Restoring a worn-out pasture : What impact on greenhouse gas exchanges ?

The restoration of permanent pastures is often required in order to restore a productive state and the palatability of the grass. The restoration process consists on destroying the former vegetation using herbicides followed by tillage and reseed. The short term and long term impacts of such operations on the carbon cycle and N2O emissions are not well defined for old permanent pastures.
Therefore, a paired flux tower measurement campaign was started in March 2018 at the Dorinne Terrestrial Observatory in Southern Belgium, with the aim to study the impact of pasture restoration on CO2 and N2O fluxes exchanged by the ecosystem. The site is a 100-year-old intensively managed grassland which last restoration was performed more than 40 years ago. It is grazed by Belgian blue beef cattle and fertilized with around 120 kgN ha-1 per year on average, reflecting common practices in the area. A former study carried out at the same site, showed that the pasture acted as significant carbon sink before the start of experiment.
Two adjacent parcels belonging to the same farm were both equipped with identical instrumentation including eddy covariance measurements of CO2 (LICOR 7000) and N2O/CH4 (Aerodyne Inc. quantum cascade laser) exchanges to allow the comparison between a control and a restored plot subject to identical pedo-climatic conditions. Preliminary results of greenhouse gas fluxes will be presented in relation to climatic conditions and management operations and the evolution of soil ammonium and nitrate.