Generalised calibrations
Most soils can be characterised simply by choosing one of the
two generalised calibrations we supply, one for mineral soils
(predominantly sand, silt or clay) and one for organic soils (with
a very high organic matter content).
a
a
0
1
Mineral soils
1.6
8.4
Organic soils
1.3
7.7
These values have been used to generate the slope and offset
conversions and linearisation tables in the
Conversion to soil
moisture
section.
Soil-specific calibration
If it is important to work to higher accuracy, you may choose to
carry out a soil-specific calibration, but please bear this in mind:
For normal agricultural soils, if you use one of the generalised
calibrations, you can expect typical errors of ~ ±0.06 m
3
.m
-3
,
including installation and sampling errors.
If instead you use a soil-specific calibration, you can expect
typical errors of ~ ±0.05 m
3
.m
-3
.
As a guideline, we suggest that you
only
need to do a soil-
specific calibration if one of the following applies:
4
Your soil is heavy clay, highly organic, or in some respect
“extreme”.
4
You are working to high levels of accuracy, or you need a
controlled error figure rather than a “typical” error figure.
not
and the following do
apply
8
Your soil is very stony (insertion errors are likely to outweigh
the calibration errors)
8
your soil cracks when it dries (again measurement errors
are likely to be higher than calibration errors)
The procedure for carrying out a soil-specific calibration is
detailed in Appendix A.
18
z
Operation
Profile Probe User Manual
3.0a
