UNIT 4: Soil and its Degradation
7 MarksDetailed handwritten-style notes in very simple English
Index / Contents
- Meaning and Importance of Soil
- Soil Composition
- Soil Profile and Horizons
- Indian Classification of Soils
- Soil Pollution
- Causes of Soil Pollution
- Impacts of Soil Pollution
- Control of Soil Pollution
- Soil Erosion
- Causes and Types of Soil Erosion
- Impacts of Soil Erosion
- Control of Soil Erosion
- Desertification
- Control of Desertification
- Important Differences
- Quick Revision Sheet
- Board Exam Questions with Answers
- Practice Questions
1. Meaning and Importance of Soil
Importance of soil
- Provides support and nutrients to plants.
- Helps in the production of food, fibres and medicines.
- Stores and filters rainwater.
- Provides habitat to insects, earthworms, bacteria and fungi.
- Participates in nutrient cycling and decomposition.
- Stores carbon and helps maintain environmental balance.
- Provides raw materials such as clay, sand and minerals.
2. Soil Composition
Soil is made of four main components. Their exact percentage changes from place to place.
| Component | Approximate amount | Role |
|---|---|---|
| Mineral matter | About 45% | Provides sand, silt, clay and minerals. |
| Soil organic matter | About 5% | Improves fertility and soil structure. |
| Soil water | About 25% | Dissolves and transports nutrients. |
| Soil air | About 25% | Needed for roots and soil organisms. |
1. Mineral matter
Mineral particles are formed by the breaking down of rocks. They include sand, silt and clay.
2. Organic matter
Organic matter comes from dead plants, animals and microorganisms. Decomposed organic matter is called humus. Humus improves water-holding capacity and fertility.
3. Soil water
Water is present in soil pores. It carries dissolved minerals to plant roots.
4. Soil air
Soil air contains oxygen, nitrogen, carbon dioxide and water vapour. Oxygen is needed for root respiration and activity of aerobic organisms.
Soil texture
- Sand: Large particles; water drains quickly.
- Silt: Medium-sized particles; generally smooth and fertile.
- Clay: Very fine particles; holds more water but may have poor drainage.
3. Soil Profile and Horizons
Organic layer
Topsoil
Subsoil
Parent material
Bedrock
| Horizon | Main features |
|---|---|
| O horizon | Organic layer containing leaf litter and partly decomposed material. It may be absent in some soils. |
| A horizon | Topsoil; rich in humus and biological activity. Most roots and organisms are found here. |
| B horizon | Subsoil; materials such as clay and minerals may accumulate here. Usually has less humus than topsoil. |
| C horizon | Partly weathered parent material with large rock fragments. |
| R horizon | Hard, unweathered bedrock below the soil. |
4. Indian Classification of Soils
Indian soils are classified according to their origin, colour, texture, chemical properties and location. The major soil groups are given below.
| Soil type | Main features | Major areas / crops |
|---|---|---|
| Alluvial soil | Deposited by rivers; generally fertile; contains sand, silt and clay. | Northern plains and river valleys; rice, wheat, sugarcane. |
| Black soil | Clayey, moisture-retaining and often rich in lime, iron and magnesium; develops cracks when dry. | Deccan Plateau; cotton, soybean, sugarcane. |
| Red and yellow soil | Red colour due to iron compounds; usually low in nitrogen and humus. | Parts of peninsular India; millets, pulses, groundnut. |
| Laterite soil | Develops under heavy rainfall and high temperature; may be low in fertility without manure. | High rainfall areas; tea, coffee, cashew with proper management. |
| Arid / desert soil | Sandy, low in humus and moisture; may contain salts. | Western Rajasthan and dry regions; farming needs irrigation and care. |
| Forest and mountain soil | Varies with altitude, slope and vegetation; often rich in organic matter in forest areas. | Himalayan and mountain regions; fruits, tea and forest vegetation. |
| Saline and alkaline soil | Contains excess soluble salts or exchangeable sodium; reduces plant growth. | Dry and poorly drained areas; needs reclamation. |
| Peaty and marshy soil | High organic matter due to incomplete decomposition in waterlogged conditions. | Wetlands and waterlogged areas. |
Important points about major soils
Alluvial soil
It is transported and deposited by rivers. It is common in the Indo-Gangetic-Brahmaputra plains. It is important for agriculture because it is generally fertile.
