STABILITY BEHAVIOR OF SOIL COLLOIDAL SUSPENSIONS IN RELATION TO SEQUENTIAL REDUCTION OF SOILS .1. TURBIDITY OF SOIL COLLOIDAL SUSPENSIONS AND CHANGE INDUCED BY SUBMERGENCE OF PADDY SOILS

Flocculation and dispersion of colloidal particles of nine inorganic p addy soils were studied mainly based on turbidity measurements of the suspensions of soils which were previously incubated at 28 degrees C u nder in vitro waterlogged conditions, After 1-week of incubation, the turbidity of the soils except for 1) two soils containing larger amoun ts of sodium salts and 2) one soil containing larger amounts of Fe and Al oxides, significantly decreased, and colloidal particles flocculat ed with 1) a decrease in soil Eh and 2) an increase in electric conduc tivity (EC). During the 3- to 4-week period of waterlogging, the turbi dity of the three soils significantly increased with the 1) decrease i n EC and 2) increase in pH of the soils although the Eh remained low, Infrared (IR) absorption analysis showed that the suspended colloidal particles consisted of layer silicates from respective soil clays, Oxi dation of suspensions of waterlogged soils by air-bubbling led to an i ncrease in turbidity with the 1) increase in Eh, and 2) decrease in pH , EC, and water-soluble Fe2+ concentration. It was suggested that the stability of the soil colloidal suspensions was affected by soil reduc tion with alterations in ionic species and their concentrations at cla y surfaces and in soil solutions.