Dr. Favreau:
 
There is a sugar beet model that was developed about 10-15 years ago by Dr.
Robert S. Loomis, University of California, Davis.  It had pretty good
physiological detail as I recall, however, it would need to be modified to
operate with the DSSAT input files, and to output simulated outcomes to the
DSSAT files for graphics, etc.  If you are up for a bit of work, you may wish
to contact Dr. Loomis.  He is officially retired, but he is still quite
active and comes in to work very regularly at the Agronomy Dept., Univ of
California, Davis.
 
Good luck,
Ken Boote