N2O Emission Characteristics Research Articles

Dissolved Nitrous Oxide and Methane in the Taiwan Strait: Distribution, Seasonal Variation, and Emission

AbstractThe global ocean plays an important role in the overall budgets of nitrous oxide (N2O) and methane (CH4), especially in continental estuaries and shelf areas. Four cruises were conducted between 2021 and 2022, covering the spring, summer, and fall seasons, to study the spatial and seasonal characteristics of N2O and CH4 distributions and emissions in the Taiwan Strait (TWS). The surface N2O and CH4 concentrations gradually decreased from the coast to the open sea, with maximum values (14.3 and 15.6 nmol L−1) occurring near the Jiulong and Minjiang estuaries, respectively. The mean surface N2O concentration (8.2 nmol L−1) was highest in the spring and approximately the same in the summer as in the fall. The mean surface concentrations of CH4 (8.8 nmol L−1) were greater in summer than in spring and fall, probably because of the high freshwater input in summer. Except for several stations in fall, surface waters were oversaturated with N2O and CH4 relative to the atmosphere in other seasons, and the TWS was a net source of atmospheric N2O and CH4 in the spring, summer, and fall. In situ production is the main source of N2O and CH4 in the TWS, with nitrification being the dominant mechanism of N2O production in the TWS. In contrast, physical influences (riverine inputs and water mass mixing) reshape the distributions of N2O and CH4. The annual emissions of N2O and CH4 from the TWS were estimated to be 0.9 × 10−3 ± 2.9 × 10−3 Tg yr−1 and 1.6 × 10−3 ± 3.0 × 10−3 Tg yr−1, respectively. Taken together, the TWS accounts for 0.025% of the surface area of the world's oceans and 0.022% ± 0.07% and 0.017% ± 0.033% of global oceanic N2O and CH4 emissions, respectively.

Variability in N2O emission controls among different ponds within a hilly watershed

While it is well established that small water bodies like ponds play a disproportionately large role in contributing to N2O emissions, few studies have focused on lowland ponds in hilly watersheds. Here, we explored the characteristics of N2O concentrations and emissions from various typical ponds (village, tea, forested, and aquaculture ponds) in a hilly watershed and examined the specific controls influencing N2O production. Our findings revealed that tea ponds exhibited the highest N2O flux (8.42 ± 8.23 μmol m-2 d-1), which was 2.8 to 3.3 times greater than other types of ponds. Remarkable seasonal variations were observed in tea and forested ponds due to the seasonality of nutrient-enriched runoff, whereas such variations were less pronounced in village and aquaculture ponds. Key factors such as nitrogen levels, temperature, and dissolved oxygen (DO) emerged as the primary controls of N2O concentrations in ponds, heavily influenced by land use and human activities in their drainage areas. Specifically, N2O production in tea and aquaculture ponds was driven by N inputs from fertilization and feed, respectively, while DO levels governed the process in village and forested ponds, influenced by abundant algae and forest vegetation. This study emphasizes that environmental factors predominantly drive N2O production in ponds within hilly watersheds, but land use in the pond drainages acts as an indirect yet crucial influence. This highlights the need for future research to develop targeted emission reduction strategies based on land use to effectively mitigate N2O emissions, promising a path toward more sustainable and climate-friendly watershed management.

Research Progress on Production and Emission of CH4 and N2O from Urban Rivers

Methane （CH4） and nitrous oxide （N2O） are concerning greenhouse gases. Urban rivers have been important emission sources of CH4 and N2O in recent years. It is meaningful for city greenhouse gas reduction to provide a systematic analysis of spatiotemporal characteristics, mechanisms, and influencing factors of the production and emission of CH4 and N2O from urban rivers. This study combed measured data of urban river CH4 and N2O dissolution concentrations and emission fluxes from related literature published in the past 20 years and also concluded the spatiotemporal characteristics of urban river CH4 and N2O emissions. This study estimated that CH4 and N2O emissions （expressed by CO2-eq） from urban rivers in Beijing were 234.63 and 59.53 Gg CO2-eq in 2018, whereas CH4 and N2O emissions （expressed by CO2-eq） from urban rivers in Shanghai were 159.86 and 260.24 Gg CO2-eq in 2018, respectively. These results demonstrated that urban rivers have become important CH4 and N2O emission sources. This study summarized the production/consumption processes and import/export pathways of CH4 and N2O in urban rivers. What is more, this study discussed the main influencing factors of urban river CH4 and N2O production and emissions from the perspectives of river environmental conditions and urbanization effects. At last, the present work prospected the future research trends of urban river CH4 and N2O emissions and provides urban rivers with scientific support for greenhouse gas reduction.

