• Blue green algae (BGA) are photosynthetic prokaryotic, simplest, living autotrophic (organisms capable of building up food materials from inorganic matter) micro-organisms.
• Blue Green Algae (BGA) or Cyanobacteria have the ability to carry out both photosynthesis as well as nitrogen fixation.
• They belong to the order Nostocales and Stigonematales.

The standing water of rice field encourages the growth of Blue Green Algae (BGA). These different species of BGA are:

1. Anabaena
2. Aulosira
3. Nostoc
4. Tolypothrix
5. Haplosiphon
6. Others

Advantages:

➢ Carry out both photosynthesis as well as nitrogen fixation (20-30 kg/ha/year). Add organic matter.

➢ Antifungal, insecticidal, nematocidal, cytotoxic.

➢ Anabaena azollae is nitrogen fixing symbiotic habitant of a tiny water fern azolla.

➢ Besides they excrete vitamin B12, auxins, AA and ascorbic acid increase available phosphorus in the soil.

➢ Increase WHC, aggregation, Permeability and exchangeable Ca.

➢ reclamation of Saline-alkali soils

➢ Release oxygen for the paddy roots, Converts Fe++ to Fe+++.

➢ Effective only in submergence rice and demands bright sunshine

➢ Algal mat in paddy fields also protects loss of moisture from the soil.