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Typescript (photocopy). / Digitized by Kansas Correctional Industries

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The effect of the plant regulator Mepiquat chloride (PIXᵀᴹ) (1,1-dimethyl-piperidinium chloride), in the early flowering stage, and combinations with soil and foliar application of fertilizers was investigated through seven field experiments conducted in 1982 and 1983 at three University of Arizona experimental locations. Three upland cotton cultivars (Gossypium hirsutum L.), 'Deltapine 55', '61' and '62' were used. Cotton yield, boll properties, fiber properties, leaf chlorophyll content, plant height, plant partitioning and maturity were investigated. Petiole nitrate, leaf area index (LAI) and LAI interrelationship with yield were also included in this study. The use of PIX resulted in an increase in seed cotton yield and boll weight in one of the experiments, while fiber properties did not show any significant response to either PIX or fertilizers. PIX, however, had the tendency to enhance maturity by about 1 week. Use of PIX reduced plant height in all tested cultivars at all locations. The reduction in plant height ranged from 7 to 28% depending on the cultivar, location and the amount of PIX applied. The chlorophyll a and b content of leaves increased significantly as a result of PIX application in two of four tests, while their ratio decreased. Leaf area index between treatments were not significantly different except at one sampling date. In a regression study, however, yield was found to be related positively to LAI when soil and foliar application of fertilizer were added, while it was negative when PIX was applied. Neither PIX nor BALANCEᵀᴹ (1:18:18:1) application affected plant partitioning nor petiole nitrate concentration at most of the sampling dates.

A single field experiment was conducted in 1998 at Marana, AZ to evaluate a scheduled (based upon stage of growth) versus a feedback approach (based upon growth parameters and crop conditions) to nitrogen (N) and mepiquat chloride (PixTM) applications on upland cotton (Gossypium hirsutum L.). The parameters used in evaluating feedback applications for both N and Pix included fruit retention (FR) levels and height to node ratios (HNRs) with respect to established baselines for cotton grown in the desert Southwest. Scheduled and feedback Pix applications were made for a total of 1.5 and 2.5 pint Pix/acre, respectively, with the feedback treatments receiving a late season application at approximately 3100 heat units after planting (HUAP 86/550 F threshold). Scheduled Pix treatments received a single 1.5 pint Pix/acre application prior to peak bloom (approximately 2000 HUAP). Scheduled applications of fertilizer N totaled 205 lbs. N/acre from three applications. Feedback applications of N received a total of 100 lbs. N/acre from two applications. Treatments consisted of all combinations of feedback and scheduled applications of both N and Pix. The highest lint yields occurred in the treatment consisting of Pix feedback and N feedback (treatment two), however, there were no significant differences (P≥0.05) among any of the treatments with respect to yield.

A series of boll measurements were taken at numerous locations in cotton producing areas across Arizona in 1998 in an attempt to continue to develop a yield prediction model with a project that began in 1993. Results from 1995 showed the strongest relationship between final open boll counts and yield compared to a number of other measurements. Based on these results, data collection on boll counts began in 1996 and has continued in 1997 and 1998. Boll counts were taken as the number of harvestable bolls meter-1. All boll count measurements were made within one week of harvest. Number of bolls per unit area were then correlated to lint yield and an estimate for the number of bolls per area needed to produce a bale of lint was calculated. Estimates using all three years data combined indicate that approximately 38 bolls meter-1 are needed to produce one bale of lint per acre.

A single field experiment was conducted at Marana, AZ in 1988 and 1999 to evaluate a scheduled (based upon stage of growth) versus a feedback approach (based upon growth parameters and crop conditions) to nitrogen (N) and mepiquat chloride (PixTM) applications on Upland cotton (Gossypium hirsutum L.). The parameters used in the feedback applications for both N and Pix included fruit retention (FR) levels and height to node ratios (HNRs) with respect to established baselines for irrigated cotton grown in the desert Southwest. Treatments consisted of all combinations of feedback and scheduled applications of both N and Pix. In 1998, the highest lint yields occurred in the treatment consisting of Pix feedback and N feedback (treatment two) management. However, there were no significant differences (P≤0.05) among any of the treatments with respect to yield. In 1999, significant light yield increases (P<0.05) were found in the treatments consisting of Pix feedback and N feedback (treatment two), Pix scheduled and N scheduled (treatment three), and Pix scheduled and N scheduled (treatment five) management approaches.

A series of experiments have been conducted from 1988 to 1999 at various locations across the cotton producing regions of Arizona to evaluate mepiquat chloride (MC) applications in terms of plant growth and yield. These experiments were designed to evaluate MC under three application regimes. These regimes included low rate multiple applications, late season applications, and a feedback vs. scheduled management of MC and nitrogen (N) applications. The objective of this summary (including a total of 31 site-years) is to determine which of these three application regimes offer the greatest opportunity for a positive lint yield response to MC. Stability analysis was conducted by regressing the treatment mean lint yield against the environmental mean for each application regime. Results from the stability analyses revealed that the most viable method of application is a feedback approach for both MC and fertilizer N. The most reliable technique associated with plant assessment in a feedback approach was the height to node ratio (HNR) to indicate vegetative tendencies for determining the appropriate rate and timing of MC applications.