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NO 2 − plays a crucial role in regulating N 2 O formation from the soil, while how it affects the production of soil N 2 O is still not well understood. In this study, N 2 O and NO emissions from an agricultural field of the North China Plain (NCP) were comparatively investigated under five different fertilizer treatments (NH 4 +, NO 3 −, NO 2 −, NH 4 + + NO 2 − and NO 3 − + NO 2 −). Additionally, soil NH 4 +, NO 2 − and NO 3 − concentrations and the abundance of functional genes associated with nitrogen cycling were also analyzed in the incubation experiment. The results showed that the N 2 O average fluxes from the complex treatments of NO 2 − + NO 3 - were 1.4–2.4 times the sum of those from the separate treatments of NO 2 - and NO 3 - whereas from the complex treatments of NO 2 - + NH 4 + were a factor of 1-1.4 larger than those from the separate treatments of NO 2 − and NH 4 +, indicating the coupling interaction of NO 2 − with NH 4 + or NO 3 − makes a remarkable contribution to N 2 O emission from the soil. Significant reduction of the activity of N 2 O reductase was found in the soil with the addition of NO 2 −, which favored the accumulation of N 2 O formed through nitrification of NH 4 + and denitrification of NO 2 −, resulting in relatively high N 2 O emissions from the complex treatments. As the intermediate product of nitrification and denitrification, NO 2 − produced is also expected to interact with NH 4 + or NO 3 - to promote N 2 O emission from the soil, especially during fertilization events when NO 2 − is easily accumulated due to the acceleration of the nitrification and denitrification processes. Unlabelled Image • Coupling interaction of NO 2 − with NH 4 + or NO 3 − is a great source of N 2 O emission. • The addition of NO 2 − could significantly promote the N 2 O emission. • The activity of N 2 O reductase decreased after the introduce of NO 2 −. [ABSTRACT FROM AUTHOR]

This study intended to evaluate the combined effects of both biochar and organic fertilizer on nitrous oxide (N 2 O) fluxes and composition of nitrifier and denitrifier of saline-alkali soil. Therefore, four different treatments such as CK (only chemical fertilizer), B (only biochar), M (only organic fertilizer), BM (B:M = 1:1) were used in this experiment. The results showed that N 2 O emissions were decreased in B and BM treatments compare to the control. In contrast, N 2 O emissions were highest before day 12 but lowest after day 19 in M treatment compare to the control. Application of biochar, organic fertilizer and biochar plus organic fertilizer decreased the nirS and nirK genes copies and enhanced the nosZ gene copies which resulting in the lower N 2 O fluxes. The ammonia-oxidizing bacteria (AOB) amoA and nirK genes copies were significantly increased by organic fertilizer before day 12, leading to high N 2 O emissions. The genera Nitrosospira (AOB) and Nitrososphaera (ammonia-oxidizing archaea, AOA) assumed absolute superiority. Additionally, Nitrosospira (AOB) was also appeared in nirK -type denitrifiers, illustrating denitrification was carried out by nitrifiers. The genera Azospirillum (nirS), Burkholderia (nosZ) and Polymorphum (nosZ) were dominant in CK. There was only one dominant genus, Mesorhizobium (nosZ) in the B treatment. The genera Mesorhizobium (nirK), Azoarcus (nirS), Kocuria (nirS) and Pseudomonas (nosZ) occupied the main status in the M treatment. The relative abundance of Rhodanobacter (nirS) and Azospirillum (nosZ) were higher in the BM treatment compared with other treatments. Soil water content (SWC), pH, NH 4 +-N and NO 3 −-N were the main factors affecting AOB and denitrifiers, which influencing N 2 O emissions. Overall, combined application of biochar and organic fertilizer can reduce the N 2 O emission where AOB and nirK -type denitrifier were the main contributors to the N 2 O emission. Unlabelled Image • Combined application of biochar and organic fertilizer decreased the N 2 O emission. • Biochar plus organic fertilizer decreased the nirS and enhanced the nosZ abundances. • The genus Nitrosospira was the main contributor for N 2 O emission. • SWC, pH, NH 4 +-N and NO 3 −-N were the main factors affecting AOB and denitrifiers, and then influencing N 2 O emissions. [ABSTRACT FROM AUTHOR]

