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International perspectives on mitigation of agricultural N2O emissions
and stabilising/enhancing soil carbon
Professor Keith Goulding
with Tom Misselbrook and Laura Cardenas
Sustainable Soils and Grassland Systems Department
NO3-
NO2 (nirK; nirS) NO (norB) N2O (nosZ) N2
nitrate nitrite nitric oxide nitrous oxide nitrogen
Denitrification
Fertilisers Manures
N2O from nitrification and denitrification
N2O nitrous oxide
NH4+
NO2
- NO3-
ammonium nitrite nitrate
Nitrification
Fertilisers Manures
Genes and N2O emissions
● Abundancies of nirK, nirS and nosZ genes increased
with N enrichment and sensitive to pH (nosZ copy
numbers decreased with pH, so greater proportion of
N2O in acid soils).
● N2O emissions correlated with excess N inputs, soil
carbon, moisture, and the abundance of nirK genes.
● Complex relationships between genes and
environment: temperature, moisture, plant functional
groups, P, management
● Pre-wetting increased the copy numbers of nosZ
genes and reduced N2O emissions.
● Extreme wetting and drying (Climate Change?)
increases N2O emissions.
Minimising N2O emissions
“We did find that greater functional diversity is significantly related to greater abundances of several genes involved in denitrification: nirK, nirS, norB, and narG …We did not, however, find that changes in taxonomic and functional diversity were related to rates of either denitrification or C mineralization. Instead, ecosystem process rates were most strongly linked to the direct effect of farm management.” Wood, S.A. et al. (2015) Farm management, not soil microbial diversity, controls nutrient loss from smallholder tropical agriculture. Front. Microbiol. 6:90. doi: 10.3389/fmicb.2015.00090
Van Groeningen et al (2010) EJSS, 61, 903-913.
One clear message: avoid excess N
N surplus (kg N ha-1)
N leached (kg/ha) Yield (t/ha)
N applied (kg/ha/yr)
Crop yields and nitrate leached from Broadbalk (mean 1990-98)
as fertiliser as manure
* +96 kg/ha N
fert. in spring
*
Biochar: effects on GHG emissions
“Beneficial interactions of biochar and the soil N cycle are beginning to be understood with effects on mineralization, nitrification, denitrification, immobilization and adsorption persisting at least for days and months after biochar addition… Although the often large suppression of soil N2O flux observed under laboratory conditions can be increasingly explained…this effect is not yet predictable and there has been only limited validation of N2O suppression by biochar in planted field soils…or over longer timeframes...”
IPCC WGIII ‘Mitigation’, Ch 11, Box 11.3 ‘Biochar’.
Subbarao, G.V. et al (2012) Adv. Agron 114, 249-302.
Biological Nitrification Inhibition (BNI)
Subbarao, G.V. et al. (2012) Adv. Agron. 114, 249-302.
Relationship between the BNI capacity of plants and N2O emissions from field plots
Control Control
Soybean
Tropical pasture grasses
Bender, F.S. et al. (2014) ISME Journal 8, 1336-1345.
Symbiotic relationships between soil fungi and plants reduce N2O emissions from soil.
“…caused by AMF-induced changes in soil microbial biomass and community composition.”
Biological Nitrification Inhibition
0
10
20
30
40
50
60
70
80
0 7 14 21
Ammonium level
Days
Water
DCD
B. decumbens root extractB. humidicola root extract
B. mulato root extract
extracts
Exudates & water
Brachialactone
DCD
Minimising N2O emissions
• 4R Nutrient Management: right nutrient source, at the right rate, right time, and in the right place – minimise excess N.
• Enhanced efficiency fertilisers: reaction, coating, encapsulation, inhibitors, compaction, occlusion, or by other means.
• N sensors and variable rate application. • Cover crops • Maintain good soil structure to avoid waterlogging: maybe No-
Till; Min-Till. • Biochar. • Livestock management – diet including legumes; manure
management; stocking rate.
Current Opinions in Environmental Sustainability (2014) 9-10, 46-54.
Finite – SOC moves
towards new equilibrium
value.
Reversible – depends on
continuing the new land
management practice
Also:
Should asses impacts on
other GHGs - N2O and CH4
- need full GHG budget
Note whether given as C or
CO2 equiv. (i.e. all GHGs)
Soil C
Time
Management change
Initial Equilibrium
Transition
Final Equilibrium
Carbon sequestration in soil is:
But extra C good for soil quality
Grassland systems sequester C?
