Nitrous oxide (N2O) emissions were measured weekly to fortnightly between April 2001 and March 2002 from two riparian ecosystems draining different agricultural fields. The fields differed in the nature of the crop grown and the amount of fertiliser applied. Soil water content and soil temperature were very important controls of N2O emission rates, with a ‘threshold’ response at 24% moisture content (by volume) and 8 °C, below which N2O emission was very low. N2O fluxes were higher at the site that had received the most fertiliser N, but NO3−was not a limiting factor at either site. There was also a ‘threshold’ effect of rainfall, in which major rainfall events (≥10 mm) triggered a pulse of high N2O emission if none of the other environmental factors were limiting. These results suggest the existence of multiple controls on N2O emissions operating at a range of spatial and temporal scales and that non-linear relationships, perhaps with a hierarchical structure, are needed to model these emissions from riparian ecosystems.