In Germany the acreage grown with winter oilseed rape (OSR) is steadily increasing because of relatively high gross margins partly caused by the high demand for OSR in biofuel production. OSR is usually fertilized with high levels of nitrogen often exceeding 200 kg N ha-^-1 to achieve maximum yields but N offtake by the seeds is comparatively low leading to high N balance surpluses. Significant N losses before harvest and early harvest lead to a potentially high mineralization of both crop residues and soil nitrogen after harvest. As a result soil mineral N content can increase during autumn and large amounts of nitrate are likely to be leached with the percolation water. To optimize nitrogen fertilization practice to oilseed rape a coordinated research project was established investigating the suitability of soil and crop parameters as indicators of optimum N rates to winter oilseed rape. Based on two years field trials data from 6 locations results will be presented highlighting the effect of autumnal crop N uptake on optimum nitrogen fertilization rates and possible savings in nitrogen fertilizer amounts by adjusting N rates according to crop N uptake in autumn. Results from a multi year field experiment with different tillage operations (mouldboard ploughing vs. conservation tillage) and different succeeding crops (winter wheat, spring oats, catch crop) were analyzed using a dynamic simulation model. Results show that nitrate leaching during winter was only marginally affected by the amount of crop residues of OSR. N mineralization after OSR therefore originates mainly from the soil mineral nitrogen pool which was highly influenced by the intensity of tillage operations in autumn. It could be shown that catch crops have a high potential to diminish the soil mineral nitrogen pool in autumn because of N uptake up to 60 kg N ha^-1 before winter