Development of chill unit calculation for peach 'Jade' fruit trees grown in northern Thailand

Abstract

Temperate fruit trees were introduced for opium substitution and reforestation in northern Thailand more than 40 years ago. Various cultivars have shown good adaptability with an annual life cycle similar to those growing in temperate areas. For good cultural management and logistics, the time of dormancy releasing should be predicted. In North America and Europe, the time of dormancy releasing is predicted using chill unit models that have been developed for temperate zone climatic conditions. Three commonly-used chill unit models in North America and Europe are the Utah model, the North Carolina model, and the Low chilling model. In the present paper, these models are evaluated and compared for use under the highland tropical zone conditions of northern Thailand. The peach (Prunus persica) 'Jade' grown at Angkhang Royal Agricultural Station, Thailand was selected as the model plant. During the period 2009-2011, the opened flower percentages were continuously observed at 3-day intervals and four randomly placed data loggers were used to record air temperatures in the tree canopies at 15-minute intervals. The results showed that a modified version of the Utah model gave reasonable flowering prediction. The Box-Jenkins method was used to develop a seasonal ARIMA model to analyze temperature time series data in order to forecast daily temperature and predict chill unit accumulation. The predicted temperature and chill unit data could be used to predict flowering of 'Jade'.