Re: Diviner 2000 access tubes

[Greg Dryden]

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I am using Diviner 2000 in Stony soils and have used the slurry technique to
install the tubes.  Indeed I have found these sites to read higher than
expected (and took a number of wetting/drying cycles to start giving
readings showing similar movements to Neutron Probe readings).  However, it
is very important to keep the oversize hole as small as possible to prevent
the slurry mix exerting an overly large influence on the reading.

To achieve a hole only slightly larger in the stony soils can be very
difficult.  I would be interested in anyones comments on their experiances
on drilling or ramming a slightly oversize hole in very
stony soils.  I have been using a steel rammer which can create some
movement when it is removed resulting in a larger than desirable hole.  I
have not tried a tungsten tip drill yet but will try this this winter.

Kind Regards

Greg Dryden





----- Original Message -----
From: <owner-sowacs@aqua.ccwr.ac.za>
Sent: Saturday, 27 May 2000 22:49
Subject: RE: Diviner 2000 access tubes


> NOTE:  To get off this list, send email to majordomo@aqua.ccwr.ac.za
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>
> Dear Jac,
> As a Diviner installer, I was interested to read what your supplier is
> doing. I expect he is using Bentonite, possibly mixed with cement.
> Personally, I avoid slurry installations because the soil moisture content
> of the slurry will always be higher than a sandy soil as the bulk
densities
> are different.  I only use slurry when the soil is very stony and I cannot
> avoid air gaps round the probe.  In such cases, I sieve some topsoil and
mix
> it with water to act as the slurry.  The danger in my method is that one
is
> putting topsoil to the bottom of the probe and encouraging roots to go
> there.  I work mostly with short term crops and I am primarily interested
in
> the top 30cm only. The Bentonite treatment is better as it is inert and
does
> not encourage rooting.
> It is important to know what you are using your Diviner for.  Is it for
> research or for managing irrigation?  If it is the latter, then the
> technique employed by your supplier will work very well.  It will tell you
> when any particular layer of soil is running out of water (usually 10cm)
and
> how deep rain or irrigation penetrated and whether the profile was brought
> back to full.  i.e. the dynamics of soil moisture will not be affected.
> The principal advantage of the slurry technique is that it is consistent,
> quick and easy.  It comes down to economics and what your supplier is
> charging.  I think it is better value for money to have lots of tubes put
in
> cheaply than one or two installed expensively!  The Sentek approved
> installation method is brilliant but time consuming and, in my opinion,
not
> always commercially justified. I use it for one or two reference sites
with
> the EnviroSCAN, but for the Diviner, cutting some corners may be
justified.
>
> Rupert Knowles
> Olivers Orchard Ltd
> (in association with Peter White Water Management)
> Olivers Lane
> Colchester
> CO2 0HH
> UK
> fax: +44 (0)1206 330208
> mob: +44 (0)860 687760
> email: r.knowles@aspects.net
>
> -----Original Message-----
> From: owner-sowacs@aqua.ccwr.ac.za [mailto:owner-sowacs@aqua.ccwr.ac.za]
> Sent: 27 May 2000 01:53
> Subject: Diviner 2000 access tubes
>
> I recently acquired a Diviner2000 moisture probe. The supplier installs
the
> access tubes by drilling a hole of 10mm  bigger OD, inserts the PVC tube
and
> settles it in with a clay mixture (similar to potters clay - the exact
> compostion I am not sure of), to ensure perfect contact between tube and
> soil.
>
> We work with sand (as in sand dunes) with moisture holding capacity as low
> as 45 mm/m.
>
> I am wondering what the effect of the clay band in direct contact with the
> tube could be.
> Can I assume that the sand-clay will reach equilibrium, in a short enough
> time to give me the correct response.
>
> Your comments will be appreciated.
>
> Thank you: Jac le Roux
> jac@besproeiing.co.za
>
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