Chapter 10 | Soil | Class-7 DAV Science Solutions

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DAV Class-8 Soil Question and Answer

Something To Know

A. Fill in the blanks.

1. Various layers in the soil are called ___________.

2. The intermediate particles, that are neither very rough, nor too smooth, are termed as ___________.

3. ___________ is the tendency of similar particles to stick to one another.

4. Soil air is important for roots to carry out ___________.

5. ___________ and ___________ cause soil pollution.

Answer: (1) soil horizons (2) silt (3) Cohesion (4) breathing (5) Insecticides, fertilisers

B. Match the following:

1. Potter’s soil ———————–> (b) Clay

2. Organic material ——————> (d) Humus

3. Vermicompost ——————-> (e) Earthworms

4. Sandy soil ———————> (c) Well aerated

5. Concrete floor ——————> (a) No percolation

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

C. Tick the correct option.

1. Which of the following is not an agent of physical weathering?

Ans 1. organic acids

2. Which of these is the lowest horizon of soil profile?

Ans 2. bedrock

3. Which organism is known as nature’s ploughman?

Ans 3. earthworm

4. Which soil can retain more water?

Ans 4. clayey soil

5. Coconut trees thrive in coastal regions where the soil present is mainly—

Ans 5: sandy loam

D. Answer the following questions in brief.

Q. 1. State the meaning of the term ‘soil.

Ans 1: Soil is the naturally occurring, loose covering of broken rock particles and decaying organic matter on the surface of the earth.

Q. 2. List the four main agents of physical weathering.

Ans 2: Temperature, water, wind, and plants are the main agents of physical weathering.

Q. 3. Write one difference between sand, clay and silt.

Ans 3: one difference between sand, clay and slit are as follows:

Sand- The bigger, coarse soil particles are termed sand.

Clay- The smaller particles, that are smooth, are termed clay.

Slit- The intermediate particles, that are neither very rough nor too smooth, are termed silt.

Q. 4. Name the types of soil classified on the basis of soil texture.

Ans 4: On the basis of soil texture, soil is classified into three categories: sandy soil, clayey soil and loamy soil.

Q. 5. Give the meaning of the term ‘Cohesion’.

Ans 5: the tendency, of similar particles, to stick to one another.

Q. 6. List any three causes of soil pollution.

Ans 6: three causes of soil pollution are:

  • (1) use of chemical pesticides 
  • (2) excessive use of fertilisers 
  • (3) oil and fuel dumping

E. Answer the following questions.

Q. 1. Classify, and explain, the categories of soil on the basis of ‘texture of the soil.

Ans 1: On the basis of soil texture, the soil is classified into three categories- sandy soil, clayey soil and loamy soil.

(1) Sandy soils – Sandy soils have soil particles that are bigger in size; the large spaces between them are filled with air. They are, therefore, said to be well aerated. Such soils cannot retain water as water can drain out quickly through the spaces between the sand particles. Sandy soil needs more frequent irrigation for successful crop growth.

(2) Clayey soils – Clayey soils have a higher proportion of fine and smooth soil particles. There is very little space between the soil particles. Such soils cannot retain air. However, clayey soils can retain more water than sandy soils. This high-water holding capacity can cause problems, like water-logging, in the fields.

(3) Loamy soil – Loamy soil is a mixture of sand, silt and clay particles. It can hold both air and water. Loamy soil has humus also. It is considered to be the best soil for growing most of the crops.

Q. 2. Differentiate between infiltration rate and percolation rate.

Ans 2: Infiltration rate – The rate at which water enters the soil is called infiltration rate. 

Percolation rate – The rate at which water moves through soil is called percolation rate.

Q. 3. Write a short note on ‘composition of soil.

Ans 3: The composition of soil depends on the nature of parent rock and the quantity and type of organic materials present in it. The following components are generally found in soil:

(1) Inorganic substances: Most of the inorganic substances, present in the soil, are derived from the parent rock.

(2) Organic material (Humus): Humus increases the productivity and water holding capacity of the soil.

(3) Soil water: It is generally present in the spaces between the soil particles. The water content of soil has a significant effect on plant productivity.

(4) Soil air: Spaces, between the soil particles, contain air. Well aerated soils are associated with healthy roots that increase crop productivity. Soil air is important for the respiration of roots. 

(5) Living organisms: A variety of organisms are found in soil. They include micro-organisms like bacteria, fungi and algae.

Q. 4. “The type of crop that may be grown in a particular field depends on the type of soil: Give three examples in support of this statement.

Ans 4: Three examples that support this statement are as follows:

(1) Rice grows well in clayey soil.

(2) Wheat grows well in a loamy soil.

(3) Cotton grows well in sandy loam or loamy soil.

Q. 5. What is soil erosion? How can it be avoided?

Ans 5: The removal of topsoil by agents, such as wind and water, is called soil erosion. Agriculture, deforestation, overgrazing and careless cultivation speed up erosion.

Soil erosion can be avoided by extensive afforestation, avoiding overgrazing and overuse of land.

Q. 6. Why is it said that ‘plasticity’ and ‘cohesion, play an important role in the workability of a soil?

Ans 6: Because of plasticity, a particular type of soil can be given any shape. Sandy soil is non-plastic, while clayey soil is plastic in nature. Plastic soil is cohesive in nature which means the particles of soil stick together. Unlike sandy soil; clayey soil can be used for making earthenware. This shows that plasticity and cohesion play an important role in the workability of soil.

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