Soil water and salt migration characteristics under freezing saline water irrigation: An isotope tracing and phase analysis perspective

In arid cold regions, optimizing saline water use for soil improvement presents significant challenges in water-salt regulation. This study investigates freezing saline water irrigation (FSWI) as a promising strategy, examining its effects on soil water-heat-salt dynamics through a three-year field experiment with varying irrigation amounts (0, 90, 180, and 270 mm, designated FSWI 0 –FSWI 270 ). Results demonstrate that FSWI considerably moderates deep soil temperature variation during freeze-thaw cycles, shortening the freezing period by up to 8 days. Meltwater from surface ice effectively leaches shallow soil (0–40 cm), evidenced by decreased soil water δ¹ ⁸O. Although irrigation introduced salt (peak salt load: 3.15 kg m⁻²), freezing-induced phase changes promoted salt migration to deeper layers, reducing shallow soil salinity by 40.47 % under FSWI 180 after thawing. Conversely, excessive irrigation (FSWI 270 ) increased surface salinity by 4.67 %, indicating salinization risk. The study identifies 180 mm as the optimal irrigation volume. These findings elucidate the mechanisms of water-salt transport under FSWI and support its potential as a viable strategy for saline soil amelioration and water conservation in cold regions.