Re: Field x laboratory

[Cliff Hignett]

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Tensiometers often misbehave in the field due to temperature fluctuations
(especially day /night) - these cause the water and air in the tensiometer to
expand and contract - try insulating the tensiometers or reading then early in
morning (before they warm up)

Cliff.hignett@soilwater.com.au

owner-sowacs@aqua.ccwr.ac.za wrote:

> Dear list members.
>
> I am working with experimental water retention data to fit parametric
> equations, which I'd like to use in numerical simulations of water fluxes.
>
> I have determined in-situ volumetric soil water content by TDR readings and
> soil pressure head by tensiometers. However, measured field data disagree
> with the determined on undisturbed soil cores samples collected at the same
> site.
>
> The problem of hysteresis was partially circumventing collecting the field
> data in the drying brunch of the hysteretic curve (it was carried out on an
> instantaneous profile method experiment).
>
> The volumes sampled by TDR and the cups of our tensiometers are not the
> same and, not only the volumes were different but they are separated
> because of installation procedures. Moreover, the soil samples for the
> laboratory measurement were collected about 2 meter apart.These factors are
> probably some explanation for the differences, but our data set is large
> with many replications and, I believe that some other factors besides soil
> variability are contributing to that difference ...
> I have found a limited number of field studies (where in situ measurements
> were carried out) in which undisturbed soil cores were taken.
>
> Someone knows studies concerning the problem of field x laboratory
> determination of the soil water retention curves ? or have some
suggestions ?
>
> Any help on this matter will be greatly appreciated
>
> Best regards.
>
> Wenceslau Teixeira
>
> _____________________________________________________________
> Wenceslau Geraldes Teixeira
> Embrapa - AmazŁnia Ocidental - Brasil
>
> Universit”t Bayreuth
> Bodenkunde - Abt. Bodenphysik
> D - 95440 - Bayreuth - Germany
> Fax: +49 (0)921 552246

--
Cliff Hignett
Soil Water Solutions
45a Ormond Ave
Daw Park
South Australia 5041
pH 61 (08) 8276 7706
WWW.SOILWATER.COM.AU