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11
Soil
KNOWTHESE PoINTS BEFORE YOU START
Learning Objectives
The students will be able to
Soil can be broadly classified as sandy soil, clayey soil and loamy soil.
Sandy soil mainly contains large-sized sand particles, is well-aerated, cannot hold
much water and nutrients, and can be ploughed easily.
Clayey soilmainly contains smaller-sized clay particles, traps very little air, can
hold water and nutrients well and is difficult to plough.
understand what is soil
and its importance.
+Study different layers of
soil.
know the varíous
components that make
up the soil.
Loamy soil contains sand, silt and clay in right proportions, has the right water
and nutrients holding capacity, is well-aerated and can be ploughed easily.
know about the different
Different types ofsoilabsorb water to different extent
Percolation rate can be calculatedusing the formula:
types of soil.
+understandthat different
soils have different water volume of water (mL)
holding capacities. Percolation rate (ml/min)
percolation time (min)
know what is soil erosion
and how it is caused. Soil erosion can lead to floods, famines and landslides.
We need to look after the soil as it takes millions of years to get formed.
Now, study the chapter in detail.
Consider the following questions and try to answer them:
How do the trees manage to stand in a forest year-after-year
What is the home of the organisms like earthworms?
What is the foundation ofour buildings?
Agriculture provides food, shelter and clothing to us. Whatis
essential for agriculture?
Well! The answer to all this lies in the soil.
nutrients required by plants to grow. Soil layers contain particles of different sizes.
s also very important as a habitat -
a
home Let us perform an activity to make.a rough
LAYERS OF 90IL
Soil enableSoil enables plants to grow. Soil provides all Soil is made up of different layers. These
the nutri
or millions of soil organisms. It also provides estimate of the amount of different particles
anchorage to trees and vegetation.
present in different layers of soil.
Soil, like air and water, is one of the most
important natural resources. Soil is found all
around us - in gardens, school playgrounds, Take a glass container (you can use an empty jam jar).
at the parks, at construction sites and also in
the fields. It ies beneath our feet and is often
hidden by roads and buildings. Probably,
this is the reason we often fail to realise how
much soil affects our lives. We depend a lot
on soil. Soil is also essential for the forests of
the world. We get many useful things from
forests. These forests provide us timber and
are also the natural habitat of many plants
Activity
Put some soil in it. Fill 3/4th of the container with
clean water. Stir the mixture well and secure the lid
firmly. Leave the set-up undisturbed (preferably for
a couple of days) in a safe place. Observe carefully
the different layers of soil. Do they look like this?
How many layers of soil can you observe? Do you
find any dead leaves or animal remains filoating on
water?
and animals.
Activity1
Collect different types of soil samples. You may find
them in your school, at construction sites, roadside or
a garden. Using a hand lens, observe these samples
carefully. You may notice pieces of grasses, pebbles
and small organisms in the soil. Make a list of all
the things, you find in the soil. The dead and rotting remains of plants and
animals form humus. Let us now study about
the different layers of soil.S. No. Things seen in the soil
Topsoil or A-horizon
The topmost layer of the soil is called
A-horizon.
It is rich in humus.
It is rich in minerals needed by plants for
their growth.
It is soft.
It is porous.
It is darker than other layers.
It can retain (hold) morewater.
What is weathering?
Topsoil
The breaking down of rocks into small
particles by the action of water and
wind is called weathering.
Subsoil
COMPONENTS OF S0IL
Soil is made up of different-sized roc
particles. These ditferent-sized
particle
infuence the properties of soil. Dependingon
their size, the rock particles are divided into
four groups. These four groups are:
Weathered
parent rock
Bedrock
Clay: Clay consists of the smallest roc
particles. These small particles are packed
tightly together, as a result of which, very
little air is present in clay. Water is heldin
the tiny gaps between the particles.
Silt: Silt consists of a little bigger rock
particles than clay. It is not so smooth.
Fig. 11.1 Layers of soil
A-horizon is the home of many living
organisms like insects and worms. The roots
of plants grow in this layer ofsoil.
Subsoil or B-horizon
B-horizon lies just below the topsoil. It has
a very small population of living organisms
and is less fertile as compared to A-horizon.
