Document Type : Research Paper
Authors
1 Assistant Professor of Plant Production and Genetic Engineering, University of Malayer, Malayer, Hamedan.
2 Department of Soil Science, Faculty of Agriculture, Malayer University, Malayer, Iran
3 Department of Water and Soil Science, Faculty of Agriculture, Malayer University, Malayer, Iran
Abstract
Keywords
Main Subjects
Agricultural production in arid and semi-arid regions is increasingly constrained by limited water availability, high climatic variability, and growing environmental pressures associated with intensive input use. In such regions, improving productivity alone is no longer sufficient to ensure sustainability; instead, production systems must also minimize environmental externalities while maintaining economic viability. Among the various environmental pressures linked to agriculture, nitrogen pollution and greenhouse gas emissions are of particular concern due to their direct impacts on air and water quality, climate change, and ecosystem health.
Nitrogen fertilizers play a central role in modern crop production, yet their inefficient use results in substantial losses to the environment in the form of ammonia volatilization, nitrate leaching, nitrous oxide emissions, and other reactive nitrogen pathways. These losses not only reduce nitrogen use efficiency but also impose significant environmental and societal costs. At the same time, agricultural activities contribute notably to carbon emissions through fertilizer production, energy consumption, irrigation, machinery operation, and the use of agrochemicals. In water-scarce regions, the energy required for groundwater extraction and irrigation further amplifies the carbon footprint of crop production.
Footprint-based indicators, such as the nitrogen footprint (NF) and carbon footprint (CF), have emerged as powerful tools for quantifying these pressures in a unified and comparable manner. However, many existing studies focus on a single spatial or functional scale, most commonly emissions per unit land area. While area-based indicators are useful for regional emission inventories, they may provide a misleading picture of environmental efficiency when used alone, particularly in regions where crop yields and economic returns differ widely among crops.
This study addresses this limitation by applying a multi-scale footprint assessment framework to four major crops—wheat (Triticum aestivum L.), tomato (Solanum lycopersicum L.), onion (Allium cepa L.), and watermelon (Citrullus lanatus Thunb.)—cultivated in Sistan and Baluchestan Province, southeastern Iran. By simultaneously evaluating nitrogen and carbon footprints at the land-area, yield-based, and economic scales, the study aims to provide a more comprehensive understanding of the environmental efficiency of cropping systems in arid environments and to support informed decision-making regarding crop selection and resource management.
The assessment was conducted using a cradle-to-farm-gate perspective, focusing on agricultural input use and field-level emissions associated with crop production. Input–output data were obtained from official agricultural statistics, field surveys, and region-specific management practices representative of Sistan and Baluchestan Province. The selected crops represent both staple (wheat) and high-value horticultural products (tomato, onion, and watermelon), which together account for a substantial share of cultivated land and water use in the region.
The nitrogen footprint was quantified by accounting for both direct and indirect nitrogen losses. Direct losses included ammonia volatilization (NH₃), nitrate leaching (NO₃⁻), nitrous oxide emissions (N₂O), and ammonium leaching (NH₄⁺) resulting from nitrogen fertilizer application. These pathways were estimated using established emission factors and stoichiometric conversion coefficients reported in the literature. Indirect nitrogen emissions were calculated by considering nitrogen losses embedded in the production and transportation of agricultural inputs such as mineral fertilizers, organic manure, diesel fuel, electricity, and pesticides.
Total nitrogen footprint was first calculated on a per-hectare basis and subsequently normalized by crop yield to obtain nitrogen footprint per ton of product. To integrate the economic dimension, an economic nitrogen footprint indicator was derived by relating total nitrogen losses to the gross economic value of crop production, based on local market prices for each crop.
The carbon footprint was calculated by aggregating greenhouse gas emissions associated with the production and use of agricultural inputs and field operations. Emission sources included mineral fertilizers, organic manure, diesel fuel, electricity for irrigation, irrigation water delivery, machinery use, seeds, and agrochemicals. Emission factors were applied to each input to estimate emissions in terms of CO₂-equivalent.
Similar to the nitrogen footprint, carbon footprint results were first expressed per unit land area (kg CO₂-eq ha⁻¹) and then normalized by yield (kg CO₂-eq t⁻¹) and economic value (kg CO₂-eq USD⁻¹). This multi-scale approach enabled a consistent comparison of environmental performance across crops with different productivity levels and market values.
At the land-area scale, the results indicated that tomato and onion production exhibited the highest nitrogen and carbon footprints due to intensive input use and high irrigation demand. Wheat, in contrast, showed relatively lower footprints per hectare, reflecting its lower input intensity. However, area-based indicators alone masked important differences in productivity and economic efficiency among crops.