Black soil
It is also called regur soil. It holds moisture for a long time and is suitable for cotton. It becomes sticky when wet and develops deep cracks when dry.
Red soil
Its red colour is mainly due to iron. It may become productive when fertilizers, irrigation and organic manure are properly used.
Laterite soil
Heavy rainfall washes away soluble nutrients. It may need manure and fertilizers for good agricultural production.
5. Soil Pollution
Examples of soil pollutants
- Pesticides and insecticides.
- Excess chemical fertilizers.
- Industrial waste and heavy metals.
- Plastic, e-waste and municipal garbage.
- Oil, petroleum products and toxic chemicals.
- Untreated sewage and biomedical waste.
6. Causes of Soil Pollution
- Agricultural chemicals: Excess pesticides and fertilizers accumulate in soil and disturb useful organisms.
- Industrial waste: Factories may release metals, chemicals, ash and other hazardous waste.
- Improper solid-waste disposal: Plastics, batteries, electronic waste and garbage release harmful substances.
- Mining: Mining removes the topsoil and may release heavy metals and acidic drainage.
- Urbanisation: Construction waste, sewage and road pollutants enter soil.
- Oil leakage: Oil from vehicles, machines and storage tanks reduces soil quality.
- Deforestation: Removal of vegetation exposes soil and increases erosion and nutrient loss.
- Improper irrigation: Poor-quality water and over-irrigation can cause salinity and alkalinity.
7. Impacts of Soil Pollution
On soil
- Loss of fertility.
- Change in pH and soil structure.
- Reduction of useful microorganisms.
- Lower water-holding capacity.
On plants
- Poor seed germination.
- Reduced growth and crop yield.
- Absorption of toxic metals.
- Damage to roots.
On humans
- Exposure through food, water and dust.
- Possible poisoning and long-term health risks.
- Entry of pollutants into the food chain.
On environment
- Groundwater contamination.
- Loss of biodiversity.
- Death of earthworms and beneficial insects.
- Food-chain contamination.
8. Control of Soil Pollution
- Use fertilizers and pesticides in the correct quantity.
- Prefer compost, green manure and biofertilizers where suitable.
- Follow the 3Rs: reduce, reuse and recycle.
- Separate wet waste, dry waste and hazardous waste.
- Dispose of batteries, e-waste and chemicals safely.
- Treat industrial wastewater and solid waste before disposal.
- Use bioremediation, in which microorganisms help break down selected pollutants.
- Plant trees and maintain vegetation cover.
- Prevent oil leakage and use safe storage systems.
- Test soil regularly and improve soil with organic matter.
9. Soil Erosion
Topsoil contains humus, nutrients and microorganisms. When topsoil is removed, agricultural productivity decreases and land becomes less fertile.
10. Causes and Types of Soil Erosion
Natural causes
- Heavy rainfall and floods.
- Strong winds.
- Steep slopes and landslides.
- Running water in streams and rivers.
Human causes
- Deforestation and removal of grass cover.
- Overgrazing by animals.
- Unplanned farming on slopes.
- Mining and road construction.
- Over-irrigation and poor land management.
- Excessive cultivation and leaving soil bare.
Types of erosion
| Type | Meaning |
|---|---|
| Sheet erosion | A thin, uniform layer of soil is removed from a large area by flowing water. |
| Rill erosion | |
| Gully erosion | |
| Wind erosion | |
| Splash erosion |
11. Impacts of Soil Erosion
- Loss of fertile topsoil and nutrients.
- Reduction in agricultural productivity.
- Increase in silt in rivers, lakes and dams.
