Agriculture’s Contribution to the Emission of Greenhouse Gas Nitrous Oxide (N₂O) and Its Feasible Mitigation Strategies

Abstract

Climate change and agriculture have a dual mode of relationship. Agriculture is an important sector of the country’s economy and it significantly contributes to climate change by releasing greenhouse gases (GHGs) to the atmosphere. On the other hand, climate change is a global threat to food security and it can affect agriculture through variation of weather parameters. Reducing GHGs emission mainly methane (CH4) and nitrous oxide (N2O) from the agriculture could play a significant role in climate change mitigation. N2O is a potent greenhouse gas mainly emitted from rice-wheat cropping system. Agricultural lands are considered as one of the important anthropogenic sources of N2O emissions and it account almost 69% of the annual atmospheric N2O emission and application of commercial fertilizers is considered as a major contributor to the N2O emission. This book chapter focuses on the feasible soil and crop management practices to reduce the N2O emission from agriculture without compromising the productivity. Different environmental factors that have a major impact on N2O production are also discussed in this chapter. On urgent basis, the world needs to reduce the anthropogenic N2O emissions from agriculture and adapt its sustainable cropping system and food-production system to survive with climate change.

1. Introduction

Global climate change is caused by the increasing concentration of many climate pollutants like carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) etc. The agriculture and food production is connected with emissions of all these three gases but emissions of CH₄ and N₂O are directly dominated by agricultural activities [1] and 10–12% of the total GHGs produced globally by anthropogenic activities [2]. Among the non-CO₂ greenhouse gases (GHGs), N₂O is an important long lived GHG and agriculture represents its largest source worldwide. N₂O is a major driver of climate change and considered as a very reactive gas and potent ozone-depleting substance in the stratosphere [3]. Moreover, it exerts adverse impacts on crop production and human health [4]. The emission of N₂O can lead to an indirect health impact, namely the depletion of the stratospheric ozone layer. This depletion results in higher levels of UV radiation reaching the earth’s surface, leading to an increased incidence of skin cancers [5]. Additionally, regions with elevated N₂O concentrations may experience air pollution due to its contribution. When N₂O combines with other pollutants, it can form ground-level ozone and fine particulate matter, which can worsen respiratory issues, particularly in individuals who already have asthma and chronic obstructive pulmonary disease (COPD) [5]. The rising earth’s temperature due to the increasing N₂O concentration can have also detrimental effects on precipitation patterns and lead to more extreme temperatures, adversely impacting plant growth and productivity. Additionally, increased N₂O levels in the atmosphere can cause higher nitrogen deposition in soils. While nitrogen is vital for plant growth but excessive amounts can disrupt the nutrient balance, depleting essential nutrients and compromising plant health [5]. Furthermore, the depletion of the ozone layer due to the emission of N₂O allows harmful UV radiation to reach the earth’s surface, potentially harming plants and hindering the process of photosynthesis.

Since 1750, concentrations of GHGs have been increasing due to anthropogenic activities. The anthropogenic N₂O is increasing annually, which has risen from a pre-industrial value of 270 ppb to a value of 324 ppb in 2011 and 332 ppb in 2019 [6].

Agriculture is the major primary anthropogenic source of N₂O emission, globally contributing around 3.8 (2.5–5.8) Tg N yr⁻¹ or 22% to the atmospheric N₂O budget [7]. The use of synthetic fertilizer, manure and increase in agricultural lands are the main reason of N₂O emissions from soil (Figure 1). When plant roots cannot uptake all the applied fertilizer due to their growth stages, some of it runs off or leached out and remaining amount is consumed by the soil microbes and convert the ammonia to nitrate and finally back to N₂ gas (Figure 2).

Figure 1.

Contribution of different sources to N₂O emission from soil (source: Gupta et al. [8]).

Figure 2.

Use of excess nitrogen and N₂O emission from the soil.

N₂O is emitted as a byproduct during the conversion of ammonia/ammonium to nitrate and nitrate to N₂ by microbial process of nitrification and denitrification respectively [8]. The excess nitrogen in the soil also leads to lower nitrogen use efficiency (NUE) by plants. Although the global agricultural food system depends of application of synthetic fertilizers to increase the crop productivity however; the abundance use of synthetic fertilizer is unsustainable due emission of N₂O from soil and pollutes waterways through nitrate leaching. The global food system is responsible for ∼21–37% of annual emissions [9]. Further, N₂O emissions are expected to increase over to coming decades due to projected increases in food demand for over increasing population, agricultural land and fertilizer use. However, active management of agroecosystems through managing soil and plants can offer a sustainable opportunity for N₂O mitigation without jeopardizing crop growth and food production. In this chapter, we have tried to address all the factors associated with agricultural N₂O emission and their feasible management practices to reduce the production and emission of N₂O.

