Use of phenoclimatic models to estimate the chill and heat requirements of four sweet cherry cultivars in Italy

During their dormant period, fruit trees require a certain amount of relatively low temperatures to complete bud differentiation processes and regularly resume growth the following spring. Unsatisfied chilling needs can result in delayed foliation, severe yield and fruit quality losses. There is a need for a method to estimate accurately the chilling requirement of a cultivar. This is especially important in those areas where the potential of chill accumulation in winter is low and for those crops, such as sweet cherry, which generally have a high chilling requirement. Historical temperature records and blooming dates of four sweet cherry cultivars widely cultivated in Italy - 'Burlat', 'Sweetheart', 'Ferrovia' and 'Giorgia' - were recorded in three sites located in the North, Centre-North and South of Italy in order to estimate the chilling and heat needs of each cultivar. The temperature-based models developed by Weinberger (1950) and Richardson (1974) for peach were used to calculate the chilling requirement of each cultivar, and their performance compared. The model proposed by Anderson (1986) for sour cherry was used to calculate the amount of heat hours needed to trigger flowering onset since chilling requirement fulfilment. While in the northern sites, both Weinberger and Richardson models provide comparable and precise results in the estimate of chilling requirement of the four cultivars, only the latter model performed adequately in the southern site. We observed a progressive reduction of blooming date estimation error with a best fit around 1,400 CU for all the cultivar studied. Moreover, from our calculation, it seems that the cherry cultivars differ more for their heat requirement(HR) rather than for their chill requirement (CR).