FREQUENT FERTIGATION DOES NOT AFFECT CITRUS TREE GROWTH, FRUIT YIELD, NITROGEN UPTAKE, AND LEACHING LOSSES

摘要

Effects of fertigation frequency on tree growth, yield and nitrate leaching losses were studied in 1999-2000 using 6-year-old 'Hamlin' orange (Citrus sinensis [L.] Osb.) trees on Swingle citrumelo (C. paradisi Macf. x Poncirus trifoliata [L.] Rat) rootstock growing in 7.6 m3 lysimeter tanks filled with native Candler sand. All trees were irrigated frequently (except for rainy periods) and fertigated with ammonium nitrate at similar annual rates of N that varied from 324 to 462 g of N per tree. Threegroups of six trees each were either fertigated with every irrigation (about 80 times per year), fertigated about 37 times per year, or about 12 times per year. There was no effect of fertigation frequency on leaf nutrient concentration, canopy size, fruit yield, or juice quality. Variability in tree size resulted in larger trees using more water, taking up more N and yielding more fruit than smaller trees. The average concentrations of N in the drainage water ranged from 27 to 86 mg L~(-1) but such variations were not related to total amounts of N leached below the root zone because of the smaller drainage volumes from below larger trees. Nitrogen uptake efficiencies ranged from 24 to 41% of N applied, but there was no effect of fertigation frequencyon the amount of N that was leached or taken up by trees. Thus, these trees received more than sufficient N regardless of fertigation scheduling and there was no significant reduction in N leaching losses when fertigation frequency was increased from 12times per year to 80 times per year.