Which soil horizons comprise the solum?

✅Explanation:
The solum, also referred to as the true soil, is the uppermost layer of the soil profile that is significantly affected by soil-forming processes (pedogenesis).
-A horizon (topsoil): This is the uppermost layer, rich in organic matter, influenced by biological activity, and often darker in color compared to the layers below.
-B horizon (subsoil): This layer lies beneath the A horizon. It can be enriched with certain minerals leached from the A horizon, exhibit different textures or colors, and may contain clay accumulations.

🔑Key Points:
The A-Horizon or Topsoil
-This layer is rich in organic material and is known as the humus layer. This layer consists of both organic matter and other decomposed materials. The topsoil is soft and porous to hold enough air and water.
-In this layer, the seed germination takes place and new roots are produced which grows into a new plant.
-This layer consists of microorganisms such as earthworms, fungi, bacteria, etc.
The O-Horizon
-The O horizon is the upper layer of the topsoil which is mainly composed of organic materials such as dried leaves, grasses, dead leaves, small rocks, twigs, surface organisms, fallen trees, and other decomposed organic matter.
-This horizon of soil is often black brown or dark brown in color and this is mainly because of the presence of organic content.
The E-Horizon
-This layer is composed of nutrients leached from the O and A horizons.
-This layer is more common in forested areas and has lower clay content.
-The B-Horizon or Subsoil
-It is the subsurface horizon, present just below the topsoil and above the bedrock.
-It is comparatively harder and more compact than topsoil. It contains less humus, soluble minerals, and organic matter.
-It is a site of deposition of certain minerals and metal salts such as iron oxide.
-This layer holds enough water than the topsoil and is lighter brown due to the presence of clay soil.
-The soil of horizon-A and horizon-B is often mixed while ploughing the fields.
The C-Horizon or Saprolite
-This layer is devoid of any organic matter and is made up of broken bedrock. This layer is also known as saprolite.
-The geological material present in this zone is cemented.
The R-Horizon
-It is a compacted and cemented layer.
-Different types of rocks such as granite, basalt, and limestone are found here.