Evaluation of three modelling approaches for almond blooming in Mediterranean climate conditions

Chilling and heat requirements for breaking dormancy and flowering were studied in seven almond cultivars in Southern Italy. Chilling portions (CP), computed through the Dynamic model, and growing degree hours (GDH) were used to determine chill and heat accumulation, respectively. Then, using full bloom dates and temperature data from nine seasons (2003/2004-2007/2008 and 2009/2010-2012/2013), three sequential methods for the estimation of thermal requirements were compared: 1) the Ashcroft Method (AM), where chilling and heat requirements were selected considering the lowest variability of the GDH at several intervals of CP, and two variations: 2) modified Ashcroft Method (AMm) that took into consideration the lowest variability in both CP and GDH, and 3) reverse Ashcroft Method (AMr) opposite to AM. All methods were effective in predicting full bloom dates; however the modified Ashcroft method was the most accurate under Mediterranean conditions and allowed to classify almond cultivars for their thermal requirements. The results from AMm, showed chilling requirements ranging between 24–62 CP and heat requirements between 3263 and 6699 GDH, respectively.