Re: Field x laboratory

[Dr. Clinton C. Shock]

NOTE:  To get off this list, send email to majordomo@aqua.ccwr.ac.za
with the body of the message containing the line:
unsubscribe sowacs

Wenceslau,

I am glad that you are working on this problem.  Maybe you can solve it.

I ran into the same sort of lack of correspondence between laboratory
and "in field" moisture retention curves for silt loams, and quit using
the laboratory values.  What soil types are you working with?

Clint
-- 
Dr. Clinton C. Shock
Malheur Experiment Station, Oregon State University 
595 Onion Ave.  
Ontario, OR 97914, USA 
Telephone (541) 889-2174 Cellular (208) 741-6074 
http://www.cropinfo.net  Email ccshock@fmtc.net and
Clinton.Shock@orst.edu


owner-sowacs@aqua.ccwr.ac.za wrote:
> 
> NOTE:  To get off this list, send email to majordomo@aqua.ccwr.ac.za
> with the body of the message containing the line:
> unsubscribe sowacs
> 
> 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