• Development of Best Management Practices for Fertigation of Young Citrus Tree

      Thompson, Thomas L.; White, Scott A.; Walworth, James; Sower, Greg; Wright, Glenn; Kilby, Mike (College of Agriculture, University of Arizona (Tucson, AZ), 2002-02)
      'Newhall' navel oranges on 'Carrizo' rootstock were planted in Mar. 1997 at the Citrus Agricultural Center. The objectives of this experiment were: i) to determine the effects of N rate and fertigation frequency for microsprinkler-irrigated navel oranges on tree N status, and crop yield and quality; and ii) to develop Best Management Practices which promote optimum tree growth and production while minimizing nitrate leaching. The trees are equipped with a microsprinkler irrigation system. The experiment is a randomized complete block factorial with N rates of 0, 0.15, 0.30, and 0.45 lb N/tree/year, and fertigation frequencies of weekly, monthly, and three times per year. Unfertilized control trees are also included in the experimental design. Each of the ten treatments is replicated five times. The trees were harvested for the first time in Feb. 2001. Fruit were processed through an automatic fruit sizer, and fruit from each plot were further evaluated for fruit quality. Although unfertilized control trees had lower leaf N content than fertilized trees, fruit yield and quality of controls was no lower than fertilized trees. Similarly, there were few statistically significant differences in fruit yield and quality between trees receiving different N rates and fertigation frequencies.
    • Development of Best Management Practices for Fertigation of Young Citrus Trees

      Thompson, Thomas L.; White, Scott A.; Maurer, Michael A.; Wright, Glenn; Kilby, Mike (College of Agriculture, University of Arizona (Tucson, AZ), 2000-10)
      Microsprinkler irrigation offers excellent flexibility for site-specific management of water and nitrogen inputs for citrus orchards in the southwestern United States. Escalating water costs, declining water availability, and increasing regulation of nitrogen (N) fertilizer use are causing growers to adopt practices to improve water and N use efficiency. 'Newhall' navels on 'Carrizo' rootstock were planted in Jan. 1997 and an experiment was initiated. This experiment was continued during 1999. The objective of the experiment was to develop appropriate management guidelines for N fertigation of 3-4 year old microsprinkler-irrigated navel orange trees. Treatments were factorial combinations of three N rates (0.15, 0.30, 0.45 lb N tree⁻¹ yr⁻¹) and three fertigation frequencies (3x/year, monthly, weekly). An untreated control was included. Trunk diameter was not responsive to N rate or fertigation frequency. Leaf N in all treatments, even controls, remained above the critical level (2.5%). However, at each N rate leaf N was highest with the weekly fertigation frequency. Nitrate analyses of soil samples indicate that nitrate leaching was highest with the highest N rate and 3x/year fertigation. Frequent fertigation is recommended because it results in higher leaf N and less nitrate leaching.
    • Development of Best Management Practices for Fertigation of Young Citrus Trees, 2002 Report

      Thompson, Thomas L.; White, Scott A.; Walworth, James; Sower, Greg; Wright, Glenn; Gibson, Rick (College of Agriculture, University of Arizona (Tucson, AZ), 2002-11)
      'Newhall' navel oranges on 'Carrizo' rootstock were planted in Mar. 1997 at the Citrus Agricultural Center. The objectives of this experiment were to i) determine the effects of N rate and fertigation frequency for microsprinkler-irrigated navel oranges on tree N status, and crop yield and quality; and ii) develop Best Management Practices which promote optimum tree growth and production while minimizing nitrate leaching. The trees are equipped with a microsprinkler irrigation system. The experiment is a randomized complete block factorial with N rates of 0, 0.15, 0.30, and 0.45 lb N/tree/year, and fertigation frequencies of weekly, monthly, and three times per year. Unfertilized control trees are also included in the experimental design. Each of the ten treatments is replicated five times. The trees were harvested in Jan. 2002. Fruit were processed through an automatic fruit sizer, and fruit from each plot were further evaluated for fruit quality. Leaf N concentration was responsive to N rate, but not to fertigation frequency. Leaf N in all fertilized plots was above tissue critical levels. Fruit yield in fertilized plots was higher than in unfertilized plots, but, in fertilized treatments, there was no significant effect of N rate or fertigation frequency on fruit yield or quality.
    • Development of Best Management Practices for Fertigation of Young Citrus Trees, 2003 Report

