Thermodynamic Concept of the Physical Quality of Soils

Abstract—: Soil physical quality is largely determined by interphase interactions at variable moisture content. This phenomenon allows us to consider the water retention curves as functions of the water content and its thermodynamic potentials as indicators of the soil physical quality and its dynamics. Diagrams of the physical quality of soils represented by water retention curves with areas of dominance of certain physical mechanisms and forces responsible for the interaction of physical phases were obtained for Eurasian soils included in the database (more than 400 samples) and grouped by five FAO/USDA textural classes. Original instrumental methods using centrifugal, gravitational, and temperature physical fields for water removal made it possible for the first time to obtain the thermodynamic characteristics of water retention in the entire range of soil water potential from 0 to 1 million J/kg. The main fundamental result is a physically based methodology for diagnosing the limiting (critical) values of the soil water content and its thermodynamic potentials, which divide the areas of dominance of various forms of soil moisture, physical forces, and mechanisms of interphase interactions on the diagrams of the physical quality of soils. The significance of non-capillary surface forces and mechanisms controlling water retention and physical quality of soils is shown. The results of determination of the optimal ranges of water content for Eurasian soils of different textures and geneses in connection with their soil-ecological and technological functions and services specify practical significance of this study. © 2021, Pleiades Publishing, Ltd.