Field studies were carried out for the purpose of evaluating fertilizer nitrogen (N) recovery of upland cotton by use of the difference technique. The treatments under study included : i) check (no fertilizer N applied), ii) standard approach (preplant and sidedress), iii) feedback approach (based upon soil and plant factors), and iv) 2X feedback approach. The studies were carried out at two locations Maricopa (MAC) and Marana (MAR). MAC is a low elevation location with a coarser textured soil compared to the MAR location. 'DPL-20' was the variety used in both locations, except for the early years at MAC where 'DPL-90' was used. The sources of fertilizer N were urea and ammonium sulphate, which were sidedress and split applied. In general, for the MAC location the final N fertilizer rates (NFR) applied were higher than for MAR due to higher yield potentials. The total N uptake increased as the NFR increased. The N use efficiency (NUE) values were reduced as NFR increased. The N fertilizer uptake (NFU) showed a decreasing pattern in the first years, and then an increasing trend; which was coupled with rather high amounts of N taken up in the check plot (soil N mineralized). When the N uptake in the check plot was high, NFU values were low, and vice versa. At MAC the N uptake in the check plot, apparently due to mineralized soil N revealed a slight increasing trend during the first years and then, after the fourth year, a rapid reduction of the mineralized soil N (check plot). A similar pattern was observed for MAR, although the total amount of N taken up was smaller compared to the MAC location.

In 1996 a single field experiment was conducted at Paloma Ranch, west of Gila Bend in Maricopa County Arizona. Nucoton 33B was dry planted and watered -up on 15 April. Treatments consisted of various rates and times of application of nitrogen (N) and calcium (Ca) from two sources (N-Carm and CAN-17), as well as a standard N source, UAN-32, along with a Calcium (Ca) check which received no Ca. Treatments], 2, and 3 each received a total of 280 lbs. N/acre. Treatment 4 received a total of 210 lbs. N/acre while treatment 5 received a total of 301 lbs. N/acre. Treatment 1 was a check plot and received only standard applications of UAN-32. Treatments 2 and 4 each received a total of 72 lbs. of Ca/acre. Treatment 5 received a total of 79 lbs. Ca/acre while treatment 4 received a total of 300 lbs. Ca/acre. No significant differences were found among the various treatments in terms of plant growth, soil water content, ECₑ values, and sodium absorption ratios. Lint yields were significantly different (P < 0.07).

Two field experiments were conducted during the 2000 growing season to address fertility recommendations for fertilizer phosphorus (P) and potassium (K). A K fertility study was conducted near Tonopah, AZ consisting of two treatments, an untreated control and a treatment receiving a total of 20 gallons of K-Sul/acre. No significant differences were observed in leaf blade K concentrations between treatments. Plant growth and development estimates revealed that fruit retention (FR) levels remained consistently higher in the untreated control versus the treated plots. A second study involved treatments consisting of both P and K fertilizers was conducted near Cibola, AZ. Four treatments in this experiment included an untreated control plus treatments of 11-52-0, 0-0-60, and 4-17-40 at 100, 200, and 300 lbs. fertilizer/acre respectively. Plant growth and development estimates were similar among treatments during the season. At the end of the season the untreated control had a slightly higher FR level than the other treatments, which also produced a significantly higher yield. No other differences in yield among the fertilized treatments were observed.

Two field experiments were conducted in Arizona in 2000 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 2000, fruit retention levels were good and crop vigor was not excessive. The more conservative, feedback approach to N management provided optimum yields at both locations.

A series of nitrogen management experiments have been conducted over the past 11 years around the state to develop and refine fertilizer nitrogen (N) recommendations for irrigated desert cotton production. Stability analysis was used to summarize the data and to determine which of the four treatment regimes is most stable over a range of environments. Results indicate that the feedback treatment (treatment 3) was the most stable treatment for both Upland and Pima cottons and provided the best probability for a higher yield under high yielding environments. The untreated control treatment (treatment 1) was the least stable over a wide range of environments. These results further validate the ‘feedback’ approach to management of fertilizer N.

