Amma et al. (2025) Balancing yield and water productivity in sweetpotato through crop evapotranspiration–based irrigation scheduling across seasons

Identification

• Journal: Irrigation Science
• Year: 2025
• Date: 2025-12-29
• Authors: Sunitha Sarojini Amma, Saravanan Raju, Suresh Kumar Jabu, Ramesh Varadharajan, G. Suja
• DOI: 10.1007/s00271-025-01070-5

Research Groups

• Indian Council of Agricultural Research - Central Tuber Crops Research Institute, Thiruvananthapuram, Kerala, India

Short Summary

This study evaluated crop evapotranspiration (ETc)-based irrigation scheduling for sweetpotato over three seasons in South India, comparing drip, sprinkler, and furrow methods. It found that irrigation at 100–112% ETc maximized tuber yield, while moderate deficit irrigation (63–75% ETc) optimized water productivity, highlighting a critical trade-off for growers.

Objective

• To compare the effects of different irrigation schedules on sweetpotato yield and water productivity across three seasons.
• To determine the crop evapotranspiration (ETc) level that optimizes yield and water productivity indices.
• To explore the relationships among yield, canopy growth, soil moisture, and water productivity parameters.

Study Configuration

• Spatial Scale: Field trials conducted at the ICAR–Central Tuber Crops Research Institute, Thiruvananthapuram, India (8.54° N, 76.91° E, 50 m above mean sea level).
• Temporal Scale: Three consecutive sweetpotato cropping seasons (2020/21, 2021/22, and 2022/23), with experiments carried out from November to April each year.

Methodology and Data

• Models used:
  • FAO methodology (Allen et al. 1998) for calculating crop evapotranspiration (ETc = Kc × Kp × Ep).
  • FAO guidelines for pan coefficient (Kp) and crop coefficient (Kc) (Allen and Pruitt 1991, Savva and Frenken 2002).
  • FAO guidelines for estimating effective rainfall (Peff).
  • Quadratic regression models to identify optimum irrigation depths for yield, irrigation water productivity (IWP), and total water productivity (TWP).
  • Combined analysis of variance (ANOVA) using a Randomized Block Design (RBD) framework.
  • R software (R Core Team 2024) with lme4, emmeans, and ggplot2 packages for statistical analysis.
• Data sources:
  • Field measurements of sweetpotato growth parameters (vine length, number of leaves, leaf area index (LAI)), yield components (fresh storage tuber yield, mean tuber number, tuber weight per plant, harvest index).
  • Gravimetric soil moisture content at 0–30 cm depth.
  • Daily weather data from an agro-meteorological observatory (air temperature, relative humidity, rainfall, solar radiation, wind speed).
  • Pan evaporation (Ep) data from the experimental site.
  • Irrigation volumes monitored using water meters.

Main Results

• Tuber yield peaked at 23.2 tonnes per hectare (t ha⁻¹) under 100% ETc drip irrigation, significantly outperforming sprinkler (14.4 t ha⁻¹) and furrow (16.6 t ha⁻¹) methods.
• Soil moisture content (0–30 cm) ranged from approximately 8.7% at 50% ETc to 14.7% at 100% ETc, directly reflecting irrigation levels.
• Irrigation Water Productivity (IWP) was highest under deficit drip irrigation (50–75% ETc), reaching 14–16 kilograms per cubic meter (kg m⁻³).
• Total Water Productivity (TWP) generally peaked under mild deficit irrigation (approximately 63–75% ETc), but its optimal level varied seasonally due to differing effective rainfall contributions.
• Quadratic regression analysis indicated an optimum ETc level of approximately 112% for maximizing tuber yield and approximately 63% for maximizing total water productivity.
• Yield advantages under optimal irrigation were primarily due to increased individual tuber weight, rather than changes in tuber number or harvest index.
• Drip irrigation consistently demonstrated superior performance in both yield and water productivity compared to sprinkler and furrow irrigation methods.

Contributions

• Provided a multi-season, comprehensive evaluation of ETc-based irrigation scheduling for sweetpotato, addressing a gap in existing literature often limited to single seasons.
• Quantified the trade-off between yield maximization and water productivity for sweetpotato, identifying distinct optimal ETc levels (112% for yield, 63% for TWP) crucial for tailored irrigation management.
• Highlighted the significant influence of seasonal rainfall on optimal water productivity, demonstrating that the most water-efficient treatment can vary with climatic conditions.
• Confirmed the superior performance of drip irrigation over conventional methods (sprinkler, furrow) for sweetpotato in tropical environments, offering practical guidance for growers.
• Generated site-specific data and recommendations for sweetpotato irrigation in South India, supporting national water-use efficiency initiatives for tropical tuber crops.

Funding

No special funding was received; the research was part of an institute project.

Citation

@article{Amma2025Balancing,
  author = {Amma, Sunitha Sarojini and Raju, Saravanan and Jabu, Suresh Kumar and Varadharajan, Ramesh and Suja, G.},
  title = {Balancing yield and water productivity in sweetpotato through crop evapotranspiration–based irrigation scheduling across seasons},
  journal = {Irrigation Science},
  year = {2025},
  doi = {10.1007/s00271-025-01070-5},
  url = {https://doi.org/10.1007/s00271-025-01070-5}
}