ZINC (65ZN) SOURCES FOR FEEDING THE ORANGE TREE NEW FLUSHES

Abstract

There are three zinc (Zn) sources for feeding vegetative growth flushes of growing orange (Citrus sinensis) trees: the Zn within the old parts of the tree; Zn absorbed from soil; and Zn from fertilizer applied on leaves. The objective of this study was to quantify the contribution of each of these Zn sources for feeding the new growth flushes of 'Valencia' orange trees. In the first experiment, young orange trees were grown hydroponically in plastic pots using a complete nutrient solution to which 65 ZnCl 2 (506 dpm/μg of Zn) was added. The growth flush that developed after 65 Zn addition was harvested when it was completely developed. In the second experiment, five-year-old orange trees, grown in a commercial potting mix, were sprayed with 80 ml/tree of a solution containing 65 ZnCl 2 (60 dpm/μg of Zn) when they were producing flower flushes. The flush growth developed after 65 Zn application was harvested when it was completely matured. In the third experiment, five-year-old orange trees were grown in pots containing an Arenosol soil, and 680 mg of Zn ( 65 ZnSO 4 .7H 2 O, 3.7 dpm/μg of Zn) were applied to the soil surface. The trees were allowed to produce two sequential growth flushes, both of which were harvested when fully mature. All harvested plant materials were partitioned into various organs, dried, and analyzed for 65 Zn radioactivity using a solid scintillation (NaI) counting system and for total Zn by atomic absorption spectroscopy. About 20% of Zn within in the old part of orange tree was distributed to the new parts (flower flush). The Zn applied to the soil surface increased the Zn content of the new organs developed during at least two growth flushes. In contrast, foliar fertilization had no effect on the Zn content of organs that developed after spraying.