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Estimation model of winter chilling availability in sweet cherry areas of Mendoza, Argentina. Part II

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Authors: E. Tersoglio, G. Naranjo
Issue: 103-4 (198-211)
Topic: Plant Production
Keywords: chilling requirements, sweet cherry, chill unit, forecasting.

During winter rest, the fruit trees of temperate climate have to be exposed to low temperatures to satisfy their chill requirements. The sweet cherry trees are one of the more demanding winter chilling of the stone fruit. These requirements are expressed in chill units (CUMU) calculated by the Modify Utah method. The chill availability varies among regions and years, and sometimes it is not enough to satisfy sweet cherry requirements. In such conditions sweet cherry trees can develop symptoms of lack of chill. Sometimes, when the chill availability is not enough, it is necessary the application of chemicals for a correct rest completion. These products must be applied in advance to the bloom begins. Therefore, the data of chill availability of the current year let improve orchard management. The objectives of this study were to develop a forecast method that allows estimating the availability of chill and the probability of completing certain requirement. It was estimated the chill availability of two sweet cherry produced areas, Tupungato and Luján counties of Mendoza province. The models show the percentages of the variability explained by the CUMU accumulated in partial dates. Those oscillated between the 83 and 90% for Luján de Cuyo and between 92 and 96% for Tupungato. Due to the data variability, prediction limits were too wide and they do not have enough precision for taking decisions. For that reason it was necessary to develop a method that permit to calculate the probability that has the current year of satisfying a certain chill demand. This complementary tool will facilitate to take right decisions and assume calculated risks. Through the estimation of the chill availability of the current year, the logistical regression model could be selected and the probability of chill completion of a particular variety could be calculated. The models explained approximately among 90 and 75% of the variability found in Luján de Cuyo and Tupungato, respectively. Luján de Cuyo has 99% probability of reaching the 900 CUMU and 26% for 1.200 CUMU. Tupungato County with colder winters has 100 and 82% probabilities of reaching the 1.200 and 1.500 CUMU respectively. After a validation phase, the forecasting will allow farmers evaluate the risks that orchards experiment lack of winter chilling damages and execute the eventual measured to minimize them.

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