The global climate change is related with greenhouse gas emission from cultivated soils – carbon dioxide, methane and nitrous oxide. The emissions of N 2 O also have negative influence on ozone layer of our planet. The major source of the nitrous oxide is denitrification process in soil, which controlled by specific soil microbe society. The pot experiment with flooding to accelerate the denitrification process and the application of the monosilicic acid as a source of soluble form of Si was carried out with barley. Several forms of nitrous oxide emission (unlimited carbon denitrification and potential denitrification with or without ethylene application) were measured. The obtained data showed that the application of monosilicic acid to brown soil when growing barley under conditions of soil flooding has a significant effect on nitrogen emission and can change the N 2 O:N 2 ratio. The application of the monosilicic acid reduced the uC-D N 2 O emission, while increased the PD N emission. Generally the application of the water soluble Si decreased the N 2 O:N 2 ratio. We suggested that the presence of monosilicic acid in the system provides a more complete denitrification process with the formation of N 2 in the NO 3 − → NO 2 − → NO→N 2 O → N 2 reaction sequence, while the deficiency of bioactive Si mainly provides the formation and emission of N 2 O. Considering that N 2 is not a greenhouse gas, we can conclude that application of monosilicic acid to the soil can reduce greenhouse gas emissions and reduce the impact of global climate change on agricultural activity. Unlabelled Image • The application of monosilicic acid increases barley resistance under hypoxia. • High concentration of the monosilicic acid in flooded soil provides N 2 emission increasing and reduction N 2 O emission. • Increasing of the monosilicic acid in the soil provides more complete denitrification process in soil. [ABSTRACT FROM AUTHOR]

Concentrations and emissions of greenhouse gases CO 2 , CH 4 , and N 2 O commonly are examined individually in aquatic environments in which each is expected to be relatively important; however, their co-occurrence and dynamic interactions in fluvial settings could provide important information about their controlling biogeochemical processes and potential contributions to global climate change. Spatial and temporal variability of CH 4 , N 2 O, and CO 2 concentrations were measured from June 1999 to September 2003 in two nitrate-rich (40–1200 μM) streams draining agricultural land in the midwestern USA that differed ~13-fold in flow. Seasonal (biweekly), diel (hourly), and transport-oriented (reach-scale) sampling approaches were compared. Dissolved gas concentrations exceeded atmospheric equilibrium values up to 700- and 16-fold, for CH 4 and N 2 O, respectively. Mean concentrations were higher in the larger stream than in the smaller stream. In both streams, CH 4 emissions were generally higher in summer-fall and negatively correlated with flow and NO 3 − concentration while N 2 O emissions were generally higher in winter/spring and positively correlated with flow and NO 3 −. In the small stream, diel variations in the concentrations, emissions, and isotopic compositions of CH 4 , N 2 O, and NO 2 − resulted from diel variations in sources, sinks, and air-water gas exchange velocities. Seasonal mean total (CH 4 + N 2 O) area-normalized emission rates, expressed as CO 2 warming potential equivalents, were similar for the two streams, but the total reach-scale emission rate for the larger stream, including CO 2 , was about 2.9 times that of the smaller stream (131.6 vs 46.0 kg CO 2 equivalents km−1 day−1, respectively). The CH 4 contribution to this flux was 9–28%, despite the relatively high NO 3 − and O 2 concentrations in the streams, indicating contributions from upwelling groundwater or reactions in streambed sediment. Unlabelled Image • CH 4 concentrations were higher than N 2 O concentration in nitrate-rich streams. • CH 4 and N 2 O concentrations exhibited seasonal, synoptic and diel variations. • CH 4 and N 2 O concentrations were inversely correlated seasonally. • Combined CH 4 and N 2 O emissions resulted in seasonally constant global warming potentials. [ABSTRACT FROM AUTHOR]

