Effects of Magnetized Water on Infiltration and Salt Redistribution in Undisturbed Saline–Alkali Soil Columns from the Hetao Irrigation District: Dependence on Irrigation Water Source

Soil salinization and freshwater scarcity are two of the most pressing challenges limiting sustainable agriculture in arid and semi-arid regions worldwide. Magnetized irrigation has been proposed as a physical water treatment that introduces no chemical additives and may improve water infiltration and mitigate secondary salinization; however, its effectiveness under contrasting irrigation water sources remains poorly understood, particularly in undisturbed saline–alkali soils. This study investigated the effects of magnetized irrigation water from two sources—Yellow River water (HW) and subsurface drainage water (DW)—on soil water infiltration and water–salt transport in the Hetao Irrigation District, Inner Mongolia. Undisturbed soil columns were irrigated under three magnetic field intensities: 0, 3500, and 5000 Gauss (Gs). Cumulative infiltration, infiltration rate, wetting front advancement, soil moisture, salt storage, and ion redistribution were analyzed. Magnetization affected infiltration and water–salt redistribution, and the magnitude of the response differed between the two water sources. Mean infiltration rate increased by 11.6–13.9% under magnetization relative to non-magnetized controls (p < 0.001), and infiltration duration decreased by 6.1–7.1% (p = 0.020), with no significant difference between the 3500 and 5000 Gs treatments (p = 0.903). The water source × magnetic intensity interaction was not significant for infiltration rate or duration. Salt storage in deep layers was reduced under magnetized treatments: by 24.74% at 40–50 cm under HW at 5000 Gs and by 29.18% at 50–60 cm under DW at 3500 Gs (both p < 0.05 relative to the respective non-magnetized controls). Magnetized irrigation was associated with reduced Na+ and Cl− accumulation in the 0–30 cm layer and with a higher relative proportion of Ca2+ and Mg2+ in the soil water extract. These findings provide experimental evidence on how the response to magnetized irrigation varies with irrigation water source in undisturbed saline–alkali soils and support further evaluation of subsurface drainage water reuse in salinized farmland.