soil is a mixture of mineral and organic material that sits just below Earth's
surface. Soil is formed from rock and mineral fragments, organic matter, water, and
air.
Formation of soil:
1.Dirt makes up the earth's outer layer or topmost layer. Soil contains minerals,
organic matter, and living organisms.
2.However, soil can apply to any loose material in general.
3.Soil is formed by the weathering or breakdown of parent rocks due to physical,
chemical, and biological factors.
4.Soil formation is a lengthy process that takes thousands of years to complete.
Soil Profile:
The soil is found in layers, which are arranged during the formation of soil. These
layers called horizons, the sequence of layers is the soil profile. The layers of
soil can easily be observed by their color and size of particles. The main layers
of the soil are topsoil, subsoil and the parent rock. Each layer has its own
characteristics.
These features of the layer of soil play a very important role in determining the
use of the soil. Soil that has developed three layers, is mature soil. It takes
many years under a favorable condition for the soil to develop its three layers. At
some places, the soil contains only two layers. Such soil is immature soil.
Horizons of the Soil:
1.Humus
Humus is dark, organic material that forms in soil when plant and animal matter
decays.The thick brown or black substance that remains after most of the organic
litter has decomposed is called humus. Earthworms often help mix humus with
minerals in the soil.Humus contains many useful nutrients for healthy soil. One of
the most important is nitrogen. When humus is in soil, the soil will crumble. Air
and water move easily through the loose soil, and oxygen can reach the roots of
plants.
Humus can be produced naturally or through a process called composting. When people
compost, they collect decaying organic material, such as food and garden scraps,
that will be turned into soil.
2. Horizon A or Topsoil
This layer consists of decomposed material and organic matter. This is the reason,
the topsoil has a dark brown color. The hummus makes the topsoil soft, porous to
hold enough air and water. In this layer, the seeds germinate and roots of the
plants grow. Many living organisms like earthworms, millipedes, and centipedes,
bacteria, and fungi are found in this layer of soil.
3.Horizon B or Subsoil
Just below the topsoil lies another layer called subsoil or horizon-B. It is
comparatively harder and compact than topsoil. It is lighter in color than the
topsoil because there is less humus in this layer. This layer is less organic but
is rich in minerals brought down from the topsoil. It contains metal salts,
especially iron oxide in a large proportion. Farmers often mix horizon-A and
horizon-B when ploughing their fields.
3. Bedrock or Horizon C
Bedrock is also known as parent rock and lies just below the subsoil. It contains
no organic matter and made up of stones and rocks, so it is very hard. This layer
represents a transition zone between the earth’s bedrock and horizon A and B.
