CARBON FARMING INITIATIVE

SOIL SAMPLING DESIGN

METHOD AND GUIDELINES

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DOCUMENT REVISION HISTORY

Version Date

1.1 14 July 2014

1.2 18 January 2018

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Table of Contents

Glossary .................................................................................................................................................. 6

1. Introduction ...................................................................................................................................... 8

1.1 CFI background ....................................................................................................................... 8

1.2 Overview of the soil sampling design ...................................................................................... 8

1.3 How to use this document ..................................................................................................... 10

1.4 Soil sampling design as part of a measurement-based soil carbon methodology ................ 11

2. Advice on soil sampling intensity and design ................................................................................ 12

2.1 How to use this section ......................................................................................................... 12

2.2 Deciding on the number of Carbon Estimation Areas ........................................................... 13

2.3 Deciding on the sampling intensity in each CEA .................................................................. 14

2.3.1 What characterises an adequate sampling intensity? .......................................................... 14

2.3.2 Variability in SOC .................................................................................................................. 16

2.3.3 Stratification of a CEA ........................................................................................................... 18

2.3.4 Numbers of strata and composites ....................................................................................... 18

2.3.5 Importance of adequate baseline sampling .......................................................................... 19

2.3.6 Modifying the sampling plan in subsequent rounds.............................................................. 20

3. Establishing the sampling plan ...................................................................................................... 20

3.1 Documenting the sampling plan ............................................................................................ 21

3.2 Identification of the project area ............................................................................................ 21

3.3 Defining Carbon Estimation Areas (CEAs) ........................................................................... 21

3.4 Stratification of a CEA ........................................................................................................... 22

3.5 Defining composites and assigning sampling locations ........................................................ 24

3.6 Locating a sampling location ................................................................................................. 25

3.7 Calculating the offset distance for subsequent sampling rounds .......................................... 26

4. Sampling over time ........................................................................................................................ 26

4.1 Offsetting the sampling locations .......................................................................................... 27

4.2 Assigning new random sampling locations ........................................................................... 28

4.3 Maintaining the same sampling plan ..................................................................................... 28

4.4 Reducing the sampling intensity ........................................................................................... 28

4.5 Increasing the sampling intensity .......................................................................................... 29

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5. Record keeping and reporting ....................................................................................................... 30

5.1 Record keeping requirements ............................................................................................... 30

5.2 Offsets report requirements .................................................................................................. 30

6. References ..................................................................................................................................... 30

7. Soil sampling design method ......................................................................................................... 31

Glossary............................................................................................................................................. 31

Part A. Sampling plan ........................................................................................................................ 32

A.1 Sampling plan .......................................................................................................................... 32

Part B. Identification of Project Area ................................................................................................. 32

B.1 Identification of project area .............................................................................................. 32

Part C. Defining CEAs ....................................................................................................................... 33

C.1 Division of project area into CEAs ..................................................................................... 33

C.2 Requirements for a CEA ................................................................................................... 33

C.3 Delineating CEA boundaries ............................................................................................. 33

Part D. Stratification of CEAs ............................................................................................................ 33

D.1 Stratification of each CEA ................................................................................................. 34

D.2 Requirements of strata ...................................................................................................... 34

D.3 Delineating stratum boundaries ........................................................................................ 34

Part E. Defining composites and assigning sampling locations in each CEA ................................... 34

E.1 Defining composites .......................................................................................................... 34

E.2 Assigning sampling locations in each CEA ....................................................................... 35

E.3 Locating a sampling location ............................................................................................. 35

E.4 Calculating the offset distance .......................................................................................... 35

Part F. Subsequent rounds of sampling ............................................................................................ 36

F.1 Offsetting sampling locations ............................................................................................ 36

F.2 Maintaining the sampling plan ........................................................................................... 36

F.3 Sampling with a reduced number of composites for a CEA ............................................. 37

F.4 Sampling with an increased number of composites in a CEA .......................................... 37

Part G. Record keeping requirements ............................................................................................... 37

G.1 Record keeping requirements ........................................................................................... 37

Part H. Offsets report requirements .................................................................................................. 38

H.1 The first offsets report ....................................................................................................... 38

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H.2 Subsequent offsets reports ............................................................................................... 38

Appendix A. Guidance on sampling intensity and frequency to support the grazing systems methodology .......................................................................................................................................... 39

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GLOSSARY

carbon estimation area (CEA) means an area of land upon which the project activity is being undertaken; and which excludes areas of land upon which the project activity is not being undertaken.

CFI Mapping Guidelines means the guidelines of that name, as published from time to time, that is used to define the boundaries of a project area or of a carbon estimation area or exclusion area in a project area. Available on the Department’s website.

composite means a sample created by bulking and thoroughly mixing individual soil cores collected from different sampling locations.

exclusion area means an area of land within the project area that is not included in a carbon estimation area and is therefore not contributing to calculation of the magnitude of soil carbon stock change.

minimum detectable change means the smallest change in the SOC stock that can be detected with a defined level of confidence between two temporally separated sampling rounds.

offset distance means the maximum radius of the region of disturbance measured at the sampling location, or a default distance specified by the method, plus the error margin of the GPS device used to locate the sampling location on the ground.

project area means an area of land on which the set of activities has been, is being, or is to be, carried out. A Project Area is subject to CFI scheme obligations. Subsets of a Project Area that may be defined under a methodology determination include CEAs and exclusion areas.

pseudo-random number generator means computer software used for generating a sequence of numbers that approximates the properties of random numbers.

region of disturbance means the area disturbed by the removal of a soil core, including both the removal of the soil core and the surrounding ground disturbed due to the removal of the core. Where the area of the region of disturbance is to be avoided it is defined as the circle formed by either the maximum radius of the region of disturbance measured from the sampling location, or by the default distance specified by the method.

sampling design means instructions on the spatial layout of sampling locations, the number of samples and compositing of soil samples.

sampling location means the location, specified by a latitude and a longitude, at which a sample has been taken or is to be taken. The intended sampling location is the location where the sample is intended to be taken from. The actual sampling location is the location where the sample has been taken from.

sampling plan means within the Project Area, the positions of the CEAs, the strata, the number of composites and the sampling locations assigned to each composite.

sampling round means soil sampling to develop an estimate of SOC stock in the CEA.

sampling variance means variation in a particular statistic (e.g. the mean) calculated from a sample after being repeated many times.

spatial variance means the amount of variation, typically about the mean, that is found from samples at different locations in space.

seed number means a number input into a pseudo-random number generator for the purposes of generating a sequence of numbers that approximates the properties of random numbers.

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separation vector means a vector used to offset a sample location for the purpose of assigning a new sampling location for the subsequent sampling round. The length of the vector is the offset distance. The direction of the vector is randomly assigned.

SOC means soil organic carbon. stratum means an area in a CEA (strata plural).

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1. INTRODUCTION

1.1 CFI BACKGROUND

The Carbon Farming Initiative (CFI) allows farmers and other land managers to earn Australian Carbon Credit Units (ACCUs) by increasing carbon sequestration or reducing greenhouse gas emissions on the land. It is a condition of eligibility that offsets projects must use a methodology approved for use under the CFI. CFI methodologies set out the rules and instructions for undertaking CFI offsets projects, estimating abatement and reporting to the Clean Energy Regulator (CER).

Proposed methodologies are assessed by an independent expert committee, the Domestic Offsets Integrity Committee (DOIC). The DOIC is required to assess whether proposed methodologies meet the requirements of the offsets integrity standards as set out in section 133 of the Carbon Credits (Carbon Farming Initiative) Act 2011. For methodology developers, the key offsets integrity standards relevant to this document can be summarised as requiring that:

• the abatement should be measurable and verifiable; • the method should not be inconsistent with the methods set out in the National Inventory Report; • the method should be supported by relevant scientific results published in peer-reviewed literature; • any estimation, assumption or projection in the methodology should be conservative.

The CFI soil sampling design method (Section 7) has been assessed by the DOIC as being consistent with these standards as a component of a soil carbon CFI methodology.

The DOIC has endorsed the CFI soil sampling design method as a component of the Carbon Credits (Carbon Farming Initiative) (Sequestering Carbon in Soils in Grazing Systems) Methodology Determination 2014 (Grazing Systems Methodology).

1.2 OVERVIEW OF THE SOIL SAMPLING DESIGN

The CFI soil sampling design method and guidelines provides instructions for implementing a simple yet rigorous soil sampling design. A soil sampling design is a key component of a measurement-based estimate of soil organic carbon (SOC1) as it provides instructions on how to develop a sampling plan for a CFI project – i.e. where to take the soil samples.

The soil sampling design is broadly applicable across all cropping and mixed farming areas of Australia2. It is suitable for on-farm use at the paddock scale and does not require any prior knowledge of the spatial variability of SOC in the Project Area. The purpose of the design is to detect changes in SOC over time while minimising sampling costs. The sampling design in this document is stratified simple random sampling with compositing across strata (see box below).

1 Where SOC is referred to in this document it is assumed to mean SOC stock, i.e. an amount of SOC per hectare, unless otherwise specified. 2 For the purposes of implementing the Grazing Systems Methodology, the methodology specifies where a project can be undertaken.

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The main elements of the soil sampling design are: 1. Stratification: The Project Area is divided into one or more carbon estimation areas (CEAs). There are no

constraints on the size of a CEA; it can be any size. Each CEA is divided into equal areas (strata) (Figure 1). A sampling location is randomly allocated within each stratum for each composite sample in the sampling plan (see element 2 “creating composites” below and Figure 1). This approach is called stratified simple random sampling. It ensures that samples are taken from each part of the CEA, which is a very good design for getting an estimate of SOC that is representative of SOC across the CEA as a whole. A minimum of three strata must be included in each CEA, but enough strata should be used to adequately sample the CEA.

2. Creating composites: A single soil sample from every stratum is combined to create a composite sample (Figure 1). A sub-sample from each composite is analysed for SOC content. Creating a composite reduces the laboratory analysis costs as there is no need to analyse the SOC content of individual samples. A minimum of three composites are required in this method, but using more composites will improve the detection of change in SOC over time.

