Decreased N2O Emissions Research Articles

Key biochar properties linked to denitrification products in a calcareous soil

Meta-analyses show an overall decrease in soil N2O emissions after biochar (BC) amendment. Nonetheless, N2O mitigation with BC cannot be extrapolated to every BC-soil combination, inasmuch as an increase in soil N2O release has been occasionally reported. We hypothesized that BC characteristics are key, and performed two microcosm experiments to advance in the understanding of the properties associated. We first investigated how 22 well-characterized BCs affect N2O emissions in a calcareous soil under denitrification conditions. Whereas most BCs decreased N2O emissions, some substantially increased N2O emissions. In a second experiment, we selected and further characterized eight of the 22 previous BCs. We applied the 15N-gas-flux method to study how these BCs affect denitrification products (N2O and N2) in the same soil. Results indicate that the interaction between BC and the denitrification process depends on the temperature of pyrolysis. Whereas BCs produced at 400 °C tended to increase total denitrification (N2O+N2) by an average of 28%, BCs produced at 600 °C significantly reduced total denitrification by 53%. Nevertheless, this decline in overall denitrification did not result in a decrease of N2O emissions, as there was a strong shift in the N2O/(N2+N2O) ratio favoring N2O. A redundancy analysis revealed a direct correlation between carboxylic groups on BCs surface and N2O emissions. This research enhances our understanding of the interaction of BC with denitrification, particularly concerning the relevance of the temperature of pyrolysis, and opens up new paths for investigation, crucial for optimizing the application of BCs in different soil environments.Graphical

Rapid Responses of Greenhouse Gas Emissions and Microbial Communities to Carbon and Nitrogen Addition in Sediments.

Massive labile carbon and nitrogen inputs into lakes change greenhouse gas emissions. However, the rapid driving mechanism from eutrophic and swampy lakes is not fully understood and is usually contradictory. Thus, we launched a short-term and anaerobic incubation experiment to explore the response of greenhouse gas emissions and microbial communities to glucose and nitrate nitrogen (NO3--N) inputs. Glucose addition significantly increased CH4 and CO2 emissions and decreased N2O emissions, but there were no significant differences. NO3--N addition significantly promoted N2O emissions but reduced CH4 accumulative amounts, similar to the results of the Tax4Fun prediction. Bacterial relative abundance changed after glucose addition and coupled with the abundance of denitrification genes (nirS and nirK) decreased while maintaining a negative impact on N2O emissions, considerably increasing methanogenic bacteria (mcrA1) while maintaining a positive impact on CH4 emissions. Structural equation modeling showed that glucose and NO3--N addition directly affected MBC content and greenhouse gas emissions. Further, MBC content was significantly negative with nirS and nirK, and positive with mcrA1. These results significantly deepen the current understanding of the relationships between labial carbon, nitrogen, and greenhouse emissions, further highlighting that labile carbon input is the primary factor driving greenhouse gas emissions from eutrophic shallow lakes.

Long‐term tillage and cover cropping differentially influenced soil nitrous oxide emissions from cotton cropping system

AbstractClimate‐smart agricultural practices, such as no‐tillage (NT) and cover cropping, have been widely adopted and are anticipated to yield multiple benefits, including soil carbon sequestration, enhancing soil health, and crop yield stability. However, their influence on nitrous oxide (N2O) emissions varies, with the potential of both increasing and decreasing N2O emissions. Increasing N2O emissions under these practices may potentially offset the climate mitigation benefits from increased soil carbon sequestration. We investigated N2O emissions in response to 42 years of long‐term adoption of NT and legume cover crop, under nitrogen (N) rates of 0 and 67 kg N ha−1, in a continuous cotton system in the Southeastern United States. Intensive manual chamber‐based measurements were conducted over two growing seasons (2021–2022 and 2022–2023). Long‐term NT did not significantly affect cumulative N2O emissions during the study period (p > 0.05). Hairy vetch cover crop‐grown plots emitted two to three times more N2O than those without cover crops in 2021–2022, with no significant effect observed in 2022–2023. Cumulative emissions in cover crop plots were greater compared to those in no cover crop plots when fertilized with 67 kg N ha−1 in 2021–2022; however, this trend did not persist in 2022–2023. While interannual variability exists, our results generally suggest that long‐term NT may not increase N2O emissions, hence its adoption could enhance its broader soil health and climate benefits via soil carbon sequestration, whereas managing legume cover crop residues in N‐fertilized systems is critical to mitigate N2O emissions.

