Increased N2O Emissions Research Articles

Long-term aged fibrous polypropylene microplastics promotes nitrous oxide, carbon dioxide, and methane emissions from a coastal wetland soil

Microplastics (MPs) has been suggested that it can greatly affect soil greenhouse gases (GHGs) emissions via altering soil physical, chemical, and biological properties. However, the difference in GHGs emissions, especially for those from coastal wetland soils, between varied aged MPs was rarely explored and the underlying mechanisms of GHGs emissions affected by the aged MPs were poorly understood. Therefore, the implications of fibrous polypropylene MPs (FPP-MPs) exposure on N2O, CO2, and CH4 emissions were examined by a 60-day soil incubation experiment. Compared with the control, the additions of un-aged FPP-MPs with both two rates (0.2 and 2 %) and aged FPP-MPs with a low rate (0.2 %) showed an insignificant effect on N2O emission, while the aged FPP-MPs added with a high rate (2 %) resulted in a remarkably increase in N2O emission, especially for those of the 30-day-aged FPP-MPs. A significant increase in CO2 emission was only observed in the 30-day-aged FPP-MPs treatments, compared with the control, and a higher addition rate produced a higher increase of CO2 emission. Regarding CH4 emission, it was significantly increased by adding aged FPP-MPs, and a longer aging period or/and a higher addition rate generated a higher degree of promotion of CH4 emission. However, compared with the CO2 emission, the quantity of CH4 emission was extremely low. These increased GHGs emissions can be ascribed to the improvements in soil physical structure and other chemical properties (e.g., pH and contents of soil organic matter and dissolved organic carbon) and enhancements in the abundances of denitrification- and carbon mineralization-related microorganisms. Overall, our results highlight the risk of elevated GHGs emissions from the soil polluted with 30-day-aged FPP-MPs, which should not be ignored as long-term aged FPP-MPs continue to increase in coastal wetland soils.

Seasonal variability of nitrous oxide concentrations and emissions in a temperate estuary

Abstract. Nitrous oxide (N2O) is a greenhouse gas, with a global warming potential 298 times that of carbon dioxide. Estuaries can be sources of N2O, but their emission estimates have significant uncertainties due to limited data availability and high spatiotemporal variability. We investigated the spatial and seasonal variability of dissolved N2O and its emissions along the Elbe Estuary (Germany), a well-mixed temperate estuary with high nutrient loading from agriculture. During nine research cruises performed between 2017 and 2022, we measured dissolved N2O concentrations, as well as dissolved nutrient and oxygen concentrations along the estuary, and calculated N2O saturations, flux densities, and emissions. We found that the estuary was a year-round source of N2O, with the highest emissions in winter when dissolved inorganic nitrogen (DIN) loads and wind speeds are high. However, in spring and summer, N2O saturations and emissions did not decrease alongside lower riverine nitrogen loads, suggesting that estuarine in situ N2O production is an important source of N2O. We identified two hotspot areas of N2O production: the Port of Hamburg, a major port region, and the mesohaline estuary near the maximum turbidity zone (MTZ). N2O production was fueled by the decomposition of riverine organic matter in the Hamburg Port and by marine organic matter in the MTZ. A comparison with previous measurements in the Elbe Estuary revealed that N2O saturation did not decrease alongside the decrease in DIN concentrations after a significant improvement of water quality in the 1990s that allowed for phytoplankton growth to re-establish in the river and estuary. The overarching control of phytoplankton growth on organic matter and, subsequently, on N2O production highlights the fact that eutrophication and elevated agricultural nutrient input can increase N2O emissions in estuaries.

Assessing nutrient budgets and N2O emission of newly constructed rice-giant freshwater prawn co-culture on reclaimed land

