Here are two papers that address the non-linear versus linear approaches 
to plant development in maize. Although these papers are not in main 
stream journals, I believe these results are valid and have wide 
applicability.  These papers are in English and available from the senior 
author.
        Albert

Comparing two versions of a non-linear model for simulating leaf number 
and
developmental stages in maize based on air temperature
Ciência Rural, Santa Maria, Online
Nereu Augusto Streck,  Luana Fernandes Gabrie, I Flavia Kaufmann 
Samboranha, 
Isabel Lago,  Ana Paula Schwantes,  Alfredo Schons


Simulating maize phenology as a function of air temperature
with a linear and a nonlinear model

2008, volume 49: 449-455
Pesq. agropec. bras., Brasília

Nereu Augusto Streck, Isabel Lago, Luana Fernandes Gabrie and Flavia 
Kaufmann Samboranha

E-mail: [log in to unmask]

Albert Weiss, Professor Emeritus
School of Natural Resources
University of Nebraska-Lincoln
507 Hardin Hall
3310 Holdrege Street
Lincoln, NE 68583-0995

Phone: 402.472.6761
Fax: 402.472.2946
Email: [log in to unmask]
SNR web site: http://snr.unl.edu





From:
"Jon I. Lizaso" <[log in to unmask]>
To:
[log in to unmask]
Date:
06/04/2010 04:31 AM
Subject:
Re: Calibration



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




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