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Review

The Impact of the Soil Environment and Surface Mulching on N2O Emissions from Farmland

by
Qian Chen
1,2,
Lei Chang
1,2,*,
Khuram Shehzad Khan
1,2,
Shouxi Chai
1,2,
Yuwei Chai
1,2 and
Fanxiang Han
3
1
College of Agronomy, Gansu Agricultural University, Lanzhou 730070, China
2
State Key Laboratory of Aridland Crop Science, Gansu Agricultural University, Lanzhou 730070, China
3
School of Environment and Urban Construction, Lanzhou City University, Lanzhou 730070, China
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(6), 2502; https://doi.org/10.3390/su17062502
Submission received: 8 February 2025 / Revised: 2 March 2025 / Accepted: 11 March 2025 / Published: 12 March 2025
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Abstract

:
A reduction in emissions of nitrous oxide (N2O), one of the three major greenhouse gases, is important for achieving environmental sustainability and carbon neutrality goals. Agricultural fields are the primary source of N2O emissions, and their management measures influence greenhouse gas emission reductions and the greening of agriculture. Among these practices, cover cropping plays a key role in promoting sustainable agricultural production as a major cropping technique for efficient water use and increasing crop yields in water-scarce regions worldwide. The present paper systematically reviews the influence of various soil environmental factors, such as soil temperature, moisture, pH, carbon, and nitrogen contents, as well as nitrogen cycle-related enzymes, microorganisms and mulching practices, including general mulching and straw mulching, on N2O emissions from agricultural fields. This review suggests that future research should explore the long-term effects of different mulching materials and their application rates and durations on soil N2O emissions. Furthermore, a networked mathematical model for causal analysis should be employed in future research to elucidate the relationships among soil environmental factors, nitrogen cycle microorganisms, and soil N2O production and consumption. These future studies will help to deepen our understanding of nitrogen cycling processes in agroecosystems with the aim of developing environmentally friendly agricultural technologies and promoting green and sustainable agricultural development.

1. Introduction

Nitrous oxide (N2O), a major global greenhouse gas, contributes approximately 5% to the overall greenhouse effect and has a warming potential that is over 300 times greater than that of carbon dioxide (CO2) [1,2]. Between 80% and 90% of the N2O generated by agricultural activities is released into the atmosphere [3], with global emissions from farmland soils estimated to be between 1.2 and 4.2 teragrams (TG). As the global population continues to grow and agricultural production intensifies, N2O emissions from agricultural practices are expected to further rise [4,5]. This poses a serious challenge to achieving the United Nations’ Sustainable Development Goals (SDGs). Nitrification and denitrification processes in soil are the primary pathways through which N2O is released from agricultural lands [6,7]. As shown in Figure 1, the N2O produced by these two processes accounts for 90% of all atmospheric N2O [8]. The nitrification process carried out by nitrifying bacteria is categorized into two stages: ammonia oxidation and nitrite oxidation [9]. The ammonia oxidation process occurs in the presence of oxygen, where NH4+ is converted to NH2OH by ammonia monooxygenase (AMO), followed by the catalysis of NH2OH to NO2− through hydroxyline dehydrogenase (HAO). The microorganisms involved in this process include ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) [10]. The nitrite oxidation process serves as a subsequent step, further oxidizing NO2− to NO3−, with nitrite-oxidizing bacteria (NOB) facilitating this transformation [11]. The nitrifying process (NCD), which involves coupling the nitrification reactions, refers to a reduction in the NO2− or NO3− generated by nitrification, ultimately producing N2O and N2 under the influence of nitrifying bacteria [12]. The nitrification process relates to the conversion of nitrite during ammonia oxidation, leading to N2O production through the action of nitrite reductase (Nir) and nitric oxide reductase (Nor) [13]. Under anaerobic or low-oxygen conditions, heterotrophic nitrifying bacteria can reduce nitrate and nitrite in the environment to N2O, which is subsequently converted to N2 with the aid of nitric oxide synthase (Nos Z). This process is referred to as heterotrophic denitrification (HD) and is typically associated with N2O production in soil [14]. These reactions can occur simultaneously; however, they are primarily influenced by factors such as soil moisture, temperature, pH, carbon-to-nitrogen ratios, and the presence of soil microorganisms [15,16,17,18]. Various environmental factors differ in their regulatory mechanisms and their degree of influence on the nitrification and denitrification pathways of N2O emissions from farmland soils.
Cover cropping practices are widely adopted in agricultural production processes within drought-prone, semi-arid, and semi-humid regions due to their significant effects on enhancing crop yields [19,20]. As environmentally friendly agricultural technologies, mulching measures play an important role in improving resource use efficiency and increasing the resilience of agricultural systems. Previous studies have confirmed that cover cropping can influence soil environmental factors, and these studies established that N2O emissions from farmland are regulated by these environmental conditions. However, there is still a lack of comprehensive research examining how cover cropping alters environmental factors and subsequently affects N2O emissions from farmland. The soil environment plays a critical role in the generation and release of N2O, and agricultural management practices further influence these emissions by modifying soil environmental conditions. A deeper understanding of this complex relationship is important for the development of climate-smart agricultural technologies and the attainment of sustainable agriculture. The present article reviews studies on the impact of various environmental factors such as soil moisture, soil temperature, pH, soil enzymes, soil microbial communities, and the soil carbon-to-nitrogen ratio on N2O emissions from farmland, as well as the associated research advancements and mechanisms involved. Our aim is to provide a scientific basis for optimizing mulch management practices, improving nitrogen use efficiency, and reducing greenhouse gas emissions, thereby promoting the development of agricultural systems in a more sustainable direction.

