A single field study was established to evaluate the effects of planting date (PD) on the yield and fiber quality characteristics of several cotton varieties commonly grown in the Upper Gila River Valley of Safford. Eight varieties selected for evaluation in 2003 ranged from medium to medium-full varieties. These varieties included two Delta and Pine varieties (DP555BR and DP655BR), two Fiber Max varieties (FM989BR and FM991BR), two Stoneville varieties (ST5303R and ST5599BR), one CPCSD variety (Riata), and one variety from the Arizona Cotton Growers Association breeding program (AG3601). These eight varieties were planted on three separate planting dates (1 April, 23 April, and 12 May; 341, 525, and 779 heat units accumulated after January 1, respectively) in a split-plot within a randomized complete block design with four replications. Overall analysis of variance revealed significant differences due to main effects (PD; OSL=0.00043), sub effects (variety; OSL=0.0029), and interaction effects (PD*variety; OSL=0.0266). Extremely cool conditions surrounding the first PD resulted in significantly lower yields that the other two planting dates. Yields for PD 1 ranged from 506 lbs. lint/acre to about 850 lbs. lint/acre with DP555BR producing the highest and CPCSD Riata producing the lowest yield. Conditions surrounding the second PD were much improved over PD 1. However, soil temperatures still hovered near to and below the optimum temperature of 65oF. Yields were dramatically higher in PD 2 when compared to PD 1, ranging from a low of 847 lbs. lint/acre (AG3601) to 1139 lbs. lint/acre (FM991BR). PD 3 resulted in the best conditions for seedling emergence and stand establishment and produced the highest yield. Yields ranged from a low of 945 lbs. lint/acre (CPCSD Riata) to 1465 lbs. lint/acre (FM991BR). Fiber quality data demonstrated a couple of interesting trends. Micronaire tended to increase with later plantings for most varieties while fiber length had an inverse relationship with PD. Micronaire levels tended to be high enough to be discounted for every variety in at least one and usually two PDs, except for Riata. Riata had the lowest micronaire, and the longest and strongest fiber grades. These results are consistent with other evaluations of the high fiber quality associated with many of the California Acala varieties. However, relatively lower yields for this variety currently make it an unsuitable variety for this region despite the high fiber quality. Results from this evaluation demonstrate the importance of monitoring soil temperature and keeping a close eye on local weather forecasts when making planting date decisions regardless of the calendar date.

Field experiments were initiated in 2001 for a cotton-based conservation tillage project at sites in Marana, Coolidge, and Goodyear, Arizona. For the 2002 season, soil and water management assessments were made to evaluate surface irrigation performance under conservation tillage, following cover and grain crops. An additional site was added in the winter of 2002 at Maricopa, Arizona. Analyses included soil texture, infiltration rate, and water advancement. At Coolidge, conservation tillage plots had higher infiltration rates and longer advance times than the conventional plots in 2002 and 2003. At Marana, infiltration rates were initially higher for the Conservation plots but the rates converged at the end of four hours in 2002. In 2003, Conventional plots infiltrated about one inch more. Advance times for Marana showed water infiltration for Conventional wheel rows to be the fastest. At Goodyear, Conservation plots infiltrated more than Conventional plots during 2002. This also resulted in a slower advance time for the Conservation plots. In 2003, treatment effects were not comparable due to tillage by the grower. At Maricopa, Conservation plots infiltrated almost 2.2 inches more water than Conventional plots and water reached the end of the field three hours ahead of the fastest Conservation plot. Seasonal irrigation water applications to each treatment were relatively equal for all sites with the exception of Coolidge. Here, the long field combined with sandy soil made it difficult to adequately irrigate the Conservation plots. In 2002, an additional 21 inches of water was applied to the Conservation plots. In 2003, that amount was reduced to 12.5 inches. The yield data show a significant difference in 2002 only at Coolidge. There, Conservation plots yielded more than the Conventional ones. This may have been due to more water applied to the Conservation plots. In 2003, the opposite occurred with the Conventional plots yielding more than the Conservation plots. This could have been due to herbicide damage. At Maricopa, the Conventional plot also yielded more than the Conservation plot. Initial indications are that the conservation tillage does impact irrigation performance and may not be suitable for all locations depending on soil type and field layout.

