PREDICTION MODELS FOR CHILLING AND HEAT REQUIREMENTS TO ESTIMATE FULL BLOOM OF ALMOND CULTIVARS IN THE CENTRAL VALLEY OF CHILE

Abstract

In the past, Chilean almond (Prunus dulcis (Mill)) production was traditionally associated to marginal lands with a low level of productivity and technology. Nevertheless, during the past few years the orchards destined to reach high yield and quality have increased. To reach this, the introduction of new varieties of almond trees which makes it necessary to perform studies on the phenology under the new conditions. The chilling and heat requirements to reach a certain phenological stage can be determined by predictive temperature models. However, these models were developed in different climate zones, and for different species and cultivars. Thus, models as the Utah Model are more appropriate for cold areas and the Dynamic Model are more reliable for warmer zones. In this sense, the objective of this study was to estimate the chilling and heat requirements for almond trees phenology by means of predictive models, developed in different conditions from the Chilean production areas. During the seasons 2003, 2004 and 2005 different chilling models were evaluated in three cultivars of almond trees, in three unwatered-land areas in the Central Valley of Chile (34°30'S;71°15'W). The cultivars in study were 'Desmayo Largueta', 'Nonpareil' and 'Ferragnes'. The methodology described by Ashcroft et al. (1977) was used. This method considers that the winter chilling enough to break dormancy, is which generates a lower variation in the heat requirements to reach full bloom (FB). The following chilling models were used: a) number of hours under 7.2°C (Weinberger, 1950), b) Utah (Richardson et al., 1974), c) North Carolina (Shaltout and Unrath, 1983), d) Florida (Gilreath and Buchanan, 1981) and e) the Dynamic Model (Fishman et al., 1987). For the heat accumulation (growing degree hours, GDH) from end of dormancy to full bloom, the used model was the Utah (Richardson et al., 1975). The results for the chilling requirements to break dormancy for 'Desmayo Largueta', 'Nonpareil' and 'Ferragnes' were: 230, 360 and 240 chill units (CU) for the North Carolina model; 280, 300 and 440 CU for the Florida model; and 220, 260 and 260 CU for Utah model, respectively. For the Dynamic Model the determined requirements were 28, 23 and 32 chilling portions, respectively for the three cultivars. The models which presented less variation to estimate the GDH for full bloom were the Utah, North Carolina and Dynamic Models.