Short-term effect of tillage intensity on N2O and CO2 emissions

The effect of tillage on the overall greenhouse gas balance of croplands is not clear. It has been suggested that ceasing tillage increases C sequestration, but has the risk of enhancing N2O emission, which could switch the greenhouse gas balance from negative to positive. We studied the short-term effect of tillage intensity on N2O and CO2 emissions. We changed reduced tillage to conventional tillage or no tillage and performed two tillage operations in two growing seasons. All other parameters such as agricultural management, climate, and crop type at the study site, an intermediately aerated Luvisol in Belgium, were similar. Nitrous oxide and CO2 emissions were measured event-directed about 40 times per year from September 2006 until December 2008 using a closed chamber technique. We did not observe any significant short-term effect of tillage intensity on N2O emissions during the 2 years following tillage conversion. The 2-year aggregated N2O emission was not affected by the absence of tillage, 5.6 kg N2O–N ha−1, compared to conventional tillage, 4.6 ± 0.9 kg N2O–N ha−1, or reduced tillage, 4.7 ± 0.3 kg N2O–N ha−1. Enhanced N2O emission events in the absence of tillage, 1 year after conversion, could be explained by the combination of higher N application and wetter conditions. Conversion to conventional tillage caused a small, but significant, increase in CO2 emission over the same period. We conclude that in the short term, none of the tillage intensities had an effect on N2O emission, and the effect on CO2 emission was slightly positive when tillage intensity increased. A low short-term risk of increased N2O emission in the absence of tillage in well-aerated croplands is beneficial agro-environmentally, but the long-term effect should also be assessed via follow-up studies.