Life cycle assessment of rice cropping systems in traditional and semimechanized planting patterns in northern Iran

Sahar Youseftabar^*, Hossein Heidari Sharifabad and Islam Majidi Heravan ^*Correspondence: Sahar Youseftabar, Department of Agronomy, Science and Research Branch, University of Islamic Azad, Tehran, Iran, Email:

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The life cycle of rice crop in different cropping systems was assessed in Mazandaran province, in northern Iran from 2016 to 2017. All the management practices/inputs of local (‘Tarom Hashemi’) cultivar were monitored without interference in farmer’s practices. The experiment was carried out as factorial based on a Randomized Complete Blocks Design (RCBD) with four replications. Five cropping systems including conventional, low-input, high-input, improved and organic systems were used as main plots. Two planting patterns (traditional and semi-mechanized) were considered as subplots, respectively. According to the findings, the share of non-renewable energy demand, CC, and GWP 100a in both methods was low for low-input and organic systems, which could increase the share of renewable energy by incorporating conservation planting approaches. Fossil CO₂ eq, biogenic CO₂ eq, Global Warming Potential 100a (GWP), Terrestrial Acidification (TA) and Fossil Depletion (FD) of semi mechanized method were higher than traditional method. The most Cumulative Energy Demand (CED) in both methods was observed in high input system followed by conventional system. The lowest amount of GWP 100a was calculated in low input and organic systems for traditional method. In both methods, the most and lowest amount of TA, Freshwater Eutrophication (FEU), Ozone Depletion (OD) and FD were emitted in high input and low input systems, respectively. Among the cropping systems, low input and high input systems had significantly lowest and most emission of heavy metal in the air, water and soil, respectively. As a result, as the findings of this research revealed that emission of environmental pollutants is directly related to the application of inputs and method of field management. Therefore, to increase the sustainability of agro-ecosystems, as well as to reduce the environmental impacts of pollutant, reforming the pattern of chemical input consumption and reducing the use of non-renewable energy sources are essential.

Introduction

Rice (Oryza sativa L.) is the earliest stable food crops with the global cultivation area of 165 million hectares, accounting for more than one tenth of the worldwide-cultivated area [1]. Mazandaran province have a high share of rice production area in Iran, which requires optimization of inputs application and identification of the best production system in order to reduce the emission of environmental pollutant.

Life Cycle Assessment (LCA) is an appropriate way for achieving sustainable agriculture goals to study the environmental impact of a crop producing in its whole life cycle in production systems [2,3]. LCA used in crop planting systems is an attempt to estimate all GHGs emission and environmental pollutants of the production chain of life cycle [4]. Several studies have been found in this regard. Dastan et al. by using LCA assessed transgenic Bt. and non-Bt. rice cultivars in northern Iran. They reported that the amount of the environmental pollutants emission is directly related to the application of inputs and method of field management, based on which the least amounts of these indices were obtained in the production of transgenic cultivars. Habibi et al. [5] by using LCA to assess 200 rice production fields in Mazandaran and Guilan provinces, Iran reported that the most Global Warming Potential (GWP 100a), Climate Change (CC) and Cumulative Energy Demand (CED) in both regions were observed in high-input system for semi-mechanized method. The result for the impact categories of Freshwater Eutrophication (FE), Agricultural Land Occupation (ALO), Terrestrial Acidification (TA), Marine Eutrophication (ME), Metal Depletion (MD), Fossil Depletion (FD) and Water Depletion (WD) was similar to the GWP, CC and CED where the highest amounts in both regions statistically went to high-input system. They reported that in both regions, high-input and conventional systems emitted higher heavy metals than low-input system. Pelesaraei et al. assessed 240 paddy fields in Guilan province, Iran [6]. Their LCA demonstrated that rice production leads to 1166.09 kg CO₂ eq. emission per ton. They found that rice production is hotspot in terms of energy utilization, GWP, TA, and FE impact categories. Using LCA, Mohammadi et al. [7] assessed 82 rice paddy fields in northern Iran, and found that spring cultivation had a weaker environmental impact (“GWP, TA, FE, CED and WD”) than summer. The main cause for these results was lower application of inputs and higher paddy yield production of springer rice cultivation compared to summer. Using LCA, Bacenetti et al. [8] assessed 70 hectares of organic rice production fields located in Lomellina of Italy, and found that compost production, CH₄ emissions from the flooded fields, nitrogen associated emissions and the mechanization of the paddy field practices were the main environmental hotspots for organic rice production. Using LCA-ReCiPe method in Bangladesh. Jimmy reported that the magnitude of impact per kg of paddy produced from the harvested field; a CO₂ eq emission of 3.15 kg as GWP, FD of 0.68 kg oil eq, a N eq emission of 0.0154 kg as ME a P eq emission of 0.00122 kg as FE, a 1, 4-DCB-kg oil eq emission of 1.15 kg as human toxicity and use of 2.97 m3 of water for irrigation purpose. Literature interview indicated that there are numerous studies about the environmental assessment for rice production in countries such as USA, Italy, Taiwan, Japan and China [9-14]. Similar studies were done based on LCA in order to make comparisons between the production systems of wheat and rice [15-17].