2. Role of rice-wheat cultivation in N₂O production and emission

The primary sources of N₂O in rice-wheat soil is the transformation of reactive N by soil microbes [10]. When N enters the soil in the form of NH₄⁺ and NO₃⁻ via organic or mineral fertilizers, various reactions might occur, resulting in N₂O production. Three main processes, namely nitrification, denitrification and nitrifier denitrification, are considered the main contributors to N₂O emissions [11]. Nitrification (NF) is regarded as the primary process involved in the global N cycle. The majority of N transformation during nitrification is mediated by autotrophic microorganisms. The initial stage in NF is NH₃ oxidation to hydroxylamine. This mechanism is mediated by ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). Denitrification (DNF) is a reduction process involving the conversion of NO₃ to N₂, mediated by facultative anaerobic bacteria [12]. This process can be completed up to N₂ production, but if it is not completed, N is released as NO and N₂O. 70% of worldwide N₂O emissions are attributed to NF and DNF microbial activities [13]. Nitrifier denitrification is the reduction of NO₂− to NO, then to N₂O and finally to N₂ [14]. The soil gets submerged or saturated with water during rice cultivation. This reduces the amount of oxygen available to nitrifying microorganisms, halting the nitrification process. In such soils NH₄-N is the major form of N. The drying of the soil at the harvest of rice crop and aerobic condition of soil in wheat cultivation favors nitrification and accumulation of NO₃-N, which is prone to losses by denitrification and leaching during flooding in subsequent rice cultivation. Moreover, the fluctuating soil moisture conditions and the intermittent drying and flash flooding in rice cultivation, cause large N losses to occur. Therefore, though continuously flooded rice paddies are not considered to be an important source of atmospheric N₂O because N₂O, an intermediary product of denitrification, would be rapidly reduced to N₂ under the intensive anaerobic conditions and rice-wheat systems may produce considerable amount of N₂O. Each process’s contribution to N₂O emission is affected by soil texture, organic C, soil pH, microbial activity, and environmental factors such as precipitation and temperature [15], as discussed in next section.

3. Factor affecting N₂O emission from rice wheat soil

N₂O production and emissions from rice wheat soil are regularly governed by different microbial-mediated activity and also depends on several pathways of gas transport, such as: plant-mediated transport (through the aerenchyma). N₂O emission from the rice wheat soil are also mediated through biologically, therefore, its emission from the soil is affected by different climatic as well as agricultural management factor which are depicted in Figure 3.

Figure 3.

Factors affecting N₂O emission from rice wheat ecosystem.

4. Sustainable mitigation strategies of N₂O emissions

There are a number of mitigation strategies that can be applied to rice and wheat grown soil that would increase productivity while lowering N₂O emissions and strengthening agriculture’s ability to withstand climate change. In this section, briefly we draw attention to some recent research advances in mitigation strategies and technology tools to expand our understanding about soil and crop management for enhanced nitrogen use efficiency (NUE) and N₂O emission mitigation (Figure 4). All mitigation strategies focus on site-specific management practices and the use of technologies that will assist limit N losses via ammonia volatilization and nitrate runoff, leaching and drainage pathways. The importance of site-specific agricultural management practices to improve crop and soil recovery of applied N (efficiency), crop productivity per unit of N applied (efficacy), and N₂O per unit of crop production has been stressed.

Figure 4.

Key principles of climate smart agriculture and associated mitigation strategies of N₂O emissions.

4.1 Agricultural management practices

4.1.1 Irrigation pattern management

Flood irrigation (FI) is the most widely used irrigation method in developing countries such as India, Pakistan, Bangladesh, and most part of Africa. High volumes of water are given to crops in FI, resulting in fertilizers dilution and easily absorbed [16]. Large irrigation volumes, on the other hand, influence the anaerobic conditions permissive to N₂O generation and nitrate leaching [17]. To avoid this, a precise water application strategy, such as alternate wetting and drying (AWD), could save water while also lowering N₂O emissions. This is because low water content requires more time for oxygen penetration into the soil, which leads to inhibition of microbial activity in the soil responsible for N₂O formation [18]. Similarly, intermittent irrigation, which means the field is alternately watered and drained, has a high potential to reduce N₂O production from soil because this irrigation method has the advantage of improving soil oxidative conditions by increasing root activity, soil bearing capacity, and ultimately minimizing water inputs that create anaerobic conditions. This promotes the penetration of oxygen into the paddy soils and, as a result, reduces N₂O emissions. Another modified irrigation strategy is sprinkler-irrigated field (SI), the surface layer in a SI is comparatively loose than FI. As a result, in such soils, the NO₃-N and NH₄-N are less leached and remain more concentrated in the root zone, making them more easily absorbed by plant roots and hence less likely to be converted to N₂O [19]. Different irrigation pattern and N₂O mitigation potential from rice-wheat fields are showed in Table 1.

Crops	Agricultural management practices	N2O mitigation potential	References
Rice	AWDI + RS 15 t ha^−1, AWDI + RS 30 t ha^−1	18.68%, 31.55%	[20]
Wheat	Sub-surface drip irrigation	56.16%	[21]
Wheat	Straw incorporation	19.4%	[21]
Rice	Reduce tillage	3–6%	[22]
Rice	Zero tillage	22%	[23]
Rice	Optimizing N rate with RT	6%	[24]
Wheat	Zero tilled with rice residue application	11–12.8%	[25]

Table 1.

Different agricultural management practices and N₂O mitigation potential from rice-wheat fields.

