Comparison of the Soil Water, Vapor, and Heat Dynamics between Summer Maize and Bare Fields in Arid and Semi-Arid Areas

In arid and semi-arid areas, water vapor transport is an important form of soil water movement and plays a crucial role in the overall water and energy balance. For better prediction of soil water and heat fluxes and understanding of root zone soil water dynamics for effective crop management, soil moisture, temperature, soil texture and micrometeorological data have been collected from field trials. Based on the data collected, a Hydrus 1D model was established to simulate the coupled transport of liquid water, water vapor and heat under summer maize (summer maize treatment; SMT) and bare soil (bare soil treatment; BT) for a 100 cm soil profile. Calibration and validation data for the model revealed a good level of agreement between simulated and measured data. Results indicated that the isothermal vapor flux was close to zero throughout the profile, while the isothermal water flux dominated the soil water movement for both SMT and BT. The vapor flux was mainly contributed by thermal vapor flux and increased with soil desiccation. Evaporation and transpiration showed two distinct phases, increasing immediately after irrigation and decreasing gradually as soil water content decreased. SMT had lower evaporation rates due to the protection provided by crop canopy. Irrigation significantly altered the dynamic characteristics of thermal liquid water and thermal vapor fluxes in the vadose, emphasizing the importance of considering the coupled transport of liquid water, vapor, and heat transport at interfaces in the soil–plant–atmosphere continuum for accurate estimates of water flux, especially under prolonged drought conditions.