For predicting ionic strength from specific conductance, a saline soil, an alkali soil, and a normal typical rice soil amended with different levels of salt (NaCl) and alkali (NAHCO3) were kept submerged with deionized water for 12 wk. Despite wide variations in the ionic composition and ionic strength of the soil solutions, a close relationship (r = 0.98) was found between the actual ionic strength (total concentrations corrected for the presence of ion pairs) and specific conductance of equilibrium soil solutions collected by gravity every other week up to 12 wk. The ionic strength (moles/L) was approximately 11.62 times the specific conductance (mhos/cm, 25°C).
Higher values were found for ionic strengths measured from stoichiometric concentrations compared with values of actual ionic strengths measured after incorporating the corrections due to the presence of ion pairs. The variations were more in NAHCO3-amended soil (25 to 51 %) than when the same soil was amended with NaCl (3 to 32%). Very good agreement was found between the ionic activities calculated from actual ionic strength and ionic strength predicted from specific conductance.