Soil and components

1. SOILAND SOIL COMPONENTS
Soil is the covering on the solid encrust of the earth land mass.
Soil is made up of broken down rock material of varying
degree of fineness from parent rock due to different kind of
erosion cause by the weather.
THERE ARE TWO BASIC CONCEPTS OF SOIL
1. The Pedology: Considers soil as a natural entity, a
biochemical weathered and synthesized product of nature.
Aspects such as origin of the soil, its classification and its
description are all related to pedeology.
2. The Edaphology: Conceives the soil as natural habitat for
plant. Edaphology is the study of soil from the stand point
of higher plants. It considers the various properties of the
soil related to plant growth and production.

2. Buckman and Brady defined “Soil as a dynamic natural
body on the surface of the earth in which plants grow,
composed of minerals, organic materials and living forms.”
Joffe and Marbut defined “Soil as a natural body developed
by natural forces acting on natural materials.” It is usually
differentiated into horizons from mineral and organic
constituents of variable depth which differ from parent
material below in morphology, physical properties,
constitution, chemical properties, composition and biological
characteristics.

3. COMPONENTS OF SOIL:
The soil consists of four major components i.e. mineral matter,
organic matter, soil air and soil water. The volumetric
composition of mineral (inorganic) soil is:
a. Mineral matter 45%
b. Organic matter 5%
c. Soil water 25 %
d. Soil air 25%
Macro organism like rodents, insects, warms and micro-
organism like bacteria, fungi and algae live in the soil in large
numbers. There is a three phase system in which the mineral
and organic matter, form the solid phase. The water containing
salts and some gasses in solution is the liquid phase and the
various gasses form the gaseous phase.

4. Each phase contains a number of constituents which make the
whole system highly complex. On the account of changes
continuously taking place in the soil, the system is never in
equilibrium.
Mineral matter: The mineral are extremely variable in size.
Some are as large as the smaller rock fragments, other such as
colloidal clay particles are so small that they cannot be seen
without the aid of an electron microscope.
Organic matter: It represents partially synthesized plant and
animal residues. Such material is continuously being broken
down by the action of soil micro- organism. Organic matter
influences soil properties and consequently on plant growth. It
improves the physical condition of the soil, it increases the water
holding capacity of the soil and is a measure source of nutrient
for the plants. It is also a main source of energy for soil micro-
organism.

5. Soil water: It is a major component of the soil in relation to
plant growth. The water is held within the soil pores, if the
moisture content of the soil is optimum then the plants can
readily absorb the soil water. Not all the water which soil holds is
available to plants. Much of the water remains in the soil as a
thin film. Soil water dissolves salts and make up the soil solution
which is an important medium for the supply of nutrients to the
plants. There is an exchange of nutrients between the soil solids
and the soil solution and then between soil solution and plants.
Soil air: A part of the soil volume that is not occupied by soil
particles known as pore space is filled partly with soil water and
partly with soil air. The pore space is occupied by both air and
water. Volume of the air varies inversely with that of water. As
the moisture content of the soil increases, the air content
decreases and vice-versa.

6. Soil air has marked effect on the plant and root growth
including sol micro- organism, plant nutrient formation and
there availability. The content and composition of soil air is
determined to a large degree by the soil- water relationship. It
contains a number of gasses i.e. nitrogen, oxygen, carbon
dioxide and water vapors. Soil air differs from atmosphere in
several respects. First soil air contains greater proportion of
carbon dioxide and lesser amount of oxygen. Soil air has higher
moisture content than the atmosphere.