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Technical Reference
Definitions
Volumetric Soil Moisture Content
𝜃
𝑉
=
𝑉
𝑊
𝑉
𝑆
where
V
w
is the volume of water contained in the sample
V
s
is the total volume of the soil sample.
The preferred units for this ratio are m
3
.m
-3
, though %vol is
frequently used.
Soil Moisture Content varies from approx. 0.02 m
3
.m
-3
for sandy
soils at the permanent wilting point, through approx. 0.4 m
3
.m
-
3
for clay soils at their field capacity, up to values as high as
0.85 m
3
.m
-3
in saturated peat soils.
Gravimetric Soil Moisture Content
where
M
w
is the mass of water in the sample, and
M
S
is the total mass of the
dry
sample.
To convert from volumetric to gravimetric water content, use the
equation
𝜃
𝐺
= 𝜃
𝑉
×
𝜌
𝑊
𝜌
𝑆
where
is the density of water (= 1g.cm
-3
), and
is the bulk density of the sample
𝑀
𝑆
𝑉
𝑆
.
𝜽
𝑮
=
𝑴
𝑾
𝑴
𝑺
g.g
-1
