Green manuring of legume crops can improve soil fertility and sustainability. To evaluate its agronomic and environmental effectiveness, gaseous losses of ammonia (NH₃) in the surface layer need to be quantified by direct measurements in the field. However, the application of the eddy-covariance technique to atmospheric NH₃ is challenging: its high reactivity, water solubility, and low background concentrations all hinder the response time of closed-path sensors for fast measurements of NH₃ concentration. Ammonia emissions following green manuring were measured for 21 days using a flux system equipped with a fast-pulsed quantum-cascade tunable-infrared-laser spectrometer. The noisy cross-covariance function for this configuration indicates flux measurements are close to the limit of detection; the low signal-to-noise ratio further increases the uncertainties, introducing a mirroring effect on the fluxes, which results in the rapid alternation between emission and deposition, within the limit of detection (around 13 and 20 ng m⁻² s⁻¹, at the 95 and 99% confidence limits, respectively). An evaluation of the measurement errors is presented, focussing on three technical aspects of the eddy-covariance system: (1) time lag, (2) random error, and (3) limit of detection. The NH₃ fluxes measured by the spectrometer are close to its limit of detection, with a random error of the same order as the flux.

豆科作物的绿色肥料可以改善土壤肥力和可持续性。为了评估其农学和环境有效性，需要通过现场直接测量来量化表层中氨气（NH ₃）的气态损失。但是，将涡度协方差技术应用于大气NH ₃具有挑战性：其高反应性，水溶性和低背景浓度都阻碍了用于快速测量NH ₃的闭合路径传感器的响应时间。专注。使用装备有快速脉冲量子级联可调谐红外激光光谱仪的通量系统，对绿肥处理后的氨气排放进行了21天的测量。此配置的噪声互协方差函数表明通量测量值接近检测极限；低的信噪比进一步增加了不确定性，对通量产生了镜像效应，从而导致了发射和沉积之间的快速交替（在检测范围内（约13和20 ng m ^-2  s ^-1，分别在95％和99％的置信度下）。提出了对测量误差的评估，重点是涡度-协方差系统的三个技术方面：（1）时间滞后，（2）随机误差和（3）检测极限。NH用分光计测得的_3个通量接近其检测极限，并具有与通量相同数量级的随机误差。