Sand: Sand consists of still larger rock
particles. Since sand particles are quite
large, they are not bound closelytogether
As a result of which, there is a lot of empty
space between them which isfilled with air
The large spaces between the sandparticles
allows water to drain quickly.
It contains comparatively less amount of
humus.
It is rich in minerals.
It is generally harder and more compact
than topsoil.
It is lighter in colour because of the Gravel: It consists of the largest rock
presence of less amount of humus. particles.
C-horizon Other components of soil are as follows:
C-horizonlies just below the B-horizon. It Humus: The organic matter like dead and
decaying remains of plants and animals
presentin the soil is called humus. Humus
is important because it makes thesoilfertile
as it contains all the nutrients required
by the plants for their proper growth. It
also improves the water holding capac1ty
of the soil. Humus also provides food to
earthworms, beetles, millipedes, etc.
is made up of small lumps of rocks. These
rocks have cracks in them, formed due to
weathering of bedrock.
Bedrock
Bedrock is also called the parent rock.
This parent rock produces soil over a long
period of time. The parent rock is very
hard.
106
Living organisms: Many bacteria, insects CheckPeINTJ
b e t w e
en soil particles Plants do not grow
A i r :Thegaps between the soil
particles are
d worms ve in the soil
Water is also
present in the space
Check PeINT 1.
Match the following.
(a)Soil dead and decaying organic
matter present in soil
natural habitat for many
plants and animals
lighter in colour
without water. The
presence of water can (b) Humus
be
shown by the following activity. () Earthworm
(d) B-horizon
filled
uith air. Soil organisms use air for
eniration. Let us pertorm a simple activity 2. Give one word for the following.
rich in humus
(e) A-horizon friends of farmers
how that air 1s
present in soil.to (a) Dead and rotting remains of plants and
animals
Activity
come soil in a beaker. Pour water over it.
(b) Parent rock
(c) The darkest layer of soil
(d) An organism that lives in soil
(e) Breaking down of small particles by the action
of water and wind
13h carefully. Do you see some air bubbles in
the water coming out of the soil?
TYPES OF SOIL
Based on the proportion of various particles
present in the soil, the soil can be broadly
classified into sandy soil, clayey soil and
loamysoil
Sandy soil
This soil mainly contains large-sized sand
particles. Clay and silt may be present in
traces. The characteristics of sandy soil are:
We can now define soil on the basis of its The space between sand particles is quite
Components. large. This is filled up by air. Sandy soil is,
therefore, well-aerated.Yes,soil is a naturallyoccurringloose covering of
broken rock particles and humus on the earth's
surtace, which is capable of supporting life.
Sornething More
Earthworms are called friends of farmers
because they help in improving the fertility of
Sol. When an earthworm moves, it turns the
SOIl Over and mixes the soil layers. This allows air
mto the soil. Earthworms also drag the leaves down
Into their burrows, which on rotting add humus to the
SOIL.Their excreta (wastes) and eventually, their dead
bodies also increase the soil fertility. Fig. 11.2 Sandy soil
Due to large spaces between the sand
particles, the water drains out quickly. soil.
Because of this, sandy soil cannot hold
much water. Sandy soil, therefore, tends
to be light and dry. This is a disadvantage
of sandy soil.
Sandy soil can be ploughed easily
Sandy soil cannot hold nutrients.
in loamy soil. Loamy soil is the most fertil.
Clayey soil
This soil mainly contains smaller-sized clay
particles. Sand and silt are present in traces.
The characteristics of clayey soil are:
Since the particle size is quite small, the
particles are
compactly arranged. Because
of this, very little air can be trapped in
clayey soil. This is a disadvantage of clayey
soil
Fig. 11.4 Loamy soil
TABLE 11.1 DiFFERENCES BETWEEN SANDY,
CLAYEY AND LOAMY SOILS
Property Sandy soil Clayey soil Loamy soil
Smaller-sized Clay, sand and
silt present
in right
proportions
1. Main Large-sized
constituent sand particles clay particles
Clayey soil can hold much water. Water
drains out very slowly through clayey soil. 2. Space Quite large Quite less Sufficient
between
This can however lead to waterlogging
which can damage the crops. Clayey soil
tends to be heavy and holds more water
than sandy soil.
particles
Can hold3. Presence of Well-aerated Not well-
aeratedair suficient air
4. Water holding Cannot hold
much water
Can hold much Rightwater
watercapacity holding capacity
Clayey soil is difficult to plough.
