A field study was conducted at the Maricopa Agricultural Center to determine the effect of nitrogen fertility level on the effectiveness of PIX and defoliants for short- season - cotton production. Increasing the nitrogen fertility level from 90 lbs N/A to 240 lbs N/A increased lint yields from 2.23 to 3.14 bales/A, respectively, in a 157-day growing season. FIX treatments did not promote earliness, and resulted in yield reductions. Increasing the application rates of Dropp from 0.1 to 0.2 lbs a.i./A and Def-6 from 0.75 to 1.13 lbs a.i./A resulted in increases in leaf drop. There was a significant linear decrease in the effectiveness of defoliants as the petiole NO3 N content increased from 850 to 2450 ppm.

A field experiment was conducted in Yuma, Arizona, to evaluate the effects of planting date on cotton yields. One Pima and the Upland cotton varieties were planted on four dates from 23 February to 5 April. DPL-90 produced the highest yield (1760 lbs lint acre⁻¹) at the second planting date (9 March). The lowest yields, for all varieties, resulted from the latest planting date (5 April). The greatest reductions in yield when comparing an early planting date to the latest planting date, were observed for DPL-90 and Pima S-6. However, in spite of the reduction in yield, DPL-90 was the highest yielding variety at the latest planting date.

A short staple variety trial was conducted on the demonstration farm, at the Maricopa Agricultural Center in 1989. Twenty varieties, received from various seed companies, were entered into the test. Results from the analysis showed significant differences among varieties with no observable performance trend in terms of maturity types (long or short season). The lint yields in this test ranged from 4679 to 3353 lbs. acre⁻¹ for DPL90, and S55 respectively.

Seven cotton varieties including Pima S -6 were demonstrated in Mohave Valley, Mohave County in 1989. Of the six upland varieties two were new varieties not previously demonstrated in this area. Trial results indicated DP77 at 1697 lbs. led other varieties by 109 lbs. of lint over DP90, 1590 lbs. and 287 lbs. over bottom variety STV115 at 1412 lbs. STV110 yielded 1482 lbs., DES 119 at 1429 lbs., DP50 at 1414 lbs. Pima S-6 yielded 950 lbs. The two new varieties STV110 and STV115 placed last and third on yield but when economic values were calculated based on grade and price they ranked third and fourth. The second attempt on Pima saw an increase in yield from 447 lbs., the previous year to 950 lbs. in current trial.

The Crop Water Stress Index (CWSI) was used to schedule irrigations on Pima S-6 cotton on 12 four-acre furrow-irrigated test plots in Coolidge and 20 drip- irrigated test plots at the Campus Agricultural Center in Tucson. Scheduling irrigations between 0.30 and 0.50 CWSI units resulted in highest lint production and plant water use efficiency at both locations.

Two years after sterilizing a sandy loam soil in Marana, we measured significant yield responses of short staple cotton. The yield response was significant in the first year as well, but was not enough to pay the cost of sterilization. This second year of yield response made the treatment economically feasible.

Incidence of Black Root Rot of cotton and soil inoculum potential of the causal agent Thielaviopsis basicola were monitored throughout the season in two adjacent fields planted in mid April, 1987 in Duncan, Arizona. Mean inoculum potential in Field 1 soil was 65 cfu/g and 20 % of the seedlings were infected. In Field 2 the inoculum potential and percentage of infected plants were 225 cfu/g and 93, respectively. No cortical decay was noted after June 6 in either field. Yields were similar in both fields.

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