Soil and components

Soil and components

1. SOIL AND 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 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 . 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: Mineral matter 45% Organic matter 5% Soil water 25 % 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.