3. Sampling over time: The first round of sampling is used to establish the baseline SOC. Second and subsequent sampling rounds (e.g. every 2-4 years) are used to determine changes in SOC over time. In second and subsequent sampling rounds, the original sampling locations can be offset by a small distance or new random sampling locations can be selected, depending upon preference. Offsetting the original locations is likely to reduce the sampling variance which increases the ability to detect change in SOC over time compared to randomly selecting new sampling locations.

The soil sampling design has been developed by the Department of the Environment (the Department) based on the approach recommended by CSIRO in a technical paper Sampling soil organic carbon to detect change over time (Chappell et al 2013) commissioned by the Department and Grains Research and Development Corporation.

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Figure 1. A grid-based CEA with 9 strata and sampling locations for three composites (represented by green triangles, orange circles, and yellow stars). Samples from the locations marked with a triangle are combined to form one composite (green bucket), samples from the locations marked with a circle are combined to form another composite (orange bucket) and samples from the locations marked with a star are combined to form the third composite (yellow bucket).

1.3 HOW TO USE THIS DOCUMENT

The CFI soil sampling design method is a mandatory component of the Grazing Systems Methodology. In particular, the method, as in force from time to time, is adopted by a number of provisions in Parts 3, 4 and 7 of the Determination. It is also available for private methodology developers to use as a component of a CFI methodology proposal.

This document includes a soil sampling design method and guidelines:

• The method – presented in Section 7 of this document – describes the steps that must be undertaken by project proponents implementing the soil sampling design and complying with the Grazing Systems Methodology. The method includes the following components:

o Identification of Project Area o Defining CEA/s o Stratifying CEA/s o Defining composites and assigning sampling locations within strata o Sampling at subsequent points in time o Record keeping and reporting

• The guidelines – Sections 2-6 of this document – provide an explanation of the method and additional advice on how to implement the method. This advice is provided as guidance only. Sections 2-6 of this document are not compulsory.

The guidelines are intended for project proponents applying the CFI soil sampling design method as part of a measurement-based soil carbon methodology determination. It is strongly recommended to project proponents

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that the person implementing this soil sampling design method has experience in developing sampling plans and experience in the use of GIS software.

• Guidance is also provided at Appendix A on the choice of sampling intensity and frequency for a CEA to assist project proponents implementing the Grazing Systems Methodology.

Note for Methodology developers This soil sampling design method is available for use by methodology developers. Methodology developers would either include or reference this method in the following sections of a CFI methodology proposal: Project Area Determination (section 9), data collection (section 10) and project monitoring and record keeping (section 12).

Methodology developers will need to cross-check the soil sampling design against the other sections of their CFI methodology proposal to ensure there is consistency across the methodology. For example, the soil sampling design will influence the equations that are used to calculate the change in SOC over time in each CEA.

The methodology template is available on the Department’s website.

1.4 SOIL SAMPLING DESIGN AS PART OF A MEASUREMENT-BASED SOIL CARBON METHODOLOGY

A soil sampling design is only one component of a measurement-based soil carbon methodology. A full methodology contains instructions for estimating changes in SOC over time, plus additional information related to the particular abatement activity(ies) and project abatement calculation.

To estimate changes in SOC within a Project Area over time the steps involved are:

1. Develop a sampling plan for the Project Area based on a soil sampling design; 2. Sample collection; 3. Sample preparation; 4. Laboratory analysis; 5. Calculation of the organic carbon content of soil samples and SOC; and 6. Calculation of the change in SOC over time within each CEA.

This document provides a method and guidelines on the first step only. An approved CFI methodology determination will include or reference instructions on each of these six steps and other components. Project proponents will need to undertake all steps, in the correct sequence, according to the instructions in the methodology determination.

A schema of a measurement-based approach to estimating changes in soil carbon stocks over time is presented in Figure 2. This document – CFI Soil Sampling Design Method and Guidelines - is circled in red. Instructions on physical soil sampling to a standard required by the CFI are in the CFI Soil Sampling and Analysis Method and Guidelines available on the Department’s website. The CFI Soil Sampling and Analysis Method and Guidelines contain instructions for collecting, preparing and analysing composite samples as required by this sampling design.

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Figure 2. Role of CFI Soil Sampling Design Method and Guidelines in a measurement-based methodology. The schema shows the points at which the CFI Soil Sampling Design Method and Guidelines are used to measure the baseline SOC and a project round of sampling. SOC would be measured a number of times during the project in addition to the baseline. The soil sampling design may be modified during the project by changing the number of composites.

2. ADVICE ON SOIL SAMPLING INTENSITY AND DESIGN

2.1 HOW TO USE THIS SECTION

The information in this section (Section 2) of the CFI Soil Sampling Design Method and Guidelines is provided as guidance and it is not a requirement to use it as part of implementing the CFI soil sampling design method (Section 7 of this document). However, a project proponent may find this guidance useful and it is recommended that project proponents read Section 2 of this document.

The guidance in this section assumes that the project proponent has decided to undertake a soil carbon sequestration project and that they have decided where they will do the project (the Project Area). Project proponents are recommended to undertake appropriate due diligence on the financial costs and any potential returns of undertaking a project prior to submitting a project application. This section does not provide guidance on undertaking a due diligence assessment on the financial costs of undertaking a project; however, it does give some indication of factors that will affect sampling costs. Guidance to support the Grazing Systems Methodology (Appendix A) provides a list of factors to consider when deciding upon the sampling intensity and frequency for a CEA.

The guidance in this section (Section 2) assumes that the project proponent is using the soil sampling design described in this document, which is based on stratified simple random sampling and compositing. This soil sampling design does not require any prior knowledge of the variability of SOC within a Project Area.

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This section provides an overview of some key factors that a project proponent may wish to consider when deciding on the soil sampling plan for their project. The soil sampling plan is essentially the result of implementing the soil sampling design. It describes the Project Area and the number and location of CEAs, strata, composites and sampling locations within the Project Area.

There are a number of components to developing a soil sampling plan. When implementing the method the project proponent needs to decide:

1. Whether the Project Area should be split into more than one CEA; and 2. The number of soil samples (strata and composites) to take from each CEA.

These decisions are interdependent and it is suggested to consider them together.

The key factors influencing these decisions are discussed generally below, and the guidance on sampling intensity (Appendix A) provides some further information relevant to deciding upon the number of samples to take from a CEA for the Grazing Systems Methodology. There are likely to be other factors for a proponent to consider that relate to the project’s particular circumstances.

2.2 DECIDING ON THE NUMBER OF CARBON ESTIMATION AREAS

When implementing the CFI soil sampling design method, a project proponent needs to consider whether to use one CEA for the Project Area or whether to divide the Project Area into two or more CEAs. The soil sampling design will give an estimate of SOC for each CEA. The SOC estimate is an average for the CEA and contains no information on the variation of SOC within a CEA, which means that the CEA boundaries cannot be changed once established.

If one part of the Project Area is very different to another it may be better to establish more than one CEA because the likelihood of detecting change in SOC is greater in more homogeneous CEAs. Differences in land use, land-use history, land form and soil type all affect the SOC stock.

In addition, if one part of the Project Area is more at risk from a natural disturbance (e.g. erosion) then it may be worthwhile defining separate CEAs so that changes to SOC in the disturbance-prone CEA are measured separately from the rest of the Project Area. If a disturbance event occurred in the disturbance-prone CEA, it may not impact the ability to detect change in SOC over time in other parts of the Project Area.

Reasons to divide the Project Area into more than one CEA include:

• Parts of the Project Area have been subject to different land use histories; • Different management actions are going to be applied in different parts of the Project Area; • The same management actions are going to be applied across the Project Area but different parts of the

Project Area are expected to respond differently (e.g. an area with a higher rate of sequestration and an area with a lower rate of sequestration);

• A project proponent has knowledge of how SOC varies in the Project Area and they wish to incorporate this into their soil sampling plan;

• To help manage the impacts of a potential natural disturbance event; • The Project Area covers more than one land title and a project proponent wishes to be able to attribute

increases in SOC to each land title separately for their own administrative purposes.

The cost of sampling also needs to be considered when deciding whether to divide the Project Area into more than one CEA. The project proponent will need to reach a compromise between the cost of sampling and the desired precision of the SOC estimate. If a Project Area has two CEAs then two separate estimates of SOC will be determined. This is likely to increase sampling costs because each CEA will need to have a certain sampling intensity to detect change over time. For example, it is suggested to take no fewer than 6 strata and 3 composites for a CEA of 100 ha (Section 2.3.4); however, a 200 ha CEA, in this particular example only, might not require 12 strata and 3 composites, but may only need 10 strata and 3 composites – hence the sampling costs for one larger

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CEA in this example are lower than two smaller CEAs (see also Section 2.3.4 for a discussion on the effect of size of a CEA). However, if two CEAs are used instead of one, this can lead to a more precise estimate of SOC if each CEA is more homogeneous and this will improve the proponent’s ability to detect changes in SOC over time. Project proponents will have to make a decision on this trade-off based on their own circumstances. Sections 3.2 and 3.3 cover how to establish a Project Area and CEA respectively.

2.3 DECIDING ON THE SAMPLING INTENSITY IN EACH CEA

The objective of implementing the soil sampling design is to take enough samples to be able to detect a change in SOC over time in a cost effective manner. The number of samples taken from a CEA is the sampling intensity, and it is calculated by multiplying the number of strata by the number of composites.

The optimal sampling intensity for a CEA is influenced by two key factors:

1. The magnitude of change over time that the sampling regime is trying to detect. More samples need to be taken to detect smaller changes in SOC. The magnitude of change to be detected depends on the expected increase in SOC between sampling rounds (this in turn is dependent on the time between sampling rounds and the expected rate of SOC sequestration) and the way the full methodology determination calculates change in SOC; and

2. The variation in SOC across the CEA. To detect a particular change in SOC, more soil samples will need to be taken in CEAs which have large variation in SOC compared to CEAs with small variation in SOC.

