Evaluation of a new inference method for estimating ammonia volatilisation from multiple agronomic plots

Abstract

Abstract. Tropospheric ammonia (NH 3 ) is a threat to the environment and human health and is mainly emitted by agriculture. Ammonia volatilisation following application of nitrogen in the field accounts for more than 40 % of the total NH 3 emissions in France. This represents a major loss of nitrogen use efficiency which needs to be reduced by appropriate agricultural practices. In this study we evaluate a novel method to infer NH 3 volatilisation from small agronomic plots consisting of multiple treatments with repetition. The method is based on the combination of a set of NH 3 diffusion sensors exposed for durations of 3 h to 1 week and a shortrange atmospheric dispersion model, used to retrieve the emissions from each plot. The method is evaluated by mimicking NH 3 emissions from an ensemble of nine plots with a resistance analogue-compensation point-surface exchange scheme over a yearly meteorological database separated into 28-day periods. A multifactorial simulation scheme is used to test the effects of sensor numbers and heights, plot dimensions, source strengths, and background concentrations on the quality of the inference method. We further demonstrate by theoretical considerations in the case of an isolated plot that inferring emissions with diffusion sensors integrating over daily periods will always lead to underestimations due to correlations between emissions and atmospheric transfer. We evaluated these underestimations as −8 % ± 6 % of the emissions for a typical western European climate. For multiple plots, we find that this method would lead to median underestimations of −16 % with an interquartile [−8-22 %] for two treatments differing by a factor of up to 20 and a control treatment with no emissions. We further evaluate the methodology for varying background concentrations and NH 3 emissions patterns and demonstrate the low sensitivity of the method to these factors. The method was also tested in a real case and proved to provide sound evaluations of NH 3 losses from surface applied and incorporated slurry. We hence showed that this novel method should be robust and suitable for estimating NH 3 emissions from agronomic plots. We believe that the method could be further improved by using Bayesian inference and inferring surface concentrations rather than surface fluxes. Validating against controlled source is also a remaining challenge.

An Assessment of Low-Cost Techniques to Measure Ammonia Emission from Multi-Plots: A Case Study with Urea Fertilization

“…The uncertainty related to the use of IDM with integration time samplers, is slightly biased in function of the measurement conditions: plot size, measurement height and integration time. Following Loubet et al [34], then at the conditions given in this study this bias is almost negligible. In period 2 the total cumulative emission from Plot 1 (R20) and Plot 2 (R5) was about 4 kg NH 3 -N ha −1 and was also consistent between the measurement techniques within Plot 1.…”

“…At low wind speed and stable atmospheric conditions (night hours), the emission and the transport of NH 3 from surface to atmosphere may be low [33]. Furthermore, at low wind speeds the samplers may be located above the field boundary layer height, especially when a plot size is small [34]. Therefore no, or low, increase in NH 3 concentration is measured at the H ZINST height during this time.…”

“…Our recommendation is to measure NH 3 concentration at integration intervals of 12 h when plots are 5 m radius and wind speed in the range of this study. On the other hand, larger intervals than 12 h exposure should be avoided, because the uncertainty associated with the flux estimation with IDM is high [34]. Loubet et al [34] highlighted that passive diffusion samplers coupled with IDM underestimate NH 3 emissions of 8 ± 6% in a typical western European climate with a single source and high integration time, where larger biases could be produced with low wind speed and low emission strengths.…”

Urea Ammonium Nitrate Solution Treated with Inhibitor Technology: Effects on Ammonia Emission Reduction, Wheat Yield, and Inorganic N in Soil

“…So, the first hypothesis of our study is supported by the data. A similar approach was also applied with success by [46] while another multi-plot method with acid trap passive flux samplers also allowed differentiation of treatment effects [26,47]. As a result, standards for multi-plot NH 3 measurements with passive flux samplers should be developed by the groups that have successfully applied this approach.…”

Nitrogen use efficiency and N<sub>2</sub>O and NH<sub>3</sub> losses attributed to three fertiliser types applied to an intensively managed silage crop

“…During the 2016 measurements we were unable to obtain wind tunnels to measure NH3 flux as originally planned. Therefore, in 2017 fluxes of NH3 were derived using the FIDES inverse dispersion model as described in detail in Loubet et al (2010Loubet et al ( & 2018. This approach requires relatively large plots (20 m 2 ), and according to the farmers requirements needed to be set up in the Upper Joiner field, diagonally opposite from the Engineers field.…”