Kanno et al. (2025) Deep sowing accelerates rice emergence under water deficit: field experiments and model development

Identification

• Journal: Plant and Soil
• Year: 2025
• Date: 2025-11-07
• Authors: Noriko Kanno, Virender Kumar, Yoichiro Kato
• DOI: 10.1007/s11104-025-08012-2

Research Groups

• Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
• International Rice Research Institute, Laguna, Philippines

Short Summary

This study investigated the potential of deep sowing to accelerate rice emergence under water deficit, finding that sowing at 4 cm or deeper significantly advanced emergence in field experiments under drought. A novel process-based model was developed and validated, accurately predicting emergence dates based on sowing depth, soil temperature, and moisture, and suggesting optimal deep sowing depths to mitigate drought risk.

Objective

• To explore the potential of the deep sowing technique under drought stress in direct-seeded rice.
• To hypothesize that there would be an optimal sowing depth for direct-seeded rice, and that this depth would depend on soil moisture.

Study Configuration

• Spatial Scale: Field experiments conducted on a lowland farm in Nishitokyo, Japan (35°44′N, 139°32′E). Growth chamber experiments (1.1 m × 0.65 m × 0.56 m or 0.62 m × 0.56 m × 0.39 m or 1.1 m × 0.62 m × 0.33 m).
• Temporal Scale: Field experiment during summer 2023 (sowing on July 24, emergence counted 4 to 25 days after sowing). Growth chamber experiments with observations up to 14, 22, 21, or 37 days after sowing. Model simulations for germination and emergence periods.

Methodology and Data

• Models used:
  • Process-based model (developed in this study) for predicting emergence date, incorporating thermal time concept and soil water coefficients.
  • Thermal time concept (Covell et al. 1986; Garcia-Huidobro et al. 1982) for temperature effects on germination.
  • Log-normal distribution for thermal time constants.
  • Gompertz function (Gan et al. 1996) for time-series germination/emergence data.
  • Bilinear models for soil water tension effects on germination and shoot elongation rates.
  • Maximum-likelihood method for parameter fitting (probit values).
  • Non-linear least-squares method for parameter estimation (water coefficients).
• Data sources:
  • Field experiments: Rainfed conditions, four sowing depths (2, 4, 6, 8 cm), two rice cultivars (Rc420, Rc222). Soil water tension and temperature monitored at 1.5, 4.5, 7.5, and 15 cm depths using TEROS 21 or MPS-2 sensors. Number of emerged seedlings counted.
  • Growth chamber experiments: Controlled environments with varying constant temperatures (20, 30, 35, 40, 42 °C) and soil water tensions (10, 20, 30, 50, 70, 170, 250, 500, 550, 1000, 1200, 1350, 2970 kPa). Germination and emergence counts.
  • Soil: Silty loam (sand 30%, silt 57%, clay 13%) from the field site.

Main Results

• In the drought field experiment, sowing at 4 cm or deeper advanced rice emergence by more than 5 days compared to sowing at 2 cm.
• The developed process-based model accurately reproduced emergence dates from both moist and dry field experiments with a root-mean-square error (RMSE) of less than 1 day for both cultivars (Rc420: RMSE < 0.40 days, Rc222: RMSE = 0.63 days).
• Model simulations under severe drought predicted no emergence for 1 cm sowing depth, while under moderate drought, 1 cm sowing greatly delayed emergence.
• Sowing at 4 cm consistently resulted in faster emergence than other sowing depths under moderate drought conditions.
• Under moist soil conditions, 1 cm sowing yielded the fastest emergence.
• The simulated emergence period generally increased with increasing sowing depth, but the differences among soil moisture profiles were small for deeper sowings (4, 6, and 8 cm).
• The model fitting for temperature effects on germination showed strong R² values (0.79 to 0.98) and small RMSE (0.07 to 0.19). Lower limits of germination (LLG) were between 2 and 3 MPa, and lower limits of shoot elongation (LLE) were > 5 MPa for both cultivars.

Contributions

• This study provides the first field experimental evidence demonstrating that deep sowing (4 cm or deeper) can accelerate rice emergence under drought conditions compared to shallow sowing (2 cm).
• A novel process-based model was developed that integrates the simultaneous effects of sowing depth, soil temperature (including supraoptimal temperatures), and soil moisture on both germination and shoot elongation stages of direct-seeded rice. This model fills a gap in existing literature, as previous models often lacked comprehensive inclusion of these factors.
• The model was rigorously validated against field data, showing high accuracy (RMSE < 1 day), making it a valuable tool for predicting delayed emergence risk and suggesting optimal sowing depths for drought adaptation in direct-seeded rice.
• The research highlights the importance of considering soil moisture profiles at different depths for effective planting strategies in drought-prone environments.

Funding

• Japan Society for the Promotion of Science (JSPS) via Grant-in-Aid for Scientific Research (no. 22KK0083)
• Grand-in-Aid for JSPS Fellows (no. 24KJ0619)
• Open Access funding provided by The University of Tokyo.

Citation

@article{Kanno2025Deep,
  author = {Kanno, Noriko and Kumar, Virender and Kato, Yoichiro},
  title = {Deep sowing accelerates rice emergence under water deficit: field experiments and model development},
  journal = {Plant and Soil},
  year = {2025},
  doi = {10.1007/s11104-025-08012-2},
  url = {https://doi.org/10.1007/s11104-025-08012-2}
}

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