PERTANIKA JOURNAL OF TROPICAL AGRICULTURAL SCIENCE

Xa Doai orange is a commercially valuable cultivar in Central Vietnam, yet its productivity and fruit quality are often limited by micronutrient deficiencies. This study aimed to evaluate the effects of foliar application of zinc sulfate (ZnSO4·7H2O), manganese sulfate (MnSO4), and boric acid (H3BO3) at varying concentrations (0%, 0.4%, 0.6%, 0.8%, and 1.0%) on nutrient uptake, fruit yield, and quality attributes of Xa Doai orange. The experiment was conducted over one growing season (2022–2023) in a randomised complete block design with five treatments and three replications. Foliar sprays were applied twice times during critical growth stages: fruit set, and fruit development. Each plot consisted of nine trees, and data were collected on leaf nutrient content, yield components, and juice quality parameters. The results showed that the 0.8% treatment (T4) significantly improved leaf nutrient concentrations (45.04 mg/kg Zn, 49.62 mg/kg Mn, 51.79 mg/kg B), fruit weight (221.79 g), and yield (39.55 kg/tree) compared to the control (P ≤ 0.05). Juice content, total soluble solids (12.92 %), and vitamin C (468.00 mg/L) were also highest at this concentration. No significant changes in soil pH or residual micronutrients were observed. These findings indicate that foliar spraying of Zn, Mn, and B at 0.8% is an effective, environmentally safe strategy to enhance productivity and fruit quality in Xa Doai orange. Further studies are needed to assess long-term effects and economic viability under diverse agroecological conditions.