Phenology of ‘Magallanes’ Pummelo (Citrus maxima) Trees and Its Growth and Development as Influenced by Potassium Nutrition

This study aimed to determine the influence of potassium (K) fertilization on the vegetative growth, flowering and fruit development 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 for 12-months duration. Five treatments were observed with increasing K levels were applied per tree: control (no fertilization), without K, 150 g K basal (recommended rate based on soil analysis), 225 g K basal, and 225 g K basal + foliar application. The critical stage of tree growth coincided with the months of May and August. Peak leaf flushing occurred in June and peak flowering with fruit set in April. The crucial stage of fruit development was noted two months after fruit set. Thus, optimum fertilization must be applied during these stages for maximum growth and production in ‘Magallanes’ pummelo. The vegetative growth of pummelo was not affected by increasing K rates. The recommended rate (150g K basal per tree) significantly increased canopy diameter by 76% but higher K rates did not increase tree height, due to the effect of fruit load and nutrient competition. On the other hand, increasing K rates to 50% higher than the recommended rate (225 g K per tree) increased the number of flushes by 36-100%. Flowering, fruit set and yield of ‘Magallanes’ pummelo were also enhanced by higher K rates. Flowering was increased by 4 times, fruit set by 86-100%, fruit number by 7 times, weight per fruit by 22-26%, and yields up to 9 times on trees composted with 225 g K rates. The fruit size (diameter and length), however, did not increase by increasing the K level.