Five field experiments were conducted from 1990-1991 at Dallas, Texas to: 1) determine the effect of supplemental drip irrigation and nitrogen (N) on cotton lint yield, and 2) approximate seasonal moisture and N requirements of cotton. Supplemental irrigation significantly increased cotton lint yields when seasonal rainfall did not exceed 17 to 25 inches, and over 80 percent of the soil moisture depletion was from the surface 2 feet of soil. Nitrogen applications significantly increased rainfed cotton yields 12 to 40 percent on N deficient sites. Single and split applications of N at first square and first flower were equally effective as the same quantity of N applied once at planting. Peak daily N accumulation rates occurred upon the appearance of green bolls and open bolls.