The Influence of Subsurface Drain on Solute Movement in Soils Severely Affected by Salinity and Alkalinity in Ordos Region

Abstract

【Background】 The wide distribution of saline and alkali soils in Ordos of Inner Mongolia is a main abiotic factor hindering crop growth. Their remediation is a prerequisite for developing sustainable agriculture in this region. Subsurface drain is a technology widely used to alleviate salt accumulation and enhance salt leaching. 【Objective】 The objective of this paper is to experimentally study the effects of subsurface drain on salt dynamics in soils heavily affected by salinity and alkalinity. 【Method】 The experiment was conducted from May to October 2015 at Dalat Banner, with the drains spaced 18 m apart and buried in a depth varying from 1.2 m to 1.5 m; the depth of the drainage ditches was 1.8~2.0 m. In each treatment, we measured soil salt distribution up to 1.0 m deep, the change in groundwater table and salinity, as well as the quality of the irrigation water and drainage water, salt ion data and their relationship. 【Result】 ①Spatial variation of salt in the top 0~100 cm soil was moderate with a coefficient of variation of 25%~75%; the majority of salt was accumulated in regions proximal to the soil surface. ②The drains dropped the groundwater table by 50~60 cm and reduced soil salinity by approximately 10%, compared with data measured before experiment. ③At the end of the experiment, the main salt ions in the soil were K++Na+, SO42- and Cl-, while in the groundwater they were K++Na+, Cl- and HCO3-. ④Irrigating using the Yellow river water increased HCO3- in soil by 56% and the decreased of other salt ions, with SO42-, K++Na+ and Cl- reduced by 36%, 34% and 31% respectively. Leaching of the irrigation water increased ion contents in both drainage water and groundwater, especially the drainage water whose salinity was 3.43 times that of groundwater. 【Conclusion】 Subsurface drains can control the groundwater depth and reduce soil salt content; it facilitates leaching of SO42-, K++Na+ and Cl- from the soil. However, care should be taken to avoid an increase in HCO3- and its consequence for soil alkalization when irrigating with the Yellow river water.

Keywords

• subsurface drain
• soil salinity
• spatial variation
• groundwater
• ionic migration