Impact of Agriculture on Greenhouse Gas Emissions—A Review

Abstract

The restrictions imposed by the European Green Deal on Europe are expected to make Europe climate-neutral by 2050. In this context, this article examines the current efforts to reduce emission levels, focusing on available international scientific papers concerning European territory, particularly Poland. The study paid special attention to the sector of agriculture, which is considered a key contributor to greenhouse gas generation. It also analysed the impact of various tillage techniques and the application of organic and inorganic fertilisers, e.g., nitrogen fertilisers, digestate, or compost, on the emissions of greenhouse gases and other environmentally harmful substances. Although there are few scientific articles available that comprehensively describe the problem of greenhouse gas emissions from agriculture, it is still possible to observe the growing awareness of farmers and their daily impact on the environment. The current study demonstrated that agricultural activities significantly contribute to the emissions of three main greenhouse gases: carbon dioxide, nitrous oxide, and methane. The tillage and soil fertilisation methods used play a crucial role in their emissions into the atmosphere. The use of no-tillage (or reduced-tillage) techniques contributes to the sustainable development of agriculture while reducing greenhouse gas emissions. The machinery and fuels used, along with innovative systems and sensors for precise fertilisation, play a significant role in lowering emission levels in agriculture. The authors intend to identify potential opportunities to improve crop productivity and contribute to sustainable reductions in gas emissions.

1. Introduction

Reports on climate change indicate that human activities contribute to an increase in greenhouse gas emissions, thus intensifying the global warming process. These observations are based on data showing that Earth’s surface temperatures are currently 1.5 °C higher than they were between 1850 and 1900 and 2010 and 2019 [1]. The authors of the report explain that this situation stems from various economic levels worldwide and unsustainable energy use (fossil fuel combustion and industrial processes), changes in land use and forestry, shifts in lifestyles, evolving consumption patterns, and considerable disparities in production levels across different regions within countries [1].

The land and oceans continue to act as absorbers for all CO₂ emissions (globally, approximately 56% per annum) from human activities. These effects are noticeable in human nutrition, water, and health economies. The climate change caused by human activities is already contributing to numerous extreme weather and climate phenomena in every region worldwide. The intensity of these processes hampers any efforts to meet the Sustainable Development Goals. The agricultural sector is among the many factors affecting the natural environment. Although agriculture is largely blamed for greenhouse gas emissions, it ranks only as the fourth most carbon-intensive economic sector. In the second quarter of 2023, greenhouse gas emissions in the European Union’s economy reached 821 million tonnes of CO₂ equivalents. The most greenhouse gas emissions were generated by manufacturing (23.5%), households (17.9%), electricity and gas supply (15.5%), and agriculture (14.3%), as well as transport and storage (12.8%) [1].

The current situation is linked to the use of agricultural machinery and the gases they emit, or interference with the structure and chemical composition of the soil through various chemical agents. The global food system alone is estimated to be responsible for approximately 21–37% of annual emissions [2]. While the productivity of the agricultural sector has been increasing, climate change has hindered this growth over the past 50 years worldwide [1]. An increase in productivity also tends to reduce the intensity of emissions from agricultural production by reducing the use of intermediate inputs in the employed technologies. However, the composition of the gases emitted by the food and agricultural systems does not reflect the overall global emission balance. At the same time, according to Mbow et al., 2019 [3], agricultural operations generate approximately half of all anthropogenic methane emissions and about three-quarters of anthropogenic N₂O emissions. Other scientific papers report that agriculture may account for 10 to 12% of global anthropogenic greenhouse gas emissions [4]. In contrast, according to Lynch et al., 2021 [2], greenhouse gas (GHG) emissions from agriculture are highly concentrated in a few products, with beef, dairy, and rice, for example, accounting for over 80% of GHG emissions in agriculture. As already mentioned, the intensity of emissions varies considerably depending on the country or region and the goods that are manufactured.

It has also been reported that 68% of total agricultural land is used for livestock production [5]. The European Commission aims to promote more sustainable livestock farming by introducing sustainable and innovative feed additives to the market. Beef farming generates the highest emissions compared with any other food product, ranging from 12.1 kg of CO₂ equivalent per kg of production in the United States to 108.3 kg of CO₂ equivalent in India [6]. In addition, Laborde et al., 2021 [6], following an analysis of agricultural support considering the carbon intensity of agricultural production, showed that any subsidies paid by the government increase both global agricultural production (0.9%) and the associated emissions (0.6%).

Such diverse data indicate the need to study this phenomenon in more detail without diminishing the fact that the carbon dioxide (CO₂) concentration in the atmosphere continues to rise and is currently almost 100 parts per million higher than that before the Industrial Revolution [7,8]. Total greenhouse gas emissions are expected to increase by approximately 50% between 2000 and 2030, with further impacts on the weather and climate [9]. Therefore, recently established European Union legislation (97/68/EC, 2010/22/EU, 2010/26/EU) [10,11] indicates that by 2050, there should be a significant reduction in greenhouse gas (GHG) emissions across various sectors of human activity. Specifically, the transportation sector is expected to achieve reductions of up to 90% compared with 1990 levels. Additionally, emissions from buildings and waste are required to be reduced by at least 55% by 2030, relative to 2005 levels. Europe is to become a climate-neutral continent as part of the measures outlined in the European Green Deal [12]. The European Union has introduced standards for exhaust emissions from passenger cars, lorries, and off-road vehicles, which also include agricultural tractors [13]. Greenhouse gas emissions from agriculture are covered by the EU’s Effort Sharing Regulation (ESR), which sets annual targets for each Member State for the years 2021–2030. Tractor manufacturers have even been imposed upon by strict exhaust emission limits on the engines being installed in recent years [14]. To comply with these regulations, manufacturers have integrated technologies designed to filter particulates from the exhaust system, e.g., exhaust purification systems and particulate filters. It is essential to note that these approaches are characterised by high costs, considerable space requirements, and the lack of possibility of completely alleviating the problem [15]. It is commonly known that agricultural tractors are the main machines powering various agricultural operations through the consumption of fossil fuels and contributing to a significant reduction in air quality. According to analyses by Renius, 2020 [16], each litre of combusted diesel produces as much as 2.7 kg CO₂ and emits other exhaust emissions into the environment [17,18] in the form of sulphur dioxide (SO₂), nitrogen oxides (NO_x), hydrocarbons (HC), carbon monoxide (CO), and particulate matter (PM) generated in the process of fuel combustion in the engine. It is also worth noting that methane (CH₄) and nitrous oxide (N₂O) are greenhouse gases that contribute to global warming. The compound CH₄ is extremely potent in warming the atmosphere, and its main sources include animal husbandry and fuel production. All of these gases form a so-called ‘blanket’ that traps heat in the atmosphere, thus raising global temperatures. Their presence in the air may also have adverse effects on human health [19,20]. It should be noted, however, that such stringent limits on exhaust emissions do not necessarily translate into positive environmental effects. According to existing reports, the exhaust gas recirculation (EGR) system, introduced to reduce NO_X emissions, leads to a 4 to 10% increase in specific fuel consumption and a similar reduction in engine efficiency [21] due to the recirculation of exhaust gases in the combustion chamber instead of clean air. Also important is the fact that the physical and chemical processes occurring in the cylinder of the internal combustion engine are complex and very difficult to define or simulate. Given the basic combustion equations, it can be assumed that the ratio of CO₂ to other toxic components of the exhaust gas is a measure of the correctness and efficiency of the fuel combustion process. Finally, it should also be noted that in the currently available literature, most studies present results focusing on the consumption of conventional fuels as well as products of biological origin [22,23], or the evaluation of agricultural machinery emissions, while determining the internal combustion engine parameters [24,25].

Recently, many studies have focused on diesel and petrol exhaust fumes, including a comparison of different methods of calculating average engine emissions for agricultural tractors [26], the simulation of fieldwork on an agricultural farm, energy consumption and the associated greenhouse gas emissions [27], and the effect of vehicle type and fuel quality on the actual emissions of toxic substances from vehicles with diesel engines [28]. A few studies have also analysed the performance levels of tractors during various real-life agricultural tasks [29,30,31], although they do not contain reference values relevant to the pollutant emissions generated.

The aim of the current publication on agricultural gas emissions is to analyse the impact of different tillage techniques and the application of organic and inorganic fertilisers, e.g., nitrogen fertilisers, digestate, or compost, on emissions of greenhouse gases and other environmentally harmful substances. The motivation for carrying out this review was the limited number of field studies conducted on this subject. This article is the introduction to a series of research articles on greenhouse gas emissions during agricultural production. A two-year field study is planned to determine the impact of tillage techniques, crop treatments, and fuel blends affecting energy consumption and gas emissions. This challenge was taken up due to the lack of data on this topic. The expected contributions of this article are to organise the research results and comprehensively analyse the current knowledge on gas emissions from agriculture. Moreover, it reviews studies on CO₂, CH₄, and N₂O emissions and their environmental and climate impact. Additionally, this article examines tillage methods and techniques, e.g., ploughing or no-plough tillage, and assesses their contributions to reducing emissions. Figure 1 presents the main areas of analysis discussed in the article.

The publication is based on a review of available scientific articles and provides a comprehensive picture of the interactions between agricultural practices and gas emissions while indicating possible solutions to the existing problem.

2. Methodology

Based on a preliminary analysis of scientific publication databases, the search was mainly focused on publications indexed in the Scopus, Web of Science, and ScienceDirect databases, and the Google Scholar search engine. The starting point for the search for articles in the abstract and citation databases, including Elsevier Scopus, was the use of various combinations of keywords, including but not limited to the following: “sustainable agriculture”, “impact of agriculture on greenhouse gas emissions”, “greenhouse gases and agricultural machinery”, “tillage and CO₂ and NO_x emissions”, “soil and CO₂ emissions”, “fertilisers in gas emissions”, “nitrogen fertilisers and greenhouse gas emissions”, “fuels in gas emissions in agriculture”, “digestate and CO₂ emissions”, “tillage techniques and gas emissions”, “composting and emission levels”, and “biodiesel and environmental impact”.

