Nitrate (NO3) loss from arable systems to surface and groundwater has attracted considerable attention in recent years in Ireland. Little information exists under Irish conditions, which are wet and temperate, on the eff ects of winter cover crops and diff erent tillage techniques on NO3 leaching. This study investigated the effi cacy of such practices in reducing NO3 leaching from a spring barley (Hordeum vulgare L.) system in the Barrow River valley, southeast Ireland. The study compared the eff ect of two tillage systems (plow-based tillage and noninversion tillage) and two over-winter alternatives (no vegetative cover and a mustard cover crop) on soil solution NO3 concentrations at 90 cm depth over two winter drainage seasons (2003/04 and 2004/05). Soil samples were taken and analyzed for inorganic N. During both years of the study, the use of a mustard cover crop signifi cantly reduced NO3 losses for the plowed and reduced cultivation treatments. Mean soil solution NO3 concentrations were between 38 and 70% lower when a cover crop was used, and total N load lost over the winter was between 18 and 83% lower. Results from this study highlight the importance of drainage volume and winter temperatures on NO3 concentrations in soil solution and overall N load lost. It is suggested that cover crops will be of particular value in reducing NO3 loss in temperate regions with mild winters, where winter N mineralization is important and high winter temperatures favor a long growing season.