Soils in india 

Soil: Definition and Formation

• Soil is the uppermost layer of the Earth’s crust, composed of mineral particles, organic matter, water, and air, supporting plant growth.
• It forms through the weathering of rocks, biological activity, and chemical processes over thousands of years.
• The process involves physical disintegration, chemical decomposition, and biological accumulation of humus.
• Factors influencing soil formation include parent rock, climate, organisms, topography, and time.
• Weathering of rocks releases minerals that mix with organic matter to develop soil fertility.
• Humification (decomposition of organic matter) and eluviation (leaching of materials) play crucial roles in soil development.
• Climate affects soil properties by controlling temperature and precipitation levels, influencing weathering intensity.
• Soil horizons (layers) develop over time, forming a soil profile with distinct characteristics.
• Examples: The black soil of the Deccan Plateau is formed from basaltic rock weathering, while laterite soil develops in regions with heavy rainfall.
• Soil conservation methods include afforestation, contour plowing, and terracing to prevent degradation.

Soil Profile

• A soil profile is a vertical cross-section of soil that shows different layers called horizons.
• The main soil horizons include:
  • O-Horizon: Organic layer with decomposed matter.
  • A-Horizon (Topsoil): Rich in minerals and organic matter, crucial for plant growth.
  • B-Horizon (Subsoil): Accumulates minerals leached from above layers.
  • C-Horizon: Weathered rock fragments, influencing soil characteristics.
  • R-Horizon: Unweathered bedrock.
• The depth of each layer varies depending on climatic and geological factors.
• The leaching process removes minerals from the upper layers, depositing them in deeper layers (illuviation).
• In arid regions, calcium carbonate accumulates, forming hardpan layers in subsoil.
• Soil profile influences fertility, drainage, and suitability for agriculture.
• Example: Black soil has a thick A-horizon due to high moisture retention, whereas laterite soil has a thin topsoil due to leaching.

Major Soil Types in India

(a) Alluvial Soil

• Formed by river deposits of the Indus, Ganga, and Brahmaputra systems.
• Found in the Indo-Gangetic plains, coastal plains, and river valleys.
• Composed of fine-grained silt, sand, and clay, making it highly fertile.
• Suitable for crops like wheat, rice, sugarcane, and pulses.
• Divided into Bhangar (older, coarse-textured) and Khadar (newer, fine-textured) alluvial soil.
• Rich in potash, phosphoric acid, and lime but deficient in nitrogen.
• Prone to soil erosion due to frequent flooding.

(b) Black Soil (Regur Soil)

• Formed from the weathering of basaltic rock in the Deccan Plateau.
• Found in Maharashtra, Madhya Pradesh, Gujarat, and parts of Andhra Pradesh and Tamil Nadu.
• Rich in clay content, retains moisture for a long time.
• High in calcium carbonate, magnesium, potash, and lime but poor in phosphoric content.
• Ideal for cotton cultivation; also supports crops like jowar, wheat, and pulses.
• Develops deep cracks during summer, aiding aeration and root penetration.

(c) Red and Yellow Soil

• Formed by weathering of crystalline igneous rocks in low rainfall areas.
• Found in Odisha, Chhattisgarh, southern Karnataka, and Tamil Nadu.
• Red due to ferric oxide; turns yellow in hydrated form.
• Rich in iron but deficient in nitrogen, phosphorus, and humus.
• Suitable for crops like millet, groundnut, pulses, and cotton.

(d) Laterite Soil

• Develops in areas with heavy rainfall and high temperature, leading to leaching.
• Found in Karnataka, Kerala, Tamil Nadu, and parts of Maharashtra.
• Rich in iron and aluminum but poor in nitrogen, phosphoric acid, and potash.
• Suitable for tea, coffee, and cashew nut cultivation.
• Used in making bricks due to its hardening property.

