Concept:Leguminous crops enrich the soil with nitrates through biological nitrogen fixation.Explanation:Calopogonium, pueraria, and centrosema are leguminous cover crops that fix atmospheric nitrogen into the soil.Nitrogen fixation converts atmospheric nitrogen into nitrates, which improves soil fertility.Exoriepus is not a leguminous nitrogen-fixing crop.Therefore, it will not enrich the soil with nitrates.Answer:D. exoriepus