CBSE Class 7 Science Soil Worksheet Set A

Soil
Soil is a renewable natural resource. It supports various living organisms and is a medium of plant growth.
Topsoil is the uppermost layer of the Earth. It consists of humus. Factors such as variation of temperature, parent rock, decomposers and running water affect the formation of soil.
Fertile soil is essential for agricultural production. It has the following characteristics:
• It has enough moisture to supply essential nutrients to plants.
• It should have sufficient depth to enable the plants to grow their roots.
• It is rich in nutrients such as nitrogen, potassium and phosphorus.
• It contains organic matter.
The fertility of soil can be improved by adding fertilisers.

Classification of Soil
Based on its formation, soil can be classified into the following categories:
Sedimentary or Residual Soil: When soil is formed in its original position by fragmentation of the parent rock, it is called in situ or residual soil. This includes black soil, red soil, laterite soil and desert soil.
Transported Soil: These soils are formed after being transported and deposited by various agents of erosion such as water and wind. This includes alluvial soil.
Soil in India can be classified based on their texture, thickness, age, chemical and physical properties.

Alluvial Soil
• It is formed by the deposition of sediments brought down by the rivers. Very fine particles of soil called alluvium are deposited by the rivers in plains.
• It is also called riverine soil because it is mainly found in the river basins. It consists of sand, clay and silt known as loam.
• It has been deposited by the three Himalayan river systems—the Ganga, the Indus and the Brahmaputra. It is also found in deltas formed by rivers Mahanadi, Godavari, Krishna and Kaveri.
• Alluvial soil is classified into two types—khadar and bhangar.

Characteristics of Alluvial Soil
• It is formed by the deposition of sediments by the rivers as it flows from its upper to its lower course.
• While in the upper plains of the river valleys, the soil is coarse; it has fine soil particles in the lower river valleys.
• While the alluvial soil is dry, porous, sandy and faint yellow in the lower Ganga Valley, it becomes compact, less coarse and moist in West Bengal and Bangladesh.
• It is fertile as it is rich in minerals such as lime and potash. It is suitable for the growth of kharif and rabi crops.
• It is however deficient in nitrogen and humus. Only the alluvial soil of the Ganga delta is rich in humus.
• The alluvial soil is alkaline in drier areas

Differences between bangar and khadar soils

Black Soil 
This soil is also known as regur soil or black cotton soil (it is suitable for the growth of cotton). It is a residual soil as it is formed at the place of its origin.

Characteristics of Black Soil
• It is clayey and is finely textured soil.
• Because it is formed from weathered lava rocks, it is black. 
• It has about 50% of clayey material and hence is highly water retentive.
• When the soil becomes wet, it expands making ploughing difficult. During the dry season, the black soil shrinks and develops cracks which help in air circulation.
• The soil is suitable for the cultivation of cotton, jowar, sugarcane, wheat, linseed and gram. Besides, it is suitable for the growth of oilseeds, pulses, cereals, tobacco and vegetables.
• Its subsoil has moisture content even during rainy season.

Red Soil
Ancient crystalline and metamorphic rocks of the Peninsular Plateau fragmented to form the red soil. This soil differs from place to place on the basis of the parental rocks. They are red as they contain large amounts of iron oxide. It looks yellow when it occurs in a hydrated form.

Characteristics of Red Soil
• It is porous and contains large quantities of iron oxide.
• It is shallow, loose and aerated.
• It is deficit in nitrogen, phosphorus, potassium and organic matter. Small quantities of soluble salt are present in it.
• Because it is not very fertile, fertilisers are added to it.
• The soil requires irrigation.
• Red soil is suitable for the cultivation of rice, ragi, tobacco, groundnut and potatoes.

Laterite Soil
• It is formed because of the atmospheric weathering of rocks caused by high temperature and high rainfall. This residual soil is formed by leaching because of tropical rains.
• Leaching is a process in which the nutrients of the soil percolate down into the soil because of heavy rainfall. This makes the topsoil infertile. This is also called desilication.
• There are two types of laterite soils—upland laterites and lowland laterites. The former are formed over hills and uplands. When these soils are transported by streams of rivers to lowlands, it is called lowland laterites.

