Hiroshi,


First let me stress that the CENTURY-based SOM/residue module of DSSAT4 did
a much better job with the validation tests we have done than DSSAT's
original module (now called the CERES-based module). This was esp. the case
for carbon, as you can see in Fig. 5 of our article "Modifying DSSAT for
low-input agricultural systems...". For nitrogen the results of the
simulation were not that clear-cut, as nitrogen is affected (and can be
lost) via many processes that are not equally well simulated:
denitrification, volatilization, leaching, mineralization and
immobilization. N is shown in Fig. 6 of the article and sometimes the
CENTURY-based module did better, but other times the CERES module was the
winner.

Concerning your follow-up question:
1. Yes, you can run the same fileX for both versions, but note that with
v4.0 there is a switch MESOM on the METHODS line for which SOM module to
use: MESOM = P for CENTURY, MESOM = G for CERES.
2. Yes, but also try the CENTURY-based SOM/residue module!
3. I am sorry, I have hardly worked with DSSAT4 and therefore never looked
at CropTest, as I am full time busy with developing the next DSSAT version
(which will incorporate a P module), but I will ask someone who does know
and then let the list know.

Cheers,
Arjan


-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, December 22, 2004 6:57 PM
To: [log in to unmask]
Subject: Re: Q about different versions

Hi Arjan,

Thank you for your informative response. I meant to email to the
DSSAT list server. Sorry.

Let me ask you more about Q2. I am interested in changing composition
(CARB, CELL, LIGN) and decay rate constants of fresh organic matter
(FOM) such as cover crop residue or maize residue and cattle compost
for simulating short-term N dynamics (14 months) in bare fallow. If I
want to compare model predictions between versions 3.5 and 4.0 after
the incorporation of FOM or compost, do I need to conduct following
steps?
  1) Prepare a FileX.
  2) Put measured or estimated parameters in SOILN980.SOL for version
3.5 and in SOILN040.SOL for version 4.0.
  3) Go to CropTest to conduct simultaneous runs of version 3.5 and
4.0. Where can I choose FileX prepared for CropTest?

Best,

Hiroshi

>2.  One of the major differences between v3.5 and v4.0 is that the
>latter has a new SOM/residue module that was based on the CENTURY
>model (see: Gijsman et al. 2002 Modifying DSSAT for low-input
>agricultural systems, using a SOM/residue module from CENTURY.
>Agron. Journal. 94:462-474). The original SOM/residue module of
>DSSAT is also still included, so that who did many simulations with
>v3.5 does not suddenly get different results with v4.0 (the two SOM
>modules do give quite different results, as shown in Fig. 5 of the
>article).
>
>The file SOILN980.SOL only serves for the original module. In v4.0
>this file has been updated and is called SOILN030.SOL. If you want
>to change some parameters of the CENTURY-based module, then you have
>to go to the file SOMFIX_C.SOL This has many parameters (about 130)
>but no parameter explanation (we should add that).