Which one of the following organisms can serve as a biofertilizer for rice crop?

1. The question asks which organism can act as a biofertilizer specifically for the rice crop. 2. Biofertilizers enhance soil fertility using microorganisms. 3. Blue-green algae (Cyanobacteria), such as Anabaena and Nostoc, thrive in the waterlogged conditions of rice paddies and can fix atmospheric nitrogen, making it available to the rice plants. They are widely recognized as effective biofertilizers for rice. 4. Rhizobium sp. fixes nitrogen in association with leguminous plants, not rice. 5. Mycorrhizal fungi primarily aid in phosphorus uptake. 6. Azotobacter sp. is a free-living nitrogen fixer in soil, but blue-green algae are more specifically associated with rice cultivation.