The greenhouse gases CO 2 and N 2O emissions were quantified in a long-term experiment in northern France, in which no-till (NT) and conventional tillage (CT) had been differentiated during 32 years in plots under a maize-wheat rotation. Continuous CO 2 and periodical N 2O soil emission measurements were performed during two periods: under maize cultivation (April 2003-July 2003) and during the fallow period after wheat harvest (August 2003-March 2004). In order to document the dynamics and importance of these emissions, soil organic C and mineral N, residue decomposition, soil potential for CO 2 emission and climatic data were measured. CO 2 emissions were significantly larger in NT on 53% and in CT on 6% of the days. From April to July 2003 and from November 2003 to March 2004, the cumulated CO 2 emissions did not differ significantly between CT and NT. However, the cumulated CO 2 emissions from August to November 2003 were considerably larger for NT than for CT. Over the entire 331 days of measurement, CT and NT emitted 3160269 and 4064138 kg CO 2-C ha -1, respectively. The differences in CO 2 emissions in the two tillage systems resulted from the soil climatic conditions and the amounts and location of crop residues and SOM. A large proportion of the CO 2 emissions in NT over the entire measurement period was probably due to the decomposition of old weathered residues. NT tended to emit more N 2O than CT over the entire measurement period. However differences were statistically significant in only half of the cases due to important variability. N 2O emissions were generally less than 5 g N ha -1 day -1, except for a few dates where emission increased up to 21 g N ha -1 day -1. These N 2O fluxes represented 0.800.15 and 1.320.52 kg N 2O-N ha -1 year -1 for CT and NT, respectively. Depending on the periods, a large part of the N 2O emissions occurred was probably induced by nitrification, since soil conditions were not favorable for denitrification. Finally, for the period of measurement after 32 years of tillage treatments, the NT system emitted more greenhouses gases (CO 2 and N 2O) to the atmosphere on an annual basis than the CT system.
