Exploratory modeling of saline irrigation of olive trees using artificially built contrasting soil barriers

Salt accumulation in soils is a major threat to the sustainability of irrigated land. However, the availability of fresh water for irrigation is decreasing sharply and alternative sources of water, e.g. saline waters, become more and more necessary to satisfy water requirements of crops, and more specifically of olive trees in southern Spain. Recent advances on the impact of precipitated salts on evaporation processes in porous media opened the venue to further research on the potential of artificially built contrasting soil barriers (CSB) to manage saline irrigation. In this work, the HYDRUS-2D model was used to evaluate different configurations and designs of soil textural barriers in terms of soil properties, distance to the tree trunk, width, and depth of the barrier. The model used weather data and saline irrigation applications as the top boundary condition and the dynamics of soil water potential and salt concentration at several depths (0.30, 0.60, 0.90 and 1.20 m) were evaluated. Global sensitivity analysis using the Morris method was conducted to evaluate the relevance of each of the different variables considered for the CSB design. The simulations showed a relevant effect of the CSB in changing the precipitation/dilution of salts in soil compared to its absence. Less concentration of salts was found in the root zone in the CSB simulations that in simulations without CSB in all the scenarios under study. However, higher accumulations of salts were found in the soil surface when including the CSB. The different configurations of native soil vs soil within the CSB provided different optimum configurations of the CSB depending on soil textural classes combinations. Based on the outcomes of this modeling exercise, a site-specific design depending on the soil texture can be performed and the optimum soil textural barrier chosen to optimize the potential of the system to keep the largest dilution of salts within the root zone and the highest accumulation of salts in the CSB.