Assessing N cycling and N2O emissions from ley within a crop rotation using measurements and modeling

Nitrous oxide (N₂O) is a significant greenhouse gas that contributes to climate change, with one of the major sources being agricultural fertilizer application. In Europe, grass-clover ley plays a crucial role in the agricultural ecosystem. However, N₂O emissions and emission factors (EFs) associated with it are not well documented. We therefore monitored N₂O emissions in grass-clover ley and assessed the feasibility of using the process-based model DayCent to simulate N₂O emissions and the underlying N cycling. The experiment was undertaken in a long-term fertilization experiment on a ley–arable rotation in Switzerland. We compared N₂O emissions and EFs from organic fertilizer (slurry), mineral fertilizer and control (unfertilized) plots over three years (2021–2023). The results showed average N₂O emissions of 0.50 ± 0.08, 0.51 ± 0.03 and 0.01 ± 0.04 kg N ha^-1 yr^-1 from organic, mineral and control treatments, respectively. The N₂O EF, which was determined from measured emissions of the fertilized treatments after subtracting of the control treatment, was much lower than the IPCC default of 1%, with values of 0.22% and 0.40% for organic and mineral fertilizer treatments, respectively. DayCent was adjusted for plant C/N ratio parameters and the biological N fixation parameter. It accurately predicted soil moisture, soil temperature, and aboveground N yield, with deviations of 2.2%, 4.4%, and 6.0% from the measured values. Concerning N₂O emissions, DayCent simulated average EFs of 0.24% and 0.28% for organic and mineral fertilizers, respectively, suggesting a good agreement with the measurements. Our field observation and model simulation results indicate that using IPCC default EF may overestimate the N₂O emission from grass-clover ley, and that, DayCent is able to reproduce the comparatively low N₂O emissions.