Blue green algae (BGA) and Azolla constitute a system, which is the main source of algal biofertiliizer in south and Southeast Asia, particularly for lowland paddy.
BGA inoculatoin with composite cultures of algal genera Anabaena, Nostoc, Plectonema, Aulosiro, Oscillatoria, Tolypothrix, etc. have been found to be more effective than single cultures. Besides being a source of Nitrogen, BGA use has the following advantages: (i) algal biomass accumulates as organic mattr; (ii) growth promoting substances are produced, which stimulate growth of rice seedling; (iii) it provides partial tolerance to pesticides and fungicides; (iv) it also helps in reclamation of saline and alkaline soils.