Soil N2O Emissions Research Articles

Stutzerimonas stutzeri culture enhances microbial community structure and tomato seedling growth in saline soil.

Plant growth-promoting rhizobacteria (PGPR) improve microbial community structure, promote crop growth, and reduce greenhouse gas emissions in agricultural soils; however, the effects of PGPR fermentation on the growth and salt tolerance of tomato plants remain unclear. In this study, we aimed to investigate the effects of the PGPR Stutzerimonas stutzeri NRCB010 on the microbial communities, tomato growth, and nitrous oxide (N2O) emissions in saline soil by performing a greenhouse pot experiment. The experiment was conducted under two soil salt concentrations (0 and 3 g kg-1 NaCl) and three treatments (LSFJ broth, NRCB010 cells, and NRCB010 culture). Both salt stress and NRCB010 treatments significantly affected the physicochemical properties and microbial community structure of tomato rhizosphere soil. Treatment with 3 g kg-1 NaCl significantly reduced the shoot and root dry weights of the plants compared with those of the control plants. Application of NRCB010 cells as well as that of culture promoted the growth of tomato seedlings and alleviated salt stress. The copy number changes in the nosZⅠ gene on day 3 and amoA gene on day 25 demonstrated that NRCB010 cells significantly reduced soil N2O emissions when treated with 0 g kg-1 NaCl. Furthermore, soil physicochemical properties, plant biomass, and soil microbial diversity were correlated with each other. The results emphasize the enormous potential of S. stutzeri NRCB010 culture to resist abiotic stress, promote crop growth, and improve the rhizosphere soil microenvironment; however, its ability to decrease N2O emissions is constrained by soil salinity.

Biochar from crop residues mitigates N2O emissions and increases carbon content in tropical soils

AbstractThe application of biochar may offer a cost‐effective solution to decrease nitrous oxide (N2O) emissions in agriculture soils while having the potential to enhance soil carbon (C) accumulation. Biochar can be produced primarily from a range of agricultural and woody residual biomass, potentially resulting in biochar types with distinct properties. This study evaluated the effects of four different biochar types on soil N2O emissions, C storage, and diversity of the soil microbial community in a tropical environment. A greenhouse experiment with sugarcane plants was conducted with six treatments: soil only (CTR); soil + N fertilizer (NF); NF + sugarcane straw biochar (NF+SB); NF + sugarcane bagasse biochar (NF+BB); NF + Pinus residue biochar (NF+PB); and NF + eucalyptus residue biochar (NF+EB). Regardless of the origin of the feedstock, all biochar reduced the cumulative N2O emissions by 25% to 50% in comparison with the nitrogen‐fertilized treatment. Only NF+EB registered higher N2O emissions than NF+SB. The feedstock material also influenced the chemical properties of biochar, showing a negative correlation between oxidized functional groups and N2O emissions. Variations in the physicochemical properties of biochar did not affect soil C levels or microbial diversity, as all treatments with biochar presented similar results. All biochar types increased soil C levels, but only those derived from wood residues showed higher C content than CTR and NF. Despite biochar having no effects on overall soil microbiome diversity, the amendment tended to increase the abundance of Bacteroidetes and Proteobacteria, while suppressing the ammonia‐oxidizing phylum Thaumarchaeota. Biochar application had no significant effect on ammonium availability; however, it exhibited the capacity to retain nitrate. The application of biochar in tropical soils can therefore be considered a nature‐based solution to decrease N2O emissions and increase C levels without changing microbial diversity.

Climate change rivals fertilizer use in driving soil nitrous oxide emissions in the northern high latitudes: Insights from terrestrial biosphere models.

