NCERT Textbook: Soil | Science & Technology for UPSC CSE PDF Download

 Page 1


SCIENCE 96
Soil
9
S
oil is one of the most important
natural resources. It provides
anchorage  to the plants and
supplies water and nutrients. It is the
home for many organisms. Soil is
essential for agriculture. Agriculture
provides food, clothing and shelter
for all. Soil is thus an inseparable
part of our life. The earthy fragrance
of soil after the first rain is always
refreshing.
9.1 SOIL TEEMING WITH LIFE
One day during the rainy season Paheli
and Boojho observed an earthworm
coming out of the soil. Paheli wondered
whether there were other organisms also
in the soil. Let us find out.
Activity 9.1
Collect some soil samples and observe
them carefully. You can use a hand lens.
Examine each sample carefully and fill
in Table 9.1.
§ Discuss your observations
with your friends.
§ Are the soil samples
collected by your friends
similar to the ones collected by
you?
Boojho and Paheli have
used soil in many ways. They
enjoy playing with it. It is a
great fun indeed.
Make a list of the uses of soil.
Fig. 9.1  Children playing with soil
Table 9.1
S. Soil source Plants Animals Any other
No. observations
1. Garden soil Grass, ………. Ant, ……….
2. Soil from the roadside ………………
3. Soil from the area where
construction is going on ………………
4. ……………… ………………
5. ……………… ………………
2022-23
Page 2


SCIENCE 96
Soil
9
S
oil is one of the most important
natural resources. It provides
anchorage  to the plants and
supplies water and nutrients. It is the
home for many organisms. Soil is
essential for agriculture. Agriculture
provides food, clothing and shelter
for all. Soil is thus an inseparable
part of our life. The earthy fragrance
of soil after the first rain is always
refreshing.
9.1 SOIL TEEMING WITH LIFE
One day during the rainy season Paheli
and Boojho observed an earthworm
coming out of the soil. Paheli wondered
whether there were other organisms also
in the soil. Let us find out.
Activity 9.1
Collect some soil samples and observe
them carefully. You can use a hand lens.
Examine each sample carefully and fill
in Table 9.1.
§ Discuss your observations
with your friends.
§ Are the soil samples
collected by your friends
similar to the ones collected by
you?
Boojho and Paheli have
used soil in many ways. They
enjoy playing with it. It is a
great fun indeed.
Make a list of the uses of soil.
Fig. 9.1  Children playing with soil
Table 9.1
S. Soil source Plants Animals Any other
No. observations
1. Garden soil Grass, ………. Ant, ……….
2. Soil from the roadside ………………
3. Soil from the area where
construction is going on ………………
4. ……………… ………………
5. ……………… ………………
2022-23
SOIL 97
9.2 SOIL PROFILE
Soil is composed of distinct layers.
Perform the following activity to find out
how these layers are arranged.
Activity 9.2
Take a little soil. Break the clumps with
your hand to powder it. Now take a glass
tumbler, three quarters filled with water,
and then add a handful of soil to it. Stir
it well with a stick to dissolve the soil.
Now let it stand undisturbed for some
time (Fig. 9.2). Afterwards, observe it and
answer the following questions:
§ Do you see layers of particles of
different sizes in the glass tumbler?
§ Draw a diagram showing these layers.
§ Are there some dead rotting leaves
or animal remains floating on water?
The rotting dead matter in the soil is
called humus.
You probably know that the soil is
formed by the breaking down of rocks
by the action of wind, water and climate.
This process is called weathering. The
nature of any soil depends upon the
rocks from which it has been formed and
the type of vegetation that grows in it.
A vertical section through different
layers of the soil is called the soil profile.
Each layer differs in feel (texture),
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.
I have seen pots
and toys made up of
soil in haat (bazaar)
Fig. 9.2  Layers of soil
I wonder why I found some
pieces of plastic articles and
polythene bags in the soil sample
collected from the roadside and
the garden.
humus
water
clay
sand
gravel
2022-23
Page 3


SCIENCE 96
Soil
9
S
oil is one of the most important
natural resources. It provides
anchorage  to the plants and
supplies water and nutrients. It is the
home for many organisms. Soil is
essential for agriculture. Agriculture
provides food, clothing and shelter
for all. Soil is thus an inseparable
part of our life. The earthy fragrance
of soil after the first rain is always
refreshing.
