Assessment of the sustainability of the traditional and mechanized cultivation process with an exergy-based approach


 Regarding the high consumption of allium vegetables such as onion and green onion in the daily food basket of families, it is important to study the sustainability of their agricultural system. Thus, a thermodynamic analysis was carried out to assess the sustainability of the cultivation method management using an exergy-based approach. Onions and green onions were evaluated for mechanized cultivation and for traditional cultivation, respectively. The use of renewable energy in the cultivation system was proposed in the numerical method. The sustainability index and exergetic improvement potential were calculated. Moreover, and the improvement of CDP and RI factors was investigated based on the CExC approach. The results indicated energy consumption of 1 ton of onion production was 2.5 times that of green onion production. The human labor and electricity as energy-intensive inputs in the process of green onion and onion production, respectively. The GHG emission of 1 ton of onion production was obtained 3 times that of green onion production. The results showed that the impact of using the new strategy in the agricultural system of green onions is less than onions, due to the high human labor requirement in green onion production, which made the production of green onions even more unsustainable than the production of onions, despite less consumption energy in green onion production.


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Dincer (Dincer 2002) showed a relationship between energy and exergy with the environment and sustainable 31 development. Energy analysis based on the first law of thermodynamics is a traditional method for estimating various 32 processes of energy conversion, however, it does not provide information on the quantity and mechanism of 33 performance reduction. The second law of thermodynamics examines the energy quality by exergy (Szargut 2005;

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The CExC approach can identify the impacts of using different inputs of production on the environment (Szargut 2005). With the help of CExC approach, farmers can improve production productivity. The CExC approach can 37 evaluate the cumulative degree of perfection (CDP) and renewability index (RI) for each stage of the production 38 process and ultimately offers solutions to increase product productivity. Some studies have used this approach for 39 some crop production. The CExC evaluation of tomato production by two methods of greenhouse cultivation and open 40 field showed very high electricity and water consumption in the open field and greenhouse cultivations, respectively 41 . A similar study was conducted to optimize strawberry production and showed that the 42 energy required to produce 1 ton of strawberries in the greenhouse cultivation is less than the open field. The CDP 43 values were 0.29 and 0.18 for greenhouse and open field production, respectively. In another study, for potato 44 production, reducing the use of pelletized manure was suggested to increase CDP and reduce CO2 emissions 45 (Yildizhan 2017). Thermodynamic analysis of greenhouse cucumber production showed that when the process of 46 greenhouse cucumber production is done with renewable energy, CDP increased from 0.23 to 0.47, while exergy 47 efficiency and RI indicated growth from 0.18 and -3.32 to 30.30 and -1.09, respectively. Investigation of energy and 48 exergy consumption and CO2 emissions during soybean, sunflower, and olive production showed that reducing diesel 49 consumption by proper farming method or replacing diesel with biodiesel will reduce exergy consumption (Özilgen

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Epidemiological studies indicated the inverse relationship of consumption of allium vegetables (such as leeks, garlic, 52 onions, green onions, and scallion) with gastric and colon cancer due to their chemical protection. Onions and alum-53 related products are the most consumed vegetables in the world (Xiao and Parkin 2007). The literature review shows 54 that although allium vegetables have high consumption in the daily food basket of families, the sustainability of their 55 production process has not been studied so far. Therefore, in this research, the sustainability of green onion production 56 as traditional cultivation and onion production as mechanized cultivation are investigated. Also human labor was 57 ignored in the thermodynamic analysis of agricultural products. Therefore, in this study, while considering the human 58 labor, the energy-exergy flow of the cultivation process of two similar plants (onion and green onion) was evaluated.

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The sustainability index and exergetic improvement potential were also calculated; the improvement of CDP and RI 60 was investigated based on the CExC approach.

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Farm data provide important information for a specific farm. Data from several farms can provide more general results.
inputs and identify the prominent elements with the highest impact on sustainability. In this study, the production 65 process of onions and green onions was investigated.

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(2) Exergy balance: Where m: mass (kg), Q: heat energy, T: temperature (K), h: enthalpy, W: work (MJ), k: heat sources, and b: available 78 exergy flow of the product, which can be calculated from the following equation:

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(4) In which, s shows the specific entropy, Ru denotes the universal gas constant and yi represents the molar fraction. The 80 amount of available flow (b) for the crops is described in Appendix A.

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The performance of the crops production process can be assessed by calculating CDP (Szargut et al. 1987): where CExC is the exergy of all raw materials and fuels consumed during crop production. Table 3 shows the 83 thermodynamic coefficients of the inputs used to produce onions and green onions.

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The renewability index, which is the exergy deviation from the ideal behavior due to the consumption of non-85 renewable resources, is calculated as follows (Berthiaume and Bouchard 1999) : where Xp is the useful work derived from the product and Wr stands for non-renewable resources consumed during 87 the production process.