Characteristics of Laterite Soil
• It is red because of the presence of iron oxide formed during leaching.
• It has a coarse texture and is porous.
• It is deficient in lime, magnesium and nitrogen.
• It is not fertile as it does not retain moisture.
• It is acidic because of the leaching of alkalis.

Mountain Soil
The mountain soil is found in the hilly mountainous regions. This includes peat, meadow, forest and hill soils.

Desert soil: It is sandy soil. It is formed because of weathering of rocks in the desert regions.

Saline and alkaline soils: It has large amount of salts and alkalis. It is formed when the tidal water
accumulates in areas located near the coasts because of poor drainage.

Marshy soil: This soil is found in waterlogged areas, especially in coastal regions or near the deltas. It
contains iron and organic matter.

Distribution of soils in India

Alluvial soil Inland Alluvium: Plains of Indus, the Ganga and Brahmaputra rivers. It extends from Punjab to Bangladesh and Assam. It is also found in Haryana, Uttarakhand, Uttar Pradesh, Bihar, West Bengal and some parts of Gujarat and Rajasthan. Deltaic Alluvium: Deltas of Rivers Ganga–Brahmaputra, Mahanadi, Godavari, Krishna and Kaveri.

Coastal Alluvium: Coastal strips of Peninsular India and in the plains of Gujarat.

Black Soil Deccan lava traps including parts of Maharashtra, Gujarat, Madhya Pradesh, Andhra Pradesh, Karnataka, Rajasthan, Uttar Pradesh and some parts of Tamil Nadu.

Red Soil Parts of Tamil Nadu, Chhattisgarh, Jharkhand, Bundelkhand, Odisha, Meghalaya, Mizoram, Manipur and Nagaland. It is found in the Plateau regions of Peninsular India.

Laterite Soil Highland areas of the Peninsular Plateau. It is found in some parts of Madhya Pradesh, Maharashtra, Odisha, West Bengal, Andhra Pradesh, Karnataka, Kerala and Tamil Nadu.

Soil Erosion
The wearing away (due to the action of winds) and washing down of soil cover (due to running water) is known as soil erosion.

Soil Erosion by Water

Gully Erosion: This occurs during heavy rainfall when running water cuts through the soil making deep channels. The land thus becomes unsuitable for cultivation and is known as bad land.

Rill Erosion: It occurs when runoff water forms small channels running down the slope. It is an intermediate stage between sheet and gully erosion.

Sheet Erosion: The washing away of the topsoil because of flowing of water as a sheet over large areas is known as sheet erosion.

Leaching: When soil is bare of any vegetation, nutrients present in the soil percolate below the soil because of heavy rainfall. It makes soil infertile.

Stream Bank Erosion: It occurs when streams of rivers change their course by cutting one bank and depositing the silt on the other bank of the river.

Sea or Shore Erosion: The powerful waves of the sea dash against the coast and break the cliff rocks.
The fragmented material is then removed by the retreating sea waves. Eastern and western coasts have
experienced this kind of soil erosion.

Soil Erosion Due to Human Action
• Deforestation has resulted in soil erosion. Absence of any vegetation on the land leads to washing away of the soil.
• Overgrazing by domestic animals also leads to soil erosion.

Soil Erosion by Winds
• When the wind blows away the topsoil, it is known as wind erosion.
• When a bare land is exposed to high speed winds, smaller soil particles are removed in bouncing and hopping manner along the surface of the ground. This is known as saltation.
• The rolling and sliding of larger soil particles along the ground surface is known as soil creep.

In India, the following regions are affected by soil erosion:
• Badlands of Chambal and Yamuna rivers
• Western Himalayan region
• Chotanagpur Plateau region
• Tapti Sabarmati valley region in Gujarat
• Regur soil area of Maharashtra
• Dry areas of Rajasthan, Gujarat and Haryana

Methods to Prevent Soil Erosion

Soil can be conserved in the following ways:

• Contour Ploughing: When one ploughs along the contour lines, it is called contour ploughing. It decreases the flow of water down the slopes and thus helps in soil conservation.

• Terrace Farming: When steps are cut out on the slopes of the hills making terraces, it reduces soil erosion.