This section (Section 2.3) provides general guidance on these factors to help project proponents decide on the sampling intensity for a CEA in their project. Each project proponent will need to balance the benefit of taking more samples with the costs of sampling.

2.3.1 What characterises an adequate sampling intensity? The minimum detectable change (MDC) is the smallest change in SOC that can be detected with a defined level of confidence between two temporally separated sampling rounds. Compared to other terms that may be used to guide sampling performance it is reasonably tangible. We use the term target MDC in these guidelines to describe the minimum amount of change in SOC that a project proponent wants to detect between two sampling rounds after having only undertaken the first sampling round. Factors that reduce the sampling variance - an increase in sampling intensity or small spatial variability in SOC in the CEA – will result in a small MDC for any given confidence interval. Figure 3 shows that when the spatial variability in SOC remains unchanged, the MDC becomes very large when a very few samples are taken (low sampling intensity). Figure 3 also shows that when a very large number of samples are taken, the MDC is small and does not reduce much with more samples. That is, the marginal benefit of taking more samples at high sampling intensities is small.

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Figure 3. The MDC at a 95% confidence level in detecting a change in mean SOC between two sampling rounds for different sampling intensities for the large spatial variation scenario in Figure 5 for a CEA of 100 ha. Figure 3 shows combinations from 1-10 strata and 1-10 composites to show the effects of sampling at very small intensities; however the minimum number of strata for this CFI soil sampling design method is 3 and the minimum number of composites is 3.

Sampling variance is a term we use in these guidelines which describes the spread in the estimate of the mean SOC. In this case it is determined from the composite soil samples. A small sampling variance is the result of each composite having a similar mean value for SOC; a large sampling variance is the result of each composite having quite a different mean value for SOC. The importance of maintaining an adequate sampling intensity can also be demonstrated using sampling variance (Figure 4). A good estimate of SOC in a CEA is where the mean SOC of the samples closely approximates the actual mean of SOC in the CEA. A good measure on whether this has been achieved is the sampling variance. Figure 4 is based on the large spatial variation scenario (Figure 5) and shows that when you take very few samples (low sampling intensity) the sampling variance becomes very large. It also shows that at high sampling intensities the sampling variance is small. When the sampling variance is very large, the sampling intensity is not adequate to provide a good characterisation of the SOC in the CEA. The best sampling intensity for a particular CEA will depend on a number of factors, including those discussed in this section.

Both sampling variance and the MDC can only be determined after a baseline sampling round for a particular CEA. To determine a sampling intensity for a CEA for a baseline sampling round, the best guidance is to understand the factors that affect the optimal sampling intensity for a CEA and to assume the CEA has large spatial variability in SOC as discussed in the next Section (Section 2.3.2).

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Figure 4. The sampling variance (t SOC ha-1)2 for one sampling round for the large spatial variation scenario in Figure 5 for a CEA of 100 ha. Figure 4 shows combinations from 1-10 strata and 1-10 composites to show the effects of sampling at very low intensities; however the minimum number of strata for this method is 3 and the minimum number of composites is 3.

The way in which a change in SOC is calculated in a full methodology may influence the choice of sampling intensity. Project proponents should seek advice on the sampling intensity that matches the method for calculating change in SOC for the full methodology that they are implementing. The guidance at Appendix A provides guidance that is relevant to the Grazing Systems Methodology.

2.3.2 Variability in SOC It is not possible to determine the number of samples required to detect a specific MDC in SOC without having prior knowledge of the variability in SOC across a CEA. The spatial variation in SOC is one of the most important factors influencing the sampling intensity that will be adequate for a CEA, and spatial variation in SOC can vary by an order of magnitude from place to place.

Figure 5 shows three hypothetical scenarios of spatial variance in SOC (large, medium and small) that were developed from global scientific literature by CSIRO and presented in the CSIRO technical report on which this method is based (Chappell et al 2013). Figure 5 shows that there is an order of magnitude difference in the semi-variance between the small and large spatial variance scenarios.

The actual spatial variation in SOC in a CEA could be determined using a reconnaissance survey; however, as that may not be a cost effective approach, it is not the approach taken in this soil sampling design method. In the absence of site specific information to undertake a baseline sampling round, the approach for this sampling design is to undertake the baseline sampling round by assuming variation in SOC in a CEA is large and to take many samples to accommodate this (see Section 2.3.4 for further guidance). It should be emphasised, however, that each CEA will differ in its actual spatial variation of SOC. The scenarios in Figure 5 are simply examples and will not match the spatial variation of the CEA that a project proponent is sampling, which may have larger or smaller spatial variation.

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Figure 5. Characteristic variograms (t SOC ha-1)2 developed by CSIRO for small, medium and large spatial variation in SOC. The scenarios were developed using published scientific literature. (Source: Chappell et al. 2013)

The effect of the size of the CEA The number of samples that need to be obtained for a target MDC in SOC depends in part on the size of the CEA. For a given location in Australia, a larger CEA will tend to have more variation in SOC than a smaller CEA. Figure 6 shows that when the number of samples taken remains the same (same sampling intensity) the MDC increases as the size of a CEA increases. This effect is less pronounced for a CEA that has a small spatial variation in SOC and more pronounced for a CEA with a large spatial variation in SOC. Furthermore, for the same spatial variability taking a large number of samples (10 x4) reduces the influence that the size of the CEA has on the MDC compared to taking a smaller number of samples (6x4). Figure 6 shows that spatial variance can increase rapidly (large scenario) as a CEA increases from a few hectares to 100 ha; therefore it should not be assumed for a baseline sampling round that small CEAs will require a small sampling intensity.

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Figure 6. The effect on MDC at a 95% confidence level of the small and large spatial variation scenarios (presented in Figure 5) at two sampling intensities (6x4 and 10x4) as the size of the CEA increases. The scenarios in this figure are not expected to match the variation in a project proponent’s CEA, but are provided for illustrative purposes.

This soil sampling design is not expected to be suitable for very large Project Areas where the increase in SOC is slow, such as in more arid areas, as it is unlikely to be cost effective to sample at an intensity required to detect a change in SOC over a reasonable time period (e.g. 4 to 5 years). For this reason, this soil sampling design is not considered suitable for areas of the Australian rangelands.

2.3.3 Stratification of a CEA This soil sampling design uses stratification to divide a CEA into equal-sized areas to ensure sampling locations are established from equally representative areas of the CEA.

Stratification for this sampling design does not require any consideration of the features that define SOC within a CEA. No regard needs to be given to soil type, topography or land use within a CEA.

Strata have to be equal sizes because a single core is taken from each stratum in the CEA to create a composite sample. This composite sample is then analysed to give a value for the average SOC in the CEA. A stratum within a CEA can be divided by a road or similar feature that is excluded from the CEA. This is described in Section 3.4.

Strata should be large enough to accommodate the sampling required in each stratum over the course of the project crediting period(s), which may include five or more sampling rounds. When developing the sampling plan the minimum size of the strata should also be a consideration, so that a CEA is not stratified into strata that are too small to allow for sampling as required by this method. Information on the required number of sampling rounds for a crediting period is not in the soil sampling design method but would be part of a full soil carbon methodology.

2.3.4 Numbers of strata and composites The sampling design requires that a minimum of 3 strata and 3 composite samples (nine samples in total) are included in each CEA to minimise the risk that a change in SOC over time is detected by chance. However, any

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CEA with only nine samples is likely to have a MDC in SOC that is too large to be able to detect changes in SOC over time within the CEA. It is recommended to take more than nine samples. It is difficult to recommend a minimum number of samples for a CEA as each CEA will differ in size, and more importantly in its spatial variability in SOC.

The sampling design does not allow for restratification of the CEA once the strata have been used for the baseline sampling round. For this reason, it is recommended to include enough strata to adequately sample a CEA with a large spatial variability in the baseline sampling plan. The more strata in the CEA the better the spatial coverage of the CEA by the soil sampling, and this leads to a better target MDC for the CEA. A sampling plan with too few strata will not achieve a good estimate of SOC for the CEA. A report by CSIRO (Chappell et al. 2013) estimated the effect of different sampling intensities on a 100 ha CEA. Based on this analysis, it is suggested, as a starting point, to undertake a baseline sampling round with no fewer than 6 strata and 3 composites for a CEA of 100 ha. It is suggested to use no fewer than 6 strata; however 8 or 10 strata may be more appropriate depending on the size of the CEA and the spatial variation in SOC. It is possible that more than 10 strata may be needed for some CEAs, especially if they are much larger than 100 ha.

It is possible to have different combinations of the number of strata and composites for a given sampling intensity (total number of soil samples). For example, a sampling plan for a CEA with 24 samples could include 6 strata and 4 composites or 8 strata and 3 composites. For this sampling design, a greater number of strata will reduce the sampling variance between composites, so it is suggested that, all other things being equal, the choice of 8 strata and 3 composites would be preferable.

The cost of field work compared to the cost of laboratory analysis should also be considered when designing a sampling plan as the cost of undertaking the sampling and analysis is an important consideration. Currently, laboratory analysis is likely to be more expensive than the cost of field work, which suggests that it may be cost effective to include more strata than composites for a given sampling intensity. Furthermore, field work is generally costed on a per day basis. A project proponent could, therefore, decide to make use of a full-day in the field by asking a contractor to take more samples than the proponent has estimated are necessary, for example by taking another sample(s) from each stratum to make up another composite(s). These extra samples, in the form of one or more composite samples, could then be kept aside and analysed later if there is higher than expected sampling variance in the CEA. It is possible to vary the sampling intensity in subsequent sampling rounds by varying the number of composites in a CEA; however, as previously stated it is not possible to vary the number or size of the strata in a CEA once they have been used for the baseline sampling round.

It is recommended that the project proponent undertakes their own analysis to decide upon the number of strata and composites to include in each CEA in the sampling plan for their Project Area. Guidance on sampling intensity at Appendix A provides a list of factors to consider as part of this analysis for project proponents undertaking the Grazing Systems Methodology.

