Spatial and dynamic sensitivity analysis of a biophysical model of nitrogen transfers and transformations at the landscape scale

oral communication, texte intégral<br/>oral communication, texte intégral

English. Modelling complex systems such as agroecosystems often requires the quantification of a large number of input factors. Sensitivity analyses are useful to fix the appropriate spatial and temporal resolution of models and to reduce the number of input factors to be measured or estimated accurately. Comprehensive spatial and dynamic sensitivity analyses were applied to the Nitroscape model, a deterministic spatially distributed model describing nitrogen transfers and transformations in a rural landscape. Simulations were led on a virtual landscape that represented five years of farm management in an intensive rural area of 3 km². Cluster analyses were applied to summarize the results of the sensitivity analysis on the ensemble of model outcomes. The 29 studied output variables were split into five different clusters that grouped outcomes with similar response to input factors. Among the 11 studied factors, model outcomes were mainly sensitive to inputs characterizing the lateral transmissivity of soil. The horizontal resolution of the model was a significant factor driving ammonium and nitrate mineralisation, and uptake by plants. The vertical resolution of the model had the highest impact on the cumulate emissions of nitrous oxides. The interactions between the amount of nitrogen used in fertilization and the lateral transmissivity of soil was the most important factorial effect driving the amount of nitrogen in the catchment discharge.