Modeling Regimes of the Appearance of a “Salt Fringe” during Drip Irrigation

Abstract

The process of fertigation, which consists in providing plants with minerals contained in irrigation water, is widespread, despite a number of negative effects. The overwhelming majority of studies are aimed at studying the spatial distribution of salts during irrigation; in interirrigation periods and at the end of the irrigation season, the processes of salt migration and concentration in soil under conditions of reduced moisture (drying conditions) are hardly covered by studies. The purpose of this research is to model the drying regimes of light and dark gray forest soils in the Chuvash Republic (Russia) after fertigation. The studies were carried out from 2020 to 2023. Since the state of soil prior to drip irrigation significantly influences the drying process, the paper considers situations that make it possible to reduce the negative effects of this process. Modeling of the movement of soil moisture during and after the end of drip irrigation makes it possible to identify different cases of the formation of a salt “fringe.” The identification of such regimes makes it possible to preliminarily prepare the soil for fertigation, taking into account the features of the initial distribution of moisture. This paper shows that salts can concentrate mainly in areas with a sharp moisture gradient, i.e., at the boundaries between dry and moist soil, during drying. This is explained by the fact that soil moisture enters an area with an already increased salt concentration due to the resulting pressure drop. The developed model makes it possible to analyze the effect of salt fringe formation according to the set initial and boundary conditions in the form of moisture gradients, porosity, specific soil surface, irrigation intensity and duration, and salt concentration.