The influence of tillage and fertilizer on the flux and source of nitrous oxide with reference to atmospheric variation using laser spectroscopy
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Abstract Nitrous oxide (N 2 O) is the third most important long-lived greenhouse gas and agriculture is the largest source of N 2 O emissions. Curbing N 2 O emissions requires understanding influences on the flux and sources of N 2 O. We measured flux and evaluated microbial sources of N 2 O using site preference ( S P ; the intramolecular distribution of 15 N in N 2 O) in flux chambers from a grassland tilling and agricultural fertilization experiments and atmosphere. We identified values greater than that of the average atmosphere to reflect nitrification and/or fungal denitrification and those lower than atmosphere as increased denitrification. Our spectroscopic approach was based on an extensive calibration with 18 standards that yielded S P accuracy and reproducibility of 0.7 ‰ and 1.0 ‰, respectively, without preconcentration. Chamber samples from the tilling experiment taken ~ monthly over a year showed a wide range in N 2 O flux (0–1.9 g N 2 O-N ha −1 d −1 ) and S P (− 1.8 to 25.1 ‰). Flux and S P were not influenced by tilling but responded to sampling date. Large fluxes occurred in October and May in no-till when soils were warm and moist and during a spring thaw, an event likely representing release of N 2 O accumulated under snow cover. These high fluxes could not be ascribed to a single microbial process as S P differed among chambers. However, the year-long S P and flux data for no-till showed a slight direct relationship suggesting that nitrification increased with flux. The comparative data in till showed an inverse relationship indicating that high flux events are driven by denitrification. Corn ( Zea mays ) showed high fluxes and S P values indicative of nitrification ~ 4 wk after fertilization with subsequent declines in S P indicating denitrification. Although there was no effect of fertilizer treatment on flux or S P in switchgrass ( Panicum virgatum) , high fluxes occurred ~ 1 month after fertilization. In both treatments, S P was indicative of denitrification in many instances, but evidence of nitrification/fungal denitrification also prevailed. At 2 m atmospheric N 2 O S P had a range of 31.1 ‰ and 14.6 ‰ in the grassland tilling and agricultural fertilization experiments, respectively. These data suggest the influence of soil microbial processes on atmospheric N 2 O and argue against the use of the global average atmospheric S P in isotopic modeling approaches.Keywords:
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The denitrification efficiency and nitrous oxide production during conventional biological denitrification and denitrification coupling with catalytic iron under different C/N ratio was studied.The results show that in both groups,the total nitrogen removal efficiency decreases while nitrous oxide production increases when C/N ratio becomes lower.But comparing control group,catalytic iron group has higher nitrate transforming efficiency and nitrous oxide emission.Futher more,the nitrous oxide could even be totally degraded when C/N was 1.
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Laboratory-scale experiments were conducted to examine nitrous oxide (N2O) production during the nitrification process. Substrate containing 400 mgN l−1 of NH4HCO3 as a nitrogen source was continuously fed into a 10 or 3 liter completely mixed reactor with varied dissolved oxygen (DO) and SRT. The DO of the continuous systems were fixed at 0.1, 0.2, 0.5, 1.7 and 6.8 mg l−1. The SRT were controlled at 3, 5, 10 and 20 days. Total amount of N2O production reached higher than 36 mgN l−1 in some conditions, and up to 16% of nitrified nitrogen was converted into N2O. N2O production was observed in all tested runs. Lower DO and shorter SRT resulted in higher N2O production. Incomplete nitrification was found at DO lower than 0.5 mg l−1 and an SRT shorter than 5 days. The highest concentration and conversion rate of N2O production was obtained at DO of 0.2 mg l−1 or when SRT was 3 days. The results suggest that N2O production is significant during nitrification process. The accumulation of NO2 may contribute to the high amount of N2O production.
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The denitrification treatment of sewage produces not only the final product N2,but also the intermediate product of Nitrous Oxide(N2O),which is one of the important potent greenhouse gases.It has important theoretical and practical significance to understanding the production mechanism and influence factors of N2O.Influence factors of N2O accumulation during denitrification are summarized and analyzed in this paper,including C/N ratio,DO,pH value,temperature and NO2--N.The relationship between the nitrous oxide reductase(Nos) activity and N2O accumulation during denitrification has also been discussed.
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Abstract Little field information is available on the amounts of nitrous oxide (N 2 O) released from soils during denitrification, or the proportion of the denitrification loss attributable to N 2 O production. The paper reports studies of N 2 O evolution and the simultaneous disappearance of nitrate (NO 3 ) in a flooded rice field which initially contained 4 g NO 3 ‐N m −2 in the top 0.08 m of soil. Measurements were made continuously for 18 days after the field was flooded. Nitrous oxide emission was calculated from the rate of increase of N 2 O in air circulating in a closed loop between a chamber installed in the field and an infrared gas analyzer. Emission rates as small as 1.8 ng N m −2 sec −1 could be measured. Nitrate disappearance was measured by chemical analysis of water samples. Nitrous oxide emission showed a diurnal cycle in phase with water temperature. Between the second and nineteenth day of flooding, 2.7 g NO 3 ‐N m −2 disappeared from the water and 0.038 g N 2 O‐N m −2 were produced, only 1.4% of the apparent N loss. In a supplementary, small‐bay experiment in which sodium nitrate and glycerol were added to the water, N 2 O production accounted for only 0.8% of the NO 3 disappearance. Even allowing for NO 3 removal through other mechanisms, the production of N 2 O in both experiments was very much less than the 7% commonly assumed for denitrification in current models of the global N 2 O budget.
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Summary Although often felt to be relatively innocuous, nitrous oxide can have significant metabolic effects in settings of abnormal vitamin B 12 and B 12 ‐related metabolism in children. These conditions can be genetic or environmental. Symptoms may not appear until days to weeks after exposure to nitrous oxide. Although overt genetic diseases are relatively uncommon, the implications of nitrous oxide interactions with much more frequent but less symptomatically obvious single nucleotide polymorphisms are potentially more concerning. In addition, nitrous oxide can have direct and differing neurotoxic effects on both immature and aged brain, the clinical impact of which remains undetermined.
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