Формы железа в почвах естественных ландшафтов Верхнего Приангарья

Abstract

Iron occupies one of the leading places among other elements in terms of content in soils and, having the ability to change valence and properties, diagnoses the typical and sub-type features of many soils, and most importantly, the direction of the soil formation process. Gypsum-bearing soils are formed on the deluvium of the Cambrian sedimentary rocks, in conditions of a hilly-flat relief, caused by water-erosion processes that have created surface dissections by numerous valleys and hollows. Gypsum-bearing soils are located on the elevated parts of the relief of the first floodplain river terraces, as well as in the lower parts of the relief and in river valleys. The climatic conditions of soil formation can be classified as arid. The amount of precipitation in the study area is much less than evaporation. The content, composition, and ratios of various forms of iron and the profile distribution of soils formed on gypsum-bearing red-colored Cambrian sedimentary rocks of the Upper Angara region were studied. For this, the composition of the soil cover in the landscape under study and the soilforming processes taking place in the soils were determined: brown arid calcareous soils are formed in the southern exposure of the slopes; in the northern exposure - chernozems, chernozems and meadow soils. An important morphoanalytical feature of soils is the presence of significant amounts of gypsum and carbonates in the profile. The leading soil-forming process in the landscape is the process of humus accumulation, which is clearly manifested in soils on the slopes of the left bank of the Zalari River. The group composition of iron was determined by analytical methods. The ratios of various iron groups, which are characteristic of landscape soils, and the regularities of the distribution of groups in soil profiles have been established. It was revealed that the degree of ferruginization of the soils of the left bank is in moderately low and very low limits; the degree of ferruginization of soils on the right bank is moderately low. The iron groups in the profiles are poorly differentiated. Silicate iron prevails over non-silicate. The significant predominance of silicate forms of iron over non-silicate forms indicates a low intensity and weak development of weathering processes. In all soils of the landscape, only traces of amorphous iron are determined. The mobility of iron in the soils of the landscape is practically absent, due to the insufficient amount of the amorphous form. In all landscape soils, the degree of oxidogenesis is very low. Crystallization of free iron oxides and hydroxides does not occur due to their absence.