Simulation of the modes of appearance of "salt frame" 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 the interirrigation periods and at the end of the irrigation season, the processes of migration and salt concentration in the soil with a decrease in moisture (drying) are practically not considered. The purpose of this work is to simulate the modes of drying of light and dark gray forest soils of the Chuvash Republic (Russia) after fertigation. The studies were carried out in the period from 2020 to 2023. Since the state of the soil before the start of drip irrigation significantly affects the drying process, the paper considers situations that allow it to be influenced in terms of reducing negative effects. Modeling the movement of soil moisture both during and after the end of drip irrigation makes it possible to identify both cases in which the formation of a salt «border» does not occur or the effect is least pronounced, and those in which the formation of areas with a high salt concentration takes place with high intensity. The identification of such regimes allows, taking into account the characteristics of the initial distribution of moisture, to carry out preliminary preparation of the soil for fertigation. The paper shows that during drying, salts can mainly concentrate in areas with a sharp moisture gradient, that is, at the boundaries between dry and moist soil. This is due to the fact that soil moisture, due to the resulting pressure drop, enters an area with an already increased salt concentration. The developed model makes it possible to analyze the effect of salt fringe formation according to given initial and boundary conditions in the form of moisture gradients, porosity, specific soil surface, irrigation intensity and duration, and salt concentration.