Pathway 2 is the pathway that is attributed to the electrical conductivity of the soil water.
Increasing the dissolved salts will increase the conductivity of pathway 2; however, like pathway
1, increases in the soil water content will increase the size of the pathway thus increasing the
electrical conductivity. That is to say, that there are two factors influencing the electrical
conductivity of pathway 2, namely the dissolved salt concentration and the size of the pathway
attributed to the amount of water in the soil.
Figure 5.2 3 Pathways of electric conductivity in soil matrix. 1 water to solid, 2 soil moisture, 3 solid. Taken from Corwin
et al. (2003
).
Pathway 3 is the electrical conductivity of the soil particles. Like the other pathways, the
contribution of pathway 3 in influenced by a number of factors that include bulk density, soil
type, oxidation/reduction reactions and translocation of ions.
The electric conductivity measurements provided by the Hydra Probe is the electrical
conductivity of the dynamic soil matrix as a whole which is the sum of the electrical
conductivities from all of the different pathways. No in situ soil sensor can distinguish the
difference between the different pathways nor can any conventional in situ soil sensor
distinguish the difference between sodium chloride and any other number of solutes that all have
an influence the electrical conductivity of the soil water matrix.
5.3.2 Solution Chemistry
Salinity refers to the presence of dissolved inorganic ions such as Mg
+
, Ca
++
, K
+
, Na
+
, Cl
-
, SO
2
4
-
,
HCO
3
-
and CO
3
2-
in the aqueous soil matrix (Hamed 2003) . The salinity is quantified as the
total concentration of soluble salts and is expressed in terms of electrical conductivity. There
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