A MODEL FOR PHOTOTHERMAL RESPONSES OF FLOWERING IN RICE .1. MODEL DESCRIPTION AND PARAMETERIZATION

Most models that predict crop development based on temperature and pho toperiod ignore critical changes in photothermal responses during crop ontogeny. A new, detailed model was developed to predict development to flowering in rice (Oryza sativa L.), based on the Beta function whi ch is commonly used for skewed probability density functions in statis tics. As the model accounts for different photothermal responses of th ree successive phases during preflowering ontogeny, it was referred to as the three-stage Beta model. The model was parameterized for 17 ric e cultivars using data of two controlled-environment experiments. Mode l parameters which do not vary strongly among cultivars and parameters which can be estimated from values of other parameters were identifie d. This analysis reduced the number of parameters to be estimated to f ive. The parameters from the controlled-environment experiments were u sed to predict rice development as observed from an independent three- location field experiment with 12 cultivars. The model accurately pred icted varietal and locational variation in rice flowering date.