Physical properties of soils as a component of the characteristics of forest-growing conditions in the steppe zone of Ukraine

Steppe zone of Ukraine is characterized by a significant predominance of artificial forest plantations over natural forests, which is associated with the peculiarities of the steppe environment. Since forests in the steppe play a number of important ecological functions, in particular, protect the soil from erosion, it becomes necessary to conserve and create new forest plantations. To solve this problem successfully, a practical and theoretical scientific justification is needed, which was developed by A. L. Belgard, creating a typology of artificial steppe zone forests. One of the main components of the developed typology is the type of forest-growing conditions, characterized by presence of a floodplain, fertility and humidification against a specific geographical area. A. L. Belgard (1971) noted that there is a significant difference between the floodplain and non-floodplain habitats. Floodplain habitats, even in the case of short floods, differ from the outland by the presence of alluvial deposits, relatively shallow groundwater occurrence, abrupt changes in seasonal moistening, and significant development of salinization processes. Also, scientists emphasize the need to distinguish soil formations depending on their mechanical or granulometric composition, which predetermines the specific physical properties of soils and the chemical processes that occur in them. A. L. Belgard (1971) divided all the soils of the steppe zone according to the granulometric composition into three groups: sandy, sandy loamy and loamy. This division is based on the binary classification of soils according to the granulometric composition developed by N. A. Kachinskiy (1958), which provides for the separation of classes according to the content of physical clay and physical sand. In the future, it may be necessary to more detailed this graduation, given the fact that the world is widely used three-member classification, developed in the USA. In this classification, soil groups are distinguished by the ratio of sand, dust and clay (Medvedev, Laktionova, 2011). Considering the fertility of soils as a gradation of forest-steppe conditions of the steppe zone, A. L. Belgard (1971) primarily pays attention to the presence or absence of salinization processes. At the same time, the scientist notes that the granulometric composition of the soil of one or another type of forest growing conditions, taking into account salinity, gives an idea primarily of the chemical fertility of the habitat. At the same time, it must be taken into account that the complex of physical properties of soils is also important, and in some cases crucial for the normal existence and reproduction of forest biogeocenosis in steppe conditions. Humidification in the steppe zone of Ukraine is an important limiting factor that determines the possibility of growing forest stands. As it was emphasized by A. L. Belgard (1971), even minor changes in hydration lead to significant changes in the forest-growing effect. The scientist noted that within the steppe zone growths can be represented by the following gradations: very dry, dry, dryish, fresh, damp, moist and wet. L. P. Traveleyev (1976) detailed the moisture gradation and proposed quantitative indicators – local moisture coefficients. The scientist noted that in its origin and the formation of moistening of soils, it could be atmospheric, soil, atmospheric-soil and transit, each of which has its own characteristics. As it is known, soils are formed as a result of interaction of five factors of soil formation-climate, plant and animal organisms, rocks, relief and time (Dokuchaev, 1952). It is the result of the interaction of all factors of soil formation and their changes in time that are the patterns of spatial distribution of soils (Dobrovolsky, Urusevskaia, 2004). Moreover, each soil zone or subzone is characterized by a specific set of soil formation factors, due to which the soils of a certain territory acquire their own special properties. Very often, when determining the complex of soil properties with a certain probability, one can say in which soil zone or subzone they were formed. Physical properties are no exception to this statement. The most informative physical properties of soils from the point of view of the characteristics of the forest-growing conditions in the steppe zone of Ukraine are the granulometric composition, structural state, the density of addition, the density of the solid phase, wilting moisture, water capacity, water permeability, and electrical conductivity.