Dear Wendy,

About your outputs " both water stress and excess water stress are high".

Please check your initial soil water condition and soil's parameters ( FC , PWP , SATURATION and KS ).

if you didn't measure that parameters you can use of some software same RETC:

 " Van Genuchten, M.Th.,
F.J. Leij and S.R. Yates, 1991. The RETC code for quantifying the hydraulic
functions for unsaturated soils. U.S.
Salinity Laboratory, Riverside,
 California."
      For create soil's parameters.
   I think your error is  in define those parameters.
    Please check your inputs files. The models give anythings you give.
     Please read this paper:
  " Eitzinger, J., Trnka, M., Hosch, J.,  Zalud, Z., Dubrovsk,  M.2004.Comparison  of CERES, WOFOST and SWAP models in simulating soil water content during growing season under different soil conditions.Eclogical Modelling 171 : 223-246."


I hope my advices are sufficient

 Best regards

 ebi



Ken Boote <[log in to unmask]> wrote: Richard and Wendy,

I think excess and deficit water stress do occur on the same day.  The
reason is that the excess water causes root water uptake to be reduced,
and that is what reduces photosynthesis and ET.  It is quite possible
that excess water has no effect on photosynthesis other than via water
uptake (and maybe on N uptake too).  That is the only way excess water
limits photosynthesis and ET.  In other words, you can have water
deficit by itself from lack of water, but when you have excess water
stress it will always cause the water deficit signal to show up too.

I did not write that bit of code and am not sure of what the intent
was.  My comment above comes from observing how the signals for excess
water stress and water deficit stress work (same ones that you mention)

So, I'd be happy to have Bill Batchelor, Jon Lizaso, or Jim Jones to
chime in on how this is coordinated in the models.  I may be wrong on
this one.

Ken Boote

Richard Ogoshi wrote:

>Hello Wendy,
>  Information about stresses can be found in:
>
>Ritchie, J.T. 1998. Soil water balance and plant water stress. p.41-54. In G.Y. Tsuji, G. Hoogenboom, and P.K. Thorton (eds.) Understanding options for agricultural production. Kluwer Academic Publishers, Dordrecht, The Netherlands.
>
>and
>
>Godwin, D.C., and U.Singh. 1998. Nitrogen balance and crop response to nitrogen in upland and lowland cropping systems.  p. 55-77. In G.Y. Tsuji, G. Hoogenboom, and P.K. Thorton (eds.) Understanding options for agricultural production. Kluwer Academic Publishers, Dordrecht, The Netherlands.
>
>  Water stress occurs when plant demand is greater than uptake. Water stress-growth affects cell extensibility and water stress-photosynthesis affects carbon accumulation.
>  If the excess water- and water-stress occur within a season, that would not be surprising. However, if they both occur on the same day, that would be surprising.
>  If it does occur on the same day, you might want to look for something causing low uptake or high demand. It might be possible that a very small root system would not be able to satisfy demand even with excess water in the soil.
>  Hope you find what you're looking for.
>Sincerely,
>Richard
>
>
>----- Original Message -----
>From: Wendy Vance
>Date: Tuesday, August 1, 2006 10:05 pm
>Subject: Outputs of water and nitrogen stress
>To: [log in to unmask]
>
>
>
>>Dear All
>>
>>
>>
>>I am using DSSAT for simulation of soybeans and maize across different
>>soil types.
>>
>>
>>
>>I have been looking at the outputs and would like to know if anyone
>>could provide me with further information to explain the following
>>outputs from the growth aspects output file;
>>
>>Water stress - photosynthesis WSPD
>>
>>Water stress - growth WSGD
>>
>>Nitrogen stress factor NSTD
>>
>>Excess water stress EWSD
>>
>>
>>
>>One of the reasons why I am asking is that in some cases I have
>>outputswhere both water stress and excess water stress are high,
>>and others
>>where water stress is high and excess water stress is low.  I am
>>assuming excess water stress is when there is high soil water
>>close to
>>saturation, which seems to match my outputs.  However, I am unsure if
>>the water stress growth and photosynthesis in these outputs occur
>>duringboth wet conditions and drought conditions.
>>
>>
>>
>>Any advice will be much appreciated.
>>
>>
>>
>>Thanks
>>
>>Wendy
>>
>>
>>
>>[log in to unmask]
>>
>>
>>



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