N2O Ratio Research Articles

The ratio of denitrification end-products were influenced by soil pH and clay content across different texture classes in Oklahoma soils

Nitrous oxide (N2O) is a potent greenhouse gas that contributes to stratospheric ozone depletion and global climate change. Soil denitrification has two potential end-products, N2O and dinitrogen (N2), and the ratio of these end-products (N2O:(N2O+N2) or the N2O ratio) is controlled by various factors. This study aims to quantify the influence of soil pH on the ratio of denitrification end-products in Oklahoma soils with different soil textures. Six natural grassland soils encompassing three distinct soil textures were incubated in the laboratory under natural and modified pH with an overall tested pH ranging from 2 to 10. Denitrification end-products were measured in the laboratory using the acetylene inhibition technique and further estimated using a process-based biogeochemical model. Both the laboratory and model results showed that soil pH and texture influenced the ratio of the denitrification end-products. Generally, as soil pH increased the N2O ratio decreased, although both lab and model results indicated that this relationship was not linear. Soil texture may have an indirect effect on the N2O ratio, as two soils of the same texture could have different N2O ratios. However, clay percentage of the soil did show a linear positive correlation with the N2O ratio, suggesting components of soil texture may be more influential than others. Overall, soil pH was a controlling factor in the ratio of denitrification end-products and the newly observed nonlinear relationship warrants further study, particularly when considering its effects in different soil textures.

Field soil properties and experimental nutrient additions drive the nitrous oxide ratio in laboratory denitrification experiments: a systematic review

Nitrous oxide (N2O), which contributes to global climate change and stratospheric ozone destruction, can be produced during denitrification. Although the N2O ratio, a measure of denitrification completion, is influenced by various properties, studies have largely been limited to site- or treatment-specific conclusions. The primary objective of this study was to identify important factors driving N2O ratios and their relationships in soils by systematically reviewing and quantitatively evaluating results from published laboratory denitrification studies. A database with 60 studies (657 observations) was compiled, including studies meeting the minimum criteria: (i) laboratory experiments on soils, (ii) nutrient (carbon and/or nitrogen) addition, and (iii) N2O and dinitrogen gas measurements. Of these, 14 studies (100 observations) had sufficient data for inclusion in the meta-analysis to assess the effect of added nutrients on the N2O ratio. Furthermore, we modeled the effect of moderators on treatment effect by fitting a meta-regression model with both quantitative and categorical variables. Close review of studies in the database identified soil pH, carbon addition, and nitrogen addition as important variables for the N2O ratio, but trends varied across studies. Correlation analysis of all studies clarified that soil pH was significantly correlated with the N2O ratio, where soils with higher pH had lower N2O ratios. The meta-analysis further revealed that nutrient addition had an overall significant, positive treatment effect (0.30 ± 0.03, P<.0001), indicating that experimentally adding nutrients increased the N2O ratio. The model was most significantly improved when soil texture was used as a moderator. The significance of soil texture for the N2O ratio was a major finding of this study, especially since the assays were usually conducted with soil slurries. Overall, this study highlights the importance of field soil properties (i.e., pH, texture) and laboratory conditions (i.e., nutrient addition) in driving the N2O ratio and N2O production from denitrification in soils.

Biochar-Compost Additions Have Strong Short-Term Effects on Carbon and Nitrogen Emissions from an Agricultural Soil

Biochar (BC) application to agricultural soils has become a promising strategy for mitigation of soil-borne greenhouse gas (GHG) emissions, i.e., carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), but little is known about the effects on nitric oxide (NO) and dinitrogen (N2) fluxes. We conducted a short-term field experiment to evaluate the effects of BC with compost and additional fertilizer on different soil GHG fluxes. Application of 1% BC-compost showed no significant effect on CH4 and CO2 fluxes but lowered NO and N2O fluxes compared to the control without BC-compost. The addition of N to BC-compost (0.5% BC-compost + 175 kg N) showed a small mitigation potential for CH4 whereas N2O and NO fluxes significantly increased for one week after the application. The N2:N2O ratio shifted towards N2O production after the application of N-enriched BC-compost. During storage of pure N-enriched BC-compost, high gaseous losses in the form of NO (71.2 ± 2 µg N g−1 h−1), N2O (1319 ± 101 µg N g−1 h−1), and N2 (337.8 ± 93 µg N g−1 h−1) were measured. Approximately 31% of applied N was lost in gaseous form even in the presence of BC. To avoid this, an optimized strategy to balance easily available N from compost and fertilizer with the amount of BC should be developed.

