Is it possible to mitigate greenhouse gas emissions from agricultural soil by introduction of temporary grassland into cropping cycles ?

International audienceAgriculture contributes strongly to greenhouse gas emissions, in particular through the emission of N2O. In this study, we investigated the intensity of such emissions from French grassland soils under contrasting management by combining an experimental and a modelling approach. The objectives of this study were to measure and estimate N2O emissions and C storage at field scale and to assess the effects of grassland management on the processes determining soil organic C-storage and greenhouse gas emissions. Our conceptual approach included modelling of N2O emissions from grasslands and the investigation of the controls of N2O emissions by means of the characterisation of soil organic matter (SOM) composition as well as microbial communities. We continuously measured greenhouse gas emissions at long term grassland experiments in France. Moreover, we investigated the nature of SOM and the abundance and the activities of microbial communities in the soils from the different grassland managements. Our data indicated that grassland management practices, such as grazing, mowing, animal density, fertilisation and length of grassland periods, influenced soil C-storage, SOM composition and microbial abundance and activity. Such effects may be observed as legacy effects even after several years of cropping. Greenhouse gas emissions, in particular those of N2O, are strongly influenced by the management practices and their effects on SOM and soil microbial parameters. As they are contrasting, a compromise has to be found in order to ensure optimal ecosystem services of grassland systems