Dr. Ines,

The DSSAT models are all based on annual crops.  Perennial traits such
as dormancy are not included in the models.  That said, you can run a
continuous, multi-year simulation in DSSAT.  The simulation will run
from the start date to the harvest date unless terminated by weather
conditions (usually a killing frost) so you can make the simulation any
length that you want by adjusting these two dates.  Some examples are
the bahiagrass experiment files included with DSSAT4 which are 2-4 year
simulations. For simulations starting with an established crop, you can
use the Transplant option in the planting details section of the
"X"-file although you are limited to 9999 kg/ha total initial plant mass
(leaf +stem+root).  Proportions of leaf, stem and root are set in the
species file using the vegetative partitioning parameters for
XLEAF=0.0.  We did this in the Ona, FL and Eagle Lake, TX experiments (I
think they are named UFON9701.G0X and UFTX7901.G0X - note that the 0 in
"G0X" is the number zero not the letter "o").  If you view the
UFON9701.G0X and UFON9701.G0T files in a text editor (not XBuild! - it
truncates the text lines at the top of the file) there is a lengthy
description of how to set up a perennial simulation.  If you end up
using a "stock" soil included with DSSAT, be sure to make the
recommended changes to the soil curve number.

If you want to simulate a hay harvest without terminating the
simulation, there is a Pest code called "MOW" that allows you to specify
how much residual leaf + stem mass is to be left after the harvest.
Alternatively, you can specify the amount or percentage of the leaf and
stem mass to be removed using the pest codes HARV or HRVS.  You enter
all pest events in the "T"-file along with any measured data.  Note that
each column is 6 characters wide and to be read properly, in the header
row, the word "MOW" must appear in the 4,5, and 6th spaces of its
6-character field.  Look in the bahiagrass pest file
(C:\DSSAT4\PEST\G0GRO040.PST) for available pest codes.

If you have a fairly warm climate, DSSAT4 can be made to work decent.
The biggest problem that we had with bahiagrass was slowing winter
growth.  If you adjust the temperature parameters enough to slow winter
growth, you also reduce spring regrowth.  Excessive winter growth
depleted soil water reserves and predicted water stress in the spring.
Another problem was termination of the simulation whenever a frost
occurred.  In a perennial crop, even a freeze that only causes the
leaves to drop (temperature drops to FREEZ1 in the species file) will
essentially terminate the simulation  -with no leaves, there is no
photosynthesis and the large remaining plant mass eventually depletes
all reserves through respiration.  For this reason, we set both FREEZ1
and FREEZ2 (killing frost temperature) well below any level that might
be experienced in the field.

One option that we didn't try was to run a sequence of 1-year
simulations where the initial conditions are based on the ending
conditions of the previous year.  I'm not sure if this would make much
difference.

We are working on a perennial forage version.  We have added several new
functions and options, including a stolon/rhizome organ, dormancy
effects on partitioning and mobilization, partial freeze damage,
enhanced mobilization controlled by LAI and plant nutrient status, and
separate partitioning schemes for seedlings and established crops.  We
also made some interface changes such as allowing larger initial plant
mass  and  more user control over initial partitioning in the transplant
routine.  We hope to have it polished and testing well under way this
spring.   I'm not sure about availability of this version.  Until it is
thoroughly tested, I don't envision it appearing as a part of DSSAT.

If you want to try using DSSAT to simulate rangeland species, I'll give
you any help that I can.

Stu

Ines, Amor wrote:
> Dear List,
>
> Does DSSAT4+ capable of modeling rangeland system?
>
> Thanks,
> Amor
>
> -----
> Dr. Amor VM Ines
> Dept. of Biological and Agricultural Engineering
> Texas A&M University
> 2117 TAMU 301B Scoates Hall
> College Station, TX 77843
> Tel: 979-458-4651
> Fax: 979-862-3442
> Email: [log in to unmask]
>
>
>

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