Measurement of ammonia emissions in multi-plot field experiments

Micrometeorological measurement techniques are regarded as standard methods for determining ammonia emissions following the field application of mineral fertilisers and animal slurries. In contrast with the standard agricultural experimental designs used to investigate crop productivity and crop nutrient status, the areas used for these measurements are large. To investigate the feasibility of making ammonia (NH3) loss measurements under field conditions using small plots, NH3 losses were determined following field application of different organic N fertilisers (pig and biogas-slurries) at two locations using conventionally designed agronomic multi-plot field trials in the federal state of Schleswig-Holstein, Germany, during 2007 and 2008. In order to handle a high number of replicate measurements in small (12 × 12 m) experimental plots, the potential influence of neighbouring plots on each other was established using passive flux samplers as used in the standard comparison method (SCM). Quantitative losses (kg [NH3] ha−1) were derived from measurements with two alternative methods: a) Dräger tube method (DTM) - a variant of an open dynamic chamber system, b) the backwards Lagrangian stochastic dispersion method (bLs) - a micrometeorological measurement method. The combination of SCM samplers with both DTM and bLs measurements proved to be appropriate for determining quantitative NH3 losses in multi-plot designed field trials. The influence of neighbouring plots on NH3 uptake could easily be identified and taken into account in the data analysis. Results determined by DTM and bLs were in good agreement and deviations from the final cumulative NH3 losses obtained by the DTM were in the range of ±4% of the bLs values.