2.3.5 Importance of adequate baseline sampling The overarching advice for the baseline sampling round is to take as many samples as are affordable (over-sample). Although the variation in SOC across a CEA is unlikely to be known prior to sampling, it should be assumed to be large and it is much better to over-sample in the initial baseline sampling round than to under-sample. Taking a large number of samples will ensure that the MDC in SOC over time is small enough to demonstrate an increase in SOC. Taking very few strata or composites is likely to result in only a very large change in SOC being detectable.

If the results of the baseline sampling round predict a very large MDC in SOC in the CEA this could be due to:

• Using too few samples and additional sampling effort is required.

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• Large spatial variation in SOC. Despite using many samples, the soil sampling plan may not be appropriate. It may be in the project proponent’s interests to abandon the existing soil sampling plan and instead undertake another baseline sampling round with an improved sampling plan.

• Inadequate sampling and sample preparation resulting in high variability between samples (see CFI Soil Sampling and Analysis Method and Guidelines for information on sample preparation and analysis).

2.3.6 Modifying the sampling plan in subsequent rounds The soil sampling design can be modified to reduce or increase the precision of the SOC estimate in a subsequent round of sampling by removing or adding composites using the existing CEA/s and strata.

If the baseline sampling round shows a smaller than expected target MDC, the sampling intensity could be reduced in a subsequent sampling round by removing a set of sampling locations from across the strata that form a composite (see Section 4.4 for instructions). This would reduce the sampling costs for that round of sampling, with the result that the project would only be able to detect a larger change in SOC. For example, the results of a baseline sampling round may have suggested that the sampling plan is sensitive enough to detect a MDC of 1 t SOC ha-1 over 4 years, and the proponent may be willing to take fewer samples in the subsequent sampling round to only detect changes of 2 t SOC ha-1 or more over the same time period. The project proponent should also be careful to understand how the approach to calculating change in SOC over time in a full methodology may influence the optimal target MDC for a CEA. For the purpose of these guidelines, MDC is a useful metric for helping to understand the implications of increasing or decreasing the sampling intensity in a CEA.

If the baseline sampling round shows larger than expected sampling variance, indicating that the sampling plan may not be adequate to detect the target MDC in SOC, it is similarly possible to modify subsequent sampling rounds to increase the sampling intensity by adding more composites (see Section 4.5 for instructions). The Grazing Systems Methodology allows 60 days for baseline sampling of the Project Area so it is possible to modify the baseline sampling round to add a composite/s after initial sampling as long as it is within this time limit (see Appendix A and the Grazing Systems Methodology for details). It is not possible, however, to add more strata or to change the strata in a CEA after the baseline sampling round. It is more difficult and costly to try to reduce the MDC in SOC after the strata have been used for the baseline sampling round. The large sampling variance in the baseline estimate is likely to limit the capacity to detect a change in SOC over time when that change is determined by the difference between the baseline estimate and the estimate from a subsequent sampling round. A methodology will provide instructions on how changes in SOC are estimated. It is recommended that the project proponent takes enough samples (over-samples) in the baseline sampling round so that this situation does not arise.

3. ESTABLISHING THE SAMPLING PLAN

A sampling plan is the result of deciding on the number and location of CEAs, strata, composites and sampling locations in the Project Area. It describes the pattern of sampling used to estimate SOC in each CEA. The method requires that a sampling plan for the Project Area must be developed in accordance with the method. The guidance in Section 2 and Appendix A and other advice may be used to help inform how to apply the method to the Project Area to develop an optimal sampling plan for the Project Area.

Sections 3.1 – 3.5 of this document are guidelines which explain the method for developing a sampling plan and give guidance on how the method may be implemented. Each section of the guidelines references the part of the method (Section 7) to which it applies. Only the method must be complied with when it is used as a component of a full soil carbon methodology determination.

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3.1 DOCUMENTING THE SAMPLING PLAN

These guidelines refer to Part A of the Method.

A sampling plan must be included in the offsets report (see Section 5.2). The offsets report will also document key parts of the process of developing the sampling plan and a number of other components of the method.

The sampling plan will document:

• The Project Area boundaries and area. • For each CEA within the Project Area, the boundaries, area and a unique identifier (name/number). • Within each CEA:

o the strata boundaries, areas and unique identifiers; o the number of composites to be taken from each CEA and unique identifiers for each composite in

each CEA. o the randomly assigned sampling locations in each stratum, identification of which composite they

are part of, and a unique identifier for each sampling location.

3.2 IDENTIFICATION OF THE PROJECT AREA

These guidelines refer to Part B of the Method.

A project proponent needs to specify the Project Area for a soil carbon sequestration project. There are a number of options for defining a CFI Project Area. The Project Area may be:

• The area where the project is being undertaken only; or • A single whole land title, including areas where the project is not being undertaken; or • Multiple land titles (properties) provided the project proponent holds the carbon property right to all the

areas included in the project.

The CFI Mapping Guidelines discusses some reasons why proponents may choose to define their Project Area one way or the other.

The CFI Mapping Guidelines provide detailed information on how to map the boundaries of the CFI Project Area, the guidelines are available on the Department’s website.

A full methodology may include additional rules for defining a Project Area and areas within the Project Area, such as exclusion areas. Project proponents implementing this method as part of a full methodology should consult that methodology to ensure they define a Project Area appropriately.

3.3 DEFINING CARBON ESTIMATION AREAS (CEAS)

These guidelines refer to Part C of the Method.

The soil sampling design requires that the Project Area is divided into one or more CEAs (see Figure 7). The sampling design will establish strata and composites separately for each CEA which will lead to a separate estimate of SOC for each CEA. This means that if a Project Area has two CEAs then two separate estimates of SOC will be determined. Section 2.2 provides a number of factors that may be considered when specifying a CEA.

A CEA must only contain land on which the soil carbon sequestration activity is being carried out. If the Project Area is the whole property, then areas where the activity is not occurring, such as a rocky outcrop or farm residence, must be excluded from a CEA (Figure 7). Refer to the CFI Mapping Guidelines for details on how to define exclusion areas.

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CEA boundaries must be mapped according to clause C.3 of the method and the CFI Mapping Guidelines.

Once the boundaries of a CEA are specified they may not be changed. This requirement differs from the CFI mapping guidelines that allows CEA boundaries to be changed. Where there is a discrepancy between the method and the CFI Mapping Guidelines, the method applies.

Figure 7. Project Area, Carbon Estimation Area and exclusion area for a soil carbon sequestration project.

3.4 STRATIFICATION OF A CEA

These guidelines refer to Part D of the Method.

This soil sampling design requires the creation of equally sized strata (areas) in each CEA using spatial coordinates only. The strata need to be the same size because one sample from each stratum will be contained in each composite sample; so each stratum needs to be equally representative of the area of the CEA as a whole. A small (five per cent) difference in the size of the strata in a CEA is allowable.

The number of strata created will depend on the project proponent’s preferred sampling intensity (Section 2.3) but a minimum of 3 strata is required. It is recommended that several strata be used to reasonably detect change over time (see Sections 2.3.3 and 2.3.4). Strata should also be large enough to accommodate the sampling required in each stratum over the course of the project crediting period or periods. Once the stratum boundaries are used to undertake a baseline sampling round they must not be changed.

If the CEA is square or rectangular, the easiest way to create strata is to use a regular grid to divide the CEA into strata of equal area (see Figure 1).

If the CEA is irregularly shaped and it is difficult to determine strata of equal area, then specialised equations and software can assist with the process (Figure 8). A useful reference for this is de Gruijter et al. (2006).

Details of the strata must be recorded in the sampling plan (Section 3.1).

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Figure 8. Evenly-sized strata in a CEA that is an irregular polygon. Each stratum has three sampling locations, one for each composite (represented by circles, triangles and squares).

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A stratum does not have to be spatially contiguous. Figure 9 illustrates an example where a road runs through a stratum.

Figure 9. This figure stratifies the CEAs from Figure 7 (above) to illustrate strata with an irregular shape in CEA 1 and a stratum in CEA 2 with a road through it. Each stratum in a CEA must have the same area. Figure 9 is not drawn to scale.

This soil sampling design does not require or use any prior knowledge of the spatial variability of SOC in the CEA to create strata. It is possible to modify the soil sampling design presented in this document to stratify a CEA based on knowledge of how SOC varies across the CEA; however, this is more complex and is beyond the scope of this document. If a proponent has prior knowledge of the spatial variability in SOC in the Project Area this can be incorporated in the soil sampling plan by influencing the number and location of the CEAs (Section 2.2).

3.5 DEFINING COMPOSITES AND ASSIGNING SAMPLING LOCATIONS

These guidelines refer to Clause E.1 and Clause E.2 of the Method.

The soil sampling design requires the creation of a minimum of three composites in each CEA, with each composite comprised of a soil core from each stratum of the CEA taken from a pre-assigned sampling location. Each composite requires a unique identifier to allow a sampling location to be identified as belonging to the composite and to allow the composites in the CEA to be identified and placed in order. It is important to be able to order the composites to allow a composite to be removed, if required, in a subsequent sampling round by removing the final composite in the sequence. For example, the unique identifier might include a name for the CEA (in this case “Top-paddock”) and an integer – so the identifiers of the composites are “Top-paddock1”, “Top-paddock2”, “Top-paddock3”, etc.

For each composite, one sampling location needs to be randomly assigned in each stratum using a pseudo-random number generator. The sampling location needs to be identifiable as belonging to that particular composite (e.g. “Top-paddock1”). The sampling location needs to be expressed in decimal degrees to 5 decimal places using Eastings and Northings. This will generate a sampling location accurate to approximately 1 metre. The assigned sampling locations must be recorded in the sample plan and the process for assigning the locations must be recorded in the offsets report. When soil sampling is undertaken, the soil core from each sampling location that belongs to a composite will be combined to form that composite sample.

