(i) Leguminous plants possess root nodules where nitrogen is fixed by symbiotic nitrogen fixing bacteria Rhizobium and fertilise the soil.
(ii) Cyanobacteria as biofertilisers
• They fix atmospheric nitrogen and increase the organic matter of the soil through their photosynthetic activity, e.g., Nostoc, Anabaena, Oscillatoria, etc.
• Blue-green algae increase the soil fertility by adding organic matter to the soil.
(iii) Mycorrhiza shows the following benefits:
a. resistance to root-borne pathogens.
b. tolerance to salinity and drought.
c. overall increase in plant growth and development.
