Call number: LD2668 .T4 1958 O65

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.

Field experiments were conducted during the 1996 and 1997 growing seasons in Mohave Valley to determine the effect of late season nitrogen (N) fertilizer applications on top crop yield potential of upland cotton. A long season production system utilizing late season nitrogen (N) applications through peak bloom (August) was compared to a short season production system in which N was applied through mid-bloom (June). Mid-season N applications were based on UA guidelines utilizing plant mapping and petiole nitrate data for the short season production system.

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.

Three different nitrogen fertilizer regimes were practiced in this study along with an unfertilized check. The same amount of nitrogen fertilizer was sidedressed in the plots in one, two or three applications. No significant differences were seen, but the trends looked like the split applications might have had some advantage.

Various field experiments were conducted during the 1997 and 1998 cotton season involving macro and micronutrient fertilization. A total of six experiments were conducted at various locations in Arizona. Each of the field experiments studied the effects of different nutrients and nutrient combinations on both Upland and Pima varieties. The purpose of these experiments were to evaluate University of Arizona fertility guidelines with respect to soil test results and to possibly fine-tune or calibrate these guidelines for common Arizona soils and cotton growing regimes. Results from these experiments based on soil test information, quantitative plant measurements, and lint yield showed no significant difference due to treatments for all the studies except for a phosphorus study conducted in Graham County.

Micronutrient fertilizers including zinc, boron, copper, and manganese in their sulfate forms were broadcast applied and incorporated preplant to determine their effects on lint yield of upland cotton.

A single field study was conducted on a sodium-affected soil at the University of Arizona’s Maricopa Agricultural Center (MAC) in 1998. NuCotn 33B was dry planted and watered-up on 5 May 1998. Two treatments were evaluated; treatment 1 received no acid and treatment 2 received water-run acid applications. The acid used in this evaluation was sulfuric acid (H₂SO₄). The acid was applied at approximately 11 gallons acid/acre at each scheduled irrigation throughout the entire growing season. All other agronomic inputs and decisions were uniformly applied to both treatments in the same manner throughout the season. The experiment was arranged in a randomized complete block design with two treatments and six replications. Significant differences were found among the two treatments in terms of plant growth and soil water content (P<0.05). Lint yields were significantly different (P=0.0013) with the check having the highest yield.

A multi-site experiment was conducted at Paloma Ranch, west of Gila Bend in Maricopa County and at Wellton in Yuma County Arizona. NuCotn 33B was dry planted and watered-up on 28 April 1998. Various rates of application of nitrogen (N) and calcium (Ca) from CN-9 [9-0-0-11Ca (5Ca(NO₃)₂•NH₄NO₃•10H₂O)] was used to evaluate the check. The CN-9 was applied as a foliar application directly to the seed bed on 27 April 1998. Treatment 1 was the check plot that received no CN-9. Treatment 2 received a 12 gal./acre application of CN-9 while treatment 3 received a 15 gal./acre application of CN-9. Each gal of CN-9 weighs approx. 12.2 lbs. and contains 1.1 lbs. of N and 1.4 lbs. of Ca. Treatment 2 received a total of 13 N/acre while treatment 3 received a total of 17 N/acre via CN-9. Treatment 1 received only farm standard applications of UAN-32. Treatments 2 and 3 each received farm standard applications of UAN-32 after the application of CN-9 for continued crop N needs. A total of 17 lbs./acre of Ca was applied to treatment 2 and 21 lbs./acre of Ca was applied to treatment 3. 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 not significantly different (P<0.05).

Three different nitrogen fertilizer regimes were practiced in this study along with an unfertilized check. The same amount of nitrogen fertilizer was sidedressed in the plots in one, two or three applications. No statistically significant differences were seen between lint yields in this study nor in the previous study, but the yield trends were very similar. Applying the fertilizer nitrogen in two equal portions at the onset of rapid vegetative growth and just before peak bloom appeared to produce the best lint yield.