The conversion from ploughing to reduced tillage is discussed in the context of increased humus accumulation as an opportunity to mitigate climate change. To date, little attention has been paid to the question whether reduced tillage systems in organic farming result in increased nitrous oxide (N2O) emissions. Thus, as part of FiBL’s long-term tillage trial in Frick (Switzerland), N2O emissions were measured over a two-year period, and soil organic carbon stocks were measured down to a depth of 50 cm thirteen years after the trial started. The results were compared with other studies conducted in central Europe. There were no differences in N2O emissions between tillage systems during the wheat and grass-clover ley phase of the crop rotation. During the full two-year observation period, N2O emissions were slightly higher under reduced tillage. After thirteen years, the reduced tillage system showed a 7–8 % increase in soil organic carbon stocks at a profile depth of 0–50 cm compared to ploughing. By contrast, the average increase of about 3 % in soil organic carbon stocks measured in the five central European studies was non-significant. In all studies, a significant reallocation of humus in the soil profile was observed. Similarly to non-organic direct-seeding methods, the reduced tillage system with organic fertilization under organic farming conditions therefore results in humus accumulation in the topsoil, thus meeting soil conservation objectives. A calculatory offset of the Frick trial’s N2O emissions against the observed soil carbon increase showed that carbon sequestration under reduced tillage was about 1.8 t CO2-eq. ha–1 a–1 higher than with ploughing, thus making a slight positive contribution to climate change mitigation.
Reduced tillage in organic farming – climate aspects