Ploughing through soil carbon: – science foundations and directions

Brian Keating, Jeff Baldock and Jon Sanderman

Business Leaders Forum on Sustainable Development: 27th May 2010

Australia’s terrestrial carbon sinks are large!

• Australian vegetation and surface soils: approx 100 Gt CO2-e

• Annual total emissions: approx 0.6 Gt CO2-e

(Source: R Waterworth, National Carbon Assessment System, DCC and Australia’s State of the Forest Report, DAFF). (Soil depth used = 30 cm)

0

10

20

30

40

50

60

70

Forest Grassland andCropland

To

tal C

arb

on

as

Gt

CO

2-e

Vegetation

Soil

Soil Carbon has often run-down under past agriculture

0

10

20

30

40

50

60

70

1982 2000 1917 2000 1980 2000

Brigalow, Qld(cropping -

soil 64)

Horsham, Vic(wheat -fallow)

Brookton, WA(ceral - lupin -

pasture)

Tot

al o

rgan

ic c

arbo

n(M

g C

/ha)

• The potential does exist to sequester carbon in Australian soils

What determines soil organic carbon content?

Soil organic carboncontent

Inputs oforganic carbon

Losses oforganic carbon

= ,f

Inputs

• Plant biomass and residue return to the soil

• Addition of waste organic materials

Losses• Conversion of

organic C to CO2

• Protection offered by soil minerals

• Extent of cultivation

Soil C has been a focus for research for a long time !

1900 1940

100

80

60

40

20

0

Control (no additions)Manure addition then stoppedManure addition maintained

Soi

l org

anic

car

bon

(Mg

C/h

a)

1900 1940

100

80

60

40

20

0

Control (no additions)Control (no additions)Manure addition then stoppedManure addition then stoppedManure addition maintainedManure addition maintained

Soi

l org

anic

car

bon

(Mg

C/h

a)

1860 1980

Continuous Manure

Initial Manure, then no additions

No additions

Hoosfield Continuous Barley Experiment, Rothamsted, UK1852 – present day

(0 -

23

cm)

Petersen et al 2005 Soil Biol Biochem 37 359

Some soil C principles

1900 1940

100

80

60

40

20

0

Control (no additions)Manure addition then stoppedManure addition maintained

Soi

l org

anic

car

bon

(Mg

C/h

a)

1900 1940

100

80

60

40

20

0

Control (no additions)Control (no additions)Manure addition then stoppedManure addition then stoppedManure addition maintainedManure addition maintained

Soi

l org

anic

car

bon

(Mg

C/h

a)

1860 1980

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

Not all soil carbon is made the same!

1-10 yearsTurnover Rates

10 - 100 years 100 – 1000’s years

• Need to combine carbon measurement with carbon modelling to predict likely rates and directions of change

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

Where is the evidence we can change agricultural practices to build soil C – internationally ?

0 0.2 0.4 0.6 0.8 1 1.2

Change in soil carbon (Mg C ha-1 yr-1)

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)

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

Expanding our soil carbon knowledge-base

0 350

Kilometres

700

Extra sampling - with additional partners

Tasmaniasoils

Qld cropping

Qld rangelands

C3/C4Kikuyu

C3/C4Panic/Rhodes

14C labelling sites

Victorian sampling sites

SA soils

Murray CMA

NSW Soils

WA Soils

NSW MER samples

(500 soil profiles)

CfOC

WA rangelandSoils*

NT DPI*

National Soil Carbon Research Program

* proposed

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

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.

Contact details

Brian KeatingDirectorSustainable Agriculture Flagship

Phone: +61 7 32142373Email: Brian.Keating@csiro.au

Contact UsPhone: 1300 363 400 or +61 3 9545 2176Email: Enquiries@csiro.au Web: www.csiro.au

Factors influencing rate of change of soil carbon

Rate of change (Mg C ha-1 yr-1)

-1.0 -0.5 0.0 0.5 1.0

Dep

th (

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

Factors influencing rate of change of soil carbon

Relative difference

Improved management

Traditional management

Trial duration (years)

-1.0

-0.5

0.0

0.5

1.0

0 10 20 30 40Rat

e of

cha

nge

(Mg

C h

a-1 y

r-1)

Drawn from 48 observations / trials around Australia

• Soil C changes in response to a management change greatest over first 10 - 20 years