Vol 120 (2007): Proceedings of the Florida State Horticultural Society
Citrus

Optimum nitrogen rate for fertigated young navel orange trees in arizona

Ayako Kusakabe
University of Florida
Published December 1, 2007
Keywords
  • Citrus sinensis,
  • microsprinkler,
  • fertigation frequency,
  • yield,
  • leaf N,
  • residual soil NO3
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Abstract

A field experiment was conducted during 1999-2002 in central Arizona to evaluate effects of N application rate and frequency on fruit yield, leaf N concentration, and residual soil N of 3 to 6-year-old 'Newhall' navel oranges (Citrus sinensis L. Osbeck) on Carrizo citrange (Porcirus trifoliate x C. sinensis) rootstock. Trees were grown in a calcareous fine sandy loam and were well-watered, producing a small positive leaching fraction. The experiment included nonfertilized control plots, and factorial combinations of three fertigation frequencies (27, 9, and 3 applications per year) and three N rates (68, 136, or 204 g/tree per year = 0.15, 0.30, 0.45 lb) from urea ammonium nitrate (32-0-0) applied through microsprinklers. Maximum yields occurred at interpolated N rates of 105 to 153 g/tree per year (= 0.23 to 0.34 lb) for the fourth to the sixth growing seasons. These rates were equivalent to only 17% to 34% of currently recommended N rates for flood-irrigated citrus grown in Arizona. Fruit size and juice quality were not affected by N rate or fertigation frequency. Leaf N concentrations were above 2.7% at yield-maximizing N rates. Highest concentrations of residual soil NO3 resulted from the highest N rate. Fertigation frequency did not significantly affect residual soil NO3. Optimum N rates for young microsprinkler-irrigated 'Newhall' navel orange trees in Arizona were much lower than the currently recommended N rates.