• Agronomic Evaluations of Transgenic Cotton Varieties, 1998

      Silvertooth, Jeffrey C.; Norton, Eric R.; Silvertooth, Jeff; University of Arizona (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      Several field experiments were conducted in many of the cotton growing areas of Arizona in 1998 for the purpose of evaluating agronomic characteristics of many new transgenic Upland cotton varieties. In many cases, the new transgenic lines were compared directly with their recurrent (nontransgenic) parents. Evaluations were carried out by collecting plant mapping data from each variety on a regular 14 day interval throughout the season and relating the resultant information to established baselines for Upland cotton in Arizona. Lint yield measurements were also taken on each variety at all locations. Results indicate that all transgenic lines tested are very similar to their recurrent parents in terms of growth, development, and yield. Some subtle differences were noted but they were very slight and should not impact management of the varieties significantly in comparison to their recurrent parents.
    • Cotton Defoliation Evaluations, 1998

      Silvertooth, Jeffrey C.; Norton, Eric R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      A field experiment was conducted near Marana, AZ in 1998 to evaluate the effectiveness of a number of defoliation treatments on Upland (var. Stoneville 474) cotton.. All treatments consisted of materials commercially available in Arizona. Results reinforce general recommendations regarding the use of low rates (relative to the label ranges) under warm weather conditions and increasing rates as temperatures cool. Defoliation treatments of Ginstar alone did a satisfactory job of defoliation and regrowth/topgrowth contol and were very similar to Dropp + Def combination treatments. Adding Prep to Ginstar in this experiment did not improve defoliation or topgrowth control.
    • Development of a Yield Projection Technique for Arizona Cotton

      Norton, Eric R.; Silvertooth, Jeffrey C.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      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.
    • Evaluation of a Feedback Approach to Nitrogen and Pix Applications, 1998

      Norton, E. J.; Silvertooth, Jeffrey C.; Norton, Eric R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      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.
    • Evaluation of Planting Date Effects on Crop Growth and Yield for Upland Cotton, 1998

      Norton, Eric R.; Silvertooth, Jeffrey C.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      A field study was conducted in 1998 at the University of Arizona Marana Agricultural Center (1,974 ft. elevation) to evaluate the effects of three planting dates on yield and crop development for three Upland varieties. Planting dates ranged from 9 April to 28 May and 342-885 heat units accumulated since Jan 1 (HU/Jan 1, 86/55o F thresholds). Crop monitoring revealed early season fruit loss leading to increased vegetative growth tendencies with all three planting dates. General trends also showed decreasing lint yield with the later dates of planting for all varieties. The more determinate variety (STV 474) was able to set and a fruit load more rapidly than the other varieties in this study at several dates of planting, which resulted in higher yields.
    • Evaluation of the Effects Added Nitrogen Interaction on Nitrogen Recovery Efficiency Calculations

      Norton, Eric R.; Silvertooth, Jeffrey C.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      Two studies were conducted in 1996 and 1997 at the University of Arizona Maricopa Agricultural Center (MAC) to evaluate the added nitrogen interaction (ANI) or ‘priming effect’ on the determination of nitrogen recovery efficiencies (NRE). The method employed was to compare NRE’s as calculated by two different methods; the difference technique and the isotopic technique. The difference in NREs observed between the two methods indicates the extent of an ANI. Results demonstrated no statistical differences between NRE’s calculated by the two methods. Therefore, no ANI was observed in the field. These results indicate that the less expensive method of calculating NREs (difference technique) is sufficient under irrigated cotton production systems in the desert Southwest.
    • Nitrogen Management Experiments for Upland and Pima Cotton, 1998

      Silvertooth, Jeffrey C.; Norton, Eric R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      Two field experiments were conducted in Arizona in 1998 at two locations (Maricopa and Marana). The Maricopa experiment has been conducted for nine consecutive seasons, the Marana site was initiated in 1994. The purposes of the experiments were to validate and refine nitrogen (N) fertilization recommendations for Upland cotton. The experiments each utilized N management tools such as pre-season soil tests for NO3 --N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location revealed a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive, N application regimes did not benefit yields at any location. In 1998, fruit retention levels were low and crop vigor was high. As a result, even slight increases in N fertilization and crop vigor translated into lower yield.