Simulation of dynamical interactions between soil freezing/thawing and salinization for improving water management in cold/arid agricultural region

In cold/arid agricultural regions seasonal freezing/thawing of soils can result in soil salinization in winter; therefore, it is crucial to understand the mechanisms behind soil salinization during winter for better water management in agriculture. In Hetao Irrigation District of Inner Mongolia, northern China, we used the CoupModel (version 5) considering dynamical impacts of salt on soil freezing point to simulate soil salt dynamics and soil freezing/thawing in three winters during 2012–2015. The simulated soil temperature at different depths was improved by ~10% with respect to the Nash-Sutcliffe coefficient NSE R2 when dynamical salt impact on freezing point was taken into accounted. Simulations revealed that ice coverage on soil surface as well as water stored in drainage ditches during winter cause more severe salinization in spring due to improper AI (Autumn Irrigation) practices combining poor drainage systems. A new AI practice with earlier irrigation date (i.e. 10 d earlier than 2012/2013 winter regulation), longer irrigation period (i.e. 7 d instead of 3 d), but with less irrigation water (reduced by 20% from 2012/2013 winter regulation) was then proposed. The new AI practice can control groundwater level and salt accumulation better during winters. Our results highlight the importance of combining detailed field irrigation tests with a process-based model accounting for interactions between soil freezing/thawing and salinization to improve water management efficiency in cold/arid agricultural regions.