Modelling of soil water and salt dynamics and prediction of salinity risks in Lezíria (Portugal) in response to different irrigation water qualities

The mitigation of soil salinization and/or sodicization phenomena are considered one of the main challenges of irrigated agriculture. In Portugal, Lezíria Grande of Vila Franca de Xira is a region with increased salinization and sodicization risks due to the influence of tidal movement on groundwater. This study aimed to evaluate soil water and salt dynamics in an irrigated Fluvisol with a crop rotation of maize and annual ryegrass and to predict irrigation-induced risks of soil salinization. We first calibrated the Hydrus-1D model for predicting soil water flow and solute transport with observed field data (from June 2017 to October 2018). Hydrus-1D successfully simulated soil water content (RMSE= 0.019 m 3 m -3 and R 2 = 0.94), the total dissolved solids (TDS) in the soil (RMSE= 0.212 g L -1 and R 2 = 0.77) and the reduction in water uptake by roots due to osmotic stress. Afterward we evaluate future risks of soil salinization performing a scenario analysis considering irrigation with different water qualities (with an electrical conductivity of the irrigation water, ECw, of 1.5, 3 and 5 dS m -1 ). We observed that when the ECw increases to 5 dS m -1 , the average solute concentration in the root zone rises to levels above the threshold tolerance of maize. Hydrus-1D successfully simulated soil water content and the total dissolved solids and is a very useful tool in planning and managing irrigation and in predicting soil salinity risks.