Reserve of potassium in soils of the West Siberian plain

The study of potassium reserves in major soil types of the West Siberian Plain revealed that the quantity is mainly conditioned by structural and chemical features of their mineral foundation - primary and potassium containing clay minerals. These results indicate that the weathering of primary minerals, including potassium containing (feldspars and micas), in boreal and subboreal soil formation is weak. This leads to a very slow release of potassium from primary minerals. In this regard, even in soils differing very much in recruitment, orientation and intensity of elementary soil-forming processes, such as chernozem soils and soddy-podzolic, the potential reserves ofpotassium are significant (79-54% of total). It is established that the magnitude and ratio of reserves were determined by different quality parent rock (loess-like loams, alluvial-lacustrine and alluvial deposits) to a large extent. Reserves of potassium are maximal in those soils that are formed on loess-like loams, clay fraction and in mineralogical composition dominated by hydromica. Having considered the study of soils, the greatest quantities of reserves of potassium, both in absolute and in relative value (% of total), are typical of chernozem soil, they make up almost half of the total stock of potassium. A sizable concentration of gross potassium in dispersed fractions mineral bases of soil creates preconditions for an easier exit of potassium from non exchange positions of the crystal lattice of minerals in the form of exchange, it provides an increased geochemical activity in the processes of weathering and soil formation. Therefore, the bulk part of gross potassium is not available for ion exchange, because of being situated in the tough positions of crystal lattices of minerals. That relatively small amount of potassium, which is able to hydrolyze or exchange for other cations, is mainly concentrated in dispersed fractions of soils, primarily in the clay fraction. For this reason, the distribution of direct reserves, represented by the most mobile forms of potassium, is largely determined by distribution of the clayfraction in the soil profile. In this regard, we can assume that the distribution of direct reserves in profile depends on the degree manifestations of the eluvial-illuvial processes. The exception is chernozem soils in which there is an increase in direct reserves of potassium in the upper humus-accumulative horizons.

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