Microbes as Biofertilizers: Microbes or microorganisms are tiny living things that are too small to be seen by the naked eye and are found all around us. They can be found in water, soil, and air. They may exist as single-celled forms or as colonies of cells. The most common types of microbes are bacteria, viruses, protozoa, fungi.

Microbes as Biofertilizers

Microorganisms used as biofertilizers:

• Azotobacter: Azotobacter grows freely in the soil and enriches the soil with nitrogen. They are mostly saprophytic. Azotobacter helps reduce the use of man-made nitrogen fertilizers in paddy fields.

• Azospirillum: Azospirillum grows in the rhizosphere of crop plants. They fix atmospheric nitrogen and transfer it to crop plants. This association is called associative mutualism.

• Rhizobium: Rhizobium forms symbiotic association with roots of higher plants. This can’t fix nitrogen as free organisms, but can only do that while in nodule due to the presence of pink pigments called leghaemoglobin. Leghaemoglobin removes oxygen which helps in nitrogen fixation. Ideally, crops should be grown in nitrogen free soil, otherwise, the ability of Rhizobium to fix nitrogen is hampered.
• Nostoc: These cyanobacteria or blue green algae grow freely in the soil. They are photosynthetic by nature and can enrich the soil with nitrogen.
• Anabaena: This nitrogen fixing cyanobacteria can develop a symbiotic association with liverworts, ferns and cycad roots. Anabaena provides nitrogen to the rhizosphere of paddy plants.
• Ectomycorrhizae: These fungi grow on the surface of the root and in the outer cortex of plants line Pinus. They help in absorption of water, minerals from the soil, production of antimicrobial substances in the rhizosphere.
• Endomycorrhizae: These fungi grow within the intercellular space of cortical regions of grasses, orchids. They produce a swollen area called a vesicle or finely branched masses called arbuscles. These fungi are also called vesicular arbuscular mycorrhizae. They help in absorption of mineral nutrition, release of growth promoting substances.

Advantages of Microbes as Biofertilizers

• They increase the nitrogen and phosphorus available to crops more naturally than chemical fertilizers.
• They are simple to use, even for novice farmers.
• They do not pollute the soil or the environment, whereas chemical fertilizers often result in excessive input of nitrogen.
• They are a cheap, easy-to-use alternative to manufactured chemical fertilizers.
• They maintain normal soil fertility and make it biologically alive.
• They increase yield because of the nitrogen and phosphorus they add to the soil.

Disadvantages of Microbes as Biofertilizers

• Since biofertilizers are alive microorganisms, they require special care for long-term storage. 
• If other microorganisms contaminate a particular biofertilizer or if the manufacturer uses the wrong strain, they become ineffective.
• The soil in itself should contain adequate nutrients for the microorganisms to thrive and work.
• Biofertilizers cannot totally replace conventional fertilizers.
• They lose their effectiveness if the soil is not moist.
• They are less effective if the soil is excessively acidic or alkaline
• The availability of some biofertilizers depends upon the availability of particular strains of microorganisms or culture media.

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By Team Learning Mantras