Madhavan et al. (2025) Quantitative assessment of cotton evapotranspiration, irrigation requirements and water productivity from weather-based estimations

Identification

• Journal: Plant Science Today
• Year: 2025
• Date: 2025-11-19
• Authors: Gnanasekaran Madhavan, S Pazhanivelan, A P Sivamurugan, D Muthumanickam, S Selvakumar, K P Ragunath
• DOI: 10.14719/pst.11843

Research Groups

• Department of Agronomy, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India
• Centre for Water and Geospatial Studies, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India
• Department of Rice, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India
• Department of Remote Sensing & GIS, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India

Short Summary

This study quantitatively assessed cotton water use and productivity in a semi-arid region, demonstrating that locally calibrated crop coefficients improve evapotranspiration estimation, leading to enhanced yield and water use efficiency through precise irrigation scheduling.

Objective

• To quantitatively assess cotton (CO 17) water use, irrigation requirements, and water productivity under semi-arid conditions using weather-based estimations.
• To estimate crop evapotranspiration (ETc) and irrigation water requirement (IWR) by integrating climatic variability and effective rainfall.
• To evaluate water productivity under full irrigation.
• To validate locally derived crop coefficient (Kc) values against FAO standards.
• Hypothesis: Weather-based ETc estimation, supported by locally calibrated Kc, can accurately quantify cotton water use and irrigation requirements, thereby improving water productivity in semi-arid Tamil Nadu.

Study Configuration

• Spatial Scale: Field experiments at the Agricultural Research Station (ARS), Bhavanisagar, Tamil Nadu Agricultural University, Coimbatore, India, on sandy loam soils.
• Temporal Scale: Three cotton-growing seasons: Season 1 (August 2023 - January 2025), Season 2 (March 2024 - July 2024), and Season 3 (October 2024 - February 2025).

Methodology and Data

• Models used:
  • ASCE standardized Penman-Monteith equation for reference evapotranspiration (ETo).
  • Locally developed crop coefficient (Kc) curve based on thermal units (TU).
  • FAO-56 standardized Kc values, adjusted for local climatic conditions and crop height.
  • USDA Soil Conservation Service method for effective rainfall (Pe = 0.8P - 0.2).
• Data sources:
  • Continuous field monitoring of weather parameters (maximum and minimum temperature, maximum and minimum relative humidity, wind speed at 2 m height, solar radiation) from a meteorological observatory and automatic weather station.
  • Soil moisture monitoring.
  • Crop parameters (seed cotton yield, lint yield, cotton seed yield).
  • Irrigation water applied and rainfall data.
  • Statistical analyses: Paired t-tests, regression analyses, Shapiro-Wilk test, Levene’s test, and Bonferroni correction.

Main Results

• Seasonal crop evapotranspiration (ETc) ranged from 386 to 607 mm, with irrigation applied varying between 170 and 336 mm.
• Seed cotton yield ranged from 1997 to 2237 kg/ha, and lint yield from 678.8 to 761.7 kg/ha.
• Water use efficiency (WUE) ranged from 0.107 to 0.155 kg/m³, and water productivity (WP) from 0.32 to 0.46 kg/m³.
• Paired t-tests showed no significant difference (p > 0.05) between locally developed and FAO-based ETc estimates.
• A strong linear relationship (R² = 0.93) was observed between adjusted ETc and irrigation applied, indicating adjusted ETc as a reliable predictor for irrigation scheduling.
• Locally calibrated Kc values improved ETc estimation by better representing canopy development and climatic variability.
• Precision irrigation, aligned with adjusted ETc, enhanced yield, water productivity, and resource-use efficiency.
• Excessive irrigation negatively impacted lint yield and water use efficiency, with strong inverse relationships observed (e.g., R² = 0.60 for irrigation vs. lint yield, R² = 0.81 for irrigation vs. ET-WUE, R² = 0.90 for total water supply vs. crop WUE).
• Locally adjusted irrigation estimates consistently exceeded FAO estimates (R² = 0.98), attributed to local climatic factors (higher wind speed, lower relative humidity) and the vigorous growth of the CO 17 cotton variety.

Contributions

• Provides site-specific validation and calibration of the FAO-56 crop coefficient (Kc) for cotton (CO 17) in a semi-arid environment (Tamil Nadu), addressing a gap where original FAO coefficients were mainly developed under sub-humid to humid conditions.
• Demonstrates that locally calibrated Kc values significantly improve the accuracy of ETc and irrigation requirement estimations, leading to enhanced water productivity and yield stability.
• Emphasizes the importance of ET-based irrigation management for sustainable cotton production in water-limited environments.
• Offers a practical, locally developed Kc equation for farmers and irrigation planners in semi-arid conditions to optimize water use, achieve higher yields, and reduce water loss.

Funding

The authors gratefully acknowledge the support and facilities provided by the Agricultural Research Station (ARS), Bhavani Sagar, and the Centre for Water and Geospatial Studies (CWGS), Tamil Nadu Agricultural University (TNAU), Coimbatore. The Department of Agronomy, TNAU, also provided guidance and assistance. No specific project or program funding codes were listed.

Citation

@article{Madhavan2025Quantitative,
  author = {Madhavan, Gnanasekaran and Pazhanivelan, S and Sivamurugan, A P and Muthumanickam, D and Selvakumar, S and Ragunath, K P},
  title = {Quantitative assessment of cotton evapotranspiration, irrigation requirements and water productivity from weather-based estimations},
  journal = {Plant Science Today},
  year = {2025},
  doi = {10.14719/pst.11843},
  url = {https://doi.org/10.14719/pst.11843}
}