Biofertilizers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilizers are bacteria, fungi and cyanobacteria.

E.g. : $(i)$ Azospirillum, Rhizobium and Azotobacter can fix atmospheric nitrogen in the soil. $(ii)$ BlueGreen Algae, Anabeana. Nostoc and etc are used as biofertilizer.