2. Environmental Factors Affecting Farmland N2O Emissions

2.1. Soil Temperature

Soil temperature influences N2O emissions by affecting soil nitrification and denitrification, with the extent of this influence being contingent upon both the temperature range and the soil type [21]. Under low-temperature conditions, microbial activity is inhibited, leading to reduced N2O emissions; in fact, negative emissions may occur when temperatures approach 0 °C [22]. The optimal temperature range for nitrification is 25–35 °C, while nitrification is inhibited at temperatures below 5 °C and above 50 °C. Within the temperature range to which microorganisms are adapted, soil microbial activity exhibits a positive correlation with temperature [23]. It is widely accepted that an increase in soil temperature generally leads to an increase in N2O emissions (Figure 2). Some studies have indicated that when the soil temperature is maintained between 15 and 30 °C, there is a positive exponential correlation between the soil temperature and N2O emissions in soybean farmland retention paddy soil [24]. Other similar research has demonstrated that during the early and late stages of wheat growth, N2O emission flux increases with rising soil temperatures and is significantly influenced by the air temperature [25]. However, the suitable temperature range for denitrification is between 5 and 75 °C, with the most favorable range being 30 to 67 °C. The reduction in the denitrification reaction rate at low temperatures is not pronounced; for instance, the nitrification reaction can still proceed at temperatures between 0 and 5 °C. Under a consistent soil water content and nitrate nitrogen concentration, an increase in the soil temperature from 5 °C to 10 °C results in an increase in the soil denitrification rate from 0.02 kg·hm−2·d−1 to 0.11 kg·hm−2·d−1 [26]. However, some studies suggest that lower temperatures can enhance denitrification by fungi, thereby increasing N2O emissions [27]. This further supports the notion that the inhibitory effect of low temperatures on denitrification is not significant, with the observed differences likely attributable to other critical influencing factors. Soil N2O emissions exhibit distinct seasonal patterns; for instance, emissions are generally higher during the humid and warm spring and summer months in the North China Plain compared to the dry and cold autumn and winter seasons [28]. Elevated temperatures accelerate the decomposition of soil organic matter, and this provides sample carbon sources for microorganisms responsible for N2O production. This process enhances the activity of nitrification-related microorganisms, increases the reaction rate, and consequently leads to higher N2O emissions. Additionally, rising temperatures result in increased soil respiration, which reduces the O2 concentration in the soil. This reduction creates anaerobic conditions conducive to denitrifying bacteria, thereby promoting the denitrification process.