In recent years, newly constructed rice-giant river prawn (Macrobrachium rosenbergii) co-culture has been widely applied on reclaimed land in southeast China. Raising M. rosenbergii in paddy fields can alter nutrient budgets and have environmental impacts. However, the exact impacts remain unclear. Here, a field experiment was conducted using M. rosenbergii and Macrobrachium nipponense in reclaimed paddy fields to assess and compare the nutrient budgets and N2O emissions of the two ecosystems, henceforth referred to as RS1 and RS2, respectively. Each ecosystem was stocked with 150,000 post-larvae per ha and then compared with a rice monoculture system (RM) to evaluate the environmental impacts of rice-shrimp co-culture. In RS1, the main inputs for N and P were fertilizer and artificial feed, accounting for 59.35% and 34.01% of the total N inputs and 53.15% and 41.43% of the total P inputs, respectively. In RS2 and RM, fertilizers dominated the nutrient budget, accounting for more than 79.28% of the total nutrient input. Nutrient exports were dominated by rice (straw+grain) and commercial shrimp in RS1, accounting for 33.44% and 18.66% of N and 55.56% and 20.02% of P, respectively. The wastewater drainage, NH3 volatilization, and N2O emissions contributed to the remainder nutrient budget. Particularly, the N2O emission fluxes in RS1 (2.21 ± 0.32 kg·ha−1·yr−1) were significantly higher than those in RS2 (1.78 ± 0.24 kg·ha−1·yr−1) and RM (1.56 ± 0.17 kg·ha−1·yr−1) over the one-year experiment. Changes in environmental variables (including NH4+-N, NO2--N, DO, pH, SP, etc.) significantly contributed to the enhanced N2O emissions following the conversion from the reclaimed paddy field to RS1. These results implied that RS1 improved the yields of shrimp and rice grains but at the cost of increasing N2O emissions. Considering the wide distribution of reclaimed paddy fields in southeast China, M. rosenbergii could serve as an ideal alternative species in rice-shrimp co-culture systems to increase nutrient utilization efficiency, although N2O emissions still need to be reduced to mitigate the negative environmental impacts.

Interactive effect of biochar and urea addition increases plant growth and rhizosphere microbial activity and decreases N2O emissions

Simultaneous addition of biochar with applied N fertilizer was proposed as useful way how to improve soil fertility and reduce negative effects of nitrogen fertilization. A hypothesis that added N decreases root growth and soil microbial activity and increases N2O emissions while addition of biochar has opposite effect was tested. We further hypothesized that increased microbial activity in biochar-amended soil stimulates growth of subsequently cultivated plants.The supposed interactive effect of biochar and N-fertilizer was studied in pot experiment with cultivation of lettuce in soil amended with urea, biochar and their combination. In each pot, yield of plant biomass was determined and basal respiration, substrate-induced respiration and content of mineral N were determined in soil samples. Soil with roots decomposing after lettuce harvest was also analyzed and subsequently used for the cultivation of wheat plants.Emissions of N2O were measured following N application and measurement continued after harvest. Contrary to the hypothesis, N fertilization stimulated the growth of not only aboveground but also belowground plant biomass. Biochar increased growth of roots in agreement with the hypothesis. The effect of treatments on microbial biomass and respiration was relatively weak in the rhizosphere of growing plants. However, when roots were decomposed, lower Nmin and higher microbial biomass were observed in biochar amended soils. Biochar amendment significantly stimulated the yield of subsequently cultivated wheat. At the beginning of the experiment, N2O emissions were higher in biochar-amended soil. However, at the later phase of the experiment, cumulative emissions were lower in biochar-amended soils. Results suggest that biochar supports more efficient N utilization by plants and increases soil fertility. Biochar also decreases N losses through N2O emissions, even with simultaneous N fertilization.

A Portable Laser Spectroscopic System for Measuring Nitrous Oxide Emissions on Fertilized Cropland.

Nitrous oxide (laughing gas, N2O) is a relevant greenhouse gas. Agriculture contributes significantly to its emissions. As nitrogen fertilization has been identified as one of the main sources of N2O, controlled application and reduction of the amount of fertilizer adapted to crop demand is essential to reduce N2O emissions. This requires detailed studies of the local distribution of the N2O emission fluxes on different croplands. Consequently, frequent spatially resolved field measurements of N2O concentrations are needed. A precision in the ppb range close to the ambient N2O level of 333 ppb is necessary. Tunable laser absorption spectroscopy using quantum-cascade lasers (QCL) as a light source is an established technique for the measurement of N2O traces. We present the development and validation of a compact portable setup for on-site measurement of N2O emissions from the soil. The setup differs from previous solutions by using an interband cascade laser (ICL), which has significantly lower power consumption compared to a QCL. The portable measurement setup allows N2O emission fluxes to be determined with a precision of 3.5% with a measuring duration of 10 min. The developed system enables the detection of increased N2O emissions because of the fertilization of fields. High N2O emission fluxes are indicators of the overfertilization of the field. Directly after fertilization, N2O fluxes between 2.9 and 5.3 µL m-2 min-1 depending on the gas acquisition site are measured during the field tests. Over time, the fluxes decrease. The obtained results compare well with data from more precise but also more complex and maintenance-intensive instruments for atmospheric research. With this system, the soil moisture as well as the air humidity and air temperature are recorded. Strong influences on N2O fluxes by soil moisture were observed. The presented measurement system is a contribution to the establishment of mobile N2O screening systems that are robust in the field and suitable for comprehensive and routine detection of N2O emissions from soil.