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If a randomly assigned sampling location is too close to a sampling location that has already been assigned then it must be discarded and a new sampling location assigned. A sampling location is too close to an existing sampling location if it is closer than the expected offset distance (see Section 3.7). The expected offset distance is the error of the GPS device expected to be used to locate the sampling location on the ground and the expected distance that will be disturbed by removing a soil core at that sampling location. If these distances are not known it is recommended to be conservative and use a GPS error of 4 metres and an effect of disturbance of 5 metres, in which case all sampling locations in the stratum must be at least 9 metres apart. A randomly assigned sampling location must not be closer than the offset distance to a previous sampling location.

Pseudo-random number generators produce lists of numbers that appear random, that is without apparent pattern, and they can be related to the sample selection. For example, random numbers could be produced within the latitude/longitude range of a stratum. A known seed value needs to be entered, and the advantage is that the same exact list can be recreated if the “seed” conditions are repeated. This recreation allows for verification of the numbers used in the sample selection. Both the generator and the seed value used must be included in the offset report. For the purposes of this sampling design a pseudo-random number generator is taken to generate random sampling locations.

3.6 LOCATING A SAMPLING LOCATION

These guidelines refer to Clause E.3 of the Method.

A GPS must be used to locate the sampling location in the field. The GPS equipment used must have a horizontal positional error of no more than ± 4 metres. GPS equipment with positional averaging will greatly improve the positional accuracy that can be achieved using the equipment.

If the project proponent wishes to offset the sampling location for the purposes of determining a new sampling location in subsequent sampling rounds (Section 3.7) it is recommended that the GPS equipment has a horizontal positioning error of no more than ± 1 metre to more precisely locate the sampling locations. At present, this requires a differential GPS, which is specialised equipment. For this reason, this level of accuracy is recommended but not prescribed in the method.

The difference between the intended and actual sampling locations can be no more than 5 metres, unless the intended sampling location is obstructed. This distance between the intended and actual sampling location must be determined by comparing the GPS reading of the actual sampling location with the intended GPS sampling location.

This method uses random sampling from all parts of the CEA. The only reason to move a sampling location is if the soil at the sampling location is completely obstructed or inaccessible. The method does not avoid sampling in areas that are stock camps or watering points. Any very large obstacle, for example, a dam, should be excluded from the CEA when the sampling plan is prepared. A project proponent may also choose to exclude a clump of trees if the project activity is not occurring in this area.

If the sampling location is obstructed by a tree, a large immovable rock or any other obstruction that prevents soil sampling at the intended sampling location, then the actual sampling location is to be located by moving north (0 degrees) until the obstacle is cleared. If moving the actual sampling location north will take it outside of the stratum boundaries then move 15 degrees to the east until the obstacle is cleared. If moving the actual sampling location in this direction also takes it outside of the stratum boundaries, then move 30 degrees to the east and continue to change the direction in 15 degree increments until the obstacle can be cleared and the sampling location is within the stratum boundaries. The distance that may need to be moved could be small, for example, about 1 to 2 metres to clear a tree, or it might require moving a greater distance of around 5 metres. Very large obstacles should be excluded from the CEA. An obstacle is considered to be cleared when it is possible to take a soil sample. The coordinates of the actual sampling location must be recorded.

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3.7 CALCULATING THE OFFSET DISTANCE FOR SUBSEQUENT SAMPLING ROUNDS

These guidelines refer to Clause E.4 of the Method.

Taking a soil core removes an amount of soil, leaving a void, and may disturb the surrounding ground. The void and surrounding disturbed area is called the region of disturbance.

It is good practice to avoid the region of disturbance in subsequent sampling rounds. One way to do this is to move a defined distance from the actual sampling location of a previous sampling round in the subsequent sampling round. This distance is the offset distance. Keeping this offset distance small should introduce less spatial variability in the second round of sampling compared to sampling from entirely new randomly assigned locations. The soil sampling design method also allows for sampling from entirely new locations in subsequent sampling rounds as this is a more conservative approach.

The offset distance includes both the error of the GPS device used to locate the sampling location on the ground and a component representing the region of disturbance. This component can be measured by the proponent or based on default values. If this component is measured it is the maximum radius of the region of disturbance and it must be measured and recorded at each sampling location in each sampling round as it may differ.

An alternative to measuring the radius of the region of disturbance is to use a default distance. The default distances are:

• 1 metre for soil cores extracted where the soil is tilled between sampling rounds, as the process of tilling the soil creates disturbance that is similar to or greater than the disturbance created when the soil core is removed;

• 2 metres for soil cores extracted using hand-held cores where soil is not tilled; • 5 metres for soil cores extracted using machinery to aid extraction where soil is not tilled.

4. SAMPLING OVER TIME

These guidelines refer to Part F of the Method.

Sections 4.1 – 4.5 of this document are guidelines which explain the method for assigning sampling locations in subsequent sampling rounds following the baseline sampling round. Each section of the guidelines references the part of the method to which it applies. Only the method must be complied with when it is used as a component of a full soil carbon methodology determination.

The soil sampling design has been developed to detect a change in SOC over time. There are two options for sampling locations in subsequent sampling rounds:

• Option 1 is to offset the actual sampling location from the previous sampling round by a small distance (the offset distance, see Section 3.7), so that the spatial variance is minimised in the estimates of SOC over time.

• Option 2 is to assign new random sampling locations for each composite. This option will capture more spatial variance in the results, and will give a more conservative result for the change in SOC over time.

It is expected that it will be easier to detect a change in SOC over time by offsetting sampling locations (Option 1) for subsequent sampling rounds. Option 2 is provided for proponents who wish to obtain more conservative estimates of change in SOC over time and who wish to avoid having to calculate the offset distance.

The number of samples taken in subsequent sampling rounds may also be varied compared to the baseline sampling round. Reducing the number of sampling locations will reduce the sampling intensity (Section 4.4) and increasing the number of sampling locations will increase the sampling intensity (Section 4.5).

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The CFI soil sampling design method does not specify rules or constraints on the timing of subsequent sampling rounds. However, a full methodology may include such rules. For example, each sampling round may need to take place at approximately the same time each year to reduce the effect of intra-annual environmental variation on the SOC estimates. The Grazing Systems Methodology contains rules on timing which are in the methodology determination.

4.1 OFFSETTING THE SAMPLING LOCATIONS

These guidelines refer to Clause F.1 of the Method.

The process for offsetting sampling locations for a subsequent sampling round is described below.

A separation vector must be used to move from the actual sampling location for the baseline sampling round (t0 in Figure 10) to the new sampling location for the second round of sampling (t1 in Figure 10). The length of the separation vector is the offset distance. The direction of the separation vector is to be randomly assigned using a pseudo-random number generator with a known seed number. A random number generated between 0 and 359 is to be read as degrees from north (0 degrees). If the separation vector moves the new sampling location outside of the stratum boundaries, then the process of randomly assigning the vector direction should be repeated until the sampling location is within the stratum boundaries. This process should be documented.

The process for a third round of sampling is to use a separation vector to move from the actual sampling location from the second round of sampling to the new sampling location for the third round of sampling (see t2 in Figure 10). In the unlikely case where this leads the project proponent back to where the baseline soil core was removed, inclusive of the region of disturbance and GPS error, then the process of assigning a random direction for the separation vector should be repeated. This process should be documented.

The new (offset) sampling locations must be given a unique identifier which includes the new latitude and longitude (to 5 decimal places using decimal degrees), the sampling round (e.g. t1 in Figure 10), the date of sampling and the composite to which the sampling location is allocated. This is the same composite as for the previous sampling round.

In the field, a GPS should be used to locate the new sampling location for the subsequent sampling round. The GPS equipment used must have a horizontal positional error of no more than ± 4m; however GPS equipment with a horizontal positioning error of no more than ± 1 metre is recommended.

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Figure 10. Offsetting the sampling location using a separation vector. Arrows represent the separation vector and blue circles represent the point where the soil core is removed. Figure 10 shows the movement of a single sampling location in a stratum in a CEA over time.

4.2 ASSIGNING NEW RANDOM SAMPLING LOCATIONS

These guidelines refer to Clause E.2 of the Method

Where new sampling locations are to be randomly assigned for a subsequent sampling round, the process is the same as the initial process for randomly assigning sampling locations for the baseline sampling round.

For each composite, a new sampling location needs to be randomly assigned in each stratum using a pseudo-random number generator. The sampling location needs to be expressed in decimal degrees to 5 decimal places using Eastings and Northings. The assigned sampling locations must be recorded in the sample plan and the process for assigning the new locations must be recorded in the offsets report.

4.3 MAINTAINING THE SAME SAMPLING PLAN

These guidelines refer to Clause F.2 of the Method

If the baseline sampling round has produced an estimate of SOC with a target MDC for SOC that is acceptable to the project proponent, then the same sampling plan should be used for the CEA in the second round of sampling, but with the sampling locations either offset (Section 4.1) or reassigned (Section 4.2).

4.4 REDUCING THE SAMPLING INTENSITY

These guidelines refer to Clause F.3 of the Method

If the project proponent wishes to reduce the intensity of sampling in a subsequent sampling round, then this can be done by removing one or more composites from a CEA. The method requires that at least three composites are retained in each CEA in the revised sampling plan. Before proceeding, the project proponent should consider the

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effect of the reduced sampling intensity on the target MDC in SOC and any impact on the estimate of project-level abatement.

To reduce the number of composites in a CEA, retain the same strata and systematically remove the desired number of composites from the CEA. To establish the new sampling locations either:

• Option 1: Offset the sampling locations for the composites that are retained (Section 4.1); or • Option 2: Assign new random sampling locations for the composites that are retained.

To systematically remove a composite, remove the last composite in the set of composites for that CEA based on the unique identifiers for each composite. For example, if there are 6 composites in the “West-paddock” CEA, and the composites are named “West-paddock1”, “West-paddock2”, “West-paddock3” through to “West-paddock6”; then “Westpaddock6” is removed first, and “Westpaddock5” would be the next composite to be removed if the sampling intensity was reduced by two composites. The systematic removal of composites reduces any bias in removing composites if the option for offsetting sampling locations is chosen. For example, West-paddock2 may be sequestering soil carbon at a lower rate and it would be tempting to remove this composite from a subsequent round of sampling; however, the method requires that West-paddock6 is the composite removed if reducing the sampling intensity by one composite.

