Determination of the petiole nitrate nitrogen concentration (PNN) in the youngest fully expanded leaf (YFEL) of cotton is a useful indicator of plant nitrogen status. In a review of literature Hearn (1981) reported for various phenological stages, l evels of petiole nitrate nitrogen (PNN) adequate for crop growth. These declined from 14000 - 25000 mg kg-1 at first square to 20QO mg kg- 1 at first open boll. He reported a critical level of 2000 mg kg- 1 above which growth would not decline.