Environmental Life Cycle Assessment in Organic and Conventional Rice Farming Systems: Using a Cradle to Farm Gate Approach

Abstract

The rising demand for agricultural products and expanding public awareness of environmental friendliness have led to the adoption of the organic farming system rather than the conventional one. The life cycle assessment (LCA) concept is a frequently used method to examine the environmental impacts of any activity across its entire life cycle. This research is the first use of LCA for the impacts of vermicompost and cattle manure as organic fertilizers in rice farming. The main goal of this study was to compare the environmental impacts of conventional and organic rice farming. This paper uses midpoint attributional LCA to analyze environmental damages during rice production. The four primary harm categories used in this strategy to categorize the environmental effects were: (1) climate change, (2) human health, (3) ecosystem quality, and (4) resources. The inventory data for the agricultural stage were obtained through farmer interviews. The system boundaries were set to cradle to farm gate, and 1 ton of final product (dry matter) was used as the functional unit. The results show that in all main damage categories, except for particulate matter formation, stratospheric ozone depletion, mineral resource scarcity, and freshwater eutrophication, conventional rice production has higher environmental impacts than organic rice production. Overall, organic rice production is more effective in diminishing the negative environmental effects of farming compared to conventional rice production.

1. Introduction

Rice (Oryza sativa L.), with around 161 million ha [1] grown globally, is one of the most significant agricultural crops in the world [2]. Over half of the world’s population bases its food security on rice [3]. In 2018, around 782 million tons of paddy rice were produced globally [3]. The Guilan province in Iran is one of the country’s key areas of rice production due to its abundant water, rich soil, and high humidity [4]. Rice is grown on more than 205,000 ha in this region, accounting for 35.8 percent of Iran’s total paddy fields [5].

Conventional agriculture requires a wide range of external inputs to sustain output and profit [6]. Chemical fertilizers and insecticides, in particular, can boost food production while efficiently decreasing crop pests and illnesses to satisfy the rising food demand linked with population expansion [7,8]. In addition, the overuse of chemical fertilizers and pesticides results in a number of environmental problems, such as greenhouse gas (GHG) emissions, nitrate leaching, water eutrophication, soil acidification, groundwater pollution, biological diversity loss, soil degradation, and toxicity across the food chain [6,9,10,11,12,13]. Due to the high proportions of non-renewable resources used in agriculture (such as fuel for machinery), as well as the fact that the production of frequently toxic chemicals causes environmental dangers, it is essential to pay special attention to these issues. To summarize, the production of agriculture is currently facing the enormous challenge of feeding a rising population [14,15]. The agricultural sector contributes 10–20% of worldwide GHGs [16], while paddy fields are the second-largest source of methane (CH₄) generation [17]. The emission of GHGs such as carbon dioxide (CO₂), CH₄, and dinitrogen monoxide (N₂O) have a considerable influence on global warming, eutrophication, human toxicity, and ozone layer depletion [18,19]. He et al. (2018) stated that organic farming methods are seen as an effective way to reduce negative environmental consequences [20]. Organic farming, which prohibits the use of synthetic agrochemicals to ensure long-term sustainability in agricultural systems and biodiversity protection, is frequently touted as an essential alternative to conventional farming. The results of some research showed that organic farming methods cause a lower toxicity and eutrophication per unit of product [19,21,22,23,24]. Due to its capacity to enhance soil fertility, the use of organic fertilizer may be a sustainable way to raise grain production [25,26,27,28,29]. For the development of sustainable cropping, it is essential to identify the factors that are affecting the crop’s reaction to organic amendment [21,22,23].

