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

Blue‑green algae (cyanobacteria) are used as biofertilisers in flooded paddy soils because they fix atmospheric nitrogen and contribute directly to soil N available to rice plants; manuals on algal use in rice document their establishment and positive effects on rice yield and soil N status [2]. Textbook treatments group blue‑green algae with other free‑living and symbiotic nitrogen‑fixers (e.g., Azotobacter, Rhizobium), but Rhizobium is primarily a symbiont of legumes and is not used for rice, while Azotobacter is a free‑living fixer more suited to non‑legume/upland crops; mycorrhizal fungi mainly assist phosphorus uptake rather than serving as primary N biofertilisers in submerged rice systems [2].

Sources

1. [2] https://www.fao.org/4/ar124e/ar124e.pdf
2. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > s r n r u l z N ,- / & f . -. : : u ' , \ S ACADEMY * d 6 # . , r '' t u f Y l ' ' J * w { d ) / u Y . / > p. 20