Re: - Field x laboratory

[Tom A. Reynolds]

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It seems obvious, but I thought I'd add:

There has to be a time and place (in this very interesting dialog) to
establish the intent of the monitoring, PRIOR to debate over the precision
and absolutness.

First, ARE reasonable trends being produced, from field trials and analysis,
that portend  future soil moisture status, with reasonable accuracy, using
low cost, highly redundantly deployed "sensorology"?  Reasonable means that
the prediction of soil moisture content is assuredly found to be in line
with ground-truthed (through highly accurate techniques) soil moisture
content, not so much on magnitude, but certainly in terms of slope.

Or is this the objective absolute soil moisture depletion differentials?

Now, if one is attempting to gauge the precise variability in soil moisture
depletion between like species treated with, for instance, different growth
regulators, then absolute soil moisture depletion is absolutely required.
Use a neutron probe.  Calibrate it in water.  Set the reading to 6" of
water, or some other method, and go forward.

But if the objective is irrigation scheduling, but the owner will not pay
for NP monitoring, then use a surrogate, like a granular matrix gypsum
block, or one of the newer rapid-response sensors like the Theta-Probe.
Understand the lag time problem using gypsum blocks, and be certain to
deploy multiple sensors to establish a single recommendation data point.

As far as producing N.P-like predictive accuracy with (in fact nothing more
than) a low cost sensor, through the application of a correlation
coefficient, or some such, this remains a daunting task.  But good luck.  We
all could benefit from the results.  What is the the correlation factor?
I'm still searching for it, but under-funded to check for myself to see if
there's potential to develop one, or two, or three.  Logic tells me that
there is hope.

Tom A. Reynolds, CID, CLIA
Water Balance
tomrinaz@earthlink.net
www.waterbalance.net
Mesa. AZ
(480) 463-5072


As for determining
----- Original Message -----
From: <owner-sowacs@aqua.ccwr.ac.za>
Sent: Sunday, March 04, 2001 11:34 AM
Subject: Re: - Field x laboratory

> Dear Sowacs members,
>
> First, I thank a lot all comments from the participants in this forum
about
> the differences in measurements on field and laboratory conditions on the
> relation between volumetric water content and pressure head.

<SNIP>

> typical for clay soil (in the dry range!).
>
> Best regards from Bavaria
>
> Wenceslau Teixeira
>
>
>
> _____________________________________________________________
> Wenceslau Geraldes Teixeira
> Embrapa - AmazŁnia Ocidental - Brasil
>
> Universit”t Bayreuth
> Bodenkunde - Abt. Bodenphysik
> D - 95440 - Bayreuth - Germany
> Fax: +49 (0)921 552246
>
>