Soil Horizons

Soil horizons are distinct layers of soil that develop over time due to various physical, chemical, and biological processes. Each horizon has unique characteristics that define its composition, color, texture, and function. Understanding soil horizons is essential for fields like agriculture, geology, and environmental science. Here’s an overview of the main soil horizons typically found in a soil profile:

1. O Horizon (Organic Layer)
   • Description: The topmost layer, rich in organic material, including decomposed leaves, plants, and other organic matter.
   • Characteristics: Dark in color, it can vary from a few centimeters to several inches thick. Vital for nutrient cycling and soil health.
2. A Horizon (Topsoil)
   • Description: The layer beneath the O Horizon, consisting of a mix of organic material and mineral particles.
   • Characteristics: Typically darker than the lower layers due to organic content. It is crucial for plant growth because it contains nutrients and supports root systems.
3. E Horizon (Eluviation Layer)
   • Description: A subsurface layer from which minerals and organic matter have been leached or eluviated.
   • Characteristics: Lighter in color compared to the A Horizon. It is generally sandy or silt-rich and poor in nutrients.
4. B Horizon (Subsoil)
   • Description: The layer beneath the E Horizon where materials like iron, aluminum, clay, and organic compounds accumulate through illuviation.
   • Characteristics: Typically denser and more compact than the layers above, it can be more enriched in certain minerals but lower in organic content. Often shows different colors due to the presence of minerals like iron oxides.
5. C Horizon (Parent Material)
   • Description: A layer consisting of partially disintegrated and weathered parent material from which the soil is formed.
   • Characteristics: Less affected by soil-forming processes, it retains some properties of the original rock or sediments. It is usually low in organic matter but high in minerals.
6. R Horizon (Bedrock)
   • Description: The unweathered rock layer beneath the C Horizon.
   • Characteristics: Very little biological activity occurs here. It serves as the parent material from which the upper soil horizons are derived through the process of weathering.

These horizons form a soil profile that can be studied to understand soil health, fertility, and suitability for various land uses. Each horizon’s distinctive attributes play a critical role in supporting plants, filtering water, and hosting numerous organisms.