Using delta15N and delta18O to evaluate the sources and pathways of NO3 - in rainfall event discharge from drained agricultural grassland lysimeters at high temporal resolutions

The origin of NO yielded in drainage from agricultural grasslands is of environmental significance and has three potential sources; (i) soil organic mater (SOM), (ii) recent agricultural amendments, and (iii) atmospheric inputs. The variation in 15N-NO and 18O-NO was measured from the inter-flow and drain-flow of two 1 ha drained lysimeter plots, one of which had received an application of 21 m3 of NH-N-rich agricultural slurry, during two rainfall events. Drainage started to occur 1 month after the application of slurry. The concentrations of NO-N from the two lysimeters were comparable; an initial flush of NO-N occurred at the onset of drainage from both lysimeters before levels quickly dropped to