Dear Guillaume,

I am relatively new to CERES MAIZE code, and the people on this email will have more detailed knowledge of CERES MAIZE. One thing I did notice was that P9 is calculated from germination, and not from planting (!P9         Growing degree days from germination to emergence, C). Based on your expected value of GDDE of 45, I assume you are calculating P9.  Therefore, the differences between observed emergence and simulated may occur if you assume that the field staff are planting into moisture, and this was NOT the case (i.e. delay in germination would cause the GDDs from planting to emergence to be larger than if seeds were planted into moisture, and the seeds germinated immediately).  I think that maybe one place you could check for this difference.  I am not sure how GDDE was initially calculated by the developers of CERES MAIZE, but the final value for P9 is more or less in agreement with at least one other model.

Hope this helps,
Saratha



-----Original Message-----
From: DSSAT - Crop Models and Applications [mailto:[log in to unmask]] On Behalf Of Guillaume Chirat
Sent: Wednesday, May 09, 2012 6:17 AM
To: [log in to unmask]
Subject: unit of an ecotype parameter in Ceres-Maize

  Dear DSSAT users,
I have a small doubt on the unit of one of the genotype parameters (in
the ecotype file of Maize): "GDDE" = thermal time from planting to
emergence / cm seed depth.
Working on Zambian data, I was able to calculate the degree days from
planting to emergence for 6 years: median value = 135 °C.days.
According to the staff in the field, the seed depth is 2 or 3 cm.
Therefore, GDDE should be between 45 and 67, but there is a problem of a
factor 10. Indeed, the fit is excellent when GDDE is between 5 and 7.
So, is the unit of GDDE "°C.days /mm" instead of "°C.days /cm"? Or did I
misunterstand something?

I am aware of the limited importance of such an interrogation...
Regards,

Guillaume C.

---------
Guillaume CHIRAT
Docteur - Ingénieur Agro
CIRAD
Systèmes de cultures annuelles
CA2AFRICA project
(+33)4 67 61 56 91
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