Clayey soil can hold nutrients.
Cannot hold
nutrients
6. Ploughing Easy to plough Difficult to
Can hold
nutrients
5. Nutrients Can hold
nutrients
Easy to plough
plough
The characteristics ofloamy soil are as follows:
It has the right water holding capacity.
It can hold sufficient air for the growth of
plants because ofthe presence of adequate
air spaces between the particles.
It canbe ploughed easily.
It can hold necessary nutrients required for
the growth of plants.Fig. 11.3 Clayey soil
ABSORPTION OF WATER BY S0ILLoamy soil
Loamy soil contains clay, sand and silt in Wehave learnt that different soils have different
right proportions. Humus is also present water holding capacities, i.e., different soils
108
b water to different extent. Let us do an
civity
to understand this. Soil has many pores orgaps which allow
water to flow down. Rainwater also passes
through these pores. This water helps the
plants to grow, and also increases the level
of groundwater.
The pores present in soil are filled with
air. Air helps the animals living in soil to
Activity
samples of ndy soil and clayey soil in equal, say 50 g each. Place them in two
separatequa helled 'S' for sandy and 'C for clayey. Dilutejadr Daint (by mixing some water with red
s o m e
paint)
This will act as coloured water. Now, prepare breathe.
two.oheakers containing each 100 mL coloured water.
Keepa stopwatch ready. Now, gently pour coloured Which type of soil, sandy or clayey,
will allow more of rainwater to seep
into the soil?
'S. Note the time taken for the colouredwaterinjar
water to appear
fn the table given beloW. Repeat the activity with
atthe base. Note your observation
the clayey soil in jar 'C'
Ooes the water take more or less time to appear
Percolation rate of water in soil
at the base?
Activity
Look for a place which has a good amount of soil,
like a park or a garden. Dig at least 2 cm deep in
the ground. Now, place a glass pipe here, as shown
in the diagram. Measure 250 mL water and slowly
pour into the pipe. Start the stopwatch immediately
when you start pouring water into the pipe and note
down the time. Note the time again when all the
water percolates into the soil. You can now calculate
the percolation rate by using the formula:
JarS Jar C
Time taken
volumeofwater(mL)
percolation time (min)Percolationrate
Suppose the sample of soil taken by you takes
25 min for 250 mL water to percolate. The percolation
rate can be calculated using the above formula as:
What do you conclude from this activity?
The larger the soil particles, the less time it
takes for the water to pass because the space
between the particles is larger.
250 ml
Percolation rate = = 10 mL/min
25 min
Can we try this activity with other
soil samples?
es, you may collect them from your
School lawn, playground, park, etc. You
Caneven try with sieved and unsieved
Soil and see the results!
Many characteristics ofsoil can be understood
Do you think the rate of percolation
of different soil samples will be the
Irom the above activity:
same?
09
of time, they eat up most of the plant
(orgrass) of that land. Ihis removes the
vegetation cover from the topsoil. This bar
topsoil can be easily carried away by rair
or wind leading to soil erosion.
Deforestation: This is another majorcaus
for soil erosion. Cutting down of trees on
large-scale is called deforestation. The t
of the trees bind the soil particles. Strong
winds and rainwater then carry away the
Check PeINT 2 -
Name the following.
1. Soil that can hold much water but is not
well-aerated. ain
2. Soil that has the right water holding capacity and
has sufficient air.
3. Soil that is well-aerated but cannot hold much
water.
4. Soil that is considered the most fertile.
5. Soil that is difficult to plough.
topsoil and cause soil erosion.
90IL EROSION
As discussed earlier, the topsoil is very fertile.
Strong winds, river water or heavy rains may
carry away the topsoil. The removal of topsoil
by either strong winds, fHowing river water or
rain is called soil erosion.