Converse Responses of Biochar Application on N2O Emissions in Soils at Different pH Values in a Subtropical Citrus Orchard

The aim of this study was to explore the effect of biochar on N2O emissions in soils with different pH levels. Soils with five pH levels (4.0, 5.1, 5.8, 6.6, and 7.2) were incubated in two conditions, with 0% biochar (CK) and 1% biochar (BC), for 23 days. N2O emissions were measured at nine time points, and soil chemical properties, AOA-amoA, AOB-amoA, nirK, nirS, and nosZ, were analyzed. Partial least squares path modelling (PLS-PM) was used to assess the effect of nitrification and denitrification pathways on potential N2O emissions. The results showed that biochar reduced N2O emissions in highly acidic soil (pH 4.0) but increased emissions in soils with pH values ranging from 5.1 to 7.2. In highly acidic soils, decreased N2O emission was associated with increased soil pH (p < 0.05) and decreased dissolved organic carbon content (p < 0.05), leading to higher nosZ gene abundance (p < 0.05). Meanwhile, in acidic to neutral soils, biochar application increased soil pH (6.6–11.7%), dissolved organic nitrogen (5.9–29.5%), dissolved organic carbon (8.6–41.0%), stimulated AOB-amoA, nirK, nirS gene abundance (p < 0.05), and thus increased N2O emissions. The results verified the influence of nitrification and denitrification genes on N2O production in soils with different pH values. In conclusion, biochar had different effects on N2O emissions based on soil pH, highlighting the need to consider pH when using biochar to mitigate N2O emissions in subtropical citrus orchards.

Low nitrous oxide fluxes from mineral affected peatland soils in Iceland

Nitrous oxide (N2O) is a potent greenhouse gas, and soil is one of its most substantial sources. Emissions are influenced by both biotic and abiotic processes, as well as the physiochemical properties of the medium. Organic soils fully drained in boreal climates are a potentially significant source of nitrous oxide. Lower, drainage levels and nutrient availability have been shown to reduce N2O emissions. Predicting N2O emissions from agriculturally managed peatlands is challenging. In situ measurements are crucial for addressing these difficulties. This study presents three years of in situ field measurements of nitrous oxide fluxes and soil hydrological status in peatland soils under different agricultural management regimes: cultivated drained (CD), uncultivated drained (UCD), and wet (W) in Western Iceland. Fluxes were quantified by analysing a time-concentration series obtained from permanent chambers and subsequently evaluated using gas chromatography in the laboratory. The minimum potential N2O consumption rate (mean ± 95 % Cl) was estimated as 0.76 ± 0.38, 0.56 ± 0.18 and 0.56 ± 0.14 mg N2O-N m⁻² day⁻¹ for CD, UCD, and W sites, respectively. Yearly accumulated emissions were estimated as 2.24 ± 1.47, 1.26 ± 0.64 and 0.26 ± 0.44 kg N2O-N ha−1 yr−1 for CD, UCD, and W sites, respectively. The relatively low emission rates observed at drained sites can be explained by the stable water content, and by limited availability of soil phosphorus, which hampers N2O production and potentially leads to more active N2O consumption. Both the stable water content and low phosphorus availability is explained by mineral inputs to the peatlands, acting through decreased soil unsaturated hydraulic conductivity and increased phosphorus retention. The effects of mineral content offer potential mitigation option to decrease N2O emissions. This study highlights the complexity of N2O emissions from peatland soils and emphasizes the significance of site-specific factors in managing greenhouse gas emissions. Further studies investigating the underlying processes behind N2O fluxes in the peatland and andic soils are recommended.