A preliminary verification of the subject matter of articles on greenhouse gas emissions from agriculture was carried out, distinguishing the impact of greenhouse gases on the changing climate, the impact of tillage techniques, fuels, and organic and inorganic fertilisers on emission levels, based on their title and abstract content as well as key words.

Approximately 300 articles were selected for further analysis. The limitations applied included the language of publication (Polish and English), access to full texts, and the lack of relevant data (articles that failed to provide sufficiently detailed data). These articles focused on theoretical, laboratory, and field research, primarily in European countries and the USA. The pre-selection stage involved reading the entire article and focusing on studies identifying the problem addressed. The next step was to focus on problems clearly related to greenhouse gas emissions in the agricultural sector, specifically concerning tillage forms, fertilisation techniques, fertiliser production, levels of gas emissions from the soil and plants, and the types of fuel used in agricultural machinery. Within the accepted time frame, the study mainly focused on the period covering the last two decades, up to and including 2024, to include the most recent and up-to-date scientific papers. This process led to the selection of approximately 190 scientific articles, the vast majority of which were peer-reviewed papers, with the remaining papers derived from reputable institutions. In the case of duplicate analyses, the pioneering study that best substantiated the required statement was cited. In contrast, when two articles provided contradictory evidence or different assumptions underlying a particular problem, they were also referenced to allow for greater nuance to be presented.

3. Greenhouse Gas Emission Sources

Poland’s greenhouse gas (GHG) emissions for 2022 were estimated at 315,467 million tonnes. This means that they were 33.2% lower than the emissions in 1988 and 4.8% lower than those in 2021. CO₂ emissions accounted for 82.9% of the total greenhouse gas emissions in Poland in 2022. The percentages of methane and nitrous oxide were significantly lower at 10.7 and 5.2%, respectively. The main source of CO₂ emissions was the subcategory fuel combustion. The proportion of this subcategory accounted for 92.2% of the total CO₂ emissions in the year 2022. As for the remaining categories, the energy industries accounted for 48.2%, manufacturing and construction for 8.7%, transportation for 21.7%, and other sectors for 13.6%. Figure 2 presents the relevant data. The net balance of CO₂ emissions and absorption in 2022 was estimated at approximately 37.7 million tonnes, which means that CO₂ absorption significantly outweighed emissions in this sector [32].

Methane emissions in 2022 amounted to 1451.32 kt, i.e., 40.64 million tonnes of CO₂ equivalent. Compared with 2021, emissions in 2022 were 3.9% lower. The proportion of methane in the total domestic GHG emissions in 2022 represented a value of 10.7%. Three major methane emission sources included volatile fuel emissions, agriculture, and fuel combustion. Their proportions in domestic methane emissions in 2022 accounted for 44.2, 39.4, and 9.5%, respectively [32]. The data are presented in Figure 3.

Nitrous oxide emissions in 2022 amounted to 74.85 kt, i.e., 19.84 million tonnes of CO₂ equivalent. N₂O emissions were 3.5% lower than those in 2021 and accounted for 5.2% of total GHG emissions. The main source of nitrous oxide emissions in Poland is the agricultural sector. The highest proportions of total N₂O emissions from agriculture in 2022 were noted for the following subcategories: agricultural soils (67.8%) and animal waste (12.3%) [32]. Figure 4 presents the relevant data.

The proportion of emissions from installations covered by the EU ETS in total domestic emissions in Poland from 2013 to 2020 accounted for almost 50%, gradually decreasing from 52.5% in 2013 to 45.6% in 2020 [32].

The above gases, including nitrogen oxides (NO), are formed within the engine combustion chamber areas with high temperatures and excess air as a result of atmospheric nitrogen oxidation. Here, NO is primarily formed, which then oxidises to NO₂. Moreover, the exhaust gases of a diesel engine also contain N₂O₃, N₂O₄, or N₂O₅. Particulate matter (PM) in diesel exhaust gases contains both organic compounds, e.g., carbon black and hydrocarbons in both condensed and crystalline forms, and inorganic compounds, such as ash, sulphur molecules, metal particles, and water. Carbon black is a residue from the incomplete combustion of fuel and engine oil, which contributes to the dark colour of exhaust emissions. Carbon monoxide (CO) is produced primarily as a result of the incomplete combustion of the carbon contained in a fuel due to oxygen deficiency. CO can also be generated via the breakdown of aldehydes, which are intermediates of fuel combustion, and as a result of CO₂ dissociation at high temperatures. Sulphur oxides (SO, SO₂, and SO₃) are found in exhaust gases because certain amounts of sulphur are present in diesel and biofuels. Sulphur is oxidised during a chain reaction, with oxygen as the stimulator. An important role is played by the production of fuels with an enhanced chemical composition that meets European standards and the requirements of modern engines, such as biodiesel [33,34]. The hydrocarbons contained in exhaust emissions can have a carcinogenic effect. Carbon dioxide is not defined as a toxic exhaust gas substance, only as a harmful one. It is the major cause of the greenhouse effect and, at higher concentrations, is toxic to living organisms. Carbon monoxide also has a strong affinity for haemoglobin, thus causing hypoxia [34].

The most harmful nitrogen oxides are NO₂ and N₂O₄, as they affect both the nervous system and the respiratory tract. Nitrogen oxide causes dizziness and numbness of the limbs. Hydrocarbons can cause poisoning and irritate the respiratory tract as well as mucous membranes, whereas PAHs are considered carcinogenic [35,36]. Greenhouse gases, such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), are emitted as a result of various human activities, e.g., unsustainable agriculture and the use of fossil fuels including coal, crude oil, and oil derivatives [37]. Therefore, a reduction in greenhouse gas emissions is possible through improving the efficiency of energy inputs in agriculture [38]. The use of energy-efficient agricultural production technologies can reduce fuel consumption in crop production, benefitting the environment. By using a suitably modified agricultural production technology, the overall level of greenhouse gas emissions in agriculture can be reduced by as much as one-third [39].

Alternative Fuels

In view of the depletion of fossil fuel resources and reports on their adverse effects on the climate and environment, efforts are being made to analyse an alternative fuel for diesel engines, e.g., biodiesel or alcohols. These alternative fuels can be used in internal combustion engines alongside diesel and petrol, either as a blend or as an additive [40]. The utilisation of biodiesel as an alternative fuel has led to a reduction in emissions, saving between 77 and 81% compared with the standard fossil fuel equivalent of 94 g CO₂eq/MJ. Consequently, in 2021, biodiesel saved approximately 45 million tonnes of CO₂eq emissions [41]. According to OECD-FAO reports from 2021 [42], the demand for vegetable oil outside the food sector is expected to decrease as the European Union simultaneously reduces its demand for diesel and emphasises the use of electric vehicles. Biodiesel production in the region alone is therefore projected to decrease by 7% by 2030, thus reducing its proportion of global biodiesel production from 34 to 30%. However, biodiesel can still be used as a substitute for diesel and is a renewable, clean-burning alternative to conventional diesel. Biodiesel is a type of fuel blend created through reactions with methanol or ethanol, resulting in methyl or ethyl esters derived from vegetable oils, animal fats, or waste fats. Typically, a blend of biodiesel and diesel that contains up to 20% biodiesel is used (B20). Biodiesel contains approximately 10% oxygen by weight, which reduces the emissions of hydrocarbons (HC), particulate matter (PM), and carbon monoxide (CO) during combustion in a diesel engine. Biodiesel contributes to a reduction in carbon dioxide (CO₂) and hydrocarbon (HC) emissions, but at the same time, it generates only a slight increase in nitrogen oxide (NO_x) emissions. The results of a study on diesel engine efficiency when using different palm-based biodiesel blends show a 73% reduction in non-combusted hydrocarbon (HC) emissions and a 46% reduction in carbon monoxide (CO) emissions. The use of a palm-based biodiesel blend at a B20 ratio reduces exhaust emissions compared with conventional diesel. It should be noted, however, that increasing the proportion of palm biodiesel in blends increases NO_x emissions while reducing CO and HC emissions [43]. Biodiesel is considered to ensure better engine lubricity compared with conventional diesel, which may contribute to its better performance. Biodiesel is mainly produced from vegetable oils, such as rapeseed oil in Europe and soybean oil in the USA. Compared with conventional diesel derived from crude oil, soybean biodiesel can reduce greenhouse gas emissions by up to 76% without considering indirect land use change (ILUC). Various available ILUC cases show that it is possible to achieve a 66 to 72% reduction in total greenhouse gas emissions. Furthermore, the rate of fossil fuel consumption when using soybean biodiesel is 80% lower than that of diesel [44]. The main components of oils and fuels are triglycerides. The most commonly employed method for their production is the transesterification of vegetable oils and animal fats. Transesterification can be homogenous, heterogenous, or enzymatically catalysed [45]. The transesterification reaction is affected by the molar ratio of glycerides to alcohol, the catalysts, reaction temperature, reaction time, and the free fatty acid and water content in oils and fats. Transesterification (also referred to as methanolysis) converts triglycerides (from vegetable oils and fats) and alcohol (methanol) into fatty acid methyl esters (FAMEs) and glycerol as a by-product in the presence of a suitable catalyst [46,47,48]. The reaction diagram is presented in Figure 5. The transesterification reaction can be catalysed by both homogeneous and heterogeneous catalysts. The most commonly used alkaline catalysts include sodium hydroxide, sodium methanolate, and potassium hydroxide [49].

Biodiesel can also be produced through the fermentation of lipids, such as algae or other microorganisms [50]. Yeasts such as Rhodotorula glutinis [51] and Lipomyces starkeyi [52] are commonly used in fermentation.

