Cui et al. (2025) Energy flux, evapotranspiration, and crop coefficients of drip-irrigated kiwifruit and citrus orchards in Southwest China

Identification

• Journal: Agricultural Water Management
• Year: 2025
• Date: 2025-11-27
• Authors: Ningbo Cui, Chenggaoge Yang, Xiuyun Yu, Daozhi Gong, Yu Feng, Xiaoxian Zhang, Lu Zhao, Zhihui Wang, Jingyuan Xue, Shouzheng Jiang
• DOI: 10.1016/j.agwat.2025.109984

Research Groups

• State Key Laboratory of Hydraulics and Mountain River Engineering & College of Water Resource and Hydropower, Sichuan University, Chengdu, China
• State Engineering Laboratory of Efficient Water Use of Crops and Disaster Loss Mitigation, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agriculture Science, Beijing, China
• Ningbo Institute of Digital Twin, Eastern Institute of Technology, Ningbo, China
• Department of Sustainable Soils and Grassland Systems, Rothamsted Research, Harpenden, Hertfordshire, United Kingdom
• Institute for Disaster Management and Reconstruction, Sichuan University, Chengdu, China

Short Summary

This study investigated energy flux, evapotranspiration (ET), and crop coefficients (Kc, Kcb) in drip-irrigated kiwifruit and citrus orchards in Southwest China using eddy covariance and sap flow measurements, providing locally calibrated coefficients and insights into their biophysical regulation for improved irrigation management.

Objective

• To study the seasonal variations in energy and water fluxes in kiwifruit and citrus orchards in Southwest China.
• To determine local single (Kc) and basal (Kcb) crop coefficients based on actual evapotranspiration (ET) and transpiration (T) measurements.
• To analyze the regulation of Kc and Kcb by biophysical variables such as leaf area index, growing degree days, and underlying conductance.

Study Configuration

• Spatial Scale: Two perennial orchard ecosystems (kiwifruit in Pujiang, citrus in Qionglai) in the humid subtropical Western Sichuan Basin, Southwest China. Each site covered an area sufficient for Eddy Covariance measurements (90% effective fetch within 240-500 meters).
• Temporal Scale: Kiwifruit growing seasons (2018–2020, 3 years); Citrus growing seasons (2020–2023, 4 years). Daily and seasonal variations were analyzed.

Methodology and Data

• Models used: Eddy Covariance (EC) system for energy fluxes (latent and sensible heat), Penman-Monteith equation (FAO-56) for reference evapotranspiration (ETo), dual crop coefficient method (Kc, Kcb, Ke), Granier heater dissipation method for sap flow (transpiration), Backpropagation neural network (BP) model for gap-filling latent heat flux, Monteith (1965) for underlying conductance (Gs), Growing Degree Days (GDD) calculation.
• Data sources: Eddy Covariance system observations (3D sonic anemometer, CO2/H2O gas analyzers), automatic weather stations (air temperature, relative humidity, precipitation, net radiation, wind speed, air pressure, soil temperature, soil moisture profile, soil heat flux), leaf area index (LAI-2000 meter, MODIS 15A2H reflectance product), sap flow sensors, gravimetric soil moisture samples, increment borer for sapwood area.

Main Results

• Energy partitioning: Latent heat flux consumed the majority of net radiation (70.9 % for kiwifruit, 69.9 % for citrus).
• Evapotranspiration (ET) and Transpiration (T): Average daily ET was 2.04 ± 0.18 mm d⁻¹ for kiwifruit and 2.49 ± 0.25 mm d⁻¹ for citrus. Average daily T was 1.15 ± 0.16 mm d⁻¹ for kiwifruit and 1.18 ± 0.09 mm d⁻¹ for citrus. T contributed approximately 57 % of total ET for kiwifruit and 52 % for citrus.
• Kiwifruit standard crop coefficients (Kc-standard): Initial stage: 0.74 ± 0.01; Mid-season stage: 0.99 ± 0.02; Late-season stage: 0.82 ± 0.01.
• Kiwifruit standard basal crop coefficients (Kcb-standard): Initial stage: 0.24 ± 0.09; Mid-season stage: 0.58 ± 0.05; Late-season stage: 0.63 ± 0.09.
• Citrus standard crop coefficients (Kc-standard): Initial stage: 0.92 ± 0.03; Mid-season stage: 1.01 ± 0.03; Late-season stage: 0.95 ± 0.07.
• Citrus standard basal crop coefficients (Kcb-standard): Initial stage: 0.59 ± 0.03; Mid-season stage: 0.61 ± 0.02; Late-season stage: 0.69 ± 0.03.
• Regulation of crop coefficients: Locally derived Kc and Kcb were significantly regulated by leaf area index (LAI), growing degree days (GDD), and underlying conductance (Gs). Seasonal rainfall and vegetation cover also notably influenced local Kc, particularly in wide-row citrus orchards.

Contributions

• Provides one of the first comprehensive, long-term datasets combining Eddy Covariance and sap flow measurements to calibrate and validate single and basal crop coefficients for drip-irrigated kiwifruit and citrus orchards in a humid subtropical climate.
• Fills a critical gap in the literature, which has largely focused on field crops in arid and semi-arid regions.
• Offers directly applicable, locally calibrated crop coefficients and insights for improving precise irrigation water management in similar humid hilly agroecosystems of Southwest China.
• Demonstrates that FAO-56 tabulated values may not be directly applicable in humid subtropical orchards with active ground cover and wide row spacing, emphasizing the need for local calibration and atmospheric correction.

Funding

• National Key Research and Development Program of China (2023YFD1901203, 2021YFD1600803-1)
• National Natural Science Foundation of China (52309055, 52279041)
• Sichuan Province Science and Technology Program (2023YFN0024)
• Fundamental Research Funds for the Central Universities (YJ202259)
• Training Program of the Innovation Guidance and Scientific and Technological Enterprise of Yunnan Province (202304BT090019)
• Technological Innovation and R&D Project of Chengdu Eastern New Area (2024-DBXQ-KJYF008-LH)

Citation

@article{Cui2025Energy,
  author = {Cui, Ningbo and Yang, Chenggaoge and Yu, Xiuyun and Gong, Daozhi and Feng, Yu and Zhang, Xiaoxian and Zhao, Lu and Wang, Zhihui and Xue, Jingyuan and Jiang, Shouzheng},
  title = {Energy flux, evapotranspiration, and crop coefficients of drip-irrigated kiwifruit and citrus orchards in Southwest China},
  journal = {Agricultural Water Management},
  year = {2025},
  doi = {10.1016/j.agwat.2025.109984},
  url = {https://doi.org/10.1016/j.agwat.2025.109984}
}