Seasonal changes in nutrient concentrations of navel orange fruit

Concentrations of the macronutrients (K, Ca, Mg, Na, P and S) and micronutrients (Fe, B, Zn, Mn and Cu) in whole fruit, pulp, rind and albedo of fruit from young and mature 'Bellamy' navel orange trees were measured at fortnightly intervals during fruit development. The general order of abundance of the macronutrients were K > Ca > Mg ˆ P > S > Na and the abundance of the micronutrients followed the order B > Fe > Mn ˆ Zn > Cu in whole fruit. The concentrations of most elements in whole fruits and fruit parts decreased during fruit development. In whole fruit K concentrations decreased throughout fruit development whereas the Ca concentration increased during stage I and early stage II, and then progressively decreased. In the pulp these trends were reversed. The K/Ca ratio of whole fruit and rind initially decreased during stage I and then remained constant or increased slightly. In contrast, the K/Ca ratio of the pulp increased linearly during most of fruit development. Seasonal trends in whole fruit, pulp and rind K/Ca and Mg/Ca ratios were similar. Fruit from mature trees, with a history of frequent and severe outbreaks of the rind disorder albedo breakdown (crease) had higher albedo K/Ca and Mg/Ca ratios during stage I of fruit development, compared to fruit from young trees. Concentrations of Fe and B in whole fruits and fruit parts changed little during fruit development, contrary to other micronutrients, such as Mn, Zn and Cu, whose concentrations declined in whole fruits and most fruit parts over the same period. Indirect evidence for high B mobility in phloem of citrus is presented. # 2000 Elsevier Science B.V. All rights reserved.