Experimental study on combustion and emission of ternary-fuel combined supply SI engine with oxyhydrogen/butanol/gasoline at different excess air ratios

Both oxyhydrogen and butanol are renewable alternative fuels. Based on gasoline/butanol compound injection mode, although the introduction of oxyhydrogen can effectually enhance the optimal BDIr (butanol direct injection ratio), it also leads to an increase in NO emission. Therefore, this paper further studies the influence of lean-burn on the combustion and emission of ternary-fuel combined supply engine with oxyhydrogen/butanol/gasoline. In this paper, three variables are set, namely five BDIr (0–80%), five ONPIv (oxyhydrogen negative pressure inhalation volume) (0–16 L/min) and five λ (1.0–1.4). The results show that the larger the λ, the more significant the impact of oxyhydrogen on improving combustion and thermal transfer inside the cylinder. With the increase of ONPIv, CoVIMEP, CA 10–90 and CA 0-10 decrease, IMEP increases. Under all lean-burn conditions, ONPI can reduce CO and HC emissions. Under the condition of λ = 1.4, when ONPIv = 16 L/min, NO emission is 49.98% lower than the value of the original engine. Moreover, based on BDIr = 40%, 16 L/min ONPIv can elevate the λ limit from 1.41 to 1.83. In summary, “1.1 = λ ≤ 1.2+ONPIv = 16 L/min+60%≤BDIr≤80%” is the excellent control strategy of ONPI + BDI + GPI engine. The synergistic influence of lean-burn and larger BDIr can greatly reduce gasoline consumption and NOx emission caused by oxyhydrogen, but also worsen the mixture combustion atmosphere. ONPI can effectively improve this problem, and further increase energy efficiency. The coupling technology of ternary-fuel combined supply and lean-burn has a positive impact on improving thermal transfer efficiency, optimizing mixture combustion and decreasing gaseous emission.

Greenhouse Gas Emissions from Double-Season Rice Field under Different Tillage Practices and Fertilization Managements in Southeast China

To better understand the effects of tillage practice and fertilization management on greenhouse gas emissions and yields, a four-year field experiment was conducted to assess the effects of tillage practices (rotary tillage (RT) and no tillage (NT)) on the emissions of methane (CH4) and nitrous oxide (N2O) and rice yield under four fertilization management strategies (no fertilizer without straw (CK), inorganic fertilizer without straw (F), inorganic fertilize with biochar (FB), and inorganic fertilizer with straw (FS)). The results showed that NT significantly reduced CH4 emissions by 21.1% and 52.6% compared to RT in early and late rice, respectively. Conversely, NT led to a significant increase in N2O emissions by 101.0%, 79.0%, and 220.8% during the early rice, late rice, and fallow periods. Nevertheless, global warming potential (GWP) and greenhouse gas intensity (GHGI) were significantly mitigated, respectively, by 36.4% and 35.9% in NT, compared to RT treatment. There were significant interactions between tillage practice and fertilization management. Compared with CK, the F and FB treatments significantly reduced the GWP, respectively, by 40.4% and 53.8%, as well as the GHGI, respectively, by 58.2% and 69.9% in the RT condition; however, no significant difference was found under the NT condition. In contrast, the FS treatment significantly increased GWP and GHGI in both the RT and NT conditions. Overall, FB treatment had the same significantly low GHGI rating, with a value of 0.44 kg CO2-eq kg−1 yield year−1 in RT and NT. Thus, the conversion of straw to biochar and its application to rice fields is a potentially sustainable agricultural strategy for mitigating GHG emissions and increasing yields. This study provides theoretical and practical support for double-season rice production in climate-smart agriculture.

