From:œ Martin Schmitz, BT (SCHMITZ)
To:œ           sowacs@aqua.ccwr.ac.za
Date:œ Monday, July 1, 1996  11:34 am
Subject:œ      spatial variability

Dear Listmembers,
depending on how much soil moisture
varies over short distances, I guess
it can make
measurements either insecure or expensive.

Spatial variability can have several
reasons, but one should be the root 
activity/transpiration.
Imagine a tensiometer in a place some
centimeters away from roots; due to the
low water-conductivity of unsaturated soil,
how do we know that the moisture around
the sensor is similar to the moisture
around the roots?
(There are reasons also not to place the 
sensors directly between roots also.)

Tests in soil filled pots (ca. 70 kg)
show, that at water suction levels of
-200 mbar over a distance of 10 cm 
the moisture doesn't redistribute
even in weeks.

Did anybody tackle this problem? 
Has this been a point of 
discussion with soil moisture measurement?

I am trying to make a little program
that can calculate moisture flow 
(by Darcy's law) via the finite-difference
method to show the effects.

Do you know of software (hydrology etc.)
that does it alraedy (and that doesn't 
cost thousands of dollars)?

Would you be interested in this topic ?


:-) Martin Schmitz
schmitz@kepler.dv.fal.de