4. Agricultural Machinery Fleet Compositions and Greenhouse Gas Emissions

Leading scientific and research centres around the world are taking measures to assess the environmental friendliness of machinery under real-life operating conditions, i.e., in the field. This enables a broader understanding of the issue of emissions and, at the same time, the development of new solutions or the modification of existing solutions to minimise the adverse impact of this group of machines on the natural environment. This is because agricultural farms all over the world have a wide range of machinery in their fleets, including farms equipped with underused and outdated machinery, as well as farms equipped with modern and updated machinery featuring the latest technological solutions. This situation ultimately affects the variability of agricultural machinery and hinders the effective quantification of agricultural pollutant emissions. These difficulties are linked to both data collection and the dependence of the variables on place and time [53]. For work to be carried out with the lowest possible fuel consumption, agricultural tractors should operate as efficiently as possible, both in and out of production operations. According to Seyyedhasani and Dvorak, 2018 [54], it can be concluded that the time taken to carry out fieldwork was reduced by 17.3%, and that the total operating time of tractors was decreased by 11.5% due to route optimisation. These effects were achieved by organising better tractor performance during fieldwork and selecting the optimum tractor and tool configurations for the intended treatment. It has been established that as the tractive force increases, so does the drive wheel spin in the soil. The spin should remain between 14 and 16% [55,56]. Above this limit, productivity and performance drop, and the soil structure suffers more damage. It is essential to note that there are ways to improve the efficiency of tractor operation, e.g., choosing the right tools and operating modes, eliminating unnecessary passes, and reducing engine idling time. The results of a study by Peca et al., 2010 [57] show that a tractor’s fuel consumption and exhaust emissions are largely determined by the engine speed and load modes. The study showed that 5–25% of fuel can be saved by selecting an operating mode where the engine speed is 70–85% of the nominal value, and the tractor is loaded in a way that allows the engine to develop 80% of its maximum power.

However, according to studies by Janulevičius et al., 2016, and Lovarelli et al., 2017 [53,58], agricultural tractors operate most of the time loaded to only 50–70% of the maximum engine power. Moreover, the idling time accounts for 20–30% of the total working time.

5. Soil Properties and Crop Cultivation Techniques vs. Gas Emissions

The agricultural sector is considered to have the potential to be both a source and an absorber of greenhouse gases [59]. Terrestrial soils, comprising a pool of soil organic carbon (SOC) and soil inorganic carbon (SIC) [60], can accumulate almost three times more carbon than the atmospheric pool. They store a large amount of organic carbon [61], and approximately 10% of CO₂ in the atmosphere passes through terrestrial soils every year [62]. This situation indicates that soil alone may also contribute to greenhouse gas emissions. The agricultural sector alone is responsible for over 80% of anthropogenic N₂O emissions, 70% of anthropogenic NH₃ emissions, and approximately 40% of anthropogenic CH₄ emissions. The main reason for these emissions is the use of livestock manure and inorganic fertilisers [63].

The overall impact of the terrestrial biosphere on regional and global scales in a changing climate remains largely unexplored. The ubiquitous physiological processes of vegetation and its photosynthetic capacity influence carbon emissions and uptake. These processes are affected by daily and seasonal variations in weather parameters as well as hydrological and climatic variables. These processes contribute to the flux of CO₂ above agricultural land, which changes over daily and seasonal time scales [64].

5.1. Environmental Factors

According to Chapuis-Lardy et al., 2007 [65], microbial activity, root respiration, and chemical decomposition processes, as well as the heterotrophic respiration of soil fauna and fungi affect the process of greenhouse gas generation in the soil. The related emission flux rates depend largely on the water content of the soil (moisture), soil temperature, nutrient availability, and the pH value [66], as well as the parameters related to land cover and the number of pores. Soils with a high proportion of large pores retain less water and thus favour emissions of gases generated under aerobic conditions. In contrast, stable soil aggregates (concretions and crusts) lead to lower soil emissions, as C and N are less available to soil microorganisms. According to Schindlbacher et al., 2004 [67], soil moisture and soil temperature can be responsible for 74 and 86% of the variation in NO and N₂O emissions, respectively. In contrast, nitrogen oxide and CO₂ increase exponentially with temperature.

A study conducted by Fang and Moncrieff, 2001 [68] showed that under field conditions, moisture and temperature relationships overlap, making it difficult to observe clear connections. The study also indicated that temperature alone regulates freezing and thawing events, which in turn drive gas emissions from soils [69]. This temperature effect can account for 50% of the total annual N₂O emissions. However, according to Groffman et al., 2006 [70], winter CO₂ emissions are considered less important in the annual emission budget, as root respiration is low in temperate or more polar environments.

The soil moisture mentioned above is considered the most important soil parameter that influences greenhouse gas emissions, as it controls microbial activity and all related processes. As reported by Ludwig et al., 2001 [66], soils with fewer water-filled pore spaces (WFPSs) exhibit higher emissions from nitrification, with the maximum at a level of 20% WFPSs. According to Dutaur and Verchot, 2007 [71], since wetlands are potent sources of CH₄, long periods of drought can significantly reduce soil emissions.

The pH of the soil also affects its microbiological activity. Acidic soil conditions result in lower soil emissions. It has been reported that the optimum pH value for methanogenesis (CH₄ generation) ranges from 4 to 7. CO₂ emissions were observed to be the highest at neutral pH values, whereas N₂O emissions only decreased under acidic soil conditions. Soil nitrification increases at higher pH values as the balance between NH₃ and NO₃⁻ shifts towards ammonia [72].

5.2. Fertilisation

Organic soil fertilisation is essential for sustainable agriculture, as it helps to improve crop growth, yields, soil carbon content, microbial biomass, and activity. It also affects the rate and extent of carbon sequestration in the soil. However, it has certain disadvantages, such as the eutrophication of surface waters and greenhouse gas (GHG) emissions. Numerous publications have presented the response of carbon and other greenhouse gas emissions to the application of fertilisation and its absence. According to these reports, nutrients are crucial for the microbial and plant respiration processes. Hence, the natural N and C contents in the soil and the atmospheric deposition of the application of fertilisers in the form of manure or fertilisers are also important. According to Pilegaard et al., 2006 [73], N₂O emissions correlate negatively with the C/N ratio, with N₂O emissions being lowest at C/N ratios ≥30 in the case of the limited decomposition of organic matter and with the highest value of C/N = 11 for optimal decomposition and humus accumulation. A study conducted by Zhang et al., 2010 [74] to assess the impact of biochar fertilisation (three different dates) on the yield, as well as methane and N₂O emissions from a rice field, showed a 12–14% higher rice yield, and 34–41% higher CH₄-C emissions due to organic amendment.

The fertiliser doses applied should be adjusted to the plant’s needs, as not all forms of nitrogen can be taken up by the plants. Such an approach will significantly contribute to minimising N₂O emissions. The supplied and not-taken-up amounts of nitrogen in plants lead to increased N₂O emissions. According to Sanz-Cobena et al., 2014 [75], the water content of the soil is also of great importance for selecting a fertiliser type that is intended to inhibit increased N₂O emissions. In addition, the use of fertilisers is also affected by the tillage system.

5.3. Agricultural Practices

The ubiquitous agricultural activities and management practices also affect CO₂ emissions, as they can alter soil organic matter or soil carbon. Therefore, tillage is a skilful agricultural management practice that affects the quality of resources in the form of soil, air, and water. It therefore appears appropriate to switch to climate-friendly agriculture, which refers to agricultural practices that promote sustainable environmental, social, and economic development, with the main focus on increasing productivity to meet food and fuel needs, reducing emissions, and increasing resilience to climate-related hazards. The form of regenerative agriculture focuses on several principles that emphasise, among others, the protection and improvement of health, including that of the soil. The existing changes to the soil structure can affect its source and absorption functions [76], and its total storage capacity is limited. The basic measures to improve the soil structure include land management practices that contribute to increasing the carbon (organic matter) resources in the soil. Even a slight change in the duration or extent of the crop growing season can result in major changes in the annual flux of CO₂ [64]. The agricultural management practices implemented play a crucial role in enhancing carbon sequestration in the soil. Properly managed agriculture helps to store carbon in the soil by increasing the input of organic matter and reducing the rate of soil organic matter decomposition [77].

An example can be tillage, which contributes to the overall reduction in soil carbon sequestration (SCS) due to the decomposition of elevated carbon (C). Reduced tillage or no-tillage is therefore considered to be a way to increase soil carbon sequestration (SCS) and reduce CO₂ emissions. This also includes crop rotation design, i.e., the introduction to crop rotation of plants increasing the organic matter content, e.g., large-seeded leguminous plants, small-seeded leguminous plants, grass mixtures, grasses on arable land, fertilisation using manure and composts (generated during waste composting or vermicomposting), or leaving crop residues (e.g., straw) on the field and introducing them into the soil [78,79]. Another approach is represented by a recent study conducted by Garnier et al., 2022 [80], which showed that several major factors contribute to soil carbon mineralisation and a reduction in greenhouse gas emissions. These authors mention the earthworm density in the soil and the time since earthworm inoculation, while maintaining appropriate levels of aeration, moisture content, and temperature in vermicompost peats.

Cultivation Technologies

Agricultural activities are considered to have a significant effect on the emissions of three greenhouse gases: carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄). As reported by Porwollik et al., 2019 [81], various types of tillage practices are currently used. These practices are employed worldwide and include, for example, conventional tillage, no-tillage (NT), reduced tillage (RT), minimum tillage (MT), ridge tillage (RiT), strip tillage (ST), strategic tillage (STR), and deep tillage (DT). The application of different crop cultivation and crop processing techniques is the major factor causing greenhouse gas emissions. The consumption of fuels and energy, including activities such as food processing, the use of agricultural inputs, and land use for farming, contributes to the intensification of agriculture. Gases, including the CO₂ emitted during energy consumption in agricultural activities, are crucial for the development of effective mitigation and adaptation strategies, such as sustainable agriculture and minimising greenhouse gas emissions from energy consumption in agriculture and industry [82]. The intensification of agricultural production and the use of inorganic and organic fertilisers are the main causes behind the increased greenhouse gas emissions from agriculture. An increase in CO₂ levels can affect the soil carbon budget, crop productivity, and nutrient metabolism driven by the soil microbiomes, both directly and indirectly. The type and number of treatments and the technologies used to support crop growth enable the production of high-quality final products (seeds and oil), which results in gas emissions into the environment. The agricultural production sector must be an integral part of any global, sustainable climate stabilisation strategy without compromising food security and increasing the costs of food production [83]. Therefore, management practices that reduce greenhouse gas emissions while increasing crop productivity are essential. According to reports, carbon dioxide (CO₂) accounts for 20% of total greenhouse gas emissions from agricultural soils. Therefore, an assessment of CO₂ emissions from agricultural soils is necessary to enable the development of mitigation strategies for environmental performance and economic planning [84].

