This project is a continuation of an ongoing phosphorus (P) fertility evaluation that began in 1998, at Safford, AZ on a grower cooperator field. The field study conducted during the 2003 season consisted of five treatments of varying rates of P fertilizers from 0 through 165 lbs. of P₂O₅ per acre. Treatments were arranged in a randomized complete block design with three replications. Plot sizes were 12, 36 in. rows wide and extended the full length of the irrigation run of 1250 feet. Three of the five treatments (treatments 3, 4, and 5) consisted of varying rates of P fertilizer applied as a liquid blend (11-30-0-5S) proprietary to United Agri Products (UAP) injected in the soil at approximately the 4 leaf stage prior to the first post plant irrigation. An additional treatment (treatment 2) of calcium thiosulfate (CATS) proprietary to Tessenderlo-Kerley was also applied. In an effort to ensure uniform application of fertilizer nitrogen (N) across all treatments, a solution of urea-ammonium-nitrate (UAN) was applied to bring uniform the level of all treatments with respect to N fertilizer. Lint yield results indicate a strong positive response to applied P, consistent with the previous fours years of P fertility work done in this area. The highest applied P treatments resulted in the highest lint yields with an increase of approximately 155 lbs. lint/acre above the control, an increase of about 12%. Fiber quality data did not indicate any significant differences among treatments for any of the fiber quality parameters measured. Compiling all yield data from the prior six years and plotting percent relative yield as a function of applied P fertilizer demonstrates a positive response to P fertilization. These results indicate the need for local growers to consider P fertilization as an important component of their fertility program. This is particularly true for cotton fields that have had very little or no rotation with small grain crops that are commonly fertilized with a P based fertilizer such as 16- 20-0.

A project was initiated in the 2004 cotton (Gossypium hirsutum) growing season in an effort to accomplish two major objectives. The first was to continue with phosphorus (P) fertilization evaluations that have taken place in the Upper Gila River Valley for the past four seasons by continuing to document the effects of P fertilization on crop yield and fiber quality. The second objective was to investigate the feasibility of utilizing a Global Positioning Systems (GPS) and Geographic Information Systems (GIS) technology for making variable rate (VR) applications of P fertilizers based upon yield data from the previous cropping season. Yield maps from a cotton picker mounted yield monitoring system were collected from the 2003 growing season and used to develop prescription applications of P fertilizers in the 2004 season. The project was established with four treatments including a control (Treatment 1 - 0 P fertilizer applied); a VR application treatment (Treatment 2 - received 52 lbs P/acre on average); a high Uniform Rate (UR) application (Treatment 3 - 75 lbs P/acre); and a low UR application (Treatment 4 - 45 lbs P/acre). These treatments were arranged in a randomized complete block design with four replications. The size of each experimental unit was 0.7 acres. Lint yield results indicated a positive response to applied P fertilizers with treatments 2, 3, and 4 producing significantly higher yields than the control. Lint yield was not significantly affected by fertilizer application technique. Yield differences among the treatments receiving P fertilizer were minimal, particularly among treatments 2 and 3. However, it is important to note that the amount of P fertilizer used in treatment 2 was reduced by 27% with the use of the VR application technique. This produces an approximate $7/acre savings to the grower. This project will be continued in the 2005 growing season and will be expanded to investigate VR application technology in nitrogen (N) fertilization also.

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 2004, 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 (Gossypium 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 reveal 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 increase 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 fertilizer N was applied. Therefore, all N taken-up by the crop was derived from residual soil N. In 2001, 2002, 2003 and even 2004 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 in 1991 and averaged 1500, 1100, and 850 lbs. lint/acre for MAC, MAR, and SAC, respectively. In 2002, results were very similar and yields averaged at 1473 and 1060 lbs. lint/acre for MAC and MAR locations respectively. The 2003 results were not different from the prior two years of results and yields averaged at 1322 and 1237 lbs. lint/acre for MAC and MAR respectively. In 2004, yields averaged 828 and 1075 lbs. lint/acre. Trends associated with residual fertilizer N effects are not evident at either location four seasons following N fertilizer applications.

The 1985 and 1986 Cotton Reports have the same publication and P-Series numbers.

The 1985 and 1986 Cotton Reports have the same publication and P-Series numbers.

Water - nitrogen production functions were determined for cotton cultivars, DPL 77 and DPL 90. Cotton yields for the DPL 90 cultivar were reduced more than the DPL 77 cultivar when water applications were reduced. Cotton yields of 3.0 to 3.4 bales/acre were predicted for nitrogen applications of 160 to 210 lbs/acre with appropriate water applications.

Effects of various fertilization histories on cotton yield were investigated for the fourth consecutive year in the same field at the Maricopa Agricultural Center. Treatments included: 1) no fertilizers added for the past 4 seasons, 2) aggressive nitrogen fertilization in the 1988 season, no fertilization for the previous 3 seasons, 3) standard nitrogen fertilization in 1988 similar treatment for the previous 3 seasons, 4) aggressive nitrogen fertilization in 1988 same history as treatment #3 for previous 3 seasons, and 5) a commercial alternative fertilization program (BioHumaNetics, Inc.). Yields in 1988 were significantly different with treatment 2 having the highest yield followed by treatments 3 and 4, followed by treatment 5; treatment 1 had the lowest yield.

Four field experiments were established in 1988 in Arizona to evaluate the effects of banded phosphorus (P) fertilizers on cotton. 2 sites involved upland cotton (Gossypium hirsutum L.) and 2 sites with pima (G. barbadense L. var Pima S-6), with 1 of each located near Marana, AZ (Vinton Anthony sandy loam). A site with 1 of each kinds was also located near Coolidge, AZ (Mohall sandy loam). At the Marana studies, P was applied 6 inches directly below the zone of seed placement at the time of listing and at the Coolidge sites, P was applied 6 inches below and 2 inches to the side of the zone of seed placement after listing but before planting. In all cases, the P source was 10-34-0 at rates of 0, 30, and 65 lb. P₂O₅ acre⁻¹. At the Marana location, a treatment of banded 10-34-0 at 30 lb. P₂O₅ acre⁻¹ plus a foliar application of 10 lb. P₂O₅ acre⁻¹ (early bloom) as 10-34-0 was included in both the upland and the pima experiments. Plant measurements for plant height, flower numbers, node numbers, boll numbers, and nodes to first fruiting branch were taken to evaluate plant response throughout the season. Plant tissue samples were also taken for leaf petiole PO₄-P and leaf blade total P analysis. Lint yield measurements were also taken. No statistically significant (P < 0.05) differences were found among any of the treatments for any of the measured parameters, except in the petiole PO₄-P levels from the upland study at Coolidge on the second sampling date.

The effect of a single preplant application of zinc sulfate on DPL 77 yield was investigated at the Maricopa Agricultural Center on a field that had tested as marginal with respect to zinc availability. No significant difference in yield was found between the plants receiving zinc sulfate and the control.

A single field experiment was conducted near Marana, AZ, in 1988 to evaluate the effects of both soil - and foliar- applied zinc (Zn) fertilizers on the yield of pima cotton. The soil had a preseason level of 0.6 ppm Zn (DTPA extractable). Treatments included 10 lbs. Zn acre⁻¹ (as ZnSO₄) broadcast incorporated preplant, 0.5 lbs. Zn acre⁻¹ applied as a foliar treatment at early bloom, and a treatment consisting of both the soil and foliar Zn applications. Yield results revealed no differences among any of the treatments in comparison to one another, or the check treatment.