Leguminous crop grown under phosphate deficiency conditions may suffer from N deficiency as well.  Explain.

Rhizobium bacteria infect the roots of leguminous plants and lead to the formation of root nodules.  These organisms derive carbohydrates from root tissues of host plant and synthesise nitrogenous compounds to fix nitrogen. Rhizobium bacteria do not grow in soils deficient of phosphorus, which means that in case of phosphorous deficiency, there will be less infection in plant roots and  thus lesser nodules and thereby lesser excretion of nitrogen compounds.  This will result into a nitrogen deficient soil.