The cultivation of animal feed crops affects the soil carbon balance. Grassland typically sequesters carbon, whereas growing annual plants, such as cereals, tends to release carbon [85]. Petersen et al. (2013) [86] suggested that changes in soil carbon can be taken into account in the life cycle assessment (LCA) by calculating a partial carbon budget for individual crops and combining it with degradation and CO₂ emissions from the soil, as well as the resulting change in atmospheric CO₂. [87] In the LCA community, a distinction is made between the attributional mode and consequential mode of analysis. The first divides existing emissions by the total number of products produced in a period most commonly applied. This is recommended for identifying priorities or hot spots relevant to environmental product policy. The second mode captures how a specific activity changes environmental impact. [88]

Tillage technologies have a significant effect on the emissions of these gases into the atmosphere [87]. No-tillage has been demonstrated to reduce methane emissions compared with plough tillage and no-plough tillage. No-tillage, or reduced tillage, has a positive impact on the sustainable development of agriculture, increasing the soil carbon content, reducing soil erosion, improving the soil’s physical conditions, and lowering greenhouse gas emissions without compromising crop yields. When comparing no-tillage farming with conventional farming, the former results in reduced CH₄ emissions [89,90]. When cultivating the soil under a no-plough tillage system, the plough is replaced with other cultivation tools, such as a disc harrow, stubble cultivator, and rotary ripper. This results in the soil not being turned over and the crop residues and intermediate crop being left on the field to form mulch, with the number of passes reduced. This technology improves field irrigation and reduces CO₂ emissions and losses due to erosion [91]. The studies conducted so far are inconclusive regarding the impact of no-plough tillage on gas emissions. The results vary depending on climate and soil type, etc. Ploughing is the most energy-intensive tillage treatment. When fuel is combusted, the main component of the exhaust gas is carbon dioxide [89]. It has been calculated that 1 L of consumed diesel equals 3.15 kg of carbon dioxide generated. The cessation of ploughing results in fuel savings and lower greenhouse gas emissions. In preliminary analyses, the fuel used under three different tillage systems was converted into CO₂. Based on these calculations, it has been found that conventional plough tillage emits 180.76 kg CO₂/ha and no-plough tillage emits 89.36 kg CO₂/ha, whereas no-tillage farming emits only 19.50 kg CO₂/ha [92].

Efforts are currently being made to move towards simplified tillage systems. Conserving tillage is one of the techniques applied in sustainable agriculture. It involves the use of mulching, which prevents soil degradation and maintains its productivity and fertility. In the United States, it is a basic tillage method, whereas in Europe, it is gaining importance due to its role in mitigating global warming. The advantages of this type of tillage are wide-ranging, including the prevention of soil water erosion, deeper root development in plants, reduced cultivation costs, reduced nitrogen losses, and improved soil structure. The method involves the incorporation of a minimum of 30% of crop residues (organic matter), which decompose with the help of soil microorganisms to build humus while increasing soil fertility. Organic matter prevents soil erosion, i.e., the leaching of the topsoil. Reducing tillage in the ploughing system results in CO₂ being sequestered in the soil, making it a carbon dioxide absorber [93,94]. Incorporating organic matter into the soil enhances water infiltration, improves aeration, and affects bulk density. It also influences the chemical properties of the soil, such as the buffer capacity and cation exchange capacity [95]. Another advantage of this tillage system is the reduction in the number of agricultural tractor passes, resulting in lower fuel costs, time savings, and reduced soil erosion [96]. Research shows that conservation tillage may increase CO₂ emissions due to the enhanced activity of soil microorganisms resulting from increased water availability [97]. Soil moisture regulation influences N₂O emissions from the soil due to the denitrification and nitrification of soil nitrogen. Increased moisture intensifies these processes. The available literature describes the impact of this tillage system on emissions differently. These differences can be due to the physico-chemical properties of the soil, e.g., the pH and nutrient concentration [96]. Kai Yue et al., 2023 [96] found that reduced tillage increases N₂O and CH₄ emissions by 31.0% and 24.7%, respectively, while reducing crop yields by 17.4%, without an effect on CO₂ emissions, whereas no tillage reduces CO₂, N₂O, and CH₄ emissions and the total global warming potential (GWP) by an average of 15.1%, 7.5%, 19.8%, and 22.6%, respectively [96]. A new, innovative technology is the highly reflective mulching membrane, which enables greater damping of the heat wave throughout the soil. It can lead to a temperature being up to 16% lower than that on the surface, which can be beneficial for plant growth (covered soil is, on average, 3 °C cooler than uncovered soil). In addition, the optical properties of the membrane enable the balancing of carbon dioxide emissions from agricultural activities by approximately 0.1 tCO₂-eq m⁻² [98]. The preliminary results of the environmental monitoring conducted by A Di Giuseppe et al., 2023 [99] showed that the soil temperature values were lower in the section covered with the mulch membrane during the middle hours of the day. The proposed agricultural technology allows for a tenfold increase in the productivity of food crops while maintaining the nutritional properties of food crops compared to crops grown using traditional techniques.

6. Organic and Inorganic Fertilisers

In the initial period of field cultivation, people used mineral and organic fertilisers in the form of manure and ground bones to improve soil fertility. The development of civilisation has contributed to the development of this industry, resulting in numerous types of commercially available fertilisers. The two main types of fertilisers include organic fertilisers and mineral (inorganic) fertilisers. The early 20th century marked the emergence of the first methods for nitrogen production: initially, by passing air through an electric arc to yield nitric acid and calcium nitrate; subsequently, by employing the reaction of lime and coke in an electric furnace to create calcium cyanamide; and ultimately, through the catalytic synthesis of nitrogen and hydrogen [100].

Organic fertilisers are produced from natural raw materials, such as manure, compost, seafood, algae, and other organic materials of agricultural and municipal origin. They are rich in nutrients, which are gradually released into the soil as a result of organic decomposition. In contrast, mineral fertilisers, also known as artificial fertilisers, are industrially produced and consist of mineral salts. They are rich in nutrients, such as nitrogen, phosphorus, and potassium, which are essential for proper plant growth. As already mentioned, the fertiliser industry is essentially involved in providing three main plant nutrients, i.e., nitrogen, phosphorus, and potassium, in plant-available forms. These components, in the form of nitrogen, are expressed in elemental form as N. Phosphorus and potassium can be expressed as oxides (P₂O₅, K₂O) or as elements (P, K). Sulphur is also supplied in large quantities, partly through sulphates found in products such as superphosphate and ammonium sulphate. The addition of both fertiliser forms to the soil provides crops with the appropriate nutrients they need to grow. It should be noted that nowadays, the production of nitrogen fertilisers relies mainly on fossil fuels, such as natural gas, which contributes to the environmental crisis worldwide. Although significant progress has been made in reducing the intensity of carbon dioxide emissions in the production of fertilisers, there is still considerable pressure to reduce these emissions [101].

The advancements in these processes have transformed artificial fertiliser-based agriculture, leading to increased crop production and doubling the number of people that can be fed from one acre of land. This transformation has played a key role in guaranteeing global food security and has contributed to a 30–50% increase in food production [100]. This increase, however, comes at a price of greenhouse gas emissions that contribute to the planet’s warming, as well as soil, water, and air pollution and loss of biodiversity. According to Erisman et al., 2008 [102], agriculture is the second largest source of climate pollution, with both the production and application of fertilisers contributing to high emissions of harmful gases. The production of inorganic (artificial) fertilisers requires large amounts of energy. Most of this energy comes from the combustion of fossil fuels, such as coal and methane or natural gas, which emit greenhouse gases, i.e., carbon dioxide [101]. The chemical and petrochemical sectors are the largest industrial energy consumers. Available fertilisers are essential to ensure food security and Europe’s strategic autonomy, which enables the production of half of the world’s food. In addition, agricultural production is considered to be among the major anthropogenic factors contributing to emissions of greenhouse gases other than CO₂ [103], whereas the production of synthetic nitrogen fertilisers alone accounts for approximately 2% of global energy consumption [104,105]. The primary greenhouse gases involved in this process include nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂), along with significant emissions of ammonia (NH₃).

Fertiliser producers affiliated with Fertilizers Europe, i.e., an organisation that associates the leading fertiliser producers in Europe, will adopt a general plan for the decarbonisation of their assets. These companies have committed to reducing greenhouse gas emissions by 70% by 2040 compared with 2020 and to making European fertiliser production climate-neutral by 2050. According to reports, ammonia production alone accounts for approximately 17% of the energy consumed in this sector. The production of fertiliser consumes approximately 1.2% of global energy and accounts for approximately 1.2% of total greenhouse gas emissions [104]. According to reports, the production of ammonia is already contributing to 1–2% of global carbon dioxide emissions [106]. It should also be noted that cultivated plants take up, on average, about half of the nitrogen they receive from fertilisers [107]. Most of the fertiliser used runs off to waterways or is decomposed by microorganisms in the soils, thus releasing potent greenhouse gases into the atmosphere, which pollutes the air (e.g., NH₃, NO, and N₂O). These N losses have resulted in a cascade of undesirable environmental effects that disrupt essential ecosystem functions and pose a hazard to human health.

