Zn, Yeast and Naa Manipulation on Growth and Nutritional Status of Washington Navel Orange.

This investigation was carried out during two successive seasons, 2022 and 2023, on 7-year-old Washington navel orange trees that budded on sour orange rootstock and grown in clay loamy soil. The study aimed to improve the vegetative growth and nutritional status of the studied trees using foliar feeding with zinc in two forms (sulfate at 6.0g/l and Zn- Nps at 6.0cm/L), yeast extract at 2.0% and NAA at 100 ppm. The treatments (single or combined) were foliar sprayed 6 times, starting from mid-February, after the fruit set (mid-April) and every month till August. The results revealed that all studied treatments significantly improved the two studied parameters as compared with water-sprayed trees. It was clear that the studied vegetative growth parameters (shoot length and diameter; the number of leaves/shoot; the number of shoots/one-meter length limb and leaf area) were highly enhanced and their values were maximized when the trees were sprayed with ZnNPs at 6.0 cm/L + yeast extract at 2%. When ZnSO₄ replaced by ZnNPs the parameter reflected approach values. Leaf N, P, Fe, Zn, Mn, and chlorophyll contents increased with ZnNPs at 6.0 cm/L + yeast extract at 2%, but leaf K content was highly improved with ZnSO₄ alone. Meanwhile, the high concentrations of both Ca and Mg in the leaves were associated with ZnSO₄ at 6.0 g/L combined with NAA at 100 ppm.