Soil erosion is more common in areas which
are not covered by trees or grass and are
bare. In the absence of any vegetation, the
topsoil becomes loose and gets easily carried Fig. 11.6 Deforestation
Excessive ploughing of fields: If farmers
plough or till their tields excessively to
grow crops, the soil in the field becomes
loose and can be easily eroded by ran and
strong wind.
away.
Fig. 11.5 Soil erosion
Soil does not get eroded if it is covered by
vegetation. The roots of the plants bind
together the topsoil particles and prevent soil
erosion. Fig. 11.7A farmer ploughing a field
Causes of soil erosion
Soil erosion can occur mainly due to: Can frequent flooding of rivers lead
to soil erosion?
Overgrazing: When cattle areallowedto
graze on the same land tor a long period
ects of soil erosion
on can harm the
environment in
E f f e c t s
Sol
Wa Soil erosion can lead to
floods, imaginenas and can also cause
landslides in hilly about 500 years to get formed! We just cant
We need to look after the soil as it takes
vironment in millions ofyears to get formed. Can you
imagine as little as 1 cm thick soil takes
a r e a s .
we need to look after our soil
replace soil in our lifetime. Life on land
depends on soil. Soil at many places is gettingDowe
and rdeners add fertilisers to the damaged
risk!
and polluted. Soil is, therefore, at
ntssos$O that they can
grow properly. But ifexcess tertilisersPs fertilisers are used over a
long time, Check PeINT 3.
risk!
damage the soil. Check PeINT 3.theymay
Fill in the blanks.
1. Topsoil is very
2. Removal of topsoil is called
3. Overgrazing removes
the topsoil
COver from
4. Cutting down trees on a large-scale is called
Fig. 11.8 A farmer adding fertiliser to crop
KNOW THESE TERMS
-
naturally occurring loose covering of
broken rock particles and humus on
the earths surface which is capable
of supporting life
Soil Humus organic matter like dead and
decaying remains of plants and
animals present in the soil
Soil erosion the removal of topsoil by either
strong winds, fowing river water
PRACTICE TIME
A. MCQs-Choose the correct answers. 3. Which of the following soils is the best for
1. Which ofthese soil particles contain the largest
rock particles?
(a) silt
growing crops?
(a) sandy
(c) loamy
b) clayey
d) none ofthese
b) clay
c)sand O(d) gravel
4. Which soil contains sand, silt and clay in right
2. The darkest layer of soil is
a) subsoil
proportions?
(a) sandy
(c) clayey
b) loamy6 ) bedrock
c) C-horizon Od) topsoil
d) noneofthese
11

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Class 7 Soil

  • 1. 11 Soil KNOWTHESE PoINTS BEFORE YOU START Learning Objectives The students will be able to Soil can be broadly classified as sandy soil, clayey soil and loamy soil. Sandy soil mainly contains large-sized sand particles, is well-aerated, cannot hold much water and nutrients, and can be ploughed easily. Clayey soilmainly contains smaller-sized clay particles, traps very little air, can hold water and nutrients well and is difficult to plough. understand what is soil and its importance. +Study different layers of soil. know the varíous components that make up the soil. Loamy soil contains sand, silt and clay in right proportions, has the right water and nutrients holding capacity, is well-aerated and can be ploughed easily. know about the different Different types ofsoilabsorb water to different extent Percolation rate can be calculatedusing the formula: types of soil. +understandthat different soils have different water volume of water (mL) holding capacities. Percolation rate (ml/min) percolation time (min) know what is soil erosion and how it is caused. Soil erosion can lead to floods, famines and landslides. We need to look after the soil as it takes millions of years to get formed. Now, study the chapter in detail. Consider the following questions and try to answer them: How do the trees manage to stand in a forest year-after-year What is the home of the organisms like earthworms? What is the foundation ofour buildings? Agriculture provides food, shelter and clothing to us. Whatis essential for agriculture?
