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[EarthNSky <erthnsky AT bellsouth.net>]

Merry Christmas, Van Dell.
For a quick, basic read on the differences (and it basically is only the
amount of water in the molecule) between drywall, drierite, gypsum,
plaster of paris, etc., I suggest reading the wiki article on gypsum for
a down and dirty tutorial.
http://en.wikipedia.org/wiki/Calcium_sulfate
But to answer your question, in theory you could break up drywall and
add it to the soil, but I am not sure you want to do that.(I do,
however, like Lynda's use of drywall under rabbit cages, then into the
compost heap-that way you can apply it in small amounts exactly where
you might need it..)
As a chemist, I advise that you really do your research on your own soil
before you amend it in any way.  It can get pretty complicated, but you
don't have to have a degree in chemistry to understand it.
It's more than just a question of pH, you have to actually look at why
the pH is as it is..Most soils that are alkaline are sodic(high in
Sodium from the salts), but not all.  Gypsum is usually good for sodic
soils because it exchanges Calcium for the Sodium, but only to a certain
extent. There are other considerations, too, like your climate..is it a
dry, desert climate or a wet subtropical climate?  That, too, would
affect whether or not you might want to use gypsum.  Also, dependent on
your soil, it might be better to add both lime and gypsum over one or
the other alone. If your starting soil is super acidic, it might benefit
more from the calcium from lime than from the calcium in gypsum, and you
can get sort of a time release effect from using both.
Gypsum does not affect pH much, if at all, which is why if your soil is
only slightly acidic, like a ph of say 6.2, you might choose gypsum over
lime to supplement calcium.. basically gypsum just supplements Calcium,
which is depleted from acidic soils.  It also probably provides some
sulfur as it breaks down and lime does not.
There's a blurb about gypsum on one of the soil sites I posted a couple
of days ago, but here are some more...

http://www.acaa-usa.org/1-Use_of_FGD_Gypsum_Soil_Amendments_for_Improved_Forage_and_Corn_Production.pdf

http://www.dpiw.tas.gov.au/inter.nsf/WebPages/TPRY-5Z529T?open

http://www.pjbs.org/pjnonline/fin420.pdf

http://www.science.org.au/nova/035/quirk.htm


VAN DELL JORDAN wrote:
> In Az we had mostly clay soils.  Gypsum was used to "loosen" the soil
>  to increase water penetration.  I never could find out if the the 
> gypsum in drywall was the same as agricultural.  In other words if 
> you had leftover drywall could you break it up and put it in the soil
>  or was the chemistry different than agricultural gypsum? Van Dell

--
Bevanron of EarthNSky Farm   Sleep well tonight, for somewhere in the
ocean's depths, MY son is protecting YOUR freedom.