Soil exhibits significant variation with depth, giving rise to distinct soil horizons. These horizons result from various physical, chemical, and biological processes occurring in the soil profile. The primary horizons commonly observed in a soil profile are as follows:

O Horizon (Organic Horizon):

- Located at the ground surface

- Consists of organic matter such as decomposing leaves, twigs, and other plant material

- Dark in color due to high organic content

A Horizon (Topsoil):

- Below the O horizon

- Mixture of mineral particles, organic matter, and living organisms

- Darker in color than the subsoil horizons

- Zone of maximum biological activity and root concentration

B Horizon (Subsoil):

- Located below the A horizon

- Contains mineral particles, clay, and iron oxides

- Lighter in color than the topsoil due to lower organic matter content

- Zone of accumulation of clay minerals and other materials leached from the topsoil

C Horizon (Parent Material):

- Beneath the B horizon

- Consists of the original geological material from which the soil developed

- Less weathered and has minimal organic matter

- Influenced by the underlying rock or sediment

R Horizon (Bedrock):

- The bottom layer of the soil profile

- Consists of solid, unweathered rock or consolidated material

- Not part of the soil but influences soil characteristics

The thickness and characteristics of each horizon vary depending on factors such as climate, topography, vegetation, and parent material. These horizons gradually transition into one another, forming a soil profile that reflects the unique environmental conditions of a particular location.