In this unit, you will learn
- what soil is made up of
- the flow of water through different types of soil
- that certain soils are more suitable for plant growth
3.1 What is soil made up of ?
Soil is very important to us because it supports plants. Many small animals live in the soil. Let us find out what soil is made up of. Soil is made up of humus, clay, silt, sand and small stones. Humus is the layer on top of the soil surface. It is black. It is formed by decaying dead animals and plants.
3.2 The flow of water through different types of soil
There are three main types of soils. These three types of soils are different in terms of the size of the soil particles. They are sand, garden soil and clay. Sandy soil are yellowish in colour. It contains a lot of air space and are grainy texture. Garden soil are brown or balck in colour. It contains some air space and are soft and moist texture. Clay soil are red, brown or grey in colour. It contains very little air space and are smooth and fine texture.
The size of the soil particles affects the flow of water through the different types of soil. Water moved through sand most easily, followed by garden soil. Water can hardly move through clay. Water moves the fastest through sand and the slowest through clay. Garden soil is able to keep the right amount of water for the use of plants.
3.3 Which type of soil is more suitable for plant growth ?
Most plants grow better in garden soil. This is because garden soil has more humus which make the soil fertile. Garden soil is also able to keep the right amount of water for the use of plants.
Exercise 3.1
2. Why is soil import?
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3. Why can animals and palnts live in soil?
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4. What is humus?
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5. A pupil shakes a mixture of water and some gaarden soil in a tall container.
Label the layers that form when the mixture has settled.
6. What is the difference between clay and garden soil?
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7. What is the difference between sand and garden soil?
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Exercise 3.2
A group of pupils carries out an experiment to test which type od soil is more suitable for plant growth. The results of their experiment are as shown in Figure 1.
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(b) Why is garden soil more suitable for plant growth?
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(c) What quantities must be kept constant in the experiment?
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(d) What quantity is changed in the experiment?
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(e) What quantity is measured in the experiment?
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(f) What conclusion can you make from the results of the experiment?
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