Dear Dr. Matthews,
We have the same problem when simulating wheat and barley in dry regions. We
have about 10 field experiments under different rainfall distributions in
Navarra (Spain). In general, CERES simulates quite well the wettest areas
(aprox. 600-800 mm rain; 6-7 t/ha), but the simulation for dry areas (aprox.
400 mm) is unrealistic. We do not know the reason, but we will be glad to share
our experience.

Miguel Quemada
Depto. Produccion Agraria
Universidad Publica de Navarra
Pamplona. Spain


Mensaje citado por: Robin Matthews <[log in to unmask]>:

> 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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