NCERT Textbook Exercises

Q1. Tick the most suitable answer in questions 1 and 2.
In addition to the rock particles, the soil contains:

(iii) minerals, organic matter, air and water.

Q2. The water holding capacity is the highest in:

(ii) clayey soil.

Q3. Match the items in Column I with those in Column II:

Column I	Column II
A home for living organisms	All kinds of soil
Upper layer of the soil	Dark in colour
Sandy soil	Large particles
Middle layer of the soil	Lesser amount of humus
Clayey soil	Small particles and packed tight

Q4. Explain how soil is formed.

Soil is formed by the breaking down of rocks by the action of wind, water and climate. This process is called weathering.

Q5. How is clayey soil useful for crops?

Clayey soil is useful for crops like wheat and paddy (rice) because:

It has very good water holding capacity.
It is rich in organic matter.
It is very fertile.

Q6. List the differences between clayey soil and sandy soil.

Clayey Soil	Sandy Soil
Fine particles.	Large particles.
Tightly packed (less air).	Loosely packed (well aerated).
Good water holding capacity.	Poor water holding capacity.
Heavy to plough.	Light to plough.

Q7. Sketch the cross section of soil and label the various layers.

(Ref: Soil Profile Diagram in textbook)

A-Horizon (Topsoil): Dark, rich in humus, soft, porous.
B-Horizon (Subsoil): Lighter colour, harder, compact, rich in minerals.
C-Horizon: Small lumps of rocks with cracks.
Bedrock: Hardest layer at the bottom.

Q8. 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.

Amount of water = 200 mL
Percolation time = 40 min
Rate of percolation = Amount of water / Percolation time
= 200 / 40
= 5 mL/min

Q9. Explain how soil pollution and soil erosion could be prevented.

Prevention of Soil Pollution:

Use of polythene bags and plastics should be banned.
Waste products and chemicals should be treated before release.
Use of pesticides should be minimised.

Prevention of Soil Erosion:

Planting more trees (Afforestation).
Preventing deforestation.
Preventing overgrazing.

Q10. Solve the following crossword puzzle... (Not included here).

(Please refer to the textbook for the puzzle).

Extra Important Questions

Q11. What is Humus?

The rotting dead matter in the soil is called humus. It makes the soil fertile and provides nutrients to plants.

Detailed Chapter Topics

1. Soil Profile (Layers)

A-Horizon (Topsoil): Dark colour, rich in Humus and Minerals. Soft, porous, holds water. Home to worms/microbes. Roots grow here.
B-Horizon (Subsoil): Lighter colour. Harder and compact. Rich in minerals, less humus.
C-Horizon: Small lumps of rocks with cracks.
Bedrock: Hard bottom layer. Difficult to dig.

2. Types of Soil

Sandy Soil: Big particles. Large air spaces. Water drains quickly. Light and dry.
Clayey Soil: Fine particles. Tightly packed. Little air. Holds lot of water. Heavy.
Loamy Soil: Mixture of Sand, Clay and Silt. Best for growing plants. Has humus and correct water holding capacity.

3. Soil Properties

Percolation Rate: Speed at which water passes down. Highest in Sandy, Lowest in Clayey.
Moisture: Soil holds water (moisture). Evaporation of this moisture cools the air.
Absorption: Soil absorbs water. Clayey absorbs most, Sandy absorbs least.

4. Soil and Crops

Clayey/Loamy: Good for Wheat, Gram (Retain water).
Clayey: Good for Paddy (Needs standing water).
Loamy: Good for Lentils (Masoor) and Pulses (Drains water easily).
Sandy Loam: Good for Cotton (Plenty of air, drains water).

Key Facts and Definitions

1. Important Terms

Weathering: Breakdown of rocks by wind, water, climate to form soil.
Humus: Dead, rotting organic matter.
Soil Erosion: Removal of land surface by water, wind or ice.
Silt: Soil particles deposited in river beds (Size between sand and clay).

2. Quick Facts

It takes hundreds of years to make just a few centimetres of soil.
Polythene bags and plastics pollute the soil and kill organisms.
Cutting of trees (Deforestation) leads to loose soil and severe erosion.
Making pots, toys and statues is done using **Clayey** soil.

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