Assessing the Effectiveness of Vacuum-Pressure Leaky Pipes in Promoting Localized Soil Desalination During Surface Leaching Events

Fields under subsurface leaky pipe irrigation require timely soil leaching to prevent salt accumulation along the pipeline, and methods for handling such localized desalination deserve to be explored. A potential application was attempted experimentally and numerically to assess whether the vacuum pressure leaky pipe (VPLP) method could promote soil desalination by absorbing saline solution during soil leaching. The laboratory results indicated that, compared with loamy sand and silty loam, loam soil could maintain more suitable saturation conditions for the extraction of soil water, resulting in 22% and 311% greater salt discharge, respectively. By modelling the wall of a leaky pipe as a finer soil layer, a series of HYDRUS-based simulations were performed to evaluate the effects of the inner-pipe operating vacuum pressure (OVP), pipe placement depth (PPD) and surface leaching size (SLS) on the salt dynamics within the leached soil profile. The model results revealed that the maximum VPLP salt discharge occurred at 20 cm PPD, and increasing the OVP led to a decrease in salt discharge when the OVP exceeded 200 cm. Additionally, reduced infiltration-induced salt downwards built-up and evaporation-induced salt surface accumulation were obtained under VPLP application, with an average 12% and 1% increase of soil desalination rate for 0–10 cm and 40–50 cm soil depth compared with those under non-VPLP conditions. This study extends the application of subsurface pipe irrigation systems in terms of soil salt management.