SOIL
Soil: The uppermost layer of the earth’s crust in which the plants and animals survive is called soil.
Humus: The organic matter which is formed by the decomposition of dead plants and animals by some microorganisms is known as humus. Or in other words the rotting dead matter in the soil is called humus.
Weathering: The process of breaking down of rocks by the action of some agents like temperature, wind, water and climate etc is known as weathering.
Biological weathering: Weathering by living organisms is called biological weathering.
Soil profile: A vertical section through different layers of soil is called the soil profile. In other words the arrangement of different layers of soil is called soil profile.
Horizons: The different layers of the soil are referred to as the horizon. Each layer differs in texture, colour, depth and chemical composition. The different layers or horizons are as under.
1. A horizon: The uppermost horizon is called top soil or the A horizon. It is dark in colour due to the presence of humus and minerals. This layer is fertile because of the presence of humus. It provides nutrients to the growing plants. This layer is generally soft, porous and having good water retaining capacity. This layer also provides shelter for many living organisms such as worms, rodents, moles, beetles and bacteria.
2. B horizon: The layer below the A-horizon is called B-horizon. This layer is lighter in colour that the A-horizon because of the presence of lesser quantity of humus. It is less fertile. This layer is rich in soluble minerals and iron oxides. It is harder and more compact than the A-horizon. It is also called the sub-soil or middle layer.
3. C-horizon: This third layer or the layer below the B-horizon is C-horizon. It is made up of small lumps of rocks with cracks and crevices. It is essentially the parent material represented by larger rock pieces.
4. D-horizon or Bedrock: Beneath the C-horizon is the bedrock. This is very hard and difficult to dig. This layer is also known as D-horizon. Ground water exists between C-horizon and D-horizon.
Types of Soil: The mixture of rock particles and humus is called the soil. Soil is classified on the basis of the proportion of particles of various sizes. The different types of soil are as under:
1. Sandy soils: If the soil contains greater proportion ( 70 to 80%) of big particles like sand , it is called sandy soil.
2. Clayey soil: If the soil contains greater proportion of fine particles like clay, it is called clayey soil. It is suitable for growing of crops like wheat, paddy etc because it is fertile due to the presence of humus and good water retaining capacity.
3. Loamy soil: If the soil contains both large and fines particles in about equal proportion, it is called loamy soil. It is a mixture of sand, clay and silt. It is suitable for growing pulses like lentils. It is also suitable for growing of crops like wheat, paddy.
Properties of sandy soil:
1. It is highly porous.
2. Sandy soil is well aerated.
3. It contains greater proportion of big particles.
4. It has poor water retaining capacity.
5. It has largest percolation rate of water.
6. It is light.
7. It is dry.
8. It does not contain humus.
9. It is not fertile.
10. It does not support plant growth.
11. It can be carried by wind.
Properties of clayey soil:
1. Particles of clayey soil are closely packed.
2. It contains greater proportion of fines particles.
3. It is less aerated.
4. It has good water retaining capacity.
5. It has least percolation rate of water.
6. It is heavy and moist in nature.
7. It contains humus and fertile.
8. It is suitable for plant’s growth.
9. It can not be carried by wind.
Properties of Loamy soil:
1. It contains about equal proportion of big and fine particles.
2. It contains humus.
3. It has good water retaining capacity.
4. It is well aerated.
5. It is very suitable for plant growth.
6. It is suitable for root penetration.
Soil is affected by both climatic factors like wind, rainfall, temperature, light and humidity and components of soil.
Uses of soil: Some uses of soil are as under:
1. Soil helps in the growth of plants as the plants get nutrients from it.
2. It supports the lives of all living organisms.
5. It is a habitat of many living organisms like worms, rodents, moles, beetles and bacteria.
3. It is a reservoir of water and helps in the purification of water.
4. We also get clay product from soil.
5. Soil contains mineral ores from which metals, chemicals etc are obtained.
Q.1 What are the constituents of soil?
A. Soil consists of the rock particles (sand, gravel and clay) humus, water, air, different types of salts, minerals and soil organisms.
Q.2. What do you mean by percolation?
A. The quantity of water
Q.3. Which type of soil is best for plant growth?
A. Loamy soil.
Q.4. Which soil is used to make toys, pots and statues?
A. Clayey soil.
Q.5. The water holding capacity is highest in which soil?
A. Clayey soil.
NCERT BOOK QUESTIONS
1. In addition to the rock particles, the soil contains
i) air and water
ii) water and plants
iii) minerals, organic matters, air and water
iii) water, air and plants
2. The water holding capacity is highest in
i) Sandy soil
ii) Clayey soil
iii) Loamy soil
iv) Mixture of sand and loam
3. i) A home for living organisms All kinds of soil
ii) Upper layer of the soil Dark in colour
iii) Sandy soil Large particles
iv) Middle layer of the soil Lesser amount of humus
v) Clayey soil Small particles and packed tight
4. Explain how soil is formed.
A. Soil is formed from the parent rock material by a very slow and gradual process called weathering. Weathering is caused by the following factors.