2.2. Soil Water

The soil moisture content significantly influences ventilation conditions, pore characteristics, pH values, the effectiveness of nitrogen oxidation compounds, and the activity of soil microorganisms. Furthermore, the moisture conditions of farmland are intricately linked to nutrient absorption and transfer, establishing a close relationship between farmland moisture and N2O emissions. The soil moisture content serves as a critical factor that differentiates between nitrification and denitrification reactions. It is generally accepted that when the water content of the soil is less than 80% of the field’s water-holding capacity, nitrification occurs; conversely, when the water content drops below 60%, nitrification can be considered negligible [29]. The soil pore water content, or the water filling pore space (WFPS), is a vital component of soil moisture content, characterizing the proportion of water within the total pore volume of the soil. The water content within soil pores is closely associated with soil ventilation [30]. At a WFPS of 80%, the contribution of nitrification reactions is enhanced. WFPS exhibits a negative correlation with O2 levels, thereby serving as an indicator of O2 content in the soil [31]. When O2 accumulates predominantly in the surface layer of the soil, it competes with electrons for nitrogen oxides, and the high oxidation–reduction potential can hinder the growth of surface desertification. Additionally, a reduction in the accumulation of denitrification substrates can adversely affect the nitrification process, leading to decreased N2O emissions from denitrification (Figure 2). Research indicates that when the soil WFPS ranges from 5% to 20%, N2O emissions in cornfields can be negative, indicating the consumption of N2O [32]. It has been found that 75–85% of the annual flux of N2O is influenced by occasional summer rainfall events [33]. This discovery further demonstrates that the alternation between wet and dry conditions due to rainfall is often associated with peaks in N2O emissions [34]. This phenomenon may occur because soil that is initially deficient in water becomes wet after receiving a small amount of rainfall or irrigation, leading to increased nitrification and activity of nitrifying bacteria in the soil. Consequently, the concentrations of NO3− and NO2− in the soil gradually rise, and related enzyme activity recovers. However, excessive rainfall and irrigation [35] can lead to a sharp increase in the soil moisture content, which expands anaerobic zones and enhances nitrification effects [36]. Similarly, rice experiences significant hypoxia during prolonged flooding [37], which promotes the degradation of nitrification under anaerobic conditions and further converts N2O back to N2, thereby reducing overall N2O emissions [38].

2.3. Soil pH

Soil pH is a critical environmental factor that regulates soil N2O emissions. The direct and indirect effects of soil pH influence microbial activity associated with nitrification, related enzyme activities [39], and the expression of relevant genes, all of which impact N2O emissions [9]. The optimal pH for nitrifying reactions is 8.5, while the most suitable pH range for denitrification is between 7.0 and 8.0. When the pH exceeds 9.5, the nitrification response rate diminishes; conversely, when the pH falls below 6.0, nitrifying microorganisms are inhibited [40]. Taking AOA and AOB as examples, their responses to pH differ [41]. Under acidic conditions, AOA contribute more to N2O during heterotrophic processes; under neutral or alkaline conditions, AOB play a more significant role in N2O production during nitrification [42,43]. Studies indicate that at higher pH levels, the increased AOB/AOA ratio enhances potential nitrification rates, leading to elevated nitrite and N2O emissions [44]. During nitrification, the lower soil pH diminishes N2O reductase (N2OR) activity while enhancing the activity of NR, NiR, and N2OR, thereby altering the N2O/N2 ratio. This phenomenon occurs because H+ ions are generated during soil denitrification, and a lower pH inhibits the positive progression of nitrification, while a higher pH promotes it through the release of OH− ions [45]. Within a certain pH range during nitrification, the N2OR activity increases with the rising pH under alkaline conditions (Figure 2), facilitating the conversion of N2O to N2 and thereby reducing cumulative N2O emissions [46]. However, as the pH decreases, N2OR activity is suppressed, preventing the further transformation of N2O to N2 and resulting in increased N2O emissions (Figure 2). It is important to note that pH not only influences the biological channels that generate N2O but also affects the non-biological channels related to N2O production in the soil. Research by some Chinese scholars has demonstrated a positive correlation between NH2OH and the non-biological conversion rate of N2O, as well as the soil pH; specifically, as the pH increases, the rate at which NH2OH is converted into N2O accelerates [47].

