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SAI International School
Subject - Chemistry

Class - VII
Topic - SOIL: A Natural Resource
Sub-topic - Soil Profile, Types of Soil

Lesson Notes

Soil Profile:

A vertical section of soil from ground surface to parent rock is called soil profile.

The different layers of soil are called its Horizons.

‘O’-Horizon: It is about one inch thick. It contains dead organic matter which later
decomposes to form humus.

‘A’-Horizon: It forms the top soil. This layer is very important for the growth of plants
as it contains humus and minerals. It is dark in colour, soft, porous and holds a lot of
water. It also provides shelter to many decomposers like microbes and worms.

‘E’-Horizon: This layer contains sand and silt particles. It is the intersection layer
between A-horizon and B-horizon.

‘B’-Horizon: It forms the subsoil. It is lighter in colour and does not contain humus.
The subsoil is rich in minerals. The roots of plants grow till this layer.

‘C’-Horizon: This layer consists of fragments broken down from the bed rock. Roots
of plants cannot penetrate through this layer. It lacks humus and is infertile. The
rainwater gets collected in this layer in the form of groundwater.

Bedrock: This is the layer of unweathered rocks which slowly undergoes weathering
to form the C-horizon. Water cannot penetrate through this layer so it is also called
the bedrock.

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