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 x 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.