Effect of foliar fertilizers on nutritional content in leaves, flowering and fruit setting of rambutan (Nephelium lappaceum L. cv. Rong Rian)

Studies on the effects of foliar fertilizers were carried out in rambutan (cv. Rong Rian) orchard at Khlung district, Chantaburi province, during October 1993 to October 1994. The purpose is to study the effects of some certain foliar fertilizers on nutritional contents in rambutan leaves in relation with flowering, panicle size, number of panicles per shoot and fruit setting. A two factor-factorial in randomized complete block design with 4 blocks was employed. Foliar spray was started when the third flush reached its fully mature stage. Factor A was consisted of monopotassiumphosphate (Mpp) at two concentrations (3 times with one week interval) : 0 (water) and 5,000 ppm. The factor B application was followed immediately after factor A for 3 times under 3 consecutive weeks. It consisted of water, two formulae of 10-52-17 and 7-13-34 +12.5 Zn with the same concentration of 1,500 ppm. The results showed that all treatment combinations exhibited the increment of total nonstructural carbohydrate (TNC) content until flowering and descended afterward. The combination of Mpp plus 7-13-34+12.5 Zn showed an especially high in TNC at 94.9 mg D-glucose/g dry wt. On the other hand a steady level of total nitrogen (TN) content between 1.4-1.6 percent was observed in all treatments. Hence, the TNC/TN ratio was directly influenced by the TNC alone. The ratio of 5.0-6.8 was found in leaves at the time of rambutan flowering. High correlations between the TNC/TN ratio and K content to flowering were obtained at 0.94 and 0.82, respectively. The high leaf P, K and Zn contents was also observed in trees applied with high P, K and Zn foliar fertilizers. Trees sprayed with Mpp and 7-13-34 + 12.5 Zn possessed the highest flowering percentage. The r=0.95 between flowering percentage and the TNC content was found in these trees. Flowering at 50 percent of trees with this treatment combination was monitored 10 days ahead of the control trees. Largest panicle size (both width and length) was found in trees sprayed with the 7-13-34 + 12.5 Zn formula alone while trees treated with Mpp and 7-13-34 + 12.5 Zn expressed the highest number of 3.2 panicles per shoot and also highest fruit number per panicle at harvest. In addition, high correlations between panicle number to TNC and Zn contents were equalled to 0.95 and 0.85, respectively. Besides tree health or leaf TNC content, panicle size and panicle number per shoot also played an important role to fruit set. Moreover, fruit set in rambutan was influenced by environmental conditions during blooming period as well.