Nitrous oxide emissions and microbial communities variation in low dissolved oxygen and low carbon-to-nitrogen ratio anoxic-oxic wastewater treatment plant.

Dissolved oxygen (DO) levels and carbon-to-nitrogen (C/N) ratio affect nitrous oxide (N2O) emissions by influencing the physiological and ecological dynamics of nitrifying and denitrifying microbial communities in activated sludge systems. For example, Nitrosomonas is a common N2O producing nitrifying bacteria in wastewater treatment plants (WWTPs), and DO conditions can affect the N2O production capacity. Previous studies have reported N2O emission characteristics under adequate DO and C/N conditions in A/O WWTPs. However, in actual operation, owing to economic and managerial factors, some WWTPs have a long-term state of low DO levels in oxic tanks and low influent C/N. Research on N2O emission characteristics in low DO-limited and low C/N ratio WWTPs is limited. This study investigated N2O emissions and the corresponding shifts in microorganisms within an anoxic-oxic (A/O) WWTP over 9-month. Quantitative PCR was used to assess the abundance of ten functional genes related to nitrification and denitrification processes, and high-throughput sequencing of the 16S rRNA gene was employed to determine the composition change of microorganisms. The findings revealed that 1) the average N2O emission factor was 1.07% in the studied WWTP; 2) the DO-limited oxic tank primarily contributed to N2O; 3) NO2-, TOC, and C/N ratios were key factors for dissolved N2O in the aerobic tank; and 4) Nitrosomonas and Terrimonas exhibited a robust correlation with N2O emissions. This research provides data references for estimating N2O emission factors and developing N2O reduction policies in WWTPs with DO-limited and low C/N ratios.

Characteristics and key driving factors of nitrous oxide emissions from a full-scale landfill leachate treatment system

The characteristics of N2O emission from a full-scale landfill leachate treatment system were investigated by in-situ monitoring over 1.4 years and driving factors responsible for these emissions were identified by statistical analysis of multidimensional environmental variables. The results showed that the maximum N2O emission flux of 2.21 × 107 mg N·h−1 occurred in the nitrification tanks, where 98.5 % of the total N2O was released, with only 1.5 % of the total N2O emitted from the denitrification tanks. Limited oxygen in nitrification tank was responsible for N2O hotspot. The N2O emissions from the parallel lines A and B (both comprising the primary biochemical system) accounted for 52.6 % and 46.6 %, respectively, while the secondary biochemical system contributed only 0.8 % to the total emissions. Higher nitrite concentration in line A and lower nitrogen loading in the secondary biochemical system caused these discrepancies. We found that during the steady state of leachate treatment, intensive N2O emissions of 253.4–1270.5 kg N·d−1 were measured. The corresponding N2O emission factor (EF) ranged from 8.86 to 49.6 %, much higher than those of municipal wastewater treatment. But N2O EF was inconceivably as low as 0.42 % averagely after system maintenance. Influent with low salinity was the key reason, followed by the high MLSS and varying microbial community after maintenance. The dominant genus shifted from Lentimicrobium and Thauera to Norank-F-Anaerolineaceae and Unclassified-F-Rhodocyclaceae. This study underscores the significance of landfill leachate treatment in urban nitrogen management and provides valuable insights into the characteristics and driving factors of N2O emissions from such systems. The findings offer important references for greenhouse gas emission inventories and strategies for N2O control in full-scale wastewater treatment plants.

Nitrous Oxide Emissions during Cultivation and Fallow Periods from Rice Paddy Soil under Urea Fertilization

