Keywords To Remember
Keyword | Definition |
Soil | The uppermost layer of the Earth’s surface that supports life; made up of minerals, organic matter, air, and water. |
Weathering | The natural process of breaking down rocks into smaller particles due to wind, water, temperature, and biological activity. |
Humus | The dark, organic material in soil formed from decayed plants and animals. It enriches the soil and improves its texture. |
Soil Profile | A vertical section of the soil that shows different layers or horizons. |
Soil Horizons | Different layers of soil in a soil profile, typically labeled as O, A, B, C, and R. |
Topsoil (A Horizon) | The uppermost layer of soil, rich in organic matter and crucial for plant growth. |
Subsoil (B Horizon) | The layer below topsoil containing minerals leached from the upper layers. |
Parent Rock (C Horizon) | The layer of large rocks from which soil is formed through weathering. |
Bedrock (R Horizon) | The solid layer of rock beneath the soil layers. |
Soil Texture | The feel of soil based on the size of its particles (sand, silt, clay). |
Clay Soil | Soil made mostly of the smallest particles; holds water well but has poor drainage. |
Sandy Soil | Soil with large particles; drains quickly but holds little water. |
Loamy Soil | A balanced mixture of sand, silt, and clay; ideal for plant growth. |
Silt | Soil particles that are medium in size, between sand and clay, smooth and powdery. |
Porosity | The amount of space between soil particles; affects water retention. |
Percolation | The movement of water through soil layers. |
Moisture | The amount of water present in soil. |
Soil Erosion | The removal of the topsoil by wind, water, or human activity. |
Soil Conservation | Techniques used to protect soil from erosion and degradation. |
Manure | Organic matter added to soil to improve fertility. |
Fertilizer | Chemical or natural substances added to soil to promote plant growth. |
Crop Rotation | The practice of growing different crops in succession to maintain soil fertility. |
Mulching | Covering the soil with leaves or straw to prevent water loss and erosion. |
Leaching | The process by which nutrients are washed away from the soil by rain or irrigation. |
Soil Fertility | The ability of soil to supply nutrients to plants. |
Organic Matter | Material derived from living organisms, important for soil structure and fertility. |
Capillary Action | The ability of water to move through the spaces in soil due to surface tension. |
Soil Pollution | The presence of harmful chemicals in soil, often due to industrial waste or excessive use of fertilizers. |
Soil Aeration | The process of introducing air into soil, which helps roots to breathe. |
Soil pH | A measure of the acidity or alkalinity of soil, affecting nutrient availability. |
Water Holding Capacity | The ability of soil to retain water for use by plants. |
Soil Structure | The arrangement of soil particles into groups called aggregates. |
Erosion Control | Methods such as planting grass or building terraces to prevent soil erosion. |
Compost | Decayed organic material used as plant fertilizer. |
Terracing | Farming method of creating steps on slopes to reduce water runoff and soil erosion. |
Afforestation | Planting trees to prevent soil erosion and enhance soil quality. |
Something To Know
A. Fill in the blanks.
- Various layers in the soil are called ____________ .
Answer – soil horizons
- The intermediate particles, that are neither very rough, nor too smooth, are termed as ____________ .
Answer – silt
- ____________ is the tendency of similar particles to stick to one another.
Answer – Cohesion
- Soil air is important for roots to carry out ____________ .
Answer – respiration
- ____________ and ____________ ; cause soil pollution.
Answer – Industrial waste and excessive use of fertilizers
B. Match the following:
- Potters soil (a) No percolation
- Organic material (b) Clay
- Vermicompost (c) well aerated
- Sandy soil (d) Humus
- Concrete floor (e) Earthworms
Answer –
Column A | Column B |
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 |
C. Tick (✓) the correct option.
- Which of the following is not an agent of physical weathering?
Wind
Water
Temperature
Organic acids
Answer – Organic acids
- Which of these is the lowest horizon of soil profile?
