Thermal growing season in Poland calculated by two different methods

Abstract Methods of identifying dates of passing determined threshold value are of significant importance in the study of thermal growing seasons. The difficulty to determine dates of beginning and end of growing season in a given year stems from the fact that daily mean air temperature changes irregularly on a day-to-day basis often crossing the threshold value (i.e. 5°C) multiple times. The most frequently used method to identify dates of threshold value crossing is the mathematical or graphical method proposed by Gumiński in 1950 which based on monthly mean air temperature values. In the 1970s, Huculak and Makowiec presented a method using daily mean values of air temperature. It is assumed that both methods give comparative results although calculations of daily mean air temperature render more accurate results. This paper presents the comparison of these two methods. Air temperatures measurements from 1966–2005 taken at 38 weather stations located in various physiographic conditions in Poland were used.