Distinguishing N2O and N2 ratio and their microbial source in soil fertilized for vegetable production using a stable isotope method

Vegetable production systems with excessive nitrogen fertilizer result in severe N2O emission. It is pivotal to identify the source of N2O for reducing N2O emission, but estimating microbial pathways of N2O production is very difficult due to the existence of N2O reduction. A promising tool can address this problem by using δ18O and δ15NSP of N2O to construct a dual isotopocule plot. For ascertaining the microbial pathways of N2O production and consumption in soil fertilized for vegetable production, four treatments were set up: urea (U), half urea and half organic fertilizer (UO), organic fertilizer (O) and no fertilizer (NF), and the experiment was carried out continuously for two years. The δ18O vs. δ15NSP plot method indicated that the nitrification/fungal denitrification was a dominant in N2O emission, and the U treatment was the highest, followed by OU, O and NF in the both years. Among the different treatments, furthermore, the N2O flux had the same trend, whereas the extent of N2O reduction showed an opposite trend. Overall, inorganic fertilizer enhances nitrification/fungal denitrification and hinders reduction of N2O to N2, resulting in a larger amount of N2O emission. However, organic fertilizer increases the contribution of denitrification and greatly improves the extent of N2O reduction, which helps to reduce N2O emission. Therefore, organic fertilizer is crucial to reducing N2O emission by enhancing N2O reduction and should be properly applied in production practice.

In silico assessment of the potential of basalt amendments to reduce N2O emissions from bioenergy crops

AbstractThe potential of large‐scale deployment of basalt to reduce N2O emissions from cultivated soils may contribute to climate stabilization beyond the CO2‐removal effect from enhanced weathering. We used 3 years of field observations from maize (Zea mays) and miscanthus (Miscanthus × giganteus) to improve the nitrogen (N) module of the DayCent model and evaluate the potential of basalt amendments to reduce N losses and increase yields from two bioenergy crops. We found 20%–60% improvement in our N2O flux estimates over previous model descriptions. Model results predict that the application of basalt would reduce N2O emissions by 16% in maize and 9% in miscanthus. Lower N2O emissions responded to increases in the N2:N2O ratio of denitrification with basalt‐induced increases in soil pH, with minor contributions from the impact of P additions (a minor component of some basalts) on N immobilization. The larger reduction of N2O emissions in maize than in miscanthus was likely explained by a synergistic effect between soil pH and N content, leading to a higher sensitivity of the N2:N2O ratio to changes in pH in heavily fertilized maize. Basalt amendments led to modest increases in modeled yields and the nitrogen use efficiency (i.e., fertilizer‐N recover in crop production) of maize but did not affect the productivity of miscanthus. However, enhanced soil P availability maintained the long‐term productivity of crops with high nutrient requirements. The alleviation of plant P limitation led to enhanced plant N uptake, thereby contributing to lower microbial N availability and N2O emissions from crops with high nutrient requirements. Our results from the improved model suggest that the large‐scale deployment of basalt, by reducing N2O fluxes of cropping systems, could contribute to the sustainable intensification of agriculture and enhance the climate mitigation potential of bioenergy with carbon capture and storage strategies.

