Hello Michael,
   It may be that your simulation is producing a stronger stress than what
occurred in the field. The field values for grains/ear and single kernel
weight (g) are 208 and 0.23. The simulated values are 11.4 and 0.20. It
looks like grains per ear has the largest effect on the yield reduction.
   The grains/ear is reduced when the average carbon assimilation rate is
low during the phase from silking to 170 degree days afterward. The factors
that can reduce carbon assimilation are water stress, nitogen stress, and
low or high temperature. You can find out whether there were stresses in
the simulation by looking in the OVERVIEW.OUT file under the section
*ENVIRONMENTAL AND STRESS FACTORS. If you see an unusually large stress,
you might try looking at the input file that may affect the stress (Weather
file (temperature and rainfall during the sensitive phase), Soil file
(SDUL, SLLL, SLRO), and Management file (initial conditions, fertilizer
rates and dates).
   To a lesser degree, the underestimate of the single kernel weight is
reducing yield. This may be caused by low growth (again the stresses that
reduce carbon assimilation) rate during grain filling, or shortened grain
fill duration (premature physiological maturity).
   Good luck with your work.
Sincerely,
Richard


At 05:58 PM 3/29/01 -1000, you wrote:
>    I am modeling aboriginal maize production using parameters derived from
>Tohono maize.  My genetic parameters are as follows:
>
>P1=200
>P2=0.0
>P5=610
>G2=311
>G3=7.4
>PHINT=38.9
>
>    When I run an experiment, I get GRAIN/m2=45, GRAINS/EAR=11.4, GRAIN YIELD
>(kg/ha)=91 as opposed to the actual GRAIN/m2=892, GRAINS/EAR=208, and GRAIN
>YIELD (kg/ha)=2050.  Clearly, 45 grains per ear is unrealistic.  While the
>genetic parameters are on the low side they are basically in the range of
other
>varieties.  When I run an experiment with another variety, I get realistic
>numbers.  Since the problem does not appear to lie in the genetic
parameters, it
>must lie elsewhere but I can not figure out exactly where.
>
>    Any ideas where the problem may be?
>
>--
>Michael Pool, RPA
>Anthropology/Geography Department
>Austin Community College
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>