1 1

A climate for change: agriculture and greenhouse gas mitigation in the 21st century

Professor Bob Rees, SRUC Edinburgh

Italian Society of Agricultural Chemistry, 24-26th September 2018

2

Two degrees matters!

0102030405060708090

2010 2050(BAU)

2050 (2Ctarget)

Nonagriculturalemissions

50 %

Gt C

O2

e/y

ear

Modified from WRI 2014

3

Reducing emissions from agriculture to meet the 2 °C target

Wollenberg et al 2016, Global Change Biology, 22, 3859-3864

4 4

Negative emissions required for 2oC

Anderson and Peters 2016, Science 354, 182-183

5 5

Nitrous oxide emissions from agricultural soils and manure management

Kt

CO

2e

Eurostat, 2018

6 6

Methane emissions from enteric fermentation and manure management

Kt

CO

2e

Eurostat, 2018

7 7

Contribution of agriculture to total GHG emissions (%), EU-28, 2015

kilo

ton

nes o

f C

O2 e

qu

iva

lents

Eurostat 2018

Total emissions,2016 4401 Mt CO2e

8 8

178

135

97

109

94

42

2007 emissions

International aviation & international shipping*

UK non-CO2 GHGs

Other CO2

Industrial CO2 (heat &

industrial processes)

Residential, public & commercial heat

Domestic transport

Electricity generation

* bunker fuels basis 2050 objective

159 Mt CO2e

679 Mt CO2e

76% cut (= 80% vs. 1990)

UK targets for greenhouse gas mitigation

DEFRA 2009

9 9

Agriculture and land-use are different

• Biological emissions

• Non-CO2 greenhouse gases

• Emissions and uptake

• Food production is a basic human need

• Wider socio-economic implications

• Net zero emissions within agriculture probably not possible

10 10

N2O

3

Zim

1

Tul

-1

PauMauLogFouEl

2

Bea

4

0

Ln N

2O

(kg

N /

ha

)

Variability in N2O emissions between arable sites

Rees et al, 2013, Biogeosciences

Ln N

2O

(kg N

ha

-1 y

-1)

2.25

1.75

Rt08

1.25

Rt07

0.75

Nt08Nt07Ht08

2.50

Ht07

1.00

2.00

1.50

Ln N

2O

(kg

N/h

a)

Italy

Zim

babw

e

UK

Germ

any

Sw

eden

Belg

ium

Spain

Denm

ark

11 11

Achieving greenhouse gas mitigation in agriculture

• Improved efficiency in fertiliser and manure use

• Increasing legume production

• Improved livestock management (feed and wastes)

• Improved livestock and crop health

• Soil management

12 12

Use of technology

• Precision farming

• Automation and

robotics

• Earth observation and

modelling

• New genetics

• Decision support tools

13 13

Shifting consumption away from carbon intensive production

Halving the consumption

of meat and dairy in the

EU would result in a 25-

40% reduction in

associated greenhouse

gas emissions.

Smith et al 2014. Nature Climate Change Westhoek at al 2014. Global Environmental Change

14 14

Management options

• Adopting systems less reliant on inputs

• Improved crop varieties

• Using biological fixation to provide N inputs

• Avoiding N excess

• Full allowance of manure N supply

• Nitrification inhibitors

• Fertilisation reduction

• Precision farming

• Land use change

• Regionally optimised plant and animal production

• Improved timing of mineral fertiliser N application

• Land drainage

• Loosen compacted soils / Prevent soil

compaction

• Biochar

• Increase feed protein quality

• Avoid drainage of wetlands

• Changing from winter to spring cultivars

• Use the right form of manufactured N fertiliser

• Improved timing of slurry and poultry manure

application

• Intensive Grazing Management

• Peat and Organic Soil: Restoration of soil

forming conditions

• Re-locate high N input cropping to drier, cooler

areas

14

15 15

Marginal Abatement Cost Curve for ALULUCF

UK 2030,CFP, 3.5%

0 4,500500 1,000

-300

-200

300

6,500

1,500 2,000 2,500 3,500 4,000

200

0

-100

100

3,000

20. ADCattleMaize

1. SynthN15. HighFat

8. GrainLegumes5. CoverCrops

22. ADMaize12. ImprovedNutr21. ADPigPoultryMaize

18. BeefBreeding

11. SoilComp17. SheepHealth

23. Afforestation 14. NitrateAdd

3. ManSpreader

24. FuelEff

Cost-effectiveness(£/tCO2e)

19. SlurryAcid

6. CRF2. ManPlanning10. PF-Crops

7. ImprovedNUE4. SpringMan

13. Probiotics

9. GrassClover16. CattleHealth

Abatement potential(ktCO2e/year)

Livestock

Forestry

Energy

Crops

Eory et al. 2015

In Scotland there is a cost effective mitigation potential of 0.88 Mt CO2e/year by 2030

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• Nationally replicated experiments and protocols

• Typically involving a comparison of 10 treatments with 15 reps

• High frequency sampling over 12 months

• Measurements of N inputs and losses

• Verification of methodologies

Improved reporting

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Environmental and soil variables: N2O emissions

Bell et all, Agriculture Ecosystems and Environment, 2015, 212, 134-347. Rainfall and N2O at: a. Rosemaund,

b. Woburn, c. Gilchriston

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Mitigation options to reduce N2O

emissions?

