Freeze–thaw cycles alter soil pore-size distribution and enhance soil water accumulation under no–tillage on the Loess Plateau

No-tillage (NT) has frequently been reported to increase the risk of soil compaction while enhancing soil water content. In cold regions, freeze-thaw cycles (FTC) strongly influence soil structure and hydrothermal regimes. However, it remains unclear whether FTC can effectively improve soil physical conditions and promote soil water accumulation under NT systems. In this study, laboratory simulation experiments were conducted to examine the effects of various freeze-thaw intensities on soil physical properties under NT and conventional tillage (CT) systems. In addition, field monitoring was performed to characterize soil water and temperature dynamics during the freezing-thawing period under the two tillage practices. The main findings were as follows: (1)The average bulk density of NT soil was 1.42 g cm −3 , significantly higher than that of CT soil (1.04 g cm −3 ), indicating NT resulted in greater soil bulk density. However, freeze-thaw altered the NT soil pore-size distribution, as shown by significant increases in macroporosity (by 32.2%) at −5/5 °C and in mesoporosity (by 105.9%) at −15/5 °C, whereas the increases in mesoporosity at −5/5 °C (by 30.3%) and in macroporosity at −15/5 °C (by 13.7%) were numerical and did not reach statistical significance ( p > 0.05). In contrast, the pore-size distribution of CT soil showed no significant response to FTC; (2) FTC increased saturated hydraulic conductivity in both tillage systems, with the increases being significant relative to the unfrozen control at −15 °C ( p < 0.05) but not at −5 °C. Field capacity decreased in both tillage systems, but only the reduction under NT at −5 °C was statistically significant ( p < 0.05); (3) FTC caused no significant change in soil thermal conductivity within either tillage system, but under −5°C and −15°C FTC treatments, NT had significantly higher soil thermal conductivity than CT; (4) Throughout the freezing-thawing period, soil water content (SWC) was higher under NT than under CT, whereas soil temperature below the 20 cm depth was generally higher under CT. Notably, surface SWC increased markedly after FTC, particularly under NT, indicating a pronounced post-freezing soil water accumulation effect. These results indicate that NT increases soil water content, whereas FTC have no significant effect on bulk density but promote soil water accumulation under NT. After FTC, NT is likely to create more favorable soil hydrothermal and structural conditions for spring sowing in the arid and semi-arid regions of Northwest China. Overall, this study provides a scientific basis for optimizing farmland management practices on the Loess Plateau.