Effects of reduced tillage on soil organic carbon and microbial activity in a clayey soilAlfredBernerauthorAndreasFliessbachauthorBrunoNietlisbachauthorPaulMäderauthorIn a long-term field trial recently launched (2002-2011), located in Frick (878 mm mean annual precipitation) near Basle, Switzerland, the effect of reduced tillage on soil fertility indicators and crop yield was studied in a heavy soil (45% clay) in a crop rotation under organic farming conditions. We present the results of soil analyses after three cropping years (2002-2005). Soil organic carbon (Corg) increased over that period by 7.4% (+1.5 g Corg kg-1 soil) in the 0-10 cm soil layer in the reduced tillage plots, while it remained constant in the ploughed plots. Soil microbial carbon (Cmic) and dehydrogenase activity (DHA, TTC-reduction) were 28% higher in reduced-tillage plots in this soil layer. Biological soil quality as calculated by Cmic to Corg was 15% enhanced under reduced tillage. In the 10-20 cm soil layer no significant Corg, Cmic, Cmic to Corg and DHA differences between the tillage schemes were found. It is suggested that reduced tillage improves important indicators of soil fertility during the conversion period. Long-term aspects of soil fertility, crop yield and weed infestation need investigation over a prolonged experimental period. Soil biology Soil quality Soil tillage2008Conference paper, poster, etc.