All changes need to be documented in a revised sampling plan (Section 3.1).

4.5 INCREASING THE SAMPLING INTENSITY

These guidelines refer to Clause F.4 of the Method

If the baseline round of sampling returns a sampling variance that is larger than desired, the intensity of the sampling design can be increased in subsequent sampling rounds to reduce the target MDC of the SOC estimate for the CEA. This can be done by increasing the number of composites. It is advisable to avoid having to increase the intensity of the sampling design in subsequent sampling rounds by adequately sampling in the baseline sampling round (see also advice in Section 2.3).

Another case where the project proponent may wish to increase the number of composites in the subsequent round of sampling is if there has been an event that has increased the spatial variation of SOC in the CEA compared to the baseline. In this case, the uncertainty in the SOC estimate in the second round of sampling is likely to be greater than in the baseline sampling round. This situation will result in a reduced ability to detect change over time (ie the actual MDC will be greater than the target (predicted) MDC). This may occur, for example, if a tillage event has occurred on only part of the CEA with no tillage on the other part.

The revised sampling design should retain the existing strata and sampling locations and add additional randomly defined sampling location/s to each stratum assigned to additional composite/s in accordance with Section 3.5. This change should be documented in a revised sampling plan.

Note that Section 2.2 separately considers the benefit of creating more than one CEA at the initial design phase to help manage how variation in management or natural disturbance can affect the estimates of changes in SOC across the Project Area.

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5. RECORD KEEPING AND REPORTING

These guidelines refer to Parts G and H of the Method

The reporting and record keeping requirements below pertain only to the soil sampling design in this document. A full methodology will contain a much greater number of monitoring, reporting and record keeping requirements. There are no monitoring requirements that are specific to the soil sampling design.

A geographic information system that meets the requirements of the CFI Mapping Guidelines must be used to report on geospatial information in accordance with the CFI Mapping Guidelines.

5.1 RECORD KEEPING REQUIREMENTS

Records must be kept of the information outlined in Part G of the Method. These records are required to be kept as they may be needed to verify that the sampling design has been carried out in accordance with this method.

5.2 OFFSETS REPORT REQUIREMENTS

The CFI requires that an offsets report is prepared and submitted to the CER three months after the end of a reporting period. An offsets report contains information about a project for the reporting period, including information used to determine whether the project has been implemented in accordance with the applicable methodology determination. For project proponents implementing the method in this document as part of a methodology, the offsets report must contain information that allows the CER to determine that the method has been implemented as required.

The information outlined in the Part H.1 of the Method must be included in the first offsets report submitted for the project.

The information outlined in Part H.2 of the Method must be included in subsequent offsets reports.

6. REFERENCES

Chappell A, Baldock JA, Viscarra Rossel RA (2013) Sampling soil organic carbon to detect change over time. CSIRO, Australia.

De Gruijter JJ, Brus DJ, Bierkens MFP, Knotters M (2006) Sampling for Natural Resource Monitoring. Springer, Berlin, Heidelberg, New York.

7. SOIL SAMPLING DESIGN METHOD

GLOSSARY

carbon estimation area or CEA means an area of land upon which the project activity is being undertaken; and which excludes areas of land upon which the project activity is not being undertaken.

CFI Mapping Guidelines means the guidelines of that name, as published from time to time, that is used to define the boundaries of a project area or of a carbon estimation area or exclusion area in a project area. Available on the Department’s website.

composite means a sample created by bulking and thoroughly mixing individual soil cores collected from different sampling locations.

exclusion area means an area of land within the project area that is not included in a carbon estimation area and is therefore not contributing to calculation of the magnitude of soil carbon stock change.

offset distance means the maximum radius of the region of disturbance measured at the sampling location, or a default distance specified by the method, plus the error margin of the GPS device used to locate the sampling location on the ground.

project area means an area of land on which the set of activities has been, is being, or is to be, carried out. A Project Area is subject to CFI scheme obligations. Subsets of a Project Area that may be defined under a methodology determination include CEAs and exclusion areas.

pseudo-random number generator means computer software used for generating a sequence of numbers that approximates the properties of random numbers.

region of disturbance means the area disturbed by the removal of a soil core, including both the removal of the soil core and the surrounding ground disturbed due to the removal of the core. Where the area of the region of disturbance is to be avoided it is defined as the circle formed by either the maximum radius of the region of disturbance measured from the sampling location, or by the default distance specified by the method.

sampling location means the location, specified by a latitude and a longitude, at which a sample has been taken or is to be taken. The intended sampling location is the location where the sample is intended to be taken from. The actual sampling location is the location where the sample has been taken from.

sampling plan means within the Project Area, the positions of the CEAs, the strata, the number of composites and the sampling locations assigned to each composite.

sampling round means soil sampling to develop an estimate of SOC stock in the CEA.

seed number means a number input into a pseudo-random number generator for the purposes of generating a sequence of numbers that approximates the properties of random numbers.

separation vector means a vector used to offset a sample location for the purpose of assigning a new sampling location for the subsequent sampling round. The length of the vector is the offset distance. The direction of the vector is randomly assigned.

SOC means soil organic carbon. stratum means an area in a CEA (strata plural).

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PART A. SAMPLING PLAN

Note: See section 4.4 of Carbon Credits (Carbon Farming Initiative) (Sequestering Carbon in Soils in Grazing Systems) Methodology Determination 2014.

A.1 Sampling plan (1) A sampling plan must be developed for the baseline sampling round and must be updated in

subsequent sampling rounds to incorporate changes to the sampling plan compared to the previous sampling round in accordance with Part F.

(2) The sampling plan must record: (a) the Project Area boundaries and area in accordance with Part B. (b) for each CEA, the boundaries, area and unique identifier (name/number) in accordance with

Part C. (c) within each CEA:

(i) the strata boundaries, area and unique identifiers in accordance with Part D. Evidence that the strata are evenly sized within a 5 per cent tolerance;

(ii) the number of composites to be taken from each CEA and unique identifiers for each composite in each CEA in accordance with Part E.

(iii) for the baseline sampling round, the randomly assigned sampling locations in each stratum, identification of which composite they are part of, and a unique identifier and coordinates for each sampling location in accordance with Part E.

(iv) for subsequent sampling rounds a statement specifying whether the sampling locations are offset or newly randomly assigned compared to the baseline sampling round; and either

a. the offset sampling locations, identification of which composite they are part of, and a unique identifier and coordinates for each sampling location in accordance with clause F.1; or

b. the randomly assigned sampling locations in each stratum, identification of which composite they are part of, and a unique identifier and coordinates for each sampling location in accordance with clause E.2.

(d) A geospatial map or maps identifying the geographic boundaries of the Project Area, each CEA, each stratum within each CEA and identifying each sampling location. The geospatial map or maps can be used to record some or all of the other information described in paragraphs (a), (b) and (c).

PART B. IDENTIFICATION OF PROJECT AREA

B.1 Identification of project area The project proponent must delineate the boundaries of the project area in accordance with the CFI Mapping Guidelines.

Note Regulation 3.1 of the Carbon Credits (Carbon Farming Initiative) Regulations 2011 includes a requirement to provide, in an application for a declaration of an eligible offsets project, a geospatial map of the project area that meets the requirements of the CFI Mapping Guidelines.

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PART C. DEFINING CEAS

Note: See section 3.3 of the Carbon Credits (Carbon Farming Initiative) (Sequestering Carbon in Soils in Grazing Systems) Methodology Determination 2014.

C.1 Division of project area into CEAs

(1) The project proponent must define in the Project Area one or more CEAs in accordance with the CFI Mapping Guidelines and that comply with clauses C.2 and C.3.

(2) Each CEA must be given a unique identifier and both the boundaries and area of each CEA must be recorded in the sampling plan.

C.2 Requirements for a CEA

(1) A CEA is made up of: (a) an area of land upon which the project activity is being undertaken; and (b) excludes areas of land upon which the project activity is not being undertaken, in accordance

with the CFI Mapping Guidelines for defining excluded areas. (c) Once the boundaries of a CEA are used to undertake a baseline sampling round they must not

be changed.

Note: The boundaries of a CEA must not change once they have been used for the baseline sampling round. This requirement overrides the advice in the CFI Mapping Guidelines that the boundaries of a CEA may change.

C.3 Delineating CEA boundaries (1) A project proponent must delineate the boundaries of CEAs included within the project area by

generating a set of spatial coordinates that define the geographic limits of the land area included within each CEA by: (a) using one of the following methods, or a combination of them, to identify the CEA boundary:

(i) conducting an on-ground survey using a global positioning system; (ii) using ortho-rectified aerial imagery in accordance with subclause (2); and

(b) using a geographic information system to generate spatial data-files to identify the CEA boundary.

Use of ortho-rectified aerial imagery (2) If ortho-rectified aerial imagery is used:

(a) the relevant land area must be digitised from the imagery; and (b) the imagery must meet the accuracy requirements specified in the CFI Mapping Guidelines;

and (c) the pixel resolution must be no greater than 2.5 metres.

(3) The boundaries of a CEA must be delineated with a resolution of at least ± 4 metres.

PART D. STRATIFICATION OF CEAS

Note: See section 4.3 of the Carbon Credits (Carbon Farming Initiative) (Sequestering Carbon in Soils in Grazing Systems) Methodology Determination 2014.

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D.1 Stratification of each CEA (1) The project proponent must define for each CEA a number of evenly-sized strata in accordance

with the CFI Mapping Guidelines that comply with clauses D.2 and D.3. (2) Each stratum must be given a unique identifier and both the boundaries and area of each stratum

must be recorded in the sampling plan. (3) The boundaries of each stratum must be delineated with a resolution of at least ± 4 metres. (4) Each CEA must include a minimum of 3 strata.

D.2 Requirements of strata (1) For each CEA:

(a) the strata must be spatially discrete; (b) the strata must be evenly sized within a five per cent tolerance; (c) each stratum should be large enough to allow for samples to be taken as specified in this method

in the sampling rounds that will occur in that stratum over the course of the project crediting period(s).

