A degree day model for durum wheat (Triticum durum, Desf.) across the Italian peninsula

Phenological field observations were used to parameterize and test a Degree Day model for durum wheat (Triticum durum, Desf.) across the Italian peninsula. Data come from different experimental fields located in northern, central and southern Italy and encompass scalar sowing dates, allowing to parameterize a model representative for a wide range of sites and growing seasons. To assure the basic assumption of the Degree Day method, wheat subphases were identified to enable the best linear relationship (less data dispersion and higher coefficient of determination) between developmental rates and average air temperature. Under proven linear temperature responses, the model gave satisfactory simulations of wheat phenology over different locations and sowing period (R2 = 0.96; RMSE = 8,4 days; no bias, minimal complexity), even if the heat supply (growing degree days counted from 0°C) was very different among sites.