  • 2. Well! The answer to all this lies in the soil. nutrients required by plants to grow. Soil layers contain particles of different sizes. s also very important as a habitat - a home Let us perform an activity to make.a rough LAYERS OF 90IL Soil enableSoil enables plants to grow. Soil provides all Soil is made up of different layers. These the nutri or millions of soil organisms. It also provides estimate of the amount of different particles anchorage to trees and vegetation. present in different layers of soil. Soil, like air and water, is one of the most important natural resources. Soil is found all around us - in gardens, school playgrounds, Take a glass container (you can use an empty jam jar). at the parks, at construction sites and also in the fields. It ies beneath our feet and is often hidden by roads and buildings. Probably, this is the reason we often fail to realise how much soil affects our lives. We depend a lot on soil. Soil is also essential for the forests of the world. We get many useful things from forests. These forests provide us timber and are also the natural habitat of many plants Activity Put some soil in it. Fill 3/4th of the container with clean water. Stir the mixture well and secure the lid firmly. Leave the set-up undisturbed (preferably for a couple of days) in a safe place. Observe carefully the different layers of soil. Do they look like this? How many layers of soil can you observe? Do you find any dead leaves or animal remains filoating on water? and animals. Activity1 Collect different types of soil samples. You may find them in your school, at construction sites, roadside or a garden. Using a hand lens, observe these samples carefully. You may notice pieces of grasses, pebbles and small organisms in the soil. Make a list of all the things, you find in the soil. The dead and rotting remains of plants and animals form humus. Let us now study about the different layers of soil.S. No. Things seen in the soil Topsoil or A-horizon The topmost layer of the soil is called A-horizon. It is rich in humus. It is rich in minerals needed by plants for their growth. It is soft. It is porous. It is darker than other layers. It can retain (hold) morewater.
  • 3. What is weathering? Topsoil The breaking down of rocks into small particles by the action of water and wind is called weathering. Subsoil COMPONENTS OF S0IL Soil is made up of different-sized roc particles. These ditferent-sized particle infuence the properties of soil. Dependingon their size, the rock particles are divided into four groups. These four groups are: Weathered parent rock Bedrock Clay: Clay consists of the smallest roc particles. These small particles are packed tightly together, as a result of which, very little air is present in clay. Water is heldin the tiny gaps between the particles. Silt: Silt consists of a little bigger rock particles than clay. It is not so smooth. Fig. 11.1 Layers of soil A-horizon is the home of many living organisms like insects and worms. The roots of plants grow in this layer ofsoil. Subsoil or B-horizon B-horizon lies just below the topsoil. It has a very small population of living organisms and is less fertile as compared to A-horizon. Sand: Sand consists of still larger rock particles. Since sand particles are quite large, they are not bound closelytogether As a result of which, there is a lot of empty space between them which isfilled with air The large spaces between the sandparticles allows water to drain quickly. It contains comparatively less amount of humus. It is rich in minerals. It is generally harder and more compact than topsoil. It is lighter in colour because of the Gravel: It consists of the largest rock presence of less amount of humus. particles. C-horizon Other components of soil are as follows: C-horizonlies just below the B-horizon. It Humus: The organic matter like dead and decaying remains of plants and animals presentin the soil is called humus. Humus is important because it makes thesoilfertile as it contains all the nutrients required by the plants for their proper growth. It also improves the water holding capac1ty of the soil. Humus also provides food to earthworms, beetles, millipedes, etc. is made up of small lumps of rocks. These rocks have cracks in them, formed due to weathering of bedrock. Bedrock Bedrock is also called the parent rock. This parent rock produces soil over a long period of time. The parent rock is very hard. 106
