This study displays the effects of conservation tillage on N-availability and the N-balance of crops. Since 1992 mouldboard ploughing to each main crop and mulching (shallow tillage to a maximum depth of 10 cm) are compared in a sugar beet - winter wheat - winter barley - mustard (catch crop) crop rotation in the Harste tillage trial near Göttingen (North-West-Germany). Besides, N-fertilization is varied in four levels respectively to the crop. All crops are grown each year on three neighbouring fields. The experimental fields are organized in split-plot designs with four replications each. N-uptake of all three main crops increased with increasing N-fertilization. In sugar beet N-uptake was influenced by the tillage system. In average of all N-levels the sugar beets of the ploughed treatment took up more N (181 kg N ha-1) than those of the mulched treatment (149 kg N ha-1). N-uptake of the cereals was not affected by tillage. Only 42 % of the total N incorporated by sugar beet plants was withdrawn from the field by the roots, i.e. more than half of the incorporated N remained in the field by tops and leaves. In cereals 77 % of the incorporated N (average N-uptake: wheat 205 kg N ha-1, barley 143 kg N ha-1) was withdrawn from the field by the grain. The tillage effects on N-uptake of sugar beet affected the N-balance of the entire crop rotation. Almost settled balances were achieved in the high fertilization levels of the cereals (210 and 180 kg N ha-1) whereas in high fertilization levels of sugar beet (170 kg N ha-1) large balance surpluses occurred. Settled balances can be achieved without significant yield losses if N-fertilization of sugar beets is reduced to an amount necessary for maximum white sugar yield (in this case 50 kg N ha-1). During the course of the experiment the absolute height of the balances of the rotations decreased slightly which was due to an increasing yield level.