Nitrous oxide (N2O) is the most important stratospheric ozone-depleting agent based on current emissions and the third largest contributor to increased net radiative forcing. Increases in atmospheric N2O have been attributed primarily to enhanced soil N2O emissions. Critically, contributions from soils in the Northern High Latitudes (NHL, >50°N) remain poorly quantified despite their exposure to rapid rates of regional warming and changing hydrology due to climate change. In this study, we used an ensemble of six process-based terrestrial biosphere models (TBMs) from the Global Nitrogen/Nitrous Oxide Model Intercomparison Project (NMIP) to quantify soil N2​O emissions across the NHL during 1861-2016. Factorial simulations were conducted to disentangle the contributions of key driving factors, including climate change, nitrogen inputs, land use change, and rising atmospheric CO2 concentration​, to the trends in emissions. The NMIP models suggests NHL soil N2O emissions doubled from 1861 to 2016, increasing on average by 2.0±1.0 Gg N/yr (p<0.01). Over the entire study period, while N fertilizer application (42 ± 20 %) contributed the largest share to the increase in NHL soil emissions, climate change effect was comparable (37 ± 25 %), underscoring its significant role. In the recent decade (2007-2016), anthropogenic sources contributed 47±17% (279±156 Gg N/yr) of the total N2O emissions from the NHL, while unmanaged soils contributed a comparable amount (290±142 Gg N/yr). The trend of increasing emissions from nitrogen fertilizer reversed after the 1980s because of reduced applications in non-permafrost regions. In addition, increased plant growth due to CO2 fertilization suppressed simulated emissions. However, permafrost soil N2O emissions continued increasing attributable to climate warming; the interaction of climate warming and increasing CO2 concentrations on nitrogen and carbon cycling will determine future trends in NHL soil N2O emissions. The rigorous interplay between process modeling and field experimentation will be essential for improving model representations of the mechanisms controlling N2O fluxes in the Northern High Latitudes and for reducing associated uncertainties.

Risk of increasing soil nitrous oxide emissions by chemical oxidation modification on biochar.

Biochar is widely recognized as a soil amendment capable of mitigating soil nitrous oxide (N2O) emissions. However, the effects of biochar modification, particularly through chemical oxidation, remain relatively unexplored. This study modified wood and corn straw biochars using H2O2 and acid (H2SO4/HNO3). Laboratory incubations were conducted to assess their effects on N2O emissions in agricultural and forest soils. The results revealed that acid modification significantly reduced biochar pH (<3) and introduced additional nitrogen, leading to substantial increases in N2O emissions by up to 181% and 7476% for wood and corn straw biochar, respectively. In contrast, H2O2-treated biochar caused limited changes in biochar properties and had minimal effects on soil N2O emissions. Correlation analyses suggest distinct pathways for N2O production, with forest soil emissions being negatively associated with potential denitrification enzyme activity, while agricultural soil emissions were positively linked to labile organic carbon and potential nitrification rates. While mild oxidation (e.g., H2O2) may better mimic natural aging process, stronger treatments (e.g., acid oxidation) pose risks of increased soil N2O emissions. This study provides valuable insights for optimizing biochar modifications to balance environmental and ecological benefits.

Bacillus thuringiensis (Bt) rice straw mulching and earthworms mediated changes in soil N2O and CO2 emissions driven by N-cycling and C-utilizing microbial communities

Bacillus thuringiensis (Bt) rice straw mulching and earthworms mediated changes in soil N2O and CO2 emissions driven by N-cycling and C-utilizing microbial communities

Contrasting effects of litter and root removals on soil N2O emissions of an evergreen broadleaved forest in southeastern China

Contrasting effects of litter and root removals on soil N2O emissions of an evergreen broadleaved forest in southeastern China

Interactions Between Bacterivorous Nematodes and Bacteria Reduce N2O Emissions.

Trophic interactions in micro-food webs, such as those between nematodes and their bacterial prey, affect nitrogen cycling in soils, potentially changing nitrous oxide (N2O) production and consumption. However, how nematode-mediated changes in soil bacterial community composition affect soil N2O emissions is largely unknown. Here, microcosm experiments are performed with the bacterial feeding nematode Protorhabditis to explore the potential of nematodes in regulating microbial communities and thereby soil N2O emissions. Removal of nematodes by defaunation resulted in increased N2O emissions, with the removal of Protorhabditis contributing most to this increase. Further, inoculation with Protorhabditis altered bacterial community composition and increased the relative abundance of Bacillus, and the abundance of the nosZ gene in soil. In vitro experiments indicated that Protorhabditis reinforce the reduction in N2O emissions by Bacillus due to suppressing competitors and producing bacteria growth stimulating substances such as betaine. The results indicate that interactions between nematodes and bacteria modify N2O emissions providing the perspective for the mitigation of greenhouse gas emissions via manipulating trophic interactions in soil.