Foliar fertilizers are not widely used for cotton production in the low desert, and data about their effects on cotton production under these conditions is therefore limited. This study documented the effects of Calcium Metalosate7 and Megafol, each applied at the rate of 1 qt/acre to DPL555BR cotton. Treatments were applied on July 7, and plants had been growing vigorously just prior to application. Plots were approximately 0.75 acres in size with four replications. Plant mapping data from late July indicated that non-treated cotton had numerically higher retention rates at each of the first three fruiting positions mapped in addition to slightly more total nodes and a greater number of reproductive nodes in part due to first fruiting structure being retained lower on the plant (node 6.75) than treated cotton (node 7.95 for Megafol, node 8.4 for Calcium Metalosate7). Tractor passage through treated plots may have also knocked off developing squares however. No statistical differences were noted for lbs. of lint/acre, although treated cotton did have slightly higher yields than the untreated check (1,162 lbs/acre) and treatments were almost identical (1,203 lbs./acre for Megafol; 1,198 lbs./acre for Calcium Metalosate7). Fiber lengths and strengths were significantly different by treatment, with shortest and weakest fibers resulting from cotton treated with Megafol. Cotton from Calcium Metalosate7 treatments were significantly longer and stronger than lint from Megafol treated cotton plots, but lint from untreated cotton plots was significantly longer and stronger than either treatment (36.6 staple, 31.0 g/tex). The reasons for these differences are unclear. It is difficult to correlate the slight yield increases noted with treatments in early July, especially in light of lower retention rates noted with treatments from plant mapping data in late July and the large amount of lint production that occurred in late 2003 due to summer heat. Multiple differences were noted for treatments in regards to lint quality, however, indicating treatments did affect cotton production. Size of bolls and cotton lint from these early summer bolls was not obtained but may have been an overlooked aspect of this study.

Field experiments were initiated at sites in Marana, Coolidge and Goodyear, Arizona, in the Fall of 2001, in a cotton-based, conservation tillage project. In the 2002 cotton season, following cover and grain crops, soil and water management assessments were made to evaluate the impact of conservation tillage on surface irrigation performance. An additional site was added in the winter of 2002 at Maricopa, Arizona. Analyses included soil texture, infiltration rate and water advancement. At Coolidge, the Conservation plots had higher infiltration rates and longer advance times than the Conventional plots in 2002, 2003 and 2004. At Marana, infiltration rates were initially higher for the Conservation plots but the rates converged at the end of four hours in 2002. In 2003, the Conventional plots infiltrated about one inch more and the opposite occurred in 2004, where the Conservation plots infiltrated about 1 inch more than the Conventional. The advance times for Marana showed the water in the Conventional wheel rows to be the fastest. At Goodyear, the Conservation plots infiltrated more than the Conventional plots in 2002. This also resulted in a slower advance time for the Conservation plots. In 2003, due to tillage by the grower, treatment effects could not be compared and the site was abandoned in 2004. At Maricopa, the Conservation plots infiltrated almost 2.2 inches more water than the Conventional plots and the water reached the end of the field three hours ahead of the fastest Conservation plot in 2003. In 2004, the Conservation plot infiltrated just over 1½ inches more water than the Conventional plots with the Conventional plots having faster advance times. Seasonal irrigation water applications to each treatment were relatively equal for all the sites with the exception of Coolidge. Here, the long field combined with sandy soil made it difficult to adequately irrigate the Conservation plots. In 2002, an additional 21 inches of water was applied to the Conservation plots. In 2003, that amount was reduced to 12.5 inches. The 2004 irrigation data are not yet available. The yield data show a significant difference between years and different sites. In 2002, only the yields measured at Coolidge were significantly different with the Conservation yielding higher than the Conventional. This may have been due to the increase water application. In 2003, the opposite occurred and the Conventional plots yielded more than the Conservation plots. This may have been due to herbicide damage. At Maricopa the Conventional plot also yielded more than the Conservation plot in 2003 but there was no measured difference in 2004. The Marana site had equal yields for both treatments except for the final year, 2004, when the Conventional yielded higher than the Conservation treatment. Indications are that conservation tillage does impact irrigation performance and it may not be suitable for all locations depending on soil type and field layout.

