Evaluating the impacts of saline water irrigation on soil water-salt and summer maize yield in subsurface drainage condition using coupled HYDRUS and EPIC model

Field experiment combined with numerical simulation is an efficient approach for evaluation the effects of saline water irrigation on soil water-salt movement, crop growth and water productivity. In this study, HYDRUS model was coupled with EPIC module to evaluate the effects of saline water irrigation on soil salinity and grain yield under subsurface drainage condition. Two years' field experiment data collected in lysimeters of summer maize irrigated with water of two different levels of salinity under different subsurface drain depths was used to calibrate and validate the coupled model. The coupled model was then adopted to evaluate the effects of salinity stress on evaporation, transpiration and water productivity (WP) and of long-term saline water irrigation on soil salinity and grain yield under subsurface drainage. Results indicated that simulated values of soil water-salt content, subsurface drainage amount and concentration, grain yield and evapotranspiration (ET) were in good agreement with observed values. Transpiration and WP were reduced by salinity stress, while evaporation was sensitive to drain depth. Soil salinity evidently increased when irrigation water salinity was higher than 4.0 dS m(-1) in each simulated year under drain depth of 80 cm. Grain yield maintained at around 7600 kg ha(-1) when water salinity is 4.4 dS m(-1) under drain depth of 80 cm, and decreased with higher water salinity across all simulated years. There were significant exponential relationships between soil salinity, grain yield and irrigation water salinity in the long-term simulation. Thus, the appropriate irrigation water salinity should be 4.0-4.4 dS m(-1) under subsurface drain depth of 80 cm in the present study. The combined application of saline water irrigation and subsurface drainage should be given more attention for long-term soil salinity and grain yield management in the future.