Hello Dr Mathews:

In trying to find out the problem in simulating wheat yields in dry
condition, You have mentioned "The difference is not just in the yield but
also in the total biomass produced, and seems to appear about mid-winter in
December(crop planted in September), ruling out summer drought affecting
grain-filling as an explanation." Please provide some more explanation for
what seems to appear about in mid-winter in Decemeber. By December how much
winter wheat would have grown?

Have you looked at the water stress factor given at the simulation overview
output file? Do you think the model simulates excessive water deficit than
actual stress experienced by the crop? Interested to know your response to
these questions? We are currently attempting to modify CERES Wheat model.
Your comments would be helpful.

Alagarswamy
Michigan State University


>From: Robin Matthews <[log in to unmask]>
>Reply-To: DSSAT - Crop Models and Applications <[log in to unmask]>
>To: [log in to unmask]
>Subject: Problems with CERES-Wheat ...?
>Date: Fri, 16 Feb 2001 10:10:27 -0000
>
>Dear DSSATers
>
>While using CERES-Wheat in a class with students with weather data from
>Silsoe in England, I found that very unrealistic yields if 1-2 t/ha are
>being predicted in drier years (rainfall ~450mm/year as opposed to ~600
>mm/year). Wet year yields appear to be OK at around 8-10 t/ha. In reality,
>in the dry years, yields of ~5 t/ha were recorded. I have only looked at it
>cursorily so far, but there appears to be little to explain this huge
>discrepancy - solar radiation is similar for the two years; temperatures
>vary a little, but not excessively; rainfall differs as mentioned above,
>otherwise nothing else. The difference is not just in the yield but also in
>the total biomass produced, and seems to appear about mid-winter in
>December
(crop planted in September), ruling out summer drought affecting
grain-filling as an explanation. Nitrogen levels are also at an optimum of
around 200 kgN/ha.
>
>I am still trying to track down the problem, but I wondered if anyone else
>had experienced similar problems under similar circumstances, and if
>so,whether they had corrected the problem?
>
>Robin Matthews.
>
>=========
>Dr Robin Matthews
>Institute of Water and Environment
>Cranfield University, Silsoe, Bedfordshire MK45 4DT, UK.
>Tel: +44 (0)1525 863008; Fax: +44 (0)1525 863384
>mailto:[log in to unmask]
>http://www.silsoe.cranfield.ac.uk/iwe/people/RobinMatthews.htm
>http://ourworld.compuserve.com/homepages/rbmatthews/
>-----
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