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Index >> Nitrogen Fixation Symbiotic Blue-Green Algae >> Azolla Anabaena Association

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Nitrogen Fixation by Symbiotic Blue-Green Algae Lichens Stages in Lichen RE Establishment Nitrogen Fixation and Assimilation

Azolla Anabaena Association

	Azolla-Anabaena Associaton A species of Anabaena (A. azolIae) is associated with the aquatic fern Azolla occurring in a ventral pore in the dorsal lobe of each vegetative leaf. The endophyte fixes atmospheric nitrogen and resides inside the tissues of the water fern. AzolIa is being used as green compost for rice cultivation in North Vietnam. An added advantage is that the plant multiplies fast and provides higher yields of green compost (200-300 t ha/yr) than conventional green manure plants such as Sesbania, Crotalaria, and Tephrosia which are known to yield 30-50 t ha/yr.
The disadvantages are that the plant is susceptible to parasites and sensitive to fluctuations in temperature, the most favourable range of temperature being 20-28°C. It is also necessary to prevent algal growth in rice fields for utilization of Azolla since algae tend to overgrow and inhibit the proliferation of the water weed. It is reported from Vietnam that a 10-ton layer of AzolIa enables the rice yield to increase by 10-25% over corresponding AzolIa-free rice fields. The benefit from Azolla growth to the associated rice crop has been variously estimated. It ranges from 95 kg N/ha/yr to 670 kg N/ha/yr, depending on the method used in determining the amount of nitrogen fixed.
The common species of AzolIa in India is A. pinnata. It is recommended that AzolIa nurseries are raised in small plots (So-100sq m) or in concrete tanks with 5-10 cm deep water (pH 7-8) containing superphosphate at 4-8 kg P20s/ha after seeding the plots with AzolIa innoculum at the rate of 0.1 to 0.4 kg per sq m. These nurseries have to be planned several weeks ahead of the date set for transplanting rice seedlings. At the end of 2-3 weeks, when full growth of AzolIa takes place, the water is drained and the AzolIa growth is incorporated into the rice fields by ploughing the mass (10-20 t/ha) into the puddled rice field.
This is followed by transplanting of rice seedlings within 7 days. Alternatively, AzolIa is grown as a dual crop with the main crop of rice. As and when the AzolIa mat formation takes place, it is ploughed into the field, a process which can be repeated depending on the growth of AzolIa. Field experiments in India have demonstrated that 10 t/ha of AzolIa is equivalent to 2S to 30 kg N/ha and similarly, an application of 20 kg N/ha as ammonium sulphate with AzolIa is equivalent to 40 kg N/ha as ammonium sulphate.

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Blue Green Algal Association with Bryophytes Blue Green Algal Association with Higher Plants Aazolla Anabaena Asociation Survial of Aazolla Limitations of Aazolla Anabaena Asociation

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