Carbon Farming Initiative
Soil Sampling Design
Method and Guidelines
Document revision history
Version / Date /1.1 / 14 July 2014
1.2 / 18 January 2018
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 19
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
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
H.2 Subsequent offsets reports 38
Appendix A. Guidance on sampling intensity and frequency to support the grazing systems methodology 39
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.
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).
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 (SOC[1]) 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 Australia[2]. 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).
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.
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 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: