Dear all,

a brief response to Dr. Anapalli's recent mail: We did use the
model "correctly" by strictly following the prescribed procedures
for running DSSAT 3.5. It took us more than 3 months
alone to calibrate the model. After completing this exercise we
came to the conclusion that this procedure is indeed "the most
cumbersome and subjective method of curve fitting that can be
imagined" to speek in Corneluis Teunis de Wit's words. I am aware
of two more large project which currently try in vain to get
the model "right".

Whether the model or the validation set is wrong is an
old argument between model developers and testers. To
my understanding validation data cannot be made subject
to dispute, because they represent reality. It is the
model (fed with appropriate data according to procedures
prescribed by the develeopers) which must compute reality
as good as possible. If it doesn't we have to look for
possible errors which leads to further model improvements.
The soil water routine of CERES is a key candidate and we have
just completed another study which focussed on
this problem. We will inform you about its outcome
when the final results become available.

Matthias