Capacities of Clay Fraction of a Latosol to Retain Cations and Anions as Inferred from the Wien Effect in Soil Suspensions

摘要

Suspensions of a latosol with a clay concentration of 30 g kg-1 were prepared from electrodialyzed clay fractions, less than 2 μm in diameter, five nitrate solutions with a concentration of 1 × 10-4/z mol L-1,where z is the valence, and five sodium salt solutions with a concentration of 3.3 × 10-5/z mol L-1. The direct current (DC) electrical conductivities (ECs) of the colloidal suspensions were measured at a constant temperature of 25 ℃, using a newly established method of measuring the Wien effect in soil suspensions at field strengths ranging from 13.5 to 150 kV cm-1, to determine their electrical conductivity-field strength relationships and to infer the order of the bonding strength (retaining force) between soil particles and various ions. The measurements with the latosol suspensions in NaNO3, KNO3, Ca(NO3)2, Mg(NO3)2 and Zn(NO3)2 solutions resulted in increments of the suspension ECs, △ECs, of 7.9, 5.0, 7.1, 7.0 and 5.8μS cm-1,respectively, when the applied field strength increased from 14.5 to 142 kV cm-1. As for the suspensions in NaNO3, NaCl, Na2SO4, Na3PO4 and Na3AsO4 solutions, the △ECs were 6.2, 5.3, 4.1, 4.0 and 3.7μS cm-1,respectively, when the applied field strength increased from 13.5 to 90 kV cm-1. Thus, it can be deduced that the retaining forces of the clay fraction of the latosol for the cations were in the descending order K+ ＞Zn2+ ＞ Mg2+ ≥ Ca2+ ＞ Na+, and for the anions in the descending order H2AsO-4 ＞ H2PO-4 ≥ SO42- ＞ Gl- ＞ NO-3.