Three cotton cultivars (DPL 41, 90 and 775) were planted at 3 seeding rates (5, 10 and 20 lbs/A). These variables were evaluated under 5 drip irrigation treatments, which included 23.3, 25.7, 28.0, 30.7 and 31.4 inches of water applied over the growing season. There were 3" of precipitation over the growing season. Only the lowest irrigation level showed significantly reduced yields. DPL 90 had superior yields as compared to DPL 775, with DPL 41 having an intermediate response. The 10 lb/a seeding rate resulted in higher yields as compared to the other 2 rates.

Three cotton cultivars (DPL 41, 90 and 775) were planted at 3 seeding rates (5, 10 and 20 lbs/A). These variables were evaluated under 5 fertilizer treatments which included increasing nitrogen levels and one treatment with nitrogen (N), phosphorus (P), potassium (K) and zinc (Zn). Residual soil N was high and variable and no clear response to applied N was found, although generally higher yields were found with the high N rate. The plots receiving P, K and Zn yielded less than plots receiving an equal amount of N. Increased seeding rates significantly increased yields which was probably an effect of early weed competition. Delta Pine 90 produced significantly more than 41 which was greater than 775. Petiole and soil nitrate values reflected the high and variable available soil N.

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The Crop Water Stress Index (CWSI) was used to schedule irrigations on drip irrigated cotton research plots in Tucson and on eight acre furrow irrigated fields at the Marana and Maricopa Agricultural Centers. Scheduling irrigations when plots reached 0.30 CWSI units resulted in highest yields with 1403 lbs/acre cotton lint using 33.8 inches of water. The Marana and Maricopa fields yielded 1322 lb/acre on 28 inches and 1767 lb/acre on 58 inches of water, respectively.

Drip irrigation of cotton in Maricopa County decreased from 13,335 acres in 1984 to approximately 600 acres in 1987 at five locations. The most common reason was that drip was not cost effective.

Cotton was grown using a computer model to schedule irrigation; yields of 2.5 bales per acre were produced. Even though some discrepancies were seen between calculated and measured soil moistures, the model was considered successful. No yield differences were seen between cotton grown with small, frequent irrigations and large, infrequent irrigations. The plant heights, however, were significantly altered.

Cotton was grown using historical evapotranspiration data in the Erie method a checkbook method using real-time AZMET weather data, an infrared thermometer, and a faint manager to schedule irrigations. Yields of 4 bales per acre were recorded with no significant differences between the scheduling methods. Differences were seen in the plant growth and maturity. More refining will be done in subsequent investigations.

Plots of pima S-6 cotton were scheduled for irrigation using the Crop Water Stress Index (CWSI). Irrigations were applied when CWSI levels reached 0.08 (wet), 0.34 (medium), and 0.68 (dry) units. The medium treatment had significantly higher lint yield. Preliminary test results indicate the CWSI can be useful in irrigation-management decisions regarding pima cotton production.