Effects of Long-Term Organic Substitution on Soil Nitrous Oxide Emissions in a Tea (Camellia sinensis L.) Plantation in China

Nitrous oxide (N2O) is a major greenhouse gas (GHG) responsible for global warming. Improper fertilization in agricultural fields, particularly excessive nitrogen (N) application, accelerates soil N2O emissions. Though partial substitution with organic fertilizer has been implemented to mitigate these emissions, the effect on perennial systems, such as tea plantations, remains largely unexplored. Therefore, the present study monitored soil N2O emissions for a year in a tea plantation in South China under the following treatments: no N fertilizer (control, CK), chemical fertilizer alone (CF), replacing 40% of chemical fertilizer with organic fertilizer (CF + OF), and organic fertilizer alone (OF). Our results showed that the annual cumulative N2O emissions from the plantation soil ranged from 1.03 to 3.43 kg N2O-N ha−1. The cumulative N2O emissions, the yield-scaled N2O emissions (YSNE), and the N2O-N emission factor (EF) from the soil were the highest under the CF + OF treatment but the lowest under the OF treatment. Further analysis revealed that fertilization, mainly chemical fertilization, increased the soil ammonium (NH4+-N) and nitrate (NO3−-N) levels by 182–387% and 195–258%, respectively, and tea yields by 120–170%. However, tea yield decreased gradually with increasing organic substitution. These results prove that complete organic substitution reduces soil N2O emissions and tea yield and suggest adopting an appropriate substitution rate for optimal effect. Further random forest (RF) modeling identified water-filled pore space (WFPS; 20.27% of total variation), soil temperature (Tsoil; 19.29%), and NH4+-N (18.27%) as the key factors significantly contributing to the changes in soil N2O flux. These findings provide a theoretical foundation for optimizing fertilization regimes for sustainable tea production and soil N2O mitigation.

Procyanidins-Mediated Biological Denitrification Inhibition Reduces Fertilizer-Induced N2O Emissions in Acidic Tea Plantation Soils

Procyanidins-Mediated Biological Denitrification Inhibition Reduces Fertilizer-Induced N2O Emissions in Acidic Tea Plantation Soils

Biochar-microplastics interaction modulates soil nitrous oxide emissions and microbial communities

Biochar has been proposed as a soil amendment in vegetable fields, where the widespread use of plastic film leads to significant retention of microplastics (MPs) in the soil. However, the interactive effect of biochar and MPs on plant growth and soil functions remains poorly understood. Here, we conducted a pot experiment to examine the effects of biochar application in the presence of conventional and biodegradable microplastics (0.05% w/w) on the growth of coriander, soil nitrogen (N) cycling processes, and microbial communities. The results showed that biochar application increased aboveground biomass by increasing plant available N of NH4+, regardless of the presence of MPs. Biochar also significantly reduced soil nitrous oxide (N2O) emissions by an average of 16% without MPs. However, when MPs were present, the effect of biochar on N2O emissions was lessened depending on the MP type. Polylactic acid consistently reduced soil N2O emissions and the abundance of N2O production genes, irrespective of biochar application. Conversely, polyethylene without biochar reduced N2O emissions primarily by inhibiting N-related functional genes responsible for nitrification and denitrification. This inhibitory effect was reversed when biochar was applied, leading to a 26% increase in N2O emissions due to increased nifH and nirK gene abundance. Although biochar and MPs did not significantly alter microbial α-diversity, they altered the composition and structure of bacterial and fungal communities, linked to changes in soil N turnover. Our study underscores the critical role of MP type in assessing the effects of biochar on soil N cycling and N2O emissions. Consequently, plastic pollution may complicate the ability of biochar to improve plant growth and soil functions, depending on the characteristics of the MPs.Graphical

Meta-analysis on the Effects of Organic Fertilizer Application on Global Greenhouse Gas Emissions from Agricultural Soils

