While the EC of a 1:5 soil/water extract (EC1:5 by Method 3A1) uses a convenient soil/extraction ratio for large-throughput soil testing laboratories, it suffers from being much more dilute than occurs naturally. This method for EC/SE, although tedious, better correlates with plant response to soil salinity (Salcon 1997). Several researches have derived regression equations for converting EC1:5 by Method 3A1 to ECSE, with examples given in Table 14.2.
Table 14.2. Relationships for Australian soils for predicting EC/SE from measured values of EC1:5 in units of dS/m.
Relationship |
Reference |
6.4 × EC1:5 |
|
6.5 × EC1:5 |
|
6.44 × EC1:5 – 0.102 |
|
6.08 × EC1:5 – 0.937 |
|
6.29 × EC1:5 – 0.27 |
For the direct determination of ECSE, proceed as for Method 3A1, using a suitably sized conductivity cell to match the volume of SE available.
Report EC/SE (dS/m) at 25°C, together with method codes for preparing and extracting the SE: e.g. 2C1/14A3/14B1.