Rice cultivation serves as a significant anthropogenic source of methane (CH4) and nitrous oxide (N2O). Although N2O emissions remain relatively small compared to CH4 emissions, they are remarkably affected by nitrogen-fertilized soil conditions during rice cultivation. While numerous studies have investigated nitrous oxide emissions in response to nitrogen fertilization, existing research assessing nitrous oxide emissions based on nitrogen fertilizer levels has often been limited to cultivation periods. Therefore, there is a need for comprehensive analyses covering the entire year, including the dry periods, to address nitrous oxide emissions as an important source throughout the entire agricultural cycle. In this case study, we investigated the characteristics of N2O emissions in a central region of South Korea, where a single rice-cropping cycle occurs annually over a span of three whole years, from May 2020 to May 2023. We investigated the impact of variations in temperature and soil moisture on N2O emissions during rice cultivation and fallow periods. In this context, we attempted to discover the complex dynamics of N2O emissions by comparing longer fallow periods with the rice cultivation periods and extended non-dry periods with irrigated periods. We discovered that the greater contribution of cumulative N2O emissions during the fallow period made a much greater contribution (up to approximately 90%) to the whole-year N2O emissions than those during the rice cultivation period. During the fallow period from rice harvest to rice planting in the following year, variations in N2O emissions were associated with high-flux events after rainy periods on dry soils. This highlights the considerable influence of soil moisture content and weather conditions on N2O emissions during the fallow period. This affects high emission events, which in turn significantly impact the cumulative emissions over the entire period. We underscore that assessing N2O emissions solely based on the rice cultivation period would underestimate annual emissions. To prevent underestimation of N2O emissions, periodic gas collection throughout a year covering both rice cultivation and fallow phases is required in alignment with the monitoring of different temperature and soil moisture conditions. We captured statistical differences in cumulative N2O emissions due to nitrogen fertilization treatments across the three years. However, no significant difference was observed in the three-year average emissions among the different (one, one-and-a-half, and double) nitrogen fertilization treatments, with the exception of the control treatment (no fertilization). Based on the findings, we recommend at least three whole-year evaluations to ensure the estimation accuracy of N2O emissions under different nitrogen fertilization conditions. The findings from this study could help prepare the further revision or refinement of N2O emission factors from rice cultivation in the national greenhouse gas inventories defined by the inter-governmental panel on climate change (IPCC).

Effect of Streptomyces JD211 application on soil physicochemical properties and N2O emission characteristics of rice rhizosphere

Biocontrol agent, as a pollution-free and sustainable plant disease control method, can inhibit the spread of soil-borne diseases and promote the growth of crops. However, there are few studies on the effect of biocontrol agent on N2O emission in rice soil. In this study, after the application of the biocontrol agent Streptomyces JD211, N2O emission from rice soil were measured, and the relationship between the agent and soil N2O emissions were studied in soil chemistry and molecular biology. The results showed that the application of Streptomyces JD211 can significantly reduce the rate of N2O emission from rice soil. The NH4+-N and NO3−-N contents in rice soil decreased in a short period of time after the application of Streptomyces JD211, while the mineral N content in the soil remained stable with rice growth. 16S rRNA gene sequencing and metagenomic sequencing revealed Streptomyces JD211 application mainly increased the relative abundance of Burkholderia and Streptomyces in the soil microbial community, reduced the relative abundance of hao, norB, norC genes, and increased the relative abundance of nosZ and hcp genes. Streptomyces JD211 application promoted N2O transformation and weakened N2O production pathways, which ultimately reduced N2O emissions from rice soils. This study provided new insight of biocontrol agents to regulate soil N2O emissions, which is of great significance for the development and application of biocontrol bacteria and farmland environmental protection.

Effect and microbial mechanism of suspended sediments particle size on nitrous oxide emission in eutrophic lakes

Suspended sediment (SPS) is an important environmental factor in eutrophic lakes, where they may play a significant role in the microbial nitrogen cycle and thus affect the N2O source and sink function. This study investigated the correlation and corresponding microbial mechanisms between N2O emission fluxes and SPS particle sizes. N2O emission characteristics were investigated in four parallel operated lab-scale microcosmic systems, in which different sizes of SPS particles were inoculated (i.e., <75, 75–150, 150–300, and >300 μm). The results show that, N2O emission fluxes in the eutrophic lakes were exponentially correlated with the lake trophic level index (TLI) (R2 = 0.94, p < 0.01) and the specific surface area of the SPS (R2 = 0.38, p < 0.05). In the microcosmic systems, SPS with 75–150 μm particles had the highest N2O emission rate of 5.94 ± 0.007 μg N/L/d, which was 2.6 times that of the <75 μm particle size system. The microcosmic system with particle size >300 μm had the highest N2O reduction rate (Vmax) of 6.776 μmol/L/h, which was 16–50 times that of the other three groups. Larger particle size SPS have a smaller specific surface area, which could affect the microenvironment on SPS surface and thus affect the microbe functions. The microbial community structure results indicated that the dominant microorganisms on the SPS surface were denitrifying bacteria. The maximum (nirS + nirK)/nosZ ratio was 30.2 for the 75–150 μm system, which was nearly 2 times higher than the other systems. The >300 μm system had the highest nosZ abundance, indicating a strong ability to reduce N2O. The co-occurrence networks analysis indicated that the cooperation and competition among nitrifiers and denitrifiers determined N2O emissions. These results provide fundamental insights into the influence of SPS size on N2O emissions in eutrophic lakes.

