Dear all:

I would also like share my views on the genetic coefficients used
CERES-Wheat and CERES-Maize. Although the  genetic coefficient of a cultivar
should not be site specific, but it is truely not like that. Between the
maize and wheat I found this more complicated on wheat than on maize.
We try to use the same cultivars on spring wheat and maize at 100m to 2500m
above sea elevation in Nepal. With respect to phenological genetic
coefficients, I did not see much problem with maize and may not need
recalibration. The same values are working more closely with respect to
anthesis and physiological maturity. However, in wheat I needed to
recalibrate the P genetic coeficients. The same value is not working. It
appears that maize coefficients are simpler to explain and understand in
contrast to wheat. Simple clues to estimate and run in close to the actual
are needed. In this regard, modellers should try to clearify.

Kishore Sherchan

----- Original Message -----
From: "ken boote" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, February 04, 2004 4:00 AM
Subject: Re: Genetic coefficients


> Rolf and Matthias:
>
> In theory, the cultivar coefficients are not site or
environment-dependent,
> and should allow universal application for a specific cultivar. That is
the
> principle on which we develop genetic coefficients.  They should work at
> new sites and new environments and should not require new calibration for
> each new site or environment.  If they differ, then something in the model
> is not correct regarding how the model is parameterized to response to
> environment (temperature or daylength for example).  We need to learn from
> those problems. Alternately, something on the site characteristics may not
> be properly input (soils traits) or simulated (unique site traits that
> affect water balance or N balance for example).
>
> I agree with Matthias only to the extent that you should check the genetic
> coefficients for the new site, and if they do not work, you should check
> with model developers as to why they do not work, so they can learn from
> the "problem".  Of course, you can re-calibrate for that new site and you
> will get a better prediction for that new site, so may be this is good
from
> the standpoint of doing extensive applications for that site. But that
does
> not mean that you have solved the problems in the model or "improved" the
> model, as the same genetic coefficients you have just created may not
> predict well for the next season even at the same site.  That is
> particularly true for the G2 by G3 coefficients affecting grain yield in
> CERES-maize.
>
> Ken Boote
>
>
> At 06:47 AM 2/3/04 -0800, you wrote:
> >Hi Matthias,
> >
> >I guess genetic coefficients are even model specific.
> >A couple of months ago I used DSSAT and APSIM to model maize growth
> >(highland early white). Though the maize module of APSIM is based at
least
> >partly on the early CERES-maize model and there is an overlap in the
> >different genetic coefficients that have to be defined, using the same
> >coefficients for both models didn't work out.
> >The original intention certainly was to create some "universal
> >coefficients", but then errors in the code are found, recalibration are
> >made, etc., confounding the original ideas a bit.
> >Only speaking about the maize genetic coefficients. It might be much more
> >straight forward in the other modules (soybean, peanut - Ken?)
> >
> >Regards,
> >Rolf
> >
>
>---------------------------------------------------------------------------
-
> >--
> >Rolf Sommer
> >CIMMYT (International Maize and Wheat Improvement Center)
> >Apdo. Postal 6-641, 06600 Mexico, D.F., Mexico
> >Tel. +52 (55) 5804 2004  Ext. 2128
> >Fax +52 (55) 5804 7558/59
> >www.cimmyt.org
>
>---------------------------------------------------------------------------
-
> >--
> >
> >
> > > -----Original Message-----
> > > From: Matthias Langensiepen [mailto:[log in to unmask]]
> > > Sent: Tuesday, February 03, 2004 06:30
> > > To: [log in to unmask]
> > > Subject: Re: Thank u _Clarification about Genetic Co.eff
> > >
> > > Dear All
> > > If it is true that genetic coefficients
> > > are cultivar but not environment specific,
> > > a corresponding calibration procedure
> > > would lead to the universal application
> > > of the model for each particular cultivar.
> > > There is experimental evidence that genetic
> > > coefficients become site and even
> > > season specific invalidating such
> > > an assumption. I would therefore
> > > strongly recommend to perform a thorough
> > > site-specific calibration in each new
> > > model application case following the
> > > procedures outlined in the DSSAT
> > > manuals.
> > >
> > > Matthias Langensiepen
> > > Modelling Plant Systems
> > > Institute of Crop Science
> > > Faculty of Agriculture and Horticulture
> > > Humboldt-University of Berlin
> > > Germany
>
>


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