The transport of nitrogen (N) in runoff waters from agricultural watersheds has caused increasing concern in recent years because of its role in the accelerated eutrophication of natural waters

The concentration and amounts of NO3-N and TN transported in surface, accelerated subsurface, and subsurface runoff and stream flow draining a 20 ha pasture watershed were measured over a period of 3 yr. A slight decrease and increase of NO3-N and particulate N concentrations, respectively, were obtained with increased flow of the runoff types and stream, due to dilution and increased sediment transport, respectively. The concentration of NO3-N in surface, accelerated subsurface and subsurface runoff and stream flow averaged for the 3 yr was 0.3, 6.6, 4.8, and 4.6 mg 1-1, respectively, amounting to 0.5, 9.4, 11.6, and 16.8 kg ha l yr -1, respectively, transported annually. Although NO3-N accounted for only a minor proportion of the TN transported in surface runoff (10%) it was the main form of N (75%) transported in the other runofftypes and in streamflow. Subsurface runoffcontributed the major proportion of stream discharge (63%), and NO3-N (69~), particulate N (44%) and TN (65%) loading of the stream. The results are discussed in terms of non-point pollution of surface waters by NO3-N.