We coupled the nitrogen assimilation model we had previously developed to our crop growth model. Previous results from the uncoupled model indicated that transfer of nitrogen from the shoot to the seeds was a key process that limited seed protein concentration. The coupled model was examined in the same manner and it's behavior reached similar conclusions. High and low protein lines were grown in the field as a means of examining physiological traits associated with seed protein concentration. Measurements were collected from these plants and used to parameterize the model. The model was able to predict growth of these lines reasonably well, although some work needs to be done to perfect predictions for the high protein line. We are awaiting nitrogen concentration analyses for these samples as those will provide more information about what traits in these plants lead to different protein concentrations.