Greenhouse gas audits were undertaken by Ruth Hall for approximately 20 mixed farms in the Tamar Valley for Tamar Natural Resource Management Reference Group. The audits used a greenhouse gas emissions calculator called the Decision Support Framework for Greenhouse Accounting on Australian Dairy, Sheep, Beef or Grain Farms developed by the Victorian Department of Primary Industries in conjunction with Melbourne University. We also have experience with FarmGas developed by the Australian Farm Institute. Both these calculators are part of the National Carbon Accounting Toolbox.
The results consistently showed that the majority of emissions from these farms are enteric methane (i.e. methane produced by rumen fermentation in sheep and cattle). The use of nitrogen fertilisers provided some emissions, with some direct carbon dioxide emissions from fuel usage as well. On a number of farms plantations of Eucalypts were identified as providing an offset for some of the GHG emissions. The numbers suggest that extensive livestock grazing enterprises could potentially offset all their greenhouse gas emissions by planting around 20-30% of the farm to trees.