• Initial Post Plant Irrigation Effects on Low Desert Upland Cotton Yields Using Leaf Water Potential Measurements

      Husman, S. H.; Barrot, D. J. Jr.; O'Leary, J. W.; Moore, M.; Wegener, R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1994-03)
      Leaf water potential (LWP) measurements using a pressure chamber were used to determine optimum timing of the first irrigation following planting on Upland cotton in 1992 and 1993. Previous studies have indicated that leaf water potentials are dependent on the vapor pressure deficit (VPD) of the surrounding air. As a result, the VPD was accounted for in the development of a Leaf Water Potential Index (LWPI). The field studies consisted of three irrigation treatments with four replicates arranged in a randomized complete block design (RCB). Targeted treatment thresholds were 0.15 LWPI (wet), 0.30 LWPI (medium), and 0.45 LWPI (dry). Timing of the first irrigation for the 1992 study occurred at 36, 53, and 63 days after planting. Timing of the 1993 first irrigation occurred at 50, 61, and 77 days after planting for the wet, medium, and dry treatments respectively. There were no significant lint yield differences between irrigation treatments in both 1992 and 1993.
    • Irrigation Efficiencies and Lint Yields of Upland Cotton Grown at the Maricopa Agricultural Center, 1993

      Sheedy, Mike; Watson, Jack; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1994-03)
      The computer program AZSCHED, with weather data obtained from AZMET, was used to schedule irrigations for a yield trial of early season Upland Cotton (DPL 20) at the Maricopa Agricultural Center. Cotton lint yields were compared between plots from five treatments involving five irrigation efficiencies (50 %, 65 %, 75 %, 90% and 110 %). As in previous years, a potassium bromide tracer was applied to select areas in each plot to monitor the movement of water and nitrates down the soil profile. The total amount of fertilizer as nitrogen applied in two split applications and sidedressed was 100 #/a. The total amount of water applied to the plots ranged from 42.7" for 50% to 26.6" for 110% (deficit) irrigation efficiency. The plots were harvested on October 5, 1993. There was a significant difference in lint yield between the irrigation efficiency treatments. The 50% irrigation efficiency treatment produced 1190 # lint /acre while the 110% efficiency produced 883 # lint /acre.
    • The Use of AZSCHED to Schedule Irrigation on Cotton, Safford Agricultural Center - 1993

      Clark, Lee J.; Carpenter, Eddie W.; Slack, Donald C.; Martin, Edward C.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1994-03)
      An irrigation scheduling trial was implemented on both long and short staple cotton on the Safford Agricultural Center in 1993. It is a continuation of studies initiated in 1991, where plots were irrigated when they reached 40 %, 50% and 60% soil water depletion level as predicted by the AZSCHED software. Results for this study are given as well as a summary of the three year study.
    • Use of Leaf Water Potentials to Determine Timing of Initial Post-Plant Irrigation

      Steger, A. J.; Silvertooth, J. C.; Brown, P. W.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1994-03)
      Presumably, from a physiological standpoint, early season water stress should be avoided to ensure early fruit initiation, good fruit retention, and optimum yield potential of cotton (Gossypium spp.). This study was conducted to determine the optimum timing of the initial post plant irrigation and the long term effect of postponement on subsequent plant growth patterns, fruit retention, and yield. A short - season Upland variety, (G. hirsutum L.), DPL 20, was planted on 19 April in Marana, AZ, elevation 1970 ft. , on a Pima clay loam (Typic Torrifluvent) soil. Plots (experimental units) consisted of eight 40 in. rows and extended the full length of the irrigation run (600 ft.). Experimental design was a randomized complete block with four replications. Initial post - plant irrigations, designated T1 , 72, and T3, were applied when the midday leaf water potential (ψ) of the uppermost, fully- developed leaf reached -15, -19, and -23 bars, respectively. All treatments received the same irrigation regime following the initial post plant irrigation. Basic plant measurements were taken weekly from each experimental unit. These included plant height, number of mainstem nodes, location of first fruiting branch, fruit retention, number of nodes above the uppermost white bloom, bloom count within a 166 ft² area, and percent canopy cover. Soil -water data at seven 25 cm depth increments was collected from a total of 36 access tubes located within the field study, with three tubes per plot. Lint yields (lb. lint /acre) were 1112, 1095, and 977 for T1 , 72, and T3, respectively. Yields were significantly lower when the initial post plant irrigation was applied after ψ, dropped below -19 bars, confirming the results of a previous study conducted in 1992. Throughout the growing season, height - node ratios (HNR) of T1 and 72 plants were at or above the upper threshold established for DPL 20, while T3 HNR remained close to the expected baseline. Fruit retention was low for all three treatments due to season -long insect pressure from lygus bug. The low fruit retention data reflects the effects of high HNR. Future work will include efforts to separate changes in ψ due to day-to-day climatic variations from those caused by soil -water depletion. A second objective will be to incorporate the data obtained from the neutron moisture meter probe into the study results in an effort to better describe the complete soil-plant-atmosphere continuum as affected by the various treatment regimes employed in this study.