N₂O emissions from the global agricultural nitrogen cycle – current state and future scenarios

Abstract. Reactive nitrogen (N_r) is not only an important nutrient for plant growth, thereby safeguarding human alimentation, but it also heavily disturbs natural systems. To mitigate air, land, aquatic, and atmospheric pollution caused by the excessive availability of N_r, it is crucial to understand the long-term development of the global agricultural N_r cycle.

For our analysis, we combine a material flow model with a land-use optimization model. In a first step we estimate the state of the N_r cycle in 1995. In a second step we create four scenarios for the 21st century in line with the SRES storylines.

Our results indicate that in 1995 only half of the N_r applied to croplands was incorporated into plant biomass. Moreover, less than 10 per cent of all N_r in cropland plant biomass and grazed pasture was consumed by humans. In our scenarios a strong surge of the N_r cycle occurs in the first half of the 21st century, even in the environmentally oriented scenarios. Nitrous oxide (N₂O) emissions rise from 3 Tg N₂O-N in 1995 to 7–9 in 2045 and 5–12 Tg in 2095. Reinforced N_r pollution mitigation efforts are therefore required.