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Ploughing through soil carbon: – science foundations and directions

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. Australia’s terrestrial carbon sinks are large!.

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Ploughing through soil carbon: – science foundations and directions

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

  2. Australia’s terrestrial carbon sinks are large! (Source: R Waterworth, National Carbon Assessment System, DCC and Australia’s State of the Forest Report, DAFF). (Soil depth used = 30 cm) • Australian vegetation and surface soils: approx 100 Gt CO2-e • Annual total emissions: approx 0.6 Gt CO2-e

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

  4. Soil organic carbon content Inputs of organic carbon Losses of organic carbon f = , Inputs Losses • Conversion of organic C to CO2 • Protection offered by soil minerals • Extent of cultivation • Plant biomass and residue return to the soil • Addition of waste organic materials What determines soil organic carbon content?

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

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

  7. Turnover Rates 100 – 1000’s years 1-10 years 10 - 100 years Not all soil carbon is made the same! • 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 • 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 Available at http://www.csiro.au/resources/Soil-Carbon-Sequestration-Potential-Key-Findings.html

  9. Where is the evidence we can change agricultural practices to build soil C – internationally ? Improved grassland mgnt. * * Reduced fallow * No-till adoption * Conservation tillage * * Forages in rotations * * Cultivation conversion * Manure inputs * * Altered fertiliser inputs * 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. National Soil Carbon Research Program NT DPI* Qld rangelands Extra sampling - with additional partners Qld cropping WA rangeland Soils* C3/C4 Panic/Rhodes NSW MER samples (500 soil profiles) NSW Soils 14C labelling sites Murray CMA C3/C4 Kikuyu SA soils Victorian sampling sites WA Soils CfOC 0 350 700 Tasmania soils Kilometres * proposed 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 CO2-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. Brian Keating Director Sustainable Agriculture Flagship Phone: +61 7 32142373 Email: Brian.Keating@csiro.au Contact details Contact UsPhone: 1300 363 400 or +61 3 9545 2176Email: Enquiries@csiro.au Web: www.csiro.au

  15. Relative difference Improved management Traditional management Factors influencing rate of change of soil carbon Drawn from 48 observations / trials around Australia Rate of change (Mg C ha-1 yr-1) -1.0 -0.5 0.0 0.5 1.0 0 • Soil C changes in response to a management change greatest in top 20 cms of soil depth 10 20 Depth (cm) 30 40 50

  16. 1.0 0.5 0.0 Rate of change (Mg C ha-1 yr-1) -0.5 -1.0 0 10 20 30 40 Trial duration (years) Relative difference Improved management Traditional management Factors influencing rate of change of soil carbon Drawn from 48 observations / trials around Australia • Soil C changes in response to a management change greatest over first 10 - 20 years

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