(e) Arid Soil

• Found in arid and semi-arid regions like Rajasthan, Gujarat, and western Punjab.
• High in salt content due to high evaporation rates.
• Low organic content, poor water retention capacity.
• Can be made fertile through irrigation (e.g., Indira Gandhi Canal in Rajasthan).
• Suitable for drought-resistant crops like barley, maize, and pulses.

(f) Forest and Mountain Soils

• Found in Himalayan regions and dense forest areas.
• Varies with altitude; acidic in higher regions and fertile in lower valleys.
• Rich in humus but deficient in phosphorus and lime.
• Supports coniferous forests and horticultural crops like apples and almonds.

Soil Erosion and Degradation

• Soil erosion is the removal of topsoil by natural forces like water, wind, and human activities.
• Causes include deforestation, overgrazing, improper farming, and mining.
• Types:
  • Sheet erosion: Uniform removal of soil by surface runoff.
  • Gully erosion: Formation of deep channels due to water flow (e.g., Chambal ravines).
  • Wind erosion: Common in arid regions, where wind carries away fine soil particles.
• Soil degradation occurs due to salinization, overuse of fertilizers, and industrial pollution.
• Desertification occurs when fertile land turns barren due to climatic and human-induced factors.
• Examples: Soil erosion in Shivalik Hills, desertification in Rajasthan, and salinity in Punjab due to over-irrigation.

Soil Conservation Measures

• Contour Plowing: Plowing along contour lines to reduce runoff and prevent erosion.
• Terrace Farming: Constructing step-like fields on slopes to reduce water erosion.
• Afforestation: Planting trees to bind soil and prevent erosion.
• Shelterbelts: Rows of trees planted to break wind speed and prevent wind erosion.
• Mulching: Covering soil with organic materials to retain moisture and reduce erosion.
• Check Dams: Small barriers built across streams to slow down water flow and control erosion.
• Crop Rotation: Growing different crops to maintain soil fertility.
• Agroforestry: Integrating trees with crops to improve soil structure and reduce erosion.

Multiple-Choice Questions

1. Which of the following statements about soil formation is/are correct?

1. Soil formation is influenced by parent rock, climate, organisms, topography, and time.
2. Weathering of rocks releases minerals that mix with organic matter to develop soil fertility.
3. Soil formation is a rapid process that takes only a few decades.
4. Humification and eluviation are key processes in soil development.

Options:
(a) 1, 2, and 4 only
(b) 1 and 3 only
(c) 2 and 4 only
(d) 1, 2, 3, and 4

Answer: (a) 1, 2, and 4 only
Explanation: Soil formation is a slow process that takes thousands of years. The other statements correctly describe factors influencing soil formation.

2. Which of the following statements regarding soil profile is/are correct?

1. The A-horizon is rich in minerals and organic matter and supports plant growth.
2. The B-horizon is also known as topsoil and is crucial for agricultural activities.
3. The C-horizon consists of weathered rock fragments.
4. The O-horizon is the lowest layer in the soil profile.

Options:
(a) 1, 2, and 3 only
(b) 2 and 4 only
© 1 and 3 only
(d) 1, 3, and 4 only

Answer: (c) 1 and 3 only
Explanation: The B-horizon is subsoil, not topsoil, and the O-horizon is the topmost layer, not the lowest.

3. Which of the following correctly describes Black Soil?

1. It is formed from the weathering of basaltic rock in the Deccan Plateau.
2. It is rich in calcium carbonate, magnesium, potash, and lime but lacks phosphoric content.
3. It develops deep cracks during summer, aiding aeration.
4. It is found in Himalayan regions and supports coniferous forests.

Options:
(a) 1, 2, and 3 only
(b) 1 and 4 only
(c) 2 and 4 only
(d) 1, 2, 3, and 4

Answer: (a) 1, 2, and 3 only
Explanation: Black soil is found in the Deccan Plateau, not in the Himalayan regions.

