Dear Harikrishna,
Leaf number in CERES-Maize is calibrated with three of the genetic
coefficients:
P1 (thermal time from seedling emergence to the end of the juvenile phase)
P2 (photoperiod sensitivity)
PHINT (termal time between successive leaf tips)
The larger P1, more leaves are differentiated and more leaves are produced;
the larger P2 the more sensitive the cultivar is to photoperiod and thus it
will remain longer differentiating leaves during the photoperiod-sensitive
phase (ISTAGE 2) resulting in more leaves; the larger PHINT, the cultivar
will require more thermal time for each leaf to appear, therefore it will
produce less leaves.
Playing with this three coefficients you should be able to simulate the
correct number of leaves, and dates of silking and physiological maturity.
A word of caution about counting leaves in the field for your cultivars. By
the time of silking, usually there are at least 6 senesced leaves. Many
times more, depending on water, N, and other environmental conditions.
Lower leaves are detached and just "disappear". You said your cultivars
produced max 15 leaves. This seems too low according to my experience.
Usually is a good practice to mark leaf number early in the season in a few
plants so you are sure about leaf numbers at silking. If you are simulating
26 leaves it might be that PHINT is too low, assuming that P1 and P2 are
about right.
Simulation of leaf numbers and leaf area has been a major concern.
CERES-Maize and other models use generic equations to calculate leaf area.
Therefore you cannot simulate variations in leaf area produced across
cultivars with the same number of leaves. What the model does is simulate
more leaf area when more leaves are differentiated. In your particular
case, you may decide that simulate the correct leaf area at silking is more
important to predict the right biomass, than simulate the right leaf number.
To overcome these problems, we developed a new leaf area model, that
predicts on a per-leaf basis leaf expansion, longevity and senescence. When
linked to CERES-Maize we were able to simulate the correct leaf area and
leaf numbers across different cultivars and environmental conditions. The
trade-off is that the new model requires three new inputs. Now that we can
simulate correctly leaf area and leaf numbers, we found problems with the
simulation of the carbon assimilation. This was partially because the model
overestimates light capture so we proposed some methods to improve this.
Still, with the right light captured and leaf area there are problems with
the carbon balance so we are currently developing a
photosynthesis/respiration model.
Hope this can be helpful. Here are the references:
Lizaso, J.I., W.D. Batchelor, and M.E. Westgate. 2003. A leaf area model to
simulate cultivar-specific expansion and senescence of maize leaves. Field
Crops Research 80:1-17.
Lizaso, J.I., W.D. Batchelor, M.E. Westgate, and L. Echarte. 2003.
Enhancing the ability of CERES-Maize to compute light capture. Agricultural
Systems 76:293-311.
At 12:42 PM 7/10/2003 +0000, you wrote:
>Dear all
>
>I am Harikrishna working on maize simulation modeling, in relation
>to
> different N doses and 4 slplits of N for each N doses. When I
>run
> the model the predicted yield level will be satisfactory but
>the
> leaf numbers are constant i.e.,26. So this leads to higher
>drymatter
>production and LAI, but in field the measured leaf numbers are
> maximum of 15. So how to calibrate this error to get
>satisfactory
> number of leaves,drymatter production and maximum LAI.
> Please suggest
>
>Yours
>Harikrishna
>
>___________________________________________________
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Jon I. Lizaso
Dep. Agricultural & Biosystems Engineering
124 Davidson Hall
Iowa State University 515 294 7350 (Voice)
Ames IA 50011 515 294 2552 (Fax)
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