Correct Option (A)
Blue-green algae, also known as cyanobacteria, are photosynthetic prokaryotes capable of atmospheric nitrogen fixation. In rice paddies, they form a symbiotic relationship with the rice plant, converting atmospheric nitrogen into ammonia, which is then utilized by the plant as a nutrient. This process enhances soil fertility and reduces the need for synthetic nitrogen fertilizers, making them effective biofertilizers for rice crops.
Incorrect Options:
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Rhizobium sp.: Rhizobium bacteria form symbiotic associations with leguminous plants, fixing atmospheric nitrogen in root nodules. They are not typically associated with rice crops as biofertilizers.
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Mycorrhizal fungi: Mycorrhizal fungi form symbiotic relationships with the roots of most plants, enhancing nutrient uptake, particularly phosphorus. While beneficial for many crops, their primary role is not nitrogen fixation, and they are not the most prominent biofertilizer for rice in the context of nitrogen supply.
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Azotobacter sp.: Azotobacter are free-living, non-symbiotic nitrogen-fixing bacteria. While they contribute to soil fertility by fixing nitrogen, their efficiency as a biofertilizer for rice is generally less pronounced compared to blue-green algae in flooded paddy conditions.