In the case of nitrogen footprint, indirect emissions associated with input production constituted the dominant share across all crops, highlighting the importance of upstream supply chains in shaping environmental outcomes. For carbon footprint, irrigation water and nitrogen fertilizer emerged as the primary emission sources, emphasizing the strong linkage between water management, energy use, and climate impacts in arid regions.
When normalized by yield, a markedly different pattern emerged. Wheat exhibited the highest nitrogen and carbon footprints per ton of product, despite its lower per-hectare emissions. This outcome was primarily driven by its low yield under the prevailing climatic and management conditions. In contrast, onion, tomato, and watermelon benefited from substantially higher yields, resulting in significantly lower footprint intensities per unit of output.
These findings demonstrate that yield plays a critical role in determining environmental efficiency. Crops with high productivity can effectively dilute the environmental burdens associated with input use, whereas low-yield systems concentrate emissions into a smaller amount of output, leading to higher footprint intensities.
The integration of economic value further amplified the contrasts among crops. Wheat displayed the highest nitrogen and carbon footprints per unit of economic return, indicating poor environmental–economic efficiency. Even with a relatively higher market price, the low yield of wheat resulted in limited economic output per hectare, thereby increasing the environmental cost per dollar earned.
Conversely, onion and watermelon showed the lowest footprint intensities per unit of economic value, reflecting a favorable combination of high productivity and reasonable market prices. Tomato occupied an intermediate position, with higher area-based footprints offset by strong yield performance.
Taken together, the results clearly demonstrate that sustainability assessments based solely on land-area indicators can be misleading, particularly in arid regions where yield variability is high. A multi-scale framework that incorporates land-area, yield-based, and economic-based indicators provides a more nuanced and policy-relevant understanding of environmental performance. Such an approach highlights trade-offs between food security, environmental protection, and economic viability that are not apparent when using a single metric.
This study underscores the importance of adopting a multi-dimensional perspective when evaluating the environmental sustainability of crop production systems in arid and semi-arid regions. The combined assessment of nitrogen and carbon footprints across land-area, yield, and economic scales revealed that crop rankings can change substantially depending on the chosen metric. Wheat, while often considered environmentally benign at the hectare scale, emerged as the least efficient crop when evaluated per unit of output and economic return. In contrast, high-yield horticultural crops demonstrated superior environmental efficiency despite higher input use.
From a management perspective, these findings suggest that efforts to reduce environmental pressures should prioritize improvements in productivity and resource-use efficiency rather than focusing exclusively on reducing input quantities. Enhancing nitrogen use efficiency, optimizing irrigation practices, and adopting energy-efficient water delivery systems can simultaneously reduce nitrogen and carbon footprints without compromising production.
At the policy level, the results highlight the need to move beyond area-based indicators in agricultural planning and subsidy schemes. Incorporating yield- and value-based footprint metrics into decision-making processes can support more sustainable cropping patterns and better alignment between environmental objectives and economic incentives. Future research should extend this framework by incorporating climate change scenarios, price volatility, and alternative management strategies to further refine sustainability assessments and guide long-term agricultural development in water-scarce regions.
This research was financially and institutionally supported by the Faculty of Agriculture, Malayer University, through the 2025 research grant awarded to the corresponding author. The authors gratefully acknowledge Malayer University for its financial and administrative support of this study.
For research articles with several authors, a short paragraph specifying their individual contributions must be provided. The following statements should be used “Conceptualization, Majid Dekamin; methodology, Majid Dekamin; software, Hossein Rezaei; validation, Hossein Rezaei, Amin Toranjian; formal analysis, Hossein Rezaei; data curation, Hossein Rezaei; writing—original draft preparation, Hossein Rezaei, Amin Toranjian; writing—review and editing, Majid Dekamin. All authors have read and agreed to the published version of the manuscript.”
During the preparation of this work the authors used ChatGPT in order to Grammer and English editing. After using this tool/service, the authors reviewed and edited the content as needed and takes full responsibility for the content of the publication.
Data available on request from the authors.
The authors gratefully acknowledge the Ministry of Agriculture Jihad of the Islamic Republic of Iran for providing access to the agricultural statistics and datasets used in this study. The availability of these official data resources was essential for conducting the analyses and achieving the objectives of this research. The authors sincerely appreciate the Ministry's efforts in collecting, maintaining, and disseminating comprehensive agricultural information that supports scientific research and evidence-based decision-making.
This study did not involve human participants, animals, clinical data, or any procedures requiring ethical approval. Therefore, according to institutional and international research ethics guidelines, ethical committee approval and an ethics code were not required for this research.
The authors declare no conflict of interest.
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