The influence of exhaust gas recirculation on combustion and emission characteristics of ammonia-diesel dual-fuel engines: Heat capacity, dilution and chemical effects

As the greenhouse effect intensifies, ammonia is garnering increasing attention as a carbon-free fuel. In the transport sector, ammonia-diesel dual-fuel (ADDF) engines are regarded as an effective means of reducing carbon emissions. The objective of this study is to investigate the combustion and emission optimization of an ADDF engine under high load conditions. To this end, an experimental optimization study of different start of diesel injection timing (SODI) and exhaust gas recirculation (EGR) rates was conducted at a load of 18 bar and an ammonia energy ratio of 80 %. The mechanism of heat capacity, dilution, and chemical effects of EGR was also revealed by numerical simulation based on the separated variables method. It was demonstrated that advancing SODI is effective in enhancing combustion efficiency. However, this approach is limited by the upper limit of in-cylinder pressure and results in higher nitrogen oxides (NOx) emissions, which can be mitigated by the EGR. The heat capacity effect of EGR increases the specific heat capacity and decreases the average temperature. The suppression of the combustion process leads to a reduction in thermal and fuel NOx, but an increase in nitrous oxide (N2O) emissions. The dilution effect of EGR results in insufficient oxygen, which decreases the heat release rate and combustion efficiency. Additionally, the NOx and N2O are significantly reduced. The chemical effect of EGR affects reactive groups and unburned components that accelerate heat release rate and increase accumulated heat release, resulting in significantly higher NOx. The comprehensive effect of EGR results in a decrease in N2O emissions and a significant reduction in thermal and fuel NOx. The EGR and further optimization of SODI enabled the ADDF engine to achieve a gross indicated thermal efficiency of 48.5 % with a load of 18 bar and an ammonia energy ratio of 80 %. In addition, NO emissions were reduced by 32.8 percent and greenhouse gas emissions by 63.3 percent.

Rice-crayfish integrated system enhances global warming potential via increasing methane emission mainly driven by continuous deep flooding

The conversion from rice monoculture (RM) to rice-crayfish integrated system (RCIS) could change soil physicochemical properties and microorganisms related to greenhouse gas (GHG) emissions. Nevertheless, it is still unclear the responses of GHG emissions and global warming potential (GWP) from paddy fields to RCIS. Here, we conducted a field experiment to investigate the changes in the emissions of methane (CH4) and nitrous oxide (N2O), GWP, soil physicochemical properties and the associated microbial abundances (methanogen, methanotrophs, denitrifier and nitrifier) under RCIS in Gaoyou City, Jiangsu Province, China from 2022 to 2023. There were three treatments, including RM, rice monoculture with continuous deep flooding (RMF) and RCIS. Compared with RM, RCIS and RMF all significantly increased CH4 emission and decreased N2O emission. But the effectiveness of increasing CH4 emission and decreasing N2O emission was larger under RCIS than RMF. The increased CH4 emission was due to the significantly higher mcrA gene abundance and ratio of mcrA/pmoA under RCIS. While the significantly higher nosZ gene abundance and ratio of nosZ/(amoA+nirK+nirS) under RCIS were responsible for its reduced N2O emission. Furthermore, the increases in gene abundances of mcrA and nosZ under RCIS were closely correlated with the significantly lower redox potential and pH as well as the significantly higher contents of dissolved organic carbon, ammonium and nitrate in soil. Averaged across two years, GWP under RCIS and RMF were 4.6-fold and 3.4-fold that under RM, respectively. This revealed that continuous deep flooding had a greater effectiveness in increasing GWP than crayfish culture under RCIS. Notably, the contribution rates of CH4 emission to the total GWP decreased in the order of RCIS (98.6%) > RMF (97.5%) > RM (86.2%). Besides, greenhouse gas intensity under RCIS was 5.1-fold that of RM due to its enhanced GWP and reduced rice grain yield. In summary, RCIS could enhance GWP from paddy fields through increasing CH4 emission mainly caused by the continuous deep flooding.

