The influence of salinity on hysteresis of soil water‐retention curves

Abstract

Taiwan is surrounded by the sea, and the southwestern seashores are suffering from a growing land subsidence problem caused by the excessive extraction of groundwater. There is also very serious intrusion by seawater along the coastline. These circumstances obstruct any land use, soil remediation or agriculture development in the area. When seawater intrudes, salt gets into the soil. The infiltration, evapotranspiration and the distribution of salinity in the unsaturated soil become a very complex problem. It is vital to investigate the hysteresis of soil water-retention curves, combined with the salinity in these areas. Therefore, this study's main focus will be the calibration of variations in salinity and their effect on the hysteresis of soil waterretention curves. In the wetting processes, the salty soil water-retention curves undergo an upper shift compared with the original soil water-retention curves because of the higher tension of saltwater. In the drying processes, there is also an upper shift compared with the original curves because the salinity influences the air-entry pressure. The saltwater's high salinity causes the hysteresis of soil water-retention curves to experience a greater shift. The changes in salinity also cause changes to the hysteresis curves' shape factors, which conforms to Huang's model (developed in 2005), the values of a and n. The value of a decreases with the increased salinity. The trend of the n value presents an irregular result. A linear regression of the a w and a d values was advanced where the R-square values of a w and a d exceeded 0.97.

Relating soil salinity, clay content and water vapour sorption isotherms

“…The WSIs are equivalent to the SWCC at the dry end. Some studies have revealed an effect of soil salinity on SWCCs: an increase in salinity causes the SWCC to move upward, thus increasing the maximum water content and resulting in a stronger hysteresis effect (Ma et al, ; Tan et al, ; Wang, Dang, & Yang, ; Zhao et al, ). Similar trends were also observed with increasing salinity in this study (Figure , Figure and Table ).…”

“…High salt content changes the morphology and structure of soil, increases the osmotic pressure of the soil solution, and eventually causes physiological drought of plants (Hu, ; Ma, Li, Wu, & Huang, ; Parida & Das, ; Xu, Zeng, Wu, & Huang, ; Zeng, Xu, Huang, Wu, & Tuller, ). Specifically, salinity can increase the proportion of small pores in soil, improve the capacity for soil water retention and enhance soil pore water suction, which leads to the upward shift of the soil water characteristic curve (SWCC, soil matric potentials > − 1.5 MPa) and the increase of the hysteresis effect (Ma, Lin, & Tan, ; Tan, Wu, Li, & Huang, ; Zhao, Zhang, & Yu, ).…”

On the importance of monsoon rainstorm impact period in soil salinization

“…In addition, unreasonable fertilizer application and irrigation can exacerbate soil salinization (Litalien and Zeeb, 2020). Thus, soil salinization is a common global problem (Ma et al, 2013;Perri et al, 2017;Shi et al, 2021;Taghizadehghasab et al, 2021). Alluvial farmland is the optimal farmland type in the Loess Hilly area of China, with high soil water contents, fertility, and crop yields (Chen et al, 2019;Xu et al, 2018;Yu et al, 2021).…”