(2) The areas of the individual strata must sum to the total area of the CEA and any discrepancies must be reconciled.

(3) Once the stratum boundaries are used to undertake a baseline sampling round they must not be changed.

D.3 Delineating stratum boundaries The stratum boundaries must be defined by generating a set of spatial coordinates that define the geographic limits of the land area included within each stratum by using a geographic information system to generate spatial data files to identify the stratum boundary.

PART E. DEFINING COMPOSITES AND ASSIGNING SAMPLING LOCATIONS IN EACH CEA

Note: See section 4.4 of the Carbon Credits (Carbon Farming Initiative) (Sequestering Carbon in Soils in Grazing Systems) Methodology Determination 2014.

E.1 Defining composites For each CEA, the project proponent must nominate the number of composites to be included in the sampling plan: (a) at least three composites must included; and (b) each composite must be given a unique identifier. The unique identifier must allow the

composites in the CEA to be placed in an order.

Note At least three strata and three composites are required in each CEA to mitigate the risk that a change in SOC over time is detected by chance. However, these are minimum requirements and in no way suggest that three strata and three composites will be adequate to detect a change in SOC over time in a CEA. It is recommended that project proponents undertake their own assessment of the required number of strata and composites to include in each CEA. It is likely that more than three strata will be needed for a CEA.

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E.2 Assigning sampling locations in each CEA (1) For each composite:

(a) a sampling location must be randomly assigned within each stratum; (b) the precision of the sampling location must be to at least 5 decimal places expressed in decimal

degrees as Eastings and Northings; (c) the sampling location must be given a unique identifier; (d) the sampling location must be able to be identified as belonging to the composite; (e) the sampling location must not be closer to an existing sampling location than the expected

offset distance; and (f) the sampling location must not be closer to a previous sampling location than the offset distance

for the previous sampling location. (2) A pseudo-random number generator with a defined seed number must be used to assign the

sampling locations for each stratum and reported in accordance with Part H. (3) Records of the selection process for sampling locations must be kept in accordance with Part G.

E.3 Locating a sampling location (1) A GPS device with an accuracy of at least ± 4 metres is to be used to locate the sampling location

on the ground. (2) The actual sampling location is where the GPS device determines the latitude and longitude for the

sampling location is met in accordance with subclause (3) and the soil core is extracted. (3) The actual and intended sampling locations must be no greater than 5 metres apart and this distance

must be determined by comparing the GPS reading at the actual sampling location with the intended GPS sampling location, however:

(a) The 5 metres may be exceeded if there is an obstacle at the sampling location that must be cleared in accordance with subclause (5); and

(b) The actual sampling location must be within the boundaries of the stratum to which the intended sampling location was assigned.

(4) The coordinates of the actual sampling location must be recorded in decimal degrees to at least 5 decimal places as Eastings and Northings.

(5) If an obstacle is at the sampling location then the actual sampling location will be determined in accordance with paragraphs (a) to (c) below.

(a) Move from the intended sampling location in a direction of 0 degrees until the obstacle is cleared.

(b) If this process moves the actual sampling location outside of the stratum boundary then change the direction of movement by 15 degree increments (to the east) and move away from the intended sampling location until the obstacle is cleared and within the stratum boundary.

(c) This process should be reported in accordance with Part H and documented in accordance with Part G.

Note It is recommended that the GPS device has an accuracy of at least ± 1 metre where the method in clause F.1 is to be used to determine sampling locations in subsequent sampling rounds.

E.4 Calculating the offset distance (1) The offset distance can be either the default offset distance in accordance with subclause (2)

below or a user-defined offset distance in accordance with subclause (3) below.

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(2) For the purpose of offsetting a sampling location in a subsequent sampling round, the default offset distance to be applied is the sum of the error margin of the GPS device used to locate the sampling location on the ground and:

(a) 5 metres for a sampling location where the soil core was extracted using machinery to aid extraction and the soil is not tilled as per paragraph (c);

(b) 2 metres for a sampling location where the soil core was extracted using a hand-held corer and the soil is not tilled as per paragraph (c);

(c) 1 metre for a sampling location where the soil is tilled between sampling rounds at the sampling location and surrounding the sampling location covering a circular area with a radius of at least 5 metres.

(3) For the purpose of offsetting a sampling location in a subsequent sampling round, a user defined offset distance is the sum of the error margin of the GPS device used to locate the sampling location on the ground and the maximum radius of the region of disturbance for the sampling location in the previous sampling round.

PART F. SUBSEQUENT ROUNDS OF SAMPLING

Note: See section 4.4 of the Carbon Credits (Carbon Farming Initiative) (Sequestering Carbon in Soils in Grazing Systems) Methodology Determination 2014.

F.1 Offsetting sampling locations For each sampling location to be offset:

(a) The distance of separation is the offset distance determined in accordance with clause E.4;

(b) Randomly assign a separation direction from the original sampling point of between 0 and 359 degrees using a pseudo-random number generator with a known seed number;

(c) Using the distance of separation from paragraph (a) and the randomly assigned direction from paragraph (b), generate a separation vector from the previous actual sampling location to determine the position of the new sampling location;

(d) If the new sampling location is outside of the stratum, repeat the process outlined in paragraphs (b) and (c);

(e) If the new sampling location is within the region of disturbance of a previous sampling point plus GPS error then repeat the process outlined in paragraphs (b) and (c); and

(f) Records of the selection process for assigning sampling locations, including the process of selecting sampling locations that are unable to be used because they meet the conditions in paragraphs (d) and (e) must be kept in accordance with Part G.

F.2 Maintaining the sampling plan For each CEA where the sampling intensity is to be maintained in a subsequent round of sampling use the same strata and same composites as for the previous round of sampling; and either: (a) offset the sampling locations in accordance with clause F.1 and assign the new sampling

locations to the same composites; or (b) randomly assign new sampling locations in accordance with clause E.2.

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F.3 Sampling with a reduced number of composites for a CEA For each CEA where the sampling intensity is to be reduced in a subsequent round of sampling: (a) At least three composites must be retained in the revised sampling plan. (b) The last composite in the ordered set of composites in the CEA is removed. The position of a

composite in the set is determined by its unique identifier. (c) For the retained composites, either:

(i) offset the sampling locations in accordance with clause F.1 and assign the new sampling locations to the same composites; or

(ii) randomly assign new sampling locations in accordance with clause E.2. (d) The processes under paragraph (c) must be reported in accordance with Part H and

documented in accordance with Part G. (e) The sampling locations from the composites excluded in accordance with paragraph (b) must

be removed from the revised sampling plan or identified as not sampled, and reported in accordance with Part H and documented in accordance with Part G.

F.4 Sampling with an increased number of composites in a CEA For each CEA where the sampling intensity is to be increased in a subsequent round of sampling: (a) Additional composites with new sampling locations should be assigned in accordance with

Part E. (b) The additional composites and sampling locations should be included in a revised sampling

plan in accordance with Part A. (c) The remaining sampling locations must be assigned either:

(i) in accordance with clause F.1 for sampling locations that are offset; or (ii) in accordance with clause E.2 for new randomly assigned sampling locations.

PART G. RECORD KEEPING REQUIREMENTS

Note: See sections 7.7 of the Carbon Credits (Carbon Farming Initiative) (Sequestering Carbon in Soils in Grazing Systems) Methodology Determination 2014.

G.1 Record keeping requirements The project proponent must create and maintain the following records: (a) The offsets reports submitted for the project in compliance with Part H. (b) Files, including geospatial data files, and images containing the information presented in the

sampling plan. (c) The files used to generate random sampling locations. (d) The files used to generate the separation vectors if sampling locations are to be offset in the

subsequent sampling round. (e) For each sampling location in each sampling round, including the baseline sampling round:

(i) if sampling locations in the current sampling round are offset from a previous sampling round, then the separation vector used to generate the intended sampling location.

(ii) the coordinates of the actual sampling location for each intended sampling location; and

(iii) either:

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i. evidence that the actual sampling location is within 5 metres of the intended sampling location; or

ii. where an obstacle was avoided, records of the process for avoiding an obstacle and determining the actual sampling location and the distance between the intended sampling location and actual sampling location; and

(iv) if sampling locations in subsequent sampling rounds are to be offset, the offset distance (in metres) from the actual sampling location determined in accordance with clause E.4. This offset distance will be the distance of the separation vector used to offset the sampling location for the subsequent sampling round.

PART H. OFFSETS REPORT REQUIREMENTS

Note: See sections 7.17 of the Carbon Credits (Carbon Farming Initiative) (Sequestering Carbon in Soils in Grazing Systems) Methodology Determination 2014.

H.1 The first offsets report The first offsets report for a project must contain the following information: (a) A sampling plan in accordance with Part A. (b) The GPS unit specifications including the accuracy of each device used in the field for the

purposes of establishing the CEA boundaries and sampling locations. (c) The pseudo-random number generator/s used and the seed value/s used for randomly assigning

sampling locations in accordance with Part E. (d) An explanation of how the strata in each CEA should be large enough to accommodate the

sampling rounds expected for the project crediting period(s) in accordance with clause D.2.

H.2 Subsequent offsets reports The following information must be included in the subsequent offsets reports for the project. For each subsequent offsets report, this information must be included for each round of sampling that is used to generate estimates of changes in soil carbon stocks from the project: (a) The sampling plan that relates to each sampling round; (b) The GPS unit specifications including the accuracy of each device used in the field for the

purposes of establishing and/or relocating sampling locations; and (c) The pseudo-random number generator/s used and the seed value/s used for randomly assigning

any of the following: (i) Sampling locations in accordance with Part E. (ii) Separation vectors in accordance with clause F.1.