Numerical simulation of lean premixed combustion characteristics and emissions of natural gas-ammonia dual-fuel marine engine with the pre-chamber ignition system

As an efficient hydrogen carrier, ammonia (NH3) has great potential to realize the target of carbon neutralization. In this paper, a natural gas-ammonia dual-fuel engine model has been established to evaluate the feasibility of ammonia application in a high-pressure medium-speed four-stroke natural gas marine engine. In order to achieve the efficient and clean combustion of ammonia, a method combining the pre-chamber ignition system with lean-burn combustion technology was proposed. In addition, a CH4/NH3 combustion mechanism with reasonable accuracy was developed to simulate the combustion process of the engine. Moreover, the effect of using various ammonia concentration in the fuel on jet flame formation, thermal efficiency, unburned ammonia, and NOx and N2O emissions were compared. The results showed that the pyrolysis of ammonia mixtures in the pre-combustion chamber promoted the formation of jet flame, which had a “chain effect” on the turbulent kinetic energy in the main combustion chamber and further enhanced the flame propagation in lean conditions. In addition, NOx emission showed a decreasing function of the split ratio of ammonia, which was caused by the NO reduction by unburned NH3. However, the low-temperature generation characteristics of N2O emissions led to the opposite trend. Furthermore, the application of ammonia increased N2O emissions by 0.18–0.49 g/kWh, which is about 0.06%–0.1% of nitrogen in ammonia fuel, resulting in a partial offset of CO2 emission reduction effect.

Nitrous oxide emissions from tea plantations: A review.

Tea plantations are an important N2O source. Fertilizer-induced N2O emission factors of tea plantations are much higher than other upland agricultural ecosystems. According to the basic information on characteristics and knowledge of N2O emissions from tea plantations around the world, we comprehensively reviewed N2O emission characteristics, production process, influencing factors, and reduction measures from tea plantations. The global means of ambient N2O emission and N2O emission stimulated by nitrogen fertilizer application from tea plantations were (2.68±2.92) kg N·hm-2 and (11.29±9.45) kg N·hm-2, respectively. The fertilizer-induced N2O emission factor in tea plantations (2.2%±2.1%) was much higher than the IPCC-estimated N2O emission factor for agricultural land (1%). N2O emission from tea plantation soil (a typical acid soil) were mainly produced during nitrification and denitrification, with denitrification being dominant. N2O emission from tea plantations were significantly related to the amount of fertilizer application. Other factors, such as fertilizer type, could also affect soil N2O emissions in tea plantations. The main reduction methods of N2O emission from tea plantations included optimizing the amount and type of fertilizer, amending biochar, and rationally using nitrification inhibitors. In future, we should strengthen in-situ observations of soil N2O emission from tea plantations at both temporal and spatial scales, combine lab incubation and field studies to elucidate the mechanisms underling tea plantation soil N2O emissions, and use a data-model fusion approach to reduce uncertainties in the estimation of global N2O emission. These would provide theoretical support and practical guidance for reasonable N2O emission reduction in tea plantations.

Characteristics of soil N2O emission and N2O-producing microbial communities in paddy fields under elevated CO2 concentrations

The effects of elevated carbon dioxide (CO2) concentration (e[CO2]) on nitrous oxide (N2O) emissions from paddy fields and the microbial processes involved in N2O emissions have recently received much attention. Ammonia-oxidizing microorganisms and denitrifying bacteria dominate the production of N2O in paddy soils. To better understand the dynamics of N2O production under e[CO2], a field experiment was conducted after five years of CO2 fumigation based on three treatments: CK (ambient atmospheric CO2), T1 (CK + increase of 40 ppm per year until 200 ppm), and T2 (CK + 200 ppm). N2O fluxes, soil physicochemical properties, and N2O production potential were quantified during the rice-growth period. The functional gene abundance and community composition of ammonia-oxidizing archaea (AOA) and bacteria (AOB) were analyzed using quantitative polymerase chain reaction (qPCR) and those of ammonia-denitrifying bacteria (nirS- and nirK-type) were analyzed using Illumina MiSeq sequencing. N2O emissions decreased by 173% and 41% under the two e[CO2] treatments during grain filling and milk ripening, respectively (P < 0.05). N2O emissions increased by 279% and 172% in the T2 treatment compared with T1 during the tillering and milk-ripening stages, respectively (P < 0.05). Furthermore, the N2O production potential was significantly higher in the CK treatment than in T1 and T2 during the elongation stage. The N2O production potential and abundance of AOA amoA genes in T1 treatment were significantly lower than those in CK treatment during the high N2O emission phase caused by mid-season drainage (P < 0.05). Although nirK- and nirS-type denitrifying bacteria community structure and diversity did not respond significantly (P > 0.05) to e[CO2], the abundance of nirK-type denitrifying bacteria significantly affected the N2O flux (P < 0.05). Linear regression analysis showed that the N2O production potential, AOA amoA gene abundance, and nirK gene abundance explained 47.2% of the variation in N2O emissions. In addition, soil nitrogen (N) significantly affected the nirK- and nirS-type denitrifier communities. Overall, our results revealed that e[CO2] suppressed N2O emissions, which was closely associated with the abundance of AOA amoA and nirK genes (P < 0.05).

