Soil Organic Carbon: Challenges & OpportunitiesAssoc. Prof. Frances Hoyle UWA School of Agriculture and Environment

Daniel Murphy, Yichao Rui, Rebecca O’Leary, Courtney Creamer, Emily Cooledge, Anna Ray, Davey Jones, Steve Rushton, Elizabeth Stockdale, Yoshi Sawada, Emilia Horn, Manjula Premaratne

Complexity of the soil matrix

• Soil properties, environment and management interact.• Large data sets enable new ways of looking at changes soil quality. • Focus is to predict how management of one property alters the others - then use these to run

scenarios to manage risk.

Pauline Mele

0%

20%

40%

60%

80%

100%

Tota

l Car

bon

Soil

N s

uppl

y

Dis

ease

pH (0

-10)

pH (1

0-20

)

pH (2

0-30

)

Elec

rical

Con

duct

ivity

Wat

er R

epel

lenc

y

Bulk

Den

sity

RedAmberGreen

Biology PhysicsChemistry

pH

Soil organic matter

Electrical Conduct.

CEC

Water repellence

Clay content

Compaction

Hardsetting

Available H2O

Erosion

Climate AgronomicManagement

Disease

Pathogenic Nematode

Labile organic matter

Microbial biomass

Biological N supply

Soil Qualitywww.soilquality.org.au

MED pH Soil strength (MPa)

Dept

h (c

m)

0 cm

10 cm

40 cm

50 cm

Net Primary ProductivityStored soil water + [Growing season rainfall – Evaporation]

x biomass/mm

Soil organic matter0.1 – 10%

Living 15%

Microorganisms75-90%

Mycorrhizae

Denitrifiers

N fixation

Decomposers

Microbial activity

Nutrient Cycling EnzymesAggregate

stabilisation

Diversity

e.g. bacteria and fungi

Resilience

Roots 5-15% Fauna 5-10%

What are the components of SOM?

Contaminantdegradation

= C (58%), O, H, S, N, P, K, Ca, Mg< 2 mm =

Soil organic carbon fractions & ‘permanence’

Particulate

Soluble & suspended

Humus & Resistant

Minerals

Soil organic carbon0.1 – 5.0 %

26%44%30%

1.5% C

0.8% C

0.3% C

Factors Driving Carbon Storage in Soil

Satellite image of the WA agricultural area – sampling sites (>1300)

Adapted from Ingram & Fernandez 2001

R² = 0.73

R² = 0.96

0

5

10

15

20

0 10 20 30 40 50

g fr

actio

n C

kg-1

soil

Clay content (%)

> 50 µm≤ 50 µm

Creamer et al. (2016) SBB

Clay content defines potential SOC

POCHOC

y = 0.64Ln(x) + 1.17R2 = 0.92

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Clay content (%)

SO

C (

%)

3-5 30-3510-15 20-25 40-5235-4025-3015-205-10(25) (34)(13)(27)(65) (7)(11)(15)(23)

Influence of clay content on SOC in a 10-hectare area under cereal-legume rotation

SOC

(%; 0

-10

cm)

Clay Content (%)Hoyle, Baldock & Murphy (2011) Book Chapter

P Poulton, Rothamsted Research, UK.

Building SOC

• A natural equilibrium exists for the retention and loss of organic matter, with significant seasonal variability

• In low cation sandy soil a lower proportion of organic inputs are protected and retained• Maintaining soil organic carbon requires continued inputs

P Grace, Australia (2006).

Silty clay loam Soil with less clay

% in

put r

etai

ned

CEC (meq/100 g)0.5

1.0

2.0

3.0

Soil

orga

nic

carb

on (%

)

WA SCaRP Carbon & FRG projects

• +1300 sites across South West WA• Seven different sample areas:

• Esperance (beef pastures).• Young River (cropping and pastures).• Kalgan (cropping and pastures).• Kojonup (cropping and pastures).• Avon (cropping).• Geographe (beef and dairy pastures).• Mingenew (cropping).

• Target specific soil types (deep sand, sandy duplexes, gravelly duplexes, red loams) and land-uses.

• Measured soil variables inc. carbon & fractions

“Under current management strategies is there any room for movement in carbon storage?”