2.4. Soil Enzymes

Soil enzymes play a crucial role in the decomposition of organic matter and the nitrogen cycle within the soil, with the magnitude of N2O emissions being closely related to the soil enzyme activity. These enzymes are primarily derived from plant root secretions, soil microorganisms, and the remnants of dead cells [48]. The activity of soil enzymes is often employed as a metric for characterizing soil nitrogen. The enzymatic hydrolysis of urea produces ammonia and carbon dioxide, which indirectly indicates the soil’s nitrogen supply capacity. Ammonia is subsequently converted to NO2− through nitrification, which represents the initial step in the soil nitrification process, catalyzed by AMO and HAD [49]. Under the action of nitrite-oxidizing enzymes, NO2− is further oxidized to NO3− [50]. NO3− is then utilized by plants through the action of nitrifying bacteria [51]. The key enzyme in this reaction process is NR, and its activity serves as an indicator of the soil’s nitrification capacity [52]. Variations in the activity of nitrifying enzymes can help distinguish N2O emissions in dryland [50]. Studies indicate that soil N2O emissions are significantly positively correlated with HAD activity [50]. Higher nitrogen levels correspond to increased soil urease activity, leading to lower soil N2O flux (Figure 2) [50]. The magnitude of N2O emissions is not influenced only by soil enzymes but also by other factors such as soil nitrogen storage, carbon sources, and growth stages [53].

2.5. Soil Microorganism

Soil microorganisms play a crucial role in soil N2O emissions. The reduction in N2O emissions can be achieved by altering the activity of nitrifying and denitrifying microorganisms during production. Specifically, the decrease in N2O emissions primarily depends on the reduction in N2O by microorganisms during the complete denitrification process. Nitrification, which is mediated by nitrifying bacteria, occurs in two stages: the first stage is catalyzed by AOB, while the second stage is facilitated by NOB [50]. Denitrification involves a diverse array of microorganisms, including over 80 genera of bacteria, as well as certain fungi, archaea, and actinomycetes [54]. In aerated soils, NOB utilize NO2− as the final electron acceptor, resulting in the production of N2O [55]; conversely, nitrification does not serve as a direct source of N2O under anaerobic conditions. Research indicates that with NOB at the microbial molecular level, the presence of N2O-reducing bacteria containing nosZ genes significantly decreases N2O emissions. Additionally, the application of plant rhizosphere growth-promoting bacteria with N2O emission-reducing capabilities can alter the structure and abundance of microorganisms associated with N2O reduction. To effectively mitigate greenhouse gas emissions [50], it is important to note that approximately 30% of denitrifying bacteria lack the nosZ gene and thus cannot reduce N2O [56]. Furthermore, studies have demonstrated that certain strains of Brachiaria humidicola can secrete biological nitrification inhibitory substances, such as linoleic acid and linolenic acid, through their roots, inhibiting the activity of nitrifying microorganisms and subsequently reducing soil N2O emissions [57]. The rate of N2O production is closely linked to the abundance of relevant functional genes, community structure, and transcript abundance. Research has shown that the ratio of (nxrA + nxrB)/(AOA + AOB amoA) in the nitrification process increases with the elevation of the NO2−/(NO2− + NO3−) ratio [58]. On saline–alkali land, the cultivation of leguminous crops can lead to an increase in soil N2O emissions. Furthermore, the average N2O emission rate exhibits a significant positive correlation with the abundance of AOB and narG-type denitrifying bacteria [59].

