Heat Unit Requirement and Prediction of Developmental Stages in Soybean

Field experiments were conducted at Coimbatore, India with four dates of sowings in each of three seasons to determine the duration of phenological phases, heat unit requirements and evaluation of heat units to predict the developmental phases of Soybean ( Glycine max L.] Merr.). The variations in development of different phenological phases and maturity of Soybean due to season and sowing dates was manifested by varied accumulation of heat units calculated. There was a linear relationship between the number of days to flower initiation and cumulative day length. Growing degree days (GDD) were better predictors for development of phenological phases whereas maturity was controlled by Calender days and was closely followed by GDD. Photothermal units were the next best predictors for soybean developmental phases.