Your advice is sought to improve nitrogen content of soil to be used for cultivation of non leguminous terrestrial crop.
(a) Recommend 2 microbes that can enrich soil with nitrogen
(b) Why do leguminous crops do not require such enrichment of soil?

 

(b) Leguminous crops have a symbiotic association with Rhizobium bacteria which traps N₂ directly from the atmosphere and provides it to the plant and in turn gets food and shelter. So Leguminous crops get their Nitrogen supply from symbiotically associated bacteria thus they do not require enrichment of soil.
Regards