2.6. Soil Carbon and Nitrogen

The soil carbon-to-nitrogen (C/N) ratio significantly influences the transformation of soil nitrogen cycling, thereby regulating N2O emissions [60]. A C/N ratio between 25 and 30 is optimal for the growth of soil microorganisms; however, when the C/N ratio exceeds 30, N2O emissions are inhibited. In contrast, when the C/N ratio falls below 25, the microbial activity intensifies, leading to the substantial decomposition of organic matter and an increase in N2O emissions [61]. Enhancing the proportion of effective soil carbon and nitrate nitrogen can facilitate the N2O’s reduction to N2 [62]. Soil organic carbon serves as the primary carbon source and electron donor for heterotrophic processes. Microbial communities, driven by soil organic carbon [63], release nitrogen from soil organic matter, with some nitrogen being converted into microbial biomass. Upon the death of microorganisms, nitrogen is lost in the form of N2O [59]. Nitrogen species, including nitrate and ammonium nitrogen, act as electron acceptors and products of microbial nitrification and denitrification. The concentration of these nitrogen forms regulates N2O emissions [64]. An increase in nitrate and ammonium nitrogen content can lead to elevated N2O emissions during both nitrification and denitrification processes. Research indicates that excessive nitrogen levels may inhibit NosZ enzyme activity, consequently increasing the N2O/N2 ratio [65]. However, other studies have suggested that the relationship between nitrogen content and N2O flux is not statistically significant [50].

3. The Impact of Farmland Coverage on N2O Emissions

3.1. Plastic Film Mulching

Covering is a primary measure to combat drought and conserve moisture in water-scarce regions worldwide, which inevitably alters the soil environment and consequently affects N2O emissions from farmland [66] (Table 1). Film covering modifies the soil environment and indirectly influences N2O emissions [67]. Most studies suggest that film covering increases N2O emission flux from farmland [68]. In the arid region of northwest China, the application of film coating results in higher N2O gas emissions compared to areas without film coating [50]. A report found that mulching elevates N2O emissions by altering the soil structure, water temperature conditions, and microbial habitats, which in turn increases both the number and activity of microorganisms and accelerates the mineralization of organic carbon and total nitrogen [69]. Furthermore, film-mulched ridge cultivation facilitates the horizontal diffusion of N2O from the film-covered ridge surface to the non-mulched furrow surface [70]. While film mulching can mitigate the erosion and leaching of inorganic nitrogen in the soil due to rainwater, it correspondingly increases the concentrations of nitrate nitrogen and ammonium nitrogen, providing soil microorganisms with abundant substrates for nitrification and denitrification reactions, thereby enhancing N2O emissions [71]. However, it is important to note that mulching may also reduce soil aeration, which could inhibit N2O emissions. Plastic film mulching can indirectly influence soil N2O emissions by regulating soil moisture, although the mechanisms involved differ. Specifically, during periods of abundant rainfall, film mulching reduces nitrogen leaching from the soil compared to areas without mulching, which promotes N2O generation through nitrification and denitrification processes. Conversely, in times of scarce rainfall, film mulching similarly reduces nitrogen leaching, resulting in minimal changes to the substrates for soil nitrification and denitrification, and consequently no significant alterations in N2O emissions. Additionally, film covering significantly elevates the soil temperature. This increase in temperature can enhance oxidation and the number of negative charges on the biochar surface, thereby improving the soil’s cation adsorption capacity, forming more organic-mineral complexes, and obstructing cracks and channels within the biochar. Ultimately, this hinders the external diffusion of N2O [72,73,74]. Some studies have indicated that there is no significant difference in cumulative N2O emissions between mulched and non-mulched conditions. This lack of difference is attributed to mulching’s role in promoting plant growth and enhancing nitrogen absorption by crops, which reduces soil nitrogen residues [75]. Research suggests that the cumulative N2O emissions from film-mulched potatoes in dryland conditions are only 56.4% to 72.1% of those in non-film-covered treatments. This finding is linked to a significantly lower gene copy number of AOB in the presence of film compared to circumstances without it [50]. Additionally, research supports the conclusion that mulching decreases soil N2O emissions by reducing the abundance of AOB-amoA genes [50].