9.1 SOIL TEEMING WITH LIFE
One day during the rainy season Paheli
and Boojho observed an earthworm
coming out of the soil. Paheli wondered
whether there were other organisms also
in the soil. Let us find out.
Activity 9.1
Collect some soil samples and observe
them carefully. You can use a hand lens.
Examine each sample carefully and fill
in Table 9.1.
§ Discuss your observations
with your friends.
§ Are the soil samples
collected by your friends
similar to the ones collected by
you?
Boojho and Paheli have
used soil in many ways. They
enjoy playing with it. It is a
great fun indeed.
Make a list of the uses of soil.
Fig. 9.1  Children playing with soil
Table 9.1
S. Soil source Plants Animals Any other
No. observations
1. Garden soil Grass, ………. Ant, ……….
2. Soil from the roadside ………………
3. Soil from the area where
construction is going on ………………
4. ……………… ………………
5. ……………… ………………
2022-23
SOIL 97
9.2 SOIL PROFILE
Soil is composed of distinct layers.
Perform the following activity to find out
how these layers are arranged.
Activity 9.2
Take a little soil. Break the clumps with
your hand to powder it. Now take a glass
tumbler, three quarters filled with water,
and then add a handful of soil to it. Stir
it well with a stick to dissolve the soil.
Now let it stand undisturbed for some
time (Fig. 9.2). Afterwards, observe it and
answer the following questions:
§ Do you see layers of particles of
different sizes in the glass tumbler?
§ Draw a diagram showing these layers.
§ Are there some dead rotting leaves
or animal remains floating on water?
The rotting dead matter in the soil is
called humus.
You probably know that the soil is
formed by the breaking down of rocks
by the action of wind, water and climate.
This process is called weathering. The
nature of any soil depends upon the
rocks from which it has been formed and
the type of vegetation that grows in it.
A vertical section through different
layers of the soil is called the soil profile.
Each layer differs in feel (texture),
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.
I have seen pots
and toys made up of
soil in haat (bazaar)
Fig. 9.2  Layers of soil
I wonder why I found some
pieces of plastic articles and
polythene bags in the soil sample
collected from the roadside and
the garden.
humus
water
clay
sand
gravel
2022-23
SCIENCE 98
colour, depth and chemical
composition. These layers are referred
to as horizons (Fig. 9.3).
soil fertile and provides nutrients to
growing plants. This layer is generally
soft, porous and can retain more water.
It is called the topsoil or the A-horizon.
We usually see the top surface of
the soil, not the layers below it. If we
look at the sides of a recently dug ditch,
we can see the inner layers of the soil,
too. Such a view enables us to observe
the soil profile at that place. Soil profile
can also be seen while digging a well or
laying the foundation of a building. It
can also be seen at the sides of a road
on a hill or at a steep river bank.
The uppermost horizon is generally
dark in colour as it is rich in humus
and minerals. The humus makes the
This provides shelter for many living
organisms such as worms, rodents,
moles and beetles. The roots of small
plants are embedded entirely in the
topsoil.
The next layer has a lesser amount
of humus but more of minerals. This
layer is generally harder and more
compact and is called the B-horizon or
the middle layer.
The third layer is the C-horizon,
which is made up of small lumps of
rocks with cracks and crevices. Below
Fig. 9.3  Soil profile
A-horizon
B-horizon
C-horizon
Bedrock
2022-23
Page 4


SCIENCE 96
Soil
9
S
oil is one of the most important
natural resources. It provides
anchorage  to the plants and
supplies water and nutrients. It is the
home for many organisms. Soil is
essential for agriculture. Agriculture
provides food, clothing and shelter
for all. Soil is thus an inseparable
part of our life. The earthy fragrance
of soil after the first rain is always
refreshing.
9.1 SOIL TEEMING WITH LIFE
One day during the rainy season Paheli
and Boojho observed an earthworm
coming out of the soil. Paheli wondered
whether there were other organisms also
in the soil. Let us find out.
Activity 9.1
Collect some soil samples and observe
them carefully. You can use a hand lens.
Examine each sample carefully and fill
in Table 9.1.
§ Discuss your observations
with your friends.
§ Are the soil samples
collected by your friends
similar to the ones collected by
you?
