This paper reviews salient findings of these works to assess all the current information available.
This review indicates that the aquatic biota Cyanobacteria and Azolla can supplement the N requirements of plants,
replacing 30–50% of the required urea-N. BNF by some diazotrophic bacteria like Azotobacter, Clostridium, Azospirillum,
Herbaspirillum and Burkholderia can substitute for urea-N, while Rhizobium can promote the growth physiology or improve the root morphology of the rice plant. Green manure crops can also fix substantial amounts of atmospheric N. Among the green manure crops, Sesbania rostrata has the highest atmospheric N2-fixing potential, and it has the potential to completely substitute for urea-N in rice cultivation