One of the following cyanobacteria, not only fixes atmospheric nitrogen but also enriches the soil with organic matter to increase soil fertility.

Blue green algae are biofertilizers which not only enrich the soil with nitrogen but also add organic matter to enhance soil fertility. Azotobacter, Azospirillum are not cyanobacteria but Eubacteria. Glomus is a fungus that forms mycorrhizae. Oscillatoria is a blue green alga used as biofertilizer in paddy fields.