Soil is the outer overing of the earth. It consists of loosely
arranged layer of materials composed of inorganic and organic constituents.
Soil provides the physical support needed for the anchorage of root system and
serves as the reservoir of air, water and nutrients that are essential for
The processes involved in the formation of soil are slow,
gradual and continuous. The sum total of environmental effects on rocks
collectively known as the weathering of rocks is a continuous phenomenon and
add more and more soil to the surface of the earth. There are different types
of parent materials of rocks available for the formation of soil.
Each type of soil is characterized by the presence of different
horizons which can be seen in a soil profile (Figure 10.1). The formation of
soil horizons depends on climate, living organisms, parent rock material,
topography and time; all of which control the weathering of rocks.
Physical properties of a soil type depends on the size of
particles, soil texture, soil temperature and soil pH.
Chemical properties of soil includes three main components which
provides nutrients for plant growth. The three components are the organic
matter, the derivatives of parent rock materials and the clay fraction.
The fertility of soil depends not only on its chemical
composition, but also on the qualitative and quantitative nature of
microorganisms inhabiting it. The branch of science dealing with study of soil
microorganisms and their activities in soil is known as 'Soil Microbiology'.