To explore the direct and indirect effects of organic fertilizer application on greenhouse gas emissions from agricultural soils, a total of 1228 groups of data from 129 published studies were selected. Meta-analysis was used to analyze the effects of organic fertilizer on global greenhouse gas emissions from agricultural soils and their influencing factors. Meanwhile, a structural equation model （SEM） was further constructed to quantify and determine the causal relationships between the factors. The results showed that, overall, compared with those under no fertilization, organic fertilizer substitution increased CO2 emissions by 70.73% （lnR： 0.53, 95%CI： 0.45-0.62）, CH4 emissions by 52.58% （lnR： 0.42, 95%CI： 0.26-0.59）, and N2O emissions by 208.14% （lnR： 1.13, 95%CI： 1.04-1.21）, respectively. Compared with those under the application of inorganic fertilizers, the substitution of organic fertilizers increased CO2 emissions by 19.24% （lnR： 0.18, 95%CI： 0.13-0.22）, CH4 emissions by 27.72% （lnR： 0.24, 95%CI： 0.15-0.34）, and N2O emissions by -3.66% （lnR：-0.04, 95%CI：-0.11- 0.04）. Under the application of organic fertilizer, the dryland system had the greatest impact on both CO2 and N2O emissions, and the rice system had the most significant effect on CH4 emission effects. The average CO2 growth rate was highest in silty soils, and sandy soils had a greater effect on the average growth rates of N2O and CH4. The average growth rate of CO2 and N2O was extremely large under straw substitution compared to that under commercial organic fertilizer and biogas. The substitution of farmyard manure had significant CH4 emissions from soil promotion. Greenhouse gas emissions were significantly increased under the nitrogen fertilizer and organic fertilizer treatments. The SEM showed that mean annual temperature （MAT） was the most important environmental determinant of CO2 and N2O emissions, in which soil CO2 emissions were significantly positively correlated with MAT （P &lt; 0.01） and soil N2O emissions were negatively correlated with MAT. The main environmental determinants of CH4 emissions in dryland, grassland, and rice systems were annual precipitation （MAP） and mean annual temperature （MAT）, respectively, which were both significantly and positively correlated with each other （P &lt; 0.05）. This research can provide a scientific basis for optimizing fertilizer management and mitigating greenhouse gas emissions from farmland.

Effects of Conservation Agriculture on Soil N2O Emissions and Crop Yield in Global Cereal Cropping Systems.

Conservation agriculture, which involves minimal soil disturbance, permanent soil cover, and crop rotation, has been widely adopted as a sustainable agricultural practice globally. However, the effects of conservation agriculture practices on soil N2O emissions and crop yield vary based on geography, management methods, and the duration of implementation, which has hindered its widespread scientific application. In this study, we assessed the impacts of no-tillage (NT), both individually and in combination with other conservation agriculture principles, on soil N2O emissions and crop yields worldwide, based on 1270 observations from 86 peer-reviewed articles. Our results showed that conservation agriculture practices significantly increased crop yield by 9.1% while significantly reducing soil N2O emissions by 6.8% compared to conventional tillage (CT). These mitigation effects were even greater when NT was combined with other conservation agriculture principles, such as crop residue retention and crop rotation, leading to reductions in N2O emissions of over 15% and yield increases of more than 30%. Additionally, conservation agriculture was more effective at mitigating soil N2O emissions in dry climates compared to humid regions. Long-term adoption of conservation agriculture practices was found to reduce soil N2O emissions by up to 26% without compromising crop yields. Smallholder farm in Central Asia, South Asia, and sub-Saharan Africa appear particularly suitable for the adoption of conservation agriculture, whereas, in humid climates, high nitrogen (N) input management and silt-clay loam soil should be applied with caution. Overall, conservation agriculture holds significant potential for mitigating soil N2O emissions while enhancing grain yields in cereal cropping systems.

Microbial mechanisms of mesofauna pattern changes affecting soil greenhouse gas emissions and ecosystem multifunctionality.

In mountainous regions, global warming has changed the biological diversity and community structure of both aboveground and belowground organisms, and it may cause biota to move from lower altitudes to higher altitudes. However, our understanding of such migrations of soil mesofauna caused by global warming on soil processes and functions remains limited. We carried out a 79-day experiment comprising treatments without mesofauna (WM), native mesofauna (NM), migratory mesofauna (MM), and both native and migratory mesofauna together (TM) to reveal the effects of soil mesofauna migration on greenhouse gas emissions, ecosystem multifunctionality, and the underlying mechanisms. We found that soil mesofauna enhanced CO2 emissions (46.59% for NM, 75.72% for MM, and 107.21% for TM) and N2O emissions (82.57% for NM, 121.47% for MM, and 204.69% for TM) when compared to WM. Soil multifunctionality was reduced by 207.64% under TM compared to NM. Partial least squares path modeling indicated that soil properties and microbial diversity have positive effects on soil multifunctionality. The diversity of soil mesofauna had a positive direct effect on soil CO2 and N2O emissions. Random forest analysis showed that mite Shannon diversity, springtail Shannon diversity, and springtail beta diversity emerged as the most critical biotic factors for predicting soil CO2 emissions, soil N2O emissions, and multifunctionality. These findings provide deeper insights into the responses of soil processes and functions to soil mesofauna migrations, as well as the management of mountain ecosystems.