This study argues that several metrics are necessary to build up a picture of yield gain and nitrogen losses for ryegrass sheep pastures. Metrics of resource use efficiency, nitrous oxide emission factor, leached and emitted nitrogen per unit product are used to encompass yield gain and losses relating to nitrogen. These metrics are calculated from field system simulations using the DAYCENT model, validated from field sensor measurements and observations relating to crop yield, fertilizer applied, ammonium in soil and nitrate in soil and water, nitrous oxide and soil moisture. Three ryegrass pastures with traditional management for sheep grazing and silage are studied. As expected, the metrics between long-term ryegrass swards in this study are not very dissimilar. Slight differences between simulations of different field systems likely result from varying soil bulk density, as revealed by a sensitivity analysis applied to DAYCENT. The field with the highest resource use efficiency was also the field with the lowest leached inorganic nitrogen per unit product, and vice versa. Field system simulation using climate projections indicates an increase in nitrogen loss to water and air, with a corresponding increase in biomass. If we simulate both nitrogen loss by leaching and by gaseous emission, we obtain a fuller picture. Under climate projections, the field with the lowest determined nitrous oxide emissions factor, had a relatively high leached nitrogen per product amongst the three fields. When management differences were investigated, the amount of nitrous oxide per unit biomass was found to be significantly higher for an annual management of grazing only, than a silage harvest plus grazing, likely relating to the increased period of livestock on pasture. This work emphasizes how several metrics validated by auto-sampled data provide a measure of nitrogen loss, efficiency and best management practise. Unlabelled Image • Provides yield-nitrogen metrics for ryegrass sheep pastures • Combination of climate, sensor and sampling data applied to agri-system modelling • Highest resource use efficiency coincides with lowest leaching per unit product. • N 2 O per unit biomass significantly lower for silage & grazing than grazing only. • Several related metrics reveal info about the system, hidden by using one metric. [ABSTRACT FROM AUTHOR]

Abstract Calculated N 2 O emission factors (EFs) of applied nitrogen (N) fertilizer are currently based upon a single, universal value advocated by the IPCC (Inter-governmental Panel on Climate Change) even though EFs are thought to vary with climate and soil types. Here, we compiled and analyzed 151 N 2 O EF values from agricultural fields across China. The EF of synthetic N applied to these croplands was 0.60%, on average, but differed significantly among six climatic zones across the country, with the highest EF found in the north subtropical zone for upland fields (0.93%) and the lowest in the middle subtropical zone for paddy fields (0.20%). Precipitation and soil pH, which showed non-linear relationships with EF, are among the factors governing it, explaining 7.0% and 8.0% of the regional variation in EFs, respectively. Annual precipitation was the key factor regulating N 2 O emissions from synthetic N fertilizers. Among crop types, legume crops had the highest EFs, which were significantly (P < 0.05) higher than those of cereals. Total soil N 2 O emissions from fertilized croplands with maize, rice, wheat, and vegetables in China, calculated using the climatic zone (regional) EFs, were estimated to be 239 Gg N yr−1 with an uncertainty of 21%. Importantly, this value was substantially (33%) lower than that (357 Gg N yr−1) derived from the IPCC default EF but close to the 253 Gg N yr−1 estimated using crop-specific EFs. N 2 O emissions from applied synthetic N fertilizer accounted for 66.5% of the total annual N 2 O emissions from China's maize, rice, wheat and vegetable fields. Taken together, our study's results strongly suggest that regional EFs should be included for accurate N 2 O inventories from croplands across China. Graphical abstract Unlabelled Image Highlights • Croplands in China had a mean soil nitrous oxide emission factor of 0.60%. • This emission factor (EF) from China's croplands varied among climatic zones. • Precipitation and soil pH contributed significantly for regional EFs variation. • IPCC's default EF would overestimates N 2 O emissions from China's croplands. • The relationship of EF to soil and climatic variables was non-linear (quadratic). [ABSTRACT FROM AUTHOR]

