A model for photothermal responses of flowering in rice .1. Model description and parameterization

Most models that predict crop development based on temperature and photoperiod 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 which is commonly used for skewed probability density functions in statistics. As the model accounts for different photothermal responses of three successive phases during preflowering ontogeny, it was referred to as the three-stage Beta model. The model was parameterized for 17 rice cultivars using data of two controlled-environment experiments. Model parameters which do not vary strongly among cultivars and parameters which can be estimated from values of other parameters were identified. This analysis reduced the number of parameters to be estimated to five. The parameters from the controlled-environment experiments were used to predict rice development as observed from an independent three-location field experiment with 12 cultivars. The model accurately predicted varietal and locational variation in rice flowering date.