Soil–Leaf–Fruit Nutrient Relationships and Coconut Water Composition in Aromatic Coconut (Cocos nucifera L.): Associations with Reproductive Traits Across Two Locations in Southern Thailand

Understanding how soil nutrient availability translates into leaf nutritional status, fruit-water mineral composition and reproductive performance is important for improving nutrient management of aromatic coconut. This study evaluated these relationships in aromatic coconut across two contrasting locations in southern Thailand. Two coconut varieties were assessed for fruit-water composition, reproductive performance, soil nutrient availability, and leaf mineral composition. Fruit-water Ca concentration was significantly higher in Trang, while Mg concentration was significantly higher in Var1 than in Var2. Fruit-water K and Na showed no significant differences between locations or varieties. Fruit-water pH was also higher in Trang, whereas TSS did not differ significantly. Bunch number and number of inflorescences were higher in Trang, while Var2 produced more female flowers per bunch and more fruits per palm. Soil P, K, Ca, Mg, and Na were substantially higher in Nakhon Si Thammarat than in Trang, but these differences were not consistently reflected in leaf nutrient concentrations. Soil Ca and K showed significant but modest relationships with their corresponding leaf nutrient concentrations, whereas Mg and Na showed no significant predictive relationships. Leaf nutrients were strongly interrelated, but their relationships with fruit minerals, TSS and reproductive traits were generally weak after accounting for location. PCA clearly separated the two locations, with PC1 and PC2 explaining 29.0% and 17.8% of the total variance, respectively, while the first four PCs accounted for 67.2%. Soil Mg and Na and leaf K, Ca, and Mg were among the major contributors to this multivariate differentiation. Nutrient relationships in aromatic coconut were nutrient-specific and strongly environment-dependent, rather than representing simple soil-to-leaf-to-fruit transfer. Integrated soil and leaf nutritional assessment may therefore provide a more reliable basis for coconut nutrient management than soil analysis alone. The findings highlight the importance of considering both soil and leaf nutrient status when evaluating nutritional variation in aromatic coconuts, while validation across multiple seasons and environments is needed before broader nutritional or agronomic recommendations can be made.