3.2. Straw Mulching and Returning to Fields

These useful reports have addressed the impact of straw returning to soil on N2O emissions, indicating promotion [88], inhibition [89], or no effect [90]. The variability in research findings may be attributed to factors such as the hydrothermal conditions of the soil, the soil nutrient levels, microbial activity, and the availability of substrates for nitrification and denitrification processes [91]. Some studies have observed a significant increase in N2O emissions following the return of wheat or corn straw to fields [92,93,94]. Conversely, other research has demonstrated a notable reduction in emissions associated with straw return, attributed to the high organic matter and nutrient content of straw, its elevated carbon-to-nitrogen ratio, and its capacity to absorb soil nitrogen, ultimately leading to emission reductions [16]. Additionally, some studies suggest that the influence of straw mulching on N2O emissions is primarily linked to soil moisture levels and the irrigation system employed [95]. Straw mulching tends to elevate the water content of the topsoil, creating an anaerobic environment that favors the proliferation of soil-denitrifying microorganisms, thereby enhancing surface N2O emissions [50]. However, another study reported that straw mulching can actually decrease soil N2O emissions [50]. Furthermore, straw mulching generally induces a cooling effect in the soil, which can alter the activity of soil enzymes involved in the nitrogen cycle and subsequently impact N2O emissions [96,97]. It has also been observed that straw mulching increases soil carbon sources and enhances the activity of nitrifying and denitrifying bacteria influenced by soil carbon levels [92,93]. Lastly, the addition of straw and biochar to soil has been shown to inhibit N2O emissions [98]. This phenomenon may occur because straw and biochar contribute to the formation of humus, carbohydrates, and other macromolecular substances in the soil that are challenging for microorganisms to absorb. In turn, this leads to an increase in the soil’s carbon-to-nitrogen (C/N) ratio and enhances the soil’s permeability and water retention capacity. Additionally, it inhibits nitrification and denitrification to some extent [99,100]. It was concluded that straw mulching, as a form of organic matter, has a minimal impact on N2O emissions, with the primary factor influencing N2O levels being the application of nitrogen fertilizers [101].
The return of straw to fields can significantly influence the types, abundance, and composition of microorganisms related to the nitrogen cycle, with its effects being contingent upon the timing of the return. For instance, the short-term addition of wheat straw has a limited impact on the soil nitrification process. Research indicates that the introduction of wheat, tadpole, and rapeseed straw does not alter the population of soil-nitrifying bacteria. In soils where straw is returned to the field, operational taxonomic units (OTUs) associated with nitrite fixation are relatively abundant, potentially accelerating the soil nitrification process and leading to increased N2O emissions [102]. A study found that in wasteland soils, the combination of fertilizers and straw enhances the populations of soil nitrogen-fixing bacteria, AOB, and nitrifying bacteria [50]. The addition of organic fertilizers and other organic materials can improve the abundance of specific microorganisms related to soil nitrogen fixation [103], nitrification [104], and denitrification [105]. During the nitrification process, some N2O is retained in soil moisture or pores, while a portion is utilized by nitrifying microorganisms, which further convert it into molecular nitrogen (N2). Only the remaining fraction is released from the soil as N2O. Additionally, straw mulching has varying effects on the abundance of different nitrogen functional genes. Some recent studies have shown that straw cover primarily increases the relative abundance of the AOB-amoA gene and Nitrosospira within AOB, thereby contributing to elevated soil N2O emissions [50].