Ure

a +

DCD

Ure

a

AN +

DCDAN

Ure

a +

DCD

Ure

a

AN +

DCDAN

Ure

a +

DCD

Ure

a

AN +

DCDAN

3500

3000

2500

2000

1500

1000

500

0

Rosemaund

Woburn

Gilchristong

N2O

-N h

a-1

Urea vs. AN? • No significant difference in annual emissions at any site

Application of DCD? • Significant reduction in annual emissions when added to urea: all sites • Significant reduction in annual emissions when added to AN: all sites

Bell et all, Agriculture Ecosystems and Environment, 2015, 212, 134-347.

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Nitrous oxide cumulative annual emissions N

2O

-N k

g N

ha

-1y

-1

0

500

1000

1500

2000

2500

N Wyke Crichton Drayton Pwllperian Hillsborough

An

nu

al ra

infa

ll (m

m)

** ** **

**

Cardenas et al, in preparation

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Metrics

N2O emission

Fertiliser N addition

0

0.5

1

1.5

2

2.5

Bell et al., 2015 Increasing N addition

Emission per unit of crop produced g N2O-N/kg DM

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-20

30

80

130

180

230

280

01-Apr-2012 21-May-2012 10-Jul-2012 29-Aug-2012 18-Oct-2012 07-Dec-2012 26-Jan-2013 17-Mar-2013

Dai

ly m

ean

N2O

flu

x (g

N2O

-N h

a-1

d-1

)

synthetic urine

urine

dung

control

urine+DCD

Spring experiment

Spring Summer Autumn

Characterising emissions from contrasting N sources

Bell et al, 2016. Geoderma, 264, 81-93

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Decision support to manage grazing

T van der Weerden, S Laurenson, I Vogeler, P Beukes, S Thomas, R Rees, C Topp, G Lanigan, C de Klein. AgResearch, New Zealand. Plant and Food

Research, New Zealand. Scotland’s Rural College, UK Teasgasc Ireland

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Setting the rules

Assess background environment

Monitor soil wetness and

compare against

threshold values

Move cattle when soil wetness exceeds threshold

value

van der Weerden et al, 2017 Agricultural Systems, 156, 126-138.

24 24

Decision support approach

0

1000

2000

3000

4000

Base-farm 4 hrs 8 hrs 21 hrs Base-farm 4 hrs 8 hrs 21 hrs

Imperfectly-drained Poorly drained

Tota

l CO

2e

/ha

/ye

ar

- 5% - 7% - 12%

+6%+3%+1%

(a)

Imperfectly drained Poorly drained

If VWC ≤ CWC If VWC > CWC If VWC ≤ CWC If VWC > CWC

Safe to graze Remove stock Safe to graze Remove stock

VWC = soil water content, on a volumetric basis; CWC = critical water content, for imperfectly drained soils

CWC= 105% of field capacity (FC) and for poorly drained soils CWC = 85% of field capacity (FC).

van der Weerden et al, 2017 Agricultural Systems, 156, 126-138.

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Enteric Fermentation • Major global anthropogenic

source (90 Tg/y)

• Ruminants are large CH4 emitters

• Mitigation

– Improve feed use efficiency

– Optimise genotype to environment and feed

– Reduce animal numbers and intensify to

maintain productive output

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Methane mitigation in livestock

0

5

10

15

20

25

Me

tha

ne

em

iss

ion

s g

/d

AA

LIM

Conc.

Forage

Waterhouse et al, 2015

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28 28

Emissions

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Is 4 per mil achievable?

• Where will it happen?

• How will we know it is happening?

• What measures are we need to undertake to

achieve it?

• What are the costs and co-benefits?

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Why soil carbon sequestration?

Contending GGRTs

• Bioenergy with Carbon Capture and Storage (BECCS)

• Direct Air Capture (DAC)

• Enhanced Weathering (EW)

• Afforestation/ reforestation (AR)

Source: Smith, P. (2016) Soil carbon sequestration and biochar as negative emission technologies. Global Change Biology 22, 1315-1424

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How will we know it is happening? Changes in soil carbon in Scotland 1978-2009

-10

-5

0

5

10

15

Ch

an

ge in

to

tal C

sto

ck (

t/h

a)

.

Lilly et al. 2013. European Journal of Soil Science, 64, 455-465

* *

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How will we know it is happening? Detailed nutrient cycling studies

Carbon stock change

(repeated soil cores)

29 (+/38) g C m-2 y-1

Flux measurements

(- export of cut grass, meat,

wool, C leaching, CH4)

-180 (+/- 180) g C m-2 y-1

Jones et al. Biogeosciences 2017, 14, 2069-2088

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Net greenhouse gas balance for a grazed grassland

Easter Bush, 2002-2008. Jones et al, Biogeosciences 2017 14, 2069-2088

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Carbon sequestration can be small relative to total net GHG emissions

Gao et al, 2018, Global Change Biology

35 35

What measures are needed? reduced tillage

Powlson et al, 2014. Nature Climate Change, 4, 678-683

36 36

4 per mil provides opportunities and challenges

• Opportunities

– Low cost GHG mitigation

– Co-benefits in terms of soil fertility, resilience and crop

productions

– Widespread opportunity

• Challenges

– Reversibility of carbon storage and carbon saturation

– Implied nitrogen costs

– Non-CO2 emissions

– Verification

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Conclusions

• There is an urgent need to reduce greenhouse gas emissions from agricultural systems

• Increasing efficiency can reduce emissions and emission intensities

• Nitrogen management will play a particularly important role in reducing N2O emissions

• In order to achieve Paris targets there will need to be significant removal of CO2 from the atmosphere by 2050

• We are likely to depend upon both supply and demand side measures to achieve policy objectives

38 38

Acknowledgements

• Thank you for your attention

• Funding from the Scottish Government, UK

Research Councils and the EU is gratefully

acknowledged