To our knowledge, this is the first large-scale effort to calibrate and validate ORYZA for US rice production systems. Furthermore,it is unique for modeling studies to have a validation data set of the quality and temporal and spatial scope such as ours here. We found that for the Southern US, the model performed well after calibration of only the four development rate parameters and calibration of RGRLMX (Table 1). This is possibly due to similarities between the Southern US and the environment that ORYZA was originally developed under. It is noteworthy that the ORYZA model can perform well outside its original domain with such a simple calibration.