Diversified crop rotations exert a profound influence on the nosZI denitrifier community.

Agricultural soils are a significant contributor to global nitrous oxide (N2O) emissions, which is primarily driven by microbial nitrification and denitrification processes. Diversifying crop rotations can enhance soil nitrogen (N) utilization and influence N-cycling microbes, particularly the denitrifiers. Here, we evaluated the abundance, diversity, and community structure of soil denitrifiers by analyzing the denitrification genes (nirS, nirK, and nosZI) with a 14-year experiment of continuous and rotated crop systems. Compared to continuous cotton (C), crop rotations altered abundance of the nirS, nirK, and nosZI genes, but the responses varied among different rotation patterns (p<0.05). Diversified crop rotations decreased Shannon index of the nirS and nirK gene communities, while increased that of the nosZI gene communities. Diversified crop rotations greatly changed community structure of the nirS, nirK and nosZI gene communities (p<0.05). Among the responsive operational taxonomic units (OTUs), 2.62%, 2.52%, and 4.31% of the nirS, nirK, and nosZI genes were involved in the responses, respectively. Notably, a significant increase in OTUs belonged to N-fixing groups (i.e., Herbaspirillum and Rhodanobacter), while a decrease in OTUs affiliated to Achromobacter and Bosea was observed in diversified crop rotations. Furthermore, soil pH and C/N ratio correlated significantly with the nirS gene community structure (p<0.05), SOC and C/N ratio correlated with the nirK gene community (p<0.05), and soil pH, TN, NO3--N, and C/N ratio correlated with the nosZI gene community (p<0.05), respectively. In conclusion, our study demonstrates that long-term diversified crop rotations significantly altered the microbial communities related to denitrification, especially the nosZI gene community. These findings highlight the importance of diversified crop rotations in fostering soil denitrifiers communities that contribute to N₂O reduction, potentially supporting sustainable agricultural practices by reducing greenhouse gas emissions. However, future studies should be focus on both the nosZI and nosZII clades communities to offer a more complete picture of microbial contributions to soil N-cycling and N2O emission reduction.

Impacts of Legacy and Contemporary Nitrogen Inputs on N2O and CO2 Emissions in Miscanthus and Maize Cultivated Soils

ABSTRACTNutrient inputs influence the sustainability of bioenergy crop production through contemporary (shortly after addition) and legacy effects (persisting over years) on microbial nitrogen (N) and carbon cycling, which contribute to greenhouse gas emissions. However, the relative importance of contemporary and legacy effects and how that could vary by crop functional types is poorly understood. Considering its rhizomatous roots and perennial growth, we hypothesized that Miscanthus × giganteus (M×g) would be more sensitive to legacy N fertilization and the historical context of its environment than an annual crop like maize. To test this hypothesis, we examined the effects of legacy and contemporary N inputs on nitrous oxide (N2O) and carbon dioxide (CO2) emissions, as well as key N cycling genes in soils where M×g and maize were grown. A 150‐day soil incubation experiment was conducted using soils from a long‐term M×g and maize fertility experiment with three historic N fertilization rates (0, 112, and 336 kg N ha−1 year−1) and a contemporary amendment (60 mg N kg−1) with negative control (0 mg N kg−1). We observed significant increases in cumulative N2O emissions in Mxg soils relative to maize soils, particularly at higher legacy fertilization rates, while contemporary N had no significant effect. Bacterial amoA gene abundance, which plays a significant role in nitrification in nutrient‐rich soils, also increased with higher legacy fertilization rates in M×g soils but was unaffected by the contemporary N. In maize soils, legacy and contemporary N did not significantly affect N2O emissions, but cumulative CO2 emissions and amoA gene abundance significantly increased. The abundances of norB genes were not significantly influenced by either legacy fertilization or contemporary N amendments in either soil. Our findings demonstrate the greater importance of fertilization history over contemporary N in mediating soil N2O emissions, particularly for perennial bioenergy crops.

Tire Wear Particles Exposure Enhances Denitrification in Soil by Enriching Labile DOM and Shaping the Microbial Community.