The scientific literature reviewing showed that it is of great necessity to assess the life-cycle of rice cropping systems to determine emissions of environmental pollutant. The findings of this study can be very effective in increasing the rice ecosystem’s sustainability, as well as reducing the environmental impacts resulting from the application of chemical inputs and the achievement of sustainable agricultural objectives. Therefore, this study was undertaken with the following objectives:

(i) to assess the life-cycle of rice cropping system; (ii) to compare the life- cycle of local rice cultivar in different cropping systems; and (iii) to identify sustainable and environmentally safer rice cropping systems for production of local and improved rice cultivars in northern Iran.

Materials and Methods

Description of the experimental site

Field trials were conducted in Babol region (in the central part of Mazandaran province) located in north of Iran between the Alborz Mountains and the Caspian Sea during the year 2016 and 2017. Babol region is geographically situated at 36°, 32’ to 36°, 39’ N latitude and 52°, 45’ to 52°, 58’ E longitude. In the rice growing season (from April to September), its climate is temperate sub-humid and its average maximum and minimum temperature and solar radiation, and rainfall are 25.9 and 18.5°C, 17.9 MJ m^-2 d^-1, and 93.4 mm, respectively [18]. Rice is usually harvested in September in research area and after that the clover, canola or wheat crops is cultivated in the rice field in a double cropping system or manage the rice residue for ratoon harvesting. The soil properties of the experimental sites are shown in Youseftabar et al.

Description of the experiment

The experiment was carried out as factorial based on a Randomized Complete Blocks Design (RCBD) with four replications. Five cropping systems including conventional, low-input, high-input, improved and organic systems were used as subplots. Two planting patterns (traditional and semi- mechanized) were considered as main plots, respectively. All the paddy fields systems pertain to local rice cultivar (‘Tarom Hashemi’) were five cropping systems along with two planting patterns considered as treatments. The size of each plot was 5 × 10 m².

In the semi-mechanized planting method, the agricultural practices (puddling, irrigation regimes, fertilization, and weeds control and plant protection) were carried out traditionally by farmers’ practice and the planting operations (using seedling box and mechanized transplanting) and harvesting practice (by combine and harvester machine) were mechanized. In the traditional planting methods, all the agricultural practices except harvest were carried out by farmers’ practice without machine.

The paddy fields were selected for the conventional, low-input, high-input and improved systems based on the soil characteristics analysis done in each region. But, the paddy fields were selected for the organic system according to the International Federation of Organic Agriculture Movements (IFOAM) protocols under the supervision and control of the experts and the inspector of IFOAM. Each cropping system was selected according to all social, economic, environmental and agricultural issues. Details of each cropping system are described in and more details of cropping systems are shown with Youseftabar et al. (Table 1) [19].

