Technical Information

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Licensed under Creative Commons Attribution 3.0 Australia. © Crown in right of the State of South Australia.

Technical Information

How much carbon is stored in our soils?

This document describes the sources of information, advice, methods, indicators and data processing procedures used to develop the reports. Reliability of data, as well as metadata attributes, are also described.

State NRM Plan Guiding Target:

Maintain the productive capacity of our natural resources.

State NRM Plan Representative Measure:

Total carbon sequestered (above ground and in soil).

Data collection period:

2014.

Expected frequency of reporting:

Annual.

Data sources:

1. Soil and Landscape Grid of Australia.

Indicators used:

1. Baseline estimate of soil organic carbon levels in the top 30 cm of soil (tonnes of carbon per hectare) . 2. Baseline estimate of total soil organic carbon in the top 30 cm of soil (tonnes of carbon).

Methods of data collection and processing:

Estimates of soil organic carbon stocks (total tonnes) for the upper 30 cm of soil profile across the state’s agricultural zone (including areas under native vegetation) have been derived from new digital soil property maps released via the Soil and Landscape Grid of Australia. In particular, depth-based raster map layers for organic carbon (per cent weight), bulk density and coarse fragment (gravel) content, developed from the disaggregation of South Australia’s legacy polygon-based soil mapping (Liddicoat et al. 2014) were used to calculate 030 cm soil organic carbon stocks. Soil organic carbon estimates do not include plant roots or fresh plant debris deposited on the surface of soil.

Soil organic carbon estimates are assumed to represent a baseline or snapshot in time, circa 2000, however they are derived from survey data gathered over 20+ years. The summary values presented are thought to be accurate within +/- 20%. More reliable estimates (derived from improved spatial modelling of soil properties) will only be gained through increased sampling of representative soils across the State.

Number of tonnes of carbon stored as soil organic carbon was converted into an approximate number of years of South Australia ’s carbon emissions, based on the South Australian carbon emission rate in 2010 of 8.28 million ton nes (30.4 million tonnes of CO2), as reported in the South Australia’s Strategic Plan (Government of South Australia 2012). That is, 600 million tonnes of soil organic carbon equates to over 70 years of South Australia’s annual carbon emissions.

Data presented are elemental carbon weights. To convert to a carbon dioxide (CO2) emissions equivalent carbon mass should be multiplied by 3.67 to account for the additional molecular weight of oxygen.

Discussion:

A recent overview of the status and trends for soil organic carbon is provided in the Australian Government (2011) State of the Environment Report 2011. Soil carbon stocks are considered to be low in many Australian agricultural systems and conversion from native vegetation to agriculture is thought to have caused losses of the order of 20-70% from the natural state. Declining soil carbon represents a shift towards a new equilibrium with lower organic matter inputs (e.g. where agricultural plants can’t make use of all the annual rainfall, crop residues largely decompose on the surface with minimal input to soil) and/or higher rate s of soil carbon decomposition (e.g. due to tillage, fallowing, soil microbial action, and erosion). Soil carbon loss from some of the extensive

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cropping lands of southern Australia, with weathered and naturally infertile soils, may have increased to some extent because soil carbon stores were naturally low to begin with and productivity in many of these soils will have benefited from the addition of fertiliser and correction of trace element deficiencies. However, few areas are expected to have increasing soil carbon stores.

Further research is needed to identify viable ‘carbon farming’ approaches. Examples may include a shift to greater use of perennial species and more conservative grazing practices.

Future reporting measures:

There is interest and investment in sequestering carbon in soils and plants in the arid regions of Australia, however currently available data does not allow for carbon stocks to be reliably estimated in the SA Arid Lands or Alinytjara Wilurara NRM regions. A national model, due to be released soon, can be used in future reports to estimate carbon stocks/trends for these NRM regions.

(This is awaiting release of the national modelling for coarse fragment/ gravel content, which is used in the calculation of soil organic carbon stocks.)

Future reporting could include an estimate of the amount of carbon that is sequestered periodically (e.g. on a 5 yearly basis), if reliably developed. This estimate could be tracked over time if calculated using a consistent method.

The following government agencies contributed to this report:

Department of Environment, Water and Natural Resources (DEWNR).

The following non-government agencies contributed to this report:

None.

Key stakeholders:

NRM Council, NRM Boards, agricultural land owners/managers, Primary Industries and Regions SA, agricultural industry groups, DEWNR.

Information reliability scoring:

Information is scored for reliability based on average scores given for information currency and applicability, and its level of spatial representation (Tables 1–3).

Table 1. Information currency Reliability Criteria

5 Information up to 3 years old 4 Information up to 5 years old 3 Information up to 7 years old 2 Information up to 10 years old 1 Information >10 years old

Table 2. Applicability of the information Reliability Criteria

5 All data based on direct indicators of the measure 4 Most data based on direct indicators of the measure 3 Most data based on indirect indicators of the measure 2 All data based on indirect indicators of the measure 1 Data are based on expert opinion of the measure

Table 3. Spatial representation of information (sampling design) Reliability Criteria

5 Information is collected from across the whole region/state (or whole distribution of asset within the region/state) using a stratified sampling design

4 Information is collected from across the whole region/state (or whole distribution of asset within the region/state) using a sampling design that is not stratified

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3 Information is collected from an area that represents less than half the spatial distribution of the asset within the region/state

2 Information is collected from an area that represents less than 25% the spatial distribution of the asset within the region/state

1 Information is collected from an area that represents less than 5% the spatial distribution of the asset within the region/state or spatial representation unknown

Based on tables 1, 2 & 3 above, respectively, the information relating to carbon stored in soil in this report has a reliability score of (1+2+4)/3 = 2.33 rounded to 2 (Fair).

This report is linked to the following report cards/snapshots:

1. How much carbon is stored in our trees?

2. How many South Australians understand the causes and consequences of climate change?

3. How many climate change adaptation plans have been completed?

4. How good is the scientific understanding of the causes and consequences of climate change?

5. How much of our agricultural land is protected from erosion?

6. Is soil acidity decreasing in our agricultural areas?

7. Is soil fertility improving in our agricultural areas?

8. Is water-use efficiency improving in our agricultural areas?

9. Are the extent and connectivity of our native vegetation improving?

10. Is the condition of our native vegetation improving?

11. How much of our native vegetation is protected?

Metadata description:

Project/Dataset name: Data provided 12/01/2015

Abstract/description Dataset is a summary of the soil organic carbon stored in soils by NRM region.

Data types Spreadsheet

Organisation/ DEWNR business area that

sponsors/holds/manages the data

DEWNR

Date range Data represents a baseline estimate circa 2000.

Study area South Australia’s agricultural areas.

Data format Excel spreadsheet

Data distribution rules Licensed under Creative Commons Attribution 3.0 Australia Is the dataset source data (raw),

value-add data

(analysed/summarised) or final indicator/score data?

Value-add

Photo credit details:

Owner: DEWNR

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Scientific literature referred to in the report:

Government of South Australia (2012). South Australia’s Strategic Plan, Target 59. Green house gas emission reduction.

Liddicoat, C., Holmes, K., Maschmedt, D., Rowland, J., Searle, R., Odgers, N. (2014) Soil and Landscape Grid Digital Soil Property Maps for South Australia (3" resolution). v3. CSIRO. Data Collection. 10.4225/08/5472DCCD081D2

Australian Government (2011) State of the Environment Report 2011, Independent report to the Australian Government Minister for Sustainability, Environment, Water, Population and Communities. Australia.