4.1.2 Tillage practices

Soil tillage has a significant impact on N₂O emissions during rice-wheat cultivation because it alters soil physiochemical and biological characteristics, stimulating microbial N₂O generation [26]. Traditional plowing or rotational tillage, which is extensively employed today, exposes the surface, which increases soil depletion and lowers the quality of cultivated land as well as the soil’s ability to continually feed fertilizer. The usage of conservation tillage (CT) techniques, such as no-tillage (NT) and reduced tillage (RT), is progressively increasing, owing to the reduction of greenhouse gases, improvement of soil and water quality and enhanced water efficiency. Six et al. [27] proposed that preserving NT throughout time could lower N₂O emissions. These findings are also corroborated by van Kessel [28]. The researchers conducted a meta-analysis on 239 direct comparisons of CT, NT and RT and found that, on average, neither NT nor RT emit more N₂O than CT. Long-term research (>10 years) using NT and RT procedures, primarily in dry regions, revealed a considerable reduction in N₂O emissions. Different tillage practices and N₂O mitigation potential from rice-wheat fields are showed in Table 1.

4.1.3 Crop residue management

Crop residue (CR) return regulates N₂O emissions by regulating microbial activity and C/N availability and it is predicted that CR return produces 0.4 million metric tons of N₂O-N yr⁻¹ globally [29]. Several authors have noted that returning CR can increase N₂O emissions by increasing C and N availability for microbial activities and modifying soil aeration by improving soil aggregation and microbial demand, which is thought to be a major factor mediating soil NF and DNF for N₂O production [29]. Other authors, on the other hand, reported that adding CR had an inhibitory effect on N₂O emission, depending on soil conditions and crop residue C/N ratio [30]. The return of CR can act as a carbon source for microbial development, promoting N uptake by microorganisms. This activity can result in a fierce competition for NH₄+ between heterotrophic microorganisms and autotrophic nitrifiers, which results in N₂O production [31]. However, in CR management, it is believed that no unambiguous behavior with regard to N₂O emission can be detected. To improve smart CR management and its contribution to reduced N₂O emissions, several factors must be considered, including CR properties and ambient circumstances.

4.2 Inorganic fertilizer management

Mitigating N₂O emissions requires increased NUE through improved temporal synchrony between N supply and plant demand. This requires efficient N management strategies, such as selection of the right source (enhanced efficiency fertilizers), right quantity, right time and right application method.

4.2.1 Altering fertilizer dose and matching N supply with crop demand

Appropriate fertilizer management can significantly reduce N₂O emissions from rice-wheat fields. It has been reported that the application of N fertilizers in soil is not totally consumed by the crop; consequently, it is more vital to enhance fertilizer usage efficiency, which can significantly reduce N₂O emissions [8]. A potential technique for reducing N₂O emissions is to reduce the amount of N input into the soil [32]. This is due to lesser N input in soil causing competition between plants and soil microorganisms, which favors soil N uptake by plants, resulting in lower N₂O emission than with high N fertilizer application. Bordoloi et al. [24] observed that reducing fertilizer rates by 25% (from 60 to 45 kg N ha⁻¹) significantly reduced N₂O emissions from fertilized rice fields. The N application method can also have an impact on N₂O production. In fact, placing N near the roots boosted NUE and lowered N₂O emissions [33]. Furthermore, optimizing N fertilizer application to better match nutrient availability with crop demand considerably reduced soil residual N, lowering N₂O emissions [34]. Split fertilizer applications at different crop stages ensure continuous N availability, which enhances NUE and decreases N₂O emissions [35].

4.2.2 Right time of fertilizer application

The right time implies applying fertilizer when the plant will benefit the most and avoiding times when fertilizer will be lost to the environment. In terms of lowering N₂O emissions, the time of fertilizer application is closely related to the amount of fertilizer used. Fertilizer application weeks after planting rather than before sowing enhances the likelihood that applied N will end up in crop tissues rather than being lost to the atmosphere and ground water.

4.2.3 Improving N fertilizer placement

Improved N placement strategies, such as urea deep placement (UDP) at a soil depth of 7 ± 10 cm, boost NUE and crop yields while lowering emissions when compared to broadcast application [36]. In flooded rice fields, UDP keeps N in the root zone as NH₄⁺-N for a longer period of time, ensuring a constant supply of N to plants throughout the growing season. It has been observed that UDP boosts rice yields by 20%, NUE by 30%, and decreases N₂O emissions by 84% when compared to broadcast urea treatment [37]. Deep placement of N fertilizers in lowland rice resulted in an 80% reduced N₂O emission than traditional surface spreading [37]. This is because a substantial part of N was maintained in the soil for a longer period of time. The positioning of N closer to the plants reduces N₂O emissions significantly, as in the case of urea band application rather than broadcasting.