1. Water:- Movement of rain and river water in liquid form causes breaking down of rock particles into finer particles through their abrasive effect. Again water which enters into the tracks of huge rocks freezes to ice in winter and expands, producing a lateral pressure which helps the rocks to break down.
2. Wind:- When strong wind blows, they collide. The wind brings heavy rain which also helps in weathering.
3. Temperature:-Due to the heat of the sun the rock expands in the day time and contracts at night. This process helps in weathering.
4. Glaciers:- Glaciers are large mass of moving ice which flows above the land. They carry large rocks which when comes into each other re resulting in weathering.
5. Trees:- The roots of the trees penetrate into the soil due to which the rocks break down. The roots of the lichens contain acids that help in the breaking down of rocks.
6. Natural process: Natural processes like earthquakes, volcanic eruptions etc help in the weathering of rocks.
7. Human activities:- Human activities like construction of roads, bridges also helps in the breaking of rocks.
5. How is clayey soil useful for crops?
A. Clayey soil being rich in humus is very fertile. It has also a very good water retaining capacity. Hence, it is very suitable for growing crops like wheat, paddy and gram.
6. List the difference between clayey soil and sandy soil.
Clayey soil sandy soil
1. It contains greater proportion of fine It contains greater proportion of
particles. big particles.
2. It is less aerated. It is well aerated.
3. It has good water retaining capacity. It has poor water retaining capacity.
4. It has least percolation rate of water. It has largest percolation rate of water.
5. It is heavy and moist in nature. It is light and dry.
6. It can not be carried by wind. It can be carried by wind.
7. It supports plant growth. It does not support plant growth.
8. It contains humus and is fertile. It does not contain humus and is not fertile.
6. Explain how soil pollution and soil erosion could be prevented?
A. Soil pollution can be prevented by the following ways:
a) Waste products and chemicals should be treated before they are released into the soil.
b) The use of pesticides, artificial fertilizers, insecticides etc should be minimized.
c) There should be a ban on polythene bags and plastic.
d) Afforestation should be done in large scale.
e) Proper drainage system should be made.
Soil Erosion can be prevented by the following ways.
a) Deforestation should be stopped and afforestation should be encouraged.
b) Maintaining porous structure of soil.
c) Shifting of cultivation.
d) In slopping areas terrace cultivation should be done.
Soil: The uppermost layer of the earth’s crust in which the plants and animals survive is called soil.
Humus: The organic matter which is formed by the decomposition of dead plants and animals by some microorganisms is known as humus. Or in other words the rotting dead matter in the soil is called humus.
Weathering: The process of breaking down of rocks by the action of some agents like temperature, wind, water and climate etc is known as weathering.
Biological weathering: Weathering by living organisms is called biological weathering.
Soil profile: A vertical section through different layers of soil is called the soil profile. In other words the arrangement of different layers of soil is called soil profile.
Horizons: The different layers of the soil are referred to as the horizon. Each layer differs in texture, colour, depth and chemical composition. The different layers or horizons are as under.
1. A horizon: The uppermost horizon is called top soil or the A horizon. It is dark in colour due to the presence of humus and minerals. This layer is fertile because of the presence of humus. It provides nutrients to the growing plants. This layer is generally soft, porous and having good water retaining capacity. This layer also provides shelter for many living organisms such as worms, rodents, moles, beetles and bacteria.
2. B horizon: The layer below the A-horizon is called B-horizon. This layer is lighter in colour that the A-horizon because of the presence of lesser quantity of humus. It is less fertile. This layer is rich in soluble minerals and iron oxides. It is harder and more compact than the A-horizon. It is also called the sub-soil or middle layer.
3. C-horizon: This third layer or the layer below the B-horizon is C-horizon. It is made up of small lumps of rocks with cracks and crevices. It is essentially the parent material represented by larger rock pieces.
4. D-horizon or Bedrock: Beneath the C-horizon is the bedrock. This is very hard and difficult to dig. This layer is also known as D-horizon. Ground water exists between C-horizon and D-horizon.
Types of Soil: The mixture of rock particles and humus is called the soil. Soil is classified on the basis of the proportion of particles of various sizes. The different types of soil are as under:
1. Sandy soils: If the soil contains greater proportion ( 70 to 80%) of big particles like sand , it is called sandy soil.
2. Clayey soil: If the soil contains greater proportion of fine particles like clay, it is called clayey soil. It is suitable for growing of crops like wheat, paddy etc because it is fertile due to the presence of humus and good water retaining capacity.
3. Loamy soil: If the soil contains both large and fines particles in about equal proportion, it is called loamy soil. It is a mixture of sand, clay and silt. It is suitable for growing pulses like lentils. It is also suitable for growing of crops like wheat, paddy.