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Depending on the value of RI, the renewability of the production process is determined as follows:

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The process is completely renewable, if RI = 1

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The process is somewhat renewable, if 0 <RI <1

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Production and reconstruction work are equal if RI = 0

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The process is non-renewable, if RI <0

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Van Gool (1997) proposed a new parameter of exergy called the improvement potential. Improvement potential is 94 commonly used to analyze various processes. This parameter indicates the extent of improvement potential for a 95 system: where is the exergy efficiency and can be defined as the ratio of total output exergy to input exergy.
Exergy sustainability is based on exergy analysis and is defined as the relationship between the input exergy and the 98 system exergy losses. This index offers information about the impact of the process on the environment and can be 99 considered as an important parameter of evaluation. The exergy sustainability index can be calculated as follows:  were compared with other agricultural products.

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The energy consumption of production inputs during the production of 1 ton of onions and green onions is shown in 111 Figure 1. The CEnC for each ton of green onion and onion were obtained 1.19 and 3.03 GJ, respectively. As Figure   112 1.a illustrates, in the green onion production system, the largest share of energy consumption is related to human labor, 113 followed by nitrogen and manure. Because green onions production is done on small scale by smallholder farmers,

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and except for land preparation, which used animal labor, other operations are carried out by the human labor.

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In the production of strawberries (Yildizhan 2018), tomatoes (Yildizhan and Taki      In this section, the sustainability indicators of onion and green onion production (improvement potential, exergetic 161 sustainability index, CDP, and RI) were investigated (Figure 4).

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The CDP was calculated as a criterion for exergy efficiency. This factor can be interpreted as the input/output ratio of 163 the exergy. The output exergy of the product depends on the chemical composition or in other words the nutritional value of the product. High CDP means either a high nutritional value of the product or low total exergy consumption 165 during the production process. Thus, the higher the CDP value, the lower the exergy losses. The CDP was obtained 166 0.13 for green onions and 0.46 for onions implying that onion production is more environmentally friendly than onion 167 in Iran.

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According to Berthiaume and Bouchard (1999), RI is a useful tool for technology and environmental decision-makers.

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The RI shows the deviation from the ideal behavior due to the use of non-renewable resources. The RI is highly 170 dependent on the limitations of the technology and applied resources. IR was -1.18 and -6.80 for onion and green 171 onion, respectively; emphasizing the non-renewability of onion and green onion production (i.e. repair work is more 172 than production work).

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Exergy improvement potential was 1297 and 13728 MJ for onions and green onions, respectively. These values 174 indicate that the green onion production process has a high potential to improve exergy efficiency. At higher exergy 175 efficiencies, the sustainability index is higher and the environmental effects will be less. The sustainability index for 176 onion and green onion production was 1.85 and 1.15, respectively. To reduce the environmental impact, exergy 177 efficiency must be improved. A comparison of the results shows that the improvement potential value of green onion 178 is much higher than that of onion which could be due to the incorrect and excessive use of inputs (especially human 179 labor) in green onion production compared to the onion production. According to Equation (7), the higher the exergy 180 efficiency and the lower the exergy losses, the lower the exergy improvement potential. In other words, the lower the 181 improvement potential, the more efficiently the inputs are used and the better the system performs. In a study by 182 Yildizhan et al. (Yildizhan et al. 2021) on apple production, the improvement potential for apple production was 183 9232.02MJ. Because human labor was neglected in apple production, the sustainability of apple production cannot be 184 compared with onion and green onion production.

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According to the results of this study, since the major part of non-renewable energy in the production of green onions 197 and onions corresponds to fertilizers and electricity; using renewable energy to extract water from wells, managing 198 water utilization, and using a more efficient irrigation system, as well as feeding plants with renewable sources can 199 enhance the ratio of renewable energy sources in onion and green onion production. Therefore, in the new model, the

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The result of using renewable energy in the green onion and onion production system is shown in

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Exergy analysis identified the losses related to the production method. Measures to increase exergy efficiency can 226 reduce environmental effects by reducing energy losses. The following results were obtained from this study:

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(1) The energy consumption of onion production is 2.5 times that of green onion production which could be due 228 to the high water requirement of onion. The irrigation operations (electricity and irrigation water) account 229 for 80.67% of the total energy consumption of onions.

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(2) The calculation of the sustainability index and exergy improvement potential showed that onion production 231 caused lower environmental impacts and the green onion production process has a high potential to improve 232 exergy efficiency.

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(3) Manure played an important role in the exergy of the production process of onions; its replacement with 234 microbial fertilizer can significantly improve the exergy efficiency and the sustainability of the production 235 process.

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(4) The impact of the new agricultural strategy on the green onions was less than onions, which made the 237 production of green onions even more unsustainable than the production of onions, despite the use of 238 renewable energy.

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The results of this study showed how human labor requirement can influence energy consumption, GHG emissions,  Small-scale agriculture is an operation that is highly dependent on human labor. As Table A.1 shows the lack of 245 consideration of human labor, shows that the exergy losses of green onion production are less than onions, and the 246 analysis of sustainability indicators also shows that green onion agriculture is more sustainable than onions. In addition 247 to the lack of consideration of human labor in onion thermodynamic analysis underestimates the energy consumption 248 and exergy waste and overestimates sustainability indicators of onion production. While the results of the present 249 study confirm the opposite of the above result and human labor should not be ignored in agricultural activities.

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The chemical compositions of onion and green onion are listed in Tables A.2