The assessment of environmental risks and health damages of rice production can be done by life cycle assessment (LCA) [2]. The LCA technique considers all input and output sources of the whole production system and can be therefore used to analyze the probable impact of agricultural production on the environment from raw material extraction to final product production and disposal [23,24]. Throughout a product’s life cycle, LCA develops an inventory of relevant environmental flows and assesses any potential environmental consequences linked with those flows [26]. The method examines additional environmental consequences, such as acidification, environmental toxicity, resource depletion, and so on, to reduce environmental impacts at various phases of the production process of various systems of farming [27]. LCA also considers how emissions could affect human health [28]. As a result, the usage of LCA in agricultural research is comprehensive and trustworthy for analyzing production systems [29]. Recently, LCA has been used in several studies throughout the world to analyze different cropping systems [30]. Mansoori et al. (2012), who compared organic and traditional rice cultivation systems, reported that the conventional system had larger energy inputs, with fuel and electricity accounting for the largest share [31]. Several studies have shown that yields in organic rice farming may be quite varying and have increased as a result of improved organic fertilizer or manure application technology [19,30,31,32,33]. The results of Jirapornvaree et al. (2021) show that the yields of organic jasmine rice cultivation were much greater than those of chemical (traditional) jasmine rice production. They stated that for supporting sustainable agriculture, organic rice production is an alternative approach [34]. Jiang et al. (2021) conducted a life cycle assessment of wheat production and stated that the environmental impacts of wheat production greatly improved by changing the conventional strategy to a manure compost strategy, especially with a biochar-amended manure compost strategy [35]. Only a few LCA research studies have been conducted on rice production in Iran, and the existing studies have mostly concentrated on traditional rice [36,37,38,39,40], paddy size [41], crop rotation [42], and organic rice [43]. So far, there has been no LCA study comparing organic and conventional rice production in Iran. Further, it is important to highlight the barriers in the role of organic fertilizers such as cattle manure and vermicompost in rice production. Therefore, the main goals of this study were to investigate the impacts of vermicompost and cattle manure as organic fertilizers in organic farming and further to compare the environmental impact assessment of conventional and organic farming to recognize the environmental damage of each system of farming.

2. Materials and Methods

2.1. Site of Study

This study was conducted in Sharafshadeh, Guilan Province, Iran (37°33’23”N, 50°10’70”E), which is located on the southwest coast of the Caspian Sea. This region has a moderate and humid climate, with a high average yearly precipitation of roughly 1850 mm, which is considerable above the average yearly precipitation of Iran, which is 236 mm [5]. The Caspian Sea, Guilan Province, and its position in Iran are depicted in Figure 1. Soil chemical and physical properties in the study area are given in

Table 1. Soil characteristics in the studied site.

Physicochemical Characteristics	Organic	Conventional
pH	6.48 ± 0.02	6.23 ± 0.06
EC (dS m−1)	1.23 ± 0.04	1.39 ± 0.08
OC (%)	1.94 ± 0.19	2.14 ± 0.16
N (%)	0.16 ± 0.01	0.18 ± 0.01
P (mg kg–1)	7.15 ± 0.20	7.45 ± 0.01
K (mg kg–1)	96.4 ± 1.60	92.4 ± 1.1
CEC (cmol(+) kg−1 soil)	30.4 ± 0.10	32.5 ± 0.2
Sand:Silt:Clay (%)	29.3:49.2:21.3	31.1:45.2:23.5
Soil Texture	loam	loam

. The chemical characteristics of cattle manure and vermicompost used in rice fields are indicated in

Table 2. Characteristics of organic fertilizers (cattle manure and vermicompost).

Chemical Characteristics	Cattle Manure	Vermicompost
Moisture (%)	29.6	32.3
Content of nitrogen (% dry weight)	1.54	1.68
Content of phosphorus (% dry weight)	0.31	0.39
Content of potassium (% dry weight)	0.81	0.86
Content of organic carbon (% dry weight)	17.5	22.3
C/N	11:1	13:1

.

2.2. Life Cycle Assessment

The LCA method used in this study is based on the standards ISO 14040 (2006) and ISO 14044 (2006) and contains four phases, including goal and scope definition, life cycle inventory (LCI), life cycle impact assessment (LCIA), and data interpretation. In this study, the environmental impacts between organic and conventional rice production in Guilan, Iran, were evaluated. The following sections provide a summary of the major decisions taken during the four LCA phases [42]. This LCA used the ReCiPe 2016 midpoint (H) impact assessment methodology, data from the AGRIBALYSE v1.2/v1.3 and Ecoinvent V.3.5 databases, and openLCA software V.11.0 [44].

2.2.1. Definition of the Scope and Goals

The aim of this study was to determine the environmental effects of organic and conventional Hashemi rice production in Guilan, Iran. For this investigation, 1 ton of final product (dry matter) was used as the functional unit. Figure 2 shows the system boundaries as well as every process from cradle to gate farm that are included in the assessment.

