While emissions of nitric oxide (NO), ammonia (NH3) and nitrous oxide (N2O) from grassland soils have been increasingly well constrained, soil dinitrogen (N-2) emissions are poorly understood. However, N-2 losses might dominate total gaseous nitrogen (N) losses. Knowledge on N losses is key for the development of climate-adapted management that balances agronomic and environmental needs. Hence, we quantified all gaseous N losses from a montane grassland in Southern Germany both for ambient climatic conditions and for a climate change treatment (+2 degrees C MAT, -300mm MAP). Monthly measurements of soil N-2 emissions of intact soil cores revealed that those exceeded by far soil N2O emissions and averaged at 350 +/- 101 (ambient climate) and 738 +/- 197 mu gN m(-2) h(-1) (climate change). Because these measurements did not allow to quantify emission peaks after fertilization, an additional laboratory experiment was deployed to quantify the response of NH3, NO, N2O, and N-2 emissions in sub daily temporal resolution to a typical slurry fertilization event (51kgN ha(-1)). Our results revealed that total N gas losses amounted to roughly half of applied slurry-N. Surprisingly, N-2 but not NH3 dominated fertilizer N losses, with N-2 emissions accounting for 16-21kg or 31-42% of the applied slurry-N, while NH3 volatilization (3.5kg), N2O (0.2-0.5kg) and NO losses (0-0.2kg) were of minor importance. Though constraining annual N-2 loss remained uncertain due to high spatiotemporal variability of fluxes, we show that N-2 losses are a so far overlooked key component of the N balance in montane grasslands, which needs to be considered for developing improved grassland management strategies targeted at increasing N use efficiency.
Zistl-Schlingmann, M; Feng, JC; Kiese, R; Stephan, R; Zuazo, P; Willibald, G; Wang, CH; Butterbach-Bahl, K; Dannenmann, M
Dinitrogen emissions: an overlooked key component of the N balance of montane grasslands
Biogeochemistry