Question

what is symbiotic nitrogen cynobacterium lives in association with azolla ?​

Answer 1

Answer:

Azolla is generally inoculated and grown as a cover crop for incorporating into the soil as a top-dressing in rice cultivation. Azolla in symbiosis with the cyanobacterium Anabaena azollae, under optimum conditions, can fix substantial amounts of N2 through BNF, and release as much as 70% of the fixed N to the rice crop upon incorporation [5]. Using the δ 15N method, Yoneyama et al. [20] estimated that 59–99% of Azolla N is derived from the atmosphere. In a separate study, based on the 15N dilution method, Watanabe and Talukdar, and Kumarasinghe [cited in 21] found that as much as 80–85% of Azolla N is Ndfa.

The reported N content in maximum standing crops of Azolla ranged from 20 to 146 kg ha−1 (Table 1) and averaged 70 kg ha−1, and N2-flxing rate ranged from 0.4 to 3.6 kg N ha−1 d−1 and averaged 2 kg N ha−1 d−1 in a growing cycle of approximately 40 days. The N balance in the 0–50-cm soil profile after 27 cropping cycles confirmed an average annual gain of 76 kg N ha−1 under Azolla treatment [22].