Reading Accuracy - Delta-T Devices PR2 User Manual

Reading accuracy

The Profile Probe is accurate and reliable.
However this doesn't guarantee that the readings you take with a
PR2 are an accurate measure of the soil moisture. There are
three particular sources of error that you need to consider when
measuring soil moisture with the Profile Probe:
♦
Installation problems
♦
Soil type and Sampling errors
♦
Salinity
Installation problems
An ideal installation would avoid creating either air gaps or soil
compaction around the access tube – and then the soil would
not shrink or swell as it dried out or rewetted. It's possible to get
remarkably close to this ideal in some deeply cultivated soils,
and close to impossible in some stony soils or hard clay.
We obviously can't quantify your potential installation errors, but
experience suggests that a loose, gappy, access tube
installation could lead to errors of ± 10% (± 0.1 m
Take as much care as you can over the installation
Remember to fit a collar to your access tube.
Soil type and sampling errors
Again, it's not really possible to quantify the potential errors
associated with soil type, but be aware of the following:
Almost all measurement problems are worst in heavy clay
soils.
If your soil cracks badly in dry conditions, the readings from
your Profile Probe may be more indicative of crack size than
soil moisture content!
The linear relationship in equation [1] is less applicable to
heavy clay so
See ref. [7].
Soil moisture content may vary significantly even within a
small volume of soil. When you rotate the Profile Probe
within its access tube the reading ch
reflect real soil moisture variability.
22 Operation
ils at low soil moisture levels (< 0.1 m
Profile Probe User Manual 3.0a
3 -3
.m ), so...
3
.m
anges you observe
-3
).