Field-scale comparison of subsurface, open-ditch, and shaft drainage for soil salinity distribution and jujube productivity in an extremely arid salt-affected orchard

Soil salinization constrains orchard production in extremely arid regions, but the performance of drainage systems under relatively deep groundwater conditions remains insufficiently documented. This three-year fixed-site field-scale assessment compared subsurface drainage, open-ditch drainage, and shaft drainage in a drip-irrigated jujube orchard in Xinjiang, China. The results showed that subsurface drainage produced the greatest salt reduction in the 0–0.4 m crop-active layer (54.96%) and improved root-zone soil physicochemical conditions, whereas shaft drainage showed stronger performance than open-ditch drainage in the 0.4–0.8 m transition layer. In the 0.8–1.6 m layer, open-ditch drainage was associated with salt accumulation, indicating a higher risk of deep-profile salt storage. Additionally, the soil sodicity-related indicators also declined with displacement of Na. Subsurface drainage produced the highest fruit set rate, yield, and net benefit, while shaft drainage achieved the highest internal rate of return in 2024 (223.16%). Therefore, subsurface drainage is recommended where long-term soil improvement and crop productivity are prioritized, whereas shaft drainage may be preferred when rapid investment recovery is the primary objective.