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>>Regarding the comment:
>>I have heard that some are loking at placing the TDR wave
>guides<
>into a ceramic tube - thereby reducing the soil's influence on<
>changes in the dielectric - and restricting the sensor to<
>measuring the water content of the ceramic in hydrologic<
>equilibrium with the soil. The pore size distribution of the
>soil<
>has then to be matched to the soil, but progress is being made
>on<
>this front too, I believe. But soil sensor contact problems are<
>alleviated.<>>
>What about 2:1 shrink/swell soils and lack of instrument-to-soil
>contact. Won't you still have problems on these soils no matter
>what medium one uses to place TDR probes in?
>The equilibrium concept would undoubtedly help solve the small
>field of influence situation inherent in TDR instrumentation,
>BUT, cracking soil is a big problem in arid areas...thus you're
>back to the same problem, or are you?
>Richard Mead Soil Scientist
<<<
<Bruce>Once before on sowacs I proposed the following solution to
this problem:
installing the sensor (of whatever type) into a volume
of medium that will not shrink and crack. As long as the medium
is fairly well matched to the texture of the soil around it, it
will surely come into water content equilibrium. Despite the soil
cracking, it must still be in hydrologic continuity at some point
of the sphere - and so provide a better estimate of soil water
content that would a sensor placed into the soil proper, but
ending up in air due to cracking.
Would a pocket of diatomaceous earth (or a non-swelling clay &
sand concoction) do the job?
Perhaps the users of tensiometers could help us here. (They use a
slurry to promote cup:soil contact.)
Regards
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.
Bruce Metelerkamp SOIL WATER RESEARCH OFFICER
Institute for Commercial Forestry Research,
University of Natal, PO Box 100281
Scottsville, ZA3209
Rep. of South Africa Voice:27 331 62314
E-mail: bruce@icfr.unp.ac.za FAX:27 331 68905
brooz@pobox.com
Bruce.Metelerkamp@pobox.com
URL http://www.icfrnet.unp.ac.za/~metele
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