Soil, Soil Profile, Humus and Formation of Soil

Soil: The uppermost thin layer covering the Earth’s surface is called soil. Soil is composed of rock particles, mineral fragments, remains of the dead, living things, water and air. The soil has five layers: humus, topsoil, subsoil, rock fragments and bedrock. There are four basic types of soil: sand, loamy, silt and clayey.

Soil Profile: Soil present on the surface of the Earth is actually present in layers. The various layers are:
O: It is the topmost fertile layer, rich in humus. It is soft, porous and retains a lot of water. It is a natural habitat of many worms and insects.
A: It has less humus and more minerals.
B: It is slightly hard and compact.
C: This layer has lumps of rocks. These rocks are cracked and have crevices.
D: Bedrock is the hardest layer that cannot be dug by spade.

Humus: Humus is dark, organic material, made up of decayed debris of dead animals and plants. It is a natural nutrient-source of plants. It takes several years for fertile soil to take shape. The main components of fertile soil are: leaf litter, twigs and other material, and remains of dead animals. These dead parts decay due to the action of bacteria. Eventually, the decomposed material turns black or brown in colour. Earthworms often help mix humus with minerals in the soil.

Formation of Soil: Soil formation is a long process. It is formed by continuous weathering of rocks. The main causative agents of rock weathering are: sun, rain, water, wind, moving ice, strong waves, plant growth and atmospheric gases. The cracking and crumbling of rock is the initial step of soil formation. Water and wind rub rocks against one another and carry them to narrow places. These rock particles further break into very small pieces. And slowly, fine particle soil is made.

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