Table 1: Contribution of non-renewable cumulative energy demand of rice cropping systems in traditional and semi-mechanized planting method

LCA methodology

“LCA is a technique to assess environmental impacts associated with all the stages of a product’s life from raw material extraction through materials processing, manufacture, use, and disposal or recycling”, and transportation [20]. LCA is carried out in four main phases: definition of goals and scope; analysis of inventory; impact assessment; interpretation. In this regard, four phases which are goal and scope definition, inventory analysis, impact assessment, and interpretation, were designed to assess life cycle index.

Goal and scope

This LCA study aimed to evaluate and compare the environmental impact of producing local and improved rice cultivars for cover crop-rice rotations. The functional unit was one ton of paddy yield (with 12%moisture content). Since straw is a co-product of paddy farms, economic allocation and environmental impact was assessed by the LCA method of SimaPro8.2.3 software [21,22]. Based on economic allocation, about 90% and 10% of dry matter of experimental farms were attributed to paddy and straw, respectively [23,24].

Life Cycle Inventory (LCI)

In this step, all emissions due to the production of inputs (indirect emission) and application of inputs (direct emission) in local and improved rice cultivars for cover crop-rice rotations produced were calculated using the Eco invent 3.1 database. Items that were considered are: (i) infrastructures, comprising construction, maintenance and depreciation of machinery and buildings (shelters for machinery); (ii) all agricultural practices including bed preparation for cultivation, fertilization, protection, irrigation, harvest, transportation supply and utilization of fuel for the practices; (iii) production of fertilizers, herbicide and fungicide and (iv) transportation of all inputs.

Life Cycle Impact Assessment (LCIA)

“LCIA aims to evaluate environmental impacts based on inventory analysis within a framework of the goal and scope of the study. In this phase, the inventory results are assigned to different impact categories” [25]. To do more comprehensive and accurate environmental impact assessment, which involves characterizing, normalizing and weighing, in the production of local rice cultivar in different cropping systems, different methods including ReCiPe 2016, Ecopoints 97 CH, Cumulative Energy Demand (CED), and Cumulative Energy Demand (CExD) were used in SimaPro8.2.3 software. Characterization, which is the first step of LCIA, is the assessment of environmental impacts of each. Inventory flow (“e.g., modeling the potential impact of carbon dioxide (CO₂) and methane (CH₄) on global warming), and provides the ability to compare LCI results within each category”. For instance, CO₂, nitrous oxide (N₂O) and CH₄ have different environmental impacts on global warming. The global warming potential of CO₂, N₂O and CH₄ are 1, 265 and 28 kg CO₂ eq, respectively. There are different classifications for impact categories depending on the method used. The most important impact categories in this study were GWP, TA, FE, ME, WD, CED and CExD. In addition, to conduct a deeper analysis, the amount of NH₃, N₂O and CH₄ emissions and heavy metals and other materials emitted in the air (Pb, Cd, Zn, Hg), water (Cr, Zn, Cu, Cd, Hg, Pb, Ni) and soil (nitrate, metals and pesticide) are reported separately in the results section. For each impact category, corresponding characterization factors were used based on the IPCC 2013 GWP 100a, ReCiPe2016, Ecopoints 97 CH, CED and CExD methods in SimaPro8.2.3 software.

Interpretation

One of the aims of LCA is to provide comprehensive information for decision makers. To achieve this goal, LCA results of a study must be interpreted. In this step, the LCA results of different cropping systems for local (‘Tarom Hashemi’) rice cultivar were assessed and compared.

Results

Interpretation of LCA results

Data analyses of LCA by ReCiPe method in different rice cropping systems are presented in are shown heavy metal and other emissions of Ecopoint 97 (CH) method (Figure 1). Displayed non-renewable and renewable Cumulative Energy Demand (CED) (Figure 2).

