Enabling better global research outcomes in soil, plant & environmental monitoring.
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2. Theory of Operation
The MP406 has a high frequency moisture detector which uses the standing wave principle to
indicate the ratio of two or more substances forming a body of material, each substance having
a different electric constant (Ka).
The moisture measurement of the material is based upon the fact that in a water/soil/air matrix,
the dielectric constant is dominated by the amount of water present. The dielectric constant of
water is approximately equal to 80 whereas the dielectric constant of soil is approximately equal
to 3 or 4 and air is equal to 1. Therefore, any changes in the volume matrix ratio of water will result
in a substantial change in the dielectric constant of the matrix. The soil water content can be
measured exactly because changes in water content of the soil result in changes in the dielectric
constant of the soil.
Materials that can be measured by the MP406 include any composition of non-metallic powder,
liquid or solid phase substance into which the needles can be inserted.
Results
The results from measurement of absolute volumetric soil water percent (VSW%) from prepared soil
samples using the MP406 are given in Figure 1. This result is typical of the results obtained from
comparative testing of the MP406 in prepared soil samples, for a wide range of agricultural soils.
Figure 1. MP406 Measurement of Absolute Volumetric Soil Water Percent from Prepared Soil Samples as a
Standard.
0
5 10 15 20 25 30 35 40
Soil Sample Volumetric
Soil Water (%)
MP406 = 1.0136x + 0.4298
R
2
=0.9931
MP406
OVEN
MP406 Measurement of VSW%
Using Soil Samples as a Standard
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35
30
25
20
15
10
Vol
um
e
tric
So
il
W
a
te
r (%
)
