1. Ploughing through soil carbon: – science foundations and directions Brian Keating, Jeff Baldock and Jon Sanderman Business Leaders Forum on Sustainable Development: 27 th May 2010

2. Australia’s terrestrial carbon sinks are large! Australian vegetation and surface soils: approx 100 Gt CO 2 -e Annual total emissions: approx 0.6 Gt CO 2 -e (Source: R Waterworth, National Carbon Assessment System, DCC and Australia’s State of the Forest Report, DAFF). (Soil depth used = 30 cm)

3. Soil Carbon has often run-down under past agriculture The potential does exist to sequester carbon in Australian soils

4. What determines soil organic carbon content? Soil organic carbon content Inputs of organic carbon Losses of organic carbon =, f Inputs Plant biomass and residue return to the soil Addition of waste organic materials Losses Conversion of organic C to CO 2 Protection offered by soil minerals Extent of cultivation

5. Soil C has been a focus for research for a long time ! 1860 1980 Continuous Manure Initial Manure, then no additions No additions Hoosfield Continuous Barley Experiment, Rothamsted, UK 1852 – present day (0 - 23cm) Petersen et al 2005 Soil Biol Biochem 37 359

6. Some soil C principles Soil C changes take place over long time periods Soil C storage capacity is finite Management changes that build soil C must be maintained to maintain soil C Useful models available with predictive skill

7. Not all soil carbon is made the same! 1-10 years Turnover Rates 10 - 100 years 100 – 1000’s years Need to combine carbon measurement with carbon modelling to predict likely rates and directions of change

8. Where is the evidence we can change agricultural practices to build soil C – from Australia ? Reviewed available trial data on soil C change in response to management Reports data for 96 trials and/or treatments across Australia Available at http://www.csiro.au/resources/Soil-Carbon-Sequestration-Potential-Key-Findings.html Rates of soil C change with “C friendly” management Within cropping or grazing management in range 0.1 to 0.3 Mg C ha -1 yr -1 Conversion of cultivation to permanent pasture in range 0.5 to 0.6 Mg C ha -1 yr -1 Many current systems are still running soil C down so some “C friendly” practices simply reduce this rundown rate Net sequestration vs emissions avoidance

9. Where is the evidence we can change agricultural practices to build soil C – internationally ? Altered fertiliser inputs Manure inputs Cultivation conversion Forages in rotations Conservation tillage No-till adoption Reduced fallow Improved grassland mgnt. * * * * * * * * * * * * Source: Hutchinson et. al. (2007) Some perspectives on carbon sequestration in agriculture. Agric. For. Meteorol. 142, 288-302. (adapted from Table 4)

10. What practices favour higher soil carbon levels ? Anything that increase carbon additions or reduces carbon losses Improved crop or pasture nutrition (including fertiliser, manures, legume fixation) Reduced fallow periods Including pasture phases in the crop rotation Retaining crop residues Reduced tillage Reducing overgrazing that damages pastures and soils Eliminating soil losses through wind or water erosion Converting from cultivation to permanent pasture or forest Adding carbon from off-site sources (e.g. biochar from waste streams) All actions need to be subject to “whole of life cycle” caveats No value in reducing emissions in one place and increasing them in another No value in reducing C loss but increasing emissions of other greenhouse gases such as methane or nitrous oxide

11. Expanding our soil carbon knowledge-base

12. Potential costs and benefits of building soil carbon Potential benefits Enhanced water holding capacity and soil structure Reduced erosion risk Enhanced soil fertility and nutrient cycling Potentially, a soil carbon offset with financial value subject to due diligence on long term obligations at 0.1 to 0.5 Mg C ha -1 yr -1 and a carbon price of $20 t -1 CO 2 -e, gross returns in the order of $7-35 ha -1 yr -1. Potential costs Management changes need to make sense in terms of farm finances Increased input costs or reduced output income Any costs associated with measurement and verification of soil carbon offsets Likely to be conditional on nature of the offset system

13. Summing up ….. Soil C is part of the solution But not the solution …. Rapid and cost effective measurement is a research priority Enables responses in both practice and policy Big step-up in soil carbon assessment now underway across the country (2000 plus locations) Limited time-series sampling (not possible in 3 years) Can’t sample everywhere so models still important Long-term soil C monitoring is also important We’re talking about processes that can take 30-50 years plus to unfold.

14. Contact details Brian Keating Director Sustainable Agriculture Flagship Phone: +61 7 32142373 Email: Brian.Keating@csiro.au Contact Us Phone: 1300 363 400 or +61 3 9545 2176 Email: Enquiries@csiro.au Web: www.csiro.au

15. Factors influencing rate of change of soil carbon Rate of change (Mg C ha -1 yr -1 ) -0.50.00.51.0 Depth (cm) 0 10 20 30 40 50 Relative difference Improved management Traditional management Drawn from 48 observations / trials around Australia Soil C changes in response to a management change greatest in top 20 cms of soil depth

16. Factors influencing rate of change of soil carbon Relative difference Improved management Traditional management Trial duration (years) -0.5 0.0 0.5 1.0 010203040 Rate of change (Mg C ha -1 yr -1 ) Drawn from 48 observations / trials around Australia Soil C changes in response to a management change greatest over first 10 - 20 years