Figure 1: Contribution of non-renewable cumulative energy demand of rice cropping systems in traditional and semi-mechanized planting method. Note: ( ) Organic, ( ) Improved, ( ) Low input, ( ) Conventional, ( ) High input

Figure 2: Contribution of non-renewable cumulative energy demand of rice cropping systems in traditional and semi-mechanized planting method. Note: () Organic, ( ) Improved, ( ) Low input, ( ) Conventional, ( ) High input

ReCiPe method

In the ReCiPe method, the most important impact categories including Climate Change (CC), Terrestrial Acidification (TA), Freshwater Eutrophication (FE), Marine Eutrophication (MEU), Ozone Depletion (OD), Water Depletion (WD), Metal Depletion (MD), Fossil Depletion (FD), Human Toxicity (HT), Photochemical Oxidant Formation (POF), Particular Matter Formation (PMF), Terrestrial Ecotoxicity (TE), Freshwater Ecotoxicity (FE), Marine Ecotoxicity (ME), Ionising Radiation (IR) and Agricultural Land Occupation (ALO) were assessed. Findings of ReCiPe method indicated that all the investigated impact categories were significantly different under the effect of cropping systems and planting method. According to findings, all the impact categories of ReCiPe method for high input system were significantly higher than other systems. In both planting method, the most CC, TA, FE, HT, FE and POF was emitted in high input system and the conventional and improved systems got ranks next. The least amount of CC, TA, FE, HT, FE and POF was observed in low input and organic systems, respectively (Table 2). In both planting method, other impact categories (PMF, TE, FE, ME and IR) was varied that high input and conventional systems demonstrated higher amounts than other systems which the lowest amount was observed in organic and low input systems (Table 3). In both cultivation methods, high input system showed the highest ALO, OD, WD, MD and FD, respectively. The lowest amount of ALO, OD, WD, MD and FD was recorded in organic and low input systems, respectively (Table 4).

Table 2: Description of rice cropping systems for local rice cultivar in traditional and semi-mechanized methods by ReCiPe method

Table 3: Description of rice cropping systems for local rice cultivar in traditional and semi-mechanized methods by ReCiPe method

Table 4: Description of rice cropping systems for local rice cultivar in traditional and semi-mechanized method by ReCiPe method

Cumulative Energy Demand (CED)

According to findings, all the impact categories of CED including non- renewable, fossil; non-renewable, nuclear; non-renewable, biomass; total non-renewable energy; renewable, biomass; renewable, wind, solar, geothe; renewable, water; and total renewable energy were statistically significant by cropping systems (data not shown). The most CED in both cultivation methods was observed for high input and conventional systems and improved system got rank next. The least amount of CED was observed in organic and low input system (Figure 1).

Cumulative Exergy Demand (CExD)

The results of Figure 2 indicated that all the investigated impact categories of renewable and non-renewable CExD were significantly different under the effect of cropping systems. Non-renewable CExD indices (non-renewable, fossil; non-renewable, nuclear; non-renewable, primary; non-renewable, metals; non-renewable, minerals and total non-renewable energy) for semi mechanized method were higher than traditional method, respectively (Figure 2). For both method, high input system shows the highest amount of total non-renewable energy and conventional and improved systems got ranks next, respectively. The minimum total non-renewable energy was utilized in organic and low input systems, respectively (Figure 2).

Ecopoints 97 (CH) method

The results of this method showed that all the investigated emission in the air, water and soil were significant under the effect of cropping systems. The findings in which are derived from the Eco points 97 method with impact categories related to the emission of heavy metals and other environmental pollutants in air, water and soil, showed that the heavy metals emitted in air (Pb, Cd, Zn and Hg), water (Cr, Zn, Cu, Cd, Hg, Pb, Ni and AOX) and soil (nitrate, metals and pesticides) were statistically less in traditional method than semi mechanized method (Table 5).

Table 5: Heavy metals emission of rice cropping system for local cultivar in the air and water and soil by Ecopoints 97 (CH) method

Among the crop systems, high input system showed highest heavy metal emission than other systems in the air, water and soil. But, the lowest heavy metals emission in the air and water were recorded in organic and low input systems, respectively. In addition, emission of pollutants from soil (nitrate, metals and pesticide) in high input system was higher than others for both cultivation methods. Emission of NH₃, COD and dust PM10 of both methods in different systems in high input and conventional systems was higher than other systems and organic and low input systems showed lowest amount (Table 6).

