Chapter 9
SOIL : A Natural Resource
Introduction
Soil is the “skin of the earth.” It is the topmost layer of Earth that supports life. Soil
is one of the most important natural resources. It supports the growth of plants by
holding the roots firmly and supplying water and nutrients. It is the home for many
organisms. Soil is essential for agriculture. Different types of soils support different
kinds of crops. Agriculture provides food, clothing and shelter for all. Soil is thus an
inseparable part of our life.
In this chapter we will be discussing formation of soil, composition of soil, soil
profile, types of soil, properties of soil, organisms found in soil, soil erosion, soil
pollution and soil conservation.
Module - 1
From this module, the students will be able to :
a) Explain the process of soil formation.
b) Discuss the composition of soil.
Formation Of Soil
Soil is formed by weathering of rocks. Weathering
is the breakdown of rocks into smaller particles by
the action of air , wind and water.These small
particles mix with humus (organic matter like dead
plants , animals , leaves etc) and form soil.
Weathering agents are
1) Wind
2) Water
3) Temperature
Weathering Process
1) Heating and cooling of the rock by sun and rain causes
cracking of rocks.
2) Water enter into these cracks and gets frozen during winter. As
water expands on cooling, cracks are formed in rocks.
3) Growth of roots of trees and other plants, also help to break the
rocks.
4) Day and night temperature variation, action of wind and water
for years also lead to soil formation.Thus the rocks are converted
into soil, which mixes with the dead plants and
animals to form humus.
The process of weathering takes millions of
years for the formation of soil.
Fun Facts
Composition Of Soil
Soil composition refers to the nutrients and
various other substances present in the soil.
COMPOSITION OF SOIL
1) Minerals
Since soil is formed by weathering of rocks, it
contains various minerals such as nitrates,
sulphates and phosphates present in the parent
rock.
2) Humus
Humus is formed by the decomposition of dead
organic matter derived mainly from fallen leaves
or other plant and animal matter. Presence of
humus makes soil fertile as it has the ability to
hold water for plants to grow.
3) Microbes,insects and worms
Microbes help in breaking down dead matter
and convert it into humus
Some microbes,insects and worms present in the soil
4) Water- is essential for all life-sustaining activities.
5) Air - is needed for the respiration of plants
through their roots.
Reference link :
1.) https://www.youtube.com/watch?v=kybPmB1zBUw
2.) https://www.youtube.com/watch?v=WeYAtoLwmP8
3.) https://drive.google.com/file/d/10Mcyq5be38EsGkQeq21fmauI-FQttUd8/view?usp=sharing
End Of Module - 1