Using a selection of Swiss long-term field experiments (LTEs), we investigate the nitrogen (N) cycling dynamics and nitrogen use efficiency (NUE) trends, to re-evaluate the NUE of selected fertilisers after repeated application. Studied LTEs follow Swiss practiced crop rotation, while differing in fertiliser treatment, amounts and experiment duration. The N cycling dynamics will be assessed for each fertiliser treatment and crop-rotation based on an approximative soil-system N balance, as defined by Oenema et al. (2003). In DEMO (conventional management situated in Zurich and running since 1989), NUE of farmyard manure, slurry, and NPK according to Swiss fertiliser norm, will be calculated for four crop rotation periods; in DOK, an experiment comparing three farming systems (biodynamic, organic and conventional), situated in Therwil since 1978, NUE of farmyard manure, slurry and NPK according to Swiss fertiliser norm will be calculated for six crop rotation periods in all three farming systems. Finally, in the Swiss oldest field experiment, ZOFE, situated in Zurich with conventional management, NUE of farmyard manure, sewage sludge, green-waste compost, combinations thereof with PK, and NPK according to Swiss fertiliser norm will be calculated for a period of 70 years since 1949 in eight crop rotation periods. The selected NUE indicators are first compared between fertiliser treatments of the same experiment to identify location related effects, and then standardised to compare analogous fertiliser treatments at differing locations. The results are then shared with Swiss policy makers to improve the overall fertiliser NUE at the legislation level, thereby fostering a reduction of the N losses at the national level. References Oenema O, Kros H, de Vries W. 2003. Approaches and uncertainties in nutrient budgets: implications for nutrient management and environmental policies. European Journal of Agronomy 20(1-2):3-16.
