Flocculation and dispersion of colloidal particles of nine inorganic paddy soils were studied mainly based on turbidity measurements of the suspensions of soils which were prev:iously incubated at 28℃ under in, vitro waterlogged conditions. After l-week of incubation, the turbidity of the soils except for l) two soils containing larger amounts of sodium salts and 2) one soil containing larger amounts of Fe and Al oxides, significantly decreased, and colloidal particles flocculated with l) a decrease in soil Eh and 2) an increase in electric conductiv-ity (EC). During the 3-t0 4-week period of waterlogging, the turbidity of the three soils significantly increased with the l) decrease in 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 sili-cates from respective soil clays. Oxidation of suspensions of waterlogged soils by air-bubbling led to an increase in turbidity with the l) 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 reduction with alterations in ionic species and their concentrations at clay surfaces and in soil solutions.

Flocculation and dispersion of clay particles in in vitro waterlogged soils at 8, 18, 28, and 380C were investigated with some indications of soil reduction. Above 280C, waterlogging for l-week in the six soils caused a significant decrease in the turbidity of their colloidal suspensions. The decrease in the turbidity, i.e., the flocculation of the clay particles, was evident with (i) a decrease of redox potential (Eh) of the soils, (ii) an increase in the values of electric conductivity (EC) and water-soluble cations (WSCs: Fe2+, Ca2+, Mg2+, NH4+ etc.) in the solutions, and (iii) an increase in the amounts of volatile fatty acids (VFAs: acetic, propionic, and n,-butyric acids) in the soils. Soilincutoation at 8℃ retarded the decrease in Eh, the increase in the values of EC, WSCs, and VFAs, and the decrease in the turbidity. At 380C, samples of four soils water-logged for 4 weeks showed a low turbidity with a low Eh, and high values of EC, WSCs, and VFAs. The samples of other two soils, however, exhibited a significant increase in the turbidity, viz. the dispersion of clay particles, with an increase in pH and decrease in the values of EC, WSCs, and VFAs under low Eh. The observed flocculation and dispersion of clay particles in the water-logged soils were discussed in relation to chemical changes under sequential reduction of soils, particularly change in ionic strength of soil solutions largely due to the (i) dissolution and precipitation reactions related to Fe2+ and Fe(III) and (ii) cation exchange reactions between Fe2+ and other exchangeable cations on clay surfaces.

The electrokinetic behavior of colloidal particles in three waterlogged soils at 38℃ was investigated with reference to the stability changes of soil colloidal suspensions under reductive conditions. The dispersed clay particles of the three sons exhibited a negative zeta (ζ) potential. The absolute value of the ζ-potential, |-ζ| of these soils in the earlier period of waterlogging decreased, which caused the flocculation of clay particles. The concentrations of divalent cations, i.e., Fe2+ and Ca2+ in the soil solutions were estimated to be higher than their critical flocculation concentrations (CFCs) on the basis of the observed CFCs of Fe2+ and Ca2+ for the clay suspension of halloysite as a reference. With the progression of the reduction process, clay particles of one soil still exhibited a low |-ζ| and fiocculated. The concentrations of Fe2+ and Ca2+ in the soil solutions were estimated to be higher than their CFCs, respectively. The clay particles of two sandy soils, however, showed an increase in |-ζ| due to the increase in pH and dispersed. The concentrations of Fe2+ and Ca2+ in the soil solutions were estimated to be lower than their CFCs, respectively. The stabil-ity changes of the soil colloidal suspensions by these divalent cations under sequential soil-reduction can be explained by the alteration of the Stern potential (-ψs), which determines the repulsion energy related to the potential energy of interaction'between two particles. The apparent decrease in the Ca2+ concentration of the soil solutions in the later period of waterlogging was explained largely by the re-adsorption of water-soluble Caz+ on the exchange sites of soil clays with the decrease in the Fe2+ concentration in the soil solution.

The cause of the decrease in the Fe2+ concentration of the soil solution in the later period of soil waterlogging was investigated. After 7-d incubation of the soil solutions separated from previously waterlogged soils (PWdS), a greyish precipitate (PPT) was observed in the soil solutions. The color of the PPT became reddish brown after separation from the solutions and freeze-drying. The PPT observed in 14-d-PWdS contained 352.6 g Fe kg-1, 62.5g C kg-1, 22.6g P kg-1, 11.3g Si kg-l, 9.9 g N kg-1, 0.7 g AI kg-1, and a trace amount of Mn. However, Ca, Mg, K, and Na could not be detected. It was concluded that the separated PPT was dominated by amorphous ferric hydroxide based on the chemical analysis, broad IR absorption band at 585 cm-q, and exothermic peak at 301℃. The data of chemical analysis and the characteristic IR bands of the PPT suggested that organic substances and presumably alununosilicate anion were adsorbed onto the freshly-formed ferric hydroxide. The dominant phase of the greyish PPT in the reductive soil solution was considered to be ferrous PPT and was assumed to consist mainly of carbonate and/or hydroxide, and conconutantly of phosphate. The formation of the ferrous PPT in the soil solution in the later period of soil waterlogging was considered to (i) cause the decrease of concentration of Fe2+ ion and of other divalent cations such as Ca2+ due to the re-adsorption of Ca2+ on soil clays through the cation exchange reaction with Fe2+ ion, and consequently (ii) enhance the dispersion of the soil colloidal suspension.

以世界卫生组织和联合国粮农组织推荐的营养素供给量标准以及我国建议的营养素供给量标准为基准，以婴儿为对象．采用混合惩罚函数法，借助计算机技术．对婴儿经常食用的营养米粉进行了优化设计．获得了最佳配方．计算过程表明，该方飞可行结果可靠，该方法亦可用于各类营养保健食品的最忧设计。