A) Azolla
B) Nostoc
C) Anabaena
D) Clostridium
Correct Answer: A
Solution :
Azolla, a small aquatic fern has a small cavity on the uppermost part of the leaf which houses different blue-green algae belonging to Anabaena azollae. These blue-green algae have the ability to fix atmospheric nitrogen, available to Azolla. Plant body analysis of Azolla (dry weight mass) has revealed that it contains 45% nitrogen (N), 26% phosphorus (P) and 0.9% potash (K). Besides N, P, K, Azolla is a good source of secondary nutrients like calcium, magnesium and sulphur. The use of Azolla m rice fields at the rate of 200 g per square metre can increase rice field by 12-38%. Experiments have revealed that the application of 10 tonnes of fresh Azolla biomass in one hectare, adds as much as 100 kg of nitogen. Cyanobacteria like Anabaena, Nostoc, etc, fix atmospheric nitrogen and also derive energy for this by carrying out photosynthesis. These have the potential to supply 28 lakh tonnes of fixed nitrogen equivalent to 15-17 lakh tonnes of urea. They also secrete growth hormones (vitamin\[{{B}_{12}}\], auxins, ascorbic acid). The use of cyanobacteria is confined only to rice crop.
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