Agricultural activities can lead to nitrogen losses in the environment, particularly nitrate (NO 3-) leaching and nitrous oxide (N 2O) emissions. This study aims to measure N losses from organic farming (OF) and conventional farming (CF) arable cropping systems, both adopted in a single farm, located on the same drained loamy soil in the Seine basin, in the North of France. Leaching was measured with ceramic cups and N 2O emissions with automatic and manual chambers over the 2011-2014 period. Manual chambers showed the same trend as automatic chambers but underestimated small variations and overestimated peak emissions. On average, N 2O emissions were lower in OF (0.650.64 kg N ha -1 yr -1) than in CF fields (0.950.77 kg N ha -1 yr -1). The mean amount of N leached was 13.3 kg N ha -1 yr -1 in the OF system during the 8-crops rotation (alfalfa 1, alfalfa 2, wheat, green bean, wheat, faba bean, wheat, flax) and 18.4 kg N ha -1 yr -1 in the CF system for a 3-crops CF rotation (legume, wheat, wheat), corresponding to 9 and 10% of total N inputs, respectively. Leached N and N 2O emissions expressed per unit of protein-N harvested were slightly higher in CF (0.11 kg NO 3-N kg -1 N yr -1 and 5.4 N 2O-N kg -1 N yr -1, respectively) than in OF systems (0.10 kg NO 3-N kg -1 N yr -1 and 4.7 g N 2O-N kg -1 N yr -1, respectively). These results show a relative lower environmental impact of OF practices compared to CF practices (-30% area-scaled and -12% yield-scaled for leaching and N 2O emissions), with further margins of progress in both systems, including a better management of fertilisers, legumes and catch-crops.
