Appendix C—Creating a customized calibration equation
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•
Md = dry mass of soil core (g)
•
V = bulk volume (cm3)
•
Bulk density p = Md/V cm-3
•
Gravimetric water content W = (Mw-Md)/Md (g g-1)
•
Volumetric water content
θ
= Wp
1
.
14.
Prepare a table to record the determined values of volumetric soil
moisture content readings per depth plane. Do not average. Keep the
samples separate.
15.
Plot SF on the Y-axis and Vol % on the X-axis in replicate pairs per
depth level and fit appropriate calibration curve.
Note:
Calibration equations may not fit all points adequately on a
single calibration for that profile. This is particularly relevant for soil
profiles with different textural layers. You may wish to generate
separate calibration equations for individual soil layers at a particular
depth level. The Diviner 2000 can process data using a different
calibration equation for each 10 cm depth level increment.
16.
Type new calibration equation(s) into the Diviner 2000 display unit
using the procedure on page.
Errors to avoid
Calibration for absolute data may incorporate the following errors. They
must be corrected.
1. In soil sampling:
•
sampling wrong depth plane in relation to sensor reading
•
sampling outside the sphere of influence of the sensor
•
soil drying process, i.e. insufficient temperature, insufficient drying
time.
2. In the timing
:
•
between sensor reading and soil sampling especially in coarse sand
with a relatively high soil moisture content, where changes occur in
seconds and in minutes.
3. In volumetric measurement:
1
Source: Soil water assessment by the neutron method – E.L. Greacen,CSIRO Australia, 1981, CSIRO Division of Soils – Adelaide)
Summary of Contents for Diviner 2000
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