The driving effects of nitrogen deposition on nitrous oxide and associated gene abundances at two water table levels in an alpine peatland

Alpine peatlands are recognized as a weak or negligible source of nitrous oxide (N2O). Anthropogenic activities and climate change resulted in the altered water table (WT) levels and increased nitrogen (N) deposition, which could potentially transition this habitat into a N2O emission hotspot. However, the underlying mechanism related with the effects is still uncertain. Hence, we conducted a mesocosm experiment to address the response of growing-season N2O emissions and the gene abundances of nitrification (bacterial amoA) and denitrification (narG, nirS, norB and nosZ) to the increased N deposition (20 kg N ha−1 yr−1) at two WT levels (WT−30, 30 cm below soil surface; WT10, 10 cm above soil surface) in the Zoige alpine peatland, Qinghai-Tibetan Plateau. The results showed that the WT did not affect N2O emissions, and this was attributed with the limitation of soil NO3−. The higher WT level increased denitrification (narG and nirS gene abundance) resulting in the depletion of soil NO3−, but the consequent NO3− deficiency further limited denitrification, while the WT did not affect nitrification (bacterial amoA gene abundance). Meanwhile, the N deposition increased N2O emissions, regardless of WT levels. This was associated with the N-deposition induced increase in denitrification-related gene abundances of narG, nirS, norB and nosZ at WT−30 and narG at WT10. Additionally, the N2O emission factor assigned to N deposition was 1.3 % at WT−30 and 0.9 % at WT10, respectively. Our study provided comprehensive understanding of the mechanisms referring N2O emissions in response to the interactions between climate change and human disturbance from this high-altitude peatland.

Effects of nitrogen addition on greenhouse gas fluxes during continuous freeze-thaw cycles in a cold temperate forest.

Both nitrogen (N) deposition and soil freeze-thaw cycles (FTCs) induce pulses of greenhouse gas (GHG) emissions in cold temperate zones due to changes in soil carbon (C) and nitrogen (N) turnover. However, the combined effects of N addition and FTCs on GHG fluxes have received little research attention, particularly in boreal forests. We conducted a laboratory incubation experiment using intact soil cores from Rhododendron dauricum-Larix dahurica plots to investigate the GHG flux response to these combined effects. We separated the soil samples into seven groups (no, low, medium, and high sodium nitrate addition and low, medium, and high ammonium chloride addition) and exposed each group to continuous FTC conditions. The N2O and CO2 emissions were eventually stimulated by the FTCs, while CH4 uptake was inhibited by FTCs but responded differently under different N addition treatments. All the treatments had substantially increased N2O emissions compared to the control. However, the soil respiration rate significantly increased only with medium sodium nitrate addition, and high levels of N addition (regardless of form) inhibited CH4 uptake. These findings demonstrate that FTCs and N addition (in various forms and levels) have considerable effects on GHG emissions in temperate forest ecosystems. Moreover, dissolved organic carbon (DOC), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and inorganic nitrogen in soil are potential factors that drive GHG emissions and are necessary considerations in predicting future feedback effects of GHG emissions on climate change.

Paddock-scale carbon and greenhouse gas budgets in the first year following the renewal of an intensively grazed perennial pasture

Pasture renewal is an important tool commonly used by land managers to maintain a healthy productive pasture sward that can be used for grazing by animals or harvesting. However, there have been few assessments of the impact of pasture renewal on greenhouse gas (GHG) emissions, particularly in grazed pastures. We investigated how pasture renewal impacted the carbon (C), nitrous oxide (N2O) and GHG budgets of an intensively managed rotationally grazed New Zealand pasture by comparing adjacent paddocks with one undergoing pasture renewal. The eddy covariance technique was used to measure carbon dioxide (CO2), N2O and methane (CH4) fluxes which were coupled to measurements and estimates of non-gaseous C flows to calculate the net ecosystem carbon balance and total GHG budget. We measured GHG emissions directly due to pasture renewal of 695 g CO2-eq m-2 during the 66 days between herbicide application and the first grazing of the new pasture sward. Using an adjacent paddock as a control, the net effect of pasture renewal was 358 g CO2-eq m-2, primarily due to an additional grazing event in the non-renewed pasture and the associated CO2 and CH4 emissions associated with digestion of the pasture by the ruminant animals. The pasture renewal emissions were primarily due to C loss with increased N2O emissions accounting for only 10% of total GHG emissions during the renewal period. Total GHG emissions were 2017 g CO2-eq m-2 y-1 for the first year (before pasture renewal), and 1452 and 1894 g CO2-eq m-2 y-1 for the non-renewed and renewed pastures, respectively, in the second (renewal) year. The only significant difference was between the first year and the non-renewed pasture in the second year. We concluded that pasture renewal increased C loss, N2O emissions and total GHG emissions during the renewal period, but when extended to the annual timescale, the effect was insignificant compared to interannual variability.

