Class 11 Geography Notes Chapter 6 (Soils) – India Physical Environment Book
Detailed Notes with MCQs of Chapter 6, 'Soils', from your NCERT textbook 'India Physical Environment'. This is a vital chapter for understanding India's geography and frequently features in government exams. Pay close attention to the classification, characteristics, and distribution of soils in India, as well as the issues of degradation and conservation.
Chapter 6: Soils - Detailed Notes for Government Exam Preparation
1. What is Soil?
- Soil is the thin surface layer on the earth, comprising mineral particles, decayed organic matter (humus), soil water, and soil air.
- It's a dynamic, living system, crucial for plant growth and hence, agriculture and ecosystems.
- Soil formation (pedogenesis) is a very slow process; it can take thousands of years to form a few centimeters of topsoil.
2. Factors Influencing Soil Formation (The Five Key Factors):
- Parent Material: The nature of the underlying rock (or deposited material) determines the mineral composition, texture, and chemical properties of the soil. (e.g., Deccan basalt leads to black soils).
- Relief/Topography: Altitude and slope influence drainage, erosion, and accumulation of soil material. Steep slopes often have thin soil cover due to erosion, while gentle slopes and plains allow thicker soil development.
- Climate: Temperature and rainfall are the most significant climatic factors.
- Temperature: Affects the rate of weathering and decomposition of organic matter.
- Rainfall: Affects leaching (washing away of soluble minerals), erosion, and moisture content. High rainfall can lead to acidic soils due to leaching of bases.
- Biological Activity (Vegetation & Organisms):
- Vegetation: Provides humus (decayed organic matter), influences soil structure, and protects against erosion.
- Organisms: Microorganisms (bacteria, fungi) decompose organic matter. Larger organisms (earthworms, rodents) help mix and aerate the soil.
- Time: The duration of soil-forming processes determines the maturity and profile development of the soil. Older soils generally have more distinct layers (horizons).
3. Classification of Soils in India:
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India has a vast diversity of soils due to varied relief, parent materials, climate, and vegetation.
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Ancient classification: Urvara (fertile) and Usara (sterile).
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Modern classification (based on genesis, colour, composition, location): The Indian Council of Agricultural Research (ICAR) has classified Indian soils into major groups. We will focus on the main types discussed in the NCERT:
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(i) Alluvial Soils:
- Formation: Formed by the deposition of sediments (silt, sand, clay) carried by rivers (Indus, Ganga, Brahmaputra systems) and coastal waves.
- Distribution: Largest soil group in India (about 40% of the area). Found in the Northern Plains (Punjab to Assam), river valleys (Narmada, Tapi, Mahanadi, Godavari, Krishna, Kaveri deltas), and coastal plains.
- Characteristics: Generally rich in potash, phosphoric acid, and lime, but poor in nitrogen and humus. Texture varies from sandy loam to clayey. Highly fertile.
- Sub-types:
- Khadar: Newer alluvium, found in floodplains, fine-textured, more fertile, replenished annually.
- Bhangar: Older alluvium, found on higher terraces away from floodplains, coarser texture, often contains calcareous concretions (kankars), less fertile than Khadar.
- Crops: Ideal for rice, wheat, sugarcane, pulses, oilseeds, jute.
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(ii) Black Soils (Regur Soils / Black Cotton Soils):
- Formation: Derived from the weathering of Deccan Trap basaltic rocks.
- Distribution: Predominant in the Deccan Plateau region (Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh, parts of Tamil Nadu, Karnataka).
- Characteristics: Clayey texture, high moisture retention capacity. Rich in lime, iron, magnesia, and alumina, but poor in phosphorus, nitrogen, and organic matter. Develop deep cracks during the dry season (aids aeration - 'self-ploughing') and become sticky when wet. Dark black colour due to titaniferous magnetite and humus.
- Crops: Famous for cotton cultivation; also suitable for sugarcane, jowar, tobacco, wheat, oilseeds.
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(iii) Red and Yellow Soils:
- Formation: Develop on crystalline igneous and metamorphic rocks (like granite, gneiss) in areas of relatively low rainfall.
