Reduced soil tillage can be an effective means of environment friendly cultivation of field crops. Farmers often criticize such systems having a negative effect on crop yields. Since 1992 two tillage systems (plough = 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 experiment in Harste (near Goettingen, Northern Germany) to evaluate the effects of tillage on yield and yield components of sugar beet (SB), winter wheat (WW) and winter barley (WB). Additionally, the nitrogen fertilizer application is varied in four levels. The fertilizer levels are adapted to the respective crop (SB: 0, 50, 110, 170 kg N ha-1; WW: 0, 110, 160, 210 kg N ha-1; WB: 0, 80, 130, 180 kg N ha-1). Effects of the mulch treatment were found in sugar beets 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 could be observed for the winter cereals which also did not differ in the yield components.