Abstract
Knowledge of the appropriate base temperature (Tb) is needed for the analysis of
meteorological effects on plant phenology using growing degree-days. However, several values
of Tb have been used for mountain grassland. The main purpose of this research was to identify
the optimal Tb for predicting changes in crude protein, acid detergent fibre and net energy for
lactation of forage grown in mountain permanent meadows in South Tyrol (Italy). Forage
samples were sequentially harvested weekly for a period of seven weeks starting from the
pasture stage (15 cm growing height) at 202 environments (sites × years). To estimate the most
appropriate Tb, growing degree day sum (GDDsum) were computed in the time interval between
one week before pasture stage and the harvest time using a range of Tb between 0 °C and 5 °C
at a 0.5 °C interval and using both observed temperatures from reference weather stations and
interpolated temperature. Optimal Tb were estimated on the basis of the R² values of the
regression equations of the different quality parameters on GDDsum and can be set at 0, 1.5 and
4.5 °C for the prediction of CP, NEL and ADF respectively. R² values exhibited in general little
variation within the investigated range.