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1. Black Soil (Regur Soil)
Origin and Formation
- Formed from the weathering of fissure volcanic rock (basaltic lava).
- Specifically created from the breakdown of Deccan Trap rocks in the northwest Deccan plateau.
- Also referred to as Lava Soil, found in regions like the Malwa Plateau.
Characteristics and Properties
- Colour: Black.
- Texture: Clayey with high iron content.
- Moisture: Highly retentive of moisture.
- Cracking: Develops deep cracks when dry.
- Swelling: Swells and becomes sticky when wet.
- Nickname: Known as “self-ploughed” soil because the cracking and swelling action naturally aerates the land.
Chemical Composition
- Rich in: Alumina, iron, lime, magnesium carbonates, and potash.
- Deficient in: Phosphorus, nitrogen, and humus.
Other Names and Classification
- Also known as Regur soil or Black Cotton soil.
- Classified by Krabs as essentially a mature soil.
Distribution in India
- Most widespread in: Maharashtra.
- Also found in: Gujarat (Saurashtra), Madhya Pradesh, Karnataka, Chhattisgarh, and the valleys of the Godavari and Krishna rivers.
- NOT found in: The Himalayan region.
Agricultural Significance
- Ideal for cotton cultivation, hence the name ‘Black Cotton soil’.
- Highly responsive to irrigation.
- Suitable for crops in low-rainfall areas due to its excellent moisture retention.
2. Laterite Soil
Formation & Characteristics
- Formation Process:
- Forms in tropical climates with high temperatures and heavy rainfall.
- The process of leaching during alternating wet and dry seasons washes away silica and lime.
- Leaves behind a soil rich in iron and aluminum compounds.
- Physical Properties:
- Generally red in colour due to high iron oxide content.
- Chemical Properties / Fertility:
- Generally low in fertility.
- Deficient in: Humus, nitrogen, phosphorus, and lime.
- Rich in: Iron and aluminum.
- The presence of excess iron is a key reason for its infertility.
Distribution in India
- Primary States: Kerala, Maharashtra, Karnataka, Andhra Pradesh, Odisha, West Bengal, Assam, Jharkhand, Meghalaya.
- Specific Regions: Western Ghats, Eastern Ghats, and the Malabar Coastal Region (Kerala coast).
- Largest Coverage: The state with the largest area of Laterite soil is Maharashtra.
Agricultural Use
- Generally not very suitable for widespread agriculture due to poor fertility.
- Crops that grow well: Tapioca (Cassava) and Cashew nuts.
Clarifications
- The soil of most of Andhra Pradesh is not laterite; the state has Red and Alluvial soils.
- Laterite soil is not rich in lime, nitrogen, or potash.
- It is not well-developed in Rajasthan, Uttar Pradesh, Himachal Pradesh, or Punjab.
- It is distinct from Alluvial soil.
3. Alluvial Soil
General Importance & Characteristics
- Considered the most productive and fertile soil in India.
- It is the largest and most widespread soil group in India.
- Covers approximately 11 lakh square kilometers (about 33.5% of India’s total land area).
- A major contributor to India’s agricultural production.
- Generally has low nitrogen content.
- Rich in phosphoric acid, potash, and alkalis.
Origin and Formation
- Primarily formed from sediments deposited by the Himalayas.
- Also formed in coastal areas when the sea recedes (coastal alluvium).
Geographical Distribution
- Found extensively in the Indo-Gangetic plains (from Punjab to West Bengal and Assam).
- Present in the deltas of major rivers like Mahanadi, Godavari, Krishna, and Cauvery.
- Also found in the valleys of the Narmada and Tapi rivers.
- Specific example: The districts of Muzaffarpur, Darbhanga, and Champaran in Bihar have newer alluvium soil.
Classification (Khadar and Bhangar)
- Khadar (Newer Alluvium): Found in floodplains.
- Bhangar (Older Alluvium):
- Found in areas above the flood level.
- Has a pale reddish-brown colour.
- Contains kankar (calcium carbonate nodules).
- Also known as “Old Kachhari clay” in the Gangetic plain.
4. Soil Properties (General)
Water Retention Capacity
- Water holding capacity decreases in the order: Clay > Silt > Sand.