4. Prospects and Outlook

This review focuses on the effects of different environmental factors on N2O emissions which are classified and summarized, and quantitative parameters are provided. While pH > 8.5 accelerated nitrification, pH < 6.0 inhibited denitrifying microbial activity. Temperatures below 5 °C significantly reduced N2O emissions, and emissions were positively correlated with temperature at 15–30 °C. N2O emission peaked when the WFPS was 70–80%, and a WFPS > 80% promoted N2O’s reduction to N2. C/N > 30 inhibited N2O emission, while C/N < 25 promoted emission. Mulching was more effective in reducing emissions than straw mulching, but the exact effect varied with soil type and climatic conditions. Based on a comprehensive overview, future research directions are proposed:
  • The complexity of the multi-pathway emissions mechanism. The primary mechanism for producing N2O in farmland is through the nitrification and denitrification processes facilitated by nitrifying bacteria. However, alternative pathways, such as fungal denitrification and chemical denitrification, also contribute to N2O production. Consequently, the mechanisms and pathways of N2O generation in agricultural settings remain incompletely understood. This complexity is particularly pronounced when multiple pathways operate simultaneously, making it challenging to isolate the contribution of a single pathway to overall N2O emissions.
  • The optimization and innovation of coverage measures. The overarching goal of emission reduction efforts is to minimize greenhouse gas emissions without compromising agricultural productivity. Currently, research examining the effects of various mulching methods, mulching materials, straw application rates, and soil amendment amounts on soil N2O production and emissions is still relatively limited, highlighting an urgent need for further investigation in this area.
  • Mechanisms of interaction between microorganisms and environmental factors. With the rapid advancement of microbial measurement technologies, the diversity of microorganisms involved in nitrification and denitrification continues to expand. Additionally, numerous environmental factors influence N2O production in farmland, and these factors interact in complex ways within the soil environment. Therefore, it is essential to employ networked causal analysis mathematical models to elucidate the correlation mechanisms between changes in soil environmental factors and N2O production, thereby providing a foundation for developing effective N2O emission reduction technologies in agricultural contexts.
  • Integrated studies of soil–crop–atmosphere systems. Numerous studies have focused on the net emissions of N2O from farmland into the atmosphere; however, there is a notable paucity of research on the dynamic changes of N2O within the soil profile and its correlation with crop growth conditions. In this respect, there is an urgent need to enhance comprehensive research on N2O emissions in the context of the soil–crop–atmosphere continuum.

Author Contributions

Conceptualization, L.C.; software, validation, L.C., Q.C., K.S.K., S.C., Y.C., and F.H.; investigation, L.C.; resources, L.C.; data curation, Q.C.; writing—original draft preparation, Q.C.; writing—review and editing, L.C.; supervision, L.C. All authors have read and agreed to the published version of the manuscript.

Funding

This study was sponsored by the National Key Research and Development Program (2021YFD1900700; 2022YFD2001304), the Industrial Support Program of Gansu Provincial Colleges and Universities (2022CYZC-48), the Science and Technology Plan Project of Gansu Province (22CX8NA046), and the National Natural Science Foundation of China (31960239).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors have no competing interests that might be perceived to influence the results and discussion reported in this paper.

Abbreviations

List of abbreviations.
AbbreviationFull Form
AMOAmmonia monooxygenase
HADHydroxylamine dehydrogenase
NiRNitrite reductase
NorNO reductase
NRNitrate reductase
N2ORN2O reductase
AOAAmmonia-oxidizing archaebacteria
AOBAmmonia-oxidizing bacteria
NOBNitrite-oxidizing bacteria
NNNitrification by nitrifying bacteria
NDDenitrification by nitrifying bacteria
NCDDenitrification coupled to nitrification reactions
HDHeterotrophic denitrification
WFPSWater filling pore space
OTUsOperational taxonomic units

