Li et al. (2025) Quantification of water uptake by winter wheat roots under different dripline burial depths using hydrogen and oxygen stable isotopes

Identification

• Journal: Agricultural Water Management
• Year: 2025
• Date: 2025-11-20
• Authors: Yanni Li, Junting You, Shangtong Yang, Zhe Zhang, Siying Huang, Guochun Li, Jun Sun, Chang Lv, Menglong Wu, Wenquan Niu, Qirui Gao, Kadambot H.M. Siddique
• DOI: 10.1016/j.agwat.2025.109983

Research Groups

• College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling, Shaanxi, China
• Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of Ministry of Education, Northwest A&F University, Yangling, Shaanxi, China
• Institute of Soil and Water Conservation, Northwest A&F University, Yangling, Shaanxi, China
• University of Chinese Academy of Sciences, Beijing, China
• Department of Hydraulic Engineering, Shaanxi Vocational and Technical University of A&F, Yangling, Shaanxi, China
• Faculty of Arts, McGill University, Gatineau, Quebec, Canada
• The UWA Institute of Agriculture, The University of Western Australia, Perth, Western Australia, Australia

Short Summary

This two-year field study investigated the optimal dripline burial depth for winter wheat under drip irrigation in the Guanzhong Plain using stable isotopes. It found that a 20 cm subsurface dripline depth significantly enhanced root water uptake efficiency and water use efficiency by optimizing root-zone water availability and promoting dynamic water uptake shifts.

Objective

• Examine soil moisture and root spatial distribution under varying dripline burial depths.
• Quantify the proportional contribution of water uptake from different soil layers across growth stages using stable isotope techniques and the MixSIAR Bayesian model.
• Explore how root–soil water interactions influence crop yield and water use efficiency (WUE) under different burial depths.

Study Configuration

• Spatial Scale: Field experiment conducted in the Guanzhong Plain, China (34°20′N, 108°23′E, altitude 520 m). Individual plots measured 20 m × 2.4 m (48 m²). Soil profile analyzed up to 100 cm for moisture and 120 cm for roots.
• Temporal Scale: Two winter wheat growing seasons, from October 2022 to June 2024.

Methodology and Data

• Models used:
  • MixSIAR Bayesian mixing model (to quantify proportional contributions of water uptake from different soil layers).
  • FAO-56 Penman–Monteith equation (to calculate reference crop evapotranspiration, ET0).
• Data sources:
  • Field experiment with five irrigation treatments: surface drip irrigation (DI) and four subsurface drip irrigation (SDI) treatments with dripline burial depths of 10 cm (S10), 20 cm (S20), 30 cm (S30), and 40 cm (S40).
  • Stable hydrogen (δ²H) and oxygen (δ¹⁸O) isotope tracers from soil water, plant stem water, irrigation water, and precipitation.
  • Soil moisture content measured gravimetrically and with Time-Domain Reflectometry (TDR) probes.
  • Root sampling to determine root weight density (RWD).
  • Meteorological data from an automated weather station at the experimental site.
  • Grain yield measurements.

Main Results

• Subsurface drip irrigation (SDI) significantly enhanced soil water storage after the jointing stage, with increases ranging from 0.63 % to 19.75 % compared to surface drip irrigation (DI).
• Winter wheat roots were predominantly concentrated in the 0–20 cm soil layer, accounting for 78.33–95.21 % of total root mass. Root weight density followed a bell-shaped curve over the growing season.
• Root water uptake (RWU) patterns varied with dripline depth:
  • In DI, water was mainly absorbed from 0–20 cm during early stages, shifting to 20–60 cm during grain filling.
  • In S20 and S30, uptake initially occurred in 0–20 cm, moved deeper (20–60 cm) during jointing to flowering, and returned to 0–20 cm during grain filling.
• MixSIAR model results indicated that the 0–20 cm layer contributed an average of 52.04 % of total water uptake, followed by 60–120 cm (27.49 %) and 20–60 cm (27.36 %).
• The 20 cm dripline burial depth (S20) consistently achieved the highest grain yield and water use efficiency (WUE) in both years.
  • Yield increase: 4.59–7.68 % compared to DI.
  • WUE increase: 8.02–13.63 % compared to DI.
• The S20 treatment established a stable moisture environment in the 20–60 cm root zone, promoting deeper root growth and enabling a dynamic RWU shift from shallow (0–20 cm) to deep (20–60 cm) layers during the critical jointing–flowering period, achieving spatiotemporal coordination between water supply and crop demand.

Contributions

• Quantitatively assessed the dynamic root water uptake (RWU) patterns of winter wheat across growth stages and under different dripline burial depths using stable isotopes and the MixSIAR Bayesian model, providing mechanistic insights into soil-plant-water interactions.
• Identified a "decoupling" between root biomass distribution and RWU contribution rates, demonstrating that plants actively deplete soil moisture and preferentially use deeper soil moisture under water stress, rather than being passively constrained by root biomass.
• Provided a theoretical and practical reference for optimizing subsurface drip irrigation (SDI) strategies, specifically recommending a 20 cm dripline burial depth combined with deficit irrigation (70 % ETc) for winter wheat in the Guanzhong Plain and similar arid/semi-arid regions.
• Demonstrated that the optimal SDI configuration maintains stable moisture in the most active root zones throughout the season, enabling flexible and efficient water use from different soil layers according to physiological needs.

Funding

• National Natural Science Foundation of China (52379048)
• National Natural Science Foundation of China (52079112)

Citation

@article{Li2025Quantification,
  author = {Li, Yanni and You, Junting and Yang, Shangtong and Zhang, Zhe and Huang, Siying and Li, Guochun and Sun, Jun and Lv, Chang and Wu, Menglong and Niu, Wenquan and Gao, Qirui and Siddique, Kadambot H.M.},
  title = {Quantification of water uptake by winter wheat roots under different dripline burial depths using hydrogen and oxygen stable isotopes},
  journal = {Agricultural Water Management},
  year = {2025},
  doi = {10.1016/j.agwat.2025.109983},
  url = {https://doi.org/10.1016/j.agwat.2025.109983}
}