EFFECT OF SODICITY ON ROOT WATER UPTAKE: ANALYSIS AND PARAMETER ESTIMATION

Abstract

The increasing prevalence of soil salinity presents a significant challenge to sustainable agricultural practices, necessitating advanced tools for understanding and managing soil–plant– water interactions under saline irrigation conditions. Notably, in the present study, although soil salinity was directly monitored through electrical conductivity (EC) measurements, the applied saline irrigation treatments involved sodium chloride (NaCl) as the primary salt source. Prolonged use of such sodium-rich water can result in the gradual accumulation of sodium ions in the soil relative to other cations, potentially leading to sodicity. The experimental context reflects conditions conducive to sodicity development, particularly in relation to its effects on root water uptake and soil moisture dynamics. This study presents a novel, integrated modeling framework that combines experimental investigation, physically-based simulation, and inverse optimization to characterize soil moisture dynamics, root water uptake (RWU) and estimation of RWU parameter β under varying salinity regimes. A forward model, based on Richards' equation, was developed to simulate unsaturated soil moisture flow across the root-zone, incorporating RWU as a depth-dependent sink term. Complementing this, an inverse modeling approach employing a Genetic Algorithm (GA) was formulated to estimate the non-linear RWU parameter β, which governs the distribution of root water uptake and is highly sensitive to salinity-induced stress. The linked model was tested and validated using synthetically generated and field-measured soil moisture datasets. The model showed high predictive accuracy, with performance indices exceeding R² > 0.94 and NSE > 0.90 at lower salinity levels, establishing its robustness and reliability for soil water modeling in saltaffected soils. Field results demonstrated that increasing salinity (0.5–25 dS/m) induced significant changes in soil hydraulic properties, particularly reduced moisture retention and hydraulic conductivity due to osmotic stress and clay particle dispersion. These changes increased gravitational drainage in sandy loam soils and limited water availability in the root zone.