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

Soil – A valuable asset

Ecosystem services are the transformation of a set of natural assets (soil, plants and animals, air and water) into things that we value.

Examples of Ecosystem Services:• Food and Animal Production

• Nutrient Cycling and Storage

• Organic Matter Storage and Decomposition

• Gas Emissions

• Water Treatment and Storage

• Soil formation and Erosion control

• Recreation

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

predictive techniques 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)

Dep

th (c

m)

0 cm

10 cm

40 cm

50 cm

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

x biomass/mm

Soil organic carbon fractions & ‘permanence’

Particulate

Soluble & suspended

Humus & ResistantMinerals & microbial biomass

Images: J Baldock CSIRO

Fresh residues, living organisms

Older residues, physically protected

Protected humus, charcoal

Humus (HOC)(< 53 µm)

Resistant (ROC)(Dominated by charcoal)

Particulate (POC) (2mm - 53 µm)

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 et al. (2011) Book Chapter

Higher nutrient turnover

Slower carbon turnover

Hoyle and Murphy (2007)

Treatment SOC (%)

POC (mg kg soil)

Residue burnt 1.2 139Residue retained 1.3 182

NS *** (31%)

- Changing a wheat–fallow rotation to permanent pasture altered SOC fractions over 75 years (Roth-C simulation)

- Management influences allocation to particulate and humus fractions of SOC- Losses to soil organic carbon are rapid; rebuilding SOC is slower

Hoyle, Baldock, Murphy (2011) Book Chapter

Organic matter fractions change on different time scalesSo

il O

rgan

ic C

arbo

n (g

C k

g-1

soil)

Carbon Storage in Soil

Satellite image of the WA agricultural area – sampling sites

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-

1so

il

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)

• Greatest separation in mean actual SOC stocks occurred when grouped by land use: • SOC stocks (0-30 cm) ranged from 3 t C ha-1 to 231 t C ha-1

• Wide range variability

Continuous crop = 25 t C ha-1

Mixed farming = 36 t C ha-1

Beef production: Annual pasture = 70 t C ha-1

Beef production: Perennial pasture = 61 t C ha-1

Dairy (Fodder removal): Annual pasture = 93 t C ha-1

Dairy (Irrigated): Annual pasture = 92 t C ha-1

Dairy (Grazed feed out): Annual pasture = 101 t C ha-1

Management influence

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

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)

So why is it so hard to do??

Modelled Capacity (0-30cm)

What does this mean?1. Carbon increased with

clay content.

2. Modelling suggests further capacity to store carbon in soil

3. Measured stocks reflect losses incurred with management and climate.

Albany Sand Plain

Model parameters• Roth-C v 26.3

• Perennial pasture:Root to shoot ratio 1:1, 33.5% net removal DM, 100% water-use efficiency, slope 16 kg DM/mm available water, 12 months DM production, 95% stubble retention.

• Historic rainfall and temperature (1889-2005)

• Modelled 0-30 cm

Hoyle et al. (2013)

Pere

nnia

l Pas

ture

Con

tinuo

us C

rop

Deep Sand Loamy Duplex What does this suggest?1. Perennial pasture >

cropping system.2. Soils with more clay have

greater capacity as a sink for carbon.

...however....

3. Capacity for storage is 0-10cm (nominal)10-20cm (50% capacity) 20-30cm (29% capacity).

How do we increase carbon down below??

Modelled Capacity (0-30cm; 10 cm increments)Albany Sand Plain

Model parameters• Roth-C v 26.3

• Perennial pasture:Root to shoot ratio 1:1, 33.5% net removal DM, 100% water-use efficiency, slope 16 kg DM/mm available water, 12 months DM production, 95% stubble retention.

• Historic rainfall and temperature (1889-2005)

• Modelled 0-10 cm increments

Hoyle et al. (2013)

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 living components of SOM?

