Two field experiments were conducted in Arizona in at two locations, Maricopa in 1991 (Casa Grande sandy loam) and Marana (Pima clay loam) in 1995. The purposes of the experiments were to evaluate the dimensions of an ¹⁵N microplot design used in a furrow irrigated row crop system. The experiments each utilized ammonium sulfate fertilizer with 5 atom % ¹⁵N enrichment applied at a rate of 56 kg N/ha in simulated side-dress band application during the early bloom stage of development of Upland cotton (Gossvpium barbadense L). At each location, microplots were 4, 1.02 m rows wide and 1.00 m in length. Whole plant samples were collected at specific locations within and near the microplots. Uptake of ¹⁵N by plants was uniform within microplots but declined symmetrically in relation to microplot borders. Collection of plant materials within 25 cm of microplot borders provided uniform ¹⁵N enrichment levels for determining fertilizer N uptake and recovery. Use of microplots with the dimensions of those used in this study are sufficient for collecting plant materials from a 1 m² area; consisting of two, 50 cm segments from the interior two rows of the four row microplot. This also allows for sufficient distance from the perimeter of the microplot to account for border effects.

In an effort to provide information on the agronomic necessity of potassium (K) fertilization in Arizona cotton (Gossypium spp.) production, a five-year study was initiated in 1991 with a single field study located near Gila Bend. Subsequent study sites selected ranged from western (Yuma) to eastern (Safford) Arizona, which totaled 11 site years. Both Upland (G. hirsutum L.) and American Pima (G. barbadense L.) cotton were cultivated, using soil and foliar applications of K. In 1992, study sites included the Safford Ag. Center (SAC), Maricopa Ag. Center (MAC), and a Cooperator site at Coolidge. In 1993, the experiment stations sites were maintained (SAC and MAC) and Yuma Valley was added. The 1994 study sites included only the two experiment stations (SAC and MAC). In 1995, SAC and MAC were maintained, and a third location was a farmer cooperator site at Buckeye. The results from all studies (12) indicated no lint yield increases due to K fertilization at any of the locations with either Upland or Pima cotton. However, in 1995, at the Buckeye location, the result revealed a significant yield reduction due to the K foliar treatments. There were, however, no significant differences among soil as well as the soil-plus-foliar treated plots in the 1995 study at Buckeye.

Summaries of cotton crop phenology, as a function of heat units (HU, 86/55°F limits) have been developed across a wide range of production conditions in Arizona. Basic phenological events such as the occurrence of pinhead squares, squares susceptible to pink bollworm, and first bloom are described in terms of HU accumulations since planting (HUAP). Fruit retention guidelines and height: node ratios, which measure a crop's vegetative /reproductive balance, are developed as a function of HUAP. Similarly, the rate of canopy closure is described in terms of HUAP. The use of the number of nodes above the top white bloom to the terminal (NAWB) is developed as a measure of a crops progression towards cut-out. Also, the expected ranges of HU's accumulated since planting that are required to accomplish crop cut-out are shown for Upland and Pima cotton.

Several plant growth regulators were applied to DPL 5415 cotton to evaluate effectiveness on cotton lint yield. Growth regulators applied in small amounts over multiple applications early in the growing season reduced yields compared with the check while a single application applied at full-bloom slightly increased lint yields. High night time temperatures from late July into early September were detrimental for cotton production. Increased squaring of early season applications compared with the check may have resulted in reduced yields due to increased stress from temperatures and/or nutrient availability. Increased stress in the early treated (more fruit) plots may have had greater fruit abscission.

Cotton crop response was evaluated using the growth regulator FIX in a conventional liquid formulation compared to an equivalent rate of a newly developed dry flowable (DF) formulation. The DF formulation will be available in 1996 in water soluble packets with each 57 gram packet the equivalent of one pint liquid PIX. Both formulations regulated plant height and height:node ratios equally.

