Leaching of nitrogen from arable land is an important factor contributing to increased nutrient loads to lakes and coastal waters. The aim of this study was to evaluate the impact of ley composition and time of incorporation on the nitrogen utilization by subsequent winter- or spring-sown crops and risks for nitrogen leaching. Therefore, a field investigation was carried out, using a split-plot design. Ten treatments with different preceding crops were used, i.e. five compositions of forage ley, three green manure treatments and two treatments with spring barley. Also three different times for incorporation of the crop residues were used (early autumn, late autumn or spring). No supplements of commercial fertilizer-N or manure were applied. The average grain yields were strongly influenced by the amounts of nitrogen in incorporated material. Early autumn incorporation gave acceptable grain yields, but rather large amounts of soil mineral nitrogen were found in late autumn which had disappeared before early spring, probably due to leaching. Late autumn and spring incorporation were both good choices with respect to reducing risks for leaching during the first winter and had positive effects on subsequent grain yields. Incorporation of ley residues in late autumn and in spring caused increased mineral-N content in soil during the following autumn.