1. O Horizon (Organic Layer): This is the topmost layer, composed of decomposing plant and animal matter. It's often called "humus" and is rich in nutrients.
* O1: The uppermost layer, consisting of fresh organic matter such as leaves, twigs, and other plant debris.
* O2: Partially decomposed organic matter, darker and more homogenous than O1.
* O3: Highly decomposed organic matter, often resembling a dark, spongy material.
2. A Horizon (Topsoil): This layer is a mix of mineral particles, organic matter, and living organisms. It's the most fertile layer and is crucial for plant growth.
* A1: The uppermost part of the A horizon, often rich in organic matter and exhibiting a darker color.
* A2: Lighter in color and less rich in organic matter than A1, often with evidence of leaching.
* A3: Transitional zone between the A and B horizons, showing characteristics of both.
3. E Horizon (Eluviated Horizon): This layer is characterized by the leaching of minerals and organic matter, often leaving behind a pale or light-colored layer. It's typically found in acidic soils and beneath the A horizon.
4. B Horizon (Subsoil): This layer is enriched with minerals and other materials that have been leached from the layers above. It's often denser and less porous than the A horizon.
* Bt: Accumulation of clay.
* Bk: Accumulation of calcium carbonate.
* Bh: Accumulation of humus.
5. C Horizon (Parent Material): This layer consists of the underlying bedrock or unconsolidated material from which the soil developed. It's relatively unweathered and doesn't show much evidence of soil formation.
It's important to remember: Not all soils have all five master horizons. The presence and characteristics of each horizon depend on factors like climate, vegetation, parent material, and time.
Additionally, there are other sub-horizons that further describe specific features within each master horizon. These sub-horizons are often designated with lower case letters (e.g., Bw, Bt, Bk, etc.) and represent specific characteristics like the accumulation of certain minerals or organic matter.