4.2.4 Selection of suitable fertilizers

Different fertilizers influence N₂O emissions due to varying levels of NH₄⁺, NO₃⁻, and organic carbon. The higher the level of N application, the greater the increase in N₂O emissions [38]. Higher quantities of N application significantly enhance the DNF, which increases N₂O emissions. Furthermore, types of fertilizers also influence NF and DNF process which ultimately affect the production of N₂O emissions. The use of anhydrous ammonia, for example, considerably enhanced N₂O emissions [39]. Grave et al. [40] investigated how different N sources affected N₂O emission in a maize-wheat rotation. They reported that, in comparison to the control plots, the application of urea and slurry increased N₂O emission by 33% and 46%, respectively. Bordoloi et al. [41] investigated the effects of various urea concentrations on N₂O emissions in a wheat cropping system and discovered that N₂O emissions rose concurrently with urea concentration, reaching a maximum of +174% with 100 kg N ha⁻¹ from urea. Furthermore, Lebender et al. [42] examined the effect of the N source calcium-ammonium-nitrate (200, 400 kg ha⁻¹) on N₂O emission from the wheat crop. They observed that 400 kg N ha⁻¹ consistently produced considerably more N₂O emissions than 200 kg N ha⁻¹ over time. Higher N₂O emissions result with the application of calcium ammonium nitrate, particularly in moist soils with high OM [43]. In another study, Nayak et al. [44] discovered that substituting ammonium sulphate for urea enhances N₂O emissions. However, changes in N₂O emission from N fertilizers can be attributed to soil parameters including as texture, bulk density, pH, organic carbon, N, and microbial population [45]. Overall, the most important domain of intervention to reduce N₂O emissions is the selection and management of appropriate fertilizers.

4.2.5 Use of nitrification inhibitors or slow-release fertilizers

Enhanced-efficiency fertilizers including nitrification inhibitors (NIs), urease inhibitors (UIs), and control release fertilizers (CRF) have been developed to increased NUE. The use of NIs, such as dicyandiamide (DCD), in conjunction with urea or ammonium-based fertilizers (at the optimal N rate), could boost NUE while decreasing N₂O emissions in a variety of agricultural systems [46]. The NI decreases N₂O emissions directly by inhibiting NF, as well as indirectly by reducing NO₃⁻ availability for DNF without compromising yield [47]. The chemical components in the NI inhibit the enzymes involved for the first step of NF (ammonia mono-oxygenase; AMO), allowing NH₄⁺ to remain in soils for extended periods of time [48]. As a result, the NI reduces the rates of NF and the availability of substrates for denitrifiers, lowering N₂O emissions from fertilizers [49]. Various authors observed a considerable reduction in N₂O emission with the application of various NI, including dicyandiamide, hydroquinol, nitropyrimidine, and benzoic acid [50]. Plant-derived products, such as neem oil, neem cakes, and karanja seed extract, can also be used to inhibit NF. CRF should be used in places where the sensitivity to N losses is significant [51]. CRF treatment reduced N₂O losses and N application rate in paddy rice by 26–50% without impacting yield [52]. However, CRF can be used as a sustainable strategy to minimize N losses in conjunction or as an alternative to urea [53]. Different inorganic fertilizers management and N₂O mitigation potential from rice-wheat fields are showed in Table 2.

Crops	Inorganic fertilizers management	N2O mitigation potential	References
Wheat	Controlled-release fertilizers	29–66%	[54]
Wheat	Polymer-coated urea, sulfur-coated urea and urea-formaldehyde	39.45%, 30.74%, 11.68%	[55]
Rice	Carbon-based slow-release fertilizer	36.69%	[56]
Rice	Dicyandiamide nitrification inhibitor, Urea deep placement	95%, 73%	[57]
Rice	25% reduction in fertilizer rate (30 kg N ha^−1) over normal rate (40 kg N ha^−1)	6.90–7.59%	[58]
Wheat	Urease inhibitor + urea	56.4%	[59]
Wheat	Rescheduled fertilizer N topdressings with moderate N (25 kg ha^−1) at sowing and remaining N dose in two equal splits	32.4%	[60]

Table 2.

Different inorganic fertilizers management and N₂O mitigation potential from rice-wheat fields.

4.3 Organic fertilizer management

Organic fertilizers (OFs) such as biochar, manure, compost etc., offer soil bacteria with a variety of C compounds with diverse chemical compositions, ranging from labile to recalcitrant, that they can use to improve their growth rates and biomass during the mineralization process. OFs have dramatic, short- and long-term effects on the soil microbiome and are critical for soil health by increasing microbial activity, microbial interactions, and nutrient cycling [61]. Application and potential of different organic based fertilizers for mitigating N₂O emission from rice wheat soil have been discussed below as well as shown in Table 3.

Crops	Organic fertilizer management	N2O mitigation potential	References
Wheat	Organic manure alone	39.4%	[62]
Rice wheat	Straw return + earthworm addition	19%	[63]
Wheat	Reduce N (140.3 kg ha^−1) + 10 t ha^−1 biochar	7.57–12.93%	[64]
Rice-wheat	Straw biochar application	16.10%	[65]
Rice	Urea with organic amendments (poultry manure, crop residues, green manure)	11–24%	[66]
Rice	Sugarcane bagasse	31%	[67]
Rice	Rice straw + green manure	38%	[68]
Rice	Biochar at the rate of 40 t ha^−1	21.5%	[19]
Rice	Biochar at the rate of 10 t ha^−1, 40 t ha^−1	58, 74	[69]

Table 3.

