Gypsum Blocks : with Aquamiser - more info required

[Harry Whittle]

I would appreciate some comments on the efficacy of using gypsum blocks
instead of stainless steel probes in conjunction with an automatic
resistance based moisture sensing system such as I am currently using to
control irrigation(Aquamiser).  The Aquamiser is supplied with two
stainless steel probes which are intended to be permanently installed at
the sod root tip level.  AC voltage is continuously applied to the
probes under normal operation.

I have had difficulty with the effects of fertilizer on these probes
and  wondering if the gyp blocks in some way block the fertilizer ions.
The only information I have on gyp blocks refers to using them with some
sort of DC resistance measuring device which is attached momentarilly.

I am interested in the effect of applying AC to the gyp blocks on a
continous basis and am wondering what sort of range of resistances are
obtained.  Are the blocks in the process of breaking down while the
current is applied such that they cannot be energized continuously?  I
am also looking for a commercial source of the blocks.  I would run my
own tests but I'm generally lazy and don't want to needlessly repeat
what others I'm sure have already done.

If no one has used the gyp blocks in this manner than I propose to test
them and report back with my results.

Harry Whittle