Determination of nutritional sufficiency ranges for pomelo (Citrus grandis Osbeck) grown on alluvial soils using DRIS.

Pomelo is an important tropical fruit with a high nutrient content and economic value in the Vietnamese Mekong Delta (VMD). The Diagnosis and Recommendation Integrated System (DRIS) helps determine the leaf nutrient status of various plants worldwide. However, the DRIS-based nutritional balance in pomelo leaves remains to be established. Therefore, in this study, we aimed to (i) construct the DRIS norms and indices for nutrients, including macronutrients (N, P, K, Ca, and Mg) and trace elements (Cu, Fe, Zn, and Mn) in pomelo leaves, and (ii) establish nutrient sufficiency value ranges for sustainable pomelo cultivation in the VMD. We collected 270 leaf samples at three stages of pomelo growth, i.e., flowering, fruit development, and postharvest, and calculated DRIS indices for various nutrients. The DRIS indices established for various nutrients in pomelo leaves were accurate and reliable, as indicated by the high coefficient of determination (R2 = 0.43-0.93, p < 0.05) between nutrient concentrations and their DRIS indices. We observed that pomelo leaves were deficient in N (IN = -6.82), P (IP = -24.0), and Fe (IFe = -0.40) at the flowering stage and most deficient in P (IP = -15.6), K (IK = -11.7), Fe (IFe = -0.50), and Mn (IMn = -2.31) at the fruit development stage. However, only N (IN = -2.64) and P (IP = -13.4) shortages were observed at the postharvest stage. Thus, in this study, we evaluated nutrient value ranges (deficient, balanced, and excess) in pomelo leaves at their different growth stages and established DRIS indices for various nutrients. The results contribute to our understanding of the nutritional status of pomelo leaves, which can help growers improve plant health for sustainable pomelo production.