The cotton (Gossypium spp.) plant is a true perennial with perhaps the most complex structure of all the major field crops. Plants can compensate to a large degree for environmental as well as physical conditions. Much research has been conducted to arrive at plant population recommendations that optimize the yield and quality of the crop. Research conducted in the low desert regions of Arizona suggest that optimum plant density lies somewhere between 25,000 and 50,000 plants per acre. However, cotton crops with plant densities outside of this optimal range still have the ability to yield similarly and maintain premium quality. Accordingly, a research project was conducted comparing four separate plant densities. Objectives included determining effects on yield and fiber quality. The study was laid out in a randomized complete block design with target plant populations of approximately 30K, 50K, 70K, and 90K plants per acre as the treatments. All other inputs were equal across treatments. Throughout the course of the season, plant measurements showed no distinct differences among the treatments. Height-to-Node ratios (an indicator of vegetative tendencies) remained above normal throughout the season for all populations. Fruit retention levels remained optimal throughout the season. Lint yield results revealed that treatment four (90K plants per acre) yielded significantly less that the other three treatments. No significant differences in fiber quality were observed among treatments.

A field experiment was conducted in 2004 at the University of Arizona Maricopa Agricultural Center (1,175ft. elevation) to evaluate the effects of five irrigation termination (IT1, IT2, IT3, IT4, and IT5) dates on yield and fiber micronaire of several Upland cotton varieties. In addition, the economic relationships of IT treatments were also evaluated. The first IT treatment (IT1) was made with the intention of terminating irrigations somewhat pre-maturely. Based upon current UA recommendations for IT to complete a single cycle fruit set, the more optimal date of IT would have included one or two additional irrigations (beyond IT1). In this experiment, IT2 was structured to provide an additional (one) irrigation before the more optimal date. For the IT3 plots, the intention was to attempt to time termination to match the conventional growers optimal date. The IT4 and IT5 were imposed to attempt to produce a second cycle fruit set and irrigations continued until 27 August and 21 September respectively. In general, lint yield and micronaire results revealed significant differences among the IT treatments. In a similar fashion to 2000-2002 IT experiments, micronaire and lint yield values consistently increased with later IT dates. The best micronaire and lint yield results were achieved with IT4 date, which received 12 in. less irrigation water than IT5. The 12 in. water saved equates to approximately 20% of the total water used under the conventional practice. The average marginal value of water for all Upland varieties in going from IT1 to IT2, IT2 to IT3, IT3 to IT4, and IT4 to IT5 using November 2004 prices and low carrying costs is calculated at $320.07, $150.15, $100.54, and -$28.16 per acre-foot of water. If steeper mike discounts (November 1999), a lower base lint price (45¢/lb.), and higher costs (i.e., more costly insecticide and chemical costs) are imputed to extend the crop, the marginal value of an acre-foot of water for all Upland varieties and replications in going from IT1 to IT2, IT2 to IT3, IT3 to IT4, and IT4 to IT5 is estimated at $164.04, $48.15, $12.97, and -$94.79. Profitability and marginal value of water sometimes vary quite markedly between different varieties and termination dates as well.

Two experiments were conducted in 2004 evaluating twin line cotton production using a conservation tillage system approach. DPL 451 BR Upland cotton was planted into oat hay stubble on April 30 and May 5, 2004 at commercial cooperator sites at Tonopah and Tolleson AZ, respectively. The two primary experimental objectives were to determine whether cotton planted into previous crop residue initiated fruiting on the mainstem once the cotton seedling grew above the crop stubble and whether there were differences in lint yield between the single and twin line system. Previous twin line cotton production research had been conducted by authors at 30 locations from 2001-2003. In almost all cases, the harvest of low set bolls presented problems with the twin line system. In 2004, the initiation of the first fruiting branch was independent of the stubble height at both locations. In addition, there were no differences in lint yield in either a single or twin line cotton production system when planting into previous crop residue using conservation tillage.

