Reduced soil tillage can be an effective means of environmentally friendly cultivation of field crops. Farmers often criticize such systems having a negative effect on crop yields. Since 1993 two tillage systems (plough = mouldboard ploughing before each main crop to a depth of 30 cm; mulch = shallow tillage to a maximum depth of 10 cm) are compared in a long term trial to evaluate the effects of tillage on yield and yield components of sugar beet, winter wheat and winter barley. Additionally, the nitrogen fertilizer application is varied in four levels. Effects of the mulch treatment were found in sugar beet resulting in a reduced white sugar yield. A distinct interaction of tillage systems and nitrogen dose occurred. With increasing nitrogen application the differences between yields of the two tillage treatments decreased but did not equal. On the other hand, no differences in yields were observed for winter cereals which also did not differ in yield components.