Proper timing of fertilizer N applications in relation to crop uptake can serve to improve fertilizer efficiency in irrigated cotton. Earlier research has identified an optimum application window extending from the formation of first pinhead squares to peak bloom, which corresponds well with maximum crop uptake and utilization. Field experiments were conducted at the University of Arizona Marana Agricultural Center (Grabe clay loam soil) utilizing sidedress applications of ammonium sulfate with 5-atom % 15-N at pinhead square, early bloom, and peak bloom at a rate of 56 kg N/ha. The objective was to compare relative efficiencies in terms of fertilizer N uptake and recovery among these three times of application. Results indicate that all treatments averaged approximately 80% total fertilizer N recovery. Of the fertilizer N that was recovered, approximately 40 % was taken up by the plants and 60 % recovered in the soil, primarily in the top 60 cm of the soil profile.

A laboratory study was initiated to investigate the potential loss of fertilizer nitrogen (N) through volatilization at four different temperatures (25, 30, 35, and 40°C) out of irrigation waters collected from a number of Arizona locations. Complete water analysis was conducted on each of the water samples. A 300 ml volume of each water was placed in 450 ml beakers open to the atmosphere in a constant temperature water bath with 10 mg of analytical grade (NH₄)₂SO₄ added to each sample. Small aliquots were drawn at specific time intervals over a 24 hour period and then analyzed for NH₄⁺-N concentrations. Results showed potential losses from volatilization to be highly temperature dependent. Total losses (after 24 hours) ranged from 30-48% at 25°C to over 90% at 40°C. In this study where (NH₄)₂SO₄ was used as the N source, the initial concentration of SO₄⁻-S in the solution had a repressive effect on volatilization due to the decreased availability of free NH₄⁺ in waters with high initial SO₄⁻-S concentrations due to the formation of complex ion pairs (NH₄SO₄⁻). It was also observed that at lower temperatures complexation and ion pair formation affected volatilization of NH₃ by reducing the NH₄⁺ activity in solution and thereby reducing NH₃ volatilization. Potential volatilization loss of fertilizer N from these irrigation waters was found to be significant and should be considered when making decisions regarding fertilizer N applications for crop production in Arizona.

Ironite and phosphorus were applied as a combined treatment and also individually to plots planted to long and short staple cotton to find their effect on crop development and lint yield. A statistically significant increase in lint yield was seen with 14 pounds of Ironite and 200 pounds of 16-20-0 per acre compared with the untreated check in the short staple plots. An increase in long staple yield was observed as the Ironite treatment increased from 7 to 28 pounds per acre when coupled with 200 pounds of 16-20-0. Few differences were seen between treatments in any of the plant mapping variables measured or with HVI values. More research and an economic analyses are needed to determine if this would be a recommended procedure in the Safford valley.

A two site evaluation of a calcium (Ca²⁺)-based soil conditioner was conducted during the 1999 cotton season. The two locations included one at the Maricopa Agricultural Center (MAC) in Maricopa, AZ and the other was on a grower-cooperator field in Tacna, AZ. Both studies involved the use of CN-9, a Ca-nitrate solution with 9% nitrogen and 11% Ca. At MAC theCN-9 solution was sprayed over the seedbed post planting but prior to the first water-up irrigation. At the Tacna site CN-9 was applied in a sidedress application at planting. Routine plant measurements were taken throughout the duration of both studies and lint yield estimates were made at each location at the end of the season. No significant differences due to the application of CN-9 were detected in any data collected.

Two soil amendments, Agriblend Plus and Superfloc A-836, were applied to cotton beds prior to planting at rates of 5, 10, 15 and 20 pounds per acre, incorporated and planted to short staple (DP 655BR) or long staple (HTO) cotton. The experimental plots were fertilized, irrigated and managed in a manner to produce optimal cotton yields. No statistically significant yield increases were seen from any of the treatments, even though a few interesting trends were observed. The report contains observations on plant mapping and lint quality data, in addition to yield data.