- Flooding and blockage of drainage channels.
- Damage to roads, fields and infrastructure.
- Loss of soil biodiversity and organic matter.
- Destruction of natural habitats.
- Increased risk of desertification in dry regions.
12. Control of Soil Erosion
Vegetative methods
- Afforestation and reforestation.
- Planting grass and cover crops.
- Maintaining forest and grassland cover.
- Planting shelterbelts to reduce wind speed.
Agricultural methods
- Contour ploughing: Ploughing across the slope along contour lines.
- Terrace farming: Making step-like fields on slopes.
- Strip cropping: Growing crops in strips to slow water and wind.
- Mulching: Covering soil with straw, leaves or other material.
- Crop rotation and minimum tillage.
Engineering methods
- Check dams and small barriers.
- Gully plugging and proper drainage.
- Rainwater harvesting structures.
- Stone bunds and retaining walls where suitable.
13. Desertification
Easy explanation
Desertification does not always mean that a new desert is formed. It means that productive land gradually loses vegetation, soil fertility and water-holding capacity and becomes more desert-like.
Causes of desertification
- Deforestation and removal of natural vegetation.
- Overgrazing.
- Soil erosion by wind and water.
- Over-cultivation and poor farming practices.
- Over-irrigation causing salinity.
- Long droughts and changing climate conditions.
- Over-extraction of groundwater.
- Mining and unplanned construction.
Impacts
- Loss of fertile land and crop production.
- Reduction in vegetation and biodiversity.
- Water scarcity and drying of wells.
- Dust storms and increased soil erosion.
- Poverty, migration and loss of rural livelihoods.
- Increase in land surface temperature and ecological stress.
14. Control of Desertification
- Afforestation: Plant trees and protect existing vegetation.
- Controlled grazing: Avoid overgrazing and use rotational grazing.
- Water conservation: Build check dams, ponds and rainwater harvesting structures.
- Soil conservation: Use contour bunding, terraces, mulching and shelterbelts.
- Sustainable farming: Use crop rotation, drought-resistant crops and organic manure.
- Control salinity: Improve drainage and use irrigation water carefully.
- Community participation: Involve local people in land and water management.
- Reduce pressure on land: Avoid unnecessary deforestation, mining and over-extraction of groundwater.
- Awareness and monitoring: Monitor land degradation and take action early.
15. Important Differences
| Term | Meaning | Main result |
|---|---|---|
| Soil pollution | Harmful substances enter soil. | Soil quality and living organisms are damaged. |
| Soil erosion | Topsoil is removed and transported. | Loss of fertile soil. |
| Desertification | Productivity of dryland decreases due to degradation. | Land becomes less productive and more desert-like. |
| Deforestation | Removal of forests. | Loss of habitat and increased erosion risk. |
Contour ploughing vs terrace farming
| Contour ploughing | Terrace farming |
|---|---|
| Ploughing along contour lines across a slope. | Making step-like fields on steep slopes. |
| Slows down surface runoff. | Reduces speed of water and holds soil on steps. |
16. Quick Revision Sheet
- Soil: Upper loose layer of land where plants grow.
- Four components: Mineral matter, organic matter, water and air.
- Topsoil: A horizon, usually rich in humus.
- Subsoil: B horizon.
- Alluvial soil: River-deposited and generally fertile.
- Black soil: Moisture-retaining and suitable for cotton.
- Soil pollution: Addition of harmful substances to soil.
- Soil erosion: Removal of topsoil by water, wind or human activities.
- Desertification: Loss of biological productivity in dry areas.
- Control: Afforestation, contour farming, terrace farming, mulching, controlled grazing and water conservation.
17. Board Exam Questions with Answers
Very Short Answer Questions
Q1. Define soil.
Answer: Soil is the upper loose layer of the Earth's surface in which plants grow.
Q2. Name the four main components of soil.
Answer: Mineral matter, organic matter, soil water and soil air.
Q3. What is soil profile?
Answer: A vertical section of soil showing different horizons or layers.
