Campbell CS616 Instruction Manual download pdf (Page 47)

Appendix A. Discussion of Soil Water

Content

The water content reflectometer measures volumetric water content. Soil water

content is expressed on a gravimetric and a volumetric basis. To obtain the

independently determined volumetric water content, gravimetric water content

must first be measured. Gravimetric water content (θg) 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

m m

= =

−

Volumetric water content (θ

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

Volume is the ratio of mass to density (ρ

) which gives:

θ ρ

water

soil

water

soil

g soil

water

volume

= =

The density of water is close to 1 and often ignored.

Soil bulk density (ρ

bulk

) is used for ρ

soil

and is the ratio of soil dry mass to

sample volume.

bulk

dry

sample

volume

Another useful property, soil porosity (ε), is related to soil bulk density as

shown by the following expression.

= −1

bulk

solid

The term ρ

solid

is the density of the soil solid fraction and is approximately

2.65 g cm

-3

Notes:

A-1

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