2.2.2. Life Cycle Inventory (LCI)

This study focused on organic and conventional rice farming systems. Organic farming according to the Organic Agricultural Standard is based on the non-use of agricultural chemicals (synthetic chemical fertilizers, insecticide, herbicides, and fungicides) [43,45]. Hence, only cattle manure and vermicompost were applied to the organic paddy field (

Table 3. The inventory data of rice cultivation per crop (1 ha).

Input/Output		Unit	Conventional	Organic
Inputs	Urea (as N)	kg ha−1	100.85 ± 11.35	-
	Triple superphosphate (as P2O5)	kg ha−1	80.41 ± 5.21	-
	Potassium chloride (as K2O)	kg ha−1	50.35 ± 3.63	-
	Manure (cattle)	kg ha−1	-	9700 ± 14.32
	Vermicompost	kg ha−1	-	5001 ± 15.86
	Insecticides	kg ha−1	5.03 ± 0.98	-
	Herbicides	kg ha−1	15.05 ± 2.32	-
	Fungicides	kg ha−1	-	-
	Diesel	L ha−1	170.4 ± 14.76	159.6 ± 14.87
	Machinery	h ha−1	50 ± 22.12	42 ± 8.96
	Seeds (kg ha−1)	kg ha−1	79.14 ± 11.54	78 ± 6.36
	Water	m3 ha−1	11,000 ± 0.12	9800 ± 0.12
Outputs	Yield paddy rice	kg ha−1	3490 ± 53.18	4000 ± 59.35
	Yield straw	kg ha−1	1240 ± 45.53	1650 ± 39.12
	NO3− SQCB model	kg ha−1	8.76	30.92
	NH3 EMEP/EEA, 2016	kg ha−1	5.04	18.67
	PO43− SALCA model	kg ha−1	0.64	0.85
	P SALCA model	kg ha−1	1	1
	CO2 IPCC	kg ha−1	258.92	174.13
	N2O IPCC	kg ha−1	1.09	2.75
	CH4 IPCC	kg ha−1	148.44	330.72

The SQCB model is based on a regression model, EMEP/EEA air pollutant emission inventory (Technical guidance to prepare national emission inventories 2016), SALCA model calculated in accordance with Swiss Agricultural Life Cycle Assessment, and IPCC calculated in accordance with the IPCC (Intergovernmental Panel on Climate Change) 2006 and 2019 methodologies (determination of field emissions).

). The weed management was done manually. Conventional farming relies on agricultural chemicals such as pesticides and synthetic fertilizers, insecticide, herbicides, and fungicides (Table 3).

The inventory data (foreground data) for the agricultural stage were obtained through farmer interviews. The appropriate sample number for this investigation was determined using Cochran’s formula [46,47]:

$$n=\frac{N{\left(s\times t\right)}^2}{\left(N-1\right)d^2+N{\left(s\times t\right)}^2}$$

where n is the required sample number, N is the population size, t is the t value at 95% confidence limit (1.96), s is the standard deviation (SD), and d is the permissible error (5%).

In March 2022, 99 farmers (conventional: 58, organic: 41) were interviewed using questionnaires to gather data on organic and conventional rice farming (Table 3).

The emissions in rice cultivation included agrochemicals used, biogenic soil emissions, and fuel used in agricultural field activities. The Ecoinvent V.3.5 [44,45,46,47,48] and AGRIBALYSE v1.2/v1.3 [44] databases were used to obtain the emissions of agrochemical production. The IPCC method was used to determine the biogenic soil emissions, which are emissions from fertilizers and agricultural residues (IPCC, 2006). Further outputs were calculated in accordance with the SQCB model (nitrate, NO₃⁻), EMEP/EEA, 2016 (ammonia, NH₃), the SALCA model (phosphate, PO₄³⁻, and phosphorus, P), IPCC 2006 guidelines (CO₂), and IPCC 2019 guidelines (N₂O and CH₄).

2.2.3. Life Cycle Impact Assessment (LCIA)

The fundamental objective of the ReCiPe method is to convert a full life cycle inventory result list to a small number of indicator scores. The midpoint indicator is focused on a particular environmental problem [49]. Eighteen indicators of environmental impacts are included in the ReCiPe midpoint method, which are further specified into four main damage categories: (1) human health, (2) ecosystem quality, (3) resources, and (4) climate change (Appendix A). The classification of emissions and resource inputs for easier interpretation is the aim of the life cycle impact assessment. Characterization, normalization, and weighting are the three processes in the evaluation.