Decrease of nitrogen cycle gene abundance and promotion of soil microbial-N saturation restrain increases in N2O emissions in a temperate forest with long-term nitrogen addition

Increases in soil available nitrogen (N) influence N-cycle gene abundances and emission of nitrous oxide (N2O), which is primarily due to N-induced soil acidification in forest. Moreover, the extent of microbial-N saturation could control microbial activity and N2O emission. The contributions of N-induced alterations of microbial-N saturation and N-cycle gene abundances to N2O emission have rarely been quantified. Here, the mechanism underlying N2O emission under N additions (three chemical forms of N, i.e., NO3−-N, NH4+-N and NH4NO3–N, and each at two rates, 50 and 150 kg N ha−1 year−1, respectively) spanning 2011–2021 was investigated in a temperate forest in Beijing. Results showed N2O emissions increased at both low and high N rates of all the three forms compared with control during the whole experiment. However, N2O emissions were lower in high rate of NH4NO3–N and NH4+-N treatments than the corresponding low N rates in the recent three years. Effects of N on microbial-N saturation and abundances of N-cycle genes were dependent on the N rate and form as well as experimental time. Specifically, negative effects of N on N-cycle gene abundances and positive effects of N on microbial-N saturation were demonstrated in high N rate treatments, particularly with NH4+ addition during 2019–2021. Such effects were associated with soil acidification. A hump-backed trend between microbial-N saturation and N2O emissions was observed, suggesting N2O emissions decreased with increase of the microbial-N saturation. Furthermore, N-induced decreases in N-cycle gene abundances restrained N2O emissions. In particular, the nitrification process, dominated by ammonia-oxidize archaea, is critical to determination of N2O emissions in response to the N addition in the temperate forest. We confirmed N addition promoted soil microbial-N saturation and reduced N-cycle gene abundances, which restrained the continuous increase in N2O emissions. It is important for understanding the forest-N-microbe nexus under climate change.

An innovative method of ammonia use in a light-duty automotive diesel engine to enhance diesel combustion, performance, and emissions

This study investigated the novel method of ammonia use in a light-duty automotive diesel engine. An emulsification technique and ammonia solution are combined and adopted to prepare ammonia solution in diesel emulsion referred to as emulsified diesel-ammonia solution (EDAS) and tested under similar diesel combustion conditions. The ammonia solution concentration in EDAS was fixed as 10% by volume (EDAS10) with 2% v/v of surfactant to avoid excessive ammonia slip, corrosive effects, and oxides of nitrogen (NOx) formation. The aim of this study is to explore the effect of presence of hydrogen in EDAS10 on the diesel combustion process under high-pressure multiple injection strategies. Experiments were performed at low, medium, and high loads at the same combustion phasing (CA50) and total energy input as that of diesel to investigate the influence of EDAS10 on combustion, performance, and emissions. The start of injection of EDAS10 and exhaust gas recirculation rate was varied to attain the CA50. The combustion results showed that the EDAS10 blend had increased the heat release rate in the premixed combustion phase with shortened duration and decreased the heat release rate in the diffusion combustion phase compared to neat diesel operation. Double and triple injection of EDAS10 blend also increased the indicated and brake thermal efficiencies by about 4–7% than neat diesel operation. A decrease in 50–67% unburnt emissions, 8–13% decrease in smoke, and 7–19% increase in NO emissions, 2–10% increase in CO2emissions were observed with EDAS10 when compared to diesel operation.