Abstract Alkaline residuals, such as wood ash and lime mud generated from pulp and paper mills, could be recycled as liming agents in sugar maple (Acer saccharum Marsh.) forests affected by soil acidification. The objectives of this study were (1) to evaluate soil chemistry, in particular soil acidity, after the application of three alkaline residuals from the pulp and paper industry, and (2) to determine if these alkaline residuals altered soil greenhouse gas (GHG) emissions as a result of the change in soil pH or due to their chemical composition. Soil properties and GHG fluxes were monitored for two years after alkaline residuals were applied to six forest sites dominated by sugar maple in southeastern Quebec, Canada. Each site received six treatments: wood ash applied at 5, 10 and 20 t ha−1, lime mud (7.5 t ha−1), a mixture of slaker grits and green liquor sludge (7 t ha−1) and an unamended control. These treatments had acid-neutralizing power from 0 to 9 t ha−1. All alkaline residuals buffered soil acidity as a function of their neutralizing power, and more neutralization occurred in the forest floor layer than in the underlying mineral soil. In the forest floor, the alkaline residual treatments significantly increased pH by more than one unit, nearly doubled the base saturation, and reduced exchangeable acidity, Al and Fe concentrations compared to control plots. The CO 2 and N 2 O fluxes were lower after application of alkaline residuals, and this was related to the soil pH increase and the type of alkaline residual applied. Lime mud was more effective at reducing GHG fluxes than other alkaline residuals. We conclude that these alkaline residuals can effectively counteract soil acidity in sugar maple forests without increasing soil GHG emissions, at least in the short term. Graphical abstract Unlabelled Image Highlights • Alkaline residuals are potential liming agents for acidified sugar maple forests. • Soil pH after liming is explained by the neutralizing power of alkaline residuals • More neutralization occurred in the forest floor layer than underlying mineral soil. • Greenhouse gas fluxes were lower after application of alkaline residuals. • Reduction in greenhouse gas fluxes was related to the increase in soil pH. [ABSTRACT FROM AUTHOR]

Abstract Nitrous oxide (N 2 O) is a major greenhouse gas (GHG) with high global warming potential. A majority of the N 2 O flux comes from agricultural sources, mainly due to nitrogen (N) fertilization. The soil N 2 O flux, induced by N fertilization, mainly originated from two different sources, i.e., fertilizer and soil organic nitrogen (SON). It is essential to know the individual contribution of these two different sources in total N 2 O flux for planning necessary mitigation strategies. It is also indispensable to know the seasonal difference of emission factors (EF) for having more accurate N 2 O inventory. Therefore, an experiment was conducted in a South Korean upland soil during summer and winter seasons using 15N labeled urea as an artificial N source and source specific N 2 O emissions were distinguished under different environmental conditions. To characterize the N 2 O emissions from urea, 0, 50, 100 and 200% of the Korean N recommendation rate was selected for specified crops. The Korean N recommendation rate for red pepper (Capsicum annuum) and garlic (Allium sativum) was 190 and 250 kg N ha−1, respectively. Direct emissions from urea were estimated from the difference of 15N 2 O flux emitted from 15N-urea treated soil and the natural abundance of 15N 2 O. From total N 2 O fluxes, urea originated N 2 O flux was 0.87% and 0.13% of the applied N in warm and cold seasons, respectively and the rest comes from SON. Nitrous oxide EF in the warm season was 2.69% of applied N and in the cold season that was 0.25%. Nitrous oxide fluxes showed a significant exponential relationship with soil temperature. The results show the necessity of considering the different N 2 O EF for warm and cold cropping seasons to reduce uncertainty in N 2 O inventory. The findings of this research may help better understand N 2 O source partitioning and the emission budget from warm and cold cropping seasons. Graphical abstract Unlabelled Image Highlights • N 2 O flux originated from urea N was small compared with that of SON. • N 2 O released from the urea application was 0.87 and 0.13% of applied urea in warm and cold seasons, respectively. • N 2 O emission factors in the warm and cold season are 2.69 and 0.25, respectively. • N 2 O emissions showed exponential relationship with soil temperature. [ABSTRACT FROM AUTHOR]

