Functional Analysis of Air Temperatures as Related to Chilling Requirements of Perennial Fruit Crops

Abstract

After more than two centuries of observation and research on chilling requirements of perennial fruit crops, there remain unresolved aspects concerning relationships between chilling condition and ambient air temperatures. The purpose of this ongoing study was to further explain association between chilling temperature and plant functions: growing, chilling, and freezing. Temperature data consisted of 5-year averages for 50 Mesonet weather sites randomly located throughout Kentucky. Based upon the Chilling Hours Model analysis, available chilling hours exceeded requirements of commonly grown perennial fruit crops. In the extended study, max and min daily temperatures were processed separately permitting their comparisons within plant functional classes. Nearly twice as many min as max temperature days were included within the chilling class function. Most consecutive days of chilling temperatures ranged from 1 to 3 days and were more clustered with min than max temperatures. Using multiple-year averages especially when the temperatures were near freezing point, resulted in a high percentage of individual years with freezing temperatures that were not reflected in the group average. Separating max and min temperatures in functional classes permitted greater focus on critical temperature-chilling relations. Within the chilling range, impact of min on chilling was nearly twice that of max. Contrariwise, widely reported research literature confirms that global warming has greater influence on min than on max or mean temperatures.