APPENDIX A. GUIDANCE ON SAMPLING INTENSITY AND FREQUENCY TO SUPPORT THE GRAZING SYSTEMS METHODOLOGY

A.1. WHAT DOES THIS GUIDANCE COVER? This guidance supports the implementation of the Carbon Credits (Carbon Farming Initiative) (Sequestering Carbon in Soils in Grazing Systems) Methodology Determination 2014 (Grazing Systems Methodology). The Grazing Systems Methodology specifies that project proponents must implement the CFI soil sampling design method (Section 7 of this document). This guidance provides information to help proponents decide on the:

• sampling intensity – the number of samples taken for each carbon estimation area (CEA) in the Project Area. The sampling intensity is part of the sampling plan; and

• sampling frequency – the number of sampling rounds in a crediting period (15 years).

The CFI soil sampling design method can be applied at different sampling intensities and the sampling intensity is dependent on the number of strata and composites in a CEA. Project proponents will need to take enough samples to be able to detect a change in soil organic carbon (SOC) over time due to the project activity. Each project proponent will need to balance the cost of sampling with the benefit of taking more samples in a given sampling round.

Project proponents will also need to decide on the number of sampling rounds to undertake during the crediting period. Within a given CEA, where SOC is increasing over time, a greater number of sampling rounds will lead to a more certain estimate of SOC change. However, each sampling round will involve the cost of soil sampling and laboratory analysis.

A.2. FACTORS TO CONSIDER WHEN DECIDING ON SAMPLING INTENSITY AND FREQUENCY The choice of an appropriate sampling intensity and frequency for a CEA will depend upon of a number of factors. These factors in turn are part of an overall assessment of the financial implications of undertaking the project.

Project proponents are strongly recommended to undertake appropriate due diligence on the financial costs and any potential returns of undertaking a project prior to submitting a project application. Carrying out the project will include costs associated with: implementing management actions, developing a soil sampling plan, undertaking soil sampling, preparation and analysis, preparing offsets reports and any audit costs. The returns from the project may include an increase in farm profitability from implementing the project management actions, the expected return from carbon credits due to net project abatement, and any co-benefits from increased SOC in the project area (e.g. increased soil water holding capacity).

The project proponent is strongly recommended to seek advice on the expected rate of SOC sequestration in their project area. The Grazing Systems Methodology does not provide assistance on this as SOC sequestration is influenced by climate, soil type, land-use history and other factors in addition to the management activities being applied. The advice on SOC sequestration should consider the implications of environmental variability, erosion and deposition on the rate of SOC sequestration. If the expected rate of SOC sequestration in the project area is very low, such as in more arid areas, the cost of soil sampling may mean that it is not profitable to undertake a project using this measurement-based Grazing Systems Methodology.

A project proponent should seek advice on the costs of soil sampling in their region as the cost of sampling is an important factor in deciding on the most appropriate sampling intensity. The CSIRO technical report (Chappell et al 2013) includes some proposed costs of sampling as a point of reference; however these costs will vary across different projects.

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Section 2 of this document describes a number of factors that will influence the choice of sampling intensity for a CEA. In addition to the factors in Section 2, proponents should also consider the cost of soil sampling, preparation and analysis and the overall financial costs and returns from the project. A list of factors to consider is provided in Table A1.

Table A1. List of factors to consider when deciding upon the sampling intensity for a CEA

For the project

The results of a due diligence assessment on financial costs and returns from the project – this provides information on the amount of money that can be allocated to soil sampling, preparation and analysis for the project to be viable.

For the project area

Create one CEA or more than one CEA in the project area (Section 2.2) – this provides information on the overall sampling intensity (and therefore cost of sampling) for the project area.

For a CEA

Expected rate of SOC sequestration over time – this affects the amount of change in SOC that needs to be detected by the sampling rounds.

Cost of soil sampling, preparation and analysis.

Variability of SOC in the CEA (known after baseline sampling round) (Section 2.3.2).

Size of a CEA (Section 2.3.2) – this can affect the variability of SOC in a CEA.

Strata cannot be modified after baseline sampling round but the number of composites can be changed (Section 2.3.3).

Number of years between baseline sampling round and subsequent sampling round – this affects the amount of change in SOC that needs to be detected by the sampling rounds (Section 2.3).

It is not possible to definitively recommend the optimal baseline sampling intensity for a given CEA because:

• The spatial variability of SOC in a CEA is unknown before undertaking a baseline sampling round; • The spatial variability of SOC in a CEA directly affects the amount of change in SOC that can be detected

for a given sampling intensity; and • The choice of sampling intensity includes a trade-off between the cost of sampling and the size of the

change in SOC that can be detected. This trade-off is a commercial decision for an individual to make.

Project proponents are strongly recommended to seek independent sources of information to help them with their decision on the best sampling intensity for a CEA in the Project Area. Project proponents should also be aware that any independent advice needs to be relevant to the CFI soil sampling design which is stratified simple random sampling with compositing across strata. Advice that is tailored for sampling designs that do not use stratification and compositing across strata will not be appropriate.

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A.4. SAMPLING INTENSITY FOR A BASELINE ROUND Section 2.3 of this document provides some detailed information on sampling intensity for the CFI soil sampling design method. Section 2.3 should be read in conjunction with this Appendix as it contains relevant information on sampling intensity that is not repeated in this Appendix. The information below provides a synthesis of the guidance as it applies to the Grazing Systems Methodology. The sampling design method requires that a minimum of three strata and three composite samples (nine samples in total) are included in each CEA. This is to minimise the risk that a detected change in SOC is not due to management but due to spatial variation in SOC. However, it is highly recommended to take more than nine samples.

It is difficult to recommend a minimum number of samples to adequately sample a CEA as each CEA will differ in size and, more importantly, in spatial variability in SOC (Section 2.3.4). A report by CSIRO (Chappell et al. 2013) estimated the effect of different sampling intensities on a 100 ha CEA with large spatial variability. Based on this analysis it is recommended that, as a starting point, the sampling plan for a CEA of 100 ha uses no fewer than 6 strata x 3 composites, which is 18 samples. This is because, in soils with a large spatial variability, a lower sampling intensity is unlikely to be able to detect reasonable rates of change in SOC over periods of 3 – 5 years. It should be noted that this recommendation does not assume that a 6 x 3 sampling plan will be adequate to detect change in SOC over time for a given CEA.

The sampling design does not allow for restratification of the CEA once the strata have been used for a baseline sampling round. For this reason, it is recommended that the sampling plan includes enough strata to adequately sample a CEA with a large spatial variability. Furthermore, the more strata in the CEA the better the spatial coverage of the CEA by the soil sampling, and this leads to a better target minimum detectable change (MDC) for the CEA. A sampling plan with too few strata will not achieve a good estimate of SOC for the CEA. It is recommended to use no fewer than 6 strata; however 8 or 10 strata may be more appropriate depending on the size of the CEA and the spatial variation in SOC. It is possible that more than 10 strata may be needed for some CEAs, especially if they are much larger than 100 ha. If a CEA is less than 100 ha, it is not recommended to reduce the number of strata unless the CEA is much smaller. Section 2.3 of this document provides more information.

The Grazing Systems Methodology allows a baseline sampling round to be modified to add more samples to the baseline sampling round if the initial sampling intensity is not adequate. This would occur, for example, if the spatial variance in the CEA was greater than expected. All sampling for a CEA for the baseline sampling round must occur within a 60-day period to reduce the amount of temporal variance in the results (and all CEA baseline sampling rounds within the project area must be undertaken within a 6-month window). The expense of requiring a contractor to return to take more samples may mean, however, that it is better to over-sample in the first instance. A contractor could take more samples than may be required, and only send a sub-set to the laboratory for analysis. The remaining samples could be sent to the laboratory for analysis if the SOC variability was greater than expected.

A.5. FREQUENCY OF SAMPLING ROUNDS

Guidance for a baseline sampling round:

1. Include more strata than composites in the sampling plan as it will lead to a lower sampling variance for the same number of samples.

2. For a CEA of approximately 100 ha, use a sampling plan with

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The Grazing Systems Methodology specifies that the time between consecutive CEA sampling rounds (sampling intervals) must be no less than one year and no more than five years. It should be noted, however, that because SOC builds over time, sampling every year may be too frequent to detect a year-to-year change in SOC. For this reason, it is suggested that the minimum time between sampling rounds is at least two years.

The use of a regression approach to calculate changes in SOC stocks over time yields more accurate results if the sampling rounds occur at regular intervals. The Grazing Systems Methodology does not prescribe a fixed sampling interval, as this would not give proponents any flexibility with respect to the timing of sampling rounds. However, the methodology does require that the sampling interval must not vary by more than two years for the project duration. For example, if there were 2 years between the baseline sampling round and the first project sampling round, and 4 years between the first and second project sampling rounds, then the sampling intervals for that project could only be 2, 3, or 4 years. This ensures that sampling rounds are relatively evenly spaced over the crediting period, while giving project proponents flexibility to increase or decrease the frequency of sampling rounds according to the particular circumstances of their project.

It is recommended that at least five sampling rounds are undertaken during the 15-year project crediting period to achieve a reasonable statistical power to the regression calculation, and six sampling rounds would be better. A regression determines a trend in the change in SOC over time, and at least five sampling rounds are recommended to be more certain that the trend is a true reflection of the change in SOC over time. Undertaking less than five sampling rounds (including the baseline round) during the crediting period is not recommended. A mixture of 3-year and 4-year sampling intervals could be used to achieve 5-6 sampling rounds over a 15-year crediting period.

A.6. WHAT OTHER INFORMATION DO I NEED? This Appendix provides guidance on the sampling intensity and frequency for a CEA for the CFI soil sampling design method as part of the Grazing Systems Methodology. In addition to the CFI Soil Sampling Design Method and Guidelines there are a number of other documents that support the Grazing Systems Methodology. A User Guide for the Grazing Systems Methodology is available on the Clean Energy Regulator’s website and provides a list of the documents that a project proponent will need to access to implement project. These documents include:

• Grazing Systems Methodology and Explanatory Statement; • Carbon Credits (Carbon Farming Initiative) Act 2011 and Carbon Credits (Carbon Farming Initiative)

Regulations 2011; • CFI Soil Sampling and Analysis Method and Guidelines; • CFI Mapping Guidelines; and • CFI Soil Carbon in Grazing Systems Net Abatement Calculator (under development).