Lessons learnt from the use of passive samplers to measure ammonia emissions in multi-plot experiments

Chemical additives can reduce ammonia emissions from ammonium-containing fertilisers. We aimed to investigate the effect of an additive based on carboxylic acid derivatives on ammonia emissions from slurry. In a randomised multi-plot field trial, three slurry treatments with increasing amounts of the additive based on carboxylic acid derivates were tested in comparison to untreated slurry and mineral fertiliser. Ammonia emissions were measured with so-called passive samplers, a method already used in numerous studies. However, problems arose during the evaluation of the collected data, so we examined the methodology used in more detail. The results of the measurements were analysed with regard to their spatial distribution and temporal variation. The results show that the more additives were used, the less ammonia was emitted, up to an emission reduction of 48% at the highest additive application rate. However, the spatial distribution of ammonia emissions reveals a drift of ammonia and, thus, an interaction between the plots. Thus, even in unfertilised plots, ammonia emissions of up to 50% of the treatment with the highest emissions were determined. Furthermore, it was also proven that the different times at which the slurry was applied influenced the level of ammonia emissions. Due to the interaction between the plots and the temporal differences in the application of the slurry, measuring ammonia emissions with passive samplers in multi-plot field trials, as presented in this study, is not suitable to quantify differences between the ammonia emissions from different treatments. Based on these results, recommendations for the use of passive samplers to measure ammonia emissions in field trials are proposed.