Quantification of ammonia losses from winter wheat using eddy covariance and low-cost samplers

Ammonia (NH₃)emissions stem mainly from agricultural sources and affect environment, climate and human health, thereby concomitantly reducing fertilizer nitrogen use efficiency. Reliable and representative measurements for typical field conditions as well as for potential mitigation options are needed as a basis for recommendations to policy makers and farmers. However, there is still uncertainty about the reliability of different NH₃ measurement methods for emissions from low intensity sources, such as synthetic fertilizers, and a lack of data on simultaneous comparative evaluations of different methods. The joint research project NH₃-Min aims at comparing combinations of different NH₃ samplers and sensors (e. g. acid traps, dynamic chamber, laser-based techniques), flux calculation approaches (e. g. IHF, ZINST, bLs-Windtrax, eddy covariance), and scales (small scale multi-plots, field scale) to accurately quantify emissions and evaluate mitigation options (e. g. use of inhibitors, injection, form of nitrogen).

This poster focuses primarily on the quantification of NH₃ concentrations and fluxes determined by a quantum cascade laser spectrometer (QCL) within an eddy covariance setup and the comparison to low-cost approaches, such as ALPHA passive diffusion samplers in combination with backwards Lagrangian stochastic (bLs) modelling (Windtrax). Measurements were carried out in Central Germany during the vegetation period in 2021 and 2022 in a winter wheat crop field, which received 3 urea fertilizer applications (to a total of 170 kg N) per year.

First results showed that under high ambient NH₃ concentrations, time-integrated QCL values compared fairly well with those from ALPHA samplers. Under a low concentration regime, however, a significant underestimation of ALPHA values was observed, thereby providing a basis for an estimation of the method-specific detection limit. High-frequency losses using a co-spectral method in the process of eddy flux calculation were estimated to be in the range of 25 to 30%. We found clear diurnal flux courses and emission peaks after each urea application. The net loss of NH₃ summed up to 3.6 kg N ha^-1 over the whole measurement period (March – July). In further steps, we will evaluate the performance of the Windtrax model for estimating NH₃ losses from field-scale fertilizer applications and investigate the sensitivity of differences in input concentrations on modelled NH₃ emissions. Our study is a step towards better comparability and integration of different NH₃ measurement techniques and is expected to provide useful tools for robust estimations of NH₃ emission factors for synthetic fertilizer applications.

The project is supported by funds of the German Government‘s Special Purpose Fund held at Landwirtschaftliche Rentenbank.