In the phase of data interpretation, the LCI and LCIA data in accordance with scope and goal were examined. Overall, the effect of Hashemi rice production was compared between conventional and organic rice farming.

3. Results

3.1. Impact Assessment

Table 4. Midpoint environmental impact assessment (1 ton of dry matter) of conventional and organic rice farming.

Impact Category	Damage Category	Abbreviation	Unit	Conventional	Organic
Particulate matter formation	Human health	PMFP	kg PM2.5 eq	0.29 ns	0.32 ns
Human carcinogenic toxicity	Human health	HTPc	kg 1.4-DCB	28.79 a	22.3 b
Human non-carcinogenic toxicity	Human health	HTPnc	kg 1.4-DCB	20.92 a	15.4 b
Ionizing radiation	Human health	IRP	kBq Co-60 eq	0.36 a	0.21 b
Ozone formation	Human health	EOFP	kg NOx eq	0.45 a	0.31 b
Stratospheric ozone depletion	Human health	ODP	kg CFC11 eq	0.30 ns	0.36 ns
Fossil resource scarcity	Resources	FFP	kg oil eq	0.49 a	0.42 b
Mineral resource scarcity	Resources	SOP	kg Cu eq	0.01 ns	0.01 ns
Water consumption	Resources	WCP	m3	11.91 a	9.25 b
Freshwater ecotoxicity	Ecosystem quality	FETP	kg 1.4-DCB	1.27 a	0.48 b
Freshwater eutrophication	Ecosystem quality	FEP	kg P eq	1.33 ns	1.24 ns
Land use	Ecosystem quality	LOP	m2a crop eq	0.04a	0.02 b
Marine ecotoxicity	Ecosystem quality	METP	kg 1.4-DCB	91.47 a	77.17 b
Marine eutrophication	Ecosystem quality	MEP	kg N eq	0.06 b	0.41 a
Ozone formation, terrestrial ecosystems	Ecosystem quality	HOFP	kg NOx eq	0.06 a	0.03 b
Terrestrial acidification	Ecosystem quality	TAP	kg SO2 eq	0.21 b	1.06 a
Terrestrial ecotoxicity	Ecosystem quality	TETP	kg 104-DCB	4.35 a	2.21 b
Global warming	Climate change	GWP	kg CO2 eq	0.38 b	0.72 a

The lower-case characters a and b represent significant differences between conventional and organic rice production, while ns indicates no significant difference.

and Figure 3 show the impact assessment of conventional and organic rice production to recognize their hot spots. In this study, there were no differences in particulate matter formation (PMFP), stratospheric ozone depletion (ODP), mineral resource scarcity (SOP), and freshwater eutrophication (FEP) between organic and conventional systems of farming. Except for the marine eutrophication potential (MEP), terrestrial acidification potential (TAP), and global warming potential (GWP), the highest emissions and negative environmental effects could be identified in the conventional system of farming in 11 impact categories. Several studies have already indicated that organic agriculture has a lower environmental impact than conventional agriculture, as avoiding chemical use in rice production has various environmental advantages [37,50,51,52,53,54,55,56].

3.1.1. Climate Change Category

The global warming potential (GWP) values found for conventional and organic rice production were 0.38 kg CO₂ eq and 0.72 kg CO₂ eq per 1 ton of dry matter, respectively (Table 4, Figure 4).

Table 5. Greenhouse gases emissions in conventional and organic systems of farming.

						CO2 Equivalent
GHGs	Conventional	Organic	Unit	Calculation Method of GHGs	GWP	Conventional	Organic
CO2	258.92	174.13	(kg ha−1)	IPCC, 2006	1	258.92	174.13
N2O	1.09	2.75	(kg ha−1)	IPCC, 2006	298	324.82	819.5
CH4	148.44	330.72	(kg ha−1)	IPCC, 2006	25	3711	8268
Total						4294.74	9261.63

shows the GHG emissions of conventional and organic systems of rice farming. The results showed that CO₂ emissions in organic rice production were 32.7% lower than in conventional production, and the amount of N₂O and CH₄ emissions in organic rice production were 152.2% and 122.7%, respectively, higher than in conventional production.

