Soil Class 7 Notes NCERT and MCQs

09-11-2023 14:04 PM IST Priyanka Chaudhary

The chapter discusses soil, soil profile, different types of soils and their characteristic features.

What is Soil?

Soil is a mixture of rock particles and humus. Living organisms like bacteria, plant roots and earthworms are also important parts of any soil. It is formed by the breaking down of rocks by the action of wind, water and climate. The process is called weathering.

The rotting dead matter in the soil is called humus. The humus makes the soil fertile and provides nutrients to growing plants. The nature of any soil depends upon the rocks from which it has been formed and the type of vegetation that grows in it.

Soil Profile

Soil is composed of distinct layers. Soil profile is a vertical section through different layers of the soil. Various layers are called horizons. Each horizon differs in feel (texture), colour, depth and chemical composition.

1. A-horizon: The topsoil or the A-horizon is the uppermost horizon. It is generally dark in colour as it is rich in humus and minerals. It is generally soft, and porous and can retain more water. A-Horizon provides shelter for worms, rodents, moles and beetles. The roots of small plants are found completely in the topsoil.
2. B-horizon or the middle layer: B-horizon or the middle layer is the next layer. It has a lesser amount of humus. But, it has more amount of minerals. It is generally harder and more compact.
3. C-horizon: C-horizon is the third layer. It is made up of small lumps of rocks with cracks and crevices. The bedrock lies below the C-horizon. Bedrock is hard and difficult to dig with a spade.

Figure showing soil profile

Types of Soil

Depending on the proportion of particles of various sizes, the soil is classified into various types. Different types of soils and their features are given below.

1) Clayey soil

If the proportion of fine particles is relatively higher, then the soil is called clayey soil.

Percolation rate of water is lowest in the clayey soil. Clay particles, being much smaller, pack tightly together, leaving little space for air. Clayey soils have less air.

2) Loamy soil

If the amount of large and fine particles is about the same, then the soil is called loamy. The best topsoil for growing plants is loam.

Loamy soil is a mixture of sand, clay and another type of soil particle known as silt. It has the right water-holding capacity for the growth of plants.

3) Sandy soil

Sandy soil contains a greater proportion of big particles. Percolation rate of water is highest in the sandy soil. Sandy soils tend to be light, well aerated and rather dry as sand particles are quite large and cannot fit close together. Large spaces between them are filled with air.

Soil and crops

Different types of soils are used to cultivate different types of crops. Clay and loam are suitable for growing wheat, gram and paddy. Cotton is grown in sandy loam soil.

Crops like wheat are grown in fine clayey soils because they are rich in humus and are very fertile. 

Soil erosion

The removal of land surface by wind, water or ice is called erosion. Plant roots firmly bind the soil and in their absence, soil becomes loose. Hence, it can be moved by wind or flowing water. 

Soil erosion is more severe in areas with little or no surface vegetation like deserts or bare lands.

Cutting of trees and deforestation should be prevented and effort should be made to increase the green areas.

MCQs based on NCERT Class 7 Science Chapter 9: Soil

1. Which of the following soil types is suitable for growing cotton?

a. Clayey

b. Loamy

c. Sandy

d. Sandy loam

Ans. d

Explanation: Different types of soils are used to cultivate different types of crops. Clay and loam are suitable for growing wheat, gram and paddy. Cotton is grown in sandy loam soil.

2. Which of the following layers of soil is rich in is rich in humus and minerals?

a. A-horizon

b. B-horizon

c. C-horizon

d. Both b and c

Ans. a

Explanation: 

The topsoil or the A-horizon is the uppermost horizon. It is generally dark in colour as it is rich in humus and minerals. It is generally soft, porous and can retain more water. A-Horizon provides shelter for worms, rodents, moles and beetles. The roots of small plants are found completely in the topsoil.

3. In which of the following soils the proportion of fine particles is relatively higher?

a. Clayey

b. Sandy

c. Loamy

d. None of the above

Ans. a

Explanation: If the proportion of fine particles is relatively higher, then the soil is called clayey soil. Percolation rate of water is least in the clayey soil. If the amount of large and fine particles is about the same, then the soil is called loamy. The best topsoil for growing plants is loam. Sandy soil contains greater proportion of big particles. Percolation rate of water is highest in the sandy soil.

4. In addition to the rock particles, the soil contains

a. air and water

b. water and plants

c. minerals, organic matter, air and water

d. water, air and plants

Ans. c

Explanation: In addition to the rock particles, the soil contains minerals, organic matter, air and water.

5. The water holding capacity is the highest in

a. sandy soil

b. clayey soil

c. loamy soil

d. mixture of sand and loam

Ans. b

Explanation: The water holding capacity is the highest in clayey soil. The percolation rate of water is lowest in clayey soil.

6. Which of the following pairs is not matched correctly?

a. Sandy soil- Large particles

b. Middle layer of the soil- Lesser amount of humus

c. Clayey soil- Percolation rate of water is lowest

d. Humus - Lowest layer of soil

Ans. d

Explanation: The correct match is given below:

a. Sandy soil- Large particles

b. Middle layer of the soil- Lesser amount of humus

c. Clayey soil- Percolation rate of water is lowest

d. Humus - Rotting dead matter in the soil