Dear DSSATers,
This issue on phyllochron in maize is becoming more and more interesting. I
would like to add a couple of additional elements to the discussion for you
to consider.
CERES-Maize and other models assume a genetically determined phyllochron.
They also assume a linear response of plant development to thermal time.
There is evidence indicating that these assumptions may fail or may need
additional considerations in some environments:
1) Does phyllochron acclimates (e.g. Birch et al., 1998. Field Crops
Research 59:187-200)?
2) Is leaf appearance rate a linear function of thermal time (e.g. Stewart
et al., 1998. Agron J 90:73-79)?
About how much variability in phyllochron may be expected, I believe there
is less variation in phyllochron than thought when PHINT was included as a
new genetic coefficient for CERES-Maize (the original model had an internal
PHINT=38.9 degree-days). However, there is evidence indicating that
phyllochron in tropical and sub-tropical cultivars is longer than in mid or
higher latitudes (e.g. Bonhomme et al., 1991. Agron J 83:153-157).
Additional comments are very much welcomed.
Best regards,
Jon
-----Mensaje original-----
De: DSSAT - Crop Models and Applications [mailto:[log in to unmask]] En
nombre de Boote,Kenneth J
Enviado el: Friday, June 04, 2010 4:40 AM
Para: [log in to unmask]
Asunto: Re: Calibration
All,
Jon Lizaso responded well on the temperature the crop sees, but I wanted to
add one more reaction.
I seriously doubt that sowing density reduces PHINT. If anything, very high
sowing density could be sufficiently severe stress that the plant may
express leaves more slowly (in fact greater PHINT). The 95% safe assumption
is that sowing density does not affect PHINT. Fertilization should also not
affect PHINT, unless N stress is so very severe that leaves cannot expand
and tip appearance is delayed (but very rare).
So, safer to consider that PHINT is not affected by plant density or
fertilization.
In fact, here is a "heresy" statement from me. I don't think anyone has
proven that PHINT truely varies among maize hybrids. So I disagree with
Ritchie and Batchelor's introduction of PHINT as a hybrid trait.
Ken Boote
________________________________________
From: DSSAT - Crop Models and Applications [[log in to unmask]] On
Behalf Of Lizaso,Jon I [[log in to unmask]]
Sent: Thursday, June 03, 2010 5:08 AM
To: [log in to unmask]
Subject: Re: Calibration
Maximiano and others interested,
To answer properly your question you should consider that plants in your
field sense soil temperature first and later canopy temperature, and based
on those temperatures differentiate and expand leaves. What your model
"senses" is air temperature input in your weather file. What population
densities and N doses are we talking about?
In the field, very high population densities may result in early canopy
closure, higher water uptake, and some other changes that may affect the
actual soil and/or canopy temperatures plant senses in different population
densities. On the other hand, these details are invisible to the model. The
only information available to the model are daily values of Tmax, Tmin, and
SRAD, and based on that it will calculate thermal time using simulated soil
Temp (when leaf number is less than or equal to 10) or air temperature.
Best regards,
Jon
Jon I. Lizaso
Dpto. Producción Vegetal. Fitotecnia
ETS Ingenieros Agrónomos
Senda del Rey s/n
28040 Madrid, SPAIN
email: [log in to unmask]
Tel: 34 91 452 4900 ext 1671
________________________________________
From: DSSAT - Crop Models and Applications [[log in to unmask]] On
Behalf Of Fidel Peña Ramos [[log in to unmask]]
Sent: Wednesday, June 02, 2010 4:38 PM
To: [log in to unmask]
Subject: Calibration
I'm calibrating DSSAT with the cultivation of maize under nine treatments
three densities and three fertilizer levels
it is reasonable that with increasing density decreases PHINT?
Fidel Maximiano Peña Ramos
Ing. En Agrobiologia
_________________________________________________________________
Hotmail: as HOT as always
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