Calculating greenhouse gas reductions

With the introduction of the Carbon Farming Initiative (CFI), have you considered what quantity of greenhouse gases a typical mixed- farming enterprise generates, or which farming enterprises generate the most and have the highest abatement potential? Obviously the answer to these questions will be different for each property and mix of enterprises.

The Australian Farm Institute with funding from MLA and DAFF has developed an online calculator to help answer these questions. The FarmGAS Scenario Tool allows a user to calculate the greenhouse gas emissions from a whole farm or from single enterprises.

The calculator is based on the greenhouse ‘accounting methods’ used by the Australian Government to calculate greenhouse gas emissions at the national level. From your own production data FarmGAS will calculate the emissions from your farm using these ‘accounting methods’. This produces a default or ‘National Greenhouse Gas Inventory (NGGI) compliant’ result.

However, there are some limitations with this approach. The national accounting methodology (NGGI) uses national and state average production figures for most calculations. For example, it assumes that 23% of wheat stubble is burnt and that 23.771% of fertiliser applied to dryland crops is nitrogen. For a NSW beef cattle farm, the NGGI assumes that, during spring the dry matter digestibility of pasture intake (DMD) is 55%; heifer calves weigh 75 kg and are growing at 0.5 kg/head/day. Of course, this may not represent what is actually happening on your property.

To overcome these limitations, FarmGAS allows the user to modify the production and emission amounts to suit their farm. For example, a user can adjust the areas of pasture and crop stubble burnt and the quantities of fertiliser applied. They can enter more representative amounts describing their livestock. For example, on a beef farm during spring the heifer calves might average 100 kg and grow at 0.9 kg/head/day, and the DMD might be 65%. These modifications produce a revised (more ‘farm-specific’) result.

So if a revised result is more farm specific, why does the FarmGAS calculator provide a default result? The answer lies in the introduction of the CFI. A default FarmGAS result can provide an estimate of abatement achieved that is consistent with national accounting method but uses your farm or enterprise area rather than the national or state average. The default result option is the simplest way to obtain an estimate of your greenhouse gas reductions without having to provide any more details than enterprise area, herd/flock structure or cropping type. This reduces the effort in reporting to the CFI Administrator on your project progress. The next step would be to provide, even more specific farm-level information and obtain a revised result.

The default calculation could be used in CFI methodologies that are going to be used by many producers across an industry. It may be far simpler to use a standard default calculation when many producers are using the same methodology and avoid the need for individual producers taking additional measurements to achieve an abatement result. The revised calculation may be more suitable for specific project methodologies that are only applicable to a few producers or a specific and well-defined area.

How else could FarmGAS be useful in implementing a CFI project? One of the principles of CFI projects is that there is no emissions ‘leakage’. This means for your project area (typically a farm), implementing a CFI project such as an environmental tree planting cannot result in an increase in emissions in another area, for example, an increase in the livestock stocking rate. FarmGAS allows a producer, advisor or researcher to calculate the effect of a CFI project on enterprises as well as the whole farm, and can help assessments of whether CFI principles such as leakage, can be met.

Although FarmGAS is flexible for assessing different production and emission scenarios, it is important to note that it is not a biophysical model. FarmGAS uses ‘static’ equations that do not include the physiology of plant and animal systems and their often complex interactions. For example, changes in pasture quality and the related effects on livestock growth factors have to be carefully considered before changing amounts to produce the FarmGAS revised results. Results will therefore differ between FarmGAS and biophysical models.

Reports allow users to download and save their results for auditing and compliance purposes or to just track trends over time. A Scenario Tool comparison report also allows comparison between scenarios and could be used to test which abatement strategy is most suited to the circumstances, or undertake what-if options. Finally, a gross margin tool allows the economics of each scenario to be assessed so a whole farm picture of economic and greenhouse gas results can be obtained.
FarmGAS can be accessed from here.

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