Tire wear particles (TWP) are emerging contaminants in the soil environment due to their widespread occurrence and potential threat to soil health. However, their impacts on soil biogeochemical processes remain unclear. Here, we investigated the effects of TWP at various doses and their leachate on soil respiration and denitrification using a robotized continuous-flow incubation system in upland soil. Fourier transform ion cyclotron resonance mass spectrometry and high-throughput sequencing were employed to elucidate the mechanisms underpinning the TWP effects. We show that TWP increased soil CO2, N2, and N2O emissions, which were attributed to the changes in content and composition of soil dissolved organic matter (DOM) induced by TWP and their leachate. Specifically, the labile DOM components (H/C ≥ 1.5 and transformation >10), which were crucial in shaping the denitrifying community, were significantly enriched by TWP exposure. Furthermore, the abundances of denitrification genes (nirK/S and nosZ-I) and the specific denitrifying genera Pseudomonas were increased following TWP exposure. Our findings provide new insights into impacts of TWP on carbon and nitrogen cycling in soil, highlighting that TWP exposure may exacerbate greenhouse gas emissions and fertilizer N loss, posing adverse effects on soil fertility in peri-urban areas and climate change mitigation.

Impact of Insect Foliar Herbivory on Soil N₂O Emission and Nitrogen Dynamics in Subtropical Tree Species

Insect foliar herbivory is ubiquitous in terrestrial ecosystems, yet its impacts on soil nitrogen cycling processes remain not yet well known. To examine the impacts of insect foliar herbivory on soil N2O emission flux and available nitrogen (N), we conducted a pot experiment to measure soil available N content and soil N2O emission flux among three treatments (i.e., leaf herbivory, artificial defoliation, and control,) in two broad-leaved trees (Cinnamomum camphora and Liquidambar formosana) and two conifer trees (Pinus massonianna and Cryptomeria fortunei). Our results showed that insect foliar herbivory significantly increased soil inorganic N (i.e., NH4+–N and NO3−–N), dissolved organic nitrogen (DON) and microbial biomass nitrogen (MBN) contents, and urease activity compared to control treatment. However, there were no differences in soil available N contents and urease activity between artificial defoliation and control treatments, implying that insect foliar herbivory had greater impacts on soil available N contents compared to physical damage of leaves. Moreover, soil N2O emission fluxes were increased by insect foliar herbivory in Cinnamomum camphora and Pinus massonianna, but not for the other two tree species, indicating various effect of insect foliar herbivory on soil N2O emission among tree species. Furthermore, our results showed the positive correlations between soil N2O emission flux and soil NO3−–N, DON, MBN, and acid protease activity, and soil inorganic N, pH, and MBN mainly explained soil N2O emission. Our results implied that insect foliar herbivory can speed up soil nitrogen availability in subtropical forests, but the impacts on soil N2O emission are related to tree species.

Mechanisms of N2O Emission in Drip-Irrigated Saline Soils: Unraveling the Role of Soil Moisture Variation in Nitrification and Denitrification

Drip irrigation generates structural bodies in soil, forming layered structures with moisture content gradients. There are four typical soil moisture characteristic values in this concentric structure as saturation capacity (θs), field capacity (FC), 60% field capacity (60% FC), and 30% field capacity (30% FC). In this study, we simulated these four soil water characteristic values to conduct an indoor soil incubation experiment under three different incubation conditions: aerobic (O), aerobic with 10 pa acetylene (OC), and anaerobic (AO). The results indicate that in soil with saturated water content, denitrification under aerobic conditions leads to high N2O emissions; in soil at field holding capacity, nitrification under aerobic conditions dominates low N2O emissions, which is most conducive to N2O reduction and greenhouse gas emission mitigation; in soil with 60% of field holding capacity, denitrification under anaerobic conditions leads to high N2O emissions; and in soil with 30% of field holding capacity, microbial activity decreases, inhibiting nitrification, denitrification, and N2O emissions. Our research has found that when conducting aerobic drip irrigation in soil at field capacity (FC), denitrification was reduced by 99%, nitrification was increased by 70%, and microbial activity was enhanced by 5%. Therefore, during drip irrigation, the position and flow rate of the dripper should be controlled to reduce soil water saturation areas, maintain soil aeration, control soil moisture content below field holding capacity, promote the nitrification process, reduce N2O emissions, and improve soil nitrogen use efficiency. Our study elucidates the characteristics of nitrogen transformation and N2O emissions across various soil moisture contents within the soil water structure under drip irrigation conditions, providing a scientific basis for the formulation of precise irrigation management practices and strategies for efficient soil nitrogen utilization.

