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The results from measurement of the absolute volumetric soil water percent (VSW%) using the
MP406 when compared with TDR technology are given in Figure 2. This result is typical of the results
obtained from comparative testing of the MP406 compared to TDR technology for a wide range
of agricultural soils.
Figure 2. The MP406 in comparison to TDR Measurement of Absolute Volumetric Soil Water Percent as a
Standard.
Definitions
Gravimetric Soil Water Content is defined as:
θG =
Mw
Ms
Where Mw is the mass of water in the soil sample and Ms is the total mass of the dry soil sample.
Volumetric Soil Moisture Content is defined as:
θV = θ
G * Ps
Where Ps is the bulk density of the soil sample (
=
Ms
Vs
)
Where Ms is the total mass of the dry sample and Vs is the total volume of the dry soil sample.
Volumetric Soil Water Percent (VSW%)
VSW% = θv * 100
The VSW% typically varies in the field from 2
–
5% for sandy soils at permanent wilting point to 45
–
55% for clay soils at saturation.
0 5 10 15 20 25 30 35 40
TDR Volumetric Soil Water (%)
TDR
A Comparison of the MP406 and TDR
as a Standard
40
35
30
25
20
15
10
Vol
um
e
tric
So
il
W
a
te
r (%
)