Different organic fertilizers management and N₂O mitigation potential from rice-wheat fields.

4.3.1 Biochar application

Recently, the use of biochar has been regarded as an effective method for improving soil fertility, agricultural productivity, and mitigating GHG emissions from soil [19]. Biochar contains unique properties such as a highly porous structure, C-rich fine grain and enhanced surface area [70], which can draw attention to an effective GHG mitigation technique [71]. Several research have been reported by various authors relating to the amendment of biochar and its impact on GHG generation [72]. Biochar has been shown to minimize N₂O emissions by inhibiting NF and DNF processes or by promoting N₂O reduction in soil. Recent meta-analyses have revealed that biochar reduces N₂O emissions after application by an average of 20% [39]. Another study found that using biochar reduced N₂O and NH₃ emissions by 16.10% and 89.60%, respectively, as compared to a control treatment in rice crops [65]. Zhang et al. [69] reported that amendment of biochar at the rate of 10 t ha⁻¹ and 40 t ha⁻¹ significantly reduced the N₂O emission by 58% and 74%, respectively when compared to field without biochar application. The use of biochar raises soil pH and causes N₂O to be completely converted to N₂, lowering N₂O emissions [73]. However, the effect of biochar on N₂O emissions varies depending on the amount of biochar used and soil parameters such as pH, C:N ratio, organic carbon, water status and microbial and enzymatic activity [74].

4.3.2 Use of organic amendments

Organic amendments (OA), which include compost, vermicompost, green manure, animal wastes (i.e., manures and slurries), etc., have been widely employed to reduce N fertilizer application, improve soil fertility and mitigate environmental deterioration [75]. Some studies have shown that OA increases N₂O emissions through DNF by acting as an energy source for denitrifiers and promoting the establishment of anaerobic micro-sites within soil aggregates [76]. Other researchers, on the other hand, found that OA reduces N₂O emissions by boosting N microbial absorption, reducing the availability of N substrates for N₂O synthesis via NF and DNF [77]. A long-term study found that the amount of OA is crucial for organic carbon accumulation and the consequent impact on N₂O emissions [78]. Furthermore, it is considered that the synthetic fertilizer substitution ratio by OA is a significant aspect in regulating N₂O emissions [78]. Application of fermented manures a type of OA can minimize GHG emissions due to the rapid depletion of OM pools during fermentation [79]. Nayak et al. [44] exposed that using composted manure reduced N₂O emissions considerably. In paddy soil, application of compost reduced N₂O emissions by more than 50% when compared to urea [80]. When compared to fresh straw, the use of organic material produced by aerobic composting of rice straw significantly reduced N₂O emissions [81], indicating that this strategy is environmentally favorable. Type of OA i.e., vermicomposting is a promising method that involves converting organic waste into compost in the presence of earthworms [82]. Because of the abundance of suitable resources, the material created as a result of their action has good structure and microbiological activity. In a rice study, the use of vermicompost reduced the transfer of NH₄⁺ and NO₃⁻ to water [83]. In contrast, the combined application of biochar and vermicompost impacted soil characteristics by increasing the abundance of nosZ genes and decreasing N₂O emission [84]. As a result, combining biochar with vermicompost may be a potential way to reducing N₂O emissions. Compost or manure which is another type of OA, can help to enhance soil structure and nutrient availability to growing crops, reducing the demand for mineral fertilizer and thereby lowering GHG emissions [85]. Green manure crops such as Cowpea, Sesbania, Azzola, and Mungbean had a high ability to reduce N₂O in rice fields [86]. Because of the gradual release of nitrogen from decaying green manure residue, plant uptake efficiency and crop production can be better aligned, while N leaching losses are decreased. Different organic fertilizers management and N₂O mitigation potential from rice-wheat fields are showed in Table 3.

4.4 Crop management practices

4.4.1 Selection of plant cultivars

The selection of suitable crop cultivars with improved resource use efficiency appears to be an auspicious and environmentally acceptable technique for minimizing N₂O emissions from soil. Before selecting suitable crop cultivars, it is more important to investigate the mechanism of exudate and aerenchyma effects under field conditions, because variations among different types of crop cultivars have been linked to deviations in N₂O emission production, oxidation, and transport capacities [87]. According to Baruah et al. [88], different rice cultivars have varying capacities for transporting N₂O from paddy soil to the atmosphere, and these approaches are suitable for lowering GHG emissions. The physiological and anatomical properties of different rice cultivars may influence N₂O emission. Rice plant shape and physiology regulate GHG emissions by giving energy sources to microorganisms via sloughed-off root cap [89]. Another study found that lower N₂O emissions were associated with a plant strategy defined by more effectively N absorption [90]. Plant cultivars with higher N uptake were demonstrated to be able to reduce the N pool, particularly NO₃⁻, resulting in lesser substrate availability for denitrifiers and, as a result, lower N₂O emission. Variation in N₂O emission among cultivars has also been documented in grain and legume intercropping [91]. In another study, researchers observed that plants contribute significantly to N₂O emissions and proposed that N₂O emission is significantly controlled by plant characteristics in the soil-crop system [92].

