# NCERT Solutions for Class 7 Science Chapter 9 Soil

These NCERT Solutions for Class 7 Science Chapter 9 Soil Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

## Soil NCERT Solutions for Class 7 Science Chapter 9

### Class 7 Science Chapter 9 Soil Textbook Exercise Questions and Answers

Question 1.
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
c. minerals, organic matter, air and water

Question 2.
The water holding capacity is the highest in
a. sandy soil
b. clayey soil
c. loamy soil
d. mixture of sand and loam
b. Clayey soil

Question 3.
Match the items in Column I with those in Column II:

 Column I Column II 1. A home for living organisms (a) Large particles 2. Upper layer of the soil (b) All kinds of soil 3. Sandy soil (c) Dark in colour 4. Middle layer of the soil (d) Small particles and packed tight 5. Clayey soil (e) Lesser amount of humus

1. (b)
2. (c)
3. (a)
4. (e)
5. (d)

Question 4.
Explain how soil is formed.
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.

Question 5.
How is clayey soil useful for crops?
Clayey soil can retain much water and consequently contains a lot of moisture even in summer. That’s why it is the most useful for crops like paddy which requires lot of water. Clayey soil is useful for wheat also.

Question 6.
List the differences between clayey soil and sandy soil.

 Clayey Soil Sandy Soil 1. Particles are of very small size. 1. Particles are of quite large size. 2. Particles are tightly packed together. 2. Particles are loosely packed. 3. Not aerated enough. 3. Well aerated. 4. Can retain water for long time. 4. Cannot retain water. 5. Water does not drain easily. 5. Water drains easily. 6. Fertile. 6. Not fertile. 7. Suitable for many crops. 7. Not suitable for crops.

Question 7.
Sketch the cross section of soil and label the various layers.

Question 8.
Razia conducted an experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.
Given amount of water = 200 mL
Percolation time = 40 min
Therefore, percolation rate = $$\frac{\text { Amount of water (mL) }}{\text { Percolation time (min) }}$$
= $$\frac{200 \mathrm{~mL}}{40 \mathrm{~min}}$$ = 5 mL/min

Question 9.
Explain how soil pollution and soil erosion could be prevented.
The persistent build-up of toxic compounds in the soil is defined as soil pollution. To prevent soil pollution, its causes must be controlled.

• 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.
• 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.
• Insecticides: Other pollutants of soil include pesticides and insecticides. Therefore, excessive use of these chemicals should be avoided.

Soil Erosion: Removal of topsoil by weathering agents, such as wind and water is known as soil erosion.

Causes of soil erosion:

• The cutting of down of forests whether for agriculture, construction of buildings, roads or dams often leads to soil erosion.
• The excessive use of chemical fertilisers and disposal of waste materials pollutes the soil, increasing the risk of erosion.
• The floods and overgrazing by animals also result in erosion of nutrient materials from the soil, making it infertile and unproductive.

Preventive measures for soil erosion: Soil erosion can be prevented to great extent by planting of trees and protecting forests. Government has started programmes like wasteland development, control and reclamation of ravines to prevent soil erosion.

Question 10.
Solve the following crossword puzzle with the clues given:
Across:
2. Plantation prevents it.
5. Use should be banned to avoid soil pollution.
6. Type of soil used for making pottery.
7. Living organism in the soil.
Down:
1. In desert soil erosion occurs through
3. Clay and loam are suitable for cereals like.
4. This type of soil can hold very little water.
5. Collective name for layers of soil.

Across:
2. Erosion
5. Polythene
6. Clay
7. Earthworm

Down:
1. Wind
3. Wheat
4. Sandy
5. Profile

Extended Learning Activities and Projects

Question 1.
Boojho would like to know the difference between raw and baked soil? Investigate how the soil from which matkas are made is different from the soil used to make statues.
Hint:

• Raw Soil: This type of soil contains many microorganisms in it like bacteria, fungi, etc., which are very useful for the growth of plants.
• Baked Soil: This soil is devoid of any living organisms because it is heated to a very high temperature as a result of which the microorganisms are killed.

Matkas are made from loamy soil as it is porous with large sized particles. Statues are made from clayey soil as it is smooth and moist.

Question 2.
Paheli is worried. She could see a brick kiln from her house. Bricks were being made there. There was so much smoke coming out of the kiln. She was told that the best quality of clay is required for making pottery, statues and bricks. She has seen truck loads of bricks being taken away for construction of buildings. At this rate, she fears, no soil will be left. Are her fears justified? Discuss this problem with your parents, teachers and other experts of your area and prepare a report.
Hint:
No, her fear is not to be justified because bricks and pots are only made by clayey soil and loamy soil is used for irrigation. Also, soil is a renewable resource.

