NCERT Class 7 Science Chapter 9 - Soil Notes

Chapter 9 - Soil Notes

1. Soil is one of the most important natural resources for supporting life on the earth.

2. The rotting dead matter in the soil is called humus.

3. Soil is formed by breaking down of rocks by the action of wind, water and climate and this process is called weathering.

4. A vertical section through different layers of the soil is called the soil profile. Each layer differs in feel (texture), colour, depth and chemical composition. These layers are referred to as horizons.

5. A-horizon is the uppermost layer. It is also known as the topsoil. This layer is rich in humus and minerals. It is dark, soft and porous. This provides shelter to many living organisms and roots of small plants are embedded entirely in the topsoil.

6. B-horizon is the layer which is just below the A-horizon and is known as the sub-soil. This layer is rich in minerals and is normally hard and compact.

7. C-horizon is the layer which is just below the B-horizon. This layer has partially weathered rock with a lot of cracks and a long narrow opening.

8. Bedrock is the bottom-most layer in soil profile and is known as the bedrock. This is the type of layer which is full of hard rock.

9. The mixture of rock particles and humus is called the soil. Soil can be classified into three main types based on the proportion of soil particles they are composed of. They are
• Sandy soil
• Clayey soil
• Loamy soil

10. Sandy soil contains a larger proportion of big particles. It is well aerated and water drains quickly in this type of soil.

11. Silt soil contain soil particles of size in between sand and clay. Silt feels smooth and powdery.

12. Clayey soil contains a larger proportion of fine particles. It has little air spaces between the particles. Water does not drain quickly in this type of soil.

13. Loamy soil contains almost equal proportion of large and fine particles. Loamy soil is a mixture of sand, clay and silt. It also has a lot of humus in it.

14. The properties of soil:
• Soil colour
• Soil texture
• Water-holding capacity
• Percolation rate

15. Soil contains water in the form of moisture.

16. Different soils have different water holding capacity. It is highest in clayey soil and least in sandy soil.

17. Percolation rate of water is different in different types of soil. It is highest in sandy soil and least in the clayey soil.

18. The factors that affect soil are wind, rainfall, temperature, light and humidity. These factors also affect the soil profile and bring changes in the soil structure.

19. The removal of topsoil by the action of water and wind is called soil erosion. The factors which lead to soil erosion:
• Large scale cutting of trees-deforestation.
• Overgrazing in forests.
• Deep ploughing and forests fires also lead to soil erosion.

20. Planting more and more trees or afforestation helps in preventing soil erosion as plant roots bind the soil.

21. Preventing overgrazing, doing terrace farming and planting windbreaks can also help in controlling soil erosion.

22. Polythene bags and plastics pollute the soil. They also kill the organisms living in the soil. That is why there is a demand to ban the polythene bags and plastics. Other substances which pollute the soil are a number of waste products, chemicals and pesticides. Waste products and chemicals should be treated before they are released into the soil. The use of pesticides should be minimised.

23. Gram (g) and kilogram (kg) are actually units of mass. A mass of 1 gram weighs 1 gram weight, and a mass of 1 kilogram weighs 1 kilogram weight. However, in daily life, and in commerce and industry, the distinction between gram and gram weight is generally omitted.

24. The removal of land surface by water, wind or ice is known as erosion. Plant roots firmly bind the soil. In the absence of plants, soil becomes loose. So it can be moved by wind and flowing water. Erosion of soil is more severe in areas of little or no surface vegetation, such as desert or bare lands. So, cutting of trees and deforestation should be prevented and effort should be made to increase the green areas.

No comments:

Post a Comment

Also read!

Class 6 Solutions

• Class 7

Class 7 Computer Kips Solutions
Class 7 Gul Mohar English Solutions
English Grammar Class 7
English Writing Skills Class 7
Class 7 Map Pointing Solutions
Class 7 NCERT Civics Solutions
Class 7 NCERT Civics Notes
Class 7 NCERT Civics Extra Questions
Class 7 NCERT Geography Solutions
Class 7 NCERT Geography Notes
Class 7 NCERT Geography Extra Questions
Class 7 NCERT History Solutions
Class 7 NCERT History Notes
Class 7 NCERT History Extra Questions
Class 7 NCERT Maths Solutions
Class 7 NCERT Science Solutions
Class 7 NCERT Science Notes
Class 7 NCERT Science Extra Questions

• Class 8

Class 8 Kips Artificial Intelligence Solutions
Class 8 Gul Mohar English Solutions
English Grammar Class 8
English Writing Skills Class 8
Class 8 Map Pointing Solutions
Class 8 NCERT Civics Solutions
Class 8 NCERT Civics Notes
Class 8 NCERT Civics Extra Questions
Class 8 NCERT Geography Solutions
Class 8 NCERT Geography Notes
Class 8 NCERT Geography Extra Questions
Class 8 NCERT History Solutions
Class 8 NCERT History Notes
Class 8 NCERT History Extra Questions
Class 8 NCERT Maths Solutions
Class 8 NCERT Science Solutions
Class 8 NCERT Science Notes
Class 8 NCERT Science Extra Questions
Class 8 NCERT Science Exemplar
Class 8 NCERT Science MCQs

Class 9 Solutions

• Class 10

Class 10 Kips Artificial Intelligence Solutions
Class 10 NCERT English Solutions
→ Class 10 Map Pointing Solutions
Class 10 NCERT Civics Solutions
Class 10 NCERT Civics Notes
Class 10 NCERT Civics Extra Questions
Class 10 NCERT Geography Solutions
Class 10 NCERT Geography Notes
Class 10 NCERT Geography Extra Questions
Class 10 NCERT History Solutions
→ Class 10 NCERT History Notes
Class 10 NCERT History Extra Questions
Class 10 NCERT Maths Solutions
Class 10 NCERT Science Solutions
Class 10 NCERT Science Notes
Class 10 NCERT Science Extra Questions

• Computer languages
Python Basics

• Extra Activities
Extra Activities

• Extra Knowledge
Extra Information
General Knowledge
Historical Places in India
Latest technology
Physical Sciences
Facts

• Mathematics quick links
Mathematical Terms
Maths Tricks

CONTACT US