4.4.2 Modifying cropping schemes

In paddy field, switching from conventional puddled transplanted rice (TPR) system to directly seeded rice (DSR) may contribute to reducing GHG emissions. Under the DSR method rice seeds are sown directly in the soil where they will grow instead of transplanting seedlings. DSR methods are classified as wet (pre-germinated seeds) or dry seeding. Wet sowing method involves broadcasting pre-germinated seeds into a puddled and leveled field that is free of standing water. However, standing water on the soil surface in conventional rice fields hinders the passage of oxygen from the atmosphere into the soil and microbial activities render the water-saturated soil practically devoid of oxygen, resulting in anaerobic conditions. Denitrification is the primary mechanism for N₂O emission in TPR, because of the anaerobic conditions. In DSR, the main mechanism for N₂O emission is nitrification, which takes place under aerobic condition. In fact, it was noticed that DSR increased N₂O emission when the redox potential (RP) crossed 250 mV [93]. Therefore, in DSR water should be applied in such a way that RP be kept at a range of 100–200 mV to reduce N₂O emissions. Furthermore, it was noted that the GWP of DSR can be further reduced by converting to no-tillage farming [94]. DSR’s lower GWP and higher production rate imply that it would reduce N₂O emissions. More extensive research involving GHG measurements under the concurrent effects of elements like as water, tillage, fertilizers, and biochar are, however, desperately needed to validate DSR as a feasible method that also minimizes the environmental impact.

4.5 Integrated nutrient management

Integrated nutrient management (INM) is the application of OA and inorganic fertilizers together to promote NUE and reduce N losses by coordinating crop demand with soil nutrient availability [36, 75]. Different components of INM are given in Figure 5. Some researchers compared the effects of NPK fertilizer, compost, and their combination on N₂O emissions [36, 95]. They exposed that combining NPK and compost lowered N₂O emissions when compared to using only compost or NPK. Furthermore, they proposed that applying composted material with a C:N ratio less than 20 considerably reduced N₂O emissions due to the release of less N during soil decomposition. The longer breakdown of C and N, as well as the slower release of mineralized N, resulted in decreased N₂O emissions when OA was used [96]. Huang et al. [97] observed a reduction in N₂O emission with increasing C:N ratio plant amendments and observed that this relationship grows stronger with the addition of inorganic N. In line with the previous findings, study found that applying OA with a lower C:N ratio alone or OA with a higher C:N ratio in combination with inorganic fertilizers reduces N₂O emissions without affecting crop productivity [98]. Application and potential of INM practices for mitigating N₂O emission from rice wheat soil are shown in Table 4.

Figure 5.

Different components of INM practices.

Crops	INM practices	N2O mitigation potential	References
Rice	Biochar (50 t ha^−1) + fertilizer	18%	[99]
Wheat	Chemical fertilizer reduction + organic manure	42%	[62]
Rice	Inorganic fertilizer + green manuring (mungbean)	17%	[86]
Rice	50% urea +50% poultry manure	11–14%	[66]
Rice	60 kg urea +30 kg Azolla	27.13%	[100]

Table 4.

Different INM practices and N₂O mitigation potential from rice-wheat fields.

5. Recent technological advancements and innovations in mitigation strategies of N₂O emissions

Several technological advancements and innovations have shown promise in further reducing N₂O emissions in agriculture. While there might have been additional developments beyond that date, here are some of the notable advancements up to that point: (a) Precision agriculture technologies, such as GPS-guided equipment and sensor-based systems, enable farmers to apply fertilizers more efficiently and accurately. By precisely matching nutrient application to crop needs, these technologies can reduce nitrogen losses and subsequent N₂O emissions. (b) Efficient irrigation systems, such as drip irrigation and sensor-based watering, can optimize water and nutrient application, reducing excess nitrogen leaching and subsequent N₂O emissions. (c) Advancements in data analytics, remote sensing, and artificial intelligence can provide farmers with valuable insights into soil health, crop performance, and weather patterns. Access to real-time data can help optimize nitrogen management, leading to reduced N₂O emissions. It is essential to note that while these technological advancements hold promise in mitigating N₂O emissions, their effectiveness can vary depending on local conditions, farming practices, and the scale of implementation.

6. Adoption of greenhouse technology for climate control

The greenhouse cultivation for field crops comprises basis climate control parameters which depend on their design and complexity. It provides more or less climate control condition for plant growth and productivity [101]. This technology is beneficial in increasing crop production with limited resources and in harsh climate. Elimination of heat load is the main concern for greenhouse climate management basically in arid and semi-arid region and this can be done by reducing incoming solar radiation; removal of extra heat through air exchange; and increasing the fraction of energy partitioned into latent heat [102]. Considering shortage of resources, climate change, urbanization and population growth, the active smart greenhouse technology can support the countries food security while meeting the sustainability [103]. The current technology like fertigation, closed hydroponics, climate control systems (natural and forced ventilation, heating and fog systems and fan and pad systems) are used in greenhouses for sustainable production.

