Four field experiments were conducted from 1988-90 at Dallas, Texas to 1) determine the effect of supplemental irrigation and nitrogen (N) applications on cotton yield; 2) approximate seasonal moisture requirements of cotton; and 3) examine the accuracy of preplant soil plus petiole nitrate-N analysis for predicting the N fertilizer requirements of cotton. Supplemental irrigation increased cotton lint yields one fold when seasonal rainfall did not exceed 350 mm. Seasonal water use ranged from 43 to 49 cm, with over 90 percent of the soil moisture depletion from the surface 60 cm depth. Nitrogen applications increased rainfed cotton lint yields 10 to 20 percent on N deficient sites. Nitrogen applied at early square was as equally effective as the same quantity of N applied at planting. Overall, petiole tissue nitrate-N analysis through peak bloom shows promise as an indicator of cotton N nutritional status early in the season.