Abstract:To modify the original physiological development time (PDT) model (YDmodel), a new model (BarleyGrow) was developed based on the data from Yangzhou field experiment on five cultivars at spring sowing date. Three processes (thermal effectiveness, photoperiod and vernalization) were quantified and used to create the model. Seven parameters were used in the model included accumulated temperatures from sowing to germination (GDD0), basic temperatures in filling period (Tbmax), physiological vernalization times (PVT), critical day lengths (DLc), start times of photoperiod response (PPs), minimum times from emergence to heading (EHmin) and from heading to maturity (FDmin). With this method, we had several important differences compared to the YDmodel. First, the ratio of daily increment of PDT and the deficit of both water and nitrogen was used to estimate the effect of environment (instead of their product). Second, a nonlinear function was adopted to describe vernalization and thermal effectiveness (instead of three-stage linear function). Third, sinusoidal function was used to describe photoperiod curve cluster for different cultivars (instead of linear function). Physiologically, our model estimated 2.6 days to reach the single ridge stage, 5.6d to the double ridge stage, 11.3d to the stamen and pistil initiation stage, 13.1d to the anther separation stage, 15.3d to the pollen mother cells stage and 18.2d to the tetrad stage. Phenologically, estimations were 13.1d to reach the jointing stage, 28.7d to the heading stage, 32.8d to the grain filling stage and 51.5d to the maturity stage. PDT was consequently used as a unified scale for measuring developmental progress of different cultivars under different climates and cultural practices.