Unit V – Materials and Matter
In this post, CBSE Class 5 Science -Soil topic is discussed. In Class 4 Science, this topic has been already discussed in general but in Class 5 this topic is in elaborated form. In this article we study:
- The process of soil formation, layers of soil and factors that causes soil erosion
Soil –The uppermost layer of the earth is called Soil. It is made up of tiny pieces of rocks and remains of dead plants and animals. Soil contains many microorganisms.
Why is Soil important?
Soil is extremely important for the living things. Plants and trees grow in the soil. Soil provides all the minerals that plants need to grow. It also protects the roots of plants from exposure to the hot rays of the sun.
Trees grow in the soil. Soil also provides shelter to many animals. Insects and small animals such as rats and many microorganisms live in the soil. These microorganisms help in maintaining the fertility of the soil.
Formation of Soil
Rocks break up to form soil. Big rocks break up to form small stones and then fine grains of soil. This process is called weathering. Wind and water are the main agents of weathering. They continuously erode the rocks, eventually turning even big rocks into tiny grains of soil. This is however, a very slow process. It takes millions of years for rocks to break down in tiny particles that form the soil.
The layers of soil are referred to as the soil profile.
- Top Soil – It contains a lots of humus or organic matter, fine particles of sand and clay, air and water. Plants receive all the necessary nutrients from the top soil.
- Sub soil – The roots of some plants grow into the subsoil. It contains organic matter in very less quantity. It has water. It also contains rock pieces.
- Bed rock – It contains large pieces of rocks. Water is present in less quantity in this layer
Topsoil is the most fertile layer of the soil. It has humus, which is necessary for the growth of plants. Sometimes, this topsoil is carried away by wind, water or other elements. This process is called soil erosion. In places where there is a lot of soil erosion, the fertility of the soil is greatly reduced. The crop yield reduces and farmers suffer. The food and Agriculture Organisation (FAO), a wing of the United Nations, estimates that the global loss of productive land due to soil erosion is 5-7 million hectares per year.
The factors that are responsible for soil erosion are known as the agents of erosion. They are discussed below:
- Water: Running water causes the maximum amount of soil erosion. When rain falls, the running water carries away the topsoil with it. Due to removal of the fertile soil topsoil, the land becomes unsuitable for farming.
- Heavy rains causes floods. Floods, together with heavy rains, can erode the soil very fast.
- Wind: In deserts and open lands, wind causes a lot of soil erosion. Strong winds blow away the humus-rich topsoil. When this fertile layer of soil is gone, new plants cannot grow well in the depleted soil.
- Human activities: You know that the roots of plants hold the soil articles together. Soil erosion increases in the absence of plants. Many human activities have led to the reduction of the plant cover.
- Indiscriminate felling of trees: Increase soil erosion. When trees are cut, the soil becomes loose. It is then easily carried away by wind and water.
- Overgrazing by cattle removes the plant cover from the soil. As a result soil erosion increases.
- Ploughing of hills for cultivation also loosens the soil and increases the risk of erosion by wind.
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