  • 4. Living organisms: Many bacteria, insects CheckPeINTJ b e t w e en soil particles Plants do not grow A i r :Thegaps between the soil particles are d worms ve in the soil Water is also present in the space Check PeINT 1. Match the following. (a)Soil dead and decaying organic matter present in soil natural habitat for many plants and animals lighter in colour without water. The presence of water can (b) Humus be shown by the following activity. () Earthworm (d) B-horizon filled uith air. Soil organisms use air for eniration. Let us pertorm a simple activity 2. Give one word for the following. rich in humus (e) A-horizon friends of farmers how that air 1s present in soil.to (a) Dead and rotting remains of plants and animals Activity come soil in a beaker. Pour water over it. (b) Parent rock (c) The darkest layer of soil (d) An organism that lives in soil (e) Breaking down of small particles by the action of water and wind 13h carefully. Do you see some air bubbles in the water coming out of the soil? TYPES OF SOIL Based on the proportion of various particles present in the soil, the soil can be broadly classified into sandy soil, clayey soil and loamysoil Sandy soil This soil mainly contains large-sized sand particles. Clay and silt may be present in traces. The characteristics of sandy soil are: We can now define soil on the basis of its The space between sand particles is quite Components. large. This is filled up by air. Sandy soil is, therefore, well-aerated.Yes,soil is a naturallyoccurringloose covering of broken rock particles and humus on the earth's surtace, which is capable of supporting life. Sornething More Earthworms are called friends of farmers because they help in improving the fertility of Sol. When an earthworm moves, it turns the SOIl Over and mixes the soil layers. This allows air mto the soil. Earthworms also drag the leaves down Into their burrows, which on rotting add humus to the SOIL.Their excreta (wastes) and eventually, their dead bodies also increase the soil fertility. Fig. 11.2 Sandy soil
  • 5. Due to large spaces between the sand particles, the water drains out quickly. soil. Because of this, sandy soil cannot hold much water. Sandy soil, therefore, tends to be light and dry. This is a disadvantage of sandy soil. Sandy soil can be ploughed easily Sandy soil cannot hold nutrients. in loamy soil. Loamy soil is the most fertil. Clayey soil This soil mainly contains smaller-sized clay particles. Sand and silt are present in traces. The characteristics of clayey soil are: Since the particle size is quite small, the particles are compactly arranged. Because of this, very little air can be trapped in clayey soil. This is a disadvantage of clayey soil Fig. 11.4 Loamy soil TABLE 11.1 DiFFERENCES BETWEEN SANDY, CLAYEY AND LOAMY SOILS Property Sandy soil Clayey soil Loamy soil Smaller-sized Clay, sand and silt present in right proportions 1. Main Large-sized constituent sand particles clay particles Clayey soil can hold much water. Water drains out very slowly through clayey soil. 2. Space Quite large Quite less Sufficient between This can however lead to waterlogging which can damage the crops. Clayey soil tends to be heavy and holds more water than sandy soil. particles Can hold3. Presence of Well-aerated Not well- aeratedair suficient air 4. Water holding Cannot hold much water Can hold much Rightwater watercapacity holding capacity Clayey soil is difficult to plough. Clayey soil can hold nutrients. Cannot hold nutrients 6. Ploughing Easy to plough Difficult to Can hold nutrients 5. Nutrients Can hold nutrients Easy to plough plough The characteristics ofloamy soil are as follows: It has the right water holding capacity. It can hold sufficient air for the growth of plants because ofthe presence of adequate air spaces between the particles. It canbe ploughed easily. It can hold necessary nutrients required for the growth of plants.Fig. 11.3 Clayey soil ABSORPTION OF WATER BY S0ILLoamy soil Loamy soil contains clay, sand and silt in Wehave learnt that different soils have different right proportions. Humus is also present water holding capacities, i.e., different soils 108
  • 6. b water to different extent. Let us do an civity to understand this. Soil has many pores orgaps which allow water to flow down. Rainwater also passes through these pores. This water helps the plants to grow, and also increases the level of groundwater. The pores present in soil are filled with air. Air helps the animals living in soil to Activity samples of ndy soil and clayey soil in equal, say 50 g each. Place them in two separatequa helled 'S' for sandy and 'C for clayey. Dilutejadr Daint (by mixing some water with red s o m e paint) This will act as coloured water. Now, prepare breathe. two.oheakers containing each 100 mL coloured water. Keepa stopwatch ready. Now, gently pour coloured Which type of soil, sandy or clayey, will allow more of rainwater to seep into the soil? 