Microsprinklers allow precise control of irrigation water applications and offer the potential for higher efficiency of water and fertilizer use compared with flood irrigation. A field experiment was conducted during 1999-2002 in central Arizona (AZ) to evaluate effects of various N rates and fertigation frequencies on fruit yield and quality, leaf N concentration, and residual soil N of 'Newhall' navel oranges (Citrus sinensis) on 'Carrizo' citrange (Porcirus trifoliata x Citrus sinensis) rootstock (planted in 1997) grown in a Gilman (coarse-loamy, mixed, superactive, calcareous, hyperthermic Typic Torrifluvents) fine sandy loam. The experiment included nonfertilized control plots and factorial combinations of three fertigation frequencies (27, 9, and 3 applications annually) and three N rates (68, 136, and 204 g N tree-1 yr-1). Maximum yields occurred at N rates of 105 to 153 g N tree-1 yr-1 for the fourth to the sixth growing seasons. The yield-maximizing N rates were equivalent to 17 to 34% of currently recommended N rates for citrus grown in AZ. Fruit and juice quality did not show significant response to N rate or fertigation frequency. Leaf N concentrations at yield-maximizing N rates were above the critical leaf tissue N range of 25 to 27 mg g-1, indicating that this range may be too low for these 'Newhall' navel orange trees. During all three seasons, higher residual soil NO3 concentrations resulted from the highest N rate. Our results suggest that optimum N rates for microsprinkler-irrigated 'Newhall' navel oranges in AZ are lower than currently recommended N rates.
ASJC Scopus subject areas
- Soil Science