The organisms found in the soil are called soil organisms. The soil microorganisms maintain the plant’s right environment to grow well.
These organisms are of two types based on their size, as
Macro-organisms: These are the organisms that can be seen through the naked eye. These include organisms like the earthworm, rodents, etc.
Micro-organisms: The organisms present in the soil that cannot be seen through the naked eye are the soil microorganisms.
Organisms like bacteria, fungi, algae, protozoa, etc., are examples.
Studying these microorganisms present in the soil is called Soil microbiology.
These microorganisms are classified according to their type of cells as;
a) Prokaryotic cells – single-cell organisms ( Bacteria, actinomycetes).
b) Eukaryotic cells – multicellular organisms (fungi, algae, nematodes, worms, etc.)
Prokaryotic cell organisms
Bacteria – Bacteria are unicellular microorganisms; these organisms are found in huge numbers as compared to other organisms.
Bacteria are beneficial organisms for the soil because they help in the nitrogen cycle and fixation of nitrogen in the soil (Nitrosomonas spp. and Nitrobacter spp.).
Two types of bacteria found in the soil like the
a) Autotrophic bacteria – These bacteria can manufacture their own food. Autotrophic bacteria are further divided into two types: photoautotrophs and chemoautotrophs.
b) Heterotrophic Bacteria – These bacteria derive their food from other sources or depend on others for food and different nutrition. Most of the soil bacteria are heterotrophs.
Bacteria are found in symbiotic associations and non-symbiotic associations.
The symbiotic bacteria are found in the roots of leguminous crops ( peas, beans, etc.). These organisms derive their nutrition from the plants and play an essential role in the nitrogen fixation in soil. For example, rhizobium, cyanobacteria
Non-symbiotic bacteria do not require any host for their survival. They help in the fixation of nitrogen in the soil. Example – Azotobacter that could fix atmospheric nitrogen in the soil.
Eukaryotic cells organisms
These types of organisms are both micro and macro-organisms.
Macro organisms – Earthworms, rodents, and frogs are vital for the soil as they help in making the soil loose and soft by breaking the soil particles; they also help in the aeration of soil by modifying the soil structure.
Microorganisms – Fungi
Fungi – These organisms depend on the dead parts of the plant and animals. They help in the decomposition of the dead part of plants. Some fungi are useful (edible mushrooms), and others are harmful.
These organisms help in the formation of humus, which increases the soil’s water-holding capacity and adds nutrition to the soil.
Algae – Algae are mostly found in wet areas where moisture is present. They can make their food with the help of carbon dioxide and sunlight.
Role of soil microorganisms
- Formation of Humus in the soil – when the dead part of a plant and animal is decomposed, it changes into humus, which is dark in color. Humus is very useful for the plant as it increases the soil water holding capacity, which helps the soil to hold water for an extended period and make water available for the plant. Humus also increases the soil fertility level. Moreover, it makes the soil more fertile and increases the yield of crops.
- Nitrogen Fixation – Nitrogen is fixed by some symbiotic and non-symbiotic bacteria; these organisms fix the atmospheric nitrogen into the soil and make it available for plant uptake.
- Microorganisms help in the growth of plants – some microorganisms help some chemicals like plant growth hormones, which help the plant to grow and attain the right size.
- Modifies the soil structure – The rodents and the earthworms present in the soil commonly do these processes. They make holes into the soil through burrowing, and these holes increase the soil aeration and increase the soil drainage system, which helps in the natural flow of water inside the soil.
- Some microorganisms are used for controlling the pest that attacks the crops – Bacillus thuringiensis is used to control the caterpillar pest of the crop. Some are used to control the battles and flies that attack the crops during their peak growth stage.
- Nutrient Cycle _- Nutrient cycles like nitrogen, carbon cycles, etc., all take place in soil with the help of microorganisms, and this helps in retaining nutrients in the soil and fulfilling the nutrient demand naturally.
Some organisms are beneficial for the farmers.
- Mushrooms – mushrooms are one of the fungi groups which are used for commercial purposes by the farmers; they earn by selling edible mushrooms in the market and starting their own business.
- Earthworm – Earthworms ( red earthworms) are also called farmer’s friends as they help in improving the soil’s physical structure. The red earthworm is also used for the production of vermicompost, which is excellent organic manure for the crops. Nowadays, vermicompost is also used for commercial purposes.
Soil microorganisms are very crucial for soil and crop growth and production.
Without microorganisms, the growth of crops is difficult because they add nutrients to soil naturally.
Some bacteria that live in symbiotic association with the legumes help in the formation of nitrogen and solubilize the phosphate and sulfates for easy absorption of roots.
People are looking for organic manures as they provide nutrients without affecting soil as the inorganic fertilizers affect the soil conditions; many soils are losing their fertility due to overuse of inorganic fertilizers, so in this, organic manures like green manures are a very good source for the supplying of nutrients to the soil.