Soil Profile of India: Layers, Types, and Agricultural Importance

Soil Profile (Soil Horizons) in India

A vertical section through different layers of the soil is called the soil profile. Soil consists of three horizontal layers. They are true soil at the top, sub soil, and bedrock

• What is Soil?
  • Soil is the topmost layer of the Earth's crust, primarily composed of organic materials and rock particles, and plays a crucial role in supporting life.

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  • A soil profile is a vertical cross-section of the soil that displays various layers called soil horizons.
• Understanding Soil Horizons
  • A soil profile is a vertical section through the different layers of soil, known as soil horizons.
  • The soil is typically divided into three horizontal layers:
    • Topsoil (True Soil)
    • Subsoil
    • Bedrock
  • Each horizon varies in texture, colour, depth, and chemical composition.
  • These layers are formed through internal processes such as leaching and capillary action (upward movement of water and minerals).
  • Soil profiles are analyzed by extracting samples in the form of a hexagonal column.
• Soil Horizon Layers
  • Soil Horizon refers to a layer of soil that exhibits distinct physical characteristics, including colour and texture, different from the layers above and below it.

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  • The topsoil or A-horizon is typically dark due to its rich content of humus and minerals.
  • The B-horizon is the middle layer, rich in minerals but with less organic content than the A-horizon.
  • The C-horizon consists of parent material, made up of weathered rocks and minerals.
• Components of Soil Profile
  • The soil profile extends from the soil surface down to the bedrock (parent material).
  • The regolith represents all weathered material within the profile, divided into two key components:
    • Solum: The uppermost, most weathered portion of the soil profile.
    • Saprolite: The least weathered portion, located just above the bedrock.

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• Types of Soil Horizons
  • Soil horizons are formed through interactions between climate, organisms, and the land surface over time.
  • These layers are shaped by selective leaching, ion removal, and mineral accumulation, resulting in two broad types:
    • Organic Horizons (O): Composed primarily of decomposed plant and animal matter.
    • Mineral Horizons: Includes A, E, B, and C horizons, which are rich in inorganic minerals.
• Detailed Horizon Breakdown

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  • O Horizon: Dominated by organic material, consisting of decomposed plant litter and humus.
  • A Horizon (Topsoil): The layer rich in both organic and mineral content, providing the essential nutrients for plant growth.
  • E Horizon: The eluviated layer, which has been leached of its nutrients, making it poor in minerals.
  • B Horizon (Subsoil): The subsoil, where minerals leached from the upper layers accumulate.
  • C Horizon: Made up of weathered rock fragments and material that are the foundation of soil formation.
  • R Horizon: The bedrock layer located beneath the soil profile, from which the soil derives its mineral content.
• Significance of the Soil Profile
  • The study of soil profiles is critical for agriculture, as it helps determine land suitability for various crops.
  • Soil profiles are integral to land classification and understanding how different layers support plant growth, water retention, and mineral availability.
  • Knowledge of soil horizons is also crucial for soil conservation and improving soil fertility for sustainable farming.