Yield and fruit quality responses of Ellendale mandarins to different nitrogen and potassium fertiliser rates

Abstract

Three rates of nitrogen fertiliser (88, 176 and 352 kg N ha-1 as ammonium nitrate) and 3 of potassium (0, 220 and 440 kg K ha-l as potassium sulfate) were applied to mature Ellendale mandarin trees, in the Central Burnett district, Qld. Optimum yield response occurred at the I76 kg N ha-1 nitrogen rate but potassium treatments did not significantly affect yield. Rind was thinner and fruit colour better at the lowest nitrogen and potassium rate. Whereas nitrogen produced no effect on internal fruit quality, the ratio of total soluble solids:acid was depressed by the highest potassium rate as a result of increased acid content. For Ellendale mandarins under Queensland conditions the lowest potassium treatment produced smaller fruit with thinner rind and earlier colour development. The results indicate that the optimum nitrogen fertiliser application rate is 160-180 kg N ha-1 and that potassium fertilisers can impair fruit quality.