Dr Mike Beare1, Dr Steve Thomas1, Dr Roberto Calvelo Pereira2, Dr Sam McNally1, Mr Craig Tregurtha1, Mr Richard Gillespie1, Ms Gina van der Klei1, Professor Mike Hedley2
1New Zealand Institute for Plant & Food Research, Lincoln, New Zealand, 2Massey University, Palmerston North, New Zealand
Increasing soil organic carbon (SOC) has been proposed as one approach to reduce atmospheric CO2 concentrations and in turn help offset agricultural greenhouse gas emissions. In New Zealand grasslands, SOC is typically concentrated at the soil surface and declines rapidly with depth (i.e. highly stratified). The use of full inversion tillage (FIT) during pasture renewal (FIT-renewal) has been proposed as a method to enhance SOC sequestration. In addition to demonstrating these benefits, it is important to ensure that FIT-renewal does not result in other environmental trade-offs, such as increased N2O emissions. Two field trials were established in New Zealand (North and South Islands) to compare N2O emissions from FIT-renewal to those of No-tillage renewal (NT-renewal) and continuous pasture. Chamber measurements of N2O emission were made during pasture re-establishment and in subplot experiments designed to derive emission factors for N fertiliser and urine (e.g. EF1 and EF3) under the same treatments. At the North Island site, losses of mineral N were increased during winter and spring under FIT compared to NT-renewal and continuous pasture, but this was not associated with an increase in N2O emissions. N2O emissions from urine were reduced under FIT-renewal compared to NT-renewal and continuous pasture. Similar results were obtained at the South Island site where N2O emissions were lower during pasture establishment and the emission factor for urine under FIT-renewal was significantly lower than NT-renewal or continuous pasture. The results of these trials offer a promising solution to reduce N2O emissions during the first year of pasture renewal, but further research is need to evaluate the effects of FIT-renewal on pasture production, SOC sequestration and N2O emissions over a longer timeframe.