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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
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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.
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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