Experimental and numerical study of product gas and N2O emission characteristics of ammonia/hydrogen/air premixed laminar flames stabilized in a stagnation flow

In order to achieve carbon neutrality, the use of ammonia as a fuel for power generation is highly anticipated. The utilization of a binary fuel consisting of ammonia and hydrogen can address the weak flame characteristics of ammonia. In this study, the product gas characteristics of ammonia/hydrogen/air premixed laminar flames stabilized in a stagnation flow were experimentally and numerically investigated for various equivalence ratios for the first time. A trade-off relationship between NO and unburnt ammonia was observed at slightly rich conditions. At lean conditions, NO reached a maximum value of 8,700 ppm, which was larger than that of pure ammonia/air flames. The mole fraction of nitrous oxide (N2O) which has large global warming potential rapidly increased around the equivalence ratio of 0.6, which was attributed to the effect of a decrease in flame temperature downstream of the reaction zone owing to heat loss to the stagnation wall. To understand this effect further, numerical simulations of ammonia/hydrogen/air flames were conducted using the stagnation flame model for various equivalence ratios and stagnation wall temperatures. The results show that the important reactions for N2O production and reductions are NH +NO = N2O + H, N2O + H = N2 + OH, and N2O (+M) = N2 + O (+M). A decrease in flame temperature in the post flame region inhibited N2O reduction through N2O (+M) = N2 + O (+M) because this reaction has a large temperature dependence, and thus N2O was detected as a product gas. N2O is reduced through N2O (+M) = N2 + O (+M) in the post flame region if the stagnation wall temperature is sufficiently high. On the other hand, it was clarified that an increase in equivalence ratio enhances H radical production and promotes N2O reduction by H radical through the reaction of N2O + H = N2 + OH.

NH3 and N2O emission durability of the heavy-duty diesel engine with DOC, DPF, SCR, and ASC through the accelerated aging method

A general accelerated aging method for aftertreatment devices of Heavy-duty Diesel Engine (HDDE) is proposed in this paper, and three sets of aftertreatment devices were aged according to this method. The error between the World Harmonized Transient Cycle (WHTC)-NOx emission factors of conventional aging and those of accelerated aging fitted by equivalent thermal accumulation is −4.12 to 3.13 %, which proves that the two methods have good equivalence. Meanwhile, the NH3 and N2O emission characteristics and durability were tested by Fourier Transform Infra-Red Spectroscopy (FTIR) equipment. The results show that NH3 and N2O emissions do not deteriorate linearly with the intensification of thermal aging like NOx. Except that the NH3 emission of AT03 exceeds the limit of China VI emission regulation (the average and maximum NH3 concentration in the WHTC test are 35.25 ppm and 350.30 ppm, separately), NH3 emission of other aged devices meet the requirements. Combined with the equivalent durability mileage of 1130000 km of AT02, the test China VI HDDE can effectively control NH3 emissions and has a large margin with the limit requirements. However, the deterioration rate of N2O emission gradually slows down with the intensification of accelerated aging. The accelerated aging tests also indicate that N2O generation is closely related to NH3 in SCR, consistent with previous studies conclusions of low-temperature and high-temperature N2O generation mechanisms. Equally important is that the N2O emission emitted from test China VI HDDE is significantly higher than the emission limit of the Environmental Protection Agency (EPA). The N2O emission factors under the WHTC test are as high as 0.15 to 0.35 g/kWh, which should draw the attention of Chinese environmental regulatory authorities, who should start to formulate N2O emission limits and put forward complementary strategies to reduce N2O emissions from HDDEs.

