Nitrous oxide emissions from applied nitrate fertiliser in commercial cherry orchards

The application of nitrate (NO₃^-) fertiliser is important worldwide in providing nitrogen (N) nutrition to perennial fruit trees. There is little information available on N losses to the environment from commercial cherry orchards, in relation to different timings of NO₃^- application. The emission of nitrous oxide (N₂O) gas is an important greenhouse gas loss from NO₃^- application, being responsible for 6% of anthropogenic global warming and a catalyst for depletion of stratospheric ozone. In a commercial sweet-cherry orchard in southern Tasmania, we applied 373 g NO₃^--N m^-2 (equivalent to 90 kg NO₃^--N ha^-1) either pre- or post-harvest, or equally split between the two, to study the resultant N₂O emissions. Emissions averaged 8.37 mg N₂O-N m^-2 day^-1 during the pre-harvest period, primarily driven by a heavy rainfall event, and were significantly greater (P < 0.05) than the average 4.88 × 10^-1 mg N₂O-N m^-2 day^-1 from post-harvest NO₃^- application. Discounting the emissions related to the rainfall event, the resultant average 1.88 mg N₂O-N m^-2 day^-1 for the rest of the pre-harvest emissions remained significantly greater (P < 0.05) than those post-harvest. Ongoing studies will help to build on these results and efforts to minimise N₂O emissions in perennial tree cropping systems.