The effects of clipping frequency and nitrogen fertilisation on greenhouse gas emissions and net ecosystem exchange in an Australian temperate grassland

Grassland ecosystems store significant amounts of organic carbon (C) and have the potential to function as a source or sink of greenhouse gases (GHGs) under different environmental conditions and management practices. However, the effects of management (clipping frequency and N fertilisation) on the GHGs remain uncertain. In this study, a field-based experiment with automated-lid gas exchange chambers was conducted to simultaneously measure different GHG fluxes (CO2, N2O, CH4), their overall global warming potential (GWP-100) impact, and net ecosystem exchange (NEE) from a grassland. The experiment had two clipping frequencies (simulating moderate and high grazing intensity) and two nitrogen (N) fertiliser treatments (0 and 40 kg N ha−1 year−1). The measurements were conducted during two periods (each approximately 2 weeks long) of varied temperature and moisture in early autumn. High clipping frequency caused higher daily NEE emissions, higher GWP-100 impact and lower photosynthesis; however, it did not significantly affect these parameters. Nitrogen fertilisation effects were lower than the clipping frequency treatment, but the impact on N2O fluxes was likely to be dependent on the time of N application. Methane (CH4) was predominantly controlled by soil moisture, whereas nitrous oxide (N2O) was more strongly affected by temperature. N2O emissions increased significantly after the break-point temperature of 20°C. Our results have highlighted the sensitivity of CH4 uptake and N2O emissions to environmental conditions, particularly their increase under warmer temperatures. The main contributor of GWP-100 impact in this study was CO2 emissions and uptake. For the observation period, the grassland was a small C sink. For a comprehensive understanding, longer-term studies spanning over several years are needed to accurately assess the impact of different management practices on GHG emissions.