John,

What went into your measured LAI?  I made some runs with the
default data in DSSAT 4 and none generate an LAI above 5.0.  You
are claiming an LAI of 7.  I am not saying that the model is right but
maybe you aren't comparing apples to apples.  Did you include leaf
sheath in your LAI or did you measure only from the ligule to the tip?

We are still working on modeling bahiagrass and LAI/SLW has been
a bit of a contentious issue.  Our measured LAI's from two
experiments never got much above 4, but we didn't include leaf
sheath.  This raised some eyebrows because we had good light
interception despite the low LAI.

I can find one citation that claims an LAI of 8 for bahiagrasss but
nothing else over 4 - I have no idea how they got 8.  We were
measuring 8 weeks of regrowth in Florida - good coverage/light
interception but no LAI.  When we used the measured SLW in the
model parameters, the predicted LAI was pretty close.

I haven't seen a lot of data on wheat LAI (a quick look online shows
a range from 2-5 for 3 studies), but the  LAl data that I have seen for
forage grasses generally falls in the 2-4 range.

Just be sure that your LAI 7.0 is measuring the same thing as
whatever the model is specifying before you worry about changing
parameters.  Since LAI is used to predict light interception and
photosynthesis, I suspect that the LAI predicted in the model will
reflect the amount of leaf above the leaf sheath and therefore, not
include the sheath itself - or if it does, only the sheaths of the
outermost leaves (that would receive light).

One more thing to look at - Did you include dead leaves in your LAI?
At least in CROPGRO, leaves are assumed to fall off as soon as
they are fully senesced, therefore they aren't included in the LAI
calculation.  This would yield a lower LAI.

Stu