Numerical analysis of soil salt leaching influenced by subsurface seepage pipe with negative pressure

Abstract

【Objective】 Subsurface seepage pipe assisted with vacuum negative pressure is an emerging technology aimed at regulating soils water dynamics. In this paper, we examine the effects of negative-pressure seepage pipe (NPSP) on soil salt leaching. 【Method】 We used the HYDRUS model to simulate salt leaching in soils with five soil textures: silty clay, clay, clay loam, sandy clay loam, and sandy loam. Five infiltration water heads (2, 4, 6, 8 and 10 cm) and five negative pressure heads (200, 500, 1 000, 1 500 and 2 000 cm) in the subsurface pipes were considered in the simulations. Based on the simulated results, we calculated the changes in soil salt content before and after a leaching event, as well as the salt leaching efficiency (salt leached per unit of irrigation water). 【Result】 ① Water discharged by the NPSP was primarily originated from the wetting zone in soil profile formed during the infiltration process, and the maximum pipe discharge was obtained as the wetting zone was saturated. ② Soil texture was a key factor in influencing water and salt discharge, with both the desalination rate and salt leaching efficiency increasing as sand content increased. ③ For all the tested soil textures, the desalination rate was positively correlated with both the surface infiltration head and the inner-pipe negative pressure. However, for sandy clay loam and sandy loam soils, increasing the infiltration head lead to a lower salt leaching efficiency. ④ As compared with no-pipe control, the maximum increase of the desalination rate under the application of NPSP was 7.91%, while increased desalination rate were obtained in the soil profile above the NPSP, and the values decreasing with the lateral distance away from the NPSP; There was a salt accumulation zone directly below the NPSP, and its region expanded with the decrease of the applied negative pressure. 【Conclusion】 NPSP is feasible to facilitate soil desalination without increase the water consumption for leaching practice, and the desalination performance of NPSP is likely be improved in field with sandy soil.

Keywords

• soil water-salt transport
• numerical simulation
• negative-pressure seepage pipe
• surface infiltration
• salt leaching