- Distribution: Large parts of the Deccan Plateau's eastern and southern periphery, Odisha, Chhattisgarh, parts of the middle Ganga plain.
- Characteristics: Red colour is due to the diffusion of iron oxides in crystalline/metamorphic rocks. Looks yellow when in hydrated form. Texture varies from sandy to clayey loam. Generally poor in nitrogen, phosphorus, and humus. Relatively less fertile but respond well to fertilizers and irrigation.
- Crops: With irrigation and fertilizers, suitable for wheat, rice, cotton, pulses, millets, tobacco, oilseeds, potatoes.
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(iv) Laterite Soils:
- Formation: Formed in areas with high temperature and high rainfall, leading to intense leaching (washing away of silica and lime). Rich in iron oxide and aluminium compounds. The term 'laterite' means 'brick' in Latin.
- Distribution: Found in patches in Karnataka, Kerala, Tamil Nadu, Madhya Pradesh, and hilly areas of Odisha and Assam.
- Characteristics: Poor in organic matter, nitrogen, phosphate, and calcium, but rich in iron oxide and potash. Often acidic. Low fertility for general agriculture but used for bricks. With manure and fertilizers, suitable for specific crops.
- Crops: Suitable for plantation crops like tea, coffee, rubber, cashew nuts, coconut.
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(v) Arid Soils (Desert Soils):
- Formation: Develop in arid and semi-arid conditions under high temperatures and low rainfall.
- Distribution: Western Rajasthan, parts of Haryana, Punjab, and Gujarat.
- Characteristics: Sandy to gravelly texture, saline in nature (high salt content due to evaporation). Poor in humus and nitrogen, moisture content is low. Often contain 'Kankar' (calcium carbonate) layers in the lower horizons, restricting water infiltration. Colour ranges from red to brown.
- Crops: With irrigation, suitable for drought-resistant crops like bajra, pulses, guar, fodder.
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(vi) Forest Soils (Mountain Soils):
- Formation: Found in hilly and mountainous areas with sufficient rainfall and forest cover.
- Distribution: Himalayan region, Western and Eastern Ghats, parts of Peninsular plateau.
- Characteristics: Highly variable depending on altitude, vegetation, and slope. Generally loamy and silty on valley sides, coarse-grained on upper slopes. Often acidic and low in humus content in snow-covered areas. Fertile in lower valleys. Prone to erosion.
- Crops: Suitable for tea, coffee, spices, fruits (in specific regions and altitudes).
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(vii) Saline Soils (Usara Soils):
- Formation: Accumulate excessive salts (sodium, potassium, magnesium) due to poor drainage, high evaporation, over-irrigation in dry climates, or seawater intrusion in coastal areas.
- Distribution: Arid/semi-arid regions (Rajasthan, Gujarat, Haryana, Punjab, UP, Bihar), waterlogged areas, coastal belts.
- Characteristics: Infertile, lack vegetative cover. Can be reclaimed by improving drainage and adding gypsum.
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(viii) Peaty/Organic Soils:
- Formation: Found in areas of heavy rainfall and high humidity, where there is a good growth of vegetation leading to accumulation of large quantities of dead organic matter (humus).
- Distribution: Parts of Kerala (Kottayam, Alappuzha districts - known as Kari), coastal Odisha, West Bengal (Sunderbans), Bihar, Uttarakhand.
- Characteristics: Rich in humus and organic content (40-50%). Often acidic. Heavy, black coloured. May be submerged during monsoon.
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4. Soil Degradation:
- Decline in soil fertility when the nutritional status declines and erosion removes topsoil.
- A major concern in India.
5. Soil Erosion:
- Removal of the topsoil layer by agents like running water and wind.
- Types:
- Sheet Erosion: Uniform removal of soil in thin layers from the surface, often unnoticed. Common on gentle slopes after heavy rain.
- Rill Erosion: Water forms small finger-like channels on the surface.
- Gully Erosion: Rills deepen and widen into large gullies, making land unfit for cultivation (e.g., Chambal ravines). Common on steep slopes.