Boojho and Paheli have
used soil in many ways. They
enjoy playing with it. It is a
great fun indeed.
Make a list of the uses of soil.
Fig. 9.1  Children playing with soil
Table 9.1
S. Soil source Plants Animals Any other
No. observations
1. Garden soil Grass, ………. Ant, ……….
2. Soil from the roadside ………………
3. Soil from the area where
construction is going on ………………
4. ……………… ………………
5. ……………… ………………
2022-23
SOIL 97
9.2 SOIL PROFILE
Soil is composed of distinct layers.
Perform the following activity to find out
how these layers are arranged.
Activity 9.2
Take a little soil. Break the clumps with
your hand to powder it. Now take a glass
tumbler, three quarters filled with water,
and then add a handful of soil to it. Stir
it well with a stick to dissolve the soil.
Now let it stand undisturbed for some
time (Fig. 9.2). Afterwards, observe it and
answer the following questions:
§ Do you see layers of particles of
different sizes in the glass tumbler?
§ Draw a diagram showing these layers.
§ Are there some dead rotting leaves
or animal remains floating on water?
The rotting dead matter in the soil is
called humus.
You probably know that the soil is
formed by the breaking down of rocks
by the action of wind, water and climate.
This process is called weathering. The
nature of any soil depends upon the
rocks from which it has been formed and
the type of vegetation that grows in it.
A vertical section through different
layers of the soil is called the soil profile.
Each layer differs in feel (texture),
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.
I have seen pots
and toys made up of
soil in haat (bazaar)
Fig. 9.2  Layers of soil
I wonder why I found some
pieces of plastic articles and
polythene bags in the soil sample
collected from the roadside and
the garden.
humus
water
clay
sand
gravel
2022-23
SCIENCE 98
colour, depth and chemical
composition. These layers are referred
to as horizons (Fig. 9.3).
soil fertile and provides nutrients to
growing plants. This layer is generally
soft, porous and can retain more water.
It is called the topsoil or the A-horizon.
We usually see the top surface of
the soil, not the layers below it. If we
look at the sides of a recently dug ditch,
we can see the inner layers of the soil,
too. Such a view enables us to observe
the soil profile at that place. Soil profile
can also be seen while digging a well or
laying the foundation of a building. It
can also be seen at the sides of a road
on a hill or at a steep river bank.
The uppermost horizon is generally
dark in colour as it is rich in humus
and minerals. The humus makes the
This provides shelter for many living
organisms such as worms, rodents,
moles and beetles. The roots of small
plants are embedded entirely in the
topsoil.
The next layer has a lesser amount
of humus but more of minerals. This
layer is generally harder and more
compact and is called the B-horizon or
the middle layer.
The third layer is the C-horizon,
which is made up of small lumps of
rocks with cracks and crevices. Below
Fig. 9.3  Soil profile
A-horizon
B-horizon
C-horizon
Bedrock
2022-23
SOIL 99
this layer is the bedrock, which is hard
and difficult to dig with a spade.
9.3 SOIL TYPES
As you know, weathering of rocks
produces small particles of various
materials. These include sand and clay.
The relative amount of sand and clay
depends upon the rock from which the
particles were formed, that is the parent
rock. The mixture of rock particles
and humus is called the soil. Living
organisms, such as bacteria, plant roots
and earthworm are also important parts
of any soil.
The soil is classified on the basis of
the proportion of particles of various
sizes. If soil contains greater proportion
of big particles it is called sandy soil.
If the proportion of fine particles is
relatively higher, then it is called
clayey soil. If the amount of large and
fine particles is about the same, then the
soil is called loamy. Thus, the soil can
be classified as sandy, clayey and loamy.
The size of the particles in a soil has
an influence on its properties. Sand
particles are quite large. They cannot fit
close together, so there are large spaces
between them. These spaces are filled
with air. We say that the sand is well
aerated. Water can drain quickly
through the spaces between the sand
particles. So, sandy soils tend to be light,
well aerated and rather dry. Clay
particles, being much smaller, pack
tightly together, leaving little space for
air. Unlike sandy soil, water can be held
in the tiny gaps between the particles of
clay. So clayey soils have less air. But
I want to know:
What kind of soil should be
used for making earthen pots
(matkas and surahis)?
they are heavy as they hold more water
than the sandy soils.