Role of N2O and equivalence ratio on NOx formation of methane/nitrous oxide premixed flames

Nitrous oxide (N2O) is often used as an oxidizer in rocket technology with plenty of potential advantages. However, the N2O/hydrocarbon combustion results in the staggering increase of NOx emission. To scrutinize the role of N2O and equivalence ratio on NO formation characteristics of N2O/CH4 premixed flame, mixtures of N2O/CH4 and N2/O2/CH4 were investigated by employing one-dimensional opposed-jet model with detailed reaction mechanism. The flame structures, NO reaction pathways, and NO formation routes were discussed. In the heat release rate analysis, the heat release is dominated by N2O route, resulting in high flame temperature in N2O/CH4 premixed flame. Regarding the mechanism of NO formation, NO is mainly produced from N2 through the thermal routes and from HNO through the HNO-intermediate routes for the N2/O2/CH4 flame but mainly comes from N2O through the N2O and HNO-intermediate routes in the N2O/CH4 flame. The thermal routes alter to the primary chemical mechanism of NO consumption. The NO production in fuel-lean N2O/CH4 flames is enhanced through the N2O route due to the increase of the mole fraction of O atom. The thermal route becomes forward reactions to produce NO for the extreme fuel-rich N2O/CH4 flame. Regarding the reaction pathways of the prompt route, it can be approximately divided into three categories: (1) N2 → CN → NCN, NO (in terminal) → N2; (2) CN → NCN, NO (in terminal) → NO, CN; (3) N2 → CN → NCN, NO (in terminal) → N → N2. In NO production rate analysis, the main NO formation comes from the N2O and HNO-intermediate routes, while NO consumption associates with the thermal and NNH-intermediate routes. In addition, the prompt-NO formation is dominated by species of N2O instead of CH radical in the extreme fuel-rich N2O/CH4 flames.

N2O-reducing activity of soil amended with organic and inorganic enrichments under flooded conditions

Changes, apparent after investigation, in the physical and chemical properties in soil, as a result of organic and inorganic enrichments under flooded conditions, influence the growth of denitrifiers. The aim of this study was to determine the effect of the addition of manure (8 kg m−2) (M), clay (50 kg m−2) (CL) and lime (1.12 kg m−2) (Ca) on the N2O-reducing activity (N2O-RA) of sandy loam soil (clay content - 24 % in 0-20 cm), during NO3 reduction under flooding. The soil samples were taken from field plots after 3 years of enrichment with grass cultivation. The enrichments had a distinct effect on the N2O-RA and N2O-released, due to the change in pH, the porosity, and the sorptive properties of the soil. The pH had the greatest impact on the N2O-RA of the soil and ranged from 4.9 to 7.6. For actual denitrification to N2O-realized (aD-N2O), the maximum N2O-releasing (mcN2O-releasing) followed the order: 1.36 for the M-treatment, 6.39 for the M+CL+Ca-treatment, 7.79 for the c-soil and 8.69 N2O-N mg kg−1 for the M+CL-treatment. For actual denitrification (aD), the mcN2O-releasing was followed the order: 10.37 for the M-treatment, 10.49 for the control soil, 14.60 for the M+CL+Ca-treatment and 20.00 N2O-N mg kg−1 for the M+CL-treatment. The N2O-RA of the soil samples increased as pH increased. The average N2O/N2+N2O ratio and the N2O-RA of the soil samples increased in the following order: M+CL, control soil, M+CL+Ca, M-enrichments. The addition of enrichments did not pose a threat to the environment due to increased N2O emissions, but as regards conserving NO3− in the soil, the addition of clay distinctly increased the complete denitrification process.

Effect on optical properties and electrical performances of antireflective coating with gradient refractive index based on p-type amorphous SiOx thin films

The electrical performances and optical properties of p-type amorphous silicon oxide (p-SiOx) thin films with gradient refractive index are studied. The composite thin films as antireflective coatings (ARCs) are widely used in solar cells and microelectronic devices. The double-layer p-SiOx thin films are deposited by plasma-enhanced chemical vapor deposition (PECVD) system. To obtain better optical properties, the refractive index of ARCs can be adjusted by SiH4 to N2O ratio. And the electrical performances of composite thin films can be improved by adjustment of B2H6 to SiH4 ratio. The computational model is built to predict the optimized range of reflection spectra corresponding to structure of p-SiOx ARCs with gradient refractive index by finite difference time domain (FDTD) method. It shows the difference of reflection spectra with gradient refractive index distribution. The optimized reflection spectra simulated by FDTD method confirms to agree well with that measured by UV–visible spectroscopy.

