1. O Horizon (Organic Layer):
* Location: Topmost layer, directly beneath the surface litter (leaves, twigs, etc.).
* Composition: Primarily composed of decaying organic matter (humus), partially decomposed plant and animal residues.
* Characteristics: Dark, loose, spongy texture; rich in nutrients; highly permeable to water.
2. A Horizon (Topsoil):
* Location: Beneath the O horizon.
* Composition: Mixture of mineral particles (sand, silt, clay), organic matter, and living organisms (roots, insects, microbes).
* Characteristics: Darker than lower horizons; crumbly structure; supports most plant growth; rich in nutrients and microorganisms.
3. E Horizon (Eluviated Horizon):
* Location: Found beneath the A horizon in some soils, especially those with a high content of acidic minerals.
* Composition: Largely depleted of minerals and organic matter due to leaching (washing out) by rainwater.
* Characteristics: Light-colored, sandy texture; often appears bleached or ashy.
4. B Horizon (Subsoil):
* Location: Beneath the A or E horizon.
* Composition: Mostly mineral particles with some organic matter; often accumulates clay, iron oxides, and other materials leached from above.
* Characteristics: Denser and less porous than topsoil; often contains different colors and textures compared to the A horizon.
5. C Horizon (Parent Material):
* Location: Beneath the B horizon.
* Composition: Unweathered or partially weathered rock fragments from which the soil formed.
* Characteristics: Similar to bedrock but more fragmented; provides the foundation for the soil profile.
6. R Horizon (Bedrock):
* Location: The base of the soil profile.
* Composition: Solid, unweathered rock.
* Characteristics: Impenetrable to roots; influences soil development by supplying minerals and affecting drainage.
Key Points to Remember:
* Horizon development: These horizons are formed over long periods through weathering, decomposition, and biological activity.
* Variations: Soil profiles can vary greatly depending on factors like climate, parent material, topography, and biological activity.
* Soil fertility: The O and A horizons are crucial for plant growth due to their high nutrient content and favorable structure.
Understanding these soil horizons helps us appreciate the complex processes involved in soil formation and their importance for supporting life on Earth.
