【摘要】 <正> 氧化铁虽是土壤粘粒中的次要矿质成分,但它具有较高的活性,对土壤性质有重要的影响。作为胶结物质之一,氧化铁的形态及其含量,对土壤团聚体的形成,亦起重要作用。某些水稻土中细孔隙增多,土块趋向紧实等问题,似乎与土壤中氧化铁存在形态有关。更多还原

【Abstract】 The transformation of iron oxides in soil in the course of submergence and drainage, and its influence on the soil structure is discussed on the basis of incubation experiment. The yellow brown earth, the red earth and the laterite were added with various amounts of dried milk vetch powder, and incubated under the submerged condition with and without percolation. After 8 months, the incubated samples were dehydrated at various intensity and samples without dehydration were used for check （Table 2）.The eomplexed iron and amorphous iron oxides contents of incubated samples were influenced obviously by the addition of organic matter, submergence and dehydration, but the influence of dehydrated intensity on the complexed iron content was insignificant （Table 3, 4 & 5）.The amounts of OH^- ions desorbed by replacement of F^- were decreased in order of laterite>red earth>yellow brown earth. Between the amounts of OH^- ion and crystal-line iron oxides content （Fe_a-Fe_o） there is positive correlation with a high significance （r=0.940, n=24）. It appears that the essence of activation of iron oxides includs the reaction of hydroxy group （-OH） on the surface of iron oxides converted into aquo group （-OH₂）.Shrinkage rate of soil clod calculated by bulk density after air-drying and ovendrying ranged from 0% to 43% （by volume） and it depended markedly on the amorphous iron contents （Fig. 1）.For incubated samples of yellow brown earth and red earth, the shrinkage rates of soil clod correlated well with the apparent destruction rates （r=0.60, n=20）. It indieates that shrinkage caused by excess amorphous iron oxides content is not favorable to the formation of waterstable aggregate. This assumption seems to be supported by the phenomenon that there is a significant positive correlation between the degree of activity of free iron oxides （represented by x） and the apparent destruction rate of microaggregate （>0.25mm, represented by y, then y=13.5（?）, r=0.68, n=35）.Based on the facts mentioned above, it is considered that it is necessary to control the conditions of activation of iron oxides （e.g. prevention the soil from long term submergence） and to strengthen the conditions of ageing of iron oxides （e.g. drainage） for the paddy soils with a highly dispersity in order to facilitate the formation of good structure of the paddy soil.更多还原