3.1.2. Human Health Categories

Table 4 and Figure 4 show the human health categories of rice production for conventional and organic farming systems. The impact assessment of human health categories included particulate matter formation potential (PMFP), human carcinogenic toxicity potential (HTPc), human non-carcinogenic toxicity potential (HTPnc), ionizing radiation potential (IRP), ozone formation potential—ecosystems (EOFP), and ozone depletion potential (ODP).

The particulate matter formation potential (PMFP) for conventional and organic rice was 0.29 kg PM2.5 eq and 0.32 kg PM2.5 eq, respectively. Accordingly, the resulting risk increases of cancer disease incidence (HTPc) for conventional and organic rice were 28.79 kg 1.4-DCB and 23.3 kg 1.4-DCB, respectively, while the risk increases of non-cancer disease incidence (HTPnc) for conventional and organic rice were 20.92 kg 1.4-DCB and 15.4 kg 1.4-DCB, respectively. The difference was significant between organic and conventional systems for both HTPc and HTPnc. The ionizing radiation potential (IRP) for conventional and organic rice was 0.36 kBq Co-60 eq and 0.21 kBq Co-60 eq, respectively, as shown in Table 4; thus, the IRP in organic rice was 41% lower than in conventional rice. The ecosystems ozone formation potential (EOFP) of conventional rice was 31% higher than for organic rice. The EOFP for conventional and organic rice was 0.45 kg NOx eq and 0.31 kg NOx eq, respectively. The ozone depletion potential (ODP) for conventional and organic rice was 0.3 kg CFC11 eq and 0. 36 kg CFC11 eq, respectively.

3.1.3. Ecosystem Quality Categories

Ecosystem quality is based on various factors such as freshwater ecotoxicity potential (FETP), freshwater eutrophication potential (FEP), agricultural land occupation potential (LOP), marine ecotoxicity potential (METP), marine eutrophication potential (MEP), terrestrial acidification potential (TAP), ozone formation potential (HOFP), and terrestrial ecotoxicity potential (TETP). Table 4 and Figure 4 show the ecosystem quality categories of rice production in conventional and organic farming systems.

The freshwater ecotoxicity potential (FETP) was 1.27 kg 1.4-DCB for conventional rice and 0.48 kg 1.4-DCB for organic rice, and there was a significant difference between systems of farming.

Organic rice reduced the marine ecotoxicity potential (METP) compared to conventional rice by 18.53%. The absolute amounts of METP for conventional and organic rice were 91.47 kg 1.4-DCB and 77.17 kg 1.4-DCB, respectively. The pollution of surface and groundwater is caused by leaching following fertilizer application [57].

The freshwater eutrophication potential (FEP) was 1.33 kg P eq for conventional rice and 1.24 kg P eq for organic rice, and there was no significant difference between conventional and organic systems. The marine eutrophication potential (MEP) values were 0.06 kg N eq and 0.41 kg N eq for conventional and organic rice, respectively. There was a significant difference between conventional and organic systems. The terrestrial acidification potential (TAP) values for conventional and organic rice were 0.21 kg SO₂ eq and 1.06 kg SO₂ eq, respectively. The ozone formation potential (HOFP) was 0.06 kg NOx eq and 0.03 kg NOx eq, respectively, for conventional and organic rice. The terrestrial ecotoxicity potential (TETP) was 4.35 kg 1,4-DCB for conventional rice and 2.21 kg 1,4-DCB for organic rice. There was a significant difference between systems of farming, and the amount in the conventional system was 96.83% higher than in the organic system.

3.1.4. Resources Categories

Table 4 and Figure 4 show the ecosystem quality categories of rice production in conventional and organic farming systems. The impact assessment of resources included fossil fuel potential (FFP), surplus ore potential (SOP), and water consumption potential (WCP).

The fossil fuel potential (FFP) of conventional and organic rice was 0.49 kg oil eq and 0.42 kg oil eq, respectively. The FFP in conventional rice was 16.67% higher than in the organic rice.

The result showed that surplus ore potential (SOP) for conventional and organic rice was 0.01 kg and 0.01 kg, respectively, with no significant difference between systems of farming.

The water consumption potential (WCP) for conventional and organic rice was 11.91 m³ and 9.25 m³, respectively.

