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

(a) Two microbes that can enrich the soil with nitrogen are:

• 1. Nostoc
• 1. Azotobacter
     (b) Leguminous plants are capable of nitrogen fixation by virtue of their partnership with the bacterium. The nitrogen fixation in leguminous plants starts with nodule formation in the roots. A common soil bacteria, Rhizobium invades the roots and multiplies within the cortex (thus forming nodules). It fixes the atmospheric nitrogen in the leguminous roots, whereas the legume provides the bacteria with energy and nutrition. Hence, due to the symbiotic relationship between the leguminous plants and the nitrogen fixating bacteria, the soil does not require nitrogen enrichment.