Effects of biodegradable microplastics and straw addition on soil greenhouse gas emissions

Large pieces of plastic are transformed into microplastic particles through weathering, abrasion, and ultraviolet radiation, significantly impacting the soil ecosystem. However, studies on biodegradable microplastics replacing traditional microplastics as agricultural mulching films to drive the biogeochemical processes influenced by GHG are still in their initial stages, with limited relevant reports available. This study sought to investigate the effects of microplastic and straw addition on CO2 and N2O emissions in different soils. Herein, yellow-brown soil (S1) and fluvo-aquic soil (S2) were utilized, each treated with three different concentrations of PLA (polylactic acid) microplastics (0.25%, 2%, and 7% w/w) at 25 °C for 35 days, with and without straw addition. The results showed that straw (1% w/w) significantly increased soil CO2 by 4.1-fold and 3.2-fold, respectively, and N2O by 1.8-fold and 1.8-fold, respectively, in cumulative emissions in S1 and S2 compared with the control. PLA microplastics significantly increased CO2 emissions by 71.5% and 99.0% and decreased N2O emissions by 30.1% and 24.7% at a high concentration (7% w/w, PLA3) in S1 and S2 compared with the control, respectively. The same trend was observed with the addition of straw and microplastics together. Structural equation modeling and redundancy analysis confirmed that soil physiochemical parameters, enzyme and microbial activities are key factors regulating CO2 and N2O emissions. The addition of microplastics is equivalent to the addition of carbon sources, which can significantly affect DOC, MBC, SOC and the abundance of carbon-associated bacteria (CbbL), thereby increasing soil CO2 emissions. The addition of microplastics alone inhibited the activity of nitrogen cycling enzymes (urease activity), increasing the abundance of denitrifying microbes. However, adding a high amount of microplastics and straw together released plastic additives, inhibiting microbial abundance and reducing the nitrogen cycle. These effects decreased NH4+-N and increased NO3−-N, resulting in decreased N2O emissions. This study indicates that biodegradable microplastics could reduce soil plastic residue pollution through degradation. However, their use could also increase CO2 emissions and decrease N2O emissions. Consequently, this research lays the groundwork for further investigation into the implications of utilizing biodegradable microplastics as agricultural mulch, particularly concerning soil geochemistry and GHG emissions.

Nanoparticles of Zinc Oxides Mitigated N2O Emissions in Tea Plantation Soil

The excessive application of nitrogen in tea plantations leads to severe soil acidification and N2O emission boosting. To promote sustainable agriculture, nanoparticles (NPs) have emerged as alternative fertilizers, but their effects on soil nitrification and greenhouse gas emissions in tea plantations remain unclear. In this study, the effects of NP type (ZnO-NPs and Fe2O3-NPs) and dose (0, 1, 10, and 100 mg·kg−1) on soil N2O emissions were investigated via a lab incubation trial. Soil pH, ammonium, and nitrate changes were also monitored during the incubation period. The abundance of functional genes related to nitrification and denitrification processes was analyzed as well. The results showed that ZnO-NPs led to a decrease in N2O emissions. The reduction effect was stronger with increasing dose and resulted in a 33% reduction at an addition rate of 100 mg·kg−1. The cumulative N2O emissions had significantly positive correlations with NH4+-N and NO3−-N. ZnO-NP addition showed a significantly negative effect on Ammonia-Oxidizing Archaea (AOA) but a positive effect on Ammonia-Oxidizing Bacteria (AOB) gene abundance. In contrast, Fe2O3-NPs showed an insignificant impact on N2O emissions and soil N content, as well as nitrification–denitrification gene abundance, regardless of different doses. These results imply that the application of ZnO-NPs may inhibit nitrification through the retarding of AOA activity. This study provided us with a potential practice to reduce N2O emissions in tea plantations by applying ZnO-NPs, but the efficiency of this reduction needs further examination under ambient conditions before field application.

NosZ I carrying microorganisms determine N2O emissions from the subtropical paddy field under elevated CO2 and strongly CO2-responsive cultivar

Elevated CO2 (eCO2) decreases N2O emissions from subtropical paddy fields, but the underlying mechanisms remain to be investigated. Herein, the response of key microbial nitrogen cycling genes to eCO2 (ambient air +200 μmol CO2 mol−1) in four rice cultivars, including two weakly CO2-responsive (W27, H5) and two strongly CO2-responsive cultivars (Y1540, L1988), was investigated. Except for nosZ I, eCO2 did not significantly alter the abundance of the other genes. NosZ I was a crucial factor governing N2O emissions, especially under eCO2 and a strongly responsive cultivar. eCO2 affected the nosZ I gene abundance (p < 0.05), for instance, the nosZ I gene abundance of cultivar W27 increased from 1.53 × 107 to 2.86 × 107 copies g−1 dw soil (p < 0.05). In the nosZ I microbial community, the known taxa were mainly Pseudomonadota (phylum) (19.74–31.72 %) and Alphaproteobacteria (class) (0.56–13.12 %). In the nosZ I community assembly process, eCO2 enhanced the role of stochasticity, increasing from 35 % to 85 % (p < 0.05), thereby inducing diffusion limitations of weakly responsive cultivars to dominate (67 %). Taken together, the increase in nosZ I gene abundance is a potential reason for the alleviation of N2O emissions from subtropical paddy fields under eCO2.