Subsoil
gravel
bed rock
humus
Answer – bed rock
- Which organism is known as nature’s ploughman?
honeybee
bird
rat
earthworm
Answer – earthworm
- Which soil can retain more water?
sandy soil
loamy soil
clayey soil
polluted soil
Answer – clayey soil
- Coconut trees thrive in coastal regions where the soil present is mainly—
clayey soil
sandy soil
loamy soil
sandy loam
Answer – sandy soil
D. Answer the following questions in brief.
- State the meaning of the term soil’
Answer – Soil is the topmost layer of the earth’s crust that supports plant life and is formed by the weathering of rocks.
- List the four main agents of physical weathering.
Answer – Wind, water, temperature changes, and glaciers.
- Write one difference between sand, clay and silt.
Answer – Sand has large particles and drains quickly.
Clay has very fine particles and holds water well.
Silt has medium-sized particles and feels smooth.
- Name the types of soil classified on the basis of soil texture.
Answer – Sandy soil, clayey soil, loamy soil, and silty soil.
- Give the meaning of the term ‘Cohesion’.
Answer – Cohesion is the property of similar soil particles sticking together.
- List any three causes of soil pollution.
Answer – Use of chemical fertilizers and pesticides
Industrial waste
Improper disposal of plastics and non-biodegradable waste
E. Answer the following questions
- Classify, and explain, the categories of soil on the basis of ‘texture of the soil’.
Answer – Sandy soil: Large particles, poor water retention
Clayey soil: Fine particles, high water retention
Loamy soil: Balanced mixture of sand, silt, and clay; best for crops
Silty soil: Smooth texture, retains water better than sand
- Differentiate between infiltrations rate and percolation rate.
Answer – Infiltration rate: Speed at which water enters the soil surface.
Percolation rate: Speed at which water moves through soil layers.
- Write a short note on ‘composition of soil’.
Answer – Soil is composed of mineral particles, organic matter (humus), air, water, and living organisms.
- ‘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.
Answer – Rice – grows well in clayey soil
Wheat – grows well in loamy soil
Coconut – grows well in sandy soil
- What is soil erosion? How can it be avoided?
Answer – Soil erosion is the removal of topsoil by wind or water. It can be avoided by planting trees, contour ploughing, and using cover crops.
- Why is it said that ‘plasticity’ and ‘cohesion’, play an important role in the workability of a soil?
Answer – Plasticity allows soil to be molded, while cohesion holds soil particles together. Both properties help in shaping and using soil for farming or pottery.
Value Based Question
On the ‘opening day’, the school principal, and teachers, welcomed the parents and guardians of their ‘new students’ The principal went on to say that the parents and the teachers, both have a crucial role to play, in the growth and development of the children. She compared their roles with the role of the physical and chemical agents that cause the weathering of the soil and make it suitable for supporting, and sustaining, the growth of all forms of life.
- State any two of the values that parents/teachers generally display during the growth of their children.
Answer – Patience
Nurturing and guidance
- Write, in brief, the role of (i) Plants and animals (ii) Solvent action of water in the ‘weathering’ of the soil.
Answer – Plants and animals: Roots break rocks; burrowing animals help in mixing soil.
Water: Dissolves minerals and breaks rocks through freezing and thawing.
Something To Do
- Visit a potter: Potters are difficult to find in cities. Try finding such a place, and visit it with your teacher and classmates. Observe the texture of the soil used by the potter. Can he make pots using sand? How does the property of plasticity differ in sand and clay?
Answer – A potter cannot make pots using sand because it lacks plasticity. Clay has high plasticity, making it moldable, while sand is loose and cannot hold shape.
- Take three pots and fill them with sand, clay and loamy soil. Sow similar wheat grains, or seeds of green gram, in each of these pots. Water them regularly, using the same amount of water, for each pot. Record your observation about the growth of the plants. What do you infer?