7. N₂O measurement techniques from soil

N₂O emissions from soil are largely affected by environmental variables such as substrate availability, redox potential and temperature etc., across various temporal and spatial scales. Therefore, it is necessary to understand the environmental variability of N₂O emissions, to further quantify the scale of soil–atmosphere N₂O exchange and create statistically viable measurement programmes to establish emission rates from plot to regional levels. The optimal method should be selected from the viewpoint of cost, required accuracy, time consumption, and so on. Here we describe different N₂O emission measurement techniques used by different researchers.

7.1 Closed chamber technique

The closed chamber technique is now the most extensively used measurement technique for estimating soil N₂O emissions. This is simple to use, inexpensive and allows us to study treatment effects as well as to carry out specific process studies. The closed chamber is made of 6 mm thick acrylic transparent sheets (50 cm length, 30 cm width and 70/90/120 cm height) used for gas sampling [24]. In each sampling plot, U-shaped aluminum channels (50 cm × 30 cm) is inserted into soil to a depth of 15 cm well in advance to accommodate the chambers. The chamber is placed on the U-shaped channels at the time of sampling. During gas sampling the aluminum channel is filled with water, which acted as air seal when the chamber is placed on the channel. Air inside the chamber is thoroughly mixed or homogenized with a battery-operated fan before sampling. Air temperature inside the chamber and soil temperature at 5 cm depth is measured by using mercury thermometers while taking gas samples. Gas samples are collected from the chambers by airtight syringe (50 ml volume) fitted with a three-way stop cork at an interval of 15 min (0, 15, 30 and 45 min). Gas samples are brought to the laboratory immediately after sampling and analyzed for N₂O concentrations using gas chromatograph (GC). However, there are several advantages to using a closed chamber technique, such as shortcomings related to environmental conditions (e.g., temperature effects, soil compaction, plant damage, disturbance of diffusion gradients [104], limited coverage of soil surfaces (usually less than 1 m²), which means that spatial heterogeneity is often not adequately addressed, collar insertion in the soil and root cutting, or temporal coverage of measurements [105].

7.2 Fast-box method

The fast-box approach is a new method that will be used to investigate spatial variability of trace gas fluxes [106]. An N₂O analyzer (e.g. Tunable Diode Laser (TDL)) is coupled to a chamber in this setup. This allows for a large reduction in closure times, allowing chamber positions to be altered in minutes and spatial variability to be investigated. Closure durations of 30–60 min are usual with standard GC procedures.

7.3 Micrometeorological measurements

Micrometeorological measurement of N₂O with TDL detection is based on the principle of diode laser absorption spectroscopy. It offers a non-intrusive, continuous spatially integrated measurement technique for detecting and quantifying baseline and episodic N₂O emissions at the paddock scale. Pattey et al. [107], analyzed the wide variety of conceivable micrometeorolgical applications of TDL technology. The TDL measurements were made using the TGA-100A (Campbell Scientific Inc.). They were reported that dried air was sampled from the two heights at 3 s intervals, raw N₂O measurements were taken at 10 Hz, and concentration data were averaged over 20 min. Micrometeorological approaches require homogeneous areas with a considerable fetch (>1 hectare) that are unaffected by structures, trees, hills, and other factors. For the straight fetch area, land use, land management, vegetation, and soil qualities should be uniform. These methods are most commonly used in flat terrain with vast, homogeneous land uses, such as pasture, grassland, maize, or wheat monocrops, woods, or tree plantations.

7.4 Modeling based approaches

Over the last few decades, a wide variety of process models for modeling soil N₂O emissions have been created, each of which is suitable to one or more specific ecosystem types (e.g., arable, grassland, forest) [108]. Models can be classified depending on their degree of complexity of the biogeochemical N cycle such as mineralization, nitrification, denitrification as well as trace gas production, consumption and emission processes.

8. Role of policies and economic incentives in promoting N₂O mitigation strategies

Policy formulation should aim to encourage farmers to adopt mitigation methods that do not compromise their productivity and profitability. To promote the use of mitigation technology in agriculture, three main paths should be pursued: investments, incentives, and information. Agricultural output as a GHG source is unique due to its small-scale, dispersed nature, and often inadequate physical and institutional infrastructure. Policy initiatives should consider these variations and implement cost-effective payment schemes to incentivize and support agricultural mitigation efforts. Establish an extension system to assist farmers in adopting climate change mitigation practices. This support can include facilitating access to new markets, especially carbon markets, providing information on new regulatory systems, and informing farmers about government goals and policies related to climate change. Increase research funding to enhance our understanding of how climate change impacts agriculture. This includes studying the interactions between climate change and agricultural practices, which can lead to better forecasts and informed policies for long-term sustainable growth, particularly with a focus on pro-poor development. By implementing these policy approaches, the government can effectively encourage farmers to adopt mitigation methods that contribute to climate change mitigation while ensuring their agricultural productivity and economic well-being.