In order to achieve reduced gas emissions, the European Union has announced plans (“The Farm to Fork Strategy”) to reduce the use of fertilisers by a quarter over the course of this decade, which is part of wider efforts to make its farms more sustainable by making food systems fair, healthy, and environmentally friendly. The Farm to Fork Strategy is aimed at helping to mitigate climate change and adapt to its effects [108]. It describes the progress of work through measures to mitigate the risks associated with pesticide use, as demonstrated by a 20% reduction in these risks over the past five years. The European Commission is undertaking additional measures to reduce the overall use of and risks associated with the use of chemical pesticides by 50% and to reduce the use of more hazardous pesticides by 50% by 2030 [109]. Furthermore, work is still ongoing to obtain an accurate assessment and comparison of potential fertilisation scenarios using precise environmental and life cycle assessments (LCAs) in the form of an emission factor (EF) tool, which is used to estimate GHG emissions and represents an integral part of these analyses. However, the proper accounting of emissions is an integral part of accurate environmental assessments. The awareness of factors affecting the EF and their impact on these assessments is limited, and the range of factors considered varies significantly from study to study. Analysis of the life cycle of fertilisers determines the emissions and absorption of greenhouse gases in the production of artificial fertilisers, during transport and storage, and during fertilisation and crop growth, i.e., at every step of the fertiliser’s “life”. Different types of fertilisers have different carbon footprints. During the production of urea, less CO₂ is emitted than during the production of ammonium nitrate. After spreading, this difference is reversed because the urea releases the CO₂ contained in its molecule. On average, it can be expected that more N₂O will be released from the soil after urea is spread [109].

6.1. Nitrogen Fertiliser

It is essential to note that numerous nitrogen fertilisers have been utilised in agriculture since the 1950s to enhance crop production [102]. Their production can have a significant environmental impact, mainly due to the large amounts of energy and natural gas required to produce them [110,111]. The reduction in energy and natural gas consumption is linked to measures aimed at reducing the amounts of mineral fertilisers used in agriculture through the more efficient use of the nutrients they contain and the search for natural, alternative methods of obtaining them, such as bio-disinfection.

A study examining the entire life cycle of nitrogen fertilisers (from production to use in the field) revealed that the greatest environmental impact is caused by fertiliser production, as well as nitrogen dioxide emissions resulting from the use of fertilisers [112]. At the production stage, the highest environmental impact indicator values were noted for climate change, the depletion of fossil fuel resources, and acidification and eutrophication of freshwater bodies. As regards transport, the impact of fossil fuel use is dominant [113].

Examples of an environmentally friendly approach to increasing the bioavailability of minerals in the soil include organic supplementation, which increases the concentration of NO₃⁻_-N, exchangeable K₂O, Ca²⁺, Na⁺, and Mg²⁺ in the soil, and the level of electrical conductivity in the soil extract [114], or bio-disinfection, which involves the fertilisation of crops with nutrients derived from biomass produced on the same farm. A study conducted by Fan et al., 2004 [115] showed that only 30–50% of the nitrogen supplied in mineral fertilisers is taken up by plants, whereas the remaining 50–70% is used by microorganisms or leached into the soil, as well as surface waters and groundwater.

The nitrogen fertilisers produced in Poland include ammonium nitrate, urea, and calcium ammonium nitrate. In the international arena, Poland ranks among the countries with an average level of mineral fertiliser production. In 2021, Poland accounted for 1.4% of global fertiliser production, of which 1.8% was related to nitrogen fertilisers. However, in the European Union, Poland is among the leading fertiliser producers, holding a leadership position in terms of nitrogen and phosphorus fertilisers in their pure components. In 2021, Poland’s share in EU fertiliser production was 18.6%, comprising 20.4% for N, 24.4% for P₂O₅, and 10.6% for K₂O, as reported by the Polish Institute of Agricultural and Food Economics [116]. In 2022, there was a decline in their production, which worsened in the following year (2023). Regarding the production of these fertilisers, it should be noted that all synthetic nitrogen fertilisers originate from ammonia (NH₃), which is synthesised from nitrogen and hydrogen. In nature, an (NH₃) fertiliser is produced as a decomposition product of protein-containing substances, whereas, in the industrial setting, the basic raw materials used for its production include natural gas and air. Artificially produced nitrogen fertilisers increase the generation of N₂O, thus providing a substrate for microbial nitrogen conversion through nitrification and denitrification. According to Erisman et al., 2008 [102], the annual global consumption of nitrogen from fertilisers is estimated at approximately 100 teragrams (Tg) of N. In conventional fertiliser production, ammonia is produced by combining nitrogen and hydrogen (in the Haber–Bosch process), with hydrogen produced from natural gas in a steam methane reforming (SMR) unit. The resulting product chain comprises natural gas–hydrogen production–ammonia production–fertiliser production. This is a highly energy-intensive process. It converts hydrogen from natural gas (CH₄) and nitrogen from the air into ammonia. The ammonia is then used to produce urea and ammonium nitrate, i.e., the most commonly used nitrogen fertilisers [117]. Nitrogen fertilisers are the main anthropogenic source of nitrous oxide (N₂O) [89]. In turn, low-carbon ammonia production technologies include carbon capture and utilisation (CCU), where CO₂ is captured and used in other final processes to produce biofuels or plastics. These also include electrolysis or alternative sources of nitrogen or the use of biomethane, which involves avoiding the CO₂ emissions from fossil sources thanks to the use of biomethane rather than natural gas. CCU does not produce a positive net atmospheric carbon balance, and several important considerations should be taken into account. As CO₂ is a thermodynamically stable form of carbon, manufacturing products from it is energy-intensive, and the profitability of CCU is partly dependent on the price of CO₂ emissions into the atmosphere [89].

According to calculations by Fertilizers Europe [118], within the framework of a technology-neutral approach, by 2030, a 35% reduction in CO₂ emissions will result in emissions of 1.33 tonnes of CO₂ per tonne of ammonia produced. By 2040, a 68% reduction in CO₂ emissions will lead to emissions of 0.67 tonnes of CO₂ per tonne of ammonia. Where possible, large amounts of the hydrogen generated via electrolysis will be used. Then, by 2050, thanks to a 100% reduction in CO₂ emissions, CO₂ emissions will be reduced during the production of ammonia in combination with the hydrogen generated using electrolysis and biomethane.

The world’s population is expected to rise to 9 billion by the year 2050 and to 11 billion by 2100 [119]. Consequently, a significant food security challenge is expected to emerge in the coming years. To meet the intensive needs of millions of people, there has been a significant increase in livestock and crop production, which has also contributed to the generation of agricultural waste. The improper disposal of these crop residues can lead to the generation of greenhouse gases (GHG), such as CO₂, N₂O, and CH₄, which pose a hazard to humans and the environment [120].

According to Zhang et al., 2022 [100], ordinary urea (46-0-0) is the most commonly used nitrogen fertiliser in agricultural production, accounting for 73.4% of the global nitrogen application. However, the rapid release of nitrogen from regular urea results in a nitrogen supply that cannot be synchronised with crop nitrogen requirements, leading to 20–70% of nitrogen not being used by crops [121]. This situation results in yields that do not meet expectations and low nitrogen use efficiency. In addition, the rapid release of N leads to several environmental problems, e.g., greenhouse gas (NH₃ and N₂O) emissions into the atmosphere and the leaching of nitrates into the soil and water. A study conducted by Sahar et al., 2012 [122] employed the method of urea splitting in the field, which involved the adjustment of the time of normal urea application. This fertiliser was applied two or more times in accordance with the critical period of crop nitrogen demand, thus improving the temporal synchronisation between crop nitrogen requirements and nitrogen supply in the soil. The validity of this method was confirmed by other researchers, who considered it suitable for several crops, including rice [123], wheat [124], maize, and sweet potatoes [125]. Additionally, these studies demonstrated that the split method yields excellent results in terms of reducing greenhouse gas emissions and nitrate leaching. However, one cannot ignore the fact that its application required significantly more fieldwork and increased labour input compared with a single basic application of the whole N fertiliser due to the lack of machinery to support the application of the N fertiliser [126].

According to Yang et al., 2022 [127], there are four main categories of products known as enhanced-efficiency nitrogen fertilisers (EENFs). These include controlled-release coated fertilisers, urease inhibitors, nitrification inhibitors, and a combination of two inhibitors [128]. Analyses of the above data showed that coated, controlled-release urea reduced all reactive nitrogen losses (e.g., ammonia volatilisation, nitrous oxide emissions, and nitrogen leaching) by 24.3–45.9% worldwide, although it did not alter the inorganic nitrogen content of the soil [127]. In addition, fertilisers in the form of coated urea increased crop yields and plant nitrogen uptake by 7.7 and 12.6%, respectively. Nitrification inhibitors brought similar environmental and agronomic benefits [129]. However, these inhibitors increased the NH₄⁺-N content of the soil by 41% and reduced NO₃-N by 41%, thus increasing ammonia volatilisation by 20%.

Recent studies indicate that the use of enhanced-efficiency nitrogen fertilisers affects the C dynamics in the soil and the associated CH₄ and CO₂ emissions for the closely coupled relationships between the biogeochemical cycles of C and N. According to a study conducted by Vilarrasa-Nogue et al., 2020 [130], nitrification inhibitors tend to reduce CH₄ oxidation, as they can inhibit ammonium monooxygenase, which shares several substrates with the methane monooxygenase enzyme of methanotrophs. Lan et al., 2013 [131] investigated the effectiveness of nitrification inhibitor dicyandiamide (DCD, C₂H₄N₄) in suppressing nitrification and N₂O emissions in rice soils, confirming that DCD reduced the nitrification rate and the amount of N₂O in nitrification emissions. However, the impact of DCD gradually diminished and could be insignificant as early as after four weeks.

6.2. Compost

According to the Polish National Centre for Emissions Management, the total greenhouse gas emissions from Poland’s agriculture in 2022 [32] accounted for 8.8% of the country’s total anthropogenic emissions. Polish agriculture is a primary source of nitrous oxide (N₂O) emissions, accounting for 80.2% of the total anthropogenic emissions of this gas. Regarding the total nitrous oxide emissions from agriculture, 83.7% originated from land use (nitrogen fertilisation) and 15.24% from livestock manure management [132]. According to data acquired by Bai et al., 2020 [133], it is estimated that landfills worldwide contribute to approximately 12% of annual methane (CH₄) emissions, i.e., 734 kg CO₂-eq/tonne of treated wet waste [133].

Greenhouse gas emissions are linked to the carbon content of the waste being utilised. Organic waste management contributes to the presence of CO₂, which is generated under strictly aerobic conditions, whereas CH₄ and N₂O are generated via the anaerobic mineralisation of this waste. An important aspect, therefore, is the implementation of reliable technology to manage the widespread availability of waste as a cornerstone of sustainable development for any nation. Considering the actual application of technology that must adhere to rules and regulations, the primary aim is to mitigate environmental and health issues [134,135].

