To whom it could concern,

I am a Grad student working with DSSAT. I am currently running
sequence
models trying to evaluate the residual nitrogen for corn.I am running
both
irrigated and rain-fed experiments. My question involves the soil
organic
matter module (SOM).

I am running DSSAT v4.5. There are two SOM modules. Century(Paton) and
Ceres(Godwin). I have read the papers on both of these modules. From
what I
understand, CENTURY was added to help with low-input systems. Thus
most or
all of the nutrients required by plants in the module would be from
decomposition of soil organic matter and plant litter.

Thus, since I'm modeling corn, a high input cultivar ( I'm actually
adding
large amounts of chemical fertilizer (143-250 kg/ha), I'm using the
CERES
module. However when analyzed , the output show zero immobilization of
N. I
am not a soil physiologist, but this seem inaccurate.

Is this a correct response for the CERES module? I tried using the
CENTURY
model, however I'm unsure about the inputs required and though the
results
show immobilization, I'm doubtful this module is more realistic in
this scenario. The soil I'm using is quite clayey. I've tried altering
the
application of N fertilizer and can't get CERES to simulate
immobilization.

Thanks for any help,

W. Lee Ellenburg
University of Alabama in Huntsville
Research Assistant
Civil and Environmental Engineering