Aquatic fern which is an excellent biofertilizer is

Your advice is sought to improve the nitrogen content of the soil to be used for the cultivation of a non-leguminous terrestrial crop.

Why do leguminous crops not required such enrichment of the soil?

Give a reason for each of the following:

Cyanobacteria increase the productivity in paddy fields.

Give the biological names of the following:

A symbiotic nitrogen-fixing bacterium found in root nodules.