Wheat straw and microbial inoculants have an additive effect on N2O emissions by changing microbial functional groups

AbstractStraw‐decomposing microbial inoculants (MIs) have been increasingly applied to straw‐amended soils. However, the interactive effects and underlying microbial mechanisms of straw and decomposing MIs on nitrous oxide (N2O) emissions remain unclear. Here, a pot experiment with an Aquic Inceptisol was conducted to determine soil N2O emissions and the abundance and composition of microbial functional genes under six amendments: wheat straw (W), Bacillus subtilis MI (B), Streptomyces rochei MI (S), a combination of straw and B. subtilis MI (WB), a combination of straw and S. rochei MI (WS), and a control without wheat straw or MI (C). Compared with the control, the amendments of straw, decomposing MIs, and their combinations decreased soil N2O emissions by 43%, 22–30%, and 46–60%, respectively. Mechanistically, the positive relationship between ammonia‐oxidizing bacteria (AOB) and soil potential nitrification rate (PNR), along with decreased AOB abundance (−36%) following straw and decomposing MI amendments, further suggested that AOB predominated soil nitrification and was responsible for the suppressed nitrification. In addition, straw amendment increased nirK gene abundance (by 48%) and potential denitrification rate (by 11%), while the increase in nosZI gene abundance (+25%) involved in N2O consumption contributed to the decrease in N2O emissions. Overall, the additive effect of straw and decomposing MIs on soil N2O emissions was associated with two amendment‐induced changes in the abundance and composition of AOB and straw‐stimulated the abundance of the nosZI gene. Our results revealed the potential for mitigating N2O emissions following the amendments of straw and MI by influencing soil N2O‐related microbial groups.

Partial substitution of manure increases N2O emissions in the alkaline soil but not acidic soils

The fertilization regimes of combining manure with synthetic fertilizer are benefits for crop yields and soil fertility in cropping systems as compared to sole synthetic fertilization, but the responses of nitrous oxide (N2O) emissions to these practices are inconsistent in the literatures. We hypothesized that it is caused by different proportions of nitrogen (N) applied as manure and various soil properties. Here, we conducted a microcosm experiment, and measured the N2O emissions from control (no N) and five manure substitution treatments (supplied 100 mg N kg−1 using the combination of urea with manure) with a range of proportions of N applied as manure (0, 25%, 50%, 75%, and 100%) in three different soil types (fluvo-aquic soil, black soil, and latosol) under aerobic condition. The stimulated effect on N2O emissions was more pronounced after manure application in an alkaline soil with high nitrification rate, due to relatively rapid soil DOC depletion and N mineralization of manure. N2O emissions from partial substitution of urea with manure were significantly higher than manure-only addition under high soil pH due to abundant labile C from manure. However, there was no difference between manure substitution treatments under acid soils. Nitrification inhibitor substantially decreased N2O emissions with increasing soil pH, but it was less effective in mitigating N2O emissions with larger proportion of manure. This is likely due to the slow nitrification under low soil pH, and denitrification derived N2O increased with increasing manure application rate. Collectively, our study shows that the application of manure substitution to alkaline soils requires careful consideration, which might have rapid nitrification potential and hence trigger significant N2O emissions. The knowledge gained in this work will help the decision-makers in optimizing a sound N fertilization regime interacted with soil properties for sustainable crop production and N2O mitigation.

