Wu et al. (2026) Spatiotemporal dynamics of soil moisture in edge zones along deep-cut channels of rainfed agricultural plateaus

Identification

• Journal: Agricultural Water Management
• Year: 2026
• Date: 2026-01-06
• Authors: Songbai Wu, Li Chen, Ninglian Wang, Na Wei, Sheng Hu, Haoyue Liu, Tal Svoray, S. Assouline
• DOI: 10.1016/j.agwat.2025.110105

Research Groups

• Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying Capacity, College of Urban and Environmental Sciences, Northwest University, Xi’an, China
• Institute of Earth Surface System and Hazards, Northwest University, Xi’an, China
• Key Laboratory of Hydrometeorological Disaster Mechanism and Warning of Ministry of Water Resources, School of Hydrology and Water Resources, Nanjing University of Information Science and Technology, Nanjing, China
• Climate Centre of Shaanxi Province, Xi’an, China
• Environmental, Geoinformatics and Urban Planning Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
• Institute of Soil, Water, and Environmental Sciences, A. R. O. - Volcani Center, Rishon Le Zion, Israel

Short Summary

This study quantifies the spatiotemporal dynamics of soil moisture in agricultural edge zones along deep-cut channels in rainfed plateaus, revealing persistent soil moisture reduction primarily due to root water uptake by sidewall vegetation, which significantly impacts crop productivity and necessitates targeted irrigation strategies.

Objective

• To characterize the spatial-temporal dynamic soil moisture in channel edge zones of the Weibei rainfed plateau.
• To analyze the effect of rainfall properties on soil moisture in the edge zone at the event time scale.
• To quantify the impact of soil water uptake by vegetation roots from the channel sidewall on soil moisture in the edge zone through a water balance analysis.

Study Configuration

• Spatial Scale: Three observation sites (L1 at 3.5 m, L2 at 7.0 m, L3 at 11.5 m from the channel edge) in a 4–5-year-old apple orchard on the Weibei rainfed Plateau, China. Soil moisture sensors installed at 10 cm, 40 cm, and 70 cm depths.
• Temporal Scale: Hourly soil moisture and rainfall monitoring from April 1 to October 31 in 2023 (wet year) and 2024 (dry year), covering the apple growing season. Analysis across 27 sub-periods based on soil moisture fluctuations.

Methodology and Data

• Models used:
  • Hydrus-1D (version 4.16.0110) for simulating one-dimensional water flow in variably saturated porous media, solving Richards equation, and calculating water balance components (surface runoff, actual evaporation, actual transpiration, deep drainage, and changes in soil water storage).
  • Van Genuchten model and Mualem model for characterizing soil hydraulic properties.
  • Feddes' model for calculating actual plant transpiration (root water uptake).
  • Penman-Monteith formula (FAO-recommended ETo Calculator) for reference evapotranspiration (ETo).
  • Multiple linear regression analysis to quantify relationships between difference in soil water storage (DSWS) and environmental factors.
• Data sources:
  • Field observations: Hourly soil moisture (SM) at 10 cm, 40 cm, and 70 cm depths using RRECT5 SM sensors. Hourly rainfall depth using a RR3665R tipping-bucket rain gauge. Daily leaf area index (LAI) of apple trees using an automatic networked vegetation canopy analyzer (XST-LAINet).
  • Soil properties: Soil texture (sand, silt, clay content), bulk density (BD), and initial soil moisture (SMi) determined by oven-dry method and laser diffraction. Root length densities measured.
  • Meteorological data: Daily maximum temperature, minimum temperature, mean relative humidity, mean water vapor pressure, mean wind velocity at 10 m height, and sunshine duration from Luochuan National Weather Station.

Main Results

• Soil moisture (SM) in edge zones (L1, L2) was consistently 8–27 % lower than in inner zones (L3), particularly at 40 cm and 70 cm depths, with the strongest impacts during the fruit growth stage.
• SM deficits intensified closer to the channel margin (L1 > L2) due to root water uptake by sidewall trees, which consumed 25–43 % of rainfall during the growing season.
• Only heavy rainstorms (e.g., 195.9 mm event) fully replenished root-zone water (0–70 cm profile), eliminating inner–edge SM deficits, while smaller rainfall events provided only short-lived relief for shallow soil layers.
• The difference in soil water storage (DSWS) between inner and edge zones increased with cumulative reference evapotranspiration and initial DSWS, but decreased with greater rainfall depth.
• In dry years, edge-zone apple trees faced intensified competition from sidewall vegetation, capturing proportionally less rainfall than inner-zone trees.
• Hydrus-1D simulations accurately represented soil water balance in the inner zone (L3) but consistently overestimated SM at 40 cm and 70 cm depths in edge zones (L1, L2), confirming additional water consumption by sidewall vegetation.
• Water balance analysis showed deep drainage varied spatially (e.g., 6.3 mm at L1 vs. 154.2 mm at L3 in 2023), and apple tree root water uptake was restricted in edge zones (58.72 % and 75.2 % of L3 at L1 and L2, respectively, in 2023).

Contributions

• Provides quantitative evidence of persistent soil moisture reduction in agricultural edge zones along deep-cut channels, extending the understanding of gully-edge effects to larger channel systems.
• Quantifies the significant role of root water uptake by channel sidewall vegetation (25–43 % of rainfall) as a primary driver of lateral soil water depletion, highlighting its greater impact compared to previously studied shrub/grass-dominated gully systems.
• Demonstrates that the horizontal influence distance of channel-side vegetation on soil moisture can extend beyond 7 m, affecting at least two rows of apple trees, which is double the previously reported limits for gullies.
• Establishes an empirical relationship (Eq. 11) to predict the difference in soil water storage (DSWS) based on rainfall depth, evapotranspiration, and initial DSWS, offering a practical tool for irrigation management.
• Highlights the critical importance of heavy rainstorms for deep soil water replenishment and suggests targeted pulse irrigation strategies that mimic such events to mitigate water stress in edge zones, especially during critical fruit growth stages.
• Proposes a management strategy of replacing deep-rooted trees with shallow-rooted shrubs and grasses on steep channel sidewalls to balance erosion control and soil water conservation for agriculture.

Funding

• National Natural Science Foundation of China (42477360, 12272186, 42007056)
• Yulin Radiance Grant (KJZG-2025-QZ-01)

Citation

@article{Wu2026Spatiotemporal,
  author = {Wu, Songbai and Chen, Li and Wang, Ninglian and Wei, Na and Hu, Sheng and Liu, Haoyue and Svoray, Tal and Assouline, S.},
  title = {Spatiotemporal dynamics of soil moisture in edge zones along deep-cut channels of rainfed agricultural plateaus},
  journal = {Agricultural Water Management},
  year = {2026},
  doi = {10.1016/j.agwat.2025.110105},
  url = {https://doi.org/10.1016/j.agwat.2025.110105}
}