Equation [4.4] is found in the literature (McBride 1994) and works well if the soil is not
extremely acidic or extremely alkaline.
To use the Soil Water Salinity calculation in equation [4.4], mix one part soil with one part water
and take a reading with the Hydra Probe’s tines completely submerged in the water extract.
Avoid using metal containers to take the reading and/or make the slurries because the metal may
interfere with the measurements.
In situ soil salinity is usually inferred by the in situ soil electrical conductivity in S/m (see soil
electrical conductivity section 4.5 and 5.3 below).
4.5 Soil Electrical Conductivity (Temperature corrected)
The Hydra Probe measures the in situ electrical conductivity in units of Siemens per meter. Soil
electrical conductivity is indicative of dissolved salts, dissolved solids, and fertilizers (McBride
1994). It may also be indicative of very high pH conditions. The soil electrical conductivity is
calculated from the temperature corrected imaginary dielectric permittivity [
E
i(tc)
] by the
theoretical expression:
EC = 2
π
f
ε
0
E
i(TC)
[4.5]
Where EC is the electrical conductivity, f is the frequency (50 MHz for the Hydra Probe) and
ε
0
is the dielectric permittivity of a vacuum. For more information on soil electrical conductivity
considerations, see soil electrical conductivity section below 5.3.
As the temperature increases, the molecular vibration increases (Levine, 1993). The molecular
vibration has a complex affect on both the orientation polarization and on the imaginary
dielectric permitivities. The temperature corrections are based on the small incremental changes
of
Ei
and
Er
with temperature.
30
