Development of a precise thermal time model for grain filling in barley: A critical assessment of base temperature estimation methods from field-collected data

•Thermal time models for grain filling were developed for four barley cultivars.•Five base temperature estimation methods were compared.•Calculated developmental base temperatures ranged from 5.9 to 9.6 °C.•A broad application model for barley grain development is presented.•Base temperature for grain growth was assessed as well.