cover, which prevents erosion. But taro and cassava grown on mounds do not cover the soil well.
So erosion is very severe.
18. To prevent erosion different crops should be grown between the barrier strips.
For example, groundnuts then a strip of fallow, then a strip of millet.
19. If the slope is very steep, it is a good thing to grow crops on terraces. These are made by building little walls of earth or stone to hold up the soil.
Sometimes earth is also heaped up behind the little walls.
Where the slopes are too steep, it is better not to cultivate them, but to let trees and grass grow there.
20. Control of wind erosion
The wind too carries away earth.
The earth can be protected
• by making ridges
• by leaving straw, millet stems, etc., on the field after the harvest
• by planting trees that break the force of the wind.
Plants that cover the soil prevent erosion.
21. Raindrops do not fall on the soil.
They fall on the leaves.
Then they drip gently onto the soil and do not take away earth.
22. When the soil is covered by plants, the rain goes into the ground more slowly, by way of the leaves.
The plants yield organic matter.
Water sinks easily into a soil with a good structure.
It goes down among the roots.
23. Plants are also able to protect the soil against wind and sun.
Plant leaves shade the soil.
The soil can be covered with
stems of millet or maize.
This cover with dead plants is called mulching.
• Mulching Is useful because:
it prevents weeds from growing,
it protects the soil against erosion and keeps it moist.
To protect the soil well, the mulch layer must be rather thick.
• Mulching is used, for instance, in growing bananas.
Mulches are also spread round certain fruit trees, such as mango, papaya, orange.
For palms and coconuts, coconut fibre is used and the residue of bunches.
Mulching requires a lot of work to collect the herbage and transport it.
You must look out for snakes, and be careful not to start a fire that might destroy the whole plantation.
25. In certain plantations people sow or plant herbaceous crops to cover the soil.
These are called cover crops.
For instance Pueraria is sown among oil palms.
26. Cover crops must be carefully chosen.
A good cover crop should grow quickly and last a long while.
Certain cover crops can be used to feed animals; for instance, Stylosanthes, Pueraria.
27. You have to take care of cover crops.
When the plants are young, cultivate among them, to get rid of weeds.
Then the cover crop can grow better.
When the plants grow too big, cut them down, and prevent them from climbing up trees.
After being cut down, the plants will grow again.
Mulching and cover crops give the soil organic matter.
A period of fallow and the addition of green manures also improve the soil.
28. Grasses and trees grow on soil that is left fallow.
These grasses and trees give the soil organic matter and humus.
29. To obtain a better fallow
• Sow a crop.
These crops grow more quickly than grasses, they cover the soil better and make more organic matter. For instance, Stylosanthes or Crotalaria are good fallow crops.
• Do not make a fire.
Fire destroys the organic matter.
• Keep a watch on animals.
The fallow land can be used to feed them; but the animals must not destroy all the plants.
30. Sow a crop.
When it has grown
cut it down and
plough it into the soil.
The plants rot
and make the soil richer;
these plants are called green manures.
For instance, you can sow millet or sorghum,
and plough it in
when the seeds begin to form.
Green manure does not yield a harvest.
It is a crop that is grown
and mixed with the soil:
it enriches the soil with humus
so that your harvests will be better afterward.
31. Crop growing and animal husbandry
The farmer who raises animals:
• has oxen for animal power,
• has cows that can give milk and calves,
• can sell animals to earn money,
• gets manure to improve his land.
But the animals must be well fed, so there must be fields with green fodder crops, or fallow fields. These green fodder crops are good both for feeding the animals and making humus.
It is worthwhile to practise both crop growing and animal husbandry.
32. 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 harvests can stay good,
and the soil does not become poor.
This is called crop rotation.
33. In the old days, people took care of the crops, but no one took care of the soil.
The crops took all the mineral salts in the soil.
Organic matter and humus were not returned to the soil.
Erosion carried away the soil.
Then the soil became very poor; and the field was left to rest for 15, 20 years or more.
Sometimes even the village had to be moved.
Crop rotation makes it possible to
• keep the soil rich,
• reduce the time for fallow,
• cultivate the same fields,
• build permanent villages.
34. Making better use of all parts of the soil
For example, in the first year,
a plant with fibrous roots
takes its nourishment near the surface.
In the second year,
a plant with a tap-root
takes its nourishment deep down in the soil.
Like that all parts of the soil are used.
35. Making better use of all the mineral sails in the soil
yams take mainly potassium,
maize takes mainly nitrogen,
cotton takes mainly phosphoric acid.
That way all the mineral salts in the soil are used.
36. Controlling insects and diseases.
For example, when you grow maize, the insects and diseases of maize develop.
If you again grow maize the following year, the insects and diseases that remain in the field do a lot of harm to the maize.
If you grow cotton after maize, the insects and diseases which attack maize do no harm to the cotton.
The insects will just disappear.
37. An example of rotation
So there are three years of crops and two years of fallow.
This is called a five-year rotation.
Every five years the same crops are grown.
38. How to choose a rotation
You have to know:
• the crops that grow best on the soil round the village.
• the crops most necessary for feeding the family and that can be sold at a good price.
• the crops that can be grown one after the other without making the soil poor.
So you can choose in advance the crops to be grown on the same field for a number of years.
