Intensive dairy farming, with grass-arable crop rotations is challenged by low N use efficiency that may have adverse environmental consequences. We investigated nitrate leaching and N fertility effects of grass-clover leys for five years in two organic crop rotations with different grassland proportions (33 and 67%) and five grassland managements in terms of cutting, grazing, fertilization and combinations thereof. In grass-clover, the combination of fertilization and grazing caused excessive leaching (average 60 kg N ha -1) but leaving out either fertilization or full-time grazing substantially reduced leaching losses to on average 23 kg N ha -1. There was no linear relationship between sward age and nitrate leaching. The annual N surplus of the grasslands was only weakly related to nitrate leaching ( R2=0.05, P50 kg N ha -1) with lupin and maize, where especially maize was consistently high in all five years (average 81 kg N ha -1). Great care should be taken during all phases of the dairy crop rotation where grasslands cause considerable build-up of fertility. With due care and the best management practice, nitrate leaching losses may be reduced to low levels.
