Soil Layers

Soil layers, often referred to as soil horizons, are distinct layers of soil that vary in physical and chemical composition, organic matter content, and other characteristics. Understanding these layers is fundamental in fields like agriculture, geology, and environmental science. Here are the primary soil layers from the surface down to the bedrock:

1. O Horizon (Organic Layer)
   • Composed mainly of organic matter such as decomposed leaves, plants, and animal materials.
   • Dark in color and rich in nutrients.
   • Important for plant growth as it holds moisture and provides nutrients.
2. A Horizon (Topsoil)
   • Known as the surface soil or the layer where most of the biological activity occurs.
   • Contains a mix of organic material with mineral particles.
   • Generally darker and looser compared to the subsurface layers.
   • Critical for root development and is often the most nutrient-rich layer.
3. E Horizon (Eluviation Layer)
   • Characterized by the removal of organic matter, clay, iron, or aluminum.
   • Light in color due to the leaching of materials, which leaves behind sand and silt.
   • Not always present in all soil profiles, more common in forested areas.
4. B Horizon (Subsoil)
   • Accumulation layer where materials leached from above (such as silicates, clay, iron, and aluminum) accumulate.
   • Denser and less fertile compared to the A horizon.
   • Often referred to as the “zone of accumulation” or illuviation.
5. C Horizon (Parent Material)
   • Consists of weathered parent material from which soil is formed.
   • Contains larger rock particles and less biological activity.
   • Significant for understanding the soil’s origin and composition.
6. R Horizon (Bedrock)
   • The unweathered rock layer that lies beneath all the other layers.
   • Composed of solid rock like granite, limestone, basalt, etc.
   • It eventually weathers into the C horizon and contributes to the formation of soil over time.

These layers contribute to the soil’s overall structure, properties, and functions in supporting plant and animal life, retaining water, and cycling nutrients. Soil scientists use these horizons to assess soil health and suitability for various land uses.