Objective The Yinbei Plain lies within the arid and semi-arid regions of Northwest China, characterized by low rainfall and high evaporation rates. Compounded by long-term flood irrigation practices that have elevated groundwater levels and inadequate drainage systems, surface runoff issues are widespread throughout the area. By examining differences in soil moisture infiltration and staining characteristics across various vegetation types, this study explores the influencing mechanisms of the moisture infiltration process. It can provide a theoretical basis for the migration of preferential soil fractions and the accumulation of salts under different vegetation types in saline-alkali soils of arid and semi-arid regions in Northwest China.

Methods The study focused on saline-alkali soils across five vegetation types on the Yinbei Plain: Sesbania cannabina (A1), Phragmites australis (A2), Echinochloa crus-galli (A3), Suaeda salsa (A4), and Atriplex spp. (A5), with bare land (CK) serving as the control. Six sample plots were established. Through field dye tracing experiments combined with image processing software techniques, preferential flow characteristic parameters were determined. Correlation analysis and redundancy analysis were further employed to investigate the preferential flow characteristics and influencing factors of saline-alkali soils across different vegetation types.

Results 1) There were differences in preferential flow patterns among soils under different vegetation types. Soils under S. salsa, E. crus-galli, and Atriplex spp. exhibited relatively uniform staining patterns, while bare land and soils under P. australis showed shallower staining depths. The staining pattern in soils under S. cannabina was less regular. 2) The soils under E. crus-galli and S. salsa exhibited the largest stained areas, reaching 35.71% and 34.70%, respectively. Their stained regions were concentrated, showing good connectivity between upper and lower soil layers without distinct, narrow preferential flow paths. Compared to bare land, the dyeing area ratios (D_AR) of soils under E. crus-galli, S. salsa, Atriplex spp., S. cannabina, and P. australis increased by factors of 4.04, 3.9, 2.97, 2.75, and 2.08, respectively. Compared to soils under S. salsa, the matrix flow depths (U_niFr) in soils under E. crus-galli, Atriplex spp., P. australis, S. cannabina, and bare land decreased by 20%, 25%, 56%, 65%, and 82.5%, respectively. The preferential flow ratios (P_F-fr) increased in the following order: soils under P. australis < Atriplex spp. < S. salsa < E. crus-galli < bare land < S. cannabina, indicating that soils under S. cannabina had the highest degree of preferential flow development. 3) The preferential flow ratio was positively correlated with soil bulk density. Redundancy analysis identified soil bulk density as the dominant factor, demonstrating its strong explanatory power for preferential flow variation.

Conclusions Saline-alkali soils under S. cannabina exhibit the highest development of preferential flow across different vegetation types, E. crus-galli, Atriplex spp. and S. salsa with a high percentage of substrate flow may be better adapted to drought-stressed environments, and their homogeneous water transport patterns are more conducive to improving regional water ecology. It is the optimal vegetation choice for ecological restoration of saline-alkali land.