39. Every year the farmer needs several different crops.
millet or cassava to eat,
cotton or maize to sell,
grass for his animals.
Every year he must grow different crops on different fields.
He must allocate his land according to crop use.
40. Organizing 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 a hectare of millet and a hectare of groundnuts, than two hectares of millet.
If a farmer grows only one crop, he has to do all his work at the same time.
With land-use allocation he can mate better use of his strength and of the richness of the soil.
41. As 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.
42. In order to have continuous cropping, to keep the richness in the soil and to have better harvests, the farmer applies fertilizers.
Fertilizers return to the soil the mineral salts absorbed by the plants.
The most important fertilizers are:
43. Nitrogen (N)
Raw sap is transformed in the leaves into elaborated sap.
Nitrogen makes the leaves grow and gives them a good green colour.
Thus nitrogen helps the formation of elaborated sap. And harvests are better.
44. Phosphorus (P)
Phosphoric acid makes the roots grow.
It also helps the formation of flowers and fruits.
Grains and fruits are finer.
45. Potassium (K)
Potassium help plants to resist drought and diseases.
It also helps the plant to build up reserves.
Then roots are bigger and there are more seeds of better quality.
46. The fertilizers you buy are not all the same.
Those that contain only nitrogen or potassium or phosphoric acid are straight fertilizers.
Others are mixtures: these are the compound fertilizers.
47. With an implement — localized placement
This implement is called a fertilizer distributor or spreader.
With some kinds of seed-planting machinery you can sow and apply fertilizer at the same time.
48. By hand — broadcast or in rows
You can broadcast the fertilizer.
You toss up the powdered fertilizer which falls all over the ground, or apply it in rows:
You put the fertilizer at the base of the plants before earthing up.
Do not put the fertilizer on the stem and leaves.
The fertilizer may burn them.
49. If organic matter (such as dry herbage, straw, stems of maize, groundnuts or millet, animal excrement) is allowed to rot, it is decomposed by microbes.
It is then called manure.
Manure is mixed into the soil, and it makes humus.
50. How to make manure
Make a dung heap
For example, if you have six oxen:
Choose a site 5 metres wide and 6 metres long.
Dig it out to a depth of 40 to 50 centimetres.
Fence it round and put up a roof.
On the dug area spread straw.
Put the animals there; their excrement falls on the straw.
The straw rots with the excrement.
Fresh straw must be added often.
The roof protects the manure.
It prevents the rain from soaking the dung heap.
It prevents the sun from drying out the manure.
If the manure becomes dry, it does not rot.
51. When you do not have an ox or a cow, and do not have any manure, you can make compost. Compost is a mixture of herbage, stems of millet and maize, and kitchen waste, that all rot together.
52. How to make compost.
Dig a pit.
Into it throw all the kitchen waste, cut herbage and all the crop residues.
Pour on water to encourage rotting.
Like manure, compost must not dry out.
By rotting, this organic matter turns into humus.
53. How to use compost and manure.
Take them to the field at ploughing time.
Mix them with the earth as you plough.
In the manure and the compost there are nitrogen, potassium and phosphoric acid.
But there is also humus:
Manure and compost are the best fertilizers but they are not everywhere available in large enough quantities and their use is not always economic.
Chemical fertilizers have to be bought.
Ask your extension agent which type and quantity to use and what yield increases and profit you can expect.
To make manure and compost no money has to be spent, but you have to work.
54. If you do not put fertilizers or manure
on a field of millet or maize,
the millet and maize have:
and small heads of grain.
If you do put fertilizer or manure on a field of millet
the millet and maize have:
big heads of grain.
55. Leaves and the stems rot on the field and yield a lot of humus.
The soil stays rich.
The farmer wants to make progress.
He must practise both anima! husbandry and crop growing.
• Animals enable the farmer:
to work the land better,
to have milk and meat,
to get manure.
• With animals the farmer can practise continuous cultivation.
He can cut down the time for fallow.
He can even get rid of it altogether.
He replaces fallow with grass crops to feed his animals.
• Like this the farmer has good harvests:
He earns more money.
He can eat better.
He does not make the soil poor.
Manure is the best fertilizer
Yes or No
Mulching assists erosion
Yes or No
Erosion is slight when the slope is steep
Yes or No
Green manure does not yield any harvest
Yes or No
If the manure gets dry it does not______________
_____________ makes the leaves grow bigger.
Rotation makes it possible to ________ the fallow period.
Plants that ___________ the soil prevent erosion.
The farmer should practise ________ crop growing and animal husbandry.
What is the use of crop rotation?
What is the use of division of fields?
What fertilizers do you know?
What is manure?
Why must the soil be covered?
Why must ridges be made following the contour lines?
Why should a farmer practise both crop growing and animal husbandry?
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Better Farming Series, no.10. This handbook is designed for intermediate level agricultural education and training. This manual is a translation and adaptation of "Le sol: Comment conserver le sol - Comment ameliorer le sol," published by the Agri-ServiceAfrique of the lnstitut africain pour le developpement economique et social (INADES), and forms part of a series of booklets. Grateful acknowledgement is made to the publishers for making this text available for English-language agricultural education and training.This illustrated manual focuses on soil conservation. It explains erosion and then covers methods and techniques for erosion control and improving the soil with fallow, manures, crop rotation, fertilizers and compost.