Recently we sought some guidance on how a participant is allowed to move and reallocate strata between Carbon Estimation Areas (CEAs). Here I outline what the process is, and why some participants may want to do it:
Firstly, what does 'moving strata' mean?
It's important to mention that we're not talking about physically moving strata, rather we're talking about 'renaming' them to change which CEA they sit in within the baseline sample round (T0). From the regulator:
"The baseline sampling plan locks in the strata boundaries for that sampling round, meaning strata cannot be changed for that sampling round once the plan has been submitted. After baseline sampling is conducted, the CEA’s can be ‘changed’ to be comprised of different strata, provided the strata boundaries remain the same and your CEA’s have at least 3 strata with 3 samples per strata collected, as per Schedule 1 s6(1)(a) of the 2021 Soil Carbon Method and Part A Requirement 6 of the Supplement."
An Example
The diagram in Figure 1 outlines the T0 Sample Plan that has just been registered with the regulator. Relatively simple - CEA 1 is in red on the left, and CEA 2 is in green on the right.
The sample plan is approved by the regulator, then sampled. Eventually, the soil test results are returned from the lab.
Once the results a returned the participant chooses to 'reallocate' their Strata to alternate CEAs.
This might be done to group strata with similar soil carbon variances for discounting purposes (this can be calculated using FarmLab's CER calculation tools so a user can test which strata fit best within a CEA) or to better adjust for new management practices across a project
In the below diagram we see the participant decides to move Strata 1-3 into CEA 2, renaming it 'Strata 2-1'. They also move Strata 2-1 into CEA 1, renaming it to 'Strata 1-3'.
The participant has now changed the boundaries of CEA 1 and CEA 2 by reallocating strata amongst them.
Importantly the BOUNDARIES of the strata have not changed. This is because the boundaries are what were sampled, and so any changes to the boundaries of strata will adjust the amount of carbon being measured. The Strata are the 'base unit' for calculating carbon across a project.
This now forms the new T0 Sample round, with carbon and variance calculated using the new CEAs as determined by the measurements collected in each strata above.
Future Sample Rounds
In future sample rounds, the participant can re-adjust strata boundaries as long as their CEA boundaries remain. This might be done to better align to management practices across the farm, or because recent soil testing results show that changes in soil carbon might impact the variance across the original strata.
In this example, the participant has decided to change their strata accordingly in the T1 sampling round below:
You'll notice in the above diagram, the boundaries for CEA 1 (red) and CEA 2 (green) have not changed from what they reset in T0. However the participant has decided to make adjustments to the Strata boundaries within each CEA. This is completely fine, and will be sent to the regulator for approval prior to sampling.
Keep in mind, at this stage the participant CANNOT adjust their CEA boundaries as they did with the T0 sampling plan. This is because any changes in Soil Carbon in T1 will need to be compared to the baseline carbon levels in T0 using the CEAs as the comparison boundaries. If the CEA boundaries changed, the project would need to recommence (in reality the T1 sample plan would be disqualified by the regulator).
Conclusion
The ability to adjust CEAs within a sample round can provide participants with additional flexibility and help reduce variance discounts. We acknowledge some of the complexities around the protocol, which is why we've tried to provide our users with simple, low cost techniques for stratification and sample plan creation in FarmLab - meaning you can build strata and test and adjust according to what works best for you.
I'd also like to extend a very big thank you to the Clean Energy Regulator team for clarifying the above and providing the diagrams shown here. For any other guidance and advice relating to the method, we recommend reaching out to enquiries@cleanenergyregulator.gov.au.
For more guidance on stratification and CEA creation, check out the 2021 Supplement on Soil Carbon Measurement.