Effect of N2O ratio on the crystallization temperature of ZrO2 film deposited on Si by reactive sputtering in Ar/O2/N2O plasma

The effect of nitrous oxide ratios in the Ar/ O2/ N2O plasma on the ZrO2 films deposited on Si using dc magnetron reactive system is studied by differential scanning calorimetry (DSC) where the Ar:O2 ratio is fixed at 4:1. Further, grazing angle x-ray reflectivity (GIXRR), grazing angle x-ray diffraction (GIXRD) and atomic force microscopy (AFM) techniques are also employed to characterize the films. The DSC study shows an anomalous variation of the glass temperature when the N2O ratio in the Ar/O2/N2O plasma changes from 0.25 to 2 with respect to the control ZrO2 sample deposited without N2O. An increase in glass temperature by ∼70 °C is observed for the N2O ratio at 1. A further rise in N2O ratio results in the reduction of the glass temperature. The GIXRR study indicates that the thickness of the samples decreases with the increase in N2O ratios beyond 0.8. Further, increasing N2O ratio results in an increase in surface and interface roughness for the as-deposited samples. But both the roughnesses decrease upon annealing the samples above their respective crystallization temperatures. The AFM results also corroborates the observation. Moreover, the GIXRD study indicates the formation of Γ-Zr2ON2 along with the monoclinic and tetragonal ZrO2 at the highest ratio of N2O in the Ar:O2:N2O plasma.

Characterization and simulation on antireflective coating of amorphous silicon oxide thin films with gradient refractive index

The optical reflective properties of silicon oxide (SixOy) thin films with gradient refractive index are studied both theoretically and experimentally. The thin films are widely used in photovoltaic as antireflective coatings (ARCs). An effective finite difference time domain (FDTD) model is built to find the optimized reflection spectra corresponding to structure of SixOy ARCs with gradient refractive index. Based on the simulation analysis, it shows the variation of reflection spectra with gradient refractive index distribution. The gradient refractive index of SixOy ARCs can be obtained in adjustment of SiH4 to N2O ratio by plasma-enhanced chemical vapor deposition (PECVD) system. The optimized reflection spectra measured by UV–visible spectroscopy confirms to agree well with that simulated by FDTD method.

Pulse increase of soil N2O emission in response to N addition in a temperate forest on Mt Changbai, northeast China.

Nitrogen (N) deposition has increased significantly globally since the industrial revolution. Previous studies on the response of gaseous emissions to N deposition have shown controversial results, pointing to the system-specific effect of N addition. Here we conducted an N addition experiment in a temperate natural forest in northeastern China to test how potential changes in N deposition alter soil N2O emission and its sources from nitrification and denitrification. Soil N2O emission was measured using closed chamber method and a separate incubation experiment using acetylene inhibition method was carried out to determine denitrification fluxes and the contribution of nitrification and denitrification to N2O emissions between Jul. and Oct. 2012. An NH4NO3 addition of 50 kg N/ha/yr significantly increased N2O and N2 emissions, but their “pulse emission” induced by N addition only lasted for two weeks. Mean nitrification-derived N2O to denitrification-derived N2O ratio was 0.56 in control plots, indicating higher contribution of denitrification to N2O emissions in the study area, and this ratio was not influenced by N addition. The N2O to (N2+N2O) ratio was 0.41–0.55 in control plots and was reduced by N addition at one sampling time point. Based on this short term experiment, we propose that N2O and denitrification rate might increase with increasing N deposition at least by the same fold in the future, which would deteriorate global warming problems.

Determination of Fluorine by Molecular Absorption Spectrometry of AlF Using a High-Resolution Continuum Source Spectrometer and a C<sub>2</sub>H<sub>2</sub>/N<sub>2</sub>O Flame

