Evaluation of energy and cumulative exergy demand indicators of different lettuce production methods in Alborz province

Document Type : Research Paper

Authors

• Hassan Ghasemi Mobtaker ¹
• Majid Khanali ²
• Mohammad Ali Ghahremani-Aghbolagh Rostam Khan ²
• Alireza Rafiei ²

¹ Department of Agricultural Machinery Engineering, Faculty of Agricultural Engineering and Technology, University of Tehran, Karaj, Iran

² Department of Agricultural Machinery Engineering, Faculty of Agriculture, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

Abstract

Keywords

• Energy
• Lettuce
• Pressurized Irrigation
• Renewable resources
• Water productivity

Main Subjects

• energy management

EXTENDED ABSTRACT

Introduction

Energy and water as essential inputs of irrigation system are key and vital elements for social and economic development. In the agricultural sector, a main part of energy utilized for crops production is for irrigation systems. Today, the use of pressurized irrigation systems along with seedlings has been developed to manage water and energy resources, However, the results of the studies indicate that although the use of pressurized irrigation increased water use efficiency, it also increased energy consumption. This can lead to environmental burdens, so effective and efficient usage of energy sources is considered as fundamental requirements of sustainable agriculture. So, the goal of the current study is to evaluate the energy, water and cumulative exergy demand (CExD) indicators of different lettuce production methods in Alborz province to introduce a stable production system.

Material and Methods

This study was undertaken in Alborz province, and four different lettuce production methods systems were studied and compared from energy and exergy point of view. The data required for this study were collected through face-to-face interviews and the completion of 60 questionnaires. The utilized inputs for lettucd production, including total direct and indirect inputs, are recorded during the growing season and then energy equivalences are computed by using energy coefficients. According to inputs/outputs as well as their energy equivalents, energy indices are computed. For the assessment of CExD indicators in this study, the CExD V1.07 method available in the SimaPro software, which utilizes data from databases such as Ecoinvent, was employed to determine the cumulative exergy of renewable and non-renewable resources in different lettuce production systems.

Results and Discussion

The results of this study highlight significant variation in energy inputs and outputs across different lettuce production systems in Alborz Province. Average energy consumption ranged from 54,734.04 MJ ha⁻¹ in seedling–drip irrigation to 107,409.79 MJ ha⁻¹ in seedling–flood irrigation. The lettuce production systems showed higher reliance on diesel fuel due to water pumping requirements. For one ton of lettuce, the major inputs were diesel fuel in seed–flood and seedling–flood, while diesel fuel and nylon dominated in seed–drip and seedling–drip. Energy indices confirmed these patterns: the highest energy ratio (0.68) and productivity (0.97 kg MJ⁻¹) occurred in seed–drip irrigation, whereas whereas seed–flood had a lowest energy ratio and productivity. Net energy gain was negative in all investigated systems, indicating inefficiency. Water productivity, however, was greatest in seedling–drip (18.75 kg m⁻³), highlighting the trade-off between water efficiency and energy performance. CExD analysis confirmed the dominance of fossil non-renewables across all methods, particularly in seed–flood (3438.51 MJ) and seedling–flood (2188.70 MJ). Diesel, nylon, electricity, and chemical fertilizers were the principal contributors to the exergy burden, which aligns with evidence from other crops where diesel and fertilizers play a decisive role in energy inefficiency. These results emphasize that achieving sustainability in lettuce production requires targeted interventions: optimizing diesel use, adopting high-efficiency machinery, integrating renewable energy for irrigation, substituting organic fertilizers for chemical ones, and replacing nylon with biodegradable alternatives. Such strategies directly address the most energy-intensive inputs and could substantially reduce fossil dependency while maintaining crop performance.

Conclusions

This study evaluated energy efficiency and CExD in lettuce production systems in Alborz Province, Iran, with emphasis on the drip irrigation systems for seedlings and seeds. Total energy inputs ranged from 54,734.04 to 107,409.79 MJ ha⁻¹, with diesel fuel dominating flood irrigation and diesel fuel and nylon as the main contributor in drip systems. Across all methods, direct and nonrenewable energy inputs prevailed, primarily from electricity, diesel fuel, and nylon. The energy ratio was less than one in all systems and water productivity was highest in seedling–drip (18.75 kg m⁻³). CExD analysis confirmed fossil non-renewables as the dominant burden, particularly in seed–flood (3,438.51 MJ) and seedling–flood (2,188.70 MJ). Strategies such as optimizing energy-intensive inputs, using organic fertilizers, adopting renewable energy, and replacing nylon with biodegradable alternatives are recommended to enhance sustainability.

Author Contributions

Conceptualization, H.GM., M.Kh. and M.A.GARKh.; methodology, H.GM. and M.A.GARKh.; software, M.A.GARKh. and A.R.; validation, H.GM. and M.Kh.; formal analysis, H.GM., M.Kh. and M.A.GARKh.; investigation, A.R.; resources, A.R. and H.GM.; data curation, H.GM., M.Kh., M.A.GARKh. and A.R.; writing-original draft preparation, H.GM. and M.A.GARKh.; writing-review and editing, H.GM. and M.Kh.; visualization, A.R. and M.A.GARKh.; supervision, H.GM. and M.Kh.; project administration, A.R. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

The data that support the findings of this study will be available from the corresponding author on reasonable requests.

Acknowledgments

The authors would like to acknowledge for all supports by Faculty of Agricultural Engineering and Technology, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

Ethical considerations

The study was approved by the Ethics Committee of the University of Tehran. authors avoided data fabrication, falsification, plagiarism, and misconduct.

Conflict of interest

The authors declare no conflicts of interest.