Biodegradable film mulching reduces the climate cost of saving water without yield penalty in dryland rice production

Global resource shortage and climate change are the grandest challenges facing traditional flooded rice cultivation. In this study, different rice production patterns were examined to quantify the effects on crop production, greenhouse gas (GHG) emissions, and synchronization index of water conservation and GHG mitigation. The results indicated that rice direct dryland seeding with biodegradable mulching showed the best performance in maintaining yield (7,802 kg ha−1), saving irrigation water (67%), increasing net profit (619 CNY ha−1), reducing CH4 emissions (73%), global warming potential (69%) and GHG intensity (69%), although it increased N2O emissions (59%), compared with continuous flooding. Rice direct dryland seeding without mulching showed similar water savings and GHG mitigation with mulching, but it caused yield and net profit reductions by 20% and 40%, and synchronization index increment by 127%. These findings can guide the implementation of dryland rice production in priority areas, contributing to high-efficiency, eco-friendly agricultural cultivation.

Effect of high labile biochar on N2O emission from upland soils: A decision tree analysis and an incubation experiment

While there are extensive studies reporting a reduction in N2O emission by biochar addition, there are some cases that showed an increase in N2O emission. To identify the primary conditions that lead to an increase in N2O emissions, we conducted a decision tree analysis of 148 observations from 25 published papers. It was verified that biochar made with rice husk, rice straw, nut-shell, pits, and stones had a higher chance of increasing N2O emissions than biochar made with wood, herbaceous, and biosolid. Moreover, it was also demonstrated that the probability of increasing N2O emission by former group biochar was higher in the low pH soils. The latter group of biochar showed the lowest probability of increasing N2O emission in soil with low soil organic carbon (SOC) content. The decision tree analysis results led us to conduct an incubation experiment to understand the underlying mechanisms under which conditions biochar increases or decreases soil N2O emissions. The soils amended with urea and 4% (w/w) biochars (cocopeat: CPB, rice husk biochar: RHB, and wood pellets: WPB) were incubated for 15 days on aerobic condition. As a result, N2O emissions increased in the soils amended with CPB and RHB, which was consistent with decision tree analysis. The high labile matter content of these biochar could stimulate both heterotrophic denitrification and nitrification-mediated processes. In the soil with the high labile matter biochar which increased soil pH throughout the experimental period (CPB treatment), NO2− was accumulated and gene abundance of nitrite-oxidizing bacteria were reduced, which might be caused by NH3 toxicity. Our results can be utilized as a practical guideline to maximize biochar's climate change mitigation potential.

Nitrous oxide emissions after struvite application in relation to soil P status

PurposeAlthough struvite (MgNH4PO4·6H2O) is mostly considered to be a novel phosphorus (P) fertiliser, it does contain a significant amount of nitrogen (N). Yet, relatively little is known about the soil N dynamics in struvite-amended soils. Here, we focus on how struvite application impacts emissions of the greenhouse gas nitrous oxide (N2O), in relation to soil P status.MethodsWe conducted a 54-day greenhouse pot experiment on two similar soils with different P status (“low-P soil”; “high-P soil”) seeded with Lolium perenne L. We applied seven fertiliser treatments (Control; Struvite granules; Struvite powder; Urea; Triple superphosphate (TSP); TSP + Struvite granule; TSP + Urea). Except for the unfertilised Control and the TSP treatments, N application rate was 150 kg N‧ha−1. Nitrous oxide (N2O) fluxes, aboveground yield, plant N and P uptake and readily plant-available soil N and P contents were measured.ResultsIn the low-P soil, none of the fertiliser treatments induced a significant increase in N2O emission compared to the control. In the high-P soil, struvite application resulted in lower emissions than urea application, statistically not different from the control treatment. Struvite powder significantly increased both plant N and P uptake compared to granular struvite and the resulting yield was similar to conventional fertilisation (TSP and Urea). Any struvite application also resulted in lower readily plant-available soil nitrate contents than urea.ConclusionOur results suggest that struvite fertilisation can reduce the risk of gaseous N losses without compromising agronomic performance. Pulverizing struvite granules further promotes its dissolution, which could be useful for crops with early nutrient needs.