A rapid heat increase from the high 80s-low 90s to high temperatures of 110o F on May 21 and 22, 2005, was recorded in the Blythe, CA, area, resulting in abnormal cotton flowers in mid-June, being especially characterized by elongated styles and stigmas being beyond the anthers. Two different cotton variety trials conducted in the Palo Verde Valley allowed data to be collected semi-weekly beginning June 17-20, with 100+ flowers per plot examined in each plot (four replications) of each of the 14 cotton variety entries. Every cotton variety had an average of 90+% of flowers expressing heat stress abnormalities (elongated styles) at the beginning of data collection even though the trials varied by planting date and location. Abnormal flowers were noted for several weeks, with some stigmas 21 mm beyond the anthers. Varieties differed in their responses to heat stress as measured by elongation later in the summer. Limited data were also collected for fruit retention and correlated with length of stigma extension beyond anthers. Retention percentages decreased as distance between anthers/stigmas increased, however boll size increased with less retention, possibly through nutrient partitioning. Various foliar fertilizers containing calcium were also evaluated for their effect on stigma elongations of DPL 449BR cotton. Significant differences existed for stigma elongations, with 2.5 qts./acre of CalMax resulting in statistical reduction of elongation when compared with the untreated check at 3 weeks after application. Statistical differences did not exist at four weeks although statistical differences did exist at this date for the percentage of flowers affected, with the highest percentage (81.7%) noted in untreated cotton.

Field experiments aimed at investigating N fertilizer management in irrigated cotton production have been conducted for the past 16 seasons at three Arizona locations on University of Arizona Agricultural Centers (Maricopa, MAC; Marana, MAR; and Safford, SAC). In 2001-2005, residual N studies were conducted at two of these locations (MAC and MAR). The MAC and SAC experiments have been conducted each season since 1989 and the Marana site was initiated in 1994. The original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (G. hirsutum L.) and American Pima (G. barbadense L.) cotton. The experiments have 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 consistently benefit yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating the residual N effects associated with each treatment regime was initiated and no N fertilizer was applied. Therefore, all N taken-up by the crop was assumed to be derived from residual soil N. However irrigation water analysis showed that NO₃⁻-N concentration levels added to the crop ranged from about 5-9 ppm. In 2001-2005 there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. The lint yields were very uniform at each location and season. Trends associated with residual fertilizer N effects are not evident at either location for five seasons following N fertilizer applications.

Field experiments were conducted in 2004 and 2005 at the University of Arizona Maricopa Agricultural Center (1,175ft. elevation) to evaluate the effects of five irrigation termination (IT1, IT2, IT3, IT4, and IT5) dates on yield and fiber micronaire of eleven Upland cotton varieties and one Pima variety. In addition, the economic relationships of IT treatments were also evaluated. The experimental design was a split plot in a randomized complete block design with three replications. The main treatments included the five IT dates and the subunits consisted of 11 Upland varieties and a Pima variety. The first two IT treatments (IT1 and IT2) were imposed with the intention of terminating irrigations very early and pre-maturely at peak bloom. Based upon current UA recommendations for IT to complete a single cycle fruit set, the more optimal date of IT would have included one or two additional irrigations (beyond IT1 and IT2). In this experiment, IT2 was structured to provide an additional (one) irrigation just past peak bloom. For the IT3 plots, the intention was to attempt to time termination in advance of cutout. The 2004 and 2005 IT4 and IT5 were imposed to attempt to complete the primary fruiting cycle development and produce a second cycle fruit set that require irrigations until late August and late September, respectively. In general, lint yield and micronaire results revealed significant differences among the IT treatments and varieties. In a similar fashion to a previous set of IT experiments (2000-2002), lint yield and micronaire values consistently increased with later IT dates. The best combined lint yield and micronaire results were achieved with IT4 date, which received 12 and 18 in. less irrigation water than IT5 in 2004 and 2005, respectively. In 2004 and 2005, the 12 and 18 in. water saved equate to approximately 20% and 30% less water used under the conventional practice, respectively. The average marginal value of water for all eleven Upland varieties in going from IT1 to IT2, IT2 to IT3, IT3 to IT4, and IT4 to IT5 for November 2004 prices and low carrying costs is calculated at $320.07, $150.15, $100.54, and -$28.16 per acre-foot of water. If steeper mike discounts (November 1999), a lower base lint price (45¢/lb.), and higher costs (i.e., more costly insecticide and chemical costs) are imputed to extend the crop, the marginal value of an acre-foot of water for all Upland varieties and replications in going from IT1 to IT2, IT2 to IT3, IT3 to IT4, and IT4 to IT5 is estimated at $164.04, $48.15, $12.97, and -$94.79. Profitability and the value of water for extending the season varies quite markedly between different varieties and termination dates.