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Re: Effectiveness of Gypsum and Tensiometers in top 6 inches.

In a message dated 96-10-19 06:10:22 EDT, you write:
(Peter Broomhall)
>I am after a little bit of information on the use of Gypsum blocks and
>tensiometers within the top 6 inches of soil.

The tensiometer does not "see" any of the effect on the ability
of the plant to extract water caused by the osmotic potential.
The salts are in solution and move across the cup of the 
tensiometer with the soil water.  If the EC of the soil solution
is such that it could impede water uptake, it would be necessary
to monitor this condition with suction lysimeters or some sort
of portable EC meter, so as to implement periodic leaching
of accumulated salts. This would apply to the 6" depth together
with any other  "depth" which contained the active portion of the
plant root system.  Depending on the effective rooting depth of
the crop, soil water status measurements  are normally taken
at the bottom of the top 1/4 of the effective rooting depth and 
at the bottom of top 3/4 of the same, with this area accounting
for roughly 90% of the water extracted by the root system of 
a well watered crop (assuming this is the goal). As far as pH
and temperature are concerned, I know of no effect which they
can have on a tensiometric measurement.  I'll leave that subject
to others better trained than I in soil chemistry and soil physics.
Regards, Bill Pogue