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Nitrous oxide (N₂O) has a global warming potential that is 300 times that of carbon dioxide on a 100-y timescale, and is of major importance for stratospheric ozone depletion. The climate sensitivity of N₂O emissions is poorly known, which makes it difficult to project how changing fertilizer use and climate will impact radiative forcing and the ozone layer. Analysis of 6 y of hourly N₂O mixing ratios from a very tall tower within the US Corn Belt—one of the most intensive agricultural regions of the world—combined with inverse modeling, shows large interannual variability in N₂O emissions (316 Gg N₂O-N·y−1 to 585 Gg N₂O-N·y−1). This implies that the regional emission factor is highly sensitive to climate. In the warmest year and spring (2012) of the observational period, the emission factor was 7.5%, nearly double that of previous reports. Indirect emissions associated with runoff and leaching dominated the interannual variability of total emissions. Under current trends in climate and anthropogenic N use, we project a strong positive feedback to warmer and wetter conditions and unabated growth of regional N₂O emissions that will exceed 600 Gg N₂O-N·y−1, on average, by 2050. This increasing emission trend in the US Corn Belt may represent a harbinger of intensifying N₂O emissions from other agricultural regions. Such feedbacks will pose a major challenge to the Paris Agreement, which requires large N₂O emission mitigation efforts to achieve its goals.

Enhanced‐efficiency N fertilizers (EENFs) have potential for mitigating N2O emissions from N‐fertilized cropping systems. Stabilized EENFs contain nitrification and/or urease inhibitors. Slow‐release EENFs contain N components that are slowly released with variable release rates. Controlled‐release EENFs release N at more predictable rates. The effectiveness of several EENFs in reducing soil N2O emissions from a clay loam soil under irrigated, corn (Zea mays L.)‐based production systems in Colorado (2002–2012) was investigated. A controlled‐release, polymer‐coated urea, ESN, reduced N2O emissions by 42% compared with urea and 14% compared with urea–NH4NO3 solution (UAN) in no‐till and strip‐till environments, but had no effect in a conventional tillage environment. A stabilized urea source, SuperU, reduced N2O emissions by 46% compared with urea and 21% compared with UAN. A stabilized UAN source, UAN + AgrotainPlus, reduced N2O emissions by 61% compared with urea and 41% compared with UAN alone. A slow‐release UAN source, UAN + Nfusion, reduced N2O emissions by 57% compared with urea and 28% compared with UAN. Urea–NH4NO3 reduced N2O emissions by 35% compared with urea. A linear increase in N2O emissions with increasing N rate was observed for untreated urea and UAN. Developers of management protocols to reduce N2O emissions from irrigated cropping systems in semiarid areas can use this information to estimate reductions in N2O emissions when EENFs are used. Policymakers can use this information to help determine financial credits needed to encourage producers to use these technologies in their crop production systems.

Acidic soils are hotspots of global nitrous oxide (N 2 O) emission. The application of organic fertilizer with low carbon (C) to nitrogen (N) ratio (C:N) often stimulated N 2 O emission in acidic soils. However, how its use increases acidic soil N 2 O emission remains largely unclear. We thus conducted an aerobic 15  N tracing incubation experiment to quantify the effects of organic fertilizer input with low C:N on the contribution of denitrification and autotrophic and heterotrophic nitrification to N 2 O emission in an acidic soil. We found a shift from nitrification to denitrification-dominated N 2 O emission after adding organic fertilizer with low C:N into the studied acidic soil, and this shift was more pronounced with increasing the application rate of organic material. Therefore, organic fertilizer application with low C:N may stimulate N 2 O emission in acidic soils due to the stimulation of denitrification.

Nitrous oxide (N 2 O) emissions occur as a consequence of the turnover of soil nitrogen (N), but gross N transformations and N 2 O production are often not studied in combination, so the relationships are poorly understood. Here, we quantified gross N transformations and the N 2 O production pathway of alkaline fluvo-aquic soils under different fertilization regimes collected from a long-term field experiment in the North China Plain and compared them with six acidic UK soils (one was alkaline for reference) with high soil organic carbon (SOC). We found that nitrification was the dominant N 2 O production pathway in the alkaline Chinese soil with a contribution of nitrification to N 2 O emissions (N 2 O nit ) of 81%. By contrast, denitrification was the main N 2 O production pathway for the acidic UK soils with the contribution of denitrification to N 2 O emissions (N 2 O den ) of 66%. Long-term manure applications significantly increased N 2 O den , compared to the synthetic N and no N treatments (25% vs. 18%). The N 2 O nit was positively correlated with gross autotrophic nitrification rates and pH but negatively correlated with gross N mineralization, SOC, soil total N content, and C:N ratios. Our findings highlight the importance of soil pH in controlling the N 2 O production in cropland soils, and suggest that the increased contribution of denitrification to N 2 O emissions should be considered, when increasing SOC through long-term manure and straw management for carbon sequestration and soil fertility improvement.