4. Discussion

The potential of global warming, which is expressed based on the carbon dioxide equivalent (kg CO₂ eq), illustrates the role of GHG emissions for climate change. Global warming is the most important parameter in the climate change category. According to the results, CO₂ emissions in organic rice were 32.7% lower than in conventional rice, and the amounts of N₂O and CH₄ emissions in organic rice were 152.2% and 122.7%, respectively, higher than in conventional rice. He et al. (2018) stated that significant greenhouse gas emissions in organic systems were linked to the usage of a lot of organic manure. They also stated that after the conversion to organic farming, the systems need some time to reach a new stable state [20]. According to Hokazono and Hayashi (2015), in the organic rice system, direct emissions and field operations significantly contribute to the environmental impacts [33]. Similar research studies showed that the usage of chemical fertilizers (especially urea) and fossil fuels had the greatest impact on global warming potential and GHG emissions in other crops [38,39].

According to the findings of Hokazono and Hayashi (2012), paddy agricultural flooding contributes significantly to GHG emissions [49]. Fertilizer use in agriculture has an influence on the environment, since nitrogen in fertilizers contributes to N₂O, nitrogen oxides (NOx), and NH₃ [41,42] emissions. Fertilizers release N₂ because of the process of nitrification followed by denitrification, which is created by microbial interactions in the soil under aerobic and anaerobic conditions [52]. Fertilizer application dosages and their impacts on yields have a large influence on GHG emissions. Changing crop management to organic fertilizers might have the opposite impact due to this relationship. For example, Saber et al. (2020) and Harun et al. (2021) estimated that moving from conventional to organic farming reduces the carbon footprint of rice by two and three times, respectively [3,53]. According to Meng et al. (2014) and Mungkung et al. (2019), organic rice cultivation is promoted because of the supposed decreased risks associated with eliminating chemical inputs, as well as the potential to lessen environmental consequences such as global warming and ecological destruction [54,55]. Organic farming systems use biological and physical controls instead of synthetic fertilizer and prevent groundwater pollution, increase microbial biodiversity, and are less reliant on external inputs [56,57,58]. The main sources of N₂O emissions to the atmosphere are nitrification proceeded by denitrification processes carried out by soil microorganisms, though these emissions can change based on agricultural waste management, soil tillage, nitrogen fertilizer used, and climate conditions [50].

According to Table 4, although there was no significant difference between organic and conventional system of farming, organic rice had lower (PMFP) values than conventional rice. The conventional farming strategy relies on a chemical technology in which an extra supplement is applied to improve productivity. Several studies have shown that these practices affect the ecosystem and also have impacts on human health [2,46,50,51]. Agrochemical contamination has a long-term impact on humans, food chains, and the environment. One of the issues with use of pesticide, especially in rice farming, is the migration of pesticide into surface water after treatment. If drinking water is obtained from surface water, pesticides can harm aquatic ecosystems and human health [59,60,61]. Contrary to that, organic agricultural techniques have been shown to be a potential way to reduce negative environmental effects [20]. One of the most important environmental stressors that causes pathogenicity is the inorganic respiration index, which is described as the influence of respiratory minerals on human health. The inorganic respiration index is influenced by field operations, fossil fuel use, and nitrogen fertilizer use [61,62,63]. Darzi-Naftchali et al. (2022) found that on the carcinogenic illnesses index, urea fertilizer had the greatest impact [16]. In rice cropping systems, excessive urea fertilizer application and inadequate nitrogen usage efficiency may exacerbate these negative environmental consequences [64]. According to Darzi-Naftchali et al. (2022), the use of diesel-based fossil fuels had the greatest influence on the ionizing radiation potential, followed by the use of triple superphosphate and urea fertilizers [16]. Agricultural machinery that operates on diesel fuel can exacerbate ozone layer depletion. The consumption of butachlor herbicides is also a source of ozone depletion. Because of the chlorine in its composition, this herbicide has high destructive power and is categorized as a category one danger for water resources and ozone depletion [61,62,63]. Organic rice cultivation is a long-term rice-growing system that uses no chemicals and has the potential to decrease ecological issues [62,63].

