Simulation of soil water, heat, and salt adsorptive transport under film mulched drip irrigation in an arid saline-alkali area using HYDRUS-2D

The film mulched drip irrigation (FMDI) in severe drought and salinity areas makes the transport of water, heat, and salt in the soil more complicated. In this paper, two-year field experiments were carried out in southern Xinjiang from 2020 to 2021 (Salt levels: 0.2%, 0.4%, and 0.6%; Irrigation levels: 30 mm and 45 mm (2020). 22.5 mm, 30 mm, 37.5 mm, and 45 mm (2021)). Using the measured data of soil moisture, heat, and salinity, the HYDRUS-2D model was calibrated and validated, and the effects of soil adsorption on the simulation results were compared. Meanwhile, six irrigation scenarios were designed (The three levels of irrigation times were 8 times, 10 times, and 12 times. The total irrigation amounts were 360 mm and 450 mm). The results indicate that the simulated results of salt transport under the condition of kinetic adsorption matched accurately with the observed data (the maximum of RMSE was 0.293 ds m−1, and the minimum values of R2 and d were 0.923 and 0.934, respectively); similarly, the simulation results of soil water and heat transport were acceptable (the maximum values of RMSE were 0.033 cm cm−1 and 1.897 °C, and the minimum values of R2 and d were 0.877, 0.99 and 0.915, 0.807, respectively). The scenario simulation indicate that salt leaching mainly occurred under plastic film, the desalination in the 0–40 cm soil layer was obvious (The rate range of salt leaching is 29.8∼58.8%), and salt accumulation appeared in the 40–100 cm layer under plastic film in the specific scenarios. Considering the optimal desalination in the cotton root zone, the irrigation mode with 8 irrigation times (The irrigation interval of 12 d during the budding period, 2 times; the irrigation interval of 8 d, 6 times) with a total irrigation amount of 450 mm was recommended, which provides a reference for the regulation of water, heat, and salt in severe drought and salinity areas.