umpen Onthong, Yanyong Plongon, and Mongkol Sea-lim

pp. 1175 - 1185

Abstract

Longkong (Aglaia dookkoo Griff.) is an important fruit tree for the southern economy of Thailand. However, yield qualities still vary greatly, possibly because of improper plant nutrient management in many locations. Therefore, this research was conducted (1) to determine the nutrient requirements for fruit
development, and (2) to study effect of fertilizer on fruit development and yield qualities of longkong. The experiment consisted of 2 treatments: (1) without fertilizer, and (2) with fertilizer (applications of fertilizer grade 15-15-15, 8-24-24 and 13-13-21 at a rate of 2 kg tree^-1 at the postharvest stage, before flowering and during fruit development). The results indicated that fruit enlargement and fruit nutrient accumulation developed slowly at the first period (0-8 weeks after fruit set), and increased rapidly during 10-13 weeks. Fertilizer application improved all fruit qualities. The length of peduncle, number of fruit per cluster, fruit weight, fruit diameter and total soluble solid of fertilized and non-fertilized longkong tree at 13 weeks after fruit set were 19.13 and 11.50 cm, 42.33 and 25.33 fruit

cluster^-1, 835.70 and 488.58 g cluster^-1, 34.53 and 33.52 mm, 17.33 and 14.80% Brix, respectively. Longkong requires a large amount of potassium and nitrogen for fruit development. Fertilizer application resulted in high amount of available phosphorus accumulation in the soil. Thus, for longkong's fertilizer management, high rate of nitrogen and potassium fertilizer should be applied, while phosphorus fertilizer should be reduced, at 4-5 weeks after fruit set, at which time the fruits develop rapidly and require abundant nutrients.