In Poland, there are more than 170 waste composting plants, excluding those located at sewage treatment plants. However, composting plants are typically part of larger facilities for the mechanical and biological treatment (MBP) of mixed municipal waste. According to information provided by the Ministry of Environment, there are more than 120 such facilities in Poland (as of December 2013) [136]. Composting plants receive green waste, mainly grass, leaves, and branches from gardens, parks, green belts, and so-called wet waste from local residents. These wastes are described as organic and inorganic materials generated from various sources. There are many more waste classifications that are also complex; however, the literature contains studies on household waste, solid municipal waste, sewage waste, ashes, manure, and many other kinds of waste [137,138,139]. Moreover, the European circular economy and waste policy increasingly regard biowaste as one of several key waste streams. These include new targets for recycling and preparing for the re-use of municipal waste and an obligation to collect waste separately. Moreover, EU Member States are required to monitor food waste generation and implement a food waste prevention programme supporting Sustainable Development Goal 12.3, i.e., halving per capita global food waste by 2030 [140].

According to the literature, approximately 2.01 billion tonnes of solid waste are generated annually, and it is estimated that this figure will increase to 3.40 billion tonnes by 2050 [141]. Biowaste recycling is, therefore, crucial to achieving the EU’s target of recycling 65% of municipal waste by 2035.

Every year, between 118 and 138 million tonnes of biological waste are generated across the European Union, of which only approximately 40% (equivalent to 47.5 million tonnes per annum [M tpa]) is effectively recycled into high-quality compost and digestate. The introduction of separate biowaste collection in all EU Member States, as stipulated in the Waste Framework Directive, is crucial for reversing the landfilling of organic waste and ensuring that high-quality secondary raw materials (compost and digestate) are consistently produced, allowing them to be introduced to the European fertiliser market [142]. The ubiquitous, complex regulations, surplus manure, variable availability, and transport of compost, as well as its variable quality and composition, continue to hinder the use of this fertiliser. Agricultural residues, e.g., livestock manure, a by-product of livestock farming, contain numerous volatile and harmful substances, including thiol, faecal odorant, acetaldehyde, and hydrogen sulphide. The presence of these compounds is linked to the generation of foul-smelling gases that permeate the atmosphere and have an adverse effect on the surrounding environment. When left untreated and exposed directly to environmental impacts, they not only contribute to the deterioration of groundwater and river quality, but also pose a hazard to the safety and integrity of aquatic ecosystems [143]. To minimise the potential consequences mentioned earlier, technologies that can process municipal, industrial, and agricultural waste should be employed. During this process, a complex community of microorganisms decomposes organic matter, converting it into two primary end products: digestate (biofertiliser) and biogas [143].

Waste management technologies encompass the conversion of waste into energy and heat through various processes, including combustion, composting, vermicomposting, pyrolysis, and gasification. The combustion of residues releases significant amounts of carbon dioxide (CO₂) and other greenhouse gases (GHGs). It is also one of the less suitable processes for managing solid waste due to its high fuel consumption [144]. The available literature presents several methods that focus on the source, separation, and economic utilisation of various waste materials of biological origin (as above: composting and vermicomposting), taking into account the problem of their disposal [145,146]. The composting process is considered environmentally friendly and cost-effective, as organic matter is biologically degraded under aerobic conditions. It is also the most widely used method from the technological, economic, and environmental perspectives. This process is part of any strategy aimed at diverting organic waste and reducing methane (CH₄) emissions from organised landfills. The amount of greenhouse gases generated during the composting process is largely determined by the type and composition of the waste. The composting process contributes to the direct treatment of organic waste or solids remaining after the anaerobic digestion (AD) of organic waste. This phenomenon ultimately reduces the total mass of waste through aerobic biochemical degradation, providing numerous nutrients to the soil and thereby complementing agricultural processes [147].

The composting of organic waste is a bio-oxidative process that leads to mass reduction, ranging from 10 to 60%, during dry composting [148]. During biomass decomposition, the oxygen (O₂) present is used up, and the carbon dioxide (CO₂) generated is released into the atmosphere, as are other volatile compounds produced by microorganisms, such as methane (CH₄) and nitrogen oxide (N₂O). The composting process also generates ammonia (NH₃), which is a critical precursor to particulate matter in the atmosphere [149]. During the nitrogen conversion process, the generation of N₂O and NH₃ cannot be avoided, with the presence of N₂O largely contributing to ozone depletion. As reported by Ermolaev et al., 2015 [150], the warming potential for a single N₂O molecule is 296 times higher than that for a CO₂ molecule. Figure 6 presents a schematic of CO₂, N₂O, and CH₄ emissions during the composting process.

A method that is becoming increasingly common is vermicomposting, which involves using earthworms, primarily the species Eisenia fetida, to process organic waste. Vermicomposting involves bio-oxidative processes and the stabilisation of organic material, similar to composting. However, in vermicomposting, this process concerns the interactions between earthworms and soil microorganisms. During the vermicomposting process, microorganisms release greenhouse gases and volatile substances, as shown in Figure 7. The process is relatively simple and can be carried out both under home conditions and on a larger scale. The role of microorganisms is to produce enzymes that cause the biochemical decomposition of organic matter, whereas earthworms contribute to a larger microorganism population by fragmenting and consuming fresh organic material. Moreover, earthworms also interact with other organisms in the soil, affecting various microflora and microfauna [151,152]. Furthermore, a study conducted by Garnier et al., 2022 [80] elucidated that earthworms play a beneficial role in soil carbon mineralisation. By applying a statistical model, the study revealed a 24% increase in carbon mineralisation with earthworms present at a density of 1.95 mg/g of dry soil mass. Vermicomposting has many advantages, inter alia, a reduction in the amount of waste disposed of in landfills, the production of valuable, nutrient-rich compost, and a positive impact on the physico-chemical properties of soil and plant growth [153,154].

There are reports indicating that vermicomposting reduces methane emissions compared with composting [155]. A study conducted by Nigussie et al., 2016 [156] showed that the reduction in N₂O and CH₄ emissions during vermicomposting, compared with composting, was higher by 40 and 32%, respectively, when the moisture content in the raw material was higher, and the reduction in these greenhouse gases accounted for 23 and 16%, respectively, at a low moisture content of the mass under study. In addition, the results obtained varied depending on the pH value, earthworm species, and the C/N ratio. A higher moisture content contributes to CH₄ and N₂O emissions, as it creates more anaerobic CH₄ pockets in the accumulated composts, resulting in increased greenhouse gas emissions. Additionally, vermicomposting reduces methane emissions compared to controlled methods or composting [157].

Although composting and vermicomposting are environmentally friendly methods for managing organic waste, one of their major disadvantages is the release of greenhouse gases (GHGs). According to Yasmin et al. (2022) [143], greenhouse gas emissions during the composting and vermicomposting processes can be controlled by various factors, including aeration, the addition of bulking agents, pH, temperature, and the C/N ratio.

The presence of gases CO₂, CO, H₂S, and NH₃ has an adverse effect on the quality of mature compost. The use of biocarbon has become an effective tool for reducing gas emissions due to its unique physico-chemical properties. Adding biocarbon to compost can significantly reduce GHG emissions (by up to 20%) while positively affecting the course of the aerobic stabilisation process [158]. Wang et al., 2018 [159] showed that the addition of biocarbon can reduce CO₂ emissions during swine manure composting by up to 26.06% at a dose rate of 10%.

The gas CH₄ is the second-most produced greenhouse gas after CO₂. Over the last 10 decades, it has been observed that CH₄ emissions are 28 times higher than those of CO₂ [160]. The level of CH₄ emissions is determined not only by the type of organic materials being composted, but also by the type of composting, gas diffusion at the heap surface, production rate, the amount of material used, moisture content, temperature, and activity of methanotrophic bacteria [161]. According to Yuan et al., 2016 [162], the lower aeration rate promotes high CH₄ emissions. Vergara et al., 2019 [163] observed an increase in CH₄ emissions at lower O₂ concentrations, a higher C/N ratio, and a higher temperature in the early composting process. Average daily emissions amounted to 1.7 ± 0.32 g CH₄ kg^−k of wet feedstock. The addition of biocarbon to the compost mass can also serve as an electron transport system to promote the conversion of NO³⁻ into N₂ and reduce N₂O emissions [164]. The presence of biocarbon can alter the structure of the mass subjected to the reaction and decrease the production of anaerobic sites, thus reducing CH₄ emissions [165]. According to Pan et al., 2021 [166], the addition of clay minerals (zeolite and montmorillonite, etc.) to compost can also accelerate organic matter degradation and promote compost maturation. Geng et al., 2024 [167] added biocarbon and zeolite to compost, which contributed to an increase in the pH value during the initial phase of measuring the microbial activity in the reactor. The presence of NH⁴⁺ organic matter containing nitrogen decomposes, thus increasing the pH value during composting.

A study conducted by Samal et al. (2022) [168] indicated that incorporating sewage sludge and cow manure into primary sludge significantly reduces greenhouse gas emissions. In contrast, analyses conducted by Wang et al., 2014 [169] showed that the addition of reed straw to duck manure reduces N₂O generation.

In many cases, vermicomposting emits lower amounts of greenhouse gases than traditional composting, primarily due to reduced methane (CH₄) emissions. However, earthworms are also significant contributors to the generation of nitrous oxide (N₂O) during vermicomposting.

