Experimental and numerical evaluation of soil water and salt dynamics in a corn field with shallow saline groundwater and crop-season drip and autumn post-harvest irrigations

In areas with shallow saline groundwater, soil salts inevitably accumulate in the root zone during the growth period due to irrigation and upward movement of salts from the groundwater. In Northern China, autumn irrigation (AIR) with large amounts of water is commonly employed post-harvest to mitigate soil salt stress on crop growth in the subsequent year. Optimizing the total irrigation depth during both crop-growth and non-growth periods is challenging because of the movement of soil salts, which is influenced by their two-dimensional distribution around drippers and the impact of the winter freeze-thaw cycles, significantly affecting water flow and solute transport during winter. In this study, the HYDRUS-1D and HYDRUS-2D models were integrated and calibrated using experimental data collected from 2021 to 2023 in China's Ordos south bank irrigation area. This model integration was conducted to assess soil water and salt dynamics during the non-growth and corn-growth periods under different irrigation strategies: a) AIR with high (A_H) and low (A_L) irrigation depths, and b) drip irrigation (DIR) with high (D_H), medium (D_M), and low (D_L) irrigation depths. The results indicated that HYDRUS effectively modeled the electrical conductivity of the saturation paste extract (EC_e) across different irrigation strategies, yielding an average coefficient of determination (R²) and the root mean square errors (RMSE) of 0.87 and 0.53 dS m⁻¹, respectively. Generally, EC_e increased during the growth period with DIR and decreased during the non-growth period with AIR. For the 0–40 cm soil layer, EC_e decreased by 5.7 % and 12 % for every 100 mm increase in the AIR and DIR depths, respectively. Compared with the A_HD_M and A_HD_L treatments, reducing an AIR depth and increasing a DIR depth resulted in lower EC_e in the 0–40 cm layer during the growth period and higher crop yield (CY) and irrigation water productivity (WP_I). Specifically, the average EC_e in the 0–40 cm layer decreased by 4.8 % during the growth period in the A_LD_H treatment compared to the A_HD_M treatment, and CY and WP_I increased by 7.2 % and 10.3 %, respectively. Additionally, the irrigation strategy was the most effective in reducing EC_e when AIR accounted for 35 % of the total irrigation. This study suggested that combining low AIR and high DIR could enhance water and field productivity.