The CERES-Maize model computes physiological maturity based on accumulating
growing degree days from silking. When the GDD's from silking exceeds the
genetic coefficient P5, physiological maturity occurs. In cool seasons in
northern climates, the plant often does not accumulate enough GDD's to
actually reach physiological maturity. This is probably what is happening
in your case. The model continues to run into late fall under cool
conditions, accumulating very few gdd's per day.
The variable RGFILL in CERES is the relative grain filling rate and is
computed based on mean daily temperature (TEMPM). It is used to compute
the grain growth rate today (GROGRN) as shown below.
RGFILL = 1.4-0.003*(TEMPM-27.5)**2
GROGRN = RGFILL*GPP*G3*0.001*(0.45+0.55*SWFAC)
The role of RGFILL is to allow the model to terminate when temperatures
(especially in the northern corn growing regions) get too cool to support
corn growth. It is a way to terminate the model under conditions where
black layer (physiological maturity) will not be reached due to cool
temperatures.
Depending upon the version of Ceres you are using, the RGRILL threshold is
different. I think that in the DSSAT35 release, if RGFILL is below 0.1 for
1 day, the model terminates growth. Other later versions of the model
required that RGFILL be below 0.1 for 2 days in a row before growth is
terminated. When growth is terminated using the RGFILL criteria, you get
the following warning message:
2700 FORMAT (2X,'Crop mature on JD',I4,' due to slowed grain filling')
We have moved this threshold into an input file in DSSAT4.0, which is
scheduled to be released in December 2002 at the DSSAT training workshop
(http://www.ICASAnet.org/conferences/dssat2002.html). Thus, you will have
more control of this behavior in the future.
Bill
At 02:03 PM 7/23/2002 -0400, you wrote:
>For CERES maize maturity is determined with P5
>(c:\dssat35\genotype\MZCER9?0.cul file) this represent the cultivar specific
>heat units (thermal units) to reach maturity from silking. The base
>temperature is 8oC. The colder the temperature the longer it will take to
>reach maturity. If their is severe stress the model will simulate maturity.
>You can play around with the P5 value to obtain better results, if the
>simulation of silking date is in reasonable limits.
>
>On the potato simulations I have no idea.
>
>Hope this help
>
>Regards
>Andre
>
>-----Original Message-----
>From: Jean-Philippe Brassard [mailto:[log in to unmask]]
>Sent: Monday, July 22, 2002 4:16 PM
>To: [log in to unmask]
>Subject: ceres and substor
>
>
>Dear listers,
>
>I'm using CERES and SUBSTOR to simulate maize and potato yields in Quebec,
>Canada. I'm having some difficulties with these models.
>
>With CERES, in some sites and years, I have 'slowed grain filling', which
>result in very late (almost ridiculously so) maturity and harvest dates
>(harvest is done at maturity). I'm not sure what is causing this, and what I
>can do to obtain better dates. Can somebody help me with that?
>
>My problem with substor is the following: when I do a simulation, I get to
>the screem titled 'SIMULATED CROP AND SOIL STATUS AT MAIN DEVELOPMENT
>STAGES' (the 3rd, I think), and, just after the data line for 'Start Sim', I
>receive the following error message:
>
>'run-time error M6101:MATH
>- Floating-point error:invalid'
>
>I don't know what it means, and I don't know how to fix it. Any help would
>be greatly appreciated.
>
>Thank you for your time and counsel,
>sincerely,
>
>Jean-Philippe Brassard
>Étudiant gradué
>Laboratoire de climatologie
>Département de géographie
>Université de Montréal
>tel: (514) 343-8039
>email: [log in to unmask]
>
>
>_________________________________________________________________
>Send and receive Hotmail on your mobile device: http://mobile.msn.com
Dr. William D. Batchelor
Associate Professor
Agricultural and Biosystems Engineering
219b Davidson Hall
Iowa State University
Ames, IA 50011
http://www.soybeans.ae.iastate.edu
ph- 515-294-9906
fax 515-294-2552
email [log in to unmask]
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