Answer – Plants grow best in loamy soil due to balanced moisture and nutrients. Poor growth in sand due to low water retention; clay holds too much water, which may rot roots.
Inference: Loamy soil is best for plant growth.
- Make a group of six. Find out the main crops grown in any three states of India. Also find out the types of soil they are grown in. Make a PowerPoint presentation on your report.
Answer – Punjab: Wheat – Loamy soil
West Bengal: Rice – Clayey soil
Gujarat: Cotton – Black soil
Rest part of making PPT will be carried out by the students.
Additional Questions And Answers – 01
Fill in the Blanks
The process of breakdown of rocks to form soil is called ____________.
Answer: weathering
____________ soil is best suited for growing cotton.
Answer: Black
The topmost layer of soil is called the ____________.
Answer: topsoil
____________ soil has the highest water holding capacity.
Answer: Clayey
Soil rich in humus and minerals is called ____________ soil.
Answer: loamy
Soil profile consists of ____________ main horizons.
Answer: three
Soil fertility can be increased using ____________ and ____________.
Answer: manure, fertilizers
The movement of water into the soil is known as ____________.
Answer: infiltration
Excessive rainfall can lead to soil ____________.
Answer: erosion
____________ are the microorganisms that help in decomposing organic matter in soil.
Answer: Bacteria
Multiple Choice Questions (MCQs)
Which of the following is the most fertile layer of soil?
Subsoil
Bedrock
Topsoil
Clay
Answer: C. Topsoil
Which soil is best suited for growing lentils and pulses?
Sandy soil
Loamy soil
Clayey soil
Gravel
Answer: B. Loamy soil
Which soil has the least capacity to hold water?
Sandy soil
Loamy soil
Clayey soil
Alluvial soil
Answer: A. Sandy soil
Soil colour is mainly determined by the amount of:
Moisture
Humus
Gravel
Sand
Answer: B. Humus
The uppermost layer of the soil that supports plant life is:
Bedrock
Subsoil
Topsoil
Parent rock
Answer: C. Topsoil
True or False
- Loamy soil contains sand, silt, and clay in equal proportions.
Answer: True - Soil is a renewable resource that forms quickly.
Answer: False - The soil profile includes humus, topsoil, and groundwater.
Answer: False - Red soil is rich in iron content.
Answer: True - Water does not percolate through clayey soil.
Answer: False
Short Answer Questions
- What is humus?
Answer: Humus is the dark, organic component of soil formed from decomposed plant and animal material. - Define percolation rate.
Answer: Percolation rate is the rate at which water moves through the soil. - What causes soil erosion?
Answer: Soil erosion is caused by water, wind, and human activities like deforestation and overgrazing. - What is the function of soil in plant growth?
Answer: Soil provides nutrients, water, and support for plant roots. - Name any two organisms that live in soil and help in improving its quality.
Answer: Earthworms and bacteria.
Competency-Based Reasoning & Assertion
- Assertion: Clayey soil is good for paddy cultivation.
Reason: It retains water for a longer period.- Both A and R are true, and R is the correct explanation.
- Both A and R are true, but R is not the correct explanation.
- A is true, R is false.
- A is false, R is true.
Answer: A
- Assertion: Loamy soil is ideal for farming.
Reason: It is a mixture of sand and clay only.
Answer: A is true, R is false - Assertion: Plants grow well in topsoil.
Reason: Topsoil is rich in minerals and humus.
Answer: Both A and R are true, and R is the correct explanation.
High Order Thinking Skills (HOTS)
- Why do farmers prefer loamy soil for agriculture despite the presence of clayey and sandy soils?
Answer: Loamy soil has the right balance of air and moisture, retains nutrients, and supports root development better than sandy or clayey soils. - How does deforestation affect the fertility of soil?
Answer: Deforestation reduces the organic content in soil, increases erosion, and reduces the ability of the soil to retain water and nutrients. - Suggest ways to reduce soil erosion in hilly areas.
