Dear Members,

I suggest Ayman and others interested on modifying DSSAT's water balance
module to get in touch with Rogerio T. de Faria ( [log in to unmask] ). He
has already done some work on that direction. Richard's equation, one
dimension, was considered when dealing with unsaturated flow. Soil hydraulic
conductivity required by Richard's equation was derived from soil-water
retention curve using vanGenuchten's model. I am not sure if he considered
the effect of soil surface mulching on evaporation.
It would be great if we can have this new option on DSSAT 4.0 water balance
module, in addition to the traditional tipping bucket approach. I've been
evaluating Ceres-Maize model using data from conventional and no-tillage
cropping system and recently using drainage lysimeters data. I notice that
water balance module works fine when soil-water content is near or higher
than the upper limit but it seems to fail for dryer soil.

Regards,

Camilo L. T. Andrade
Embrapa Maize and Sorghum
Rod. MG 424, Km 65, PO Box 151
35701.970, Sete Lagoas, MG
Brazil
Phone: +55 21 31 3779 1235
Fax: +55 21 31 3779 1088


----- Original Message -----
From: "Gijsman, Arjan J. (CIAT)" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, December 19, 2002 1:39 PM
Subject: Re: Databases


> Hi Ayman,
>
>
> You write that you will be working on a new water-balance model in DSSAT
and
> also will consider the soil evaporation. Wouldn't that be a good
opportunity
> to tackle the impact on the evaporation of a litter layer on top of the
> soil, as well? The new DSSAT4, which is soon going to be released, has a
new
> soil-organic-matter/residue module based on the CENTURY model. This brings
> with it the consideration of residue decomposition in a surface litter
> layer, which was ignored in earlier DSSAT versions. But a litter layer on
> top of the soil may have a big impact on the evaporation, particularly if
it
> is a thick layer, like e.g. with sugarcane trash. However, with the new
> DSSAT4 this is still on the list of future dreams. I don't want to push
you
> in doing more that you have time for and don't know how easy/difficult
this
> is, but anybody familiar with this topic is welcome to jump in and fill
this
> gap.
>
>
>
> Arjan Gijsman
>
> Univ. Florida / Centro Internacional de Agricultura Tropical (CIAT), Cali,
> Colombia
>
>
>
> -----Original Message-----
>
> From:  SULEIMAN AYMAN [mailto:[log in to unmask]]
>
> Sent:    Tuesday, December 17, 2002 4:41 PM
>
> To:      [log in to unmask]
>
>             Subject: Databases
>
>
>
> Dear Colleagues,
>
>
>
> In the ICASA meeting last month in Indianapolis, it was mentioned that the
> water balance of DSSAT4.0 is the same one that has been used in the older
> versions. I among other colleagues have suggested that many parts of the
> water balance need to be updated. For now, I will be working on adding new
> modules for soil water redistribution. After I have done adding these
> modules, I want to compare the performance of the new drainage and soil
> evaporation models with the original ones. I have some data to do that but
> looking for more. Please if you have or know of any good data set that I
can
> use in the comparison let me know.
>
>
>
> Thanks for your cooperation,
>
>
>
> Ayman
>