Nitrous oxide emissions and nitrate leaching in an organic and a conventional cropping system (Seine basin, France)

Agricultural activities can lead to nitrogen losses in the environment, particularly nitrate (NO3-) leaching and nitrous oxide (N2O) 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 N2O 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, N2O 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, 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 N2O emissions expressed per unit of protein-N harvested were slightly higher in CF (0.11 kg NO3-N kr, N yr(-1) and 5.4 N2O-N kg(-1) N yr(-1), respectively) than in OF systems (0.10 kg NO3-N kg(-1) N yr(-1) and 4.7 g N2O-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 N2O emissions), with further margins of progress in both systems, including a better management of fertilisers, legumes and catchcrops. (C) 2015 Elsevier B.V. All rights reserved.