Question 3.
Try to find out the moisture content of a soil sample. One method is given here.
Activity: Take 100 g soil. (Take help from any shopkeepers to weigh the soil). Place it on a newspaper in the sun and allow it to dry for two hours. This activity is best done in the afternoon. Take care that the soil does not spill outside the newspaper. After drying it, weigh the soil again. The difference in the weight of the soil before and after drying and is called the percentage moisture content.
Suppose your sample of soil loses 10 g on drying. Then percent of moisture in soil
= $$\frac{\text { wt. of moisture }(\mathrm{g})}{\text { Original wt. of soil sample (g) }} \times 100$$
In this example,
Percent of moisture in soil = $$\frac{10 \times 100}{100}$$ = 10%
Hint:
Do it yourself according to the activity.

Activity 1

Objective: To identify the various layers of the soil.
Materials Required: A glass tumbler, a sample of soil from your garden.
Procedure:

• Put some soil sample from your garden and place it in a glass tumbler.
• Fill the jar up to two-third of its height with water.
• Stir the mixture with the help of a spoon and allow it to stand for a few hours.
• Observe the contents of the tumbler.

Observations: Different layers appear in the tumbler. Gravel particles are the biggest and weigh more than sand, so the bottom layer will be the gravel part of the soil. Next up is the sand layer. Silt particles are smaller than sand and weigh less so they appear over the sand. Next up is the clay layer. Next up you will have the water. This is likely to be discoloured. Humus will be present on the topmost layer.

Conclusion: In this activity, we conclude that soil has different layers which include gravel, sand, silt, clay, water and humus.

Horizons: Layers of soil are referred to as horizons. Horizons of soil are categorised into four types: A-horizon, B-horizon. C-horizon and Bedrock.

• A-horizon: It is the topmost soil which is dark in colour and rich in humus. It is soft, porous and has the ability to retain water. It contains many organisms and plant roots.
• B-horizon: It is the middle next layer of the soil profile. It has lesser humus and more minerals. This layer is harder and more compact.
• C-horizon: The third layer of soil is known as C-horizon. C-horizon is made of small lumps of rocks with cracks and crevices.
• Bedrock: The layer below the C-horizon is known as bedrock. Bedrock is composed of rocks and is hard to dig with spades.

Types of Soil: The size of particles of the soil is very important for determining the properties of soil. Hence, soils are categorised mainly in three types based on the proportion of size of particles. These are sandy soil, clayey soil and loamy soil.
i. Sandy soil: It contains soil particles with a diameter of 0.2 to 2.0 mm. It comprises of around 60% sand along with some clay. It has very low water retention capacity. It is not rich in humus.
ii. Clayey soil: It contains soil particles with a diameter of less than 0.2 mm. It has an excellent water retention capacity and little space for air.
iii. Loamy soil: It is the most suitable soil for plant growth as it contains some large particles to keep the soil porous and some smaller particles for increasing its water holding capacity. This soil is a mixture of sand, silt and day. Silt occurs as a deposit in riverbeds and has particle size intermediate between sand and clay. Loamy soil is also rich in humus.

Important Uses of Soil: The soil is our most important natural resource. It is useful to us in many ways:

• Soil is used for growing food crops (like grains, pulses, fruits, vegetables, etc.).
• Soil is used to grow trees for obtaining wood for building purposes (timber), for burning as fuel (firewood) and for making paper.
• Soil is used to grow cotton plants which give us cotton clothes. Soil is also used to grow mulberry trees for rearing silkworms which provide us silk for making silk clothes.
• Soil is used to make bricks and mortar for building houses.
• Soil is used to make earthenware or pottery (such as matkas, surahis, etc.), crockery (cups and plates), toys, statues, etc.

Properties of Soil:
i. Percolation Rate of Water: Amount of water drained through the soil in unit time is known as percolation rate of water in that soil. Percolation rate of water can be calculated using the formula given below:
= $$\frac{\text { Amount of water (in mL) }}{\text { Time taken to percolate }}$$
Time taken to percolate The percolation rate of water in sandy soil is the fastest and in clayey soil is the slowest.

