The electrical conductivities (ECs) of suspensions containing 25 and 30 g kg-1 solids prepared from theelectrodialyzed clay fraction (＜ 2 μm in diameter) of latosol, yellow-brown soil, and black soil, dispersed invarious nitrate solutions having concentrations of 1 × 10-4/z mol L-1, where z is the valence, and in distilledwater, were measured at field strengths ranging from 14 kV cm-1 to 210 kV cm-1. On the basis of analysesof the charge density and exchangeable ion composition on the surfaces of soil particles in the suspensions,and of the characters of the EC-field strength curves of the various suspensions, it was inferred that theincrement of EC (△EC) and/or relative electrical conductivity (REC) can indicate the bonding strengthbetween cations and soil particles. The bonding strengths of various cations with the soils diminished in theorder: K+ ＞ Zn2+ ＞ Mg2+ ＝ Ca2+ ＞ Na+ for latosol, Ca2+ ＞ Zn2+ ＞ Mg2+ ＝ K+ ＞ Na+ for yellow-brownsoil, and Zn2+ ＞Ca2+ ＞ Mg2+ ＞ K+ ＞ Na+ for black soil.
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