Soil
The uppermost layer of the earth's crust is called soil.
It consists of pebbles of different sizes, remains of dead plants and animals also contains air and water.
Soil is home for burrowing animals and many other organisms like bacteria, fungi, worms and insects.
Soil is used for making bricks, pottery, toys, etc.
Soil is important for the production of crops. The crops are necessary for human and animal food.
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FORMATION OF SOIL
Soil is formed due to weathering of rocks. The process of weathering is carried further by agents like temperature changes, frost, water, wind and living organisms.
Weathering
Weathering is a very slow and gradual process in which parent rock breaks down into fine particles.
Weathering takes about 200 to 400 years for the formation of just 1 cm of topsoil.
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Friends Of Farmers
The earthworms move inside the soil which loosen and turning the soil soft. The wastes of earthworms and their dead bodies increase the fertility of soil so that Earthworms are called Friends Of Farmers.
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SOIL PROFILE
The layers of soil are called soil profile.
Layers of Soil
Soil is composed of three layers. They
are called
★ The Topsoil
★ The Subsoil
★ The Bedrock
Topsoil
The uppermost most fertile layer of soil is called top soil. It is dark in colour, rich in humus, with dead and decaying parts of plants and animals.
Subsoil
The light coloured layer just below the topsoil is called the subsoil. subsoil is light coloured because it contains less amount of humus as compared to topsoil. Below the subsoil, there is a layer of lumps of parent rock.
Bedrock
It is hard and non-porous. It produces soil over a long period of time due to the weathering.
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SOIL EROSION
The removal of top fertile layer of soil by wind and water (rain and floods) is called soil erosion.
When the fertile topsoil is eroded, the less fertile subsoil comes to the surface which leads to a fall in crop production. Gradually, the land loses its fertility and becomes barren.
Activities like deforestation and overgrazing by animals also cause soil erosion.
Soil erosion is likely to occur when plants are removed from the soil as roots of plants hold soil particles together.
Agents of Soil Erosion
Reason which remove the uppermost layer of the soil are called agents of soil erosion.
These are Strong Wind and water (rain and floods).
They are called agents of soil erosion.
Afforestation or vegetation prevents soil erosion.
Erosion due to wind is more in areas where there is less vegetation. If the soil is covered by vegetation, the roots of the plants hold the topsoil particles. Afforestation or vegetation prevents soil erosion.
Human Activities Are Also Responsible for Soil Erosion.
Deforestation, overgrazing by animals, Using as a way.
Silting
On reaching the plains, the river slows down and the soil thus carried is deposited at the bottom of the river. This is called silting.
Pollution
The presence of unwanted and harmful materials or substances in the ------- is called ------ pollution.
Air Pollution
The presence of unwanted and harmful materials or substances in the soil is called soil pollution. These harmful substances are called pollutants chemicals, polythene bags, etc.
Causes of Soil pollution
Soil pollution is caused ue to a number of human activities. Some of hem are as follows:
★ Dumping of wastes into open areas. Releasing industrial wastes into the soil.
★ Excessive use of pesticides, insecticides and chemical fertilisers by farmers.
What are the effects of soil pollution?
★ Dirty water seeps into the soil from wastes.
★ Soil pollution reduces the fertility of soil. This also reduces crop yield.
★ The number of friendly microbes living in the soil are killed due to soil pollution.
★ Soil pollution ultimately makes the land barren..
Note
★ Soil erosion make the land barren and ★ can cause floods ★ water pollution ★ famines, and ★ landslides in hilly areas which can result in the ★ loss of life and property.
SOIL CONSERVATION
The protection of topsoil from erosion is called soil conservation.
Soil erosion reduces soil fertility. Therefore, Conservation is Important to protect the topsoil from erosion. Conservation means the steps taken to protect our natural environment.
Different methods adopted to protect the soil from erosion are as follows:
★ Planting trees or afforestation: Afforestation is an effective method to prevent soil erosion. Roots of plants hold the soil particles together and thus protect the soil from being carried away by wind or water. Trees, bushes, grasses and hedges along the boundaries of farmlands shield the topsoil and prevent soil erosion.
★ Terrace farming: On hill slopes, farming is done by cutting steps and terraces to reduce soil erosion. This reduces the speed of water with which the soil flows downhill.
★ By Growing Grass: When the land is not being used for farming, it is good to grow grass or some other creepers on it. The grass has spreading roots. It covers the topsoil and holds it firmly.
★ Constructing Dams And Embankments: During a flood, running water washes away a large part of the topsoil. Dams and embankments are built on rivers to check.
SCIENCE VOCABULARY
Weathering
wearing away of rock
Humus
Decayed remains of plants and animals in the soil
Soil erosion
carrying away or removal of topsoil from one place to another by various agents
Silting
deposition of soil at the bottom of a river
Landslide
Moving of loose rocks down a slope of a hill or a mountain
Deforestation
cutting down of trees on a large scale
Afforestation
planting trees in large numbers
Embankment
A strong wall built along a river to prevent floods
★ Soil is formed by breaking up of rocks into very small particles. This is called weathering.
★ Soil consists of three layers - topsoil, subsoil and bedrock.
★ Deforestation, excessive ploughing and overgrazing by animals are main causes of soil erosion.
★ Removal of top fertile layer of soil is called soil erosion.
★ Various human activities cause soil pollution.
★ Soil can be conserved by afforestation, growing grasses and other plants, terrace farming on hill slopes and by constructing dams across rivers.
EXERCISES
A. Fill in the blanks.
1. The upper most layer of soil is called ..........
2. Breaking up of .......... into tiny pieces forms soil.
3. Settling of soil at the bottom of rivers is called ..........
4. Soil erosion on hill slopes is prevented by ..........
5. Soil erosion causes .......... Polution.
Ans.
B. Write True or False.
1. Deforestation causes soil erosion.
2. The protection of soil against erosion is called weathering.
3. Soil erosion increases fertility of the soil.
4. Wind does not cause soil erosion.
5. Cutting down of trees increases soil erosion.
C. Name the following.
1. Cutting down of trees on large scale
2. Carrying away of the topsoil from one place
natural agents
3 . Moving of loose rocks down a slope of a hill
4. Protection of soil from erosion
5. Slow, gradual process of soil formation
D. Tick (✔) the correct answer.
(a) afforestation
(c) humus
1. Decayed remains of plants and animals in the soil is called
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