ESTIMATING THE ELECTRICAL-CONDUCTIVITY OF SATURATED PASTE EXTRACTS FROM 1-5 SOIL, WATER SUSPENSIONS AND TEXTURE

This paper presents a method of estimating the electrical conductivity (EC) of a saturated paste extract (ECe) from the EC of a 1 to 5 soil/water suspension (EC1:5) and an estimate of soil texture. The method has application in soil testing laboratories which routinely determine EC1:5 but not ECe. The method of preparing the saturated paste by capillary wetting is also compared with the standard method of hand mixing. The coefficient (f) relating ECe to EC1:5, i.e. ECe = fEC1:5 was found to be related to the water content of the saturated paste (theta(SP) kg/kg) by f = 2.46+3.03/theta(SP). The relationship between theta(SP) and texture, determined by hand working, indicates that the uncertainty associated with use of this relationship could be significant in sandy soils. Wetting the soil by capillarity rather than by hand mixing resulted in a lower saturation percentage and higher ECe but dissolved the same amount of salts. The capillary wetting method is preferred as it-greatly reduces labour time.