Biofertilizers are organisms which are used to enhance the fertility of the soil and availability of nutrients like nitrogen and phosphorus to the crops. 

There are three types of bio fertilizers 

Example 

1. Bacteria, (Rhizobium Azotobacter). 

2. Cyanobacteria or Blue green algae (Anabaena Nostoc). 

3. Fungi (Mycorrhizae like glomus, VAM). 

1. Free living nitrogen fixing bacteria 

They fix atmospheric nitrogen in the soil and made available to plants. 

Example: The best example is Azotobacter. 

2. Symbiotic nitrogen fixing bacteria 

These bacteria show symbiotic association with the root nodules of leguminous plants. They convert atmospheric nitrogen and made available to plants. 

Example : Rhizobium the most important symbiotic nitrogen fixing bacteria. 

Frankia, mycelia bacterium (actinomycetes) shows symbiotic association with the root nodules of several non leguminous plants like casurina, rubus etc. 

3. Free living nitrogen fixing cyanobacteria 

Cyanobacteria are group of autotrophic microbes also called Blue green algae (BGA), they help in nitrogen fixation in paddy fields. These are extremely low cost biofertilizers. 

Example: Anabaena, Nostoc. 

4. Symbiotic nitrogen fixing cyanobacteria. 

These nitrogen fixing cyanobacteria lead symbiotic mode of life with several plants like cycas roots, lichens, liver worts, Azolla (fern) 

Example : Anabaena and Nostoc in the corolloid roots of cycas. 

5. Mycorrhizae 

The symbiotic association of fungus with the roots of higher plants is called mycorrhizae. 

Example : Glomus species fix phosphorus in the soil and made available to plants.