Annual rainfall- SOC (t C/ha) linked to annual rainfall

(mm)- Rainfall drives net primary productivity- Larger range of data in medium-high

rainfall driven by management and soil properties

- SOC differences between pasture and cropping often correlated with climate (‘fit for purpose’)

- Drying climates??? Hoyle et al. 2016 Sci. Rep. Annual average rainfall (mm)

300 400 500 600 700 800 900So

il or

gani

c ca

rbon

(t C

/ha,

0-

30cm

)0

5010

015

020

0Meta-analysis results

Soil

Org

anic

Car

bon

(t/ha

, 0-3

0 cm

)

Annual Rainfall (mm; 30y average)

WA SCaRP Carbon & FRG projects

30y average5y average

TemperatureChange point regression analysis

- When average daily temperature is >17°C, there is a significant decrease in SOC

- Represents critical limit for SOC storage potential for different climatic regions in WA????

- Linked to net primary productivity and decomposition rates

Annual average daily temperature (30y; °C)So

il or

gani

c ca

rbon

(t C

/ha,

0-3

0cm

)

Hoyle et al. 2016 Sci. Rep.

Soil

Org

anic

Car

bon

(t/ha

, 0-3

0 cm

)Avg. Annual Daily Temperature (30y; °C)15 16 17 18 19 20 21

050

100

150

200Meta-analysis results

WA SCaRP Carbon & FRG projects

• SOC influenced by the interaction between temperature and rainfall

Bubble size = rain

Griffin DPIRD (Source TERN, ASRIS)

Climate influence

Soil

Org

anic

Car

bon

(%)

0

1

2

3

4

5

6

7

15 20 25 30 35 40

Maximum Temperature (30y; °C)

UWA Big data (SOC)e.g. Measuring, modelling and managing soil carbon

Hoyle F.C., O’Leary R.A. and Murphy D.V. (2016)

Primary drivers of SOC in WA (79%) - Depth- Climate (Rainfall,

Temperature)- Soil type - Rotation- Soil pH

Soil and agronomic variables (e.g. stock, fertiliser) also have a significant though smaller influence on SOC.

TOCrelative

importanceARain30yr 0.287Rotation10yr 0.188AVPD30yr 0.182ATemp30yr 0.144Skg_Last5 0.075Stock.presabs 0.059Supergroup2 0.049Pkg_Last5 0.008pH_ca 0.007Nkg_Last5 0.001Kkg_Last5 0.000

Organic matter fractions change on different time scales

- Labile fraction not a constant % of total OM- Early indicator of SOM status and trends- Responds to management

0123456

0 5 10 15 20 25Total C (t/ha)

Labi

le C

(t/h

a)

5%

50%

0123456

0 5 10 15 20 25Total C (t/ha)

Labi

le C

(t/h

a)

5%

50%

Hoyle, Baldock & Murphy (2011) Book Chapter

Higher nutrient turnover

Slower carbon turnover

- Management influences fractions of SOC- SOC losses rapid; rebuilding SOC slower and in altered

state- Changing a wheat–fallow rotation to permanent pasture

altered SOC fractions over 75 years (Roth-C simulation)

• Deep yellow sand (Tenosol)• 6% clay, 0.7% SOC• 0-10cm pH 6.2 (CaCl2), declining to pH 4.7 10-30cm• Annual rainfall 328 mm (2003-16)

(254 mm GSRF)

2016: Wheat, 2015: Oats, 2014: Oats, 2013: Barley, 2012: Canola, 2011: Wheat , 2010: Wheat, 2009: Lupin

Aim: Determine retention of organic matter in a low rainfall cropping system.