The response of nitrifier and denitrifier populations and associated N2O emissions to different carbon-to-nitrogen (C/N = 17 or 45) straw amendments was monitored under flooding-drying and non-flooding conditions. A 10-week laboratory mesocosm study was conducted in two soils, (i) a paddy soil with a long history of managed flooding-drying (CN), and (ii) a wheat cropping soil with no previous history of flooding (UK). We measured N2O fluxes and the abundances of ammonia-oxidizing archaea (AOA) and bacteria (AOB), nitrite reductase (nirK and nirS) genes, and nitrous oxide reductase (nosZI and nosZII) genes during flooding (4 weeks) and post-flooding (6 weeks). Straw addition enhanced N2O emissions, with higher fluxes apparent after incorporation of narrow C/N residues. Moreover, the impact of crop amendment on N2O emission was exacerbated when soil was under flooding-drying conditions. The abundances of nirS and nosZI genes in CN soil and AOA gene in UK soil were increased by straw amendment, with highest in narrow C/N straw amendments. Structural equation modeling showed that the impact of denitrifier gene abundance on the N2O flux was stronger than that of nitrifier gene abundance in the two soils, and significant correlations were observed between N2O fluxes and the consumption of DOC and NO3−, indicating that denitrification was the dominant N2O production pathway during the drying phase. The ratio of (nirS + nirK)/(nosZI + nosZII) in the narrow C/N amendment was greater than in the wide C/N treatment after flooding, suggesting that the straw C/N ratio had an effect on the capacity for N2O production via denitrification. We conclude that crop amendments with an appropriate C/N ratio could minimize N2O fluxes through regulating the denitrification process when soils are subjected to regular flooding and drying and also experiencing greater frequencies of flooding.

Variations of N transformation processes, N 2 O release rates, and N 2 O emission pathways were investigated at different levels of salinity (stage 1, low salinity inhibition stage; stage 2, medium salinity promotion stage; and stage 3, high salinity promotion stage) using 15  N- 18 O dual-isotope labeling technique. Potential nitrification rates were reduced by saltwater incursion in stage 1, increased markedly in stage 3, and significantly inhibited potential denitrification rate under higher salinity. N 2 O emission significantly increased along salinity gradient in stage 3 due to the changes of potential nitrification rates. Saltwater incursion significantly increased the contribution of heterotrophic denitrification to N 2 O emission in stage 1. In stages 2 and 3, contributions of nitrifier denitrification and nitrification-coupled denitrification to N 2 O emission increased gradually, and nitrifier denitrification became the dominant pathway of N 2 O emission under high salinity. Changes of N transformations, N 2 O emission rates, and their pathways were regulated both by composition of microbial community and physicochemical properties of the sediment. Due to increased ammonification rate, organic N decomposition accelerated by saltwater can reduce the wetland N sink and may turn coastal wetland to significant reactive N source.

Recently, sustainability of tourism growth has become an international issue due to environmental and economic uncertainty that needs recent researchers’ focus and also requires the policymakers’ attention. Therefore, the present research has examined the role of economic and environmental factors and tourism policy related to tourist arrival on the sustainability of tourism growth in China. The economic factor includes the gross domestic product (GDP), national income, and foreign direct investment (FDI), while environmental factors include carbon dioxide (CO 2 ) emission, greenhouse gas (GHG) emission, and nitrous oxide emission. The study has extracted the data from World Development Indicators (WDI) from 1990 to 2020. The present research has employed nonlinear autoregressive distributed lagged (NARDL) to check the linkage among variables. The current study also examines the unit root using Augmented Dickey-Fuller (ADF) and Phillips-Perron (PP) tests. The results revealed that GDP, national income, tourism policy related to tourist arrival, and FDI have a positive linkage with the sustainability of tourism growth. The results also exposed that environmental factors such as CO 2 emission, GHG emission, and nitrous oxide emission have a negative linkage with the sustainability of tourism growth. This study provides the guidelines to the relevant authorities and regulators in developing and implementing the regulators regarding the sustainability of tourism growth by promoting economic and environmental conditions and effective tourism policies in the country.

