It refers to the living organisms used to increase the fertility of soil. For example, symbiotic bacteria and blue green algae fix gaseous nitrogen as ammonia and release it hence increasing the fertility of soil and water respectively. They are used as bio fertilisers in the coastal areas. These life forms can be grown artificially and introduced into the soil as bio fertilisers. These bio fertilisers not only fix nitrogen but also contribute to the organic matter which increases the fertility of the soil. Azolla, has an appropriate balance of amino acids and high amount of anthocyanin and alpha carotene in it.

Benefits of Bio fertilisers: –

• i) De-gradation of toxic organic materials. ii) They provide protection against diseases.
• iii) Helps to improve soil porosity, drainage, aeration and water retention.
• iv) Reduces soil erosion.
• v) They provide optimal conditions for soil biological activity and hence replenish and maintain the fertility of the soil.
• vi) They promote the breakup of unproductive soil.
• vii) Nutrients such as nitrogen and phosphorus, calcium and copper are added to the soil when these bio fertilisers interact with other soil organisms and biodegradable components.