Reduction of greenhouse gas emissions from closed activated sludge- to aerobic granular sludge-based biosystems via gas circulation

Greenhouse gas (GHG) emissions from biological treatment units are challenging wastewater treatment plants (WWTPs) due to their wide applications and global warming. This study aimed to reduce GHG emissions (especially N2O) using a gas circulation strategy in a closed sequencing-batch reactor when the biological unit varies from activated sludge (AS) to aerobic granular sludge (AGS). Results show that gas circulation lowers pH to 6.3 ± 0.2, facilitating regular granules but elevating total N2O production. From AS to AGS, N2O emission factor increased (0.07–0.86 %) due to decreasing ammonia-oxidizing rates while the emissions of CO2 (0.3 ± 0.1 kg-CO2/kg-chemical oxygen demand) and CH4 remained in the closed biosystem. The gas circulation decreased N2O emission factor by 63 ± 15 % after granulation higher than 44 ± 34 % before granulation, which is implemented by heterotrophic denitrification. This study provides a feasible strategy to enhance heterotrophic N2O elimination in the biological WWTPs.

Fertilizer Application Method Provides an Environmental-Friendly Nitrogen Management Option for Sugarcane

PurposeNitrogen fertilizer management is an important agricultural tool that must be optimized to promote sustainable practices since the nitrogen-fertilizer recovery by plants (NRP) is low, leading to nitrogen losses to the environment. In sugarcane, N-fertilization has been investigated over the years but little attention has been given to N-fertilizer application methods. Sugarcane crop production and environmental impact regarding N-fertilizer application methods (i.e., applied onto the sugarcane straw layer and incorporated into the soil) were investigated in the present study aiming to achieve an environmental-friendly cropping system.MethodsSugarcane yield and NRP, N2O emissions, relevant components of the soil microbiological community and N-fertilizer retention in soil layers were quantified. The experiment was carried out in field conditions where N-fertilizer application methods using 15N-labelled ammonium nitrate (15NH415NO3) were compared to a control treatment with no N-fertilization.ResultsIncorporation of N-fertilizer into the soil increased the sugarcane yield by 17% (two-year average) compared to N-fertilizer applied onto the sugarcane straw layer, which was similar to control treatment. There was an increase in NRP-fertilizer of 79% due to the application of N-fertilizer incorporated into the soil. Furthermore, soil incorporation of N-fertilizer decreased N2O emission by 22% with the fertilizer N emission factor reduced four-fold. The N2O emissions were mostly associated with ammonium-oxidizing bacteria (AOB).ConclusionsOur results show that application of N-fertilizer incorporated into the soil is an environmental-friendly N-fertilization management which will improve agricultural sustainability and reduce environmental impacts.Graphical

Zeolite application coupled with film mulched drip irrigation enhances crop yield with less N2O emissions in peanut field

Zeolite has been previously reported to increase nitrogen (N) use efficiency in lowland paddy fields. However, few results are available regarding its effect on N2O emissions from upland field, especially with mulched drip irrigation. In present study, two-year peanut field experiments were conducted utilizing a split-plot design to assess the impact of zeolite application and irrigation regimes on plant dry weight and N accumulation, soil inorganic N content, peanut yield, N2O emissions, and soil physicochemical properties. Different irrigation regimes (MD, mulched drip irrigation; RF, rain-fed) as well as zeolite application rates (0 t ha−1 (Z0, control), 5 t ha−1 (Z5), and 10 t ha−1 (Z10)) were applied. Results showed that the MD treatment increased plant dry weight, N accumulation, soil NH4+-N, NO3−-N content and mean soil temperature compared to the RF control. Furthermore, cumulative N2O emissions and peanut yield were raised by 24.3% and 15.8%, respectively, with the MD treatment. The increased peanut yield by mulched drip irrigation might be resulted from the promoted soil inorganic N, soil temperature, and plant N accumulation. Regardless of irrigation, zeolite addition increased dry weight and N accumulation during all measured stages except seedling, mean soil NH4+-N, NO3−-N content, mean soil pH, and peanut yield. In contrast, cumulative N2O emissions were decreased compared to the non-zeolite control. Moreover, findings showed that Z10 performed better in increasing peanut yield by 12.7% and decreasing N2O emissions by 35.7% than Z5. Increasing soil inorganic N content with zeolite addition contributed to improve plant N accumulation and promote dry weight and peanut yield. Furthermore, the reduction of N2O emissions by zeolite was related to improved soil inorganic N and pH. Though MD increased N2O emissions, the MDZ10 treatment had 20.6% of cumulative N2O emissions lower than the conventional practice (RFZ0), indicating that zeolite application alleviated the adverse effect of mulched drip irrigation on N2O emissions. It was concluded that zeolite dose at 10 t ha−1 coupled with mulched drip irrigation gave a high peanut yield with less N2O emissions. Our findings could be adopted in arid areas to enhance peanut production and mitigate environmental risk induced by N2O emissions.