All plant growth regulators and nutritional products applied to Pima S-7 cotton during bloom economically increased lint yields, with increases ranging from 80 - 261 lbs. /acre. Greatest increase was noted with Boll-Set Plus, a product that contains raised levels of calcium and zinc. Cytokin and Boll -Set Plus significantly increased yields at one location. A lint yield increase of approximately 40 lbs/acre was noted when Tech-Flo Alpha was added to Cytokin. A single application of Foliar Triggrr resulted in equal yields as two applications of the Cytokin plus Tech-Flo Alpha.

Methanol, Cytokin, Cytoplex, PGR IV and Foli-Zyme plant growth regulators were tested on long and short staple cotton on the Safford Agricultural Center in 1995. It was a follow up study on Methanol, Cytokin and PGR IV and a first time look at Cytoplex and Foli-Zyme. Trends toward increased lint yield were seen with Cytokin and Cytoplex with the other treatments yielding near or below the untreated check Some increase in maturity was seen on the short staple plots by all of the treatments. Some differences in HVI data were also observed.

Three field experiments were conducted in Arizona in 1995 at three locations (Maricopa, Marana, and Safford). The Maricopa and Safford experiments have been conducted for seven consecutive seasons, the Marana site was initiated in 1994. The purposes of the experiments were to validate and refine nitrogen (N) fertilization recommendations for both Upland and Pima 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. The effects of N fertility levels have also been consistently evident in crop maturity and its relationship to lint yields.

A single field experiment was conducted in 1995 at Maricopa, AZ to compare a scheduled approach (based on stage of growth) versus a feedback approach (based on vegetative status) to both nitrogen (N) and mepiquat chloride (PIX™) applications on Upland cotton (Gossypium hirsutum L.). PIX feedback treatments were based upon fruit retention (FR) levels and height to node ratios (HNRs) according to established baselines. Scheduled and feedback PIX applications were made for a total of 1.0 pt./acre over two applications, with the scheduled treatments-taking place earlier in the fruiting cycle (early and peak bloom). Feedback PIX treatments began with a single 0.5 pt. /acre application near peak bloom (approx. 2200 heat units after planting (HUAP), 86/55 °F threshold) and followed with a second 0.5 pt. /acre application in late bloom. Scheduled applications of fertilizer N totaled 200 lbs. N/acre from three applications and feedback N treatments received a total of 100 lbs. N/acre from two applications. Treatments consisted of all combinations of scheduled or feedback applications of both N and FIX. The highest lint yields were from a treatment receiving feedback N and FIX, but all treatment yields were not significantly different (P ≥ 0.05) from one another. From a practical (economic) standpoint, however, these treatments were different in terms of the differences of fertilizer N and the timing of the PIX applications required to produce comparable yields. Results from 1995 are consistent with 1993 and 1994 results from the same study.

Three field trials were conducted in Arizona in 1995 at three locations (Safford, Maricopa and Buckeye) to evaluate yield benefits associated with potassium (K) fertilization. The 1995 and previous years studies were aimed at assessing the agronomic necessity of K fertilization in Arizona cotton (Gossvpium spp.) production. At the Safford Agriculture center (Pima clay loam), both Upland (G hirsutum L., var. DPL 90) and Pima (G. barbadense L., var. S-7) cotton included treatments of both soil and foliar K applications. The trial at Maricopa Agricultural Center (Casa Grande sandy loam) included four foliar K applications over the growing season on Pima (G barbadense L., var. S-7) cotton. The third trial was at the Buckeye location (Superstition silty loam) where a single foliar application over split plots preceded by soil application on Pima (G. barbadense L, var. S-7) cotton was undertaken. The results of the experiments at the Safford and Maricopa locations indicated no lint yield responses to K fertilization by either Upland or Pima cotton; however, at the Buckeye location, the result indicated a significant difference between the means of the soil-only and the soil-plus-foliar treatments. There were however no significant differences among soil-only treatments as well as the soil-plus-foliar treated plots when compared to their respective controls.