Soil salinity dynamics and optimal groundwater depth for salt control in farmland under surface irrigation and subsurface drainage

【Background】Soil salinization is a widespread abiotic stress that significantly impacts agricultural productivity and water resource management in the Yinbei region of Ningxia Province. This study explores the inter-annual dynamics of soil salinity and groundwater depth in areas within this region that use surface irrigation and subsurface drainage.【Method】Field investigations were conducted in Huinong, a representative area in northern Yinbei characterized by surface irrigation and subsurface drainage systems. Spatiotemporal variation of soil salinity and groundwater depth were analyzed using measured data with the help of correlation analysis and the inverse distance weighting (IDW) interpolation method.【Result】Temporally, areas with high soil salinity were accounting ting for 23.57% of the study region in April. In contrast, areas with soil salinity greater than 2 g/kg decreased by 52.99% in July and 26.3% in October, compared to April. Soil salinity decreased gradually with increasing groundwater depth, and the relationship between them was well fitted by a proposed model (R2＞ 0.82).【Conclusion】Soil salinity in the region peaks in spring and declines by summer, showing spatial variability influenced primarily by topography and irrigation practices. Salinity in the 40-100 cm soil layer was more responsive to groundwater depth than in the 0-40 cm layer. Maintaining a groundwater depth between 1.8 and 2.2 m can facilitate crop growth and reduce salinization risk.