Table 6: AOX, nitrate, metals and pesticides emission of rice cropping systems for local cultivar in the air, water and soil by Eco points 97 (CH) method

Discussion

Agricultural and non-agricultural practices such as the production and transfer of fertilizers and pesticides in rice production play roles in global warming by producing 80-98 and 16-91 kg CO₂ eq ha^-1,y respectively [26]. Different natural and human causes create global warming but global warming is mostly considered to be due to an increase in emission of greenhouse gases because of human activities which induces many changes in global climate patterns [27]. In order to report the amount of produced GHGs, all the produced gases with a CO₂ which reflects the GWP, are reported. Pelesaraei et al. demonstrated that diesel, at 44.34%, had the highest share of energy utilization in paddy rice production in Guilan province, and total energy input was equal to 51585 MJ ha^-1. In another study in rice dieselbased production in Iran, diesel accounted for about 46.41% of the total energy utilization in Guilan province, and 29.67% of total energy utilization in Mazandaran province [28]. Komleh et al. showed that the largest energy utilization in rice production was related to fuel (46% of total energy utilization) which included diesel, natural gas and electricity. Soltani et al. reported the emissions with GWP to be 621 kg CO₂ eq for producing a ton of wheat in Gorgan, Iran. GWP impact category in the farming section was reported to be 119.5 kg CO₂ eq for wheat production in China (Wang et al. 2009), 1484-1847 kg CO₂ eq for rice in Rasht, Iran 340 kg CO₂ eq for wheat in Marvdasht, Iran and 381 kg CO₂ eq for wheat in Switzerland [29,30]. The demand for non-renewable energy in wheat production in Gorgan, Iran was 6641 MJ t^-1. The total energy utilized, which depended on the type of soil and field practices and production systems, was 274 to 557 MJ t^-1 in the UK and 521 MJ t^-1 for sugar beet production in Japan [31,32]. The reason for the high or low share of non-renewable energy in different scenarios was the difference in fuel usage, fertilizer, and machinery performance, which was also reported by other researchers on similar issues [33]. The share of NH₃ in acidification potential was more significantly than that of N₂O and SO₂. In fact, the NH₃ emission resources are urea fertilizer. Ammonia sublimation has an important impact on eutrophication and acidification [34]. The release of NH₃ in sublimation from urea is a physical and chemical process, and it is more sensitive than N₂O to the management of fertilizer application. In a study on rice in China, it was observed that the depletion of fossil resources for fossil fuel consumption was 106 MJ t^-1 and the final eco-index was 0.008 [35]. To produce one ton of crops, the following amount of diesel fuel needs to be consumed: 25.63 L for canola in Turkey 87.78 L for soybean in Iran and 25.08 L for rice in Guilan, Iran [36]. The water consumption during rice production in China was 379 cm t^-1, and the final eco-index obtained was 0.14 for the reduction of water resources. In another study in the north of China, the final eco-index for the reduction of fossil resources was 0.02 for one ton of wheat production and 0.009 for one ton of corn production. To produce one ton of wheat in Germany, acidification and global warming are the main environmental impacts [37].

Conclusion

Different impact categories of life cycle assessment were evaluated in three rice production systems in the two semi-mechanized and traditional planting methods. Thus far, no report has been shown on various production systems with different planting methods. Hence, the findings of this study can be very effective in increasing the rice ecosystem's sustainability, as well as reducing the environmental impacts resulting from the use of chemical inputs and the achievement of sustainable agricultural objectives. The findings of this study indicate that the share of inputs and outputs was different in each rice production systems. The main reason for the observed difference was the amount of input and output, diversity of farm management practice, and input consumption. According to the findings, the share of non-renewable energy demand, CC, and GWP 100 a in both methods was low for low-input and organic systems, which could increase the share of renewable energy by incorporating conservation planting approaches. This issue is of great importance from the ecological point of view, because the source of nonrenewable energies, which is mostly fossil fuels, and the reliance on these resources in the future, are fraught with great risks.

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