In Africa many soils can become bad.
The sun, the rain and the wind change the soil a great deal.
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 So we have to protect the soil from sun, rain and wind by stopping the water from flowing away; by covering the soil.
· If you always farm the same field, the plants will take all the mineral salts out of the soil.
You must let the earth rest by fallows; by crop rotation; by land- use allocation.
This is water erosion.
Let us see what happens when it rains heavily.
Every drop of heavy rain that falls on the soil takes away a little earth.
Around the house, the water that falls from the roof makes holes and takes away earth.
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.
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. Along the sides of the road, the water runs very fast, it carries away the earth, and makes deep ditches.
Water erosion is worse
· when the soil slopes: the water flows quickly and carries away a lot of earth;
· when there are no plants growing on the soil: plant roots hold the earth and the leaves shelter it from the rain.
For instance, at Adiopodoume, Ivory Coast, the weight of earth in kilogrammes (kg) carried away by the rain in one year has been calculated as follows:
from 1 hectare of kg carried away
land under crops
In some very dry regions where the wind is very strong, it carries away earth.
Bare soils, without plants, and soils with a bad structure (see Booklet No. 4, page 24) are most easily carried away by the wind. What remains in the field is poor soil.
When there are no plants on the soil, the soil is bare, the earth is not protected. The earth becomes dry. The humus is quickly destroyed. The soil structure becomes bad. Good earth is easily carried away. The soil becomes poor.