Hint:Biofertilizers are microorganisms such as fungi algae and bacteria which derive nutrition from non-usable sources and provide it to the plant.
Complete answer: Biofertilizers are eco – friendly and unlike chemical fertilizers doesn’t harm the environment. Azolla is a pteridophyte that contains a cyanobacterium Anabaena azollae in leaves that helps in fixing atmospheric nitrogen In rice or paddy fields and helps in fixing atmospheric nitrogen into ammonia which is then utilized by rice plants and also fertility is increased. 5% of nitrogen fixed by Azolla anabaena is directly available to the plant and 95% remain assimilated in Azolla and is released after death as ammonia. Anabaena azollae is the microorganism living in the leaves of Azolla pinnata (fern) and is responsible for nitrogen fixation and thereby acts as a biofertilizer.
Hence option d) is correct Azolla pinnata is the biofertilizer in Indian rice fields.
Additional Information:
Some important types of biofertilizers are-
1. Nitrogen-fixing bacteria example Rhizobium and Azospirillum.
2. Symbiotic nitrogen-fixing cyanobacteria living with ferns, liverworts. Examples are Anabaena.
3. Free-living nitrogen-fixing bacteria: Saprophytic anaerobes such as Clostridium beijerinckii, Azotobacter, etc.
Importance of biofertilizers :
It increases the yield of plants and protects the plants from plant pathogens.
They are environment friendly and don’t cause soil pollution.
Cost-effective.
Improves the soil texture.
Note: Azolla pinnata is cultivated before or along with rice plantations. Anabaena azollae is the biofertilizer that is present in the leaves of the fern Azolla pinnata and helps in nitrogen fixation and releases in the form of ammonia. This increases the fertility of the soil.
