Class 7 NCERT Solutions Science Chapter 9 - Soil

105

106

Soil Exercise 105

Solution 1

In addition to the rock particles, the soil contains
(iii) Minerals, organic matter, air and water.

Concept insight: Recall the composition of soil.

Solution 2

The water holding capacity is the highest in
(ii) Clayey soil

Concept insight: The particles of clayey soil is very compact so it has highest water holding capacity.

Solution 3

Concept insight: List the properties of soil.

Solution 4

Soil is formed through the process of weathering. Weathering is a process of physical breakdown and chemical decomposition of rocks and minerals near or at the surface of the earth. This physical and chemical decomposition is primarily done by wind, water, and climate. As a result of these processes, large rock pieces are converted into smaller pieces and eventually to soil.

Concept insight: Weathering is a very slow process through which soil is formed from rocks.

Solution 5

Following are the properties of clayey soil:

i. It has very good water holding capacity.

ii. It is rich in organic matter.

For growing crops such as wheat, gram, and paddy, the soil that is good at retaining water and rich in organic matter is suitable. Therefore, clayey soils having these characteristics are useful for such kind of crops.

Concept insight: Particles of clayey soil are very small so it has good water holding capacity and is also rich in humus.

Solution 6

	Clayey soil		Sandy soil
(i)	The proportion of fine particles is higher.	(i)	The proportion of large particles is higher.
(ii)	Particles are packed tightly.	(ii)	Particles are loosely packed.
(iii)	It can hold good amount of water.	(iii)	Its ability to retain water is low.
(iv)	Water cannot drain quickly.	(iv)	Water can drain quickly.
(v)	It is heavy in weight.	(v)	It is light in weight.
(vi)	Less air is trapped between the particles.	(vi)	More air is trapped between the particles.
(vii)	It is rich in humus.	(vii)	It is not rich in humus.

Concept insight: Differences between the properties of different types of soil.

Solution 7

Concept insight: A vertical section through the soil showing its different layers is called soil profile.

Solution 8

Concept insight: Recall the formula for calculating the rate of percolation of water in soil.

Soil Exercise 106

Solution 9

Prevention of soil pollution:
The persistent build-up of toxic compounds in the soil is defined as soil pollution. To prevent soil pollution, its causes must be controlled.
(i) Reduce the use of plastics: Plastics and polythene bags destroy the fertility of soil. Hence, these should be disposed off properly and if possible, their use should be avoided.
(ii) Industrial pollutants: Some waste products from industries and homes pollute soil. These pollutants should be treated chemically to make them harmless before they are disposed off.
(iii) Insecticides: Other pollutants of soil include pesticides and insecticides. Therefore, excessive use of these substances should be avoided.
Prevention of soil erosion:
Removal of the upper fertile layer of the soil (top soil) by strong wind and flowing water is known as soil erosion. Following steps can be taken to reduce soil erosion:
i.Mass awareness to reduce deforestation for industrial purposes.
ii.Helping local people to regenerate degrading forest.
iii.Planting trees.

Concept insight: List the ways to prevent soil pollution.

Roots of plants bind the soil firmly and prevent soil erosion. Absence of plants leads to soil erosion. Therefore, soil erosion can be prevented by planting trees and checking indiscriminate cutting of trees.

Solution 10

Concept insight: Important from Exam Point of View.