The contributions of ammonia oxidizing bacteria and archaea to nitrification-dependent N2O emission in alkaline and neutral purple soils

Nitrification is believed to be one of the primary processes of N2O emission in the agroecological system, which is controlled by soil microbes and mainly regulated by soil pH, oxygen content and NH4+ availability. Previous studies have proved that the relative contributions of ammonia oxidizing bacteria (AOB) and archaea (AOA) to N2O production were varied with soil pH, however, there is still no consensus on the regulating mechanism of nitrification-derived N2O production by soil pH. In this study, 1-octyne (a selective inhibitor of AOB) and acetylene (an inhibitor of AOB and AOA) were used in a microcosm incubation experiment to differentiate the relative contribution of AOA and AOB to N2O emissions in a neutral (pH = 6.75) and an alkaline (pH = 8.35) soils. We found that the amendment of ammonium (NH4+) observably stimulated the production of both AOA and AOB-related N2O and increased the ammonia monooxygenase (AMO) gene abundances of AOA and AOB in the two test soils. Among which, AOB dominated the process of ammonia oxidation in the alkaline soil, contributing 70.8% of N2O production derived from nitrification. By contrast, the contribution of AOA and AOB accounted for about one-third of nitrification-related N2O in acidic soil, respectively. The results indicated that pH was a key factor to change abundance and activity of AOA and AOB, which led to the differentiation of derivation of N2O production in purple soils. We speculate that both NH4+ content and soil pH mediated specialization of ammonia-oxidizing microorganisms together; and both specialization results and N2O yield led to the different N2O emission characteristics in purple soils. These results may help inform the development of N2O reduction strategies in the future.

Characteristics of Greenhouse Gas Emissions from Yellow Paddy Soils under Long-Term Organic Fertilizer Application

Reducing greenhouse gas emissions from rice fields is essential to respond to the national “dual-carbon” strategy, achieve green agricultural development, and ensure food security. The substitution of organic fertilizers for chemical fertilizers is an important means to achieve zero growth and has a positive impact on crop yield and soil nutrients; however, the impact on the greenhouse effect is inconsistent. The effects of organic fertilizers on soil greenhouse gas emissions vary depending on factors such as soil, geography, ecological environment, and human management. However, previous research has shown that the combined application of organic fertilizer can increase soil carbon storage and increase crop yield, and may be an effective fertilization measure to reduce greenhouse gas emissions from yellow paddy fields. To clarify the effects of different ratios of organic fertilizer on the greenhouse gas emission characteristics of Guizhou yellow paddy soil, CH4, CO2, and N2O emissions from rice fields were monitored by static opaque chamber-gas chromatography, and the effects of different fertilization treatments on the cumulative greenhouse gas emissions and global warming potential (GWP) were investigated. Results showed that organic fertilizer application increased CH4 emissions from rice fields, and the effect increased with increasing organic fertilizer application. The peak period was from the heading stage to the filling and ripening stage, and there was almost no emission during the fallow period. Compared with the balanced application of chemical fertilizer (NPK), the treatment with organic fertilizer alone (M) significantly increased CO2 emissions, but the replacement of 1/2 chemical fertilizer nitrogen with 1/2 organic fertilizer (1/2 M + 1/2 N-PK) and the replacement of 1/4 chemical fertilizer nitrogen with 1/4 organic fertilizer (1/4 M + 3/4 N-PK) did not significantly increase CO2 emissions; emissions were 5% lower in the 1/2 M + 1/2 N-PK treatment than in the NPK treatment. Compared with the NPK treatment, the application of organic fertilizer alone significantly reduced N2O emissions by 32.16%, while the 1/2 M + 1/2 N-PK and 1/4 M + 3/4 N-PK treatments increased N2O emissions by 6.31% and 16.02%, respectively. However, there were no significant differences between the organic–inorganic combined treatments and NPK. During the flooding period, N2O emissions were relatively low, but the emissions increased rapidly after field drying. The application of organic fertilizer increased the GWP of rice fields. Compared with the NPK treatment, the M treatment increased GWP by 47.07%, 1/2 M + 1/2 N-PK increased GWP by 10.16%, and the 1/4 M + 3/4 N-PK treatment increased GWP by 2.93%. Except for the M treatment, the differences between treatments were not significant. Our results concluded that replacement of chemical fertilizers with organic fertilizers at a ratio of 1/4 to 1/2 did not significantly increase greenhouse gas emissions in rice fields, besides, it mitigate the greenhouse effect and increase soil carbon sequestration and yield in rice fields.