Activity 2

Objective: To determine the percolation rate of water in a soil sample.
Materials Required: PVC pipe (diameter 5 cm, length 20 cm) open from both ends.
Procedure:

• Fix one end of the pipe into the soil up to a depth of 2-3 cm.
• Pour 100 mL or 200 mL of water into the pipe and immediately note the time in your watch.
• Note the time when whole of the water has percolated down, i.e., there is no water left in the pipe.

Observation: Volume of water poured in the pipe, (say) V = 200 mL
Time taken by water to percolate down, (say) t = 40 min
Percolation rate of water in the soil = $$\frac{\text { Volume of water percolated }}{\text { Time taken for percolation }}$$
= V/t = 200 mL/40 min
= 5 mL/min

Conclusion: The percolation rate of water in the given soil sample is 5 mL per min.

ii. Moisture Content in Soil: Amount of water present in the soil naturally between the particles is called moisture present in soil. The amount of moisture present in clayey soil is the highest and that in the sandy soil is the lowest.

Activity 3

Objective: To find the moisture content of a soil sample.
Materials Required: A plastic funnel, filter paper, dry powdered soil, measuring cylinder and a dropper.
Procedure:

• Take a plastic funnel.
• Take a filter paper (or a piece of newspaper sheet), fold and place it in the funnel as shown in the figure.
• Weigh 50 g of dry, powdered soil and pour it into the funnel.
• Measure a certain amount of water in a measuring cylinder and pour it drop by drop on the soil. You can use a dropper for this purpose.
• Do not let all the water fall at one spot.
• Pour water all over the soil. Keep pouring water till it starts dripping.

Observations: Subtract the amount of water left in the measuring cylinder from the amount you started with. This is the amount of water retained by the soil. Record your results in the following manner:
Weight of soil = 50 g
Initial volume of water in the measuring cylinder = UmL
Final volume of water in the measuring cylinder = VmL
Volume of water absorbed by the soil = (U – V) mL
Weight of water absorbed by the soil = (U – V)g
(1 mL of water has weight equal to 1 g)
Percentage of water absorbed = $$\frac{(\mathrm{U}-\mathrm{V})}{50}$$ × 100
Conclusion: The given sample of soil contains _________ % (by mass) of moisture.

iii. Absorption of Water: Different soils absorb or hold different amounts of water. Clayey soil holds the highest amount of water because of its higher water retention capacity. On the other hand, sandy soil absorbs the least amount of water because of its lower water retention capacity.

Soil and Crops: The climatic factors as well as the composition of soil, determine the various types of vegetation and crops that might grow in any region.

• Clayey and loamy soils are both suitable for growing cereals like wheat and gram. Such soils are good at retaining water.
• For paddy, soils rich in clay and organic matter and having a good capacity to retain water are ideal.
• For lentils (Masoor) and other pulses, loamy soil, which drain water easily, are required.
• For cotton, sandy loam or loam, which drain water easily and can hold plenty of air are more suitable.
• Crops such as wheat are grown in the fine clayey soils because they are rich in humus and are very fertile.

Soil Pollution: Soil gets polluted by plastics and polythene bags thrown into it. They also kill the organisms living in the soil. Hence, we should ban the use of plastics and polythene bags. Pesticides sprayed on the crops in excess also pollute the soil. Waste products and chemicals released from factories also pollute the soil. They should be properly treated before their disposal.

Soil Erosion: Removal of topsoil by weathering agents, such as wind and water is known as soil erosion.
Causes of soil erosion:

• The cutting down of forests, whether for agriculture, construction of buildings, roads or dams, often leads to soil erosion.
• The excessive use of chemical fertilisers and disposal of waste materials pollutes the soil, increasing the risk of erosion.
• The floods and overgrazing by animals also result in erosion of nutrient materials from the soil, making it infertile and unproductive.

Preventive Measures for Soil Erosion: Soil erosion can be prevented to great extent by planting of trees and protecting forests. Government has started programmes like wasteland development, control and reclamation of ravines to prevent soil erosion.

### Class 7 Science Chapter 9 Soil Additional Important Questions and Answers

Question 1.
What is soil?
Mixture of rock particles, sand and humus is known as soil.

Question 2.
What is soil profile?
A vertical section through different layers of soil is known as soil profile.

Question 3.
What is soil erosion?
Removal of topsoil by weathering agents such as wind, water and ice is known as soil erosion.

Question 4.
What are horizons?
Layers of soil are called horizons. Horizons of soil are categorised into four types: A-horizon, B-horizon, C-horizon and Bedrock.