'S. Note the time taken for the colouredwaterinjar water to appear fn the table given beloW. Repeat the activity with atthe base. Note your observation the clayey soil in jar 'C' Ooes the water take more or less time to appear Percolation rate of water in soil at the base? Activity Look for a place which has a good amount of soil, like a park or a garden. Dig at least 2 cm deep in the ground. Now, place a glass pipe here, as shown in the diagram. Measure 250 mL water and slowly pour into the pipe. Start the stopwatch immediately when you start pouring water into the pipe and note down the time. Note the time again when all the water percolates into the soil. You can now calculate the percolation rate by using the formula: JarS Jar C Time taken volumeofwater(mL) percolation time (min)Percolationrate Suppose the sample of soil taken by you takes 25 min for 250 mL water to percolate. The percolation rate can be calculated using the above formula as: What do you conclude from this activity? The larger the soil particles, the less time it takes for the water to pass because the space between the particles is larger. 250 ml Percolation rate = = 10 mL/min 25 min Can we try this activity with other soil samples? es, you may collect them from your School lawn, playground, park, etc. You Caneven try with sieved and unsieved Soil and see the results! Many characteristics ofsoil can be understood Do you think the rate of percolation of different soil samples will be the Irom the above activity: same? 09
  • 7. of time, they eat up most of the plant (orgrass) of that land. Ihis removes the vegetation cover from the topsoil. This bar topsoil can be easily carried away by rair or wind leading to soil erosion. Deforestation: This is another majorcaus for soil erosion. Cutting down of trees on large-scale is called deforestation. The t of the trees bind the soil particles. Strong winds and rainwater then carry away the Check PeINT 2 - Name the following. 1. Soil that can hold much water but is not well-aerated. ain 2. Soil that has the right water holding capacity and has sufficient air. 3. Soil that is well-aerated but cannot hold much water. 4. Soil that is considered the most fertile. 5. Soil that is difficult to plough. topsoil and cause soil erosion. 90IL EROSION As discussed earlier, the topsoil is very fertile. Strong winds, river water or heavy rains may carry away the topsoil. The removal of topsoil by either strong winds, fHowing river water or rain is called soil erosion. Soil erosion is more common in areas which are not covered by trees or grass and are bare. In the absence of any vegetation, the topsoil becomes loose and gets easily carried Fig. 11.6 Deforestation Excessive ploughing of fields: If farmers plough or till their tields excessively to grow crops, the soil in the field becomes loose and can be easily eroded by ran and strong wind. away. Fig. 11.5 Soil erosion Soil does not get eroded if it is covered by vegetation. The roots of the plants bind together the topsoil particles and prevent soil erosion. Fig. 11.7A farmer ploughing a field Causes of soil erosion Soil erosion can occur mainly due to: Can frequent flooding of rivers lead to soil erosion? Overgrazing: When cattle areallowedto graze on the same land tor a long period
  • 8. ects of soil erosion on can harm the environment in E f f e c t s Sol Wa Soil erosion can lead to floods, imaginenas and can also cause landslides in hilly about 500 years to get formed! We just cant We need to look after the soil as it takes vironment in millions ofyears to get formed. Can you imagine as little as 1 cm thick soil takes a r e a s . we need to look after our soil replace soil in our lifetime. Life on land depends on soil. Soil at many places is gettingDowe and rdeners add fertilisers to the damaged risk! and polluted. Soil is, therefore, at ntssos$O that they can grow properly. But ifexcess tertilisersPs fertilisers are used over a long time, Check PeINT 3. risk! damage the soil. Check PeINT 3.theymay Fill in the blanks. 1. Topsoil is very 2. Removal of topsoil is called 3. Overgrazing removes the topsoil COver from 4. Cutting down trees on a large-scale is called Fig. 11.8 A farmer adding fertiliser to crop KNOW THESE TERMS - naturally occurring loose covering of broken rock particles and humus on the earths surface which is capable of supporting life Soil Humus organic matter like dead and decaying remains of plants and animals present in the soil Soil erosion the removal of topsoil by either strong winds, fowing river water PRACTICE TIME A. MCQs-Choose the correct answers. 3. Which of the following soils is the best for 1. Which ofthese soil particles contain the largest rock particles? (a) silt growing crops? (a) sandy (c) loamy b) clayey d) none ofthese b) clay c)sand O(d) gravel 4. Which soil contains sand, silt and clay in right 2. The darkest layer of soil is a) subsoil proportions? (a) sandy (c) clayey b) loamy6 ) bedrock c) C-horizon Od) topsoil d) noneofthese 11