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A-1

Appendix A. Definition of Water

Content Terms

A.1 Definition of Water Content Terms

Soil water content is expressed on a gravimetric or volumetric basis.

Gravimetric water content (

) is the mass of water per mass of dry soil. It is

measured by weighing a soil sample (m

wet

), drying the sample to remove the

water, then weighing the dried soil (m

dry

water

soil

wet dry

dry

−

Volumetric water content (

) is the volume of liquid water per volume of soil.

Volume is the ratio of mass to density (

) which gives

θρ

water

soil

water

soil

gsoil

water

volume

===

∗

Soil bulk density (

bulk

) is used for

soil

and is the ratio of soil dry mass to

sample volume. The density of water,

water

is close to 1 and is often ignored.

Another useful property, soil porosity, (

) is related to soil bulk density as

shown by the following expression.

=−1

bulk

solid

The term

solid

is the density of the soil solid fraction and is well approximated

by the value 2.6 g cm

-3

A simple data set is given here as an example. A sample of known volume was

weighed before and after oven drying at 105°C for 24 hours.

wet

94 g

dry

78 g

sample volume 60 cm

water

soil

−

94 78

0205

g g

g g.

bulk

dry

volume

===

−

g cm.

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