Q4. Which soil is suitable for cotton?
Answer: Black soil.
Q5. Define soil erosion.
Answer: Soil erosion is the removal and transport of fertile topsoil by water, wind or other agents.
Q6. Define desertification.
Answer: Desertification is the degradation of land in dry areas, causing loss of biological productivity.
Short Answer Questions
Q1. Explain the composition of soil.
Answer: Soil contains mineral matter, organic matter, water and air. Mineral matter comes from rocks. Organic matter comes from dead plants and animals. Water carries nutrients, while air provides oxygen for roots and soil organisms.
Q2. Explain the main horizons of a soil profile.
Answer: The O horizon contains organic material. The A horizon is humus-rich topsoil. The B horizon is subsoil where materials may accumulate. The C horizon contains weathered parent material. The R horizon is hard bedrock.
Q3. Write four causes of soil pollution.
Answer: Excess pesticides and fertilizers, industrial waste, improper garbage disposal and mining activities.
Q4. Write four methods of controlling soil erosion.
Answer: Afforestation, contour ploughing, terrace farming and mulching.
Q5. Differentiate between soil erosion and desertification.
Answer: Soil erosion is the removal of soil particles, especially topsoil. Desertification is the wider degradation of dryland that reduces biological productivity.
Long Answer Questions
Q1. Describe the major soil types of India.
Answer: Major Indian soils include alluvial, black, red and yellow, laterite, arid, forest and mountain, saline and alkaline, and peaty and marshy soils. Alluvial soil is deposited by rivers and is generally fertile. Black soil holds moisture and is suitable for cotton. Red soil gets its colour from iron. Laterite soil develops in areas of heavy rainfall. Arid soil is sandy and low in humus. Forest soil varies with altitude and vegetation.
Q2. Explain the causes, impacts and control of soil pollution.
Answer: Soil pollution is caused by pesticides, fertilizers, industrial waste, plastics, mining, oil leakage and untreated sewage. It reduces soil fertility, harms microorganisms, contaminates groundwater and allows pollutants to enter the food chain. It can be controlled through safe waste disposal, reduced chemical use, composting, recycling, treatment of industrial waste, bioremediation and afforestation.
Q3. Explain soil erosion, its causes, effects and control.
Answer: Soil erosion is the removal of topsoil by water and wind. Deforestation, overgrazing, heavy rainfall, strong winds, mining and unplanned farming increase erosion. It causes loss of nutrients, reduced crop yield, siltation and flooding. It can be controlled through afforestation, contour ploughing, terrace farming, strip cropping, mulching, check dams and proper land management.
Q4. What is desertification? Explain its causes and control measures.
Answer: Desertification is the loss of biological productivity in dry areas due to land degradation. Its causes include deforestation, overgrazing, soil erosion, poor farming, over-irrigation, drought and groundwater overuse. It can be controlled through afforestation, controlled grazing, water conservation, soil conservation, sustainable farming, drainage improvement and community participation.
18. Practice Questions
- Define soil and explain its importance.
- Describe the four main components of soil.
- Explain the soil profile with its horizons.
- Write the major soil types found in India.
- Explain the characteristics of alluvial and black soil.
- Define soil pollution and write its causes.
- Explain the impacts of soil pollution on humans and the environment.
- Write methods to control soil pollution.
- Define soil erosion and explain its types.
- Write the causes and impacts of soil erosion.
- Explain contour ploughing and terrace farming.
- Define desertification and explain its causes.
- Write control measures of desertification.
- Differentiate between soil pollution, soil erosion and desertification.
- Prepare a flow chart showing how deforestation can lead to desertification.
Exam Writing Tips ✍️
- Begin with a clear definition.
- Use separate headings: causes, impacts and control.
- Draw a labelled soil profile diagram.
- Remember examples of Indian soils and their crops.
- Use keywords such as humus, topsoil, salinity, contour ploughing, erosion and land degradation.
- Write points in simple sentences for better presentation.
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