Surface-chemical study on effects of wet and dry conditions to soil colloids.

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The abnormal hardening of topsoil after puddlig so called "itsuki" has been serious problem in some rotational paddy fields of middle- to coarse-textured soils. This study was carried out for the purpose of clarifying the itsuki phenomenon by application of surface chemistry. The results is summarized as follows :Total contents of iron oxides decreased, but amorphous iron oxides which affect closely to pH-dependent charge of soil colloides increased relatively, in the re-wetted soils after a strongly reductive procedure of the air-dried ones which were collected from continuous cropping paddy fields. Organic materials in these soils were also decreased by the reductive procedure, and it was suggested that this losted organic materials combined with reached iron oxides.Charge characteristics of soil colloids were estimated by applying several species of clay minerals. Montmorillonite had high negative charge constantly in the wide range of pH values, and negative charge of kaolin minera … More ls were pH-independent but it was low. On the other hand, positive and negative charge of allophane were both extremely pH-dependent, pont of zero net charge was observed at pH 5.5.A casium ion adsorption methods which had been presented in this study was very effective for the investigations on characteristics of cation exchange capacity and point of zero net charge in soil colloids. This new method was able to prevent contaminations during the measurement procedures compared with the previous methods by using sodium or potassium ions.Determination of particle-size distribution of soils by a laser scattering method was compared with the customary sedimentation method, the high correlation was established between them. This method was useful especially for the observation of continuous distribution of particle size in same clay or soil sample.An electrokinetic sonic amplitude method should be effective for the estimation of ζ potential of clay minerals and soil colloids because of probability to measure rapidly it in wide rage of pH value. Less