Optimization of Winter Irrigation under Freeze-Thaw Conditions: A Case Study of the Yellow River Delta, China

Optimal winter irrigation may be an alternative method for controlling soil salinization under seasonal freezing and thawing conditions in the Yellow River Delta. However, few studies have focused on optimal winter irrigation based on the dynamics of soil water, heat, and salt during the freezing-thawing period in this region. Taking the seedling stage of winter wheat in the Yellow River Delta as the research object and using observation data of hydrothermal salt from the Shandong agricultural high-tech demonstration base from 17 October 2019 to 15 June 2021, a numerical simulation of the hydrothermal coupling process of freeze-thaw soil in the experimental area was carried out through the Simultaneous Heat and Water Model (SHAW). The simulation results of the model were evaluated according to the mean error (ME), root mean square error (RMSE), and Nash efficiency coefficient (NSE). The results showed that the SHAW can well simulate the soil moisture (SM), soil temperature, and soil salt during the growth of winter wheat in this region: the SM at the depth of 0-80 cm with an ME < 0.038 cm(3) cm(-3), RMSE < 0.064 cm(3) cm(-3), and NSE > 0.669; the soil temperature with an ME < 1.311 & DEG;C, RMSE < 1.493 & DEG;C, and NSE > 0.738; and the soil salinity with an ME < 0.005 g kg(-1), RMSE < 0.014 g kg(-1), and NSE > 0.607. Moreover, the model was used to simulate the distribution of soil water and salt in the winter wheat seedling stage under different winter irrigation methods during wet, normal, and dry years. It was suggested that the appropriate winter irrigation amount was 80 mm in wet years and normal years and 100 mm in dry years, which could be beneficial to winter wheat growth during the seedling stage. These results provide a reference for irrigation optimization in the Yellow River Delta and other similar areas.

Automated summary

Optimal winter irrigation can be an effective method to control soil salinization in the Yellow River Delta under freezing-thawing conditions. However, there is limited research on optimal winter irrigation based on soil water, heat, and salt dynamics in this region. This study used the Simultaneous Heat and Water Model (SHAW) to simulate the hydrothermal coupling process in freeze-thaw soil during the seedling stage of winter wheat. The model successfully simulated soil moisture, temperature, and salinity, providing recommended winter irrigation amounts for wet, normal, and dry years. These findings have important implications for irrigation optimization in the Yellow River Delta and similar areas.