Theory:

The substances which contain living microorganisms that increase the nutrients plants when applied are known as biofertilizers.
When applied to the seeds, plant surfaces, or soil, these substances colonize the rhizosphere or the interior of the plant, and promote growth of the plant by increasing the supply or availability of primary nutrients to the host plant.
 
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Bio-fertlizer
Types of biofertilizers:
Rhizobium:
  
Rhizobium is a bacteria that is found in the soil. This bacteria colonizes the roots of the leguminous plants to form root nodules. This bacteria take in the atmospheric nitrogen from plants and converts them into ammonia which is readily used by plants.
 
Azospirillum:
  
Azospirillumis a bacteria which has the ability to use atmospheric nitrogen and transport it to the plants. This bacteria is mainly used on the maize, barley, oats and sorghum crops to increase the productivity of cereals by \(5-20\)%, of millets by \(30\)% and fodder by over \(50\)%. It is considered the safest bacteria that can be as a biofertilizer at the commercial level for several crops.
 
Azotobacter:
  
It is a free-living soil bacteria that plays an important role in the fixation of nitrogen. Application of this bacteria to wheat, rice, maize and sorghum has been found to increase the yield. Apart from these this bacteria can also produce of producing antifungal and antibacterial compounds.
 
Mycorrhizae:
  
It is fungi that has a symbiotic association with the roots of vascular plants. This fungi aid in the increase uptake of phosphorous and other nutrients.
Example:
Citrus and papaya
It is a free-floating aquatic fern found on the surface of the water. It has acyanobacterial symbiotic association with Anabaena. It is commonly known as a live floating nitrogen factory that uses the energy from photosynthesis to fix atmospheric nitrogen.
Biofertilizer scheme:
The Government of Tamil Nadu has recently launched the biofertilizer scheme. This scheme aims to provide better management of natural farming. It also helps to boost and maintain the fertility of the soil.