• Nitrogen and Water Inputs for Trickle-Irrigated Winter Vegetables

      Thompson, T. L.; Doerge, T. A.; McCreary, T. A.; Rodriguez-Casas, J.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      An experiment was conducted during 1992-93 at the University of Ariwna Maricopa Agricultural Center to investigate the effects of nitrogen (N) and water management on yield, midrib nitrate-N, and N and water use efficiency of subsurface trickle-irrigated leaf lettuce, collard, and spinach. The experiment was a randomized complete block factorial with three water levels (deficient, optimum, excessive), four N fertilizer levels (deficient, suboptimal, supraoptimal, excessive) and four replications. Trickle tubing was placed in the center of the beds at 15 cm depth. Irrigation was applied daily as needed to maintain the appropriate target soil water tension and N fertilizer (urea ammonium nitrate solution) was applied in 4 to 5 split applications. Midrib samples were collected for nitrate -N analysis at 4 growth stages, and portions of the plots were harvested when plants were marketable size. The 1992-93 growing season was excessively wet, therefore optimum yields were achieved in the deficient irrigation treatment. The wet conditions apparently led to excessive N losses, therefore high rates of N fertilizer were needed for optimum yields. Nitrogen and water use efficiencies were maximized at low rates of water and fertilizer input. Midrib nitrate-N concentrations were responsive to N fertilizer treatments.
    • Pepper Variety Trial in Cochise County, 1993

      Clark, L. J.; Call, R. E.; Oebker, N. F.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      A variety trial including 12 long green chile varieties, 6 jalapeño varieties and 3 paprika varieties was implemented in Cochise county in 1993. Alpha was the top yielding green chile with a yield of 23.8 tons per acre and Fresno lead the jalapeño varieties with a yield over 30 ton per acre. Conquistador variety of paprika appeared to have a slight advantage over the other varieties in its class. A characterization of the fruit from the varieties tested are given in this paper.
    • The Response of Leaf Lettuce to Phosphorous Fertilizer Placement and Rate

      Pritchard, Kevin H.; Doerge, Thomas A.; McCreary, Ted W.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      A one-year field study was conducted at the Maricopa Agricultural Center in the winter and spring of 1991-92 with the purpose of comparing the response of leaf lettuce grown with subsurface drip irrigation to various broadcast and banded phosphorus (P) fertilizer applications and rates. Two rates of banded treble superphosphate, 250 lbs. (1X) and 125 lbs. (1/2X) of P2Osper acre, were applied immediately before planting in a concentrated strip 1 inch directly below the row to be seeded. One broadcast rate, 250 lbs. (1X) of P205 per acre of the same material, was applied and folded into the planting beds during listing. Control plots, in which zero P fertilizer was applied, were also maintained. Whole plant total P concentrations were higher in the first one-third of the growing season for the band treatments, though the differences in responses between band and broadcast applications were not statistically significant in the final third of the season. The 1X band treatment exhibited both greater plant heights and diameters than all other treatments during the first one-half of the growing season, and maintained greater height dimensions in the second half. The 1X broadcast and 1/2X band treatments exhibited similar growth throughout the season. By harvest there were not significant differences in head or plant size or in marketable yield among the three P treatments.
    • Sampling Schemes and Action Thresholds for Sweet Potato Whitefly Management in Spring Melons

      Palumbo, John C.; Tonhasca, Athayde, Jr.; Byrne, David N.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      Early season infestations of sweet potato whiteflies, Bemisia tabaci ( Gennadius) were monitored in fields of cantaloupe, Cucumis melo L., near Yuma, Arizona. We used these data to describe the relationship between the proportion of infested leaves and mean adult population density for the entire field. This model was used to develop a binomial sampling plan based on a presence- absence approach. We evaluated the model with three independent data sets, and the level of agreement between the model and data was reasonable for pest management purposes. A minimum sample size of 200 leaves is suggested for maximum accuracy. By turning over 50 leaves in the four quadrants of a field and determining what proportion have whiteflies (i.e., are there whitefly adults on the leaf or not), growers can estimate field populations. We recommend that if 60% of the sampled leaves have whiteflies then it is time to make a pesticide application because that tells you that population levels are approaching 3 adults per leaf.