Your advice is sought to improve the nitrogen content of the soil to be used for cultivation of a non-leguminous terrestrial crop.
1) Recommend two microbes that can enrich the soil with nitrogen
2) Why do leguminous crops not require such enrichment of the soil?
1) Two microbes that can enrich the soil with nitrogen are Nostoc and Anabaena.
2) Legumes are very good for enriching the soil. They do not require any enrichment as in their case nitrogen is fixed symbiotically. They have nodules on their roots, with bacteria rhizobium whose function is to fix the atmospheric nitrogen directly into the soil. These nodules contain all the necessary components for nitrogen fixation.