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. Silt occurs as a deposit
in riverbeds. The size of the silt particles
is between those of sand and clay. The
loamy soil also has humus in it. It has
the right water holding capacity for the
growth of plants.
Activity 9.3
Collect samples of clayey, loamy and
sandy soils. Take a fistful of soil from
one of the samples. Remove any pebbles,
rocks or grass blades from it. Now, add
water drop-by-drop and knead the soil
[Fig. 9.4 (a)]. Add just enough water so
that a ball [Fig. 9.4 (b)] can be made
from it, but at the same time it should
not be sticky. Try to make a ball
[Fig. 9.4 (c)] from this soil. On a flat
surface, roll this ball into a cylinder
[Fig. 9.4 (d)]. Try to make a ring from
this cylinder [Fig. 9.4 (e)]. Repeat this
activity with other samples also. Does
the extent to which a soil can be shaped
indicate its type?
Can you suggest which type of soil
would be the best for making pots, toys
and statues?
2022-23
Page 5


SCIENCE 96
Soil
9
S
oil is one of the most important
natural resources. It provides
anchorage  to the plants and
supplies water and nutrients. It is the
home for many organisms. Soil is
essential for agriculture. Agriculture
provides food, clothing and shelter
for all. Soil is thus an inseparable
part of our life. The earthy fragrance
of soil after the first rain is always
refreshing.
9.1 SOIL TEEMING WITH LIFE
One day during the rainy season Paheli
and Boojho observed an earthworm
coming out of the soil. Paheli wondered
whether there were other organisms also
in the soil. Let us find out.
Activity 9.1
Collect some soil samples and observe
them carefully. You can use a hand lens.
Examine each sample carefully and fill
in Table 9.1.
§ Discuss your observations
with your friends.
§ Are the soil samples
collected by your friends
similar to the ones collected by
you?
Boojho and Paheli have
used soil in many ways. They
enjoy playing with it. It is a
great fun indeed.
Make a list of the uses of soil.
Fig. 9.1  Children playing with soil
Table 9.1
S. Soil source Plants Animals Any other
No. observations
1. Garden soil Grass, ………. Ant, ……….
2. Soil from the roadside ………………
3. Soil from the area where
construction is going on ………………
4. ……………… ………………
5. ……………… ………………
2022-23
SOIL 97
9.2 SOIL PROFILE
Soil is composed of distinct layers.
Perform the following activity to find out
how these layers are arranged.
Activity 9.2
Take a little soil. Break the clumps with
your hand to powder it. Now take a glass
tumbler, three quarters filled with water,
and then add a handful of soil to it. Stir
it well with a stick to dissolve the soil.
Now let it stand undisturbed for some
time (Fig. 9.2). Afterwards, observe it and
answer the following questions:
§ Do you see layers of particles of
different sizes in the glass tumbler?
§ Draw a diagram showing these layers.
§ Are there some dead rotting leaves
or animal remains floating on water?
The rotting dead matter in the soil is
called humus.
You probably know that the soil is
formed by the breaking down of rocks
by the action of wind, water and climate.
This process is called weathering. The
nature of any soil depends upon the
rocks from which it has been formed and
the type of vegetation that grows in it.
A vertical section through different
layers of the soil is called the soil profile.
Each layer differs in feel (texture),
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.
I have seen pots
and toys made up of
soil in haat (bazaar)
Fig. 9.2  Layers of soil
I wonder why I found some
pieces of plastic articles and
polythene bags in the soil sample
collected from the roadside and
the garden.
humus
water
clay
sand
gravel
2022-23
SCIENCE 98
colour, depth and chemical
composition. These layers are referred
to as horizons (Fig. 9.3).
soil fertile and provides nutrients to
growing plants. This layer is generally
soft, porous and can retain more water.
It is called the topsoil or the A-horizon.
We usually see the top surface of
the soil, not the layers below it. If we
look at the sides of a recently dug ditch,
we can see the inner layers of the soil,
too. Such a view enables us to observe
the soil profile at that place. Soil profile
can also be seen while digging a well or
laying the foundation of a building. It
can also be seen at the sides of a road
on a hill or at a steep river bank.
The uppermost horizon is generally
dark in colour as it is rich in humus
and minerals. The humus makes the
This provides shelter for many living
organisms such as worms, rodents,
moles and beetles. The roots of small
plants are embedded entirely in the
topsoil.
