Agricultural activities can lead to nitrogen losses in the environment, particularly nitrate (NO 3 ) leaching and nitrous oxide (N 2 O) 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 2 O 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 2 O emissions were lower in OF (0.65 0.64 kg N ha 1 yr 1 ) than in CF fields (0.95 0.77 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, fl ax) 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 2 O 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 2 O – 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 2 O – 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 2 O emissions), with further margins of progress in both systems, including a better management of fertilisers, legumes and catch- crops.