Paper in preparation

Buntine organic inputs trial(established 1993)

Main Treatments:

No Till (Control)

Burnt

Till

Till+organic matter (5 x 20 t OM/ha)

FIELD TRIALBuntine (2016) – 13 years on

• In 2016 having added 100 t/ha organic matter (48 t C/ha), SOC stocks increased by 7 - 8 t C/ha• 61% SOC in surface 10 cm (66% in min till)• Stubble retention vs. burning – no change, till vs. no till – no change*• ‘New’ OM loss equivalent to 1.1 t C/ha/year without new inputs

0

5

10

15

20

25

30

Burnt (Min till) Control (Mintill)

Till Till+OM Rundown

Soil

orga

nic

carb

on(t

C/h

a; e

quiv.

mas

s)

0-10 cm 10-20 cm 20-30 cm

LSD Treatment x depth (P=0.05)

0.71 0.76 0.57 1.13

0.30 0.31

0.40

0.44

0.28

0.22

0.220.22

Numbers in graph are % organic carbon

0.76

0.38

0.19

7.4 t/ha R² = 0.3105

0

5

10

15

20

25

Mar

-03

Aug-

04D

ec-0

5Ap

r-07

Sep-

08Ja

n-10

Jun-

11O

ct-1

2M

ar-1

4Ju

l-15

Nov

-16

SOC

sto

ck

(0-1

0 cm

; t C

/ha)

Till+OM

Mamanning 2000, wheat(Pluske and Bowden)

14 ppm K0.6 t/ha

27 ppm K1.9 t/ha

Soil property Control (Tilled)

OM Min till

Carbon (t/ha) 17(0.57%)

25 (1.13%)

20(0.76%)

Potassium 72 208 75Nitrogen (ppm) 11 21 9Sulphur 8 21 15Phosphorous 25 34 28CEC (meq)* 4.1 6.1 4.6pH (CaCl2) 6.2 6.2 6.3WHC (%)* 27 33 27MBC (kg/ha)* 108 151

Soil properties measured at Buntine (2016) in selected treatments

SOM and nutrient supply

*2014 data

Merredin (low rainfall, Chromosol), 2 stubble treatments, 31 years old

02468

1012

1980 1990 2000 2010 2020

Soil

orga

nic

carb

on

stoc

k (t

C h

a; 0

-5

cm)

Stubble BurntStubble Retained

• Maintaining high amounts of organic matter inputs can increase SOC

• However lower input systems (e.g. stubble retention in low yielding environments) are often still losing SOC over time

• More nutrient turnover associated with POC

Merredin Trial (18 y)

Treatment SOC (%)

POC (mg kg soil)

Residue burnt 1.2 139Residue retained 1.3 182

NS *** (31%)

Study 2: Albany Sand PlainFour paddock management systems:

• Continuous cropping.• Mixed cropping.• Annual pastures.• Perennial pastures.

Three soil types:• Deep Sand.• Sandy Duplex.• Loamy Duplex.

Other features:• Tight rainfall gradient.• Water repellence.

What does this suggest?• Perennial > annual pasture > cropping

systems.• 0-0.1 m soil layer contained 63% of measured

SOC within the top 0.3 m of the soil.

CC=continuous croppingMC= mixed cropping (B/C/P)AP= annual pasturePP=perennial pasture

Albany Sand Plain – Measured

What does this suggest?• Pasture systems dominate high rainfall – nearer

potential SOC but wider range in values.• Cropping systems – NPP constraints such as

waterlogging; inputs; low pH; water repellence?

& ModelledSo

il O

rgan

ic C

arbo

n St

ock

(t C

/ha)

Soil

Org

anic

Car

bon

Stoc

k (t

C/h

a; 0

-30

cm)

• Carbon storage capacity limited in sandy soils. Majority of ‘new’ carbon within the particulate fraction (permanence??)

• Management solutions need to focus on getting carbon into soil at depth.

• Where SOC content high – potential for ‘new’ storage less

• Warming climates likely to see a loss in organic matter build up

• Carbon is highly variable – sampling and measurement cost high

• Inputs must be maintained

Challenges Opportunities• Target degraded paddocks

• Get carbon deeper where viable

• Protect your topsoil….

• Improve water use efficiency by plants (e.g. remove sub-soil constraints) to increase potential C inputs to soilo Measurable change often takes decades

• Increase proportion of year (or area) with actively growing plants where viable

• Utilise organic input streams where viable

Soil organic carbon is critical to maintaining function & resilience …….

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Hoyle F.C., Baldock J.A. and Murphy D.V. (2011). Soil organic carbon – Role in rainfed farming systems with particular reference to Australian conditions. In: Rainfed Farming Systems (P. Tow, I. Cooper, I. Partridge and C. Birch; Eds.). Springer International.