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Secondary salinization has long been reported in the Roxo irrigation district (RID), southern Portugal, due to the use of saline-prone irrigation water and the existence of poorly structured soils. This study assessed the soil water and salt budgets in nine commercial orchards located in the RID using the multiple ion chemistry module available in the HYDRUS-1D model during the 2019 and 2020 growing seasons. The studied crops were almond, olive, citrus (orange, mandarin, and clementine), and pomegranate. The model successfully simulated soil water contents measured in the different fields but there was a clear underestimation of the electrical conductivity of the soil saturation paste extract (EC e) in some locations, while simulations of the sodium adsorption ratio (SAR) were generally acceptable. Modeling errors were mostly associated with missing information on fertigation events rather than related to the effects of irrigation water quality. The water and salt balances were also computed for the 1979–2020 period. Considering the probability of non-exceedance of salt accumulation during this period, the risk of salinity build-up was high to very high for the very dry years in most fields, except in the citrus sites. The factors influencing the salt accumulation were the irrigation strategy, the seasonal irrigation and rainfall depths, the duration of the crop growth period, the rainfall distribution in the late and non-growing stages, the soil drainage conditions, and the irrigation water quality. For the current climate conditions and irrigation water quality, the risk of soil salinity levels affecting crop development and yields was found to be minor. This means that, despite salts tended to accumulate in the rootzone over a season, under current conditions the salinity stress did not reach harmful levels for plants. Only in two of the study sites, there was a need to promote salt leaching. Hence, this study shows that soil salinization risks in the study area are low but, for given locations during drier seasons, there is a need for tailored irrigation solutions aimed at the conservation of soil and water resources. • Soil salinization risks in nine commercial orchards were assessed with HYDRUS-1D. • The probability of non-exceedance of salt accumulation was computed for 1979–2020. • The risk of salinity build-up was high to very high for the very dry years in most fields. • For current conditions, the risk of soil salinity levels affecting crop development was minor. • Tailored irrigation solutions should be considered in some cases in dry and very-dry years. [ABSTRACT FROM AUTHOR]

Soil salinization problems are widespread in the Hetao plain, Inner Mongolia, resulting from arid climate conditions, a shallow saline water table, poor irrigation water management, and insufficient drainage. This study follows previous research aimed at evaluating crop water use and controlling the salinity build-up in the region, namely using weighing and static water table lysimeters to parameterize a water balance model aimed at the development of appropriate irrigation scheduling. Two sets of five static water table lysimeters, which fixed depths ranged from 1.25 to 2.25 m, were used over two maize crop seasons. The mechanistic HYDRUS-1D model was further used to daily predict measured data on soil water contents, boundary fluxes in the interface between the saturated and unsaturated zones, the electrical conductivity of the soil saturation paste extract (EC e), and the actual crop evapotranspiration (ET c act). The soil water balance helped quantify the combined effect of water and salinity stresses on root water uptake as well as groundwater fluxes into the rootzone. The salt balance showed that the salinity build-up was much related to irrigation and capillary fluxes, and that the autumn irrigation carried out during the non-growing season was essential for controlling soil salinity. The efficiency of the autumn irrigation much depended on groundwater depth and the amount of water applied for salt leaching, with the best results found for the lysimeters with water table depths at 2.0 and 2.25 m (85–100%) for irrigation depths ≥ 220 mm. The lysimeters with shallower water tables never showed a leaching efficiency higher than 88%. This research shows that the sustainability of irrigation in Hetao depends on finding adequate solutions for controlling the depth of the saline groundwater, minimizing capillary fluxes to the rootzone, and developing consequent approaches for autumn irrigation leaching. • Soil water contents and fluxes, EC e , and ET c act were measured using water table lysimeters. • The HYDRUS-1D model successfully simulated lysimeter data during two seasons. • The water table depth influenced the effectiveness of autumn irrigation leaching. • The leaching efficiency only increased by improving soil drainage conditions. • Reducing autumn irrigation depth (<200 mm) promoted soil salinization. [ABSTRACT FROM AUTHOR]