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As one global issue, soil salinization has caused soil degradation, thus affecting the sustainable development of irrigated agriculture. A two-year study was conducted in 2018 and 2019 to identify the effects of subsurface drainage spacing on soil salinity and groundwater level, the latter of which is in a high-water table in drip irrigation cotton fields in the Tarim Basin oasis in southern Xinjiang, China. Three subsurface drainage treatments, with a drain spacing of 10 m (W10), 20 m (W20), and 30 m (W30), respectively, and a drainage-absent treatment (CK), are tested. With CK, soil salinity in the 0–60 cm layer was accumulated within a year. In contrast, the subsurface drainage reduced the soil salinity at a leaching rate of 10–25%. When decreasing the drain spacing, it was found that the soil desalination rate increased significantly (p < 0.05) with good repeatability. Experimental results showed that the fitting equation of the soil salinity leaching curve could accurately describe the soil salinity leaching pattern of drip irrigation, and thus could be further used to inversely determine the theoretical drip irrigation leaching quota for those soils with different salinity degrees. As such, subsurface drainage could effectively control the groundwater table. Compared with CK, subsurface drainage deepened the groundwater table and mitigated the fluctuation of the groundwater level. These effects were strengthened by reducing the drain spacing. Correspondingly, the influence of the fluctuation of the groundwater table was reduced. [ABSTRACT FROM AUTHOR]

The contradiction between land improvement in saline-alkali areas and water-saving irrigation in the arid regions is becoming increasingly prominent, affecting the movement of soil water and salt as well as cotton growth. To effectively improve soil quality and alleviate soil salinization issues under the premise of water conservation to increase cotton yields, a method involves conducting brackish water leaching during the non-growing season and utilizing freshwater drip irrigation during the growing season for cotton under subsurface drainage. A 2-year field experiment using six subsurface drainage systems at different depths of 0.8 and 1.1 m and different spacings of 10, 20, and 30 m respectively, alongside a non-drainage treatment as control (CK) was conducted in Aral, Xinjiang, China. Furthermore, efficient simulations of soil water and salt dynamics as well as cotton growth in arid regions under subsurface drainage conditions could be achieved using AquaCrop and DRAINMOD-S models. The results showed that soil salinity leaching could be achieved effectively with the use of appropriate brackish water and subsurface drainage pipes with the proper technical parameters during the non-growing season. Compared with the non-drainage treatment, the subsurface drainage and drip irrigation with freshwater reduced soil salinity effectively and improved growth indices and cotton yield considerably during the growing season. The rate of soil desalination exhibited an upward trend as the distance of subsurface pipes decreased, and the growth indices of cotton increased with the decrease in distance and depth of t subsurface pipes. This study concluded that using brackish water in the non-growing season, appropriate selection of irrigation water volume, spacing, and depth of subsurface pipes can simultaneously improve soil salinity drainage and cotton yield. This research suggests new irrigation and management recommendations for agricultural production and achieves more efficient water use and crop cultivation under arid conditions, providing a new insight into the efficient use of saline soil resources in the arid regions in Xinjiang. • Leaching with brackish water and drip irrigation with freshwater reduced salinity. • Subsurface drainage is beneficial to soil salt leaching and cotton growth. • Drainmod-S and AquaCrop models can simulate soil salt transport and cotton growth. [ABSTRACT FROM AUTHOR]