Biofertilizers are the organisms that enrich the nutrient quality of soil. Bacteria, cyanobacteria and fungi are the three groups of organisms used as biofertilizers.
i) Bacteria
a) symbiotic bacteria Rhizobium.
b) Free living bacteria Azospirillum & Azotobactor.
c) They fix the atmospheric nitrogen and enrich soil nutrients.
ii) Cyanobacteria
Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environment. Many of them can fix atmospheric nitrogen and increase the organic matter of the soil through their photosynthetic activity. In paddy field cyanobacteria serves as important biofertilizers. Commercially farmers use these cyanobacteria in their fields to replenish soil nutrients and to reduce dependency on chemical fertilizers.
Important examples are Anabaena, Nostoc and Oscillatoria.
iii) Fungi/ Mycorrhiza
Fungi are also known to develop symbiotic relationship with plant roots. Such a relationship is called mycorrhiza. Many members of the genus Glomus form mycorrhizae. The fungus absorbs phosphorus from the soil and passes it to the plant. Plants having such association show other benefits also
a) Resistance to root borne pathogens
b) Tolerance to salinity.
c) Tolerance to drought
d) Overall increase in the plant growth and development.