4. Consider the following statements regarding Laterite Soil:

1. It develops in areas with heavy rainfall and high temperature.
2. It is rich in nitrogen and phosphorus.
3. It is suitable for tea, coffee, and cashew nut cultivation.
4. It is widely used in brick-making due to its hardening property.

Options:
(a) 1, 2, and 4 only
(b) 1, 3, and 4 only
(c) 2 and 3 only
(d) 1, 2, 3, and 4

Answer: (b) 1, 3, and 4 only
Explanation: Laterite soil is poor in nitrogen and phosphorus, making statement 2 incorrect.

5. Which of the following statements about Alluvial Soil is/are correct?

1. It is found in the Indo-Gangetic plains, coastal plains, and river valleys.
2. Bhangar is the newer and fine-textured alluvial soil.
3. It is rich in potash, phosphoric acid, and lime but deficient in nitrogen.
4. It is formed by river deposits of the Indus, Ganga, and Brahmaputra systems.

Options:
(a) 1, 2, and 4 only
(b) 1, 3, and 4 only
(c) 2 and 3 only
(d) 1, 2, 3, and 4

Answer: (b) 1, 3, and 4 only
Explanation: Khadar is the newer and fine-textured alluvial soil, while Bhangar is older and coarse-textured.

6. Which of the following correctly describes Arid Soil?

1. It is found in Rajasthan, Gujarat, and western Punjab.
2. It has high salt content due to high evaporation rates.
3. It has high organic content and excellent water retention capacity.
4. It can be made fertile through irrigation, as seen in the Indira Gandhi Canal project.

Options:
(a) 1, 2, and 4 only
(b) 2, 3, and 4 only
(c) 1 and 3 only
(d) 1, 2, 3, and 4

Answer: (a) 1, 2, and 4 only
Explanation: Arid soil has low organic content and poor water retention capacity, making statement 3 incorrect.

7. Which of the following is NOT a type of soil erosion?

1. Sheet erosion
2. Gully erosion
3. Leaching erosion
4. Wind erosion

Options:
(a) 1 and 3 only
(b)1, 2, and 4 only
(c) 2 and 4 only
(d) 3 only

Answer: (d) 3 only
Explanation: Leaching is a process of nutrient removal but is not categorized as a type of soil erosion.

8. Consider the following statements about Soil Conservation Measures:

1. Contour plowing reduces runoff and prevents erosion.
2. Terrace farming is commonly practiced in arid regions to control wind erosion.
3. Shelterbelts are rows of trees planted to reduce wind speed.
4. Check dams help slow water flow and control erosion.

Options:
(a) 1, 3, and 4 only
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1, 2, 3, and 4

Answer: (a) 1, 3, and 4 only
Explanation: Terrace farming is used in hilly regions, not arid regions, making statement 2 incorrect.

9. Which of the following statements about Red and Yellow Soil is/are correct?

1. It is formed by the weathering of crystalline igneous rocks in low rainfall areas.
2. The red color is due to the presence of iron oxide.
3. It is found in Maharashtra, Gujarat, and Rajasthan.
4. It is suitable for crops like millet, groundnut, pulses, and cotton.

Options:
(a) 1, 2, and 4 only
(b) 1 and 3 only
(c) 2, 3, and 4 only
(d) 1, 2, 3, and 4

Answer: (a) 1, 2, and 4 only
Explanation: Red and yellow soil is found in Odisha, Chhattisgarh, southern Karnataka, and Tamil Nadu, not in Maharashtra, Gujarat, and Rajasthan.

10. Which of the following factors contribute to soil degradation?

1. Salinization due to over-irrigation
2. Overuse of fertilizers and pesticides
3. Afforestation
4. Industrial pollution

Options:
(a) 2 and 3 only
(b) 1, 2, and 4 only
(c) 1 and 3 only
(d) 1, 2, 3, and 4

Answer: (b) 1, 2, and 4 only
Explanation: Afforestation helps in soil conservation, not degradation, making statement 3 incorrect.