Answer: Planting trees, building terraces, and using contour plowing can help reduce soil erosion in hilly areas.
Long Answer Questions (50–60 words)
- Explain the process of soil formation and factors affecting it.
Answer: Soil forms through weathering of rocks due to temperature changes, wind, water, and biological activity. Over time, these forces break down rocks into fine particles mixed with organic matter. Factors like climate, topography, parent rock, and organisms influence the nature and fertility of the soil. - Describe the composition of soil and how each component contributes to plant growth.
Answer: Soil is made up of minerals, organic matter (humus), air, and water. Minerals provide nutrients, humus improves fertility, air helps in root respiration, and water dissolves minerals for root absorption. Each component is essential for healthy plant development. - How does human activity contribute to soil pollution?
Answer: Use of chemical fertilizers, industrial waste disposal, deforestation, and plastic waste lead to soil pollution. These activities degrade soil quality, harm soil organisms, and affect the growth of plants by introducing harmful chemicals and reducing soil fertility.
Additional Questions And Answers – 02
Fill in the Blanks
- Soil is formed by the process of ________, which includes physical and chemical processes.
Answer: Weathering
- The top, organic layer of soil, made up of leaf litter and humus, is called the ________ horizon.
Answer: O
- ________ soils have larger particles with spaces filled with air, making them well aerated.
Answer: Sandy
- The rate at which water enters the soil is called the ________ rate.
Answer: Infiltration
- ________ is the removal of top soil by agents like wind and water.
Answer: Soil erosion
- The arrangement of soil horizons in a soil is known as a soil ________.
Answer: Profile
- ________ soils are a mixture of sand, silt, and clay, ideal for growing most crops.
Answer: Loamy
- The property that allows moist soil to change shape and retain it is called ________.
Answer: Plasticity
- Earthworms are known as nature’s ________ because they improve soil structure.
Answer: Ploughmen
- Soil pollution is caused by the build-up of toxic compounds, chemicals, and ________ materials.
Answer: Radioactive
Multiple Choice Questions (MCQs)
- What is soil primarily composed of?
- a) Solid rocks and water
- b) Broken rock particles and humus
- c) Air and sunlight
- d) Only organic matter
Answer: b) Broken rock particles and humus
- Which horizon is also known as top soil?
- a) O Horizon
- b) A Horizon
- c) B Horizon
- d) R Horizon
Answer: b) A Horizon
- Which type of soil is best for growing most crops due to its balanced texture?
- a) Sandy soil
- b) Clayey soil
- c) Loamy soil
- d) Silt soil
Answer: c) Loamy soil
- What is the main cause of soil erosion in areas without human activity?
- a) Afforestation
- b) Wind and water
- c) Overgrazing
- d) Industrial development
Answer: b) Wind and water
- Which of the following is a cause of chemical weathering?
- a) Expansion and contraction due to temperature
- b) Solvent action of water
- c) Abrasive action of wind
- d) Growth of plant roots
Answer: b) Solvent action of water
- What type of soil is ideal for growing paddy?
- a) Sandy soil
- b) Loamy soil
- c) Clayey soil rich in organic matter
- d) Silt soil
Answer: c) Clayey soil rich in organic matter
- Which layer of soil consists of unweathered bedrock?
- a) A Horizon
- b) B Horizon
- c) C Horizon
- d) R Horizon
Answer: d) R Horizon
- What property of soil enables it to retain its shape after being molded?
- a) Cohesion
- b) Plasticity
- c) Infiltration
- d) Percolation
Answer: b) Plasticity
- How long does it take to produce just under an inch of top soil?
- a) 50 years
- b) 100 years
- c) 500 years
- d) 1000 years
Answer: c) 500 years
- Which of the following helps prevent soil erosion?
