The Efficacy of Subsurface Drain in Desalinizing Cotton Field with Shallow Groundwater and Mulched Drip-irrigation in Southern Xinjiang

Abstract

【Objective】 Soil problems in southern Xinjiang of China are many and vary, characterized by scarce rainfall, shallow groundwater and high soil salinity. To safeguard crop production, mulched drip irrigation coupled with subsurface drain have been developed as the dominant cultivation in this region. The purpose of this paper is to experimentally study the efficacy of this system in desalinizing cotton fields. 【Method】 A two-year experiment was carried out in a cotton field with shallow groundwater table. Spacing of the subsurface drains varied from 10 m to 30 m, and their buried depth varied from 0.8 m to 1.1 m. Treatment without drains was taken as the control (CK). The field was mulched, and the cottons were drip-irrigated. The effect of the drains on spatiotemporal dynamics of soil salt was measured, and its variation in response to irrigation amounts was analyzed. 【Result】 A lack of drainage system resulted in inter- and intra-annual salt accumulation in the soil surface; installing subsurface drains reduced salt accumulation, with the reduction increasing significantly with the decrease in drain spacing and increase in their burying depth. Irrigation amount did not show a noticeable impact on salt leaching when the drains were absent, while having the drains in place increased the leaching rate by 10%~30%. Significance analysis of the desalination rate of the irrigation showed that salt leaching rate increased significantly with the decrease in drain spacing and the increase in drain depth. Regression analysis found that the desalination rate was impacted by drain spacing more than by the drain depth. The difference in soil salt content before and after the irrigation can be fitted to a leaching curve with R2 > 0.90. Using this curve, we calculated the irrigation amount required to leach salt in the 0~60 cm of soil below a critical value, which can be used to design the subsurface drainage system 【Conclusion】 The optimal design parameters for the areas we studied were: drain spacing 10 m, and drain depth 0.8 m. This can meet the requirement by keeping the salt content in the cotton field below a critical value.

Keywords

• subsurface drainage
• salt leaching
• drip irrigation
• saline soil
• salt leaching curve