Contaminantdegradation

Challenges: Building microbial biomass

Microbial biomass is the living component of soil organic matterMeasured by weight microorganisms are the power-house of the soil.Responsible for residue decomposition and nutrient release.

What is the microbial biomass?

Illustration supplied by Professor Phil Brookes, Rothamsted Research, UK

For a dryland agricultural soil:• Microbial biomass = 12 sheep/ha• 60% located in the surface soil• Mass declines with soil depth• They contain 50-100 kg N/ha • 100-200 kg of N/ha can be released

seasonally as they die/grow• They contain and release S & P

Developing messages arising from GRDC's investment in soil biology

soilquality.org.au

Experiment:Soil samples (0-10 cm) were collected from 1987 monitoring sites in Western Australia.

• pHCa from 3.5 to 8.0• Total organic carbon 0.2 to 9.8% • Microbial biomass 12 to 796 mg C/kg

What regulates microbial survival and growth (microbial biomass) in soil?

Challenges: Building microbial biomass

Soil moisture, access to food, physical/chemical habitat

D Murphy, E Stockdale, S Rushton, F Hoyle, D Jones, L Barton and A O’Donnell (2019) Ionic composition of soil reactive surfaces explain microbial biomass and carbon sequestration. Soil Biology & Biochemistry, submitted.

• Soil buffer groups linked to pH regions explained microbial biomass and soil organic carbon.

• Soil microbial biomass carbon determined by interacting processes involving total soil organic carbon, soil acidity and base cations

• High soil organic carbon in low pH soils associated with constrained microbial biomass.

What regulates microbial survival and growth (microbial biomass) in soil

TreatmentSoil organic C

(%)Labile C

(mg kg-1 soil)MBC

(mg kg-1 soil)

Straw burned 1.2 139 142

Straw retained 1.3 182 211

Difference (%) 10% (NS) 31% 49%Hoyle and Murphy (2007)

Microbial biomass influenced by management & physical habitat (C availability)

0

100

200

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400

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600

ClayLoam

Sandyloam

Loamysand

Sand

Soil type (topsoil)

Mic

robi

al b

iom

ass

(mg

C/k

g so

il) Data from ACC region

Sampled 2006

66% Microbial biomass

Clay contentpHLabile Carbon

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

• Topsoils theoretically ‘full’ in terms of C storage.- Lower layers have capacity to store more- Management solutions need to focus on getting carbon into soil at depth.- Measurable change is often decadal

• A limitation is converting rainfall into plant biomass. Improving water use efficiency by plants (e.g. removal of sub-soil constraints that restrict plant root growth) would increase potential C in soil - though large external additions needed for big changes.

• Primary SOC drivers = depth, climate, soil type, rotation and pH

• Increasing net primary productivity within cooler environments (<17°C) may increase SOC storage.

• Improved management = average change -5 to 0.25 t C/ha/y - often still showed absolute declines in SOC stock over time

Summary

• The top 10 cm soil contains ~60% of the SOC (0-30 cm).

• Soils already contain billions of microbes which only colonise a small fraction (less than 1%) of the soil surface area.

• Most surfaces in soil are not favourable to microbial growth and survival.

• Soil pH buffer groups can be used to explain microbial biomass and soil organic carbon sequestration in WA agricultural soils.

• Increasing proportion of year receiving organic inputs and maintaining residues will increase the number of biologically ‘active’ days.

• Challenge: Soil organic carbon and microbial biomass carbon are differentially regulated by soil buffer groups. Managing for one is not always at the benefit of the other.

Summary

Summary - Dairy

• SOC content already high in many instances – potential for storing additional less

• Climates getting hotter and drier are likely to see a loss in organic matter build up.

• ‘Permanence’ of carbon in soil for newly acquired carbon remains an issue.

• Carbon is highly variable – sampling and measurement cost high.

• Target degraded paddocks.

• Choose deep rooting species where viable.

• Increase water use efficiency

• Delivering organic inputs to depth

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

• Protect your topsoil….

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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.

Acknowledgements

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