Effects of subsurface drainage and year-round irrigation on crop water-salt stress and yield in an arid region

Agricultural drainage mitigates soil salinization in farmland and enhances economic yield. As water resource challenges intensify, the need for effective and sustainable irrigation and drainage strategies increases. This study presents a 3-year experiment (2020–2022) on the effects of three irrigation quotas and subsurface drainage on soil water and salt dynamics, groundwater depth, and crop productivity in the Hetao Irrigation District. Drainage pipes were installed at a 1.5 m depth with a spacing of 45 m. The irrigation quotas for the subsurface drainage (SD) districts (SD1, SD2, and SD3) were 100, 140, and 180 mm during the preplanting period; 70, 100, and 130 mm during the sunflower growth period; and 160, 180, and 200 mm, during autumn, respectively. The control treatment (CK) followed the same quotas as SD3 without subsurface drainage. The annual SD volume was 75–99 mm. The groundwater depths in CK were 0.15–0.25 m shallower than SD areas. SD quickly regulated the groundwater depth, affecting soil water storage. During the irrigation–drainage period (May–November), the amount of salt discharged by the SD was 3.12–4.29 t ha−1. The 33.96–46.02 % of soil salt storage changes in the 0–150 cm were drained away by subsurface pipes, whereas the remainder leached into deeper soil layers or groundwater. Preplanting irrigation combined with SD provided an optimal soil water and salinity environment for sunflower emergence. SD reduced salinity stress during the sunflower growth period and increased sunflower yields by 9.68–14.70 % over 3 years. Autumn irrigation and SD were crucial for soil salt leaching and soil moisture conservation. Considering the effects of SD, year-round precipitation and irrigation on sunflower yield and water productivity, a year-round water replenishment of 510 mm is optimal with SD in an arid region.