- Wind Erosion: Common in arid/semi-arid areas, lifts and transports loose soil particles.
6. Causes of Soil Degradation/Erosion:
- Deforestation
- Overgrazing
- Faulty methods of agriculture (e.g., shifting cultivation or Jhumming, ploughing up and down the slope)
- Over-irrigation (leading to salinity/alkalinity)
- Excessive use of chemical fertilizers and pesticides
- Construction activities, mining.
7. Soil Conservation:
- Protecting soil from erosion and fertility loss.
- Methods:
- Afforestation & Reforestation: Planting trees reduces runoff and binds soil.
- Contour Bunding/Ploughing: Building bunds or ploughing along contours (lines of same elevation) on slopes to check water flow.
- Terrace Farming: Cutting step-like terraces on steep slopes to slow down runoff and allow cultivation.
- Shelterbelts: Planting rows of trees to check wind erosion, especially in arid/coastal areas.
- Strip Cropping: Growing crops in alternate strips, some of which may be cover crops, to check erosion.
- Mulching: Covering the ground with organic matter (straw, grass) to retain moisture and prevent erosion.
- Regulated/Controlled Grazing: Preventing overgrazing by livestock.
- Sustainable Farming Practices: Crop rotation, mixed farming, organic farming.
- Gully Plugging: Checking gully erosion using check dams.
- Land Use Planning: Using land according to its capability.
Remember to link these soil types to the physical map of India and understand their relationship with climate, relief, and vegetation zones.
Multiple Choice Questions (MCQs):
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Which soil type is predominantly found in the Deccan Trap region of India and is known for its high moisture retention capacity?
(a) Alluvial Soil
(b) Red Soil
(c) Laterite Soil
(d) Black Soil -
The terms 'Khadar' and 'Bhangar' are associated with which type of soil?
(a) Black Soil
(b) Alluvial Soil
(c) Laterite Soil
(d) Arid Soil -
Laterite soils are typically formed under conditions of:
(a) Low temperature and low rainfall
(b) High temperature and low rainfall
(c) Low temperature and high rainfall
(d) High temperature and high rainfall with intense leaching -
Which factor of soil formation determines the mineral composition and texture of the soil?
(a) Climate
(b) Biological Activity
(c) Parent Material
(d) Time -
'Regur Soil' is another name for:
(a) Red Soil
(b) Black Soil
(c) Alluvial Soil
(d) Forest Soil -
Which soil type is characterized by the presence of 'Kankar' (calcium carbonate) layers in the lower horizons and is found mainly in Western Rajasthan?
(a) Peaty Soil
(b) Laterite Soil
(c) Arid Soil
(d) Saline Soil -
Gully erosion is a major problem in which of the following regions mentioned in the context of soil degradation?
(a) Coastal plains of Kerala
(b) Chambal Valley
(c) Sunderbans delta
(d) Thar Desert -
Which soil conservation technique involves planting rows of trees to reduce the impact of wind erosion?
(a) Contour Ploughing
(b) Terrace Farming
(c) Shelterbelts
(d) Mulching -
Red soils derive their colour primarily due to:
(a) High humus content
(b) Presence of potash and phosphate
(c) Diffusion of iron in crystalline and metamorphic rocks
(d) High clay content -
Peaty soils, rich in organic matter and often acidic, are typically found in areas with:
(a) Arid conditions and low vegetation
(b) Heavy rainfall, high humidity, and abundant vegetation
(c) Cold temperatures and snow cover
(d) Moderate rainfall and basaltic parent rock
Answer Key for MCQs:
- (d) Black Soil
- (b) Alluvial Soil
- (d) High temperature and high rainfall with intense leaching
- (c) Parent Material
- (b) Black Soil
- (c) Arid Soil
- (b) Chambal Valley
- (c) Shelterbelts
- (c) Diffusion of iron in crystalline and metamorphic rocks
- (b) Heavy rainfall, high humidity, and abundant vegetation
Study these notes thoroughly. Refer back to your NCERT textbook for diagrams, maps, and further details. Understanding the distribution map is crucial for answering location-based questions. Good luck with your preparation!