Properties of sandy soil:
1. It is highly porous.
2. Sandy soil is well aerated.
3. It contains greater proportion of big particles.
4. It has poor water retaining capacity.
5. It has largest percolation rate of water.
6. It is light.
7. It is dry.
8. It does not contain humus.
9. It is not fertile.
10. It does not support plant growth.
11. It can be carried by wind.
Properties of clayey soil:
1. Particles of clayey soil are closely packed.
2. It contains greater proportion of fines particles.
3. It is less aerated.
4. It has good water retaining capacity.
5. It has least percolation rate of water.
6. It is heavy and moist in nature.
7. It contains humus and fertile.
8. It is suitable for plant’s growth.
9. It can not be carried by wind.
Properties of Loamy soil:
1. It contains about equal proportion of big and fine particles.
2. It contains humus.
3. It has good water retaining capacity.
4. It is well aerated.
5. It is very suitable for plant growth.
6. It is suitable for root penetration.
Soil is affected by both climatic factors like wind, rainfall, temperature, light and humidity and components of soil.
Uses of soil: Some uses of soil are as under:
1. Soil helps in the growth of plants as the plants get nutrients from it.
2. It supports the lives of all living organisms.
5. It is a habitat of many living organisms like worms, rodents, moles, beetles and bacteria.
3. It is a reservoir of water and helps in the purification of water.
4. We also get clay product from soil.
5. Soil contains mineral ores from which metals, chemicals etc are obtained.
Q.1 What are the constituents of soil?
A. Soil consists of the rock particles (sand, gravel and clay) humus, water, air, different types of salts, minerals and soil organisms.
Q.2. What do you mean by percolation?
A. The quantity of water
Q.3. Which type of soil is best for plant growth?
A. Loamy soil.
Q.4. Which soil is used to make toys, pots and statues?
A. Clayey soil.
Q.5. The water holding capacity is highest in which soil?
A. Clayey soil.
NCERT BOOK QUESTIONS
1. In addition to the rock particles, the soil contains
i) air and water
ii) water and plants
iii) minerals, organic matters, air and water
iii) water, air and plants
2. The water holding capacity is highest in
i) Sandy soil
ii) Clayey soil
iii) Loamy soil
iv) Mixture of sand and loam
3. i) A home for living organisms All kinds of soil
ii) Upper layer of the soil Dark in colour
iii) Sandy soil Large particles
iv) Middle layer of the soil Lesser amount of humus
v) Clayey soil Small particles and packed tight
4. Explain how soil is formed.
A. Soil is formed from the parent rock material by a very slow and gradual process called weathering. Weathering is caused by the following factors.
1. Water:- Movement of rain and river water in liquid form causes breaking down of rock particles into finer particles through their abrasive effect. Again water which enters into the tracks of huge rocks freezes to ice in winter and expands, producing a lateral pressure which helps the rocks to break down.
2. Wind:- When strong wind blows, they collide. The wind brings heavy rain which also helps in weathering.
3. Temperature:-Due to the heat of the sun the rock expands in the day time and contracts at night. This process helps in weathering.
4. Glaciers:- Glaciers are large mass of moving ice which flows above the land. They carry large rocks which when comes into each other re resulting in weathering.
5. Trees:- The roots of the trees penetrate into the soil due to which the rocks break down. The roots of the lichens contain acids that help in the breaking down of rocks.
6. Natural process: Natural processes like earthquakes, volcanic eruptions etc help in the weathering of rocks.
7. Human activities:- Human activities like construction of roads, bridges also helps in the breaking of rocks.
5. How is clayey soil useful for crops?
A. Clayey soil being rich in humus is very fertile. It has also a very good water retaining capacity. Hence, it is very suitable for growing crops like wheat, paddy and gram.
6. List the difference between clayey soil and sandy soil.
Clayey soil sandy soil
1. It contains greater proportion of fine It contains greater proportion of
particles. big particles.
2. It is less aerated. It is well aerated.
3. It has good water retaining capacity. It has poor water retaining capacity.
4. It has least percolation rate of water. It has largest percolation rate of water.
5. It is heavy and moist in nature. It is light and dry.
6. It can not be carried by wind. It can be carried by wind.
7. It supports plant growth. It does not support plant growth.
8. It contains humus and is fertile. It does not contain humus and is not fertile.
6. Explain how soil pollution and soil erosion could be prevented?
A. Soil pollution can be prevented by the following ways:
a) Waste products and chemicals should be treated before they are released into the soil.
b) The use of pesticides, artificial fertilizers, insecticides etc should be minimized.
c) There should be a ban on polythene bags and plastic.
d) Afforestation should be done in large scale.
e) Proper drainage system should be made.
Soil Erosion can be prevented by the following ways.
a) Deforestation should be stopped and afforestation should be encouraged.
b) Maintaining porous structure of soil.
c) Shifting of cultivation.
d) In slopping areas terrace cultivation should be done.