Inoculation with Stutzerimonas stutzeri strains decreases N₂O emissions from vegetable soil by altering microbial community composition and diversity.

Plant growth-promoting rhizobacteria (PGPR) have been applied to mitigate nitrous oxide (N₂O) emissions from agricultural soils, but the microbial ecological mechanisms underlying N₂O mitigation are poorly understood. That is why only limited PGPR strains can mitigate N₂O emissions from agricultural soils. Therefore, it is of substantial significance to reveal soil ecological mechanisms of PGPR strains to achieve efficient and reliable N₂O-mitigating effect after inoculation. Inoculation with Stutzerimonas stutzeri strains decreased N₂O emissions from two soils with contrasting textures probably by altering soil microbial community composition and gene abundance involved in nitrification and denitrification. Our findings provide detailed insight into soil ecological mechanisms of PGPR strains to mitigate N₂O emissions from vegetable agricultural soils.

Nitrification inhibitor addition to farm dairy effluent to reduce nitrous oxide emissions

ABSTRACT Increasing the use of nitrogen (N) fertilizers will be necessary to enhance grain and pasture yields to satisfy the growing world demand for food. Organic amendments, such as farm dairy effluents (FDE), are an alternative to traditional synthetic fertilizers. However, part of the applied N could be lost as ammonia (NH 3 ) volatilization or nitrous oxide (N 2 O) emission, decreasing N availability to plants. Nitrification inhibitors, such as dicyandiamide (DCD), suppress the microbial process of nitrification, decreasing soil nitrate concentration and, therefore, N 2 O emission. Reducing N 2 O losses from agricultural soils is a key subject for sustainable production. This research aimed to quantify the effect of DCD addition to the FDE on the emissions of N 2 O and the volatilization of NH 3 from the soil. A field trial was carried out in which NH 3 volatilization and N 2 O emission were measured over 49 days after applying FDE, FDE with DCD (DCD), and control (C, without N added) treatments. The amount of N applied as FDE was 120 kg of N ha -1 . Accumulated N 2 O emission during the 49 days after the application was 526, 237, and 174 g N 2 O-N ha -1 from the soil in the FDE, DCD, and C treatments, respectively. No significant differences were observed in accumulated NH 3 volatilization. Pasture yield was higher in DCD treatment, followed by C and FDE. Under low temperatures and high soil moisture conditions, adding DCD to the FDE could be considered an effective alternative to increase pasture yields, decrease N 2 O emissions, and maintain NH 3 volatilization, reducing total N losses to the atmosphere by about 14 %. Adding DCD to the FDE is a promising alternative for the more efficient N use of farm dairy effluents as fertilizer to mitigate N losses, tending to reduce N losses as N 2 O emissions. More studies are necessary to verify the result of using FDE + DCD under different soils and climates.

Drought effects on soil greenhouse gas fluxes in a boreal and a temperate forest

AbstractChanging water regimes (e.g. drought) have unknown long-term consequences on the stability and resilience of soil microorganisms who determine much of the carbon and nitrogen exchange between the biosphere and atmosphere. Shifts in their activity could feedback into ongoing climate change. In this study, we explored soil drought effects on soil greenhouse gas (GHG; CO2, CH4, N2O) fluxes over time in two sites: a boreal, coniferous forest in Finland (Hyytiälä) and a temperate, broadleaf forest in Austria (Rosalia). Topsoil moisture and topsoil temperature data were used to identify soil drought events, defined as when soil moisture is below the soil moisture at the permanent wilting point. Data over multiple years from automated GHG flux chambers installed on the forest floor were then analyzed using generalized additive models (GAM) to study whether GHG fluxes differed before and after drought events and whether there was an overall, multiyear temporal trend. Results showed CO2 and N2O emissions to be more affected by drought and long-term trends at Hyytiälä with increased CO2 emission and decreased N2O emissions both following drought and over the entire measurement period. CH4 uptake increased at both sites both during non-drought periods and as an overall, multiyear trend and was predominantly affected by soil moisture dynamics. Multiyear trends also suggest an increase in soil temperature in the boreal forest and a decrease in soil moisture in the temperate forest. These findings underline forests as an important sink for CH4, possibly with an increasing rate in a future climate.

