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This study aimed to determine the influence of Potassium (K) fertilization on the flowering and fruit yield of 13-year old ‘Magallanes' pummelo [Citrus maxima (Burm. ex Rumph.) Merr.] trees. The experiment was conducted at South Davao Corporation (SODACO) farm, Davao City, Philippines for 12-month duration. Five treatments with increasing K levels were applied per tree: control, no K, 150 g K basal, 225 g K basal, and 225 g K basal + foliar application. Flowering, fruit set and yield of pummelo were enhanced by higher K rates. Flowering was increased by 4 times while fruit set by 86-100%. Fruit number was increased by 7 times, weight per fruit by 22-26%, and yields up to 9 times with 100% (return of investment) ROI on trees applied with 225 g K rates. The results of the study indicated the important role of K in improving the flowering, fruit yield and income of ‘Magallanes' pummelo.