Biofertilisers were not favoured during the Green Revolution period because they could not produce the desired results in the presence of chemical fertilisers. In organic farming, in the presence of organic manure, they do a much better job in adding their mite to the fertility and productivity of the soil.

Biofertilisers are microbial inoculates that contain live cells. There are two types of microorganisms, the nitrogen fixing and the phosphate solubilising. Since these microorganisms help in making the normally unavailable atmospheric nitrogen and phosphate in the soil, available to plants, they are called biofertilisers. When dead, they add to the fertility of the soil substantially. Among the nitrogen fixing microorganisms, Rhizobium, Azotobactor, Azospirillum, Azolla and Blue Green Algae are important. The phosphate solubilisers are Bacillus, Pseudomonas, Aspergillus and Penicillium. Mycorrhizae help to bridge soil with plant root for transporting phosphorus to plants from the soil.

Rhizobium

They are nodule-forming bacteria in the roots of leguminous crops. The atmosphere has 78 per cent of nitrogen, but the plants are not able to get this essential nutrient without the help of nitrogen fixing bacteria. These bacteria are multiplied in the laboratory, and incorporated into the soil through seed treatments. After germination, the Rhizobia get into the roots and fix the atmospheric nitrogen and stores it in the galls formed on the roots. Not all plants have this advantage.