Asymbiotic Nitrogen Fixers.
Azotobacter and Azospirillum (also Bacillus polymyxa, etc.), when applied to rhizosphere, fix atmospheric N₂ and make it available to crop plants. They also synthesize growth promoting antibiotic substances, helpful to the plant. Most efficient strains of Azotobacter fix 30 kg of N₂ from 1000 kg of organic matter. When applied to fields, positive responses by field crops were observed leading to saving of 10 to 25 kg/ha of N₂. Similarly, Azospirillum with farmyard manure (FYM), led to saving of 15 to 25 kg equivalent of N₂ per hectare in crop like sorghum and other millets. Azospirillum colonized not only the roots, but also the above round portions of the plant through associative symbiosis.

BGA is also supplied with Azolla (an aquatic fern), which harbours Anabaena azolle (a BGA) in leaf cavities, providing symbiotic association. Azolla with Anabaena has been used with some success, but there are following limitations: (i) Azolla as a green manuring crop is labour intensive; (ii) raising of Azolla needs assured and adequate supply o water; (iii) damage of Azolla (in th nursery) is caused by pest diseases, heat etc. (iv) optimum temperature is required for Azolla multiplication