Soil Layers, Types and 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.
Soil Profile - 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.
Soil Profiles and Horizon - 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.
Components of Soil Profile
- 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
Four Main Mineral Horizons - 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.