Abstract Nitrogen fertilization contributes significantly to crop production globally. However, low efficiency application management approaches lead to substantial N losses of which ammonia and nitrous oxide are known as environmental threats. Urea, the largest N fertilization source globally, is associated with high ammonia losses. A large variety of application modes are practiced under different environmental conditions worldwide. Yet, the complexity of N-processes in different soils, under changing agro-environmental conditions, challenges the evaluation of fertilization approaches efficiency in reducing N-gaseous losses. In this research a simply designed static incubation cell was connected to a Long-Path gas cell and a Fourier Transform IR spectrometer (LP-FTIR), allowing online determination of ammonia and nitrous oxide emissions in parallel to tracking mineral N-dynamics in soil samples. The static chamber was used to evaluate different application approaches of urea (i.e., incorporation or surface application with or without wetting) in a Sandy Loam and to compare surface applied regular urea vs. urea amended with the urease inhibitors NPPT+NBPT [N-(n-butyl) thiophosphoric triamide and N-(n-propyl) thiophosphoric triamide, respectively] in four different representative soils. Ammonia emissions peaked few days after application, where highest losses were observed for surface application mode. Highest emissions, up to 5% (w/w) of applied Urea-N, were obtained with the lighter and more basic soils (Sandy Loam and Loess; pH > 7.9). Nitrous oxide emissions showed a lag period of ~1 week and were higher under lower urea application rates, and when nitrification was faster (~1–1.3% (w/w) of applied N). Urease inhibitors significantly reduced ammonia losses in all tested soils and particularly in the Sandy Loam and Loess. Their effect on nitrous oxide losses were observed with the Sandy Loam and particularly after 2 weeks. The static system may underestimate realistic ammonia losses, but it offers a rather simply operated system, providing information about N-gaseous losses for improving N-fertilization management. Graphical abstract Unlabelled Image Highlights • Static cell designed for direct tracking NH 3 and N 2 O emissions from fertilized soils • Urea application under different conditions and urease inhibitor were tested. • Highest NH 3 emissions obtained from a Sandy Loam & N 2 O from a clay soil (Grumusol) • Urease inhibitors clearly reduced NH 3 emissions from 4 different representative soils. • Reduced N 2 O emissions via urease inhibitors observed mainly with the Sandy Loam [ABSTRACT FROM AUTHOR]

Abstract Grazing degrades worldwide grasslands and possibly suppresses soil greenhouse gas (GHG: CO 2 , CH 4 and N 2 O) fluxes. However, the global patterns of these three gas fluxes in response to grazing and the general mechanisms remain poorly understood. Here, we performed a meta-analysis of 63 independent grazing studies that measured soil GHG fluxes across global grasslands. Our results revealed that light and moderate grazing had no significant effect on soil CH 4 uptake, N 2 O and CO 2 emission, but heavy grazing consistently reduced them. The magnitudes of their responses to grazing were regulated by grazing duration and precipitation. In comparison with CO 2 emission, soil CH 4 uptake and N 2 O emission were reduced much more under heavier grazing, longer grazing duration or less precipitation. The decrease in soil CO 2 emission was possibly caused by grazing-induced reduction in root biomass and soil moisture, while the decline in soil CH 4 uptake and N 2 O emission was due to decreased soil moisture and substrate availability. Overall, this study provides the first large-scale evaluation on three main soil GHG fluxes in response to grazing, highlighting grazing inhibition of GHG emission but at the cost of plant productivity and soil fertility. We call for future efforts to identify an appropriate grazing intensity that is optimal to balance these complicated impacts. Graphical abstract Unlabelled Image Highlights • Heavy grazing consistently reduced grassland soil CH 4 uptake, CO 2 and N 2 O emission. • Soil trace gas flux was more sensitive than CO 2 to heavy or long grazing. • GHG decline by grazing was due to reduced soil water, nutrient and root growth. • These reveal grazing repression of GHG emission but impairing grassland production. [ABSTRACT FROM AUTHOR]