The next layer has a lesser amount
of humus but more of minerals. This
layer is generally harder and more
compact and is called the B-horizon or
the middle layer.
The third layer is the C-horizon,
which is made up of small lumps of
rocks with cracks and crevices. Below
Fig. 9.3  Soil profile
A-horizon
B-horizon
C-horizon
Bedrock
2022-23
SOIL 99
this layer is the bedrock, which is hard
and difficult to dig with a spade.
9.3 SOIL TYPES
As you know, weathering of rocks
produces small particles of various
materials. These include sand and clay.
The relative amount of sand and clay
depends upon the rock from which the
particles were formed, that is the parent
rock. The mixture of rock particles
and humus is called the soil. Living
organisms, such as bacteria, plant roots
and earthworm are also important parts
of any soil.
The soil is classified on the basis of
the proportion of particles of various
sizes. If soil contains greater proportion
of big particles it is called sandy soil.
If the proportion of fine particles is
relatively higher, then it is called
clayey soil. If the amount of large and
fine particles is about the same, then the
soil is called loamy. Thus, the soil can
be classified as sandy, clayey and loamy.
The size of the particles in a soil has
an influence on its properties. Sand
particles are quite large. They cannot fit
close together, so there are large spaces
between them. These spaces are filled
with air. We say that the sand is well
aerated. Water can drain quickly
through the spaces between the sand
particles. So, sandy soils tend to be light,
well aerated and rather dry. Clay
particles, being much smaller, pack
tightly together, leaving little space for
air. Unlike sandy soil, water can be held
in the tiny gaps between the particles of
clay. So clayey soils have less air. But
I want to know:
What kind of soil should be
used for making earthen pots
(matkas and surahis)?
they are heavy as they hold more water
than the sandy soils.
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. Silt occurs as a deposit
in riverbeds. The size of the silt particles
is between those of sand and clay. The
loamy soil also has humus in it. It has
the right water holding capacity for the
growth of plants.
Activity 9.3
Collect samples of clayey, loamy and
sandy soils. Take a fistful of soil from
one of the samples. Remove any pebbles,
rocks or grass blades from it. Now, add
water drop-by-drop and knead the soil
[Fig. 9.4 (a)]. Add just enough water so
that a ball [Fig. 9.4 (b)] can be made
from it, but at the same time it should
not be sticky. Try to make a ball
[Fig. 9.4 (c)] from this soil. On a flat
surface, roll this ball into a cylinder
[Fig. 9.4 (d)]. Try to make a ring from
this cylinder [Fig. 9.4 (e)]. Repeat this
activity with other samples also. Does
the extent to which a soil can be shaped
indicate its type?
Can you suggest which type of soil
would be the best for making pots, toys
and statues?
2022-23
SCIENCE 100
9.4  PROPERTIES OF SOIL
You have listed some uses of soil. Let us
perform some activities to find the
characteristics of the soil.
Percolation rate of water in
soil
Boojho and Paheli marked two different
squares of 50 cm × 50 cm each, one on
the floor of their house and the other
on the kutcha (unpaved) road. They filled
two bottles of the same size with water.
They emptied the water from the bottles,
one each, at the same time in the two
squares. They observed that the water
on the floor flowed down and was not
absorbed. On the kutcha road, on the
other hand, the water was absorbed.
Now let us perform an activity to
understand this.
Activity 9.4
For this activity divide yourself into
three teams. Name the teams A, B and
C. You will be finding out how fast the
water passes down the soil. You will
need a hollow cylinder or a pipe. Ensure
that each team uses pipes of the same
diameter. Some suggestions for
obtaining such a pipe are given below:
1. If possible, get a small tin can and
cut off its bottom.
2. If PVC pipe (approx. diameter 5 cm)
is available, cut it into 20 cm long
pieces and use them.
At the place where you collect the soil,
place the pipe about 2 cm deep in the
ground. Pour 200 mL water in the pipe
slowly. For measuring 200 mL water you
can use any empty 200 mL bottle. Note
the time when you start pouring water.
When all the water has percolated
Fig. 9.5 Measuring rate of percolation
(a) (b)
(e)
Fig. 9.4  Working with the soil
(d)
(c)
Boojho wondered why there
was a difference in the
absorption of water in the
two squares.
2022-23