Horizons Of Soil

Key Notes :

1. What Are Soil Horizons?

  • Soil horizons are layers in the soil that differ in color, texture, structure, and composition.
  • They form through processes like weathering, organic decomposition, and leaching.

2. Major Soil Horizons

  1. O Horizon (Organic Layer)
    • Contains organic matter like decomposing leaves and plants.
    • Found on the surface.
    • Dark in color due to high organic content.
  2. A Horizon (Topsoil)
    • Known as the most fertile layer.
    • Contains a mix of organic matter and minerals.
    • Crucial for plant growth.
  3. E Horizon (Eluviation Layer)
    • Found beneath the A horizon.
    • Lighter in color due to leaching of minerals like clay, iron, and aluminum.
    • Often found in forested areas.
  4. B Horizon (Subsoil)
    • Rich in minerals leached from the upper layers (e.g., iron, aluminum).
    • Denser than topsoil, with less organic material.
  5. C Horizon (Parent Material)
    • Made up of partially weathered rocks.
    • Provides the base material for the formation of soil.
  6. R Horizon (Bedrock)
    • The lowest layer.
    • Consists of unweathered rock.
    • Forms the foundation of the soil profile.

3. Formation of Soil Horizons

  • Weathering: Rocks break down into smaller particles over time.
  • Organic Activity: Plants and animals contribute organic matter.
  • Leaching: Water carries minerals from upper layers to lower ones.
  • Deposition: Accumulation of materials in specific layers.

4. Importance of Soil Horizons

  • They help determine the soil’s ability to support plant growth.
  • Different crops require different soil conditions, which are influenced by the horizon characteristics.
  • Understanding horizons aids in soil conservation and management.

5. Visual Representation

A labeled diagram showing the soil profile with layers (O, A, E, B, C, and R) will help students visualize the structure.

Let’s practice!