Soil Organisms of Plant and Animal Nature

After reading this article you will learn about the soil organisms of plant and animal nature.

Soil Organism of Plant Nature:

The microbes in this class of micro-flora are bacteria, fungi, algae and actinomycetes. Of these, bacteria are the most abundant in soil, next in order are actinomycetes, followed by fungi (Table 13.1). Algae are found under specific situations.

The soil environment under the influence of plant roots is called the rhizosphere. The rhizosphere is not a well-defined uniform region, but a zone of microbial gradient extending from the root surface having maximum microbial population in soil.

Bacteria:

These are very small organisms and occur everywhere. In the soil, bacteria are estimated to average one billion per gram of soil. Bacteria are mostly unicellular and vary widely in their size and shape.

The bacteria are:

(1) Spherical

(2) Spiral and

(3) Rod- shaped.

A bacterial cell consists of a small speck of protoplasm and has no nucleus.

The bacteria are or two types:

(a) Autotrophic Bacteria:

These bacteria manufacture their food (complex compounds) by using very simple inorganic substances. Autotrophic bacteria oxidize ammonia, nitrate, sulphur, manganese, iron, carbon monoxide, hydrogen and methane, so that plant can utilize these substances.

(b) Heterotrophic Bacteria:

These bacteria depend upon organic matter or living body for their food. These bacteria decompose the organic wastes and dead bodies of plants and animals and release chemical elements locked up in them. Functionally, they bring about mineralization of organic matter through hydrolysis and oxidation and release nitrogen, phosphorus and other nutrients in form available to plants. They also fix atmospheric nitrogen in the soil.

Fungi:

These are non-green plant (no chlorophyll); thus, they cannot manufacture their own food and so they depend on others for their food. Some are parasites, taking food from living organism, and others are saprophytic deriving nutrients from dead remains of plants and animals. Fungi are estimated to average one million per gram of soil.

They decompose the organic matter in form available to the plants. The chemical substances such as streptomycin, a widely used antibiotic, is obtained from soil fungus called Streptomyces and Penicillin from Penicillium fungus.

Algae:

They contain chlorophyll and therefore, they manufacture their own food. Some algae are unicellular and some algae are multicellular. Algae are commonly found in fresh water ponds, damp soil, such as paddy fields. They add organic matter to the soil and fix atmospheric nitrogen. Algae are estimated to average 100 thousand per gram of soil. The mam groups of algae are: 1. Green, 2. Blue-green, 3. Yellow-green, and 4. Diatoms.

Actinomycetes:

Actinomycetes have characteristics which are transitional between bacteria and fungi. They are next to bacteria in abundance in soil. Of the genera commonly found in soils, the streptomyces is more abundant.

Soil Organism of Animal Nature:

Micro Organism:

Protozoa:

This phylum includes microscopic animals consisting of single celled bodies. They live chiefly in water and the soil. Amoeba, Paramecium, Euglena etc., are free-living forms. Soil protozoa feed either on soil organic matter or on bacteria, thus, regulating the number of the bacteria in the soil.

Nematodes:

They live in soil and water and cause disease in many crop plants such as rice, tomato etc.

Macro Organism:

Earthworm:

They are found in moist soil containing decaying organic matter. Earthworms make burrows by eating through the soil. The soil is finely ground in its gizzard (grinding mill), moved through its alimentary canal. In the burrowing process, they bring the sub-soil to the surface and add it to the top soil.

The burrows improves the aeration of soil. Further, the larger soil particles are made smaller by grinding process and thus the water-holding capacity of the soil is also improved. Nitrogen waste products of the worm are also added to the soil, thus increasing its nitrogen content.

Worm and Insects:

They feed on plants and their remains. Termites are very harmful to the crops as they damage the roots.

Insects and some other large animals promote aeration and water percolation.