Ono et al. (2025) Multi-year water and carbon flux contrasts between high-yielding and conventional rice cultivars

Identification

• Journal: Agricultural and Forest Meteorology
• Year: 2025
• Date: 2025-12-18
• Authors: Keisuke Ono, Hiroki Ikawa, Akira Miyata
• DOI: 10.1016/j.agrformet.2025.110983

Research Groups

• Institute for Agro-Environmental Sciences, National Agriculture and Food Research Organization, Tsukuba, Japan
• Hokkaido Agricultural Research Center, National Agriculture and Food Research Organization, Sapporo, Japan

Short Summary

This study used eddy covariance to compare multi-year water and carbon fluxes between a high-yielding indica rice (Oonari) and a conventional japonica rice (Koshihikari) in farmers' fields, finding Oonari exhibited significantly higher gross primary production and generally higher evapotranspiration, leading to greater water use efficiency.

Objective

• To clarify the seasonal dynamics of field-scale water and carbon fluxes (evapotranspiration, photosynthesis, respiration, and water use efficiency) for a high-yielding indica rice variety (Oonari) compared to a widely cultivated japonica variety (Koshihikari) under actual farming conditions.

Study Configuration

• Spatial Scale: Two farmers' fields in Ibaraki, Japan, approximately 25 kilometers apart. The Ryugasaki (RGS) site (35°56′N, 140°15′E, 3 m above sea level) was planted with Oonari, and the Mase (MSE) site (36°03′N, 140°01′E, 11 m above sea level) was planted with Koshihikari. Both sites were flat paddy areas, 160 m and 200 m from the field boundary, respectively.
• Temporal Scale: Three consecutive growing seasons (2018, 2019, 2020), from transplanting (May) to harvest (September). Flux and meteorological data were collected continuously and processed into half-hourly and daily sums.

Methodology and Data

• Models used:
  • FAO56 (Allen et al., 1998) for calculating reference evapotranspiration (ET0).
  • Kondo and Xu (1996) for calculating potential evaporation (Ep).
  • REddyProc R package (Wutzler et al., 2018) for gap-filling of water vapor flux (ET).
  • Standard non-linear approach by Reichstein et al. (2005) and Lasslop et al. (2010) for partitioning net ecosystem production (NEP) into gross primary production (GPP) and ecosystem respiration (RE), also using REddyProc.
• Data sources:
  • Eddy covariance flux measurements: 3-D sonic anemometers (CSAT3, DA-600) and open-path CO2/H2O analyzers (LI-7500) at approximately 3 m above ground, recorded at 10 Hz.
  • Meteorological measurements: Double-wall shielded and ventilated humidity and temperature sensors (HMP155), four-component radiometer (MR-40), and pyranometer (CMP6), sampled every 5 seconds and averaged over 30 minutes.
  • Crop growth monitoring: Plant sampling (10 hills per stage) for green leaf area (optical leaf area meter LI-3100C) and dry weight (leaves, stems, roots, panicles) after drying at 70 °C for 2 weeks.
  • Field management data: Total nitrogen (N) application, yield, transplanting, heading, and harvest dates, and duration of growth period.

Main Results

• Evapotranspiration (ET): Oonari generally exhibited higher ET. In 2018 and 2019, Oonari's seasonal total ET was 9.6 % higher than Koshihikari (2018: 549.6 mm vs 501.2 mm; 2019: 472.0 mm vs 430.5 mm). In 2020, Oonari's ET was 6.0 % smaller (426.5 mm vs 453.9 mm) due to a shorter growth period.
• Gross Primary Production (GPP): Oonari showed significantly higher GPP, averaging 24 % more than Koshihikari (Oonari: 1175.2 ± 76.5 g C m⁻²; Koshihikari: 946.5 ± 32.7 g C m⁻²).
• Leaf Area Index (LAI): Oonari exhibited faster LAI development, leading to earlier canopy closure (approximately 13 days earlier) and maintaining a consistently higher LAI throughout the growing season (maximum 7.1 ± 0.3 m² m⁻² for Oonari vs 4.8 ± 0.6 m² m⁻² for Koshihikari, 47.9 % larger on average).
• Crop Coefficient (Kc) and Radiation Use Efficiency (RUE): Oonari had higher average Kc values (approximately 13 % higher in 2018 and 2019) and generally higher RUE, with differences being more pronounced during early growth (Stage 2) and senescence (Stages 4 and 5).
• Water Use Efficiency (WUE): Ecosystem WUE was consistently higher in Oonari across all indicators: GPP-based WUE (+16.9 ± 3.9 %), NEP-based WUE (+11.6 ± 2.0 %), total weight-based WUE (+9.2 ± 7.3 %), and panicle weight-based WUE (+29.4 ± 12.6 %).
• Carbon Allocation: Oonari demonstrated a higher harvest index (DWpanicle/DWtotal) of 0.49 ± 0.01 compared to Koshihikari's 0.41 ± 0.01, indicating a greater proportion of fixed carbon allocated to grain production. The RE/GPP ratio was nearly identical for both varieties (approximately 53 %).

Contributions

• Provided the first field-scale, full-season comparison of water and carbon fluxes between a high-yielding indica rice variety (Oonari) and a conventional japonica variety (Koshihikari) using eddy covariance under actual farmer management practices.
• Demonstrated that varietal differences in leaf area index (LAI) development, including earlier canopy closure and sustained higher LAI, are primary drivers for observed differences in evapotranspiration and gross primary production, particularly during early growth and senescence.
• Quantified that the cultivation of Oonari has a more pronounced impact on the carbon cycle (higher GPP and WUE) than on water use, despite generally higher evapotranspiration.
• Emphasized the critical need for integrated, full-season, field-based evaluations of water and carbon dynamics to accurately assess the water use efficiency and productivity of high-yielding rice varieties, moving beyond leaf-level or controlled experimental settings.

Funding

• Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Numbers 19H03077, 19H03085, and 20H02889.
• Japan Science and Technology Agency (JST), PRESTO Grant Number JPMJPR17O4.

Citation

@article{Ono2025Multiyear,
  author = {Ono, Keisuke and Ikawa, Hiroki and Miyata, Akira},
  title = {Multi-year water and carbon flux contrasts between high-yielding and conventional rice cultivars},
  journal = {Agricultural and Forest Meteorology},
  year = {2025},
  doi = {10.1016/j.agrformet.2025.110983},
  url = {https://doi.org/10.1016/j.agrformet.2025.110983}
}