Abstract:In northern saline-affected irrigation districts, spring irrigation significantly increases soil moisture and reduces soil salinity. However, traditional spring irrigation quotas are relatively high, and the optimal timing for spring irrigation is difficult to determine. Therefore, optimizing spring irrigation patterns (quotas and timing) is crucial for enhancing agricultural water use efficiency and productivity. The research was conducted in the irrigation district south of the Yellow River in Ordos City, Inner Mongolia, during 2022—2023. Two spring irrigation quota levels (135mm and 180mm, denoted as W1 and W2) were established, along with three irrigation timing points: 18 days before sowing (T1), 12 days before sowing (T2), and 6 days before sowing (T3), totaling six treatments. Additionally, two indoor infiltration experiments were conducted to examine the effects of spring irrigation quotas and timing on soil infiltration and sunflower emergence rates. Using the HYDRUS model, the pre-sowing soil water-salt dynamics under different treatments and the relationship between pre-sowing water-salt conditions and various spring irrigation patterns were explored. It was found that higher spring irrigation quotas resulted in greater wetting front migration distances and cumulative infiltration volumes. By establishing a quantitative relationship between sunflower emergence rate and pre-sowing soil water-salt content, the optimal soil water content (SWC) and electrical conductivity (EC) were determined to be 0.254cm3/cm3 and 0.683dS/m, respectively. The HYDRUS model was employed to simulate water-salt transport under different spring irrigation patterns. Results indicated that the HYDRUS model effectively simulated water and salt dynamics during the pressurized infiltration and redistribution phases of spring irrigation. During the validation period, the root mean square error (RMSE), coefficient of determination (R2), and mean relative error (MRE) for SWC averaged 0.02cm3/cm3, 0.96, and 7.7%, respectively, while corresponding values for EC were 0.32dS/m, 0.90, and 9.9%. Under identical spring irrigation quotas, earlier irrigation resulted in higher pre-sowing EC and lower SWC. Compared with the 18days pre-sowing irrigation treatment, delaying irrigation by 6days and 12 days reduced the 2-year average EC in the tillage layer (0~30cm) by 10.1% and 16.8%, respectively, while increasing the average SWC by 3.4% and 6.2%. Under identical spring irrigation timing, compared with the low spring irrigation quota (W1), the high spring irrigation quota (W2) reduced the 2-year average pre-sowing EC in the plow layer by 13.4% and increased the average SWC by 4.5%. Based on HYDRUS model scenario analysis of pre-sowing soil water and salt content under spring irrigation regimes with irrigation quotas ranging from 90mm to 315mm and timing from 3 days to 18 days before sowing, optimization was conducted using optimal SWC and EC values. The optimal spring irrigation regime for this region was determined as follows: spring irrigation quota of 180mm with timing 18 days before sowing, or spring irrigation quota of 135mm with timing 15 days before sowing. These findings can provide theoretical support for agricultural water conservation and production in saline-affected irrigation areas of the Yellow River Basin.
