Hi John,

Have you checked the various stress factors? You may be losing LAI and
crop biomass because of excessive water or N stress. Besides checking the
stress factors, you can run the model with no water or N balance.

If that doesn't help, then I would contact Tony Hunt to get guidance on
modifying the ECO coefficients.

Best regards,
Jeff

Jeffrey W. White
USWCL, USDA-ARS
4331 E Broadway Rd
Phoenix, AZ 85040
Tel. 1-602-437-1702 x 268
Fax 1-602-437-5291
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Subject
how to jack up LAI for winter wheat






Hi all,

I am calibrating the wheat model of DSSAT v4 using measured data.  The
measured maximum leaf area index was about 7.0, but the simulated was only
4.5.  The model seems to overestimate stem weight but underestimate the
leaf weight for the most part of the growing season.  However, the
simulated specific leaf weight was similar to measured values.  My
question is: Which parameters should be tapped in order to increase LAID
while decreasing stem weight?  I have tried a few leaf area related
paramters in the ECO file, but had no luck.  Anyone out there has a magic
bullet for this?  BTW, the biomass at harvest was underpredicted by some
20% by the model.

Any advice or suggestion will be greatly appreciated.

Thanks and Regards,

John Zhang
Hydrologist
USDA-ARS Grazinglands Research Lab
El Reno, OK