The Analysis of Frost and Chilling Hazards on Horticultural Crops in West Azerbaijan

As annual frost and chilling cause damage to horticultural crops in West Azerbaijan Province, the first early fall, late spring frost date, severity and continuation of frost were investigated for a 10-year period (2003-2012). The main goal of this study was to know different types of frosts and chilling (radiative,  convective and combination), to give advices for reduction of damages on horticultural crops. The analysis was carried out only for Orumieh, Salmas and Miandoab regions due to availability of data and their importance for fruit production viz., apple, grape and walnut over the Province. In order to  analyse harmful frost and chilling, they were divided into the early fall and late spring frosts. In the next step, the first early fall and late spring frost date were found and according to Julian day, the best probability distribution function was fitted on data and probability of 25, 50, 75 and 95 percentages were worked out. The results showed that crop damages were mainly due to frost temperatures (minimum temperature below zero) rather than chilling temperatures (minimum temperature more than zero and below 4 degree Celsius) in the months of November, March and April. The results also indicated that the most damaged frost for three crops of the year was happened in 2011 with the loss of 2403.7, 501, and 1363.3 hectares in Orumiyeh, Salmas and Miandoab regions, respectively. According to crop growth stages, the threshold temperature to damage Grape was happened when minimum temperature falls below -6oC during the months of October and November (harvest time) and the most losses of apple and walnut occurred when minimum temperature falls below -5oC during the months of March and April (at bud stage). It is suggested that the frost study could be carried out with the help of  upper air data (specially 850 mb level) along with statistical analysis for a precise distinguish between frost types.