Optimal depth and spacing of subsurface drains for soil desalination in Yanqi basin farmlands

Abstract

【Objective】 Subsurface drain is a drainage system widely used in northwestern China to keep the groundwater below the critical depth and facilitate soil salt leaching. This paper presents an experimental study on the combined effect of drain depth and spacing on soil salt leaching in a representative oasis in Yanqi Basin. 【Method】 The drains were buried at the depth of 1.2 or 1.5 m, with the spacing being 20, 30 or 40 m. Overall, there were six treatments. For each treatment, we measured the spatial changes in soil salt contents before and after the leaching, which were then used to analyze the variation in salt leaching efficiency between different treatments. 【Result】 ① When initial soil moisture was at the field capacity, leaching could quickly saturated the soil and displace the water in the soil above the drains. There were no significant correlations between soil moisture content and the depth and spacing of the drains. ② Salt leaching from the top 0-60 cm soil layer was significantly related to the depth and spacing of the drains. The spacing and depth of the drains combined to affect soil salt removal rate. When the spacing was the same, increasing the burial depth of the drains enhanced salt removal from the 0-60 cm soil layer; when the burial depth of the drains was the same, salt removal rate from the 0-60 cm soil layer was the highest when the spacing was 30 cm (P0.05). Compared to the burial depth of 1.2 m, the burial depth of 1.5 m considerably improved the drainage efficiency and accelerated soil salt removal. 【Conclusion】 For maximum soil salt removal rate, the optimal depth and spacing of the subsurface drains for the study area was 1.5 m and 30 m, respectively.

Keywords

• drainage
• soil moisture
• salinity
• desalination rate
• spacing of subsurface drainage pipe
• depth of subsurface drainage pipe
• saline-alkali land treatment