The molecular absorption of the diatomic AlF molecule in the C2H2/N2O flame was studied using a highresolution continuum source flame atomic absorption spectrometer. AlF has a structured absorption spectrum in the range of 227.30 nm and 227.80 nm. From this band system, the remarkably narrow absorption band at 227.66 nm proved to be the optimum for analytical purposes. The signal intensity was studied as a function of the C2H2 : N2O ratio, the aspiration flow, and the aluminum concentration added to the analytical solution to generate the AlF molecules in the flame. The AlF molecule formation is significantly affected by the bonding state of the fluorine source used. Compared to ionic bound fluorine, organic bound fluorine leads to a markedly less sensitive molecular absorbance of AlF. Furthermore, several ions, such as Na+, K+ and NH4+ +, and acids, such as HCl, CH3COOH, and HNO3, affect the AlF signal intensity severely. It has to be concluded that the determination of fluorine by AlF F MAS only leads to reliable analytical results in simple matrices. Keywords: Aluminum monofluoride (AlF), fluorine determination, high resolution continuum source absorption spectrometry, molecular absorption spectrometry (MAS), non-spectral interference.

New high precision approach for measuring 15N–N2 gas fluxes from terrestrial ecosystems

Dinitrogen (N2) production from denitrification and anaerobic ammonium oxidation represents a loss of reactive nitrogen (N) from terrestrial and aquatic ecosystems to the atmosphere. The large 15N additions required to detect 15N2 production against the high atmospheric background precludes the use of the 15N tracer technique in natural terrestrial ecosystems. We present an isotope ratio mass spectrometry technique that dramatically improves the precision of 15N2 measurements. The approach uses gas chromatography to remove oxygen and gas purification techniques to remove water vapor and trace gases that can interfere with 15N2 analysis. The analytical precision for manual gas sample injection was 0.018‰ δ15N; this translates to a minimum detectable N2 flux of 0.12 ng-N g−1 h−1 over a 24 h incubation using our experimental parameters. We measured denitrification-derived N2 production rates of 0.67 ± 0.04 ng N g−1 dry soil h−1 following the addition of 0.1 μg 98 atom % 15N–NO3− g−1 dry soil to anaerobically-incubated soils; rates were significantly higher with the addition of 1.0 μg 98 atom % 15N–NO3− g−1 dry soil (p < 0.001, n = 5), averaging 1.3 ± 0.03 ng N g−1 dry soil h−1. The N2:N2O ratio at 24 h after 15N addition was 48 ± 12 and 5.4 ± 1.9 for the 0.1 μg 15N g−1 and 1.0 μg 15N g−1 treatments, respectively. The decrease in the N2:N2O with the addition of only 1 μg 15N g−1 underscores the need to use very low rates of 15N addition to accurately characterize denitrification dynamics. This analytical advance will allow us to better estimate the N2:N2O ratio of denitrification, constrain ecosystem N budgets, and explore the mechanisms of and controls on N2 production.

Characterization of Silicon Oxide Films Deposited from a Permanent‐Magnet Helicon Plasma Source

AbstractSilicon oxide films were deposited by an individual PM helicon source using HMDSO as a precursor and N2O as the reactive gas at low temperature. The chemical structure and elemental composition of the films are characterized by Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy, and the optical and mechanical properties of the films are evaluated by a thin‐film metrology system using reflectance spectra and a nanoindenter. The experimental results show that the N2O ratio in the plasma has a strong impact on the optical and structural characteristics of the deposited films: with increasing N2O flow ratios, the hardness of the deposited films increases while the deposition rate and carbon content decreases. At the same time, the characteristics of the oxide films gradually shift away from those of polymers towards those of SiO2. The technique presented here may find applications in making barrier films for polymer substrates. magnified image

Regional N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O fluxes in Amazonia derived from aircraft vertical profiles