- Clay soil has the highest water retention capacity due to very small pore spaces.
- Sandy soil has the minimum water retention capacity due to large pore spaces.
- False Statement: “Clay has pore spaces of large size.”
Soil Composition
- Loamy soil is a mixture of sand, clay, and silt (typically around 40% sand, 40% clay, and 20% silt).
5. Other Soils and Regional Distribution
Major Soil Types by Predominant State
- Alluvial Soil: Predominantly found in Uttar Pradesh.
- Black Soil: Predominantly found in Maharashtra.
- Red Soil: Predominantly found in Andhra Pradesh.
- Desert Soil: Predominantly found in Rajasthan.
- Karewas Soil: Found in the Kashmir Valley, Himalaya. Useful for cultivating Zafran (a local saffron).
Specific Soil Characteristics
- Red Soil:
- Red colour is due to ferric oxides.
- Deficient in nitrogen, lime, magnesium, phosphates, and humus, but rich in potash.
- Desert Soil (Western Rajasthan):
- Has a high content of calcium.
- Generally alkaline and saline.
- Himalayan Soil: Not rich in humus.
Soil Particles
- Clay: Diameter of less than 0.002 mm.
- Silt: Diameter ranges from 0.002 mm to 0.06 mm.
6. Soil Fertility and Nutrients
Micronutrient Deficiency
- Zinc is the most deficient micronutrient in Indian soils.
Crops that Improve Fertility
- Leguminous crops like Pea and Black Gram (Urd) fix atmospheric nitrogen, improving soil fertility.
7. Soil Acidity and Alkalinity
General Properties & Fertility
- A pH value between 6 and 7 is ideal for nutrient availability and is considered fertile for common crops.
- Extreme acidity or alkalinity is harmful.
Problem Soils: Usar (Alkali) Soil
- Usar soil is an alkali soil with a pH greater than 7.
- Characteristics: Deficient in bacteria, nitrogen, and zinc.
- Reclamation Methods: Treated with gypsum, pyrites, and green manure. (Lime is not used).
- Crop Suitability: Tolerant paddy varieties like Narendra Shankar Usar Paddy-1 and Usar Paddy-2.
Saline & Alkali Soil Reclamation
- Salinization: A Process where irrigation water evaporates, leaving behind salts that make soil impermeable.
- Reclamation: Gypsum is the primary amendment used for long-term reclamation, followed by leaching with water.
Geographic Distribution of Problem Soils
- Largest Alkali Soil Area: Uttar Pradesh (35.75% of India’s total). Other states: Gujarat, Maharashtra, Tamil Nadu, Haryana, Punjab.
- Largest Saline Soil Area: Gujarat (has the largest total area under salt-affected soils).
Crop-Specific Soil Requirements
- Tea plantation requires acidic soil (low pH).
8. Soil Erosion and Conservation
Types and Process of Erosion
- The sequential process of water erosion is:
- Splash Erosion: Caused by raindrop impact.
- Sheet Erosion: Uniform removal of a thin layer of topsoil.
- Rill Erosion: Formation of small, removable channels.
- Gully Erosion: Formation of deep, permanent channels.
- Gully erosion is responsible for the formation of the Chambal Ravines.
Critical Erosion Areas in India
- Barren lands of the Chambal and Yamuna valleys.
- Foothill areas of the Shiwalik ranges.
- Chotanagpur Plateau, Malwa Plateau, and the black soil region of Maharashtra.
- In Madhya Pradesh, the Chambal Valley (districts like Morena, Bhind) is severely affected.
Factors Causing Soil Erosion
- Major Cause: Deforestation.
- Not a Cause: Terrace cultivation is a conservation method.
- Crop Type: Farmland erodes most rapidly with Sorghum and least with Clover.
Soil Conservation Methods
- Agricultural Practices:
- Crop Rotation
- Mixed/Multiple Cropping
- Allowing crop residue to remain in the field.
- Reduced/Zero tillage to conserve soil moisture.
- Physical Structures:
- Terracing
- Windbreaks
- Afforestation
- Not a conservation method: Seed modification (increases yield but does not enhance soil fertility).
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