Large parts of East Germany are characterised by sandy soils with a high hydraulic conductivity. The risk of nitrogen leaching and groundwater pollution may be minimised by organic farming, which has expanded in Germany during recent years. The study was conducted on an organically. farmed rye field next to a lake in the state of Brandenburg between 2002 and 2004. In order to show how far organic farming may affect lake water quality, soil inorganic nitrogen (CaCl2 extraction) and denitrification (acetylene inhibition method) were studied along an aquatic terrestrial transition zone (A field site: 5 in above water level, B = field site: 1 in above water level, C riparian zone with macrophytes: 0.5 in above water level). Although the field did not receive any organic and mineral fertiliser there was a nitrogen leaching from the field to the groundwater caused by the weather. Nitrogen loss during the winter was 29 kg N ha(-1) y(-1) and 12 kg N ha(-1) y(-1) in 2002/03 and 2003/04, respectively. Deviation between the two years seemed to be caused by great differences in precipitation. No nitrogen loss was observed from a control site. High denitrification was measured at sites B and C indicating an efficient nitrogen removal capacity within the riparian buffer zone.