FETP in conventional rice was 62.2% higher than in organic rice. The acidification impact is mostly caused by the emission of sulfur dioxide (SO₂), NH₃, and nitrogen dioxide (NO₂) into the air or soil, which are significantly reduced in the organic system compared to the conventional one. These results may be influenced by significant reductions in chemical inputs and diesel rates [3]. The usage of fertilizers and chemical pesticides in agriculture has a direct relationship with soil toxicity. Because of the adsorption of particles to the soil surface, soil is an important pollution sink [24,62,63,64]. Leaching of soil pollutants and toxic elements lead to groundwater pollution. Therefore, high use of these chemicals threatens the lives of animal and plant species [6,9,10,11,12,13]. In general, organic rice reduced the negative environmental effects compared with conventional rice farming.

Organic farming systems generate less damage to marine and freshwater ecosystems per unit of rice production, owing to lower pesticide and synthetic fertilizer use. Utilizing nitrogen-fixing plants in a crop rotation can be a good way to avoid overuse of nitrogen in the production system [65]. On the other hand, increasing resource usage efficiency is a long-term option for reducing agricultural output’s environmental impact, especially in rice production systems [66].

MEP in the organic system was 85.37% higher than for conventional rice production. Fertilizer emissions of nitrogen and phosphorus are a key contribution to eutrophication and acidification effects related to rice cultivation, as well as a cause of climate change and field flooding-related CH₄ emissions [29]. According to Darzi-Naftchali et al. (2022), in terms of eutrophication potential, phosphorus fertilizers and pesticides had a much larger percentage than other input sources. They also stated that the use of nitrogen fertilizer has a significant impact on the eutrophication of water sources [16]. In accordance with Table 3, the amount of phosphorous emissions to water for the organic system was higher than for the conventional system (0.85 kg ha⁻¹ and 0.64 kg ha⁻¹, respectively). The high AP content of the applied manure, which enhances the percentage of bioavailable P in the soil surface, especially in the first few days following fertilizer applications, might be the cause of this finding [67]. In terms of nutritional levels and solubility, the impacts of organic replacements are obviously a major cause for worry for P loss through surface runoff [68]. According to reports, phosphorous is the most important element in eutrophication intensification among other inputs [37,50,51,52,53,54,55,56]. In rice cultivation, one way for phosphorous to enter water sources is by leaching [69,70]. Since rice production is carried out in flooded conditions and leaching is common in rice production, improved fertilizer management is critical for reducing the effects of climate change, acidification, and freshwater eutrophication all at the same time [71,72,73].

TAP in the organic system was 80.19% higher than in the conventional system. According to Table 3, the amounts of ammonia emissions to water for organic and conventional systems were 18.67 kg ha⁻¹ and 5.04 kg ha⁻¹, respectively. This is consistent with the reports of Regina et al. (2013) and Schmidt Rivera et al. (2017), who claimed that ammonia (NH₃) emissions from fertilizer usage cause these effects [52,72].

In conventional system of rice, high doses of phosphate, potassium, and nitrogen produced from synthetic fertilizers contribute to the terrestrial ecotoxicity potential due to the release of NH₃, SO₂, and NO_x into the soil [50]. Terrestrial ecotoxicity potential (TETP) caused by inorganic substance deposition in the atmosphere allows one to examine the environmental effect of sulfates, nitrates, and phosphates, as well as their subsequent deposition, which can lower soil pH [71]. Increased leaching and the production of acidic chemicals in water sources are caused by a rise in anthropogenic sulfur and nitrogen emissions. In sensitive catchments, this sediment heads to negative environmental consequences on aquatic habitats, as well as ecological loss or extinction. Therefore, as a result of the existence of shallow groundwater and surface water bodies in rice farming, pollution from sulfur and nitrogen sources should be decreased in areas that are vulnerable to acidification [16].