Effects of Long-Term Nitrogen Fertilization on Nitrous Oxide Emission and Yield in Acidic Tea (Camellia sinensis L.) Plantation Soils

The responses of nitrous oxide (N2O) emissions to nitrogen (N) application in acidic, perennial agricultural systems, and the factors driving these emissions, remain poorly understood. To address this gap, a 12-year field experiment was conducted to investigate the effects of different N application rates (0, 112.5, 225, and 450 kg N ha−1 yr−1) on N2O emissions, tea yield, and the associated driving factors in a tea plantation. The study found that soil pH significantly decreased with long-term N application, dropping by 0.32 to 0.85 units. Annual tea yield increased significantly, by 148–243%. N application also elevated N2O emission fluxes by 33–277%, with notable seasonal fluctuations observed. N2O flux was positively correlated with N rates, water-filled pore space (WFPS), soil temperature (Tsoil), and inorganic N (NH4+-N and NO3−-N), while showing a negative correlation with soil pH. Random forest (RF) modeling identified WFPS, N rates, and Tsoil as the most important variables influencing N2O flux. The cumulative N2O emissions for N112.5, N225, and N450 were 1584, 2791, and 45,046 g N ha−2, respectively, representing increases of 1.33, 2.34, and 3.77 times compared to N0. The N2O-N emission factors (EF) were 0.35%, 0.71%, and 0.74%, respectively, and increased with higher N rates. These findings highlight the importance of selecting appropriate fertilization timing and improving water and fertilizer management as key strategies for mitigating soil acidification, enhancing nitrogen use efficiency (NUE), and reducing N2O emissions in acidic tea-plantation systems. This study offers a theoretical foundation for developing rational N fertilizer management practices and strategies aimed at reducing N2O emissions in tea-plantation soils.

Efficiency of 3,4-Dimethylpyrazole Phosphate in Mitigating N2O Emission Varied with Irrigation Regime in Drip-Irrigated Wheat Field

Agricultural soils are major anthropogenic sources of N2O emissions. The application of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) has been proved to be an effective management measure to mitigate N2O emissions. However, the influence mechanism of DMPP on the mitigation of soil N2O emissions under different irrigation regimes remains unclear. Therefore, a lysimeter experiment was conducted to study the effects of irrigation level (lower irrigation limits of 75%, 65%, and 55% of field capacity (FC), signed as WH, WM, and WL) and DMPP addition (0% and 1% of N application, signed as D0 and D1) on N2O emissions, soil environmental factors such as ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), water-filled pore space (WFPS), soil temperature, and the abundances of N2O-related genes (AOA amoA, AOB amoA, nirS, and nirK). The results showed that soil N2O emissions increased with the increasing of irrigation level. The efficiency of DMPP mitigating N2O emissions varies depending on irrigation regime. Compared to D0, D1 strongly decreased cumulative N2O emissions by 11.27%, 18.96%, and 15.05% in the WL, WM, and WH conditions, respectively. Meanwhile, D1 caused an obvious reduction in the AOB amoA gene by 29.73%, 47.02%, and 22.41%, respectively, but there was no significant effect on the AOA amoA gene. D1 was effective in decreasing nirS and nirK genes except in the WL condition; the percentages of reduction were 48.45%, 40.84% and 37.18%, 44.97% in the WM and WH conditions, respectively. In addition, D1 caused an increase in NH4+-N content and a decrease in NO3−-N content, WFPS, and soil temperature in all irrigation regimes. A higher significant correlation was observed between N2O emissions and NH4+-N and AOB amoA in the WL and WM conditions, while a significant correlation was observed between N2O emissions and NO3−-N, nirK, and nirS in the WH condition. It was revealed that with the increase in irrigation level, the main source of N2O emissions might change from nitrification to denitrification. Overall, our study indicated that in the WL and WM conditions, the mitigation of N2O emissions by DMPP was primarily attributable to the inhibition of the AOB amoA gene, whereas the inhibition of nirS and nirK genes was likely the dominant mechanism in the WH condition. The findings of this study will provide a theoretical basis for the application of a nitrification inhibitor for drip-irrigated winter wheat fields in the North China Plain.