�From:�	Graeme D Buchan (BUCHAN)
�To:�		SOWACS@aqua.ccwr.ac.za
�Date:�	Tuesday, May 21, 1996  12:45 pm
�Subject:�	Measuring water potential by `AquaLab'

Greetings from: Graeme Buchan, Reader in Environmental Physics,Dept 
of Soil Science, Lincoln University, NZ.

Re: Measuring water potential in soils via `AquaLab', a system 
designed to measure `water activity' in foods etc.,
produced by Decagon Devices, Inc., Pullman, Washington, USA
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I am contemplating securing funds to purchase an `AquaLab' water 
activity meter, and seek advice from anyone who has had experienceof 
its use for measuring soil water potential (psi) in the drierrange.

A paper on its use appeared in SSSAJ 56:1068-1070 (1992).
AquaLab measures psi of a small sample placed in a holder, via its 
relative humidity, which is measured by a chilled mirrortechnique.

It seems to me this offers an improved method of determining the 
drier-end part of the soil moisture characteristic, since it would 
measure psi on an `as is' basis, in contrast to e.g. pressureplates, 
which attempt to IMPOSE a fixed matric potential (but don'tproperly 
equilibrate, according to research findings).
Can anyone offer advice on a) the usefulness, and b) theoperational 
range of this equipment ?

Yours hydroscholastically,
Graeme Buchan
Dr Graeme D Buchan,  
Reader in Environmental Physics & Environmental Education,
Dept. of Soil Science, PO Box 84, Lincoln University, 
Canterbury, New Zealand