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Nodulation and nitrogen fixation by legumes is adversely affected by higher doses of fertilizer N. Fertilizer N. especially nitrate, affects nodulation mainly by destroying indole aCetic acid, reducing lectin production by the host, decreased root hair formation and root hair curling, limiting the attachment ofrhfzobia on rOot hair, decrease in lectin binding site:;, decrease in infection thread formation, inhibits initial cell division in the root cOrtex and integrity of bacteroids in the nodules. Nitrogen fixation is inhi~.'ited by fertilizer N, even if nodules are formed and this has been attribuIed due to the decreased supply of photo, ynthate to nodules. Further formation of nitrite from nitrate can damage the nodules and leads to early nodule senescenc~. Formation of a complex by nitrous oxide (NO) and leghemoglobin (lb NO) results in the loss of Oa binding ability of leghemoglobin and thereby inhibit the process of nitrogen fixation.