As shown in Table 4 and Figure 3, organic rice had lower values of agricultural land occupation potential (LOP) than conventional rice (0.04 m²a crop eq and 0.02 m²a crop eq for conventional and organic rice, respectively). In this study, the grain yields of organic rice were 4000 (kg ha⁻¹) and for conventional rice 3290 (kg ha⁻¹); thus, the organic rice grain yield was 14.6% higher than the conventional rice grain yield. Therefore, to produce the same amount of paddy, less land is required. One of the factors contributing to the higher yield is the higher amount of organic matter content in organic farming. In fact, organic matter that is accumulated in the soil will help to improve the yield in an organic farming system [34]. Meta-analysis research carried out by Liu et al. (2021), who studied the response of rice yield and agronomic characters to organic fertilization, stated that the use of organic fertilizer improved N absorption by rice by 5.2% on average across all studies [45]. Similarly, when organic fertilizer was applied to rice, it increased P and K uptake by 7.2% and 10.5%, respectively, as compared to the control. In addition, when organic fertilizer was utilized, rice’s physiological N, P, and K usage efficiency increased by 6.2%, 4.6%, and 3.7%, respectively. They also stated that in terms of organic fertilizer types, using animal manure increased rice production more than applying biochar or crop straw. Specifically, animal manure treatment enhanced rice output by 10.5%, whereas organic fertilization using biochar or crop straw increased rice grain yield by only 7.2% and 8.3%, respectively [45]. When organic fertilizer is applied, soil organic carbon, one of the key measures of soil fertility, considerably rises, mostly due to the high carbon content of organic fertilizers [45,55,74,75,76]. More importantly, the increase in nutrients that are accessible with the application of organic fertilizer is greater than the increase in total nutrients for each mineral element, indicating that the increase in nutrients that are available promote the improvement of nutrient use efficiency [45]. The significant increase in plant-available nutrients might be related to the increased soil microbial community activity, which is necessary for nutrient cycling and transformation, and hence improves nutrient availability [72,73,74,75,76]. The application of organic fertilizers may change the architecture of the rice root system, promoting nutrient absorption from the soil, because they include amino acids and other physiologically active chemicals [77]. Organic fertilization could also improve the physical properties of paddy soil and help rice roots grow deeper into the soil, resulting in the absorption of more nutrients [74,75,76]. In general, it can be stated that the use of organic fertilizers compared to chemicals leads to increased yields of rice, and as a result, land occupation potential in organic farming is less than in conventional farming.

The FFP in conventional rice was 16.67% higher than in organic rice. The overuse of non-renewable resources for energy production and fuel significantly increase the risk of climate change. Diesel is a common fuel for agricultural equipment and is an expensive and non-renewable source [77,78]. The use of lower amounts of fertilizers and diesel fuel, as well as ecological methods for disease and insect prevention, could help to lessen the negative environmental impact. The production of fertilizers, which uses a lot of coal or natural gas as a source of hydrogen (to synthesize ammonia), increases CO₂ emissions [78,79]. Further, around 1.3–1.8% of the world’s fossil fuel consumption is attributable to the manufacturing of nitrogen fertilizers [50]. According to previous studies, non-renewable inputs have been shown to account for 60–80 % of the overall costs of agricultural crops, with chemicals such as fertilizers and insecticides accounting for 25–97 % of all non-renewable inputs [80,81,82,83,84]. Around 14% of the world’s ammonia production is based on coal gasification, 77% on natural gas reforming, and 9% on the partial oxidation of heavy hydrocarbon fractions and oil products [50].

5. Conclusions

One of the most essential tools for evaluating environmental impacts in production is the life cycle assessment (LCA). In this study, there were no differences in particulate matter formation potential (PMFP), ozone depletion potential (ODP), and surplus ore potential (SOP) between organic and conventional systems of rice farming. Except for marine eutrophication potential (MEP), terrestrial acidification potential (TAP), and global warming potential (GWP), the highest emissions and negative environmental effects could be identified in the conventional system of farming in 11 impact categories. The findings of the study indicated that (1) GHG emissions in organic rice farming were higher than in conventional rice. This is related to the application of a large amount of organic manure in the first year of conversion to organic farming, as the transition of the systems takes some time to reach a new stable state. Therefore, it is important to examine the organic and conventional system of farming in a period of several years. (2) Overall, organic rice production was more effective in diminishing negative environmental effects of farming compared to the conventional system. (3) The total environmental impact indices decreased in organic farming. (4) Higher environmental impacts were associated with conventional rice, while organic rice had lower human toxicity potential, ionizing radiation, ozone formation, water consumption, freshwater ecotoxicity and eutrophication, agricultural land occupation, marine ecotoxicity, ozone formation, and terrestrial ecotoxicity potential. (5) The use of chemical fertilizers and pesticides for conventional rice was one of the main causes of the environmental damage. In conclusion, when compared to traditional ways, organic rice cultivation has the potential to be a sustainable agricultural practice.