Simple carbon compounds are mineralised and metabolised by microorganisms to generate CO₂, NH₃, H₂O, organic acids, and heat [170]. Compost is produced from crop remains, municipal waste, and organic substances. Such organic additives, when introduced into the soil, provide organic carbon, thus increasing the stability of soil aggregates and reducing the risk of erosion. Another advantage is the release of nutrients. It should be noted, however, that compost contains significantly lower amounts of nutrients than inorganic fertilisers. This fertiliser is exposed to carbon and nitrogen losses, which leads to a reduction in its agronomic value and contributes to greenhouse gas emissions [171]. Due to composting, cattle manure loses approximately 67% of organic carbon and poultry manure loses approximately 57%, whereas swine manure loses approximately 72%. There may also be nitrogen losses through ammonia oxidation and denitrification, resulting in N₂O emissions into the atmosphere [170]. Emissions of air pollutants other than greenhouse gases from composting facilities impact both local and regional air quality, and consequently, human health in the surrounding communities. The volatile gases generated from the composted mass (NH₃) and volatile organic compounds (VOCs) from composting are of particular concern, as they are precursors to secondary fine particulate matter (PM 2.5), which are the major health-affecting factor associated with air pollution. Additionally, the resulting VOC gases serve as precursors to the formation of tropospheric ozone, which impacts sensitive vegetation and the surrounding ecosystem [172].

It should be noted that the rate of CO₂ emissions during waste composting does not imply the rapid decomposition of total organic matter and high microbial activity. Composting operations generate two forms of CO₂, i.e., biogenic CO₂ and non-biogenic CO₂ [173]. Biogenic CO₂ gas is generated through biological processes, such as litter degradation and soil respiration, whereas non-biogenic CO₂ is produced by the combustion of fossil fuels, such as coal and crude oil.

6.3. Livestock Manure

With the rapid development of the global economy and society, the demand for food has changed significantly. The use of livestock manure on agricultural land as an organic fertiliser has improved crop productivity and soil fertility, increased organic carbon (OC) reserves in the soil, and affected greenhouse gas emissions. According to Vac et al., 2013 [174], livestock manure accounts for 37% of global greenhouse gas emissions. The use of livestock manure and synthetic fertilisers can be considered the best indicator of CH₄ emissions from agricultural land [122].

This situation has led to an increase in the demand for meat, resulting in higher livestock manure production [175]. Livestock manure has become the third largest source of pollutants, following industrial and household sewage, and is also considered one of the major sources of agricultural pollution. If not properly treated, the agricultural waste generated will not only cause an enormous waste of renewable resources, but also pose a serious hazard to the environment through increased greenhouse gas (GHG) and ammonia emissions, water pollution, and soil degradation. The beef cattle sector can be divided into two main beef categories: beef for meat production and beef for dairy production, both of which include beef derived from young bulls, heifers, and cows. Furthermore, within each of these main beef categories, production systems differ in terms of several parameters, including breed, age, body weight at slaughter, housing system, nutritional level, and feed ration composition [175]. Nguyen et al., 2010 [176] investigated the main European beef production systems and found enormous differences in the utilisation of resources under different systems, referring to the dry matter of feed/kg of carcass weight for beef from a beef cattle breeding system and the carbon footprint (CF) per kg of carcass amounting to 16.0–27.3 kg CO₂ for beef derived from the two systems.

However, the livestock breeding sector is considered primarily responsible for the emissions of CH₄ and N₂O, i.e., compounds with a global warming potential (GWP) index value significantly higher than that of CO₂. For CH₄, it is 21-fold, and for N₂O, 310-fold higher than that for CO₂. The sources of emissions for these compounds include enteric fermentation in ruminants, manure, and the use of nitrogen fertilisers. The contribution of animal husbandry to agricultural gas emissions is as follows: 37% of total methane emissions, 65% of nitrous oxide emissions, and 9% of carbon dioxide emissions [177].

The use of livestock manure has a significant impact on greenhouse gas emissions, while also enhancing soil fertility, increasing nutrient availability to plants, and improving the water retention capacity and cation exchange capacity [171]. However, untreated livestock manure, which is directly exposed to environmental effects, not only deteriorates water quality in rivers, but also poses a hazard to the safety and integrity of aquatic ecosystems. Livestock manure often contains PTE and antibiotics, which enter the soil as a fertiliser and can cause further contamination and disrupt the ecological balance. Poultry manure was found to increase CO₂, CH₄, and N₂O emissions significantly more than swine and cattle manure [122]. A study was carried out to prove that the use of livestock manure increased the soil contents of organic carbon, total nitrogen, available N, and available P by an average of 19.2%, 14.4%, 13.2%, and 78.3%, respectively, compared with the soils on which no manure had been used [178]. The use of this organic fertiliser increased N₂O emissions by an average of 32.7% (95% confidence interval: 5.1–58.2%) compared with a synthetic nitrogen fertiliser [179]. According to the Environmental Protection Agency’s (EPA) estimates, livestock manure in the USA generates approximately 20 million tonnes of methane per year, which accounts for approximately 8% of the country’s annual methane emissions from human activities [180].

According to the available scientific studies, the use of fertilisers in the form of polluted manure may result in the contamination of crops with faecal bacteria. A study conducted in Italy on lizards found the presence of changes in liver biosynthesis that are typical of oestrogen contamination in the bodies of these reptiles living in manure-fertilised areas, which reduced their reproductive capacity (Verderame et al., 2016) [181]. The enrichment of water with nutrients, such as nitrogen and phosphorus from manure, leads to the eutrophication of water and degradation of aquatic ecosystems [182]. According to Yasmin et al., 2022 [143], manure should not be used in the vermicomposting process, since it increases greenhouse gas generation. A study conducted in China [183] found that in areas where large amounts of livestock manure were used on agricultural farms, surface waters became polluted, and the nitrogen and phosphorus level standards were exceeded, resulting in water eutrophication.

6.4. Digestate

One of the solutions that can help reduce CO₂ emissions is the development of biogas plants used to process and produce biomethane digestate. The utilisation of all types of agri-food waste can contribute to reducing the greenhouse gas emissions originating from agriculture by up to 80%. Biomethane production alone would reduce greenhouse gas emissions in Poland by 26 million tonnes. It is worth noting that Poland’s agricultural sector emits approximately 33 million tonnes of greenhouse gases. Between January and November 2023, Poland’s electricity production totalled 148 TWh, representing a 7.2% decrease compared to the previous year. At the end of 2023, there were 218 agricultural biogas plants and 148 municipal biogas plants in Poland. The increased demand for food production has led to a growing volume of agricultural waste being generated annually, significantly contributing to the availability of feedstock in biogas facilities across Europe. Increased crop production and livestock breeding have seen intensive growth to meet the demands of the growing human population in Europe and worldwide. According to the analyses conducted by Róźyło and Bohacz, 2020 [184], livestock accounts for approximately 40% of the global value of agricultural produce, thus ensuring the livelihoods and food security of almost 1.3 billion people worldwide. This situation has contributed to the need for the recycling and sustainable utilisation of most waste.

Both digestate and biogas are generated by the anaerobic digestion method, which is currently among the most developed processes in terms of industrialisation and involves a biological process that enables the conversion of organic matter/waste into biogas (a mixture of methane and carbon dioxide). At the end of 2018, the annual production of biomethane from AD in the EU amounted to 2.3 billion (109) m³ [185]. According to the Polish National Agricultural Support Centre data, at the end of 2021, 128 biogas facilities were operating in Poland, which together generated 513 million m³ of agricultural biogas. In total, they generated 374 million m³ of biogas and produced 795.613 GWh of electricity.

A tenfold increase in the biomethane market in Europe is planned by 2030, from the current 3.5 to 35 billion m³. The European Biogas Association (EBA) has estimated the total fermentate production in Europe based on the current and potential European biogas production. The total volume of fermentate produced in 2022 was estimated at 31 million tonnes (Mt) of dry matter (DM). It was also estimated that 75 Mt DM fermentate will be produced by 2030, whereas the total fermentate potential for the year 2050 will amount to 177 Mt DM of fermentate [185].

The partly degraded organic material remaining after the fermentation process in a biogas plant is referred to as digestate, which is divided into a liquid and a solid fraction. The degradation of organic material is determined by the feedstock, retention time, pretreatment, and process type. A fertiliser in the form of digestate is rich in plant-available nutrients. Polymers are also often added to the resulting fertiliser to improve separation. The solid fraction is known to contain mainly organic N, whereas the liquid fraction usually contains a higher proportion of ammonium. In some cases, further treatment methods are also employed, including acidification aimed at reducing ammonia volatilisation from the digestate liquid phase. Given the high concentration of plant-available nitrogen (N), digestate is a good fertiliser that can replace commercially available mineral fertilisers [186]. In addition, the biofertiliser produced has a high pH value and, when untreated, a high water content, with the percentage of ammonium nitrogen being higher in the digestate than in the original feedstock, which increases its manurial value.

A study conducted by Möller and Müller, 2012 [187] showed the effects of the application of digestate and digestate products on soil quality and fertility, while Losak et al., 2014 [188] presented the results concerning soil chemical properties, and Nkoa, 2014 [189] demonstrated the effects on crop yields and other consequences for the crops.

The application of the anaerobic digestion (AD) method will contribute to reducing greenhouse gas emissions. All organic materials, if left exposed, will release potent greenhouse gases, including CH₄ and NO_x. Therefore, fermentation prevents this undesirable phenomenon, as organic matter is transferred to the closed and controlled environment of AD plants. This is because the methane generated in the biogas plant is captured and utilised rather than released into the atmosphere. The second way is that fermentation reduces the energy-intensive production of synthetic fertilisers. The production of foods and feeds in Europe is largely dependent on industrially produced synthetic fertilisers [185].

According to Möller and Müller, 2012 [187], natural input in the AD reactor (from 20 to 95% of the input organic matter) is converted into biogas, and the remaining organic matter is found in a more stable form. This residual carbon has greater potential for sequestration as soil organic carbon, which enables soils to serve as carbon absorbers. It should be noted, however, that the input material, in the form of digestate, can improve soil properties, but also result in the accumulation of heavy metals in this soil. The accumulation of heavy metals in the soil leads to an increase in toxicity, posing a serious threat to the health of the soil and the safety of crops. This situation can lead to chronic exposure to heavy metals, which will contribute to the development of health problems in humans, such as lung cancer, weakened immune systems, kidney damage, and bone fractures [190].