Abstract Process-based models are useful tools to integrate the effects of detailed agricultural practices, soil characteristics, mass balance, and climate change on soil N 2 O emissions from soil - plant ecosystems, whereas static, seasonal or annual models often exist to estimate cumulative N 2 O emissions under data-limited conditions. A study was carried out to compare the capability of four models to estimate seasonal cumulative N 2 O fluxes from 419 field measurements representing 65 studies across China's croplands. The models were 1) the DAYCENT model, 2) the DNDC model, 3) the linear regression model (YLRM) of Yue et al. (2018), and 4) IPCC Tier 1 emission factors. The DAYCENT and DNDC models estimated crop yields with R2 values of 0.60 and 0.66 respectively, but both models showed significant underestimation for all measurements. The estimated seasonal N 2 O emissions with R2 of 0.31, 0.30, 0.21 and 0.17 for DAYCENT, DNDC, YLRM, and IPCC, respectively. Based on RMSE, modelling efficiency and bias analysis, YLRM performed well on N 2 O emission prediction under no fertilization though bias still existed, while IPCC performed well for cotton and rapeseed and DNDC for soybean. The DAYCENT model accurately predicted the emissions with no bias across other crop and fertilization types whereas the DNDC model underestimated seasonal N 2 O emissions by 0.42 kg N 2 O-N ha−1 for all observed values. Model evaluation indicated that the DAYCENT and DNDC models simulated temporal patterns of daily N 2 O emissions effectively, but both models had difficulty in simulating the timing of the N 2 O fluxes following some events such as fertilization and water regime. According to this evaluation, algorithms for crop production and N 2 O emission should be improved to increase the accuracy in the prediction of unfertilized fields both for DAYCENT and DNDC. The effects of crop types and management modes such as fertilizations should also be further refined for YLRM. Graphical abstract Unlabelled Image Highlights • DAYCENT, DNDC, linear regression model and IPCC tier 1 approach were evaluated to estimate N 2 O emissions in China's cropland. • DAYCENT emerged as the best performing model for application under Chinese conditions. • Algorithms should be improved to increase the accuracy in the prediction of unfertilized fields. [ABSTRACT FROM AUTHOR]

Abstract Biochar can reduce both nitrous oxide (N 2 O) emissions and nitrate (NO 3 −) leaching, but refining biochar's use for estimating these types of losses remains elusive. For example, biochar properties such as ash content and labile organic compounds may induce transient effects that alter N-based losses. Thus, the aim of this meta-analysis was to assess interactions between biochar-induced effects on N 2 O emissions and NO 3 − retention, regarding the duration of experiments as well as soil and land use properties. Data were compiled from 88 peer-reviewed publications resulting in 608 observations up to May 2016 and corresponding response ratios were used to perform a random effects meta-analysis, testing biochar's impact on cumulative N 2 O emissions, soil NO 3 − concentrations and leaching in temperate, semi-arid, sub-tropical, and tropical climate. The overall N 2 O emissions reduction was 38%, but N 2 O emission reductions tended to be negligible after one year. Overall, soil NO 3 − concentrations remained unaffected while NO 3 − leaching was reduced by 13% with biochar; greater leaching reductions (>26%) occurred over longer experimental times (i.e. >30 days). Biochar had the strongest N 2 O-emission reducing effect in paddy soils (Anthrosols) and sandy soils (Arenosols). The use of biochar reduced both N 2 O emissions and NO 3 − leaching in arable farming and horticulture, but it did not affect these losses in grasslands and perennial crops. In conclusion, the time-dependent impact on N 2 O emissions and NO 3 − leaching is a crucial factor that needs to be considered in order to develop and test resilient and sustainable biochar-based N loss mitigation strategies. Our results provide a valuable starting point for future biochar-based N loss mitigation studies. Graphical abstract Unlabelled Image Highlights • N 2 O emissions were reduced by 38% with biochar. • Soil NO 3 − concentrations remained unaffected. • NO 3 − leaching was reduced by 13% with biochar. • Biochar strongly reduced N 2 O-emission in paddy and sandy soils. [ABSTRACT FROM AUTHOR]

Abstract Cities are increasingly being recognized as important contributors in global warming, for example by increasing atmospheric nitrous oxide (N 2 O). However, urban ecosystems remain poorly understood due to their functional complexity. Further, few studies have documented the microbial processes governing the N 2 O emissions from urban soils. Here, a field study was performed to assess in situ N 2 O emissions in an urban and agricultural soil located in Xiamen, China. The mechanisms underlying the difference in N 2 O emission patterns in both soils were further explored in an incubation experiment. Field investigations showed that N 2 O emission (3.5–19.0 μg N 2 O-N m−2 h−1) from the urban soil was significantly lower than that from the agricultural soil (25.4–18,502.3 μg N 2 O-N m−2 h−1). Incubation experiments showed that the urban soil initially emitted lower denitrification-derived N 2 O because of the lower nirS (encoding nitrite reductases) abundances, whereas overall N 2 O accumulation during the incubation was mainly controlled by the initial nitrate content in soil. Nitrate addition in a short period (5 days) did not change the total bacterial and denitrifier abundances or the soil bacterial community composition, but significantly altered the relative distribution of some key genera capable of denitrification. Although the urban soil exhibited lower N 2 O emission than its agricultural counterpart in this study, the expanding urban green areas should be taken into account when building N 2 O emission reduction targets. Graphical abstract Unlabelled Image Highlights • The urban soil had significantly lower abundances of nirS and nosZ. • Nitrate shifted neither soil bacterial composition nor denitrifier abundances. • Nitrate changed relative abundances of some genera capable of denitrification. • Nitrate controlled final denitrification-derived soil N 2 O emission. • The urban soil emitted lower N 2 O than the agricultural soil. [ABSTRACT FROM AUTHOR]