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Figure 1. Process and mechanism of nitrous oxide production and emission in farmland. Note: AMO, ammonia monooxygenase; HAD, hydroxylamine dehydrogenase; NiR, nitrite reductase; Nor, NO reductase; NR, nitrate reductase; N2OR, N2O reductase; AOA, ammonia-oxidizing archaebacteria; AOB, ammonia-oxidizing bacteria; NOB, nitrite-oxidizing bacteria; NN, nitrification by nitrifying bacteria; ND, denitrification by nitrifying bacteria; NCD, denitrification coupled to nitrification reactions; HD, heterotrophic denitrification.
Figure 1. Process and mechanism of nitrous oxide production and emission in farmland. Note: AMO, ammonia monooxygenase; HAD, hydroxylamine dehydrogenase; NiR, nitrite reductase; Nor, NO reductase; NR, nitrate reductase; N2OR, N2O reductase; AOA, ammonia-oxidizing archaebacteria; AOB, ammonia-oxidizing bacteria; NOB, nitrite-oxidizing bacteria; NN, nitrification by nitrifying bacteria; ND, denitrification by nitrifying bacteria; NCD, denitrification coupled to nitrification reactions; HD, heterotrophic denitrification.
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Figure 2. Effect of soil environmental factors on N2O emissions. Note: NN, nitrification by nitrifying bacteria; ND, denitrification by nitrifying bacteria; NCD, denitrification coupled to nitrification reactions; HD, heterotrophic denitrification.
Figure 2. Effect of soil environmental factors on N2O emissions. Note: NN, nitrification by nitrifying bacteria; ND, denitrification by nitrifying bacteria; NCD, denitrification coupled to nitrification reactions; HD, heterotrophic denitrification.
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Table 1. Effect of surface mulching on N2O emissions.
Table 1. Effect of surface mulching on N2O emissions.
Coverage MethodsEffects on N2O EmissionsReference
Plastic filmIncreased N2O emissions from soil nitrogen and temperature increase in radish season and lower emissions from low soil water content in pepper season(Zhao, M. et al., 2020) [76]
Plastic filmLower N2O production in long-term mulched soils attributed to reduced nitrifying microbial activity(Gao, N. et al., 2023) [77]
Straw mulchReduced N2O emissions without fertilizer compared to fertilizer under straw mulch(Zhao, Y. et al., 2025) [78]
Plastic filmIncrease in soil nitrogen content by cover crop residues compared to no cover contributes to cumulative N2O emissions(Kim, G.W. et al., 2017) [79]
Plastic filmLong-term mulching negatively affects microorganisms by reducing N2O(Gao, N. et al., 2024) [80]
Bark mulchBark mulch as a strategy for mitigating N2O emission in sandy loam soils of vineyard systems(Fentabil, M.M. et al., 2016) [81]
Straw mulchUnder high moisture conditions, high straw volume mulching was more effective in reducing N2O emissions than medium straw volume mulching(Zhang, Z. et al., 2025) [82]
Straw mulchA meta-analysis revealed that both straw and mulch increased N2O emission(Wang, H. et al., 2021) [83]
Plastic filmMulching increases N2O emissions by influencing soil properties(Nawaz, A. et al., 2021) [84]
Plastic filmPlanting rye may reduce soil temperature to suppress N2O emissions(Dix, B.A. et al., 2024) [85]
Straw mulchStraw as a carbon source, prompting nitrogen fertilization to increase N2O emissions(Yan, Z. et al., 2024) [86]
Straw mulchIncrease in cumulative N2O emissions under conventional N fertilization, no effect under optimized N inputs(Wei, H. et al., 2024) [87]
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Chen, Q.; Chang, L.; Khan, K.S.; Chai, S.; Chai, Y.; Han, F. The Impact of the Soil Environment and Surface Mulching on N2O Emissions from Farmland. Sustainability 2025, 17, 2502. https://doi.org/10.3390/su17062502

AMA Style

Chen Q, Chang L, Khan KS, Chai S, Chai Y, Han F. The Impact of the Soil Environment and Surface Mulching on N2O Emissions from Farmland. Sustainability. 2025; 17(6):2502. https://doi.org/10.3390/su17062502

Chicago/Turabian Style

Chen, Qian, Lei Chang, Khuram Shehzad Khan, Shouxi Chai, Yuwei Chai, and Fanxiang Han. 2025. "The Impact of the Soil Environment and Surface Mulching on N2O Emissions from Farmland" Sustainability 17, no. 6: 2502. https://doi.org/10.3390/su17062502

APA Style

Chen, Q., Chang, L., Khan, K. S., Chai, S., Chai, Y., & Han, F. (2025). The Impact of the Soil Environment and Surface Mulching on N2O Emissions from Farmland. Sustainability, 17(6), 2502. https://doi.org/10.3390/su17062502

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