Class 7 Science — Soil Chapter Complete Notes & Questions Answers (NCERT) | Detailed Soil Types, Conservation, MCQs & Exam Tips

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Soil — Class 7 Science: Complete Notes & Questions and Answers

This post gives you a complete, exam-focused treatment of the NCERT Class 7 chapter Soil. The page contains clear notes, practical examples, tips for exams and long/short practice questions. Use the Jump buttons at the top to move quickly between Notes and Q&A. All content is written to be student-friendly, SEO-optimized and AdSense-safe.

Notes: Understanding Soil (Detailed & Student-Friendly)

What is soil?

Soil is the loose upper layer of the Earth’s surface that supports plant growth. It is a dynamic natural body composed of mineral particles, organic matter, water, and air. Soil is not just “dirt” — it is a complex, living system that stores water and nutrients, hosts many organisms, and forms the base of agriculture.

How does soil form?

Soil forms by the weathering of rocks and the decomposition of organic material over long periods. Physical weathering breaks rocks into small particles through temperature changes, wind, and water. Chemical weathering alters minerals using water and acids. Biological activity (roots, microbes, earthworms) mixes the particles and adds organic matter, gradually producing fertile soil.

Components of soil

The main components are:

• Mineral matter: Sand, silt and clay particles derived from rocks.
• Organic matter: Decayed leaves, roots and humus that enrich soil fertility.
• Water: Held in soil pores; essential for plant uptake and chemical reactions.
• Air: Oxygen in the pores supports roots and soil organisms.
• Living organisms: Bacteria, fungi, earthworms and insects that improve structure and nutrient cycling.

Soil profile and horizons

When we dig a deep pit, we can see distinct layers called horizons. The typical sequence is:

• O horizon: Surface litter of leaves and decomposing matter (in forests).
• A horizon (topsoil): Dark, rich in humus and most fertile — where most plant roots grow.
• B horizon (subsoil): Zone of accumulation with finer particles and minerals leached from the topsoil.
• C horizon: Weathered parent rock fragments.
• R layer: Unweathered bedrock beneath the soil.

Soil texture and structure

Texture refers to the proportion of sand, silt and clay. Sandy soils drain fast but hold fewer nutrients. Clay soils hold water and nutrients but may be heavy and poorly drained. Loam soils — a balanced mix — are best for agriculture. Structure refers to how particles clump into aggregates; a good structure improves aeration and root penetration.

Soil types in India (important for exams)

India has several major soil types, each with unique properties:

• Alluvial soil: Found in plains of rivers like the Ganges and Brahmaputra. Fertile and good for agriculture (wheat, rice, sugarcane).
• Black (Regur) soil: Found in Deccan plateau, rich in clay and good for cotton.
• Red soil: Found in Tamil Nadu, parts of Odisha and Maharashtra — red due to iron content, suitable for pulses and millets with proper irrigation.
• Laterite soil: In high rainfall areas and hills — rich in iron and aluminium but poor in organic matter.
• Desert soil: Arid, sandy, low in organic matter — found in Rajasthan.
• Forest soil: Found in forest regions; rich in organic matter but often shallow.

Soil fertility and pH

Fertility means the soil’s capacity to supply essential nutrients to plants. It depends on organic matter, nutrient content (N, P, K), soil texture and pH. Most crops prefer a near-neutral pH; very acidic or alkaline soils reduce nutrient availability. Soil testing helps farmers apply the right fertilizers and lime where needed.

How does soil support agriculture?

Soil acts as a reservoir of nutrients and water, anchors plant roots, and supports beneficial microorganisms. Different crops have specific soil needs — e.g., wheat likes well-drained loamy soils, rice prefers clayey, water-retentive soils.

Soil erosion: causes and effects

Soil erosion is the removal of the topsoil layer by wind and water. Causes include deforestation, overgrazing, intensive farming, and construction. Effects include loss of fertility, reduced crop yields, silting of rivers, and desertification.

Soil conservation methods

Conservation techniques protect topsoil:

• Afforestation: Planting trees prevents wind and water erosion.
• Terracing: On slopes, steps reduce runoff and soil loss.
• Contour ploughing: Ploughing along contours slows water flow.
• Cover cropping & mulching: Protects soil surface and retains moisture.
• Crop rotation & mixed cropping: Keep soil healthy and lower pest pressure.
• Using organic manure & compost: Improves structure and fertility without harming soil life.

