Chapter 9 – Soil

These NCERT Class 7 Science Chapter 9 notes explain the importance of soil in supporting plant life and agriculture. The chapter introduces soil as a natural resource formed by weathering of rocks and mixed with humus, air, water, and living organisms.

Soil also explains soil profile, different types of soil, and their suitability for crops. This chapter helps students understand why soil conservation is necessary for food security and environmental balance.

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1. Introduction: why soil is important

•  Soil is the uppermost layer of the Earth’s crust.
•  It supports plant growth and agriculture.
•  Food production and life on Earth depend on soil.
•  Soil works like the kitchen of plants.

2. What is soil

•  Soil is a mixture of rock particles, humus, air, water, and living organisms.
•  Humus comes from dead plants and animals.
•  Air and water in soil help roots breathe and absorb nutrients.

3. Formation of soil

•  Soil is formed by weathering of rocks.
•  Weathering means breaking rocks into smaller pieces.
•  Physical, chemical, and biological processes cause weathering.

4. Soil profile

•  A soil profile shows different layers of soil.
•  Topsoil (A-horizon) is rich in humus and best for plant growth.
•  Subsoil (B-horizon) has less humus but more minerals.
•  Parent rock (C-horizon) is the lowest layer made of rock pieces.

5. Types of soil

•  Sandy soil has large particles, drains water quickly, and is less fertile.
•  Clayey soil has fine particles, holds water, and suits crops like rice.
•  Loamy soil is a mix of sand, clay, and silt and is best for farming.

6. Properties of soil

•  Percolation rate is the speed at which water passes through soil.
•  Sandy soil has high percolation, while clayey soil has low percolation.
•  Moisture is the amount of water present in soil.
•  Water absorption is the ability of soil to absorb water.

7. Soil and crops

•  Different crops need different types of soil.
•  Loamy soil supports most crops.
•  In India, rice grows well in clayey soil and wheat in loamy soil.

8. Soil erosion

•  Soil erosion is the removal of topsoil by wind or water.
•  It reduces soil fertility and crop yield.
•  Major causes include deforestation, overgrazing, and floods.

9. Prevention of soil erosion

•  Plantation of trees holds soil together.
•  Terrace farming reduces water flow on slopes.
•  Contour ploughing slows down soil erosion.

10. Importance of humus

•  Humus improves soil fertility.
•  It helps in water retention.
•  It provides essential nutrients to plants.

11. Importance of soil organisms

•  Earthworms loosen soil and improve aeration.
•  Microorganisms increase soil fertility.
•  Soil organisms act like farmers inside soil.

12. Soil pollution

•  Soil pollution is caused by chemicals and waste.
•  It reduces soil quality.
•  It negatively affects crop yield.

13. Important keywords with simple definitions

•  Soil – upper layer of Earth that supports plant life.
•  Weathering – breaking of rocks into smaller particles.
•  Humus – decayed plant and animal matter in soil.
•  Soil profile – vertical section showing soil layers.
•  Percolation – movement of water through soil.
•  Erosion – removal of topsoil by wind or water.

Understanding NCERT Class 7 Science Chapter 9 – Soil is important to learn how soil is formed, its types, and its role in agriculture. The chapter clearly explains soil erosion, conservation methods, and the importance of humus and soil organisms.

These concepts are highly useful for school examinations and foundation-level science preparation. Students should next read Chapter 10: Respiration in Organisms to understand how living beings obtain energy from food.

FAQs

Q1. What is explained in NCERT Class 7 Science Chapter 9?
The chapter explains soil formation, soil profile, types of soil, and soil conservation.

Q2. What is soil profile?
Soil profile is the vertical section of soil showing different layers like topsoil, subsoil, and parent rock.

Q3. Which soil is best for farming?
Loamy soil is best for farming as it holds nutrients and water properly.

Q4. What is soil erosion?
Soil erosion is the removal of topsoil by wind or water.

Q5. Why is NCERT Class 7 Science Chapter 9 important for exams?
It explains basic concepts of soil and agriculture that are frequently asked in school and foundation-level exams.

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