• Strip Cropping: When strips of grass are grown between the strips of crops, they are known as strip cropping. It breaks down the speed of winds.

• Shelter Belts: When trees are planted in a row, it breaks the force of the winds. This method has proved very useful in the station of dunes in the deserts of western India.

• Plugging of Gullies: The gullies made in the soil are plugged with deposition of silt during heavy rainfall.

Soil conservation is required to prevent the loss of soil fertility and agricultural productivity. Soil erosion may also increase the risks of droughts and floods. Landslides also occur because of deforestation and soil erosion.
In India, many programmes have been undertaken to prevent soil erosion. These are

1. Integrated watershed management programme was launched during the Sixth Plan in flood-prone rivers. The programme enhances the ability of the catchment by absorbing rainwater and reducing erosion.

2. A scheme for reclamation and development of ravine area was launched in 1987–88 in Madhya Pradesh, Uttar Pradesh and Rajasthan. The scheme included afforestation and reclamation of ravines.

3. The scheme was also launched for controlling shifting cultivation in the states of Arunachal Pradesh, Mizoram, Nagaland, Tripura and Assam.

4. National Project on Development and Use of Biofertilisers and National Project on Quality Control were implemented during the Seventh Five Year Plan. It aimed at balancing the use of fertilisers.

soil

ACTIVITY- 9.1 : To identify pH of soil. 

Question 1- What is the chemical nature of the soil having pH 3?
Answer- Acidic.

Question 2- What is the chemical nature of the soil having pH 10?
Answer- Basic.

Question 3- Write down the pH of neutral soil.
Answer- 7 (seven).

ACTIVITY- 9.2 : To find the rate of percolation of water. 

Question 1- In which type of soil rate of percolation is highest?
Answer- Sand.

Question 2- Which soil has maximum water retention capacity?
Answer- Clay.

ACTIVITY- 9.4 : To show the presence of air in the soil. 

Question 1- Why is soil tilled or ploughed?
Answer- The soil is tilled or ploughed to make it porous. Porous soil contains more air in it.

Question 2- What is the use of air present in soil?
Answer- Roots of plants use air present in soil.

EXERCISE

1- Fill In The Blanks.

(i) The top layer of earth up to a depth of 30-40 cm where crops can grow is called soil.
(ii) A section of earth shows horizons of soil.
(iii) Acidic nature or alkaline nature of soil can be tested by using a pH paper.
(iv) Clay has the finest particles which can even pass through muslin cloth.
(v) Sand soil has least water retention capacity.
(vi) Loamy soil is best for growing crops.
(vii) In western states of India like Gujarat and Maharashtra, the soil is of black colour.
(viii) Clay is used by potter for making earthen pots.
(ix) The soil which is used for making cement is clay
(x) Bricks are made from soil.

2- State True Or False.

(i) pH paper is used to test the acidic or alkaline nature of soil. (True)
(ii) Below a depth of 100 cm, the layer of earth is called soil. (False)
(iii) All crops grow better in sandy soil. (False)
(iv) Overgrazing of pasture lands is also responsible for soil erosion. (True)
(v) Mining can check soil erosion. (False)
(vi) Water can easily percolate through clayey soil. (False)

3- Match The Column ‘A’ With Column ‘B’
Column A                                                               Column B
(i) Water can easily percolate through                      (a) Pollution of soil
(ii) This soil is best for growing cotton                      (b) Soil erosion
(iii) Polythene, plastic and use of insecticides cause   (c) Clay
(iv) Mining, Overgrazing and deforestation cause      (d) Black soil
(v) This soil is used in the manufacture of cement     (e) Sandy soil
Ans.(i)-e,(ii)-d,(iii)-a,(iv)-b,(v)-c

4. Choose The Correct Answer.

Question. Which of these does not cause soil erosion:
a) Deforestation
b) Building of check dams 
c) Grazing cattle
d) Mining
Ans.b) Building of check dams

Question. Soil is polluted by:
a) Rotation of crops
b) Use of manure
c) Use of insecticides and fertilizers 
d) Using green manure
Ans.c) Use of insecticides and fertilizers

Question. Soil is not used for:
a) Making insecticides 
b) Making check dams
c) Making cement
d) Making earthen pots
Ans.a) Making insecticides

Question. Which of the following can check soil erosion:
a) Deforestation
b) Afforestation
c) Grazing of cattle
d) Mining
Ans.b) Afforestation

Question. Soil is used for:
a) Making cement
b) Growing crops
c) Making dams
d) All of these
Ans.d) All of these 

5- Very Short Answer Type Questions.

