Page 100 - ACTIVE SCIENCE 4 TOC

down by the action of micro-organisms

present in soil. This produces a fertile layer
of soil called humus. Soil occurs in different

colours like dark-brown, black and red,

depending on the climate and place.

Hence, soil is the topmost layer of the earth’s

surface. It contains fine particles like sand,

humus, minerals, air, organic matter and
water.

S oil Composition

Soil is a mixture of many different things. The five basic components of soil are as
listed below:

1. Rock material 2. Organic material

3. Air 4. Water 5. Soil creatures

Rock Material

Sand, silt and clay are small particles of rock. These are

formed by weathering of rock and constitute the inorganic
or the non-living component of the soil. Some of these are
large enough to be visible while others are very fine and
microscopic. The stones and pebbles are the large visible

components while sand and silt, although small; also form
a part of the visible matter. Very fine particles, closely
packed together form clay. The inorganic component of the Rock Material

soil constitutes about half of its total mass.

Organic Material
The dark-brown material formed by the decay of plant

and animal residue is called humus. It forms the organic
component of the soil. Humus is a rich source of minerals

and makes the soil fertile. It helps in the growth of plants
and helps the soil to hold more water. It is rich in nutrients
essential for the growth of plants.
Humus

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