Effect of soil application of KClO₃ on off-season flowering of 'T6' longan in Song Ma district, Son La province

Longan is one of the major fruit trees in Son La province. In 2017, Son La produced longan under 12,400 ha with the productivity of 62,000 t. Longan in Son La province is usually harvested from July 25 to August 15 every year. Production of the longan cultivar ‘T6’, of which many traits are valuable, is expanding in Son La province. Induction of off-season flower to prolong the harvest season of longan in general and cultivar ‘T6’ in particular would contribute to higher profit for farmers in the province. In the study, soil application of KClO₃ at 20, 30 and 40 g m^‑1 of canopy diameter was conducted on March 15, 2017, resulting in 100% flowering rate in all treatments, with the duration from KClO₃ application to emergence of flower buds ranging from 50.5 to 65.5 days and from KClO₃ application to flowering ranging in 82.4-98.2 days. There was no difference in fruit weight, edible proportion and Brix of the treatments. Higher yields were recorded in the KClO₃ treatments at 30 and 40 g m^‑1 of canopy diameter, with the yields of 60.4 and 61.5 kg tree^‑1. The harvest season fell from December 18-25, 2017. At different timing of KClO₃ soil application (on October 15, 2017; January 15, 2018; and April 15, 2018), treatment of 30 g m^‑1 resulted in 100% of the trees producing flowers. Days from KClO₃ treatment to flower emergence and flowering were 55.0-59.2 and 90.5-100.7 days, respectively. The highest yield, at 59.8 kg tree^‑1, was observed on the treatment that applied KClO₃ on October 15, 2017. Soil application of KClO₃ on January 15, 2018 and April 15, 2018 yielded lower, at 55.3 and 55.7 kg tree^‑1, respectively.