Question. What is humus?
Answer- Dead and decaying leaves or plants, dead bodies of insects or other animals buried in soil, cow dung etc. make the organic matter known as humus.

Question. Name the organic constituents of soil.
Answer- Dead and decaying leaves or plants, dead bodies of insects or other animals buried in soil, cow dung etc. make the organic constituents of soil.

Question. Name the inorganic constituents of soil.
Answer- Sand, gravel, clay, stones and minerals are the inorganic constituents of the soil.

Question. What do you mean by loamy soil?
Answer- The soil having particles size between clay and sand is known as loamy soil.

Question.Define soil erosion.
Answer- The washing away of the top layer of the soil by the action of floods, winds, storms and mining etc. is called soil erosion.

6- Short Answer Type Questions.

Question. What is soil profile?
Answer- Soil profile shows different layers of soil.

Question. Draw a labeled diagram of soil profile.
Answer-

Question. How does soil get polluted?
Answer- Soil gets polluted by –
(1) Excessive use of insecticides and chemical fertilizers,
(2) Throwing industrial waste, polythene and plastic waste in soil.

Question. Why should we plant more bamboo plants?
Answer- Growing bamboo plants are best for checking soil erosion.

Question. List the difference between clay soil and sandy soil?
Answer-
Clayey Soil                                                        Sandy Soil
1. It has very small particles.                          1. It has large particles.
2. Water holding capacity is very high.             2. Water holding capacity is very low.
3. It is fertile.                                                3. It is not fertile.
4. Very less air is trapped between particles.    4. Large air is trapped between particles.
5. Particles are tightly packed.                        5. Particles are loosely packed.

Question. What is check-dam? Why is it built?
Answer- In hilly areas check dams are built across small streams. This helps in preventing soil erosion.

7- Long Answer Type Questions.

Question. Explain how is soil formed?
Answer- Soil is formed by the breaking down of rocks by the action of wind, water and climate. This process is called weathering. It takes many years for the formation of fertile soil.

Question. Explain the various factors responsible for soil erosion.
Answer- (1) Floods- floods wash away the top layer of soil.
(2) Wind or Storm- Wind or storm carry away the top layer of the soil.
(3) Deforestation- When trees are uprooted, the soil becomes loose and is easily washed away.
(4) Over Grazing- When a grassland is grazed by cattle again and again, the soil becomes bare and loose and is easily eroded.
(5) Mining- Mining for stones and minerals is also a major factor for soil erosion.

Question. How is soil erosion checked? Explain.
Answer- (1) Afforestation- By planting more and more trees we can check soil erosion.
(2) Controlled Mining- Mining should be done in such a way that the mining area should not become prone to soil erosion.
(3) Alternate Grazing- The cattle should not be allowed to graze in the same pasture regularly.
(4) Making check dams- In hilly areas check dams should be built across small streams. This helps in preventing soil erosion.
(5) Fields should be surrounded by soil embankments and grass should be grown on these.
(6) Banks of rivers, canals should be made with stones and concrete.

Question. Classify the soil on the basis of size of particles?
Answer- (1) Clay- Soil in which particles are very fine, can even pass through muslin cloth.
(2) Sand- The particles of sand are bigger than clay. Generally, the desert soil is sand.
(3) Gravel- This type of soil has very large size of particles which can be picked by hand.
(4) Loamy soil- Its particles are of the size between clay and sand. It is the best for soil for crops.

More Question

1. GIVE ONE WORD FOR THE FOLLOWING___

a) The process of breaking down of the rocks due to climatic conditions_

b) Mixture of rock particles & humus___

c) The vertical section of different layers of soil___

d) The uppermost layer of the soil___

e) The soil best suitable for growing plants___

2. Give reason__

i) Clayey soil has a good water holding capacity

ii) Loamy soil is best suitable for growing plants

3. Differentiate between clayey soil & sandy soil (any 3 points)