Soil is an ecosystem with different entities relating and interacting together to improve the condition within to favor plant growth and development. Parts of the entities of the soil are the soil microorganisms. They are of cogent importance in the soil and major prerequisites to plant growth and yield.

What are soil microorganisms?

Soil organisms are the living things residing within the soil, which aid in the degradation and decomposition of the non-living things in the soil to release nutrient in the soil for plants to utilize. In order words, they breakdown non-living materials in the soil, to provide nutrient for the soil.

There are two main types or divisions of soil microorganisms

They are:

  • Micro soil organisms or microfauna
  • Macro soil organisms or macrofauna


Micro soil organisms are soil organisms that are small and may not be seen with the naked eyes. Examples are bacteria, fungi, actinomycetes, algae, and protozoa, etc. While the soil macro-organisms or macrofauna are soil-living organisms that can be seen with the naked eyes; they are relatively larger in size, examples are earthworms, beetles, centipedes, slugs, snails and ants, etc.


How soil microorganisms affect crop yield

As said earlier, soil organisms breakdown organic matter or non-living materials in the soil to release nutrients into the soil. The soil contains organic matters; these organic materials are the raw form of nutrient or let’s just say they are the unprocessed soil nutrients. Soil organisms help in the processing of this organic matter through a process known as mineralization. At the end of this process, nutrients are made available in the soil for plants to utilize through their roots.

Bacteria help as a decomposing agent; they break down organic material in its initial stage of decomposition due to moderate moisture levels conducive for their growth. Also, some bacteria help in nitrogen-fixing, they help in converting nitrogen gas into simpler forms that can be consumed by plants.


Activities of soil organisms in the soil

Different soil microorganisms play a major role in the decomposition and release of nutrients into the soil, each type of soil organisms have a distinct role they play during these processes.


Microfauna or soil microorganisms

They are very small in size; they are the most important during the process of soil organic matter decomposition to release nutrients.

  • Bacteria

Bacteria are very small soil organisms; they are the most abundant in the soil, a hand full of soil may contain millions of bacteria but they cannot be seen with the naked eyes. They are decomposing agents; their primary role is to breakdown organic matter in the soil.

Some bacteria help to fix nitrogen into the soil, thus, increasing the soil fertility. Examples of important bacteria are Pseudomonas, Arthrobacter, Achromobacter, Bacillus, Clostridium, Micrococcus, Flavobacterium, Chromobacterium, and Mycobacterium.


  • Fungi

Fungi are other microorganisms that play an active role in the wellness of the soil; they are made up of spores. They help to bind the soil, thus, increasing water retention capacity of soil; they also aid in the decomposition of organic matter in the soil and are helpful in the preservation of organic materials in the soil.. Examples of notable fungi are Alternaria, Aspergillus, Cladosporium, and Dematium;


  • Protozoa

Protozoa are part of the soil organisms; they are relatively larger in size compare to the aforementioned soil organisms. They feed mainly on the decay soil matters and bacteria, thus, controlling the explosive population of the bacteria.

They release nitrogen in form of ammonia into the soil; they help to attain equilibrium of soil organisms or fauna. Notable protozoans present in the soil are Allantion, Biomyxa, Nuclearia, Trinema, Balantiophorus, Colpoda, Gastrostyla, Oxytricha, Pleurotricha and Vorticella.


  • Nematode

These are roundworms present in the soil. The earthworm is a good example; it helps to improve the aeration of the soil through its burrowing activities. Also, supply moisture as a result of the nature of their body.


  • Algae

Algae are present on the surface of moist soils, where adequate sunlight is available. The presence of algae helps in soil conservation and in improving soil structure. In paddy fields, blue-green algae play a significant role in nitrogen fixation. Important algae to crop production are Chlorella, Chlorococcum, Protosiphon, Aphanocapsa, Anabaena, Chroococcus, Nostoc and Scytonema.


  • Actinomycetes

These soil organisms are also abundant in soils with high decomposed organic material. They are responsible for the pungent and earthy smell that evolves during or after ploughing operations. They are capable of degrading complex chemical substance in the soil, they play an important role in the nutrient availability in the soil. Examples of actinomycetes present in the soil are Nocardia, Streptomyces, Micromonospora, and Nocardia.


Factors that enhance the activities of soil organisms

Truly, these soil organisms are good and important to the soil and nutrient availability but their activities are facilitated by good environmental conditions. This is why nutrient availability differs from one location to another, depending on the prevailing weather conditions in those areas. These conditions are:


  • Temperature:

Temperature plays an active role in the activities of the soil microorganisms. The rate of reaction in the soil is influenced by the temperature of the soil; the higher the temperature, the higher the activities of the soil microorganisms.

At high temperature, the soil organisms carry out their various activities actively in the soil; decomposition and degradation of organic matter are faster and the release of nutrients into the soil is also very faster. Thus, soil in areas with high temperature like the tropical region has abundant nutrient as a result of the high activities of the soil organisms.

However, in an area with low temperature and soil of high organic matter, such soil is said to be less fertile because of the reduced activities of the soil organisms as a result of the low temperature. Low temperature does not favor the activities of the soil organisms; it keeps them docile.

The organic matters in such soil are just there, untouched; thus the release of nutrient, if any, is always slow and low to meet the plant’s nutrient requirement.


  • Rainfall

Rainfall is very good as it helps to condition the soil and dissolves mineral nutrients. However, too much of anything is bad and detrimental; when rainfall is highly intense and resulting in a waterlogging situation, it becomes a problem to the soil and its organisms. Soil organisms are living things as well; too much water blocks the pore spaces and reduces respiration, leading to the death of the organisms.


  • Soil air

A well-aerated soil favors the activities of soil organisms, soil organisms respire. Nematodes like worms improve the aeration of the soil through burrowing.


  • Organic matter

The presence of organic matter in the soil excites the soil organisms. Soil organisms feed on the organic matter; without the organic matter, living becomes unbearable to them. At times, leads to their detrimental effects on crop; this facilitates the need for the addition of compost manure or any other organic manure to the soil to increase the organic matter content of the soil.


  • Soil pH

Soil pH is the degree of alkalinity and acidity of the soil. Soil microorganisms thrive best as pH ranging from 6-8; that is a neutral pH.


  • Man activities

Man activities like bush burning kill the soil organisms; bush burning should be discouraged on the farm to conserve soil organisms.


How to preserve soil organisms

Soil microorganisms can be preserved through the addition of organic fertilizer only; adding inorganic fertilizer to soils kills the soil organisms because they are hygroscopic in nature, they tend to absorb moisture from the soil and scorch the soil organisms.

Organic fertilizers like compost manure are the main food for soil organism; when soil organisms feed on them, they release nutrients for the plants to take up. Apart from serving as food for microorganisms, organic manure helps to build the soil structure and conserve moisture at the same time.

in conclusion,

Importance of soil microorganisms in plant growth needs to be emphasized; they can increase crop yield when treated well and under favorable conditions. A good farmer must think of how to cater for the soil organisms as he does for the plants too.

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