Specific cation effects on soil water infiltration and soil aggregate stability-Comparison study on variably and permanently charged soils

Improving soil hydraulic properties is one of important purposes of soil tillage. Recent studies on permanently charged soil have shown specific cation effect on soil water infiltration. In this study, specific cation effects on soil water infiltration and soil aggregate stability of both variably and permanently charged soils were comparatively examined. It was found that, specific cation effects on soil water infiltration and soil aggregate stability are quite different for permanently and variably charged soils. For the permanently charged soil, the sequence of specific cation effects on soil water infiltration was Li+ << K+ < Cs+, which was in accordance with the cation polarizability sequence of Li+ (0.029 & Aring;(3)) << K+ (0.88 & Aring;(3)) < Cs+ (2.56 & Aring;(3)); but for the variably charged soil, the sequence changed to Cs+ > Li+ > K+. Moreover, the sequence of cation concentration effect on permanently charged soil water infiltration rate (SWIR) was SWIR (0.0001 mol/L) < SWIR (0.001 mol/L) < SWIR (0.01 mol/L) < SWIR (0.1 mol/L) whereas that for the variably charged soil changed to SWIR (0.1 mol/L) < SWIR (0.0001 mol/L) approximate to SWIR (0.01 mol/L) < SWIR (0.001 mol/L). The differences of specific cation and cation concentration effects on soil water infiltration for the two soils came from those on soil aggregate stability. For permanently charged soils, soil electric field determined soil aggregate stability. However, for variably charged soils, besides soil electric field, osmotic pressure, positively charged colloids and surface reaction of metal cation may possibly play critical role in soil aggregate stability.