Quick Exam Tip: Remember “ALB” — Alluvial (plains), Laterite (hills/rain), Black (Deccan): match soil types to regions in map questions.

Problems of modern farming and sustainable solutions

Overuse of chemical fertilizers and mono-cropping has reduced soil health in many areas. Sustainable practices — organic farming, green manures, conservation tillage, integrated nutrient management — restore soil balance and protect long-term productivity.

Remember: Soil is a living resource — treat it like a bank account: withdraw (harvest) but also deposit (organic matter & nutrients).

Questions & Answers — Practice for Exams

Multiple Choice Questions (7) — choose the correct option

1. Q1. Which soil is best suited for growing cotton?
   A. Red soil    B. Alluvial soil    C. Black soil    D. Laterite soil
2. Q2. Which horizon of the soil contains the most organic matter?
   A. A horizon (topsoil)    B. B horizon    C. C horizon    D. R layer
3. Q3. Which of the following is a major cause of soil erosion?
   A. Afforestation    B. Crop rotation    C. Heavy rainfall on bare slopes    D. Mulching
4. Q4. Loam soil is considered good because it has a balance of:
   A. Clay only    B. Sand and silt only    C. Sand, silt and clay    D. Organic matter only
5. Q5. Terracing is a conservation method used mainly on:
   A. Plains    B. Desert    C. Hills and slopes    D. Coastal areas
6. Q6. Which practice increases soil organic matter naturally?
   A. Burning crop residue    B. Adding chemical fertilizer only    C. Using compost and green manure    D. Heavy tilling
7. Q7. Soil pH indicates:
   A. Texture    B. Acidity or alkalinity    C. Color    D. Presence of earthworms

Answers: Q1: C, Q2: A, Q3: C, Q4: C, Q5: C, Q6: C, Q7: B

Very Short Answer Questions (7)

1. Q1. What is topsoil?
   Ans: The topmost dark layer (A horizon) rich in humus and nutrients where most plant roots grow.
2. Q2. Name one soil conserving crop practice.
   Ans: Crop rotation or cover cropping helps conserve soil by maintaining nutrients and preventing erosion.
3. Q3. What do you mean by soil texture?
   Ans: Texture is the relative proportion of sand, silt and clay in a soil.
4. Q4. Give one use of compost in soil management.
   Ans: Compost improves soil structure, increases fertility and enhances water-holding capacity.
5. Q5. What is salinization?
   Ans: Accumulation of salts in soil, often due to improper irrigation, which reduces fertility.
6. Q6. Which soil type is common in the Indo-Gangetic plains?
   Ans: Alluvial soil.
7. Q7. What role do earthworms play in soil?
   Ans: Earthworms improve structure, aerate soil and accelerate decomposition of organic matter.

Short Answer Questions (7)

1. Q1. Describe black soil and name the crop it supports well.
   Ans: Black soil is clayey, retains moisture and is rich in minerals suited for cotton cultivation; it develops deep cracks on drying and is often called regur soil.
2. Q2. Explain how contour ploughing reduces soil erosion.
   Ans: Contour ploughing follows the natural elevation lines of a slope. It slows down water runoff, allowing water to infiltrate and reducing the washing away of topsoil.
3. Q3. How can farmers restore nutrient-deficient soils?
   Ans: By adding organic manure, compost, green manures, and appropriate chemical fertilizers based on soil test results; crop rotation with legumes also restores nitrogen.
4. Q4. Distinguish between sandy and clayey soils in terms of water retention.
   Ans: Sandy soils drain quickly and retain little water; clayey soils hold water for longer due to tiny pores but may lead to poor drainage and waterlogging.
5. Q5. What is soil profile and why is it important?
   Ans: Soil profile is the vertical sequence of horizons; studying it reveals fertility, depth, and suitability of land for crops and helps in planning land use.
6. Q6. Mention two human activities that cause soil degradation.
   Ans: Deforestation and overgrazing remove vegetation cover and accelerate erosion; excessive use of chemical fertilizers and improper irrigation cause salinization and deterioration of structure.
7. Q7. What are the benefits of mulching?
   Ans: Mulching conserves moisture, suppresses weeds, moderates soil temperature and adds organic matter as it decomposes.

Long Answer Questions (7)

1. Q1. Explain how soil is formed and state the main factors that affect soil formation.
   Ans: Soil formation is a slow process starting with rock weathering. Physical weathering (temperature changes,