Excessive nitrogen fertilizer application in greenhouse vegetable production (GVP) is of scientific and public concern because of its significance to international environmental sustainability. We conducted a meta-analysis using 1174 paired observations from 69 publications on the effects of nitrogen fertilizer application and reducing nitrogen fertilizer application on the nitrogen losses on a broad scale. We found that the increase in nitrogen loss is much higher than that in production gain caused by excessive application of nitrogen fertilizer: nitrate leaching (+187.5%), ammonium leaching (+28.1%), total nitrogen leaching (+217.0%), nitrous oxide emission (+202.0%), ammonia emission (+176.4%), nitric oxide emission (+543.3%), yield (+35.7%) and nitrogen uptake (+24.5%). Environmental variables respond nonlinearly to nitrogen fertilizer application, with severe nitrate leaching and nitrous oxide emission when the application rate exceeds 570 kg N/ha and 733 kg/N, respectively. The effect of nitrogen fertilizer on yield growth decreases when the application rate exceeds 302 kg N/ha. Appropriate reduction in nitrogen fertilizer application rate substantially mitigates the environmental cost, for example, decreasing nitrate leaching (−32.4%), ammonium leaching (−6.5%), total nitrogen leaching (−37.3%), ammonia emission (−28.4%), nitrous oxide emission (−38.6%) and nitric oxide emission (−8.0%), while it has no significant effect on the nitrogen uptake and yield.

Incorporation of crop residues into the soil has been widely recommended as an effective method to sustain soil fertility and improve soil carbon sequestration in arable lands. However, it may lead to an increase in the emission of nitrous oxide (N 2 O) and leaching of nitrate (NO 3 − ) to groundwater due to higher nitrogen (N) availability after crop residue incorporation. Here, we conducted a meta-analysis based on 345 observations from 90 peer-reviewed studies to evaluate the effects of crop residue return on soil N 2 O emissions and NO 3 − leaching for different locations, climatic and soil conditions, and agricultural management strategies. On average, crop residue incorporation significantly stimulated N 2 O emissions by 29.7%, but decreased NO 3 − leaching by 14.4%. The increase in N 2 O emissions was negatively and significantly correlated with mean annual temperature and mean annual precipitation, and with the most significant changes occurring in the temperate climate zone. Crop residues stimulated N 2 O emission mainly in soils with pH ranging between 5.5 and 6.5, or above 7.5 in soils with low clay content. In addition, crop residue application decreased NO 3 − leaching significantly in soils with sandy loam, silty clay loam, and silt loam textures. Our analysis reveals that an appropriate crop residue management adapted to the site-specific soil and environmental conditions is critical for increasing soil organic carbon stocks and decreasing nitrogen losses. The most important novel finding is that residue return, despite stimulation of N 2 O emissions, is particularly effective in reducing NO 3 − leaching in soils with loamy texture, which are generally among the most productive arable soils.

A soil column experiment was conducted to examine the effects of fertilizer N source and depth of placement on soil profile N2O accumulation and surface emissions at 44% and 77% water-filled pore space (WFPS). The used N fertilizers were polymer-coated urea, stabilized urea with urease and nitrification inhibitors, and conventional granular urea. Conventional urea and stabilized urea were applied either uniformly at 0–65 cm or deeply at a 40- to 65-cm depth of 65 cm repacked soil columns, whereas polymer-coated urea was subsurface banded at a 10-cm depth to reflect fertilizer application practices at a field scale. Profile N2O concentrations at 5, 15, 30, and 60 cm and surface flux were monitored over 3 months. Compared to conventional urea, stabilized urea and polymer-coated urea generally reduced N2O accumulation in the column, but not cumulative emissions. Across fertilizer sources, compared with uniform addition, deep placement reduced column N2O accumulation at 44% but not at 77% WFPS. Deep placement also reduced emissions 56–71% than for uniform placement. Column N2O accumulation doubled at 77% than 44% WFPS, whereas cumulative emissions and applied N–based emission factors were lower at the former WFPS value. Cumulative N2O emissions increased exponentially with total accumulation at 44% but not 77% WFPS. Reduced N2O emissions at high WFPS were likely due to consumption and low diffusivity of the gas in the soil profile, rather than low production by denitrification. These results suggest fertilizer N leached down the profile is less prone to N2O loss while emission reductions by using more efficient fertilizers may be limited.