Method for obtaining water retention properties of soils by fractions of their granulometric composition

This paper presents the method of obtaining water retention properties of soils (water retention curve (WRC) and water conductivity functions) is presented. These properties, or functions, allow describing the vertical movement of water in unsaturated soils as one of the components of the water balance expenditure item. They are widely used during the substantiation of water reclamations and during modelling of water transfer in the soil. The method is based on laboratory studies of soil samples taken in the field for granulometric composition. Currently, the results of laboratory analyses in Ukraine are obtained according to the Kachynskyi method with two components, the percentage of clay and sand. They are transformed graphically, using integral (cumulative) curves, into data corresponding to the international classification – with three components: the content of sand, dust, clay. The world community of soil scientists uses the latter factional distribution. Therefore, using data on the content of sand, dust, clay, thanks to the open access computer program “Rosetta” USDA (United States Department of Agriculture), water retention properties are found in the form of water constants (total water content, minimum hygroscopic water content, filtering coefficient), coefficients of the equations of Van Genuchten’s mathematical model. This paper provides examples of calculating the water retention properties of soils using the method of dark chestnut soils and ordinary chernozems. The advantages of the proposed method include the low complexity of experimental studies, the availability of analyses and the presence of many experimental studies of the granulometric composition of soils, including in literature sources. As a development of the research area, the author showed the application of the obtained dependencies for modelling water transfer during water reclamation (irrigation in irrigation control systems). As for future research areas, the publication suggests comparing the accuracy of obtaining water retention properties of soils according to various methods, as well as obtaining an important water constant – the minimum soil water capacity (MSWC)