New trends in sugarcane fertilization: Implications for NH3 volatilization, N2O emissions and crop yields

Recycling nutrients helps to reduce the environmental impact of agriculture and contributes to alleviating the effects of global climate change. A recent trend in sugarcane cultivation is the application of concentrated vinasse (CV) combined with fertilizers into an organo-mineral formulation to improve logistics, reduce costs and foster the circular economy. However, the implications of the application of such organo-mineral formulation in sugarcane fields are unclear. In this study, we evaluated the effects of the organo-mineral formulation containing granular urea (UR), and a nitrification inhibitor (NI) on crop yields, NH3 volatilization, and N2O emissions. Field experiments were conducted during two fertilization seasons, dry and wet, and the treatments were: control; UR; UR + NI; CV; CV + UR; and CV + UR + NI. CV was applied at 7 m3 ha−1. The treatments (except control and CV) were balanced to receive the same amount of N and K. Compared with UR, the organo-mineral formulation of CV + UR decreased NH3 volatilization losses from 7% to 4% in the dry season and from 3.5% to 0.5% in the wet season. Conversely, compared with UR, N2O emissions increased significantly (p ≤ 0.05) in CV + UR in the wet season from 1% to 2% of applied N. In the dry season, no differences were observed. The addition of NI was effective in mitigating N2O emissions in both seasons. Emission reductions ranged from 43 to 48% in the dry season and from 71 to 84%, in the wet season. Fertilization with UR or the organo-mineral formulation influenced sugarcane yield only in the dry season, with the highest yield in CV + UR. NI did not affect crop yield. In general, emission intensities (kg CO2eq Mg−1 of stalk) were highest in CV + UR. We conclude that the organo-mineral formulation reduced NH3 losses and increased N2O emissions compared with regular solid fertilizer and that NI was effective for mitigating N2O emissions.

Opposite response of N2O emissions in different seasons to warming and precipitation addition on a temperate steppe

AbstractClimate change is an important issue that affects both global warming and precipitation, and the main cause is increased N2O emissions. Temperature and moisture are key factors in grassland ecosystem's response to climate change, and they can affect N2O fluxes. To clarify the impacts of warming and precipitation changes on N2O fluxes, an experiment was conducted in a semiarid steppe in Inner Mongolia, China over a nine‐year period (2011–2019). Plant productivity and soil nutrient dynamics were examined concurrently from 2017 to 2019, and N2O fluxes were monitored in response to different treatment conditions: control (C), warming (W), precipitation addition (P), and warming and precipitation addition (WP). The results showed that N2O emissions in the growing season were higher than those in the nongrowing season. Warming and precipitation addition had no significant effect on N2O fluxes compared with ambient conditions. Compared with P treatment, warming increased N2O flux in nongrowing season and decreased it in growing season. N2O flux was positively correlated with soil temperature and moisture (p < 0.05). Warming had a significant positive effect on soil NH4+‐N, whereas additional precipitation had a large positive effect on soil total nitrogen and soil nitrate nitrogen. With the WP treatment, soil microbial biomass nitrogen (MBN) and soil microbial biomass carbon (MBC) increased by 53.8% and 41.9%, respectively. The decrease in N2O emissions during the growing season in the W treatment compared with the P treatment may be largely attributed to the greater dominance of Leymus chinensis. The results highlight that changes in species dominance play an important role in regulating N2O emissions, and that the N2O fluxes in the nongrowing season account for a large proportion of the changes in N2O fluxes. Therefore, The warming effects on N2O emissions during nongrowing seasons should be further investigated.

Arbuscular mycorrhizal fungi mitigate earthworm-induced N2O emissions from upland soil in a rice-rotated wheat farming system

Earthworms are important for soil processes in arable cropping systems, and affect the development of arbuscular mycorrhizal fungi (AMF) which may combinely play a crucial role in soil nitrogen (N) cycling. However, the information is limited about their interaction on N2O emissions. A two-factorial microcosm field experiment was established to identify the interactive effects of earthworms and AMF on N2O emissions from a rice-rotated wheat field and explore its underlying mechanisms about nitrification and denitrification processes. The results showed that earthworm addition (+E) increased cumulative N2O emissions during the whole growth stage by 236.7 % compared with no earthworms (−E). Cumulative N2O emissions during the jointing and booting stages contributed to 58.7 % of that during the whole growth stage. Higher N2O emissions under +E were attributed to changes in soil organic carbon (SOC) and NH4+ concentration. SOC was positively correlated to gene abundances associated with N2O reduction (e.g., nosZ), and earthworm activity enhanced SOC mineralization and reduced SOC concentration, thus increasing N2O emissions. A negative correlation between NH4+ and N2O emissions, and lower NH4+ under +E indicated that earthworms enhanced nitrification intensity using NH4+ as substrates. Interestingly, AMF normal (+A) significantly decreased cumulative N2O emissions by 37.3 % compared with mycorrhizal suppression (−A) and the interaction with earthworms can further decreased N2O emissions by 37.0 % compared with -E-A (P < 0.05). This can be explained by higher NH4+, lower NO3− concentrations, and lower abundance of nitrification-associated genes (e.g., AOA and AOB) at the booting stage under +A, suggesting that AMF reduced N2O emissions mainly through lowering nitrification intensity. The results highlight that earthworms increase N2O emissions while AMF can mitigate earthworm-induced N2O emissions, and enhance our understanding on the soil N cycle in terms of N2O production in the presence of AMF and earthworms.

