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Optically controlled millimetre-wave switch with stepped-impedance lines
摘要： Nitrogen (N) placement can impact nitrogen use efficiency, but its effect on greenhouse gas (GHG) emissions remain unclear. The objective of this study is to compare the effects of four different N horizontal placement methods (i.e., annular canal (An), radial canal (Ra), band (Ba), and nest fertilization (Ne)) with urea broadcast (Br) on nitrous oxide (N2O), methane (CH4), and soil heterotrophic respiration carbon dioxide (CO2) emissions from an apple orchard to assess the seasonal and spatial variations in these gas emissions. The total cumulative GHG emissions are determined through spots that are differentiated as fertilized or unfertilized. A field simulation study is conducted in an apple orchard, and all N sources have an application rate of 300 kg N ha?1. from the Br treatment are significantly lower than those of other treatments, and the emissions from the Ne treatment are 1.7-fold higher than those of the Br treatment. Surprisingly, the cumulative N2O emissions from the Br treatment are significantly higher than those of the other four treatments. N horizontal placement does not significantly influence the soil CH4 sink. The CO2 emissions in the Br treatment are higher than in other treatments. High N2O emissions in the Br treatment result in a significantly higher GHG exchange than in other treatments, while the Ne treatment significantly reduces the GHG exchange throughout the measurement period. Therefore, optimizing N placement may serve as an effective way to reduce GHG emissions from arable soils.
关键词： nitrogen placement,nitrous oxide,nest fertilization,greenhouse gas emissions,nitrogen use efficiency
更新于2025-09-23 15:19:57
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Gas chromatography vs. quantum cascade laser-based??N <sub/>2</sub> O flux measurements using a novel chamber design
摘要： Recent advances in laser spectrometry offer new opportunities to investigate the soil–atmosphere exchange of nitrous oxide. During two field campaigns conducted at a grassland site and a willow field, we tested the performance of a quantum cascade laser (QCL) connected to a newly developed automated chamber system against a conventional gas chromatography (GC) approach using the same chambers plus an automated gas sampling unit with septum capped vials and subsequent laboratory GC analysis. Through its high precision and time resolution, data of the QCL system were used for quantifying the commonly observed nonlinearity in concentration changes during chamber deployment, making the calculation of exchange fluxes more accurate by the application of exponential models. As expected, the curvature values in the concentration increase was higher during long (60 min) chamber closure times and under high-flux conditions (FN2O > 150 μg N m?2 h?1) than those values that were found when chambers were closed for only 10 min and/or when fluxes were in a typical range of 2 to 50 μg N m?2 h?1. Extremely low standard errors of fluxes, i.e., from ～ 0.2 to 1.7 % of the flux value, were observed regardless of linear or exponential flux calculation when using QCL data. Thus, we recommend reducing chamber closure times to a maximum of 10 min when a fast-response analyzer is available and this type of chamber system is used to keep soil disturbance low and conditions around the chamber plot as natural as possible. Further, applying linear regression to a 3 min data window with rejecting the first 2 min after closure and a sampling time of every 5 s proved to be sufficient for robust flux determination while ensuring that standard errors of N2O fluxes were still on a relatively low level. Despite low signal-to-noise ratios, GC was still found to be a useful method to determine the mean the soil–atmosphere exchange of N2O on longer timescales during specific campaigns. Intriguingly, the consistency between GC and QCL-based campaign averages was better under low than under high N2O efflux conditions, although single flux values were highly scattered during the low efflux campaign. Furthermore, the QCL technology provides a useful tool to accurately investigate the highly debated topic of diurnal courses of N2O fluxes and its controlling factors. Our new chamber design protects the measurement spot from unintended shading and minimizes disturbance of throughfall, thereby complying with high quality requirements of long-term observation studies and research infrastructures.
关键词： gas chromatography,soil–atmosphere exchange,chamber design,nitrous oxide,quantum cascade laser,flux measurements
更新于2025-09-19 17:13:59
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Applicability of a gas analyzer with dual quantum cascade lasers for simultaneous measurements of N2O, CH4 and CO2 fluxes from cropland using the eddy covariance technique
摘要： We evaluated the applicability of a closed-path gas analyzer with two mid-infrared quantum cascade lasers (QCLs) for simultaneous measurement of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes from a cropland using the eddy covariance (EC) technique. The measurements were carried out in a typical vegetable field in the subtropical China during the wintertime, when the gas fluxes are at their lowest level in the year. A new approach was proposed to optimize the determination of lag times between the wind and gas concentration data, which was proven efficient to increase the reliability of the measured fluxes when the gas exchanges are weak. The dual-QCL analyzer showed a median precision (1σ) of 0.14 nmol mol?1 for N2O, 3.3 nmol mol?1 for CH4 and 0.36 μmol mol–1 for CO2 at sampling frequency of 10 Hz under the field conditions. Such precisions are better than, or comparable with, those of other commonly used closed-path or open-path gas analyzers, which are capable of measuring only one or two of the three gases. The detection limit of the EC system for measuring half-hourly fluxes were 0.05 nmol m?2 s?1 for N2O, 1.12 nmol m?2 s?1 for CH4 and 0.14 μmol m–2 s–1 for CO2. The results showed that 100% of the N2O, 87% of the CH4 and 96% of the CO2 fluxes were larger than the above detection limits. This study suggests that the EC technique using a closed-path gas analyzer with two quantum cascade lasers is qualified for reliable and simultaneous measurements of N2O, CH4 and CO2 fluxes from a subtropical cropland throughout the year. Moreover, EC method based on this type of gas analyzer provides an additional option for long-term and simultaneous flux measurements of the three greenhouse gases in a wide range of agricultural and natural ecosystems.
关键词： Nitrous oxide,eddy covariance,cropland,methane,flux,quantum cascade laser,carbon dioxide
更新于2025-09-19 17:13:59
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Quantifying Isotopic Signatures of N <sub/>2</sub> O Using Quantum Cascade Laser Absorption Spectroscopy
摘要： Nitrous oxide, N2O, is the environmentally most relevant constituent of the biogeochemical nitrogen cycle. Human activities, e.g. the agricultural use of mineral fertilizers, accelerate nitrogen transformations, leading to higher emissions of this strong greenhouse gas. Investigating the stable isotopic composition of N2O provides a better understanding of formation mechanisms to disentangle its variable source and sink processes. Mid-infrared (mid-IR) laser spectroscopy is a highly attractive technique to analyze N2O isotopocules based on their specific ro-vibrational absorption characteristics. Specifically, quantum cascade laser absorption spectroscopy (QCLAS) in combination with preconcentration has shown to be powerful for simultaneous and high-precision analysis of the main N2O isotopocules. Recently, in the scope of my PhD project, we have been advancing this analytical technique for the analysis of the very rare doubly substituted N2O isotopic species 15N14N18O, 14N15N18O, and 15N15N16O, also known as clumped isotopes. Currently, we are investigating the potential of these novel isotopic tracers to track the complex N2O production and consumption pathways. Improved understanding of the nitrogen cycle will be a major step towards N2O emission reduction.
关键词： Laser spectroscopy,Nitrous oxide,Greenhouse gas,Biogeochemical nitrogen cycle,Clumped isotopes
更新于2025-09-12 10:27:22