- a) Overgrazing
- b) Deforestation
- c) Afforestation
- d) Careless cultivation
Answer: c) Afforestation
True/False Questions
- Soil is formed quickly and can be replaced within a human lifespan.
Answer: False (It takes 500 years to form less than an inch of top soil)
- The O Horizon is primarily composed of unweathered bedrock.
Answer: False (It is composed of leaf litter and humus)
- Sandy soils retain water better than clayey soils.
Answer: False (Clayey soils retain more water)
- Loamy soil is considered the best for growing most crops.
Answer: True
- Chemical weathering involves the growth of plant roots in rock crevices.
Answer: False (That is physical weathering; chemical weathering involves organic acids and water)
- Soil air is essential for the respiration of plant roots.
Answer: True
- The R Horizon is the most productive layer for plant growth.
Answer: False (The A Horizon, or top soil, is the most productive)
- Soil pollution can be caused by excessive use of chemical pesticides.
Answer: True
- Clayey soils are well aerated due to large spaces between particles.
Answer: False (Sandy soils are well aerated; clayey soils have little space between particles)
- Vermicompost is a nutrient-rich fertiliser produced by earthworms.
Answer: True
Short Questions and Answers
- What is soil?
Answer: Soil is the naturally occurring, loose covering of broken rock particles and decaying organic matter (humus) on Earth’s surface, capable of supporting life.
- What are the two types of weathering involved in soil formation?
Answer: Physical weathering and chemical weathering.
- Name two agents of physical weathering.
Answer: Temperature and water.
- What is the A Horizon?
Answer: The A Horizon, or top soil, is the layer where seeds germinate and plants grow, made of humus and mineral particles.
- Why is loamy soil ideal for crop growth?
Answer: Loamy soil is a balanced mixture of sand, silt, and clay, with humus, providing good aeration and water retention for crops.
- What is soil erosion?
Answer: Soil erosion is the removal of top soil by agents like wind and water, often accelerated by human activities.
- How does soil air affect plant growth?
Answer: Soil air, present in spaces between particles, is essential for root respiration, supporting healthy plant growth.
- What causes soil pollution?
Answer: Soil pollution is caused by toxic compounds, chemical pesticides, excessive fertilisers, industrial waste, and leaching from landfills.
- Why are earthworms called nature’s ploughmen?
Answer: Earthworms burrow through soil, consuming organic matter, and their casts enrich the soil while improving drainage and aeration.
- How can soil erosion be prevented?
Answer: Soil erosion can be prevented by afforestation, avoiding overgrazing, and reducing overuse of land to protect the top soil.
Competency-Based Questions (Reasoning and Assertion)
- Assertion (A): Loamy soil is ideal for growing most crops. Reason (R): Loamy soil has a balanced mixture of sand, silt, and clay, with good aeration and water retention.
- a) Both A and R are true, and R is the correct explanation of A.
- b) Both A and R are true, but R is not the correct explanation of A.
- c) A is true, but R is false.
- d) A is false, but R is true.
Answer: a) Both A and R are true, and R is the correct explanation of A.
- Assertion (A): Sandy soils are not suitable for crops requiring high water retention. Reason (R): Sandy soils have large spaces between particles, allowing water to drain quickly.
- a) Both A and R are true, and R is the correct explanation of A.
- b) Both A and R are true, but R is not the correct explanation of A.
- c) A is true, but R is false.
- d) A is false, but R is true.
Answer: a) Both A and R are true, and R is the correct explanation of A.
- Assertion (A): The B Horizon is the most productive layer for plant growth. Reason (R): The B Horizon contains clay and mineral deposits like iron and calcium carbonate.
- a) Both A and R are true, and R is the correct explanation of A.
- b) Both A and R are true, but R is not the correct explanation of A.
- c) A is true, but R is false.
- d) A is false, but R is true.
Answer: d) A is false, but R is true. (The A Horizon is the most productive for plant growth.)