Question 5.
Define soil texture.
The soil texture is determined by the relative proportion of particles of different sizes. Soils of different textures feel different when rubbed between fingers.

Question 6.
What is bedrock?
The layer below the C-horizon is known as bedrock. Bedrock is composed of rocks and is hard to dig with spades.

Question 7.
Define weathering.
Soil is formed by the breakdown of the parent rock material by a very slow and gradual process called weathering.

Question 8.
Which absorbs more water-sandy soil or clay?
Clay absorbs more water.

Question 9.
Which is the layer of soil that contains the largest rock pieces?
Gravel or bedrock contains the largest rock pieces.

Question 10.
What is the role of plants in the formation of soil?
The roots of plants penetrate into the rocks and break them. In this way, plants help in the formation of soil.

Question 11.
How many layers are there in the soil profile?
There are four layers in the soil profile.

Question 12.
What is humus?
The rotting dead organic matter in the soil is called humans.

Question 13.
Name three different types of soils.
Sandy soil, Clayey soil, Loamy soil.

Question 14.
Which layer of soil contains humus.
The topsoil or A-horizon contains humus.

Question 15.
Which type of soil has the highest percolation rate of water?
Sandy soil.

Question 16.
Which type of soil would be the best for making pots, toys and statues?
Clayey soil.

Question 17.
What is C-horizon made up of?
It is made up of small lumps of rocks with cracks and crevices.

Question 18.
Define percolation rate.
It is the ratio of the amount of water percolated through the soil to the percolation time. It indicates the water holding capacity of the soil.

Question 19.
Name the five factors controlling soil formation.
Soil formation is controlled by five factors namely, nature of parent rock, the topography, the climate, the organisms in the soil and time.

Question 20.
What are natural resources?
Natural resources are the resources which are provided by nature to support life. For example, water, air, minerals, sunlight and various life forms.

Question 1.
Which soil will hold more water-sandy soil or clayey soil? Why?
Clayey soil will hold more water. Clayey soil mostly contains clay. Water drains through it very slowly since the particles are very small and tightly packed.

Question 2.
What is humus?
Humus is dark brown in colour and consists of decaying remains of plants and animals. A variety of dead and decaying organisms contribute to the formation of humus. Humus makes the soil fertile by providing organic nutrients. It also provides food to earthworms and other animals living in the soil.

Question 3.
Explain which horizon of soil is most suitable to grow plants and why?
Top layer of soil, i.e., A-horizon is the most suitable for this. A-horizon is generally dark in colour. It is rich in humus and is hence fertile. A-horizon is generally soft and porous. It retains more water. Roots of small plants are entirely embedded in topsoil. Topsoil also provides shelter to many living organisms, such as worms, insects, moles, rats, snakes, etc., which all enhance soil fertility.

Question 4.
How is loamy soil very useful for the crops?
Particles of loamy soil are smaller than sand and larger than clay. Loamy soil is the mixture of sandy soil, clayey soil and silt. Silt is the deposit in riverbeds. Loamy soil has right water holding capacity and is well aerated. Hence, this is considered as the best soil for the growth of plants.

Question 5.
What makes soil a shelter for many living organisms?
Soil contains organic materials, such as starch, sugar, cellulose, fats, proteins and remains of dead organisms. These give energy to living organisms. Air, water and minerals present in soil also give enough energy to living organisms to sustain themselves.

Question 6.
List the different processes that help to produce soil.
There are four processes responsible to produce soil:

1. Weathering of rocks
2. Earthquakes or volcanic eruptions
3. Corrosion or decomposition of rocks by chemical processes

Question 7.
How is soil erosion harmful for the soil?

• It is leads to the loss of soil fertility,
• It results in the formation of gullies by flowing water.
• The soil taken away by wind or flood often gets deposited which is bad for aquatic life.

Question 8.
What factors affect the soil profile and bring changes in the soil structure?
Soil is affected by wind, rainfall, temperature, light and humidity. These are some important climatic factors which affect the soil profile and bring changes in the soil structure.

Question 9.
Why is there a demand to ban the use of polythene bags and plastics?
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 use of polythene bags and plastics.

Question 10.
What are the properties of loamy soil?

• 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.
• The loamy soil also has humus in it.
• It has the right water holding capacity for the growth of plants.
• It’s particle size is in between those of clay and sand.

Question 11.
What are the properties of clayey soil?

• Clay particles, being much smaller, pack tightly together leaving little space for air.
• Water can be held in the tiny gaps between the particles of clay. So clay soils have little air.
• They are heavy as they hold more water than the sandy soils.

