Question

Which soil horizon contains humus?
A.A-horizon
B.B-horizon
C.C-horizon
D.Bedrock

Answer 1

Hint: Humus is defined as the fertile and one of the most important constituents of the soil. It is the dark organic material present on the top of the soil. It is basically the partially decayed organic matter which makes the soil porous.

Complete step by step answer:
The soil is the topmost layer of the Earth’s crust which is mainly composed of organic minerals and rock particles that support life. Basically, a soil profile is a vertical cross- section of the soil which is made up of layers running parallel to the surface. These layers are further known as soil horizons.
Now, the soil profile is further composed of horizons represented by the letters O, A, E, C, B and R. Let’s discuss the various kinds of horizons:
A horizon or topsoil – This layer is known as a humus layer and is mainly rich in organic materials. It consists of both organic matter and other decomposed materials. Moreover, the topsoil is soft and porous to hold enough water and air.
B horizon or subsoil – It is the horizon present just below the topsoil and above the bedrock. It contains less humus. Moreover, this layer holds more water than topsoil and is light brown due to the presence of clay soil.
C horizon or Saprolite- This layer is made up of broken bedrock. Moreover, the geological material present in this zone is cemented.

Hence, option A is correct.

Note:
Soil is mainly formed by the breakdown of bigger rocks into smaller and fine particles with the continuous action of wind, rain and other agents of natural force. It further takes hundreds to thousands of years for the formation of soil.