- Assertion (A): Soil erosion is accelerated by deforestation. Reason (R): Vegetation protects soil by acting as a windbreaker and holding soil with roots.
- a) Both A and R are true, and R is the correct explanation of A.
- b) Both A and R are true, but R is not the correct explanation of A.
- c) A is true, but R is false.
- d) A is false, but R is true.
Answer: a) Both A and R are true, and R is the correct explanation of A.
- Assertion (A): Clayey soils are well aerated. Reason (R): Clayey soils have very little space between particles, limiting air content.
- a) Both A and R are true, and R is the correct explanation of A.
- b) Both A and R are true, but R is not the correct explanation of A.
- c) A is true, but R is false.
- d) A is false, but R is true.
Answer: d) A is false, but R is true.
High Order Thinking Skill (HOTS) Questions and Answers
- Why does it take 500 years to form less than an inch of top soil, and why is this significant?
Answer: Top soil forms slowly due to the gradual weathering of rocks and decomposition of organic matter. This slow process makes top soil a non-renewable resource within a human lifespan, highlighting the need to protect it for sustaining agriculture and ecosystems.
- How do earthworms contribute to soil fertility and structure?
Answer: Earthworms improve soil fertility by consuming organic matter and excreting nutrient-rich casts. Their burrowing enhances soil structure by mixing minerals, increasing aeration, and improving drainage, which supports plant growth and creates a healthier soil environment.
- Why are clayey soils more suitable for paddy cultivation than sandy soils?
Answer: Clayey soils have fine particles with high water retention, ideal for paddy, which requires standing water. Sandy soils, with larger particles, drain water quickly and are well aerated, making them unsuitable for paddy but better for crops needing less water.
- How does the infiltration rate of soil affect its suitability for crop growth?
Answer: The infiltration rate determines how quickly water enters the soil. Sandy soils with high infiltration rates drain water fast, unsuitable for water-intensive crops. Clayey soils with low infiltration retain water, ideal for crops like paddy, while loamy soils balance infiltration for diverse crops.
- Why does deforestation accelerate soil erosion, and how can afforestation help?
Answer: Deforestation removes vegetation that protects soil from wind and water, accelerating erosion. Afforestation restores this protective canopy, with tree roots holding soil in place and leaves reducing the impact of rain, thus preventing erosion and preserving the top soil.
Long Questions and Answers (50-60 words)
- Explain the process of soil formation through weathering.
Answer: Soil formation occurs through weathering, where physical agents like temperature, water, and wind break down rocks, and chemical processes like organic acid decomposition and water solvation dissolve minerals. These processes, combined with biological activity from plants and animals, gradually transform rocks into soil over centuries, forming a life-supporting layer.
- Describe the A Horizon and its role in plant growth.
Answer: The A Horizon, or top soil, is a dark layer beneath the O Horizon, composed of humus and mineral particles. It supports plant growth by providing nutrients and a medium for seed germination and root development, making it the most productive layer for agriculture.
- How do sandy, clayey, and loamy soils differ in their properties?
Answer: Sandy soils have large particles, good aeration, but poor water retention. Clayey soils have fine particles, high water retention, but poor aeration. Loamy soils, a mix of sand, silt, and clay, balance aeration and water retention with humus, making them ideal for most crops due to their versatility.
- What is soil pollution, and what are its causes?
Answer: Soil pollution is the build-up of toxic compounds, chemicals, salts, or disease-causing agents in soil, harming plant and animal health. Causes include chemical pesticides, excessive fertilisers, industrial waste discharge, oil dumping, and leaching from landfills, which degrade soil quality and affect ecosystems.
- How does soil erosion occur, and what measures can prevent it?
Answer: Soil erosion occurs when wind and water remove top soil, accelerated by deforestation, overgrazing, and careless cultivation. Preventive measures include afforestation to restore vegetation cover, avoiding overgrazing, and sustainable land use practices to maintain soil stability, protecting this vital resource for future generations.