Permanent Farming Systems Based on Animal Traction: Farmers Handbook (GTZ, 1995, 183 p.) PART IV: The soil (introduction...) 4.1 What is soil? 4.2 How is the soil made up? 4.3 Soil composition

Permanent Farming Systems Based on Animal Traction: Farmers Handbook (GTZ, 1995, 183 p.)

PART IV: The soil

Figure

4.1 What is soil?

In general, soil is the upper layer of the earth e.g. soil of the bush, soil of roads, soil of the fields.

Fig. 4.1: A farmer will only call soil, all those soils which are cultivated or which can be cultivated (virgin or fallow land).

The soil is essential for the production of crops. It provides the structure the plant is standing in. It supplies minerals and stores water and air for the plant.

Depending on the natural fertility of the soil, you can have high and low yields.

After clearing, the soil is fertile and the harvests in the first one or two years are good.

If you don't care for your soil, the soil gets poor and the harvest becomes smaller. Your soil has to rest. Soil at rest is called fallow.

The fertility of the soil is destroyed by

-too much cultivation without soil conservation and soil improvement
-too many animals kept on an area (overgrazing) .
-fire which can destroy vegetation and soil life

How to conserve and improve your soil. Read Chapter V.

4.2 How is the soil made up?

The soil is made up of the following layers the top soil - cultivated soil
Can be worked with a hoe or prow. The roots of nearly all the plants are found in this layer. the plant soil
Lighter in colour than the top soil because it is less rich in humus. Only deep roots are found.

There are often pebbles at the bottom of this layer. the sub soil
Is often very thick. It is hard and difficult to dig. From this layer, the roots of big trees get their water during the dry season. the parent rock
Is very hard and full of stones and rock. It transforms itself very slowly into soil.

Fig. 4.2: The soil is made up of the following layers

Fig. 4.3: RICH SOIL is characterized by:

Fig. 4.4: POOR SOIL is characterized by:

Fig. 4.5: Soil in a hilly Area

The soils along a slope typically vary in quality. On top of the hill, there are shallow layers of the top soil and of plant soil. In the steep parts of the slope. most of the cultivated soil has been washed away. At the foot of the hill, all the good soil is deposited. We find thick layers of top soil and plant soil.

4.3 Soil composition

The top soil of our fields is a mixture of sand, silt, clay, organic matter and humus.

4.3.1 Sand

Sand consists of small grains which are very hard. Sand is found everywhere, rain carries the sand into hollows and into streams.

Fig. 4.6: Sand is permeable: Take a tin. Make a hole in the bottom of it. Fill the tin with sand. If you pour water on to the sand, it goes through. ]

Fig. 4.7: Sand is unstable:
Take some dry sand in your hand, let it run. Sand runs like water. You cannot make a ball of sand.

Soils that contain a lot of sand are sandy soils.

Like sand itself, sandy soils

-are permeable, water passes through easily and can carry away the food (minerals) of the plant.

-are unstable and easily washed away by rain, water or carried away by wind.
-store water and mineral salts (NPK) badly.
-are light and loose and easy to work.
-do not stick to tools after rain like clay.
-wear out the tools more than other soils when you work them.

Groundnuts, Cassava, Yam and Potatoes grow well in sandy soils: The roots penetrate easily.

4.3.2 Clay

Housewalls and earthenware pots are made of clay. Clay has mostly a red colour. Clay is usually found in deeper layers of the soil. Wet clay takes whatever shape it is given. Wet clay sticks to the fingers, it makes mud. When it is dry, it forms hard lumps. When a lump of clay is crushed, it forms dust.

Fig. 4.8: Clay is impermeable

Take a tin. Make a hole in the bottom of it. Fill the tin with clay. If you pour water on the clay, it does not go through.

Water does not go through the hole in the bottom

Soils that contain a lot of clay are called clayey soils.

Like clay itself, clayey soils

-are impermeable, water does not go through very easily. The water takes a long time to disappear.

-Store water and mineral salts (NPK) well.
-are not so easily carried away by water or by wind when moist.
-stick to the tools and are difficult to work after the rains. Clayey soils are called heavy soils.
-become very hard in the dry season. Cracks form in them.
-dry lumps are difficult to break.

Rice, Maize, Wheat and Cocoyams grow well in clayey soil.

4.3.3 Silt

Some soils are neither sandy nor clayey soils. They are made up of silt.

Silty Soils:

-are not as light as sandy soils, water does not go through so easily.

-do not dry quickly and are not easily carried away by water and wind. They store water and mineral salts well.

-are less heavy than clayey soils and easier to work.

Palm Trees, Yam and Cassava grow well in silty soils.

4.3.4 Organic Matter and Humus

Many worms and insects and other living things you cannot see (microbes) live in the soil and in rotting organic matter. They feed on organic matter and break it into small particles (decomposition). The result we call Humus. Humus you cannot see like sand or clay. To form good soils, the sand, clay and silt must be mixed with humus. Soil without humus is no good soil.

Fig. 4.9: Bad soil structure
Clay, Silt and Sand form big hard lumps. Air and water cannot pass, roots cannot penetrate.

Fig. 4.10: Good Soil structure

Clay, Silt and Sand form small lumps which are joined together by humus. Air and water circulate in the holes and roots penetrate well.

Humus improves sandy soils:

-sandy soils with humus hold water better.
-sandy soils with humus store minerals better.
-sandy soils with humus are less easily carried away by wind and water.

Humus improves clayey soils:

- clayey soils with humus are less hard.
- Air and water circulate better.

Fig. 4.11: Humus makes soil richer. Humus returns Mineral Salts (Plant Food) to the plants and improves the soil structure