The upper crust of the earth, which is capable of supporting vegetation is called soil. We usually see the surface of the soil. If you look at the sides of trench, sides of a hill or steep river banks you will notice clearly visible different zones or layers. The side-view of soil zones or layer is known as soil profile.

The upper most layer of the soil is called the A-horizon or top soil. It absorbs maximum water. The top soil consists of soil particles, minerals, water and humus. The decomposed organic matter (decayed plant and animal remains) forms a spongy and brownish or blackish material known as humus. The humus makes the soil very fertile. It also increases water holding capacity of the soil.

Worms, insects, algae and fungi are found in the top soil. You will also find roots of plants in this layer. Plants get essential nutrients from the top soil through roots.

The second layer, called B-horizon, is more compact and harder than the top soil. It consists of sand, silt and clay. This layer contains very little organic matter. It is rich in soluble minerals and iron oxides.

The third zone, called C-horizon, consists of weathered rock. It is made up of small lumps of rocks with cracks and crevices. Below the C-horizon is found the bedrock.

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