Abstract. Nitrous oxide (N2O) is the third most important anthropogenic greenhouse gas. Globally, the main sources of N2O are nitrification and denitrification in soils. About two thirds of the soil emissions occur in the tropics and approximately 20% originate in wet rainforest ecosystems, like the Amazon forest. The work presented here involves aircraft vertical profiles of N2O from the surface to 4 km over two sites in the Eastern and Central Amazon: Tapajós National Forest (SAN) and Cuieiras Biologic Reserve (MAN), and the estimation of N2O fluxes for regions upwind of these sites. To our knowledge, these regional scale N2O measurements in Amazonia are unique and represent a new approach to looking regional scale emissions. The fluxes upwind of MAN exhibited little seasonality, and the annual mean was 2.1±1.0 mg N2O m−2 day−1, higher than that for fluxes upwind of SAN, which averaged 1.5±1.6 mg N2O m−2 day−1. The higher rainfall around the MAN site could explain the higher N2O emissions, as a result of increased soil moisture accelerating microbial nitrification and denitrification processes. For fluxes from the coast to SAN seasonality is present for all years, with high fluxes in the months of March through May, and in November through December. The first peak of N2O flux is strongly associated with the wet season. The second peak of high N2O flux recorded at SAN occurs during the dry season and can not be easily explained. However, about half of the dry season profiles exhibit significant correlations with CO, indicating a larger than expected source of N2O from biomass burning. The average CO:N2O ratio for all profiles sampled during the dry season is 94±77 mol CO:mol N2O and suggests a larger biomass burning contribution to the global N2O budget than previously reported.

P-Type ZnO Nanowire Arrays

Well-aligned ZnO nanowire (NW) arrays with durable and reproducible p-type conductivity were synthesized on alpha-sapphire substrates by using N2O as a dopant source via vapor-liquid-solid growth. The nitrogen-doped ZnO NWs are single-crystalline and grown predominantly along the [110] direction, in contrast to the [001] direction of undoped ZnO NWs. Electrical transport measurements reveal that the nondoped ZnO NWs exhibit n-type conductivity, whereas the nitrogen-doped ZnO NWs show compensated highly resistive n-type and finally p-type conductivity upon increasing N2O ratio in the reaction atmosphere. The electrical properties of p-type ZnO NWs are stable and reproducible with a hole concentration of (1-2) x 10(18) cm(-3) and a field-effect mobility of 10-17 cm2 V(-2) s(-1). Surface adsorptions have a significant effect on the transport properties of NWs. Temperature-dependent PL spectra of N-doped ZnO NWs show acceptor-bound-exciton emission, which corroborates the p-type conductivity. The realization of p-type ZnO NWs with durable and controlled transport properties is important for fabrication of nanoscale electronic and optoelectronic devices.

Study of SiOxNy as a bottom antireflective coating and its pattern transferring capability

To meet such challenges for the controlling of critical feature dimension at sub-50–100‐nm, it has been a general industrial trend to employ shorter wavelength (193nm, for example) lithography for better resolution and to use bottom antireflective coating (BARC) for a reduced standing wave formation and thus, a better critical dimensional control. Matching the optical constants (n,k) between the BARC, photoresist, and the underlayer to be patterned is critical for the elimination of such standing waves. SiOxNy and SiOxCy are two attractive inorganic BARC candidates in view of their easily adjustable optical constants by varying the deposition parameters and their etching compatibility with standard semiconductor plasma processes. In this article, SiOxNy films were prepared by plasma enhanced chemical vapor deposition approach. These films have been further characterized using x-ray photoelectron spectroscopy for chemical composition depth profile, Fourier transform infrared spectroscopy for local chemical bonding, and ellipsometry for optical constants. It has been demonstrated that the refractive indices of SiOxNy can be tuned from 1.6 to 2, while the absorption constants k can be adjusted from 0.1 to 0.9 by changing the process parameters, such as SiH4 flow rate, NH3 flow rate, and SiH4∕N2O ratio. To integrate the SiOxNy BARC film into the storage device manufacturing, the pattern transferring capability of SiOxNy has been discussed. A film stack structure of photoresist∕SiOxNy∕carbon or SiC hard mask∕magnetic device layer has been used to evaluate the performance of the SiOxNy BARC. SiOxNy film was opened via inductively coupled plasma etching with CHF3+O2 chemistry, while carbon and SiC hard masks were opened using He–O2 and SF6–He–O2 chemistries, respectively. SiF emission line at 388nm wavelength was used for end point during the SiOxNy etching, while the 778nm O peak and 685nm F peak have been used for carbon and SiC end pointing. The profiles of the etched SiOxNy and carbon∕SiC were analyzed by cross-section transmission electron microscopy.