Fuel Consumption and Emission Reduction for Non-Road Diesel Engines with Electrically Heated Catalysts

In this study, an exhaust system compliant with future regulations was developed for a non-road 110PS engine with a Tier-4f aftertreatment system, and the emission characteristics of the engine were investigated in the non-road transient mode (NRTC). For the system to comply with future exhaust regulations, a DPF was installed, and an electrical heated catalyst (EHC) device was installed to manage exhaust gas temperature. The emission characteristics of exhaust gas were examined according to the power and applied duration of EHC, and the effects of catalyst coating and the urea water solution (UWS) injection map on NOx reduction, NH3 slip, and N2O emissions in NRTC mode were investigated. The application of a 4 kW class EHC system enables the lowering of the injection starting temperature of the UWS, as reliable gas heating (heating duration control) is guaranteed. When the injection starting temperature (based on the SCR inlet temperature) was set to 150 °C, NSR map, (III) in conjunction with the operation of the EHC, effectively achieved significant NOx reduction in NRTC mode without deposit and wetting occurring in the mixer and exhaust pipe. Regarding changes in EHC power from 3 kW to 4 kW, it was observed that a NOx reduction of 0.05 g/kWh occurs in the cold NRTC mode, but in the hot NRTC mode, it was found that the relative decrease in the UWS is due to the increased NO2 conversion efficiency as a result of the oxidation catalyst, making 3 kW more advantageous. Furthermore, due to the increase in NO2 concentration caused by the oxidation catalyst and the increase in the low-temperature injected UWS, NH4NO3 was formed, which resulted in an increase in PM emissions and a significant increase in N2O emissions around an exhaust temperature of 250 °C. When the EHC power was set to 3 kW and the volume of oxidation catalyst and the amount of UWS injection were adjusted, applying EHC in the NRTC mode resulted in an additional NOx reduction of 58.6% and 88.4% in cold and hot modes, respectively, compared with not using EHC, with a fuel penalty of approximately 1.67%, while limiting the peak concentrations of N2O and NH3.

Trade-offs between wheat soil N2O emissions and C sequestration under straw return, elevated CO2 concentration, and elevated temperature

The feedback between nitrous oxide (N2O) emissions, straw management and future climate scenarios is not well understood, especially in wheat ecosystems. In this study, the changes in N2O emissions, soil properties, enzymes, and functional genes involved in N cycling were measured with straw return (incorporation and mulching) and straw removal, under elevated [CO2] (+200 μmol mol−1 above ambient [CO2]), elevated temperature (+2 °C above ambient temperature), and their combination. The net global warming potential (NGWP) and greenhouse gas intensity (GHGI) were evaluated in combination with greenhouse gas emissions, yield, and soil organic carbon (C) sequestration. Compared with the ambient condition, elevated [CO2] and elevated temperature suppressed N2O emission by 41 %–46 %. Straw return significantly increased N2O emission by 31 %–109 % through increasing soil C and N substrates and denitrifying genes abundance, compared with straw removal. In addition, the impact of straw return on N2O emission was greater than that of elevated [CO2] or temperature. Straw return generally reduced NGWP by 166.2–3353.3 kg CO2-eq ha−1 and GHGI by 0.4–1.1 kg CO2-eq kg−1 through increasing soil organic C sequestration by 0.1–1.1 t C ha−1 and grain yield by 280.8 kg ha−1–1595.4 kg ha−1. Straw return would stimulate N2O emissions from this wheat cropping system under future warmer, elevated [CO2] climates, but simultaneously increase grain yield and soil organic C sequestration to a greater extent. Overall, straw return is beneficial to climate change mitigation; in particular, straw incorporation would be more effective than straw mulching.