An approximate indication of the concentration of soluble salts in soil can be obtained by calculation from EC1:5. Assumptions include (a) that Cl– dominate the soluble anions in the soil, which is not always the case, and (b) the gram-equivalent weight of the soluble salts is around 51 or greater (Jackson 1958). In addition, the presence of gypsum can upset the relationship with EC1:5, as can the different ionic conductivities of particular soluble salts and the influence of soil surface properties.
Rayment and Higginson (1992) suggested the approximate percentage of TSS could be obtained by multiplying the EC1:5 value by 0.34, which derives from the relationships reported by Jackson (1958) and US Salinity Laboratory Staff (1954), with allowance for a 1:5 soil/water ratio. Earlier, Piper (1944) used a factor of 0.375, derived from actual correlations of specific conductivities (at 20°C) with the amounts of soluble salts determined gravimetrically in a large number of Australian soils.
While the value 0.336 is used in the following calculation, it is noteworthy that more refined estimates are available for particular Australian locations. For example, Williams and Semple (2001) reported the following relationship for saline seepage scalds from Central Western New South Wales, where measured soil salt concentrations ranged from 0.19–1.8%. Specifically, TSS (%) = 0.165 + 0.225*EC1:5, where EC1:5 has units of dS/m. This relationship gives higher values (relative to the calculation provided below) at EC1:5 values around 0.15 dS/m and similar values in the EC1:5 range 0.9–2.0 dS/m.
Soil soluble salts (% air-dry soil) = [EC1:5 (dS/m) × 0.336]
Report approximate soluble salts (% of air-dry soil).