Soil water dynamics in a 450-year-old natural landslide-dammed valley farmland: Insights into precipitation responses

• High-frequency monitoring of soil water content and rainfall dynamics were conducted over a continuous two-year period. • Relatively low soil water content at ∼60 cm depth facilitated the rapid infiltration of surface soil water. • Fertility of the landslide-dammed valley farmland is attributed to stable and suitable soil water content at ∼100 cm depth. Tens of thousands of sediment check dams have historically played vital ecological functions in China’s Loess Plateau, and dammed valley farmland has been a significant agricultural resource for centuries. However, newly created valley farmlands under the “Gully Land Consolidation” project often face lower arable quality and frequent soil salinization compared to their natural counterparts. To draw insights from natural dammed valley farmland, we selected the 450-year-old Huangtuwa natural landslide-dammed valley farmland (NLDF) for high-frequency, long-term monitoring and analysis of soil water content and precipitation during 2019–2020 and used the HYDRUS-1D model to assess its water storage capabilities. The results indicate that the soils from 0–100 cm can be clearly categorized into three groups: the rapid response layer (0–40 cm), which reacts quickly to rainfall; the water transport and emergency reservoir layer (∼60 cm), characterized by lower water content that fluctuates rapidly during extreme rainfall, functioning as both a reservoir and drainage pathway; and the stable water supply layer (∼100 cm), with the most stable water content (16.6 %, SD: 1.2 %), crucial for fertility and cultivation. Based on HYDRUS-1D model calculations, the soil water storage of NLDF remained stable under low precipitation but showed a sharp rise and decline when precipitation exceeded 9.8 mm. We employed a random forest model to assess the factors influencing the soil layers’ response rates to rainfall and their soil moisture expansion potential during extreme rainfall events. The results emphasized that soil total nitrogen, organic carbon, and pH were more influential than physical properties, highlighting the significant interaction between soil moisture and nutrients and the potential important influence of vegetation on water movement in NLDF. Overall, NLDF’s sustained arability is attributed to its multi-dimensional, synergistic ecological layout. New dammed valley farmland should replicate NLDF’s structure by pre-establishing vertical soil layer distribution during landform reshaping and adopting a synergistic ecological layout that integrates vegetation, soil, and precipitation.