A potential of iron slag-based soil amendment as a suppressor of greenhouse gas (CH4 and N2O) emissions in rice paddy

Iron slag-based silicate fertilizer (SF) has been utilized as a soil amendment in rice paddy fields for over 50 years. SF, which contains electron acceptors such as oxidized iron (Fe3+) compounds, is known to reduce methane (CH4) emissions, which have a global warming potential (GWP) of 23, higher than that of carbon dioxide (CO2). However, the dynamics of nitrous oxide (N2O), which has a GWP of 265, were questionable. Since the reduced Fe (Fe2+) can react as an electron donor, SF application might suppress N2O emissions by progressing N2O into nitrogen gas (N2) during the denitrification process. To verify the influence of SF application on two major greenhouse gas (GHG) dynamics during rice cultivation, three different kinds of SF were prepared by mixing iron rust (&amp;gt;99%, Fe2O3) as an electron acceptor with different ratios (0, 2.5, and 5%) and applied at the recommended level (1.5 Mg ha−1) for rice cultivation. SF application was effective in decreasing CH4 emissions in the earlier rice cropping season, and seasonal CH4 flux was more highly decreased with increasing the mixing ratio of iron rust from an average of 19% to 38%. Different from CH4 emissions, approximately 70% of seasonal N2O flux was released after drainage for rice harvesting. However, SF incorporation was very effective in decreasing N2O emissions by approximately 40% over the control. Reduced Fe2+ can be simultaneously oxidized into Fe3+ by releasing free electrons. The increased electron availability might develop more denitrification processes into N2 gas rather than NO and N2O and then decrease N2O emissions in the late rice cultivation season. We could find evidence of a more suppressed N2O flux by applying the electron acceptor-added SFs (SF2.5 and SF5.0) to a 49%–56% decrease over the control. The SF application was effective in increasing rice productivity, which showed a negative-quadratic response to the available silicate (SiO2) concentration in the soil at the harvesting stage. Grain yield was maximized at approximately 183 mg kg−1 of the available SiO2 concentration in the Korean rice paddy, with a 16% increase over no-SF application. Consequently, SF has an attractive potential as a soil amendment in rice paddy to decrease GHG emission impacts and increase rice productivity.

Selected Carbon and Nitrogen Compounds in a Maize Agroecosystem under the Use of Nitrogen Mineral Fertilizer, Farmyard Manure, Urease, and Nitrification Inhibitors

Carbon and nitrogen compounds in agroecosystems have attracted much attention in recent years due to their key roles in crop production and their impacts on environment quality and/or climate change. Since fertilization profoundly disrupted the C and N cycles, several mitigation and/or adaptation strategies, including the application of farmyard manure (FYM) and/or urease and nitrification inhibitors (UI and NI), have been developed. The aim of this study was to evaluate the contents of soil organic carbon and its fractions, the total and mineral forms of nitrogen, as well as CO2 and N2O emissions under mineral and organic fertilization with and without urease and nitrification inhibitors in a maize agroecosystem. A two-year field study was carried out on Cambisols (silt) in Poland. The experiment scheme included nine treatments: C (the control without fertilization), UAN (Urea Ammonium Nitrate), UAN+UI, UAN+NI, UAN+UI+NI, FYM with N mineral fertilizer base, FYM with N mineral fertilizer base+UI, FYM with N mineral fertilizer base+NI, and FYM with N mineral fertilizer base+UI+NI. It was found that treatments fertilized with cattle FYM were higher sinks and sources of C and N compounds in comparison to the UAN plots. The organic carbon, humic and humin acid, and total nitrogen concentrations, in contrast to ammonium and nitrate nitrogen, were not affected by the inhibitors added. Nitrification and urease inhibitors were effective in decreasing N2O emissions only in treatments that were exclusively applied with UAN and had no significant influence on CO2 emissions.