N2O and NO emissions from different N sources and under a range of soil water contents

Emissions of nitrous oxide (N2O) and nitric oxide (NO) have been identified as one of the most important sources of atmospheric pollution from grasslands. Soils are major sources for the production of N2O and NO, which are by-products or intermediate products of microbial nitrification and denitrification processes. Some studies have tried to evaluate the importance of denitrification or nitrification in the formation of N2O or NO but there are few that have considered emissions of both gases as affected by a wide range of different factors. In this study, the importance of a number of factors (soil moisture, fertiliser type and temperature) was determined for N2O and NO emissions. Nitrous oxide and NO evolution in time and the possibility of using the ratio NO:N2O as an indicator for the processes involved were also explored. Dinitrogen (N2) and ammonia (NH3) emissions were estimated and a mass balance for N fluxes was performed. Nitrous oxide and NO were produced by nitrification and denitrification in soils fertilised with \(\hbox{NH}_{4}^{+}\) and by denitrification in soils fertilised with \(\hbox{NO}_{3}^{-}\). Water content in the soil was the most important factor affecting N2O and NO emissions. Our N2O and NO data were fitted to quadratic (r=0.8) and negative exponential (r=0.7) equations, respectively. A long lag phase was observed for the N2O emitted from soils fertilised with \(\hbox{NO}_{3}^{-}\) (denitrification), which was not observed for the soils fertilised with \(\hbox{NH}_{4}^{+}\) (nitrification) and was possibly due to a greater inhibiting effect of low temperatures on microbial activity controlling denitrification rather than on nitrification. The use of the NO:N2O ratio as a possible indicator of denitrification or nitrification in the formation of N2O and NO was discounted for soils fertilised with \(\hbox{NO}_{3}^{-}\). The N mass balance indicated that about 50 kg N ha−1 was immobilised by microorganisms and/or taken up by plant roots, and that most of the losses ocurred in wet soils (WFPS >60%) as N2 and NH3 losses (>55%).

Dehydrogenase activity, redox potential, and emissions of carbon dioxide and nitrous oxide from Cambisols under flooding conditions

Samples from topsoils (0–10 cm) of 16 Polish arable Cambisols developed from different parent materials (sand, silt, sandy gravel, loess, loam and clay), were incubated under flooded conditions with NO3 –. Dehydrogenase activity, redox potential (Eh), and emissions of CO2 and N2O were measured. According to dehydrogenase activity, the soils were divided into two groups: those of low activity (I), where the final dehydrogenase activity was 0.03 nmol TPF g–1 min–1. Generation of CO2 and of N2O under flooded conditions was shown to be significantly related to dehydrogenase activity. Soil dehydrogenase activity increased curvilinearly with organic matter content, showed a maximum at pH 7.1, and decreased curvilinearly with Eh. The final cumulative CO2 production increased linearly with soil organic matter content and curvilinearly with dehydrogenase activity and decreased linearly with Eh. The most significant relationship was found with dehydrogenase activity (R 2=0.74, P<0.001). The final cumulative N2O production decreased linearly with Eh and increased curvilinearly with pH and dehydrogenase activity but linearly with organic matter content; the most significant relation being found with dehydrogenase activity (R 2=0.69, P<0.001). The CO2:N2O ratio in the gases evolved increased curvilinearly with Eh and decreased with dehydrogenase activity and N2O and CO2 production.

Role of Oxygen in the Nitrous Oxide/Carbon Reaction

An investigation of the role of oxygen in the nitrous oxide/carbon reaction was carried out on various carbon samples (both graphitic and nongraphitic) over a range of temperatures and partial pressures. Previous work reported that oxygen strongly inhibited the nitrous oxide/carbon reaction. Large ratios of O-2/N2O were used in all previous work. In this work, the O-2/N2O ratio was kept below 1, and we found that oxygen did not inhibit the rate of the C + N2O reaction. Instead, the rate of the reaction in the presence of oxygen was essentially that predicted by the two independent reactions, nitrous oxide/carbon and oxygen/carbon, occurring simultaneously. A simple theoretical explanation is given for the observations, both past and present, on the basis of competitive chemisorption of nitrous oxide and oxygen on active sites.