7. Summary

This article aimed to analyse the available scientific papers on the reduction in greenhouse gas emissions in one of the industrial sectors of European countries, including Poland. Agriculture, due to its diversity, is among the key sectors that contribute to the generation of major greenhouse gases, including carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). The article focused on the causes of their formation, e.g., the agricultural machinery fleet owned, the fuels used, tillage methods and techniques, soil properties, emission levels during plant growth, fertilisation, and waste management.

The current study yielded several important observations regarding the types of treatments employed. No-tillage, or reduced tillage, has a positive impact on the sustainable development of agriculture, increasing the soil carbon content, reducing soil erosion, improving the soil’s physical conditions, and lowering greenhouse gas emissions without compromising crop yields. Ploughing is the most energy-intensive tillage treatment, during which the carbon stored in the soil is released, leading to CO₂ emissions from the soil. When fuel is combusted, the main component of the exhaust gas is carbon dioxide. No-plough tillage reduces the number of passes, which results in reduced emission levels and fuel consumption. This technology prevents CO₂ emissions, reduces soil erosion, and enhances field irrigation. The use of organic and inorganic fertilisers, e.g., nitrogen fertilisers, manure, compost or digestate, leads to emissions of greenhouse gases such as N₂O or methane. The adverse effects can be minimised through correct dosing and precise fertilisation methods. One of the solutions that can help reduce CO₂ emissions is the development of biogas plants used to process and produce the digestate of biomethane. All organic materials, if left exposed and unattended, will release potent greenhouse gases. The use of livestock manure has a significant effect on greenhouse gas emissions, but also improves soil fertility and increases nutrient availability to crops. The current study emphasises that the implementation of these practices can lead to a significant reduction in greenhouse gas emissions and contribute to the development of sustainable agriculture. However, there are also limitations involved. These include the factors that mobilised the authors to address the present subject. Firstly, a small number of studies, referred to as “field” studies, are currently being conducted. Secondly, the level of difficulty in their application is due to their complexity and the large number of necessary treatments that must be carried out during the entire cycle, from field preparation to seed harvesting. For such studies to be meaningful, they must be carried out systematically during each necessary field operation throughout the crop’s growing season. This labour input will allow for the whole range of tillage to be performed, and help to explain how agriculture contributes to greenhouse gas emissions. Because of the scarcity of data/papers on the above subject, many aspects require the carrying out of reliable research. This article is the introduction to a series of research articles on greenhouse gas emissions during agricultural production. In order to achieve this, a two-year field study has been planned to determine how selected tillage techniques, crop treatments or, inter alia, fuel blends affect energy consumption and greenhouse gas emissions. This carefully considered course of work and its execution will contribute to the enrichment of knowledge and the improvement of climate policy in Europe. A summary of the most important information is provided in

Table 1. Summary of the analysed studies on emission levels in agriculture.

Feature/Characteristic	Results	Authors
Use of biodiesel as an alternative fuel	The use of alternative fuels, specifically biodiesel, resulted in savings ranging from 77 to 81% when compared to an official fossil fuel equivalent of 94 g CO2eq/MJ. Consequently, in 2021, biodiesel saved approximately 45 Mtonnes of CO2eq emissions.	European Biodiesel Board, 2023 [41]
Fuel consumption and tractor exhaust emissions	These are largely determined by the engine speed and load modes. The study showed that fuel consumption can be reduced by 5–25% by selecting an operating mode where the engine speed is 70–85% of the nominal value, and the tractor is loaded in a manner that allows the engine to develop 80% of its maximum power.	Peca et al., 2010 [57]
Agricultural gas emissions	The agricultural sector alone is responsible for over 80% of anthropogenic N2O emissions, 70% of anthropogenic NH3 emissions, and approximately 40% of anthropogenic CH4 emissions. The primary contributors to these emissions are the use of livestock manure and inorganic fertilisers.	Birch, E.L., 2014 [63]
N2O emissions from the soil	Under field conditions, the relationships between moisture and temperature overlap, which hampers the observation of clear relationships. Temperature alone regulates freezing and thawing events, forcing gas emissions from soils and accounting for up to 50% of total annual N2O emissions.	Fang and Moncrieff, 2001 [68]; Holst et al., 2008 [69]
Appropriate fertiliser dose	The fertiliser dose should be adjusted to the crops’ needs, as not all forms of nitrogen can be taken up by plants. Such an approach will significantly contribute to minimising N2O emissions. The nitrogen supplied to crops that is not taken up leads to increased N2O emissions.	Sanz-Cobena et al., 2014 [75]
Use of fuels	The application of various crop cultivation and processing techniques is a major factor responsible for greenhouse gas emissions. In the agricultural sector, the consumption of fuels and energy in agriculture, including activities such as food processing, the use of inputs on a farm, and the use of land for agricultural purposes, contributes to intensification.	Robinson, S., 2020 [82]
No-tillage and reduced tillage	No-tillage has been demonstrated to contribute to reducing methane emissions compared with plough tillage and no-plough tillage. No-tillage, or reduced tillage, has a positive effect on the sustainable development of agriculture, increases the soil carbon content, reduces soil erosion, improves the physical conditions of the soil, and reduces greenhouse gas emissions without compromising crop yields. When comparing no-plough tillage to conventional tillage, the former reduces CH4.	Chataut, G. et al., 2023 [89] Zhao, R.F. et al., 2006 [90]
Ploughing	Ploughing is considered the most energy-intensive tillage operation. When fuel is combusted during machinery operation, the main component of the exhaust gas is carbon dioxide. It has been calculated that 1 litre of consumed diesel equals 3.15 kg of carbon dioxide generated.	https://www.farmer.pl/bez-pluga/uprawa-bezorkowa-a-klimat,117580.html (accessed on 2 August 2024) [92]
Ploughing, no-plough tillage, no-tillage	Conventional plough tillage emits 180.76 kg CO2/ha, no-plough tillage emits 89.36 kg CO2/ha, whereas no-tillage farming emits only 19.50 kg CO2/ha.	https://www.farmer.pl/bez-pluga/uprawa-bezorkowa-a-klimat,117580.html (accessed on 2 August 2024) [92]
Reduced tillage	Reduced tillage increases N2O and CH4 emissions by 31.0 and 24.7%, respectively, while reducing crop yields by 17.4%, without an effect on CO2 emissions, whereas no tillage reduces CO2, N2O, and CH4 emissions and the total global warming potential (GWP) by an average of 15.1, 7.5, 19.8, and 22.6, respectively.	Kai Yue et al., 2023 [96]
Fertiliser production	The production of fertilisers consumes approximately 1.2% of global energy and accounts for approximately 1.2% of total greenhouse gas emissions.	Kongshaug, 1998 [104]
Ammonia production	According to reports, the production of ammonia is already contributing to 1–2% of global carbon dioxide emissions.	International Federation for Information Processing, 2024 [106]
Nitrogen fertiliser	A study examining the entire life cycle of nitrogen fertilisers (from production to field use) reveals that the greatest environmental impact is caused by fertiliser production, as well as nitrogen dioxide emissions resulting from the use of fertilisers.	Torrellas et al., 2012 [112]
Fertiliser production in Poland	In 2021, Poland’s share in fertiliser production in the EU was 18.6%, comprising 20.4% for N, 24.4% for P2O5, and 10.6% for K2O, as reported by the Institute of Agricultural and Food Economics (IERiGŻ).	Institute of Agricultural and Food Economics [116]
Urea split method	This study showed that the split method produces excellent results in terms of reducing greenhouse gas emissions and nitrate leaching. However, one cannot ignore the fact that its application resulted in significant additional field work and increased labour input, compared with a single basic application of the whole N fertiliser, due to the lack of machinery to support the application of N fertiliser.	Lu et al., 2021 [126]
Poland’s agriculture and emissions	Poland’s agriculture is a primary source of nitrous oxide (N2O) emissions, accounting for 80.2% of the country’s total anthropogenic emissions of this gas. Regarding total nitrous oxide emissions from agriculture, 83.7% originated from land use (nitrogen fertilisation) and 15.24% from livestock manure management.	Ministry of Agriculture and Rural Development [132]
Methane emissions	According to data acquired by Bai et al., it is estimated that landfills worldwide contribute approximately 12% of annual methane (CH4) emissions, i.e., 734 kg CO2-eq/tonne of treated wet waste.	Bai et al., 2020 [133]
Biowaste recycling	Every year, 118 to 138 million tonnes of biological waste are generated across the European Union, of which only approximately 40% (equivalent to 47.5 million tonnes per annum [M tpa]) is effectively recycled into high-quality compost and digestate.	ECN Data Report, 2022 [142]
Composting	This process is part of any strategy aimed at diverting organic waste and reducing methane (CH4) emissions from organised landfills. The amount of greenhouse gases generated by the composting process is largely determined by the waste type and composition.	Nordahl et al., 2023 [147]
Vermicomposting vs. composting	A study showed that the reduction in N2O and CH4 emissions during vermicomposting, compared with composting, was higher by 40 and 32%, respectively, when the moisture content in the raw material was higher, and the reduction in these greenhouse gases accounted for 23 and 16%, respectively, at a low moisture content of the mass under study.	Nigussie et al., 2016 [156]
Manure	According to a study, livestock manure contributes to 37% of global greenhouse gas emissions.	Vac et al., 2013 [174]
Livestock breeding sector	The livestock breeding sector is primarily responsible for the emissions of CH4 and N2O, i.e., compounds with a global warming potential (GWP) index value significantly higher than that of CO2. For CH4, it is 21-fold, and for N2O, 310-fold higher than that for CO2.	Kolasa-Więcek, 2012 [177]
Nitrous oxide emissions from manure	The use of this organic fertiliser increased N2O emissions by an average of 32.7% (95% confidence interval: 5.1–58.2%) compared with a synthetic nitrogen fertiliser.	Zhou, M. et al., 2017 [179]
Biomethane	Biomethane production alone would enable a 26 million tonne reduction in greenhouse gas emissions in Poland. It is worth mentioning that all of Poland’s agriculture sectors combined emit 33 million tonnes of greenhouse gases. Between January and November 2023, Poland’s electricity production totalled 148 TWh, representing a 7.2% decrease compared to the previous year.	Różyło, K.; Bohacz J., 2020 [184]

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