      Thompson, Thomas L.; White, Scott A.; Walworth, James; Sower, Greg; Wright, Glenn (College of Agriculture, University of Arizona (Tucson, AZ), 2003)
      ‘Newhall’ navel oranges on ‘Carrizo’ rootstock were planted in Mar. 1997 at the Citrus Agricultural Center. The objectives of this experiment, conducted during 2000 - 2003, were to i) determine the effects of N rate and fertigation frequency for microsprinkler-irrigated navel oranges on tree N status, and crop yield and quality; and ii) develop Best Management Practices which promote optimum tree growth and production while minimizing nitrate leaching. The trees were equipped with a microsprinkler irrigation system. The experiment was a randomized complete block factorial with N rates of 0, 0.15, 0.30, and 0.45 lb N/tree/year, and fertigation frequencies of weekly, monthly, and three times per year. Each of the ten treatments was replicated five times. The trees were harvested in December or January of each growing season. Fruit were processed through an automatic fruit sizer, and fruit from each plot were further evaluated for fruit quality. Leaf N concentration and fruit yield of 4-6 year old trees were responsive to N rate, but not to fertigation frequency. Fruit quality and packout were not significantly affected by either N rate or fertigation frequency. Fruit yield was optimized at annual N rates of 0.25 lb/tree (four-year-old trees) to 0.35 lb/tree (six-year-old trees) during this experiment. We propose new tissue guidelines for guiding N fertilization of young microsprinkler-irrigated navel oranges.
    • Nitrogen and Phosphorus Fertilizer Management for Young, Bearing Microsprinkler-Irrigated Citrus, Final Report

      Thompson, Thomas L.; White, Scott A.; Kusakabe, Ayako; Wright, Glenn (College of Agriculture, University of Arizona (Tucson, AZ), 2005)
      Higher nutrient and water use efficiency are possible with microsprinkler-irrigated citrus compared to flood-irrigated citrus. Therefore, new N and P fertilizer recommendations are needed for microsprinkler-irrigated citrus. The objectives of this project were to i) determine the effects of N applications of 0 - 0.8 lb/tree/yr on fruit yield, fruit and juice quality, and N and P removal in fruit for microsprinkler-irrigated navel oranges; ii) determine the effects of P applications of 0 - 0.2 lb/tree/yr on fruit yield, fruit and juice quality, and N and P removal in fruit, and iii) develop Best Management Practices for N and P fertigation of microsprinkler-irrigated citrus. Field experiments were conducted at the University of Arizona Citrus Agricultural Center in separate blocks of ‘Newhall’ and ‘Fukumoto’ navel oranges, both on ‘Carrizo’ rootstock. In each block, ten treatments, consisting of all possible combinations of 5 N rates (0, 0.2, 0.4, 0.6, and 0.8 lb N/tree/yr) and 2 P rates (0, 0.2 lb P/tree/year) were applied to five replicate trees per treatment. The maximum predicted yields for both varieties during all three seasons occurred at N rates of 0.4 to 0.55 lb N tree-1 yr-1. There were no significant effects of P application on fruit yield or quality. There were few significant effects of N or P fertilization on packout or fruit quality. The amounts of N removed in harvested fruit at the yield-maximizing N rates were equivalent to 50-84% of the N applied. New N fertilizer recommendations for microsprinkler-irrigated navel oranges are proposed.
    • Nitrogen and Phosphorus Fertilizer Requirements for Young, Bearing Microsprinkler-Irrigated Citrus, 2005 Report

      Thompson, Thomas L.; White, Scott A.; Kusakabe, Ayako; Wright, Glenn (College of Agriculture, University of Arizona (Tucson, AZ), 2004)
      Higher nutrient and water use efficiency are possible with microsprinkler-irrigated citrus compared to flood-irrigated citrus. Therefore, new N and P fertilizer recommendations are needed for microsprinkler-irrigated citrus. The objectives of these experiments were to i) determine the effects of N applications on tree growth, fruit yield, fruit and juice quality, and N and P removal in fruit for microsprinkler-irrigated navel oranges; ii) determine the effects of P applications on tree growth, fruit yield, fruit and juice quality, and N and P removal in fruit, and iii) develop Best Management Practices for N and P fertigation of microsprinkler-irrigated citrus. Field experiments were conducted at the University of Arizona Citrus Agricultural Center in separate blocks of 'Newhall' and 'Fukumoto' navel oranges, both on 'Carrizo' rootstock. In each block, ten treatments, consisting of all possible combinations of 5 N rates (0, 0.2, 0.4, 0.6, and 0.8 lb N/tree/yr) and 2 P rates (0, 0.2 lb P/tree/year) were applied to five replicate trees per treatment. Maximum yields of the ‘Newhall' trees were 132 lb fruit/tree at a N rate of 0.5 lb N/tree/yr. Maximum yield of the 'Fukumoto' trees was119 lb fruit/tree at 0.5 lb N/tree/yr. Both varieties maintained appropriate leaf N and P concentrations at the yield-maximizing N rates. Total N in the fruit accounted for about 60 % of the N applied at the yield-maximizing N rates in both varieties. The results confirmed that microsprinklers effectively reduced the amounts of N fertilizer needed while maintaining adequate N status in the trees, with excellent N use efficiency.