The Influence of N2O Emission to Water and Nitrogen Coupling Mechanism in Black Soil under Drip Irrigation Mode

This experiment is aimed at revealing the main characteristics of N2O emission from soybean in black soil and clarifying the relationship between N2O emission and environmental factors; in this experiment, static chamber-gas chromatography field observation method was used; meanwhile, three different drip irrigation amounts (300 mm, 350 mm, and 400 mm) and five different nitrogen application amounts (0, 63, 72, 81, and 90 kg/hm2) were set up to study the effects of different coupling modes on soybean N2O emission and the relationship between N2O emission and environmental factors. The results showed that the peak value of N2O emission flux of soybean mainly occurred in July and August, and the amount of N2O emission flux in each growth period was flowering-podding period &gt; branching period &gt; seedling period &gt; grain filling period. N2O emission increased with the increase of drip irrigation amount and nitrogen application amount. The effects of drip irrigation and nitrogen application on N2O emission were significantly different. Under the three drip irrigation modes, the N2O emission fluxes of most treatments were significantly correlated with the temperature in that day, and the soil temperature in different soil depths was significantly correlated with the N2O emission fluxes. The correlation relationship between the temperature of each soil layer under drip irrigation 300 mm and N2O emission fluxes was less than that under drip irrigation 350 mm and drip irrigation 400 mm. There was no significant correlation between N2O emission flux and NH4+-N and NO3-N, and there was no significant correlation between N2O cumulative emission and dry matter quality in the aboveground part of soybean. It shows that the emission of N2O itself is affected by multiple environmental factors and shows certain randomness. The research results can provide important theoretical basis and technical support for realizing nitrogen reduction and efficient utilization of soybean water and fertilizer in the black soil region of northeastern part of China.

Effects of biochar and biogas residue amendments on N2O emission, enzyme activities and functional genes related with nitrification and denitrification during rice straw composting

This study was carried out to determine the response characteristics of N2O emission, enzyme activities, and functional gene abundances involved in nitrification/denitirification process with biochar and biogas residue amendments during rice straw composting. The results revealed that N2O release mainly occurred during the second fermentation phase. Biogas residue amendment promoted N2O emission, while biochar addition decreased its emission by 33.6%. The nirK gene was abundant through composting process. Biogas residues increased the abundance of denitrification genes, resulting in further release of N2O. Biochar enhanced nosZ gene abundance and accelerated the reduction of N2O. Nitrate reductase (NR), nitrite reductase (NiR), N2O reductase (N2OR), and ammonia monooxygenase (AMO) activities were greatly stimulated by biochar or biogas residue rather than their combined addition. Pearson regression analysis indicated that N2O emission negatively correlated with ammonium and positively correlated with nosZ, nirK, 18S rDNA, total nitrogen, and nitrate (P < 0.05).

Effect of a Ridge-Furrow Mulching System and Limited Supplementary Irrigation on N2O Emission Characteristics and Grain Yield of Winter Wheat (Triticum aestivum L.) Fields under Dryland Conditions

Knowledge of the characteristics of N2O emissions and the influential mechanism is of great significance to mitigate greenhouse gas emissions in semi-arid areas. In the present study, a three-year water-control study was conducted; three simulated rainfall amounts (heavy, normal, and light rainfall = 275, 200, and 125 mm, respectively), two wheat (Triticum aestivum L.) planting modes (RF (ridge–furrow mulching system) and TF (traditional flat planting)) and four supplementary irrigation amounts (150, 75, 37.5, and 0 mm) were set up. The effects of different cultivation methods and irrigation amounts on soil N2O emissions, the soil water content, available nitrogen content, and denitrifying enzyme activity were investigated to clarify the N2O emission mechanism in winter wheat fields (Triticum aestivum L.). The results obtained after three years showed that compared with TF, the N2O emissions under RF decreased by 21.62–30.72% (p &lt; 0.001), whereas the soil water content increased by 6.26–8.82%, the available nitrogen content decreased by 1.71–16.24%, and the denitrifying enzyme activities increased by 0.2–24.16% under heavy rainfall conditions. Under conditions with normal and light rainfall, the N2O emission fluxes under RF increased by 3.66–12.46% and 6.08–15.57% (p &gt; 0.05), while the soil water contents increased by 6.13–11.49% and 8.05–13.88%, the soil available nitrogen contents decreased by 11.0–21.42% and 19.93–34.44%, and the denitrifying enzyme activities increased by 0.01–24.08% and 0.03–20.79% compared with TF. Principal component analysis showed that the main factors related to N2O emissions under RF were the soil moisture content and available nitrogen content; these factors combined explained 94.37% the variation of the N2O emissions. However, the main factors under TF were the soil moisture content and denitrifying enzyme activity; these factors combined explained 85.81%. In the heavy and normal rainfall years, compared with TF, using RF and 75 mm irrigation achieved the goal of reducing water usage as well as decreasing the N2O emissions (or N2O increase was not significant). In light rainfall years, RF with 150 mm irrigation obtained significant reductions in water usage compared with TF but it also increased the N2O emission flux. Under different rainfall years, the yield of RF increased by 2.89–50.44% compared with the TF system, and the increase in wheat grain yield increased with decreasing rainfall.

