Neutron Probe calibration

[Steve Evett]

Dear Luke,

How you go about it depends on what kind of accuracy you need.  If you
need very good accuracy see the methods described in Evett and Steiner.
1995. Precision of neutron scattering and capacitance type soil water
content gauges from field calibration. Soil Sci. Soc. Am. J. 59:961-968.
(Don't worry, I've put a copy in the mail to you).  These methods allow
calibration by soil horizon but are a lot of work.  Having used the bore a
hole, take a sample down the hole, bore some more, repeat... followed by
neutron probe readings in the hole... repeat for another hole, etc.
method, I have concluded that it doesn't work well enough, and isn't that
much less work than what we described in our '95 paper, which involved
trenching alongside tubes installed in wet and dry sites (after reading
them with the neutron probes of course) and taking samples horizontally on
both sides of each tube.  The problem with taking samples down a hole is
that you can't tell when the samples are being compacted or broken up so
that the bulk density is wrong.

Hope this helps, and best wishes, Steve