Abstract Little is known about the effects of nitrogen (N) fertilization rates on ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) and their differential contribution to nitrous oxide (N 2 O) production, particularly in greenhouse based high N input vegetable soils. Six N treatments (N1, N2, N3, N4, N5 and N6 representing 0, 293, 587, 880, 1173 and 1760 kg N ha−1 yr−1, respectively) were continuously managed for three years in a typically intensified vegetable field in China. The aerobic incubation experiment involving these field-treated soils was designed to evaluate the relative contributions of AOA and AOB to N 2 O production by using acetylene or 1-octyne as inhibitors. The results showed that the soil pH and net nitrification rate gradually declined with increasing the fertilizer N application rates. The AOA were responsible for 44–71% of the N 2 O production with negligible N 2 O from AOB in urea unamended control soils. With urea amendment, the AOA were responsible for 48–53% of the N 2 O production in the excessively fertilized soils, namely the N5–N6 soils, while the AOB were responsible for 42–55% in the conventionally fertilized soils, namely the N1–N4 soils. Results indicated that overdose fertilization induced higher AOA-dependent N 2 O production than AOB, whereas urea supply led to higher AOB-dependent N 2 O production than AOA in conventionally fertilized soils. Additionally, a positive relationship existed between N 2 O production and NO 2 − accumulation during the incubation. Further mechanisms for NO 2 −-dependent N 2 O production in intensive vegetable soils therefore deserve urgent attention. Graphical abstract Unlabelled Image Highlights • Soil pH induced by N gradients controlled the abundance/contribution of AOA and AOB. • AOA-derived N 2 O were greater than AOB in the control and overdose fertilized soils. • AOB-derived N 2 O dominated in conventionally fertilized vegetable soils. [ABSTRACT FROM AUTHOR]

Abstract Previous studies demonstrated that finer soil particles have smaller rates of CO 2 emission but larger Q 10 values (the proportionate increase in the rate for a warming of 10 °C) than coarser particles. However, it has not been tested whether there is a regular pattern for rates and Q 10 for N 2 O emission (net production) across soil particle size fractions, considering the known positive correlation between soil CO 2 and N 2 O emissions. A short-term incubation study with different soil particle fractions was conducted for soils from a grassland, a forest, an upland (including organic manure (OM) and chemical nitrogen, phosphorus, and potassium fertilizers (NPK) treatments), and a paddy (including manure plus chemical fertilizer (MNPK) and NPK treatments) under a series of increasing and decreasing temperatures between 5 °C and 30 °C with 5 °C intervals. For all the soils, net N 2 O production per unit mass of soil N was smaller from the silt (2–50 μm) fraction than from the sand (>50 μm) and clay (<2 μm) fractions. In paddy soils, Q 10 for net N 2 O production was highest from the clay fraction. In contrast, Q 10 was highest in the sand fraction for the grassland soil. In the upland and paddy soils, the rates of net N 2 O production were higher in OM or MNPK treatment than in their corresponding NPK treatment, but Q 10 values were similar between the manure and NPK treatments. The net N 2 O production rates positively correlated with CO 2 emission across all soil samples, and this was also the case for their Q 10 values. Q 10 values for net N 2 O production averaged 8% lower than those for CO 2 emissions. In conclusion, the net N 2 O production rates appear to be the smallest from the silt fraction. Graphical abstract Unlabelled Image Highlights • Net N 2 O production is the minimum from the intermediate-size (silt) particle. • Q10 of N 2 O emission is not always the maximum from the clay (finest) fraction. • Fertilizer type does not affect temperature sensitivity of net N 2 O production. • Q10 for N 2 O emission averaged 8% lower than that for CO 2. [ABSTRACT FROM AUTHOR]