Responses of N2O Production and Abundances of Associated Microorganisms to Soil Profiles and Water Regime in Two Paddy Soils

Soil moisture is one of the critical factors affecting N2O emissions. The water regime affects the physical and chemical properties of paddy soil in different soil layers, which, in turn, affects N2O emissions and microbial growth. However, there are few reports on the effects of different soil layers and soil moisture conditions on N2O emission characteristics and microbial mechanisms. A 21-day microcosm experiment was performed to research the effects of soil moisture levels (60%, 100%, and 200% water holding capacity, WHC) and different soil layers (0–10, 10–20, and 20–40 cm) on N2O emissions in hydromorphic and gleyed paddy soils. Function microbes involved in nitrification and denitrification were determined by quantitative PCR. Moreover, the abiotic variables pH, Eh, and exchangeable Fe2+, Fe3+, NH4+-N, and NO3−-N were also analyzed. Results showed that N2O emissions of gleyed paddy soil were significantly higher than that of hydromorphic paddy soil, which was consistent with the result of the abundance of nitrifier and denitrifier in the two paddy soils. Soil depth, water content, and their interaction significantly affected N2O emission (p &lt; 0.05). Cumulative emissions of N2O from each layer of the two paddy soils at 100% and 200% WHC were significantly higher than that under 60% WHC (p &lt; 0.05). N2O emissions decreased significantly with the increase of soil depth (p &lt; 0.05), which was consistent with the change in the abundance of soil nitrifier (AOB and AOA) and denitrifier (nirK and nosZ) function genes with soil depth. The abundance of AOB, AOA, and nirK and nosZ genes decreased significantly with soil depth (p &lt; 0.05), but did not respond significantly to the water regime. Based on the results of redundancy analysis, the contents of Fe2+ and Fe3+ were positively correlated with N2O emissions and the abundance of AOB, AOA, and nirK and nosZ genes. These results indicate that N2O emissions and the abundance of associated microbes are selectively affected by soil moisture and soil layers in the two paddy soils.

Effect of Film Mulching, Straw Retention, and Nitrogen Fertilization on the N2O and N2 Emission in a Winter Wheat Field

In order to explore the characteristics of N2O emissions from winter wheat fields in the Loess Plateau under different farming methods and nitrogen levels, the dynamic changes in N2O emissions from rain-fed winter wheat fields were quantified using static box-gas chromatography. Winter wheat 'Xiaoyan22' was used as the material, and a two-factor split area design was adopted. The conventional tillage (CT), straw incorporated into soil (SM), and flat film mulching (FM) were assigned as the main plot, and three nitrogen fertilizer rates (no nitrogen fertilization, 20% nitrogen reduction (144 kg·hm-2), and conventional nitrogen application (180 kg·hm-2)) were assigned as a split plot. Taking CT as a control, the effects of FM and SM on soil N2O emissions under different nitrogen rates were assessed. Furthermore, the correlation between relevant environmental factors and N2O emission flux were analyzed, and N2 emissions were estimated using empirical formulas. The results showed the following:the N2O emissions from the soil of each nitrogen treatment occurred within 20 days, and N2O emission flux peaked within two weeks post-fertilization. The average N2O flux, the total N2O emissions, and the global warming potential of N2O were 1.92-22.75 μg·(m2·h)-1, 0.10-0.46 kg·hm-2, and 26.72-122.15 kg·hm-2, respectively. The N2O emission coefficient of fertilizer nitrogen was 0.05%-0.28%. The total N2 emissions ranged from 0.70-1.82 kg·hm-2. The N fertilization and film mulching significantly increased the N2O emission flux (P<0.05) and the cumulative N2O emissions (P<0.05); however, SM marginally reduced the total N2O emissions. The N2O emission coefficient and global warming potential of fertilizer nitrogen under FM were significantly higher than those under CT and SM (P<0.05). The N2O emissions without nitrogen treatment were only significantly positively correlated with soil water-filled pore spaces (WFPS) (P<0.05); the N2O emissions in the N fertilization condition were significantly positively correlated with WFPS, ω(NO3--N), ω(NH4+-N), and 0-5 cm soil layer temperature (P<0.05). Overall, under the condition of no fertilization, water was the main factor to control the nitrogen transformation and soil N2O emission; nevertheless, under the N fertilization condition, both nitrification and denitrification contributed to the N2O emissions in the rain-fed winter wheat fields. Film mulching practice and nitrogen application markedly increased the N2O emissions, fertilizer nitrogen emission coefficient, and global warming potential in the rain-fed winter wheat fields. Nonetheless, straw incorporated into the soil resulted in a marginal reduction in N2O emissions.