Capitalising on the carbon economy – Greenhouse gas abatement in viticulture
Nitrous oxide (N2O) is a potent greenhouse gas (GHG) with a 100-year global warming potential 298 times that of carbon dioxide. N2O emissions from agricultural soils, especially those that receive nitrogen fertiliser, contribute significantly to the total pool of atmospheric GHGs. The purpose of this project was to establish baseline levels of N2O emissions from vineyards in a range of Australian wine regions and to assess the potential of different cover crops to mitigate N2O emissions and increase carbon sequestration in soil. In addition to field experiments, the project included presentations and workshops designed to raise the awareness of GHG mitigation strategies among grape and wine producers. This project was funded by the Department of Agriculture (DA) as part of the ‘Action on the Ground’ program.
Five on-farm trial sites, in the Hunter Valley, Margaret River, Murray Darling, Eden Valley and McLaren Vale regions, were established in 2012 to evaluate regional differences in N2O emissions from vineyards. N2O emissions from the Australian vineyards studied ranged between median values of 0.6 and 9 g N2O expressed as N per hectare per day. These values are low compared to the typical values from other crops, such as dairy pasture (22 g N2O-N/ha/day) or broccoli (72 g N2O-N/ha/ day), and reflect the efficiency of water and nitrogen use in Australian wine-grape production.
There is limited scope to make significant reductions in the already low levels of N2O emissions from vineyards. However, there may be an opportunity to reduce the total GHG emissions using alternative cover crop species or, in vineyards which use high volumes of organic nitrogen, by changing management practices.
Experiments at McLaren Vale compared the use of native Wallaby grass (Austrodanthonia) grown in the vineyard midrow with rye grass. N2O emissions during the growing season (spring and summer) were found to be significantly lower from the Wallaby grass midrow cover crop than the rye grass in the same vineyard. Furthermore, the low growth habit of the Wallaby grass meant that there was less requirement for slashing compared to the rye grass. This presented a further opportunity to reduce GHG emissions by using fewer tractor passes per season.
At Margaret River, N2O emissions were measured from a vineyard before and after the application of compost. The peak N2O emission (800 g N2O-N/ha/day) measured from the compost two days after application was significantly higher than any other N2O measurement from that vineyard. This represented both a significant contribution of GHGs to the atmosphere and an opportunity to more efficiently use the nitrogen being applied to the vines in the form of compost.
The measurement phase of the project is now complete. Results have been presented at a range of extension events across Australia and continue to be extended as part of the Extension and Outreach project.