Question 12.
Why is soil regarded as one of the most important natural resources?
Or
Why is soil an inseparable part of our life?
Soil is one of the most important natural resources. It supports the growth of plants by holding their roots firmly and supplying water and nutrients to them. 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.

Question 13.
What are the properties of sandy soil?

• Sand particles are quite large.
• Sand particles cannot fit closely together, so there are large spaces between them. These spaces are filled with air. So, the sand is well aerated.
• Water can drain quickly through the spaces between the sand particles. So, sandy soils tend to be light and dry.

Question 14.
Is it a good practice to remove grass and small plants that are growing in an open, unused field? Give reasons for your answer.
No, it is not a good practice. Plants cover the soil surface and their roots bind the soil particles and hold them in place. During strong winds and rains they prevent soil erosion and thereby protect the topsoil. Hence, we should not remove them.

Question 1.
What is soil erosion? What are the preventive measures for soil erosion.
Soil Erosion: Removal of topsoil by weathering agents, such as wind, water and ice is known as soil erosion. Soil erosion affects the fertility of soil, as humus present in the soil is eroded along with the soil. Hence, it is important to prevent soil erosion.

Preventive measures for soil erosion:

• Deforestation should be prevented at all costs to prevent soil erosion.
• Shelterbelt plantation of trees is good for preventing soil erosion.
• Terrace farming in hilly areas is effective in preventing soil erosion.

Question 2.
What is soil? Discuss its properties?
Soil: Mixture of rocks particles, sand and humus is known as soil. Soil supports the growth of plants by holding their roots and supplying water to them.

Properties of soil are:
a. Percolation Rate of Water: The Amount of water drained through the soil in unit time is known as percolation rate of water in that soil. Percolation rate of water can be calculated using the formula given here.
Percolation rate (mL/min) = $$\frac{\text { Amount of water in } \mathrm{mL}}{\text { Time taken to percolate }}$$
The percolation rate of water in sandy soil is the highest and in clayey soil is the lowest.

b. Moisture in Soil: Amount of water present naturally between the particles in soil is called moisture present in soil. The amount of moisture present in clayey soil is the highest and that in sandy soil is the lowest.

c. Absorption of Water: Different soils absorb different amounts of water. Clayey soil holds the highest amount of water because of its higher water retention capacity. On the other hand, sandy soil absorbs the least amount of water because of its lower water retention capacity.

Question 3.
Distinguish between clay, silt and sand.
a. Clay has the smallest size of particles. In fact, you cannot see a single clay particle. Clay feels smooth because of its small particle size. It has highest water holding capacity and least air spaces.

b. Silt has particles larger than clay (diameter between 0.002 mm and 0. 2 mm). Therefore, it is not so smooth. For example, it can be found in a river bed. It has intermediate air spaces and water holding capacity as compared to clay and sand.

c. Sand has the largest-sized particles, which can easily be seen (diameter greater than 0.2 mm). They are coarse to touch. It has highest air spaces and least water holding capacity.

Question 4.
Describe the different layers of soil profile.
Different layers of soil profile are as follows:
a. The uppermost horizon is generally dark in colour as it is rich in humus and minerals. The humus makes the 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. 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.

b. 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.

c. The third layer is the C-horizon, which is made up of small lumps of rocks with cracks and crevices.

d. Below this layer is the bedrock, which is hard and difficult to dig with a spade.

Question 5.
How does absorption of water by the soil differ from percolation of water through the soil?
Water absorption capacity of a soil is described in terms of the amount of water absorbed by a particular type of soil. High water absorption means higher water retention capacity of the soil. Percolation property of any material is linked to its porosity. Different soils have different porosity. Therefore, water percolates differently through different soils. Higher the percolation rate through a soil, lower is its water retention capacity.

Percolation rate of water in the soil = $$\frac{\text { Volume of water percolated (mL) }}{\text { Time taken for percolation (min) }}$$

Picture-Based Questions

Question 1.
Observe the given picture and answer the following questions.

a. Some people are doing work in the given picture. Guess and tell what are they doing?
b. Which type of soil is used to do this?
c. What is the main property of such type of soil?
a. In the above picture, people are making pots.
b. Clayey soil is used for making pots.
c. The water holding capacity of this soil is the highest among all soils and the particles are compactly held.

Question 2.
Observe the given picture and answer the following questions.

a. Which is the heaviest rock material?
b. Which is the lightest soil component?
c. Why different layers of soil components are formed?