Modelling nitrous oxide emissions from mown-grass and grain-cropping systems: Testing and sensitivity analysis of DailyDayCent using high frequency measurements.

The DailyDayCent biogeochemical model was used to simulate nitrous oxide (NO) emissions from two contrasting agro-ecosystems viz. a mown-grassland and a grain-cropping system in France. Model performance was tested using high frequency measurements over three years; additionally a local sensitivity analysis was performed. Annual NO emissions of 1.97 and 1.24kgNhayear were simulated from mown-grassland and grain-cropland, respectively. Measured and simulated water filled pore space (r=0.86, ME=-2.5%) and soil temperature (r=0.96, ME=-0.63°C) at 10cm soil depth matched well in mown-grassland. The model predicted cumulative hay and crop production effectively. The model simulated soil mineral nitrogen (N) concentrations, particularly ammonium (NH), reasonably, but the model significantly underestimated soil nitrate (NO) concentration under both systems. In general, the model effectively simulated the dynamics and the magnitude of daily NO flux over the whole experimental period in grain-cropland (r=0.16, ME=-0.81gNhaday), with reasonable agreement between measured and modelled NO fluxes for the mown-grassland (r=0.63, ME=-0.65gNhaday). Our results indicate that DailyDayCent has potential for use as a tool for predicting overall NO emissions in the study region. However, in-depth analysis shows some systematic discrepancies between measured and simulated NO fluxes on a daily basis. The current exercise suggests that the DailyDayCent may need improvement, particularly the sub-module responsible for N transformations, for better simulating soil mineral N, especially soil NO concentration, and NO flux on a daily basis. The sensitivity analysis shows that many factors such as climate change, N-fertilizer use, input uncertainty and parameter value could influence the simulation of NO emissions. Sensitivity estimation also helped to identify critical parameters, which need careful estimation or site-specific calibration for successful modelling of NO emissions in the study region.