• Evaluation of Irrigation Termination Effects on Yield and Fiber Quality of Upland Cotton, 2004

      Silvertooth, J. C.; Galadima, A.; Tronstad, R.; Tronstad, Russell; Husman, Steve; Norton, Randy; University of Arizona Cooperative Extension (College of Agriculture, University of Arizona (Tucson, AZ), 2005-05)
      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.
    • Residual Soil Nitrogen Evaluations in Irrigated Desert Soils, 2004

      Silvertooth, J. C.; Galadima, A.; Norton, E. R.; Tronstad, Russell; Husman, Steve; Norton, Randy (College of Agriculture, University of Arizona (Tucson, AZ), 2005-05)
      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.