9. Co-benefits and potential trade-offs associated with N₂O mitigation strategies

N₂O mitigation strategies in agriculture can offer both co-benefits and potential trade-offs. These strategies aim to reduce nitrous oxide emissions from agricultural practices, thereby addressing its negative impact on climate change and the environment. However, the effectiveness of these strategies may vary, and they can have additional implications for agricultural productivity, soil health, and economic aspects. There are several co-benefits associated with N₂O mitigation strategies. By implementing N₂O mitigation strategies, such as better nitrogen management practices, farmers can help reduce greenhouse gas emissions and contribute to global efforts to combat climate change. Some N₂O mitigation strategies, such as using cover crops, reduced tillage, and organic farming practices, can enhance soil health. These practices can increase soil organic matter, improve nutrient cycling, and enhance soil structure, leading to better water retention and reduced erosion. Implementing N₂O mitigation measures often involves optimizing nitrogen use on farms. This can lead to better nitrogen use efficiency, which benefits farmers economically by reducing input costs and minimizing nitrogen losses to the environment. N₂O is not the only nitrogen compound emitted from agricultural practices. Nitrogen runoff and leaching can lead to water pollution, affecting aquatic ecosystems and human water supplies. N₂O mitigation strategies can also reduce other forms of nitrogen pollution, thereby improving water quality. Beside these co-benefits there are also some potential trade-offs associated with N₂O mitigation strategies. Some N₂O mitigation strategies, particularly those that involve reducing synthetic nitrogen fertilizers, can lead to decreased crop yields if not managed properly. Balancing nitrogen inputs to optimize both yield and environmental benefits can be challenging. Implementing certain N₂O mitigation strategies may involve initial investments in new technologies or changes in farm management practices, which can impose additional costs on farmers. While some practices may have long-term economic benefits, short-term financial constraints can be a trade-off. Agricultural systems are complex, and the effectiveness of N₂O mitigation strategies can vary depending on factors such as soil type, climate, and local management practices. The uncertainty associated with their outcomes can be a trade-off.

10. Knowledge and capacity building in promoting N₂O mitigation strategies

The adoption of N₂O mitigation strategies in agriculture requires more than just the availability of technologies and practices. Awareness campaigns, training programs, and knowledge-sharing platforms play a critical role in promoting the understanding and adoption of these strategies among farmers and stakeholders. These initiatives can address barriers to adoption, disseminate valuable information, and foster behavioral change toward sustainable agricultural practices. Many farmers might not be aware of the environmental impact of N₂O emissions or the available mitigation strategies. Awareness campaigns can help disseminate knowledge about the link between agricultural practices, GHGs emissions, and climate change, thus creating a sense of urgency and responsibility among farmers. Training programs provide farmers and agricultural stakeholders with the necessary skills and knowledge to implement N₂O mitigation strategies effectively. These programs can cover various topics, such as precision agriculture, improved fertilizer management, and soil health practices. Farmers might be hesitant to adopt new technologies due to unfamiliarity or uncertainty about their benefits. Knowledge-sharing platforms can showcase successful case studies, demonstrations, and testimonials from other farmers who have successfully implemented N₂O mitigation practices. Different regions and farming systems have varying challenges and opportunities for N₂O mitigation. Awareness campaigns and knowledge-sharing platforms can tailor information and strategies to suit specific contexts, making it more relevant and applicable for farmers. Overall, fostering awareness, providing relevant training, and establishing knowledge-sharing platforms are essential components of promoting the adoption of N₂O mitigation strategies in agriculture.

11. Conclusions

It is becoming obvious that no single management strategies can result in increased crop yields and lower N₂O emissions across the wide geographical areas. While site-to-site variability and climate influences on N₂O emissions are significant, site-specific adjustments in agricultural management strategies can provide remedies and should be given more attention. Understanding the mechanisms of N₂O formation in rice-wheat fields has led to the development of various mitigation techniques to reduce N₂O emissions. Site-specific fertilizer management, modifying irrigation strategies such as AMD, intermittent irrigation and the use of DSR all help to reduce N₂O emissions. N₂O emissions can be reduced by using fermented manures, altering N fertilizer sources, timing, placement methods, applying NI, or using slow-release fertilizers. Similarly, biochar, compost, straw ash inclusion, and INM have the ability to significantly reduce N₂O emissions while maintaining crop production. On the other hand, farmers will only accept mitigation techniques that do not reduce grain yield. More agricultural focus may be drawn to site-specific management adjustments and the use of technologies that will assist limit N losses via ammonia volatilization and nitrate runoff, leaching, and drainage pathways. The mitigation measures outlined above are scientific discoveries, but effective implementation of these options alone or in combination at the farmer level requires a deliberate policy and strong government backing. The policy to reduce or eliminate N₂O emissions into the atmosphere will differ depending on the region or country and it will be heavily reliant on government financial assistance. However, in order for such techniques to be effective and fruitful in reducing GHG emissions and maintaining crop output in a changing environment, all social, economic, educational, and political barriers must be addressed. More research on climate-smart agriculture is needed to validate at the agricultural system level and to inform policymakers about the projected implications of climate change and the effectiveness of mitigation strategies.

Acknowledgments

Authors are grateful to SERB (File No. EEQ/2018/000125), GOI, New Delhi, India, for financial support and Central University of Jharkhand, Brambe, Ranchi, India, for facilitating and supporting the activities.

Conflict of interest

The authors declare no conflict of interest.