Spatiotemporal patterns of ammonia fluxes on temperate dairy farm production grassland (Lolium perenne L.)

Abstract

The nitrogen cycle is significantly altered by agricultural activities such as animal husbandry and fertilization, which can turn the landscape from a natural sink of ammonia (NH3) to a net source. Ammonia fluxes at broader spatiotemporal scales have been well studied, however, smaller-scale, point source studies are needed to quantify atmosphere-biosphere nitrogen balances around individual agricultural sources such as extensively managed production grassland. The aim of this study was to quantify the spatiotemporal variation in NH3 fluxes on dairy farm production grassland (Lolium perenne L.) throughout a full year. We focused on the dairy stable as a point emission source, as well as on the management practices (such as slurry application) performed by farmers. The temporal variation in NH3 fluxes was assessed using novel automated dynamic flux chambers adapted for NH3. Manual flux chambers were deployed to determine spatial variation. While fluxes did vary spatially, we found significant losses of NH3 (99.6 %) during the growing and harvesting season (March to September). This was largely attributed to substantial emission rates directly after slurry application while net emission/deposition was close to zero during late-fall and winter. Overall, the net annual NH3-N emission of this production grassland was 12 kg ha-1 y-1. Post slurry application emissions were especially high during warm and dry weather conditions. Optimizing the timing of fertilization application according to local weather conditions can therefore serve as a management practice to limit NH3 emission, benefitting both farmers and the natural environment.