Abstract

Azolla is a small water fern that assimilates nitrogen in symbiotic association with Anabaena azollae. The algal symbiont resides in the leaf cavity of Azolla and provides fixed nitrogen and other growth promoting substances to the host Azolla in exchange for nutrients and carbon sources. The heterocyst frequency of algal symbiont A. azollae under nitrogen limiting condition was 30 per cent. The algal symbiont showed polymorphism in different Azolla cultures. The growth of Azolla is influenced very much by season, phosphorus, growth regulators, herbicides and salinity. Azolla mineralizes rapidly and its nitrogen is made available to the rice in a very short period. It is estimated that nitrogen contribution by Azolla is 40-60 kg ha" besides improving the soil health. Azolla inoculation at 500 kg ha on 7 DAT along with 75 kg N ha increased the grain and straw yield of rice significantly. Inoculation of Azolla hybrid AH-C2 coupled with USG at 75 kg N ha increased the grain and straw yield of CO 43 rice besides increasing the plant N content and N uptake in sodic soil.

Keywords: Ammonia assimilation, Azolla, A. azollae, Mineralization, N, fixation, N use efficiency, Phosphorus nutrition, Rice yield