Determinants of annual fluxes of CO2 and N2O in long-term no-tillage and conventional tillage systems in northern France
Résumé
The greenhouse gases CO2 andN2O 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 CO2 and
periodical N2O 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 organicCand mineral N, residue decomposition, soil potential forCO2 emission and climatic dataweremeasured.CO2 emissions were significantly larger in NTon 53% and in CTon 6% of the days. From April to July 2003 and from November 2003 to March 2004, the cumulated CO2 emissions did not differ significantly between CT and NT. However, the cumulated CO2 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 3160 269 and 4064 138 kgCO2-C ha-1, respectively.The differences in CO2 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 CO2 emissions in NTover the entiremeasurement period was probably due to the decomposition of old weathered residues.NTtended to emit more N2O than CT over the entiremeasurement period.However differences were statistically significant in only half of the cases due to important variability. N2O 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 N2O fluxes represented 0.80, 0.15 and 1.32 0.52 kg N2O-N ha-1 year-1 for CT and NT, respectively. Depending on the periods, a large part of the N2O emissions occurred was probably induced by nitrification, since soil conditions were not favorable for denitrification. Finally, for the period ofmeasurement after 32 years of tillage treatments, theNTsystem emitted more greenhouses gases (CO2 and N2O) to the atmosphere on an annual basis than the CT system.