NCS = Net Carbon Storage (kg C/ha/yr)
Grazed = 1290
Cut = 980
Mixed = 710
Including GHG fluxes, the net balance of on- and off-site C
sequestration for 9 European soils
= 380 kg CO2eq/ha/yr.
European mineral soils:
Soussana, J-F. et al. (2010) Animal 4:3, 334-350.
Grassland systems
No, but “…judicious management of previously poorly managed grasslands can increase the sink capacity.”
Deep(er) rooting crops
Roots are a means of delivering carbon and natural plant-produced chemicals into soil with potentially beneficial impacts: carbon sequestration (at depth) biocontrol of soil-borne pests and diseases inhibition of the nitrification process in soil (conversion of ammonium to nitrate) with possible benefits for improved nitrogen use efficiency and decreased N2O emissions.
Kell, D. (2011) Annals of Botany 108, 407-418.
● Festulolium grass and clover grown together as mixtures
can enhance soil water, C and nutrient retention in soils.
● Modified grass and clover root growth and design aimed
at improved drought resistance and/or as an aid to flood
mitigation is achievable without compromise to crop
performance.
SUREROOT: Roots For The Future
Single plant Plot Field
Festulolium loliaceum cv Prior reduced event runoff by 51% compared to the UK National Listed perennial ryegrass cultivar L. perenne cv AberStar and by 43% compared to a meadow fescue cultivar Festuca pratensis Huds. cv. Bf993.
Festulolium reduced runoff
Macleod, CJA et al. (2013) Sci. Repts. 3, 1683
Subsoil sequestration by Miscanthus (Agostini et al. (2015) AGEE 200, 169-177)
• 2 non-tuft (M. giganteus, M sacchariflorus) and 3 tuft-growing (M sinensis) genotypes
• SOC and roots analysed for C3 ( ) and C4 ( ) contributions based on δ13C
• Considerable miscanthus-based enrichment in 0-30 cm soil
• Some evidence of subsoil sequestration in two genotypes
www.carbo-biocrop.ac.uk
SOC in arable reference soil (brown line) or archive soil (blue line)
0–30 cm
30–100 cm
0-30 cm
30-100 cm
1. Avoid tillage and the conversion of grasslands
to arable
2. Moderately intensify nutrient-poor permanent
grasslands
3. Light grazing instead of heavy grazing (what
about ‘mob grazing?)
4. Increasing the duration of grass leys
5. Converting grass leys to grass-legume
mixtures or to permanent grasslands
Maintaining SOC in grassland
McKinsey & Co (2009) ‘Pathways to a low-carbon economy. Version 2 of the Global Greenhouse Gas Abatement Cost Curve’.
GHG abatement potential of farm management changes
General conclusions
Too much emphasis on soil C sequestration risks less attention to major climate change threats:
Land clearance for food or biofuels
Other deforestation
Wetland drainage
Priorities:
good land stewardship
including increased
efficiency of N use,
reduced tillage, maintaining
‘green’ cover
integrated solutions
Deforestation in Brazil down 23% - only 2040 km2 in last 12 months! (2013 data)
Rothamsted Research where knowledge grows
Rothamsted Research where knowledge grows
Acknowledgements
Maintaining SOC in cropping systems
1. Ley-arable farming – i.e. intermittent pasture
2. Add crop residues
3. Add manures or other organic “wastes”
4. Min-Till / No-Till
mainly redistribution in early years, but useful to concentrate SOC near surface
C sequestration long-term?
5. Grow plants with larger/longer roots
6. Fertilisers
Plough Min till
Some small net SOC accumulation under zero-till in long-term: Angers & Eriksen-Hamel, SSSAJ 72, 1370-1374 (2008)
Increased N2O emissions in some situations
Depends on soil wetness:
Rochette Soil & Tillage Research 101, 97-100 (2008)
Extra 3 kg N2O ha-1 yr-1 could offset sequestration of 0.3 t C ha-1
yr-1 *. (Rothamsted experiments found an extra net emission of 4 kg N2O ha-1 yr-1 from min-tilled land compared to ploughed land)
* Johnson, J.M-F. et al. (2007) Env. Poll. 150, 107-124.
Conclusions for C sequestration
Not all increases in SOC genuinely sequester C. Incorporation of organic ‘wastes’ or crop residues does
not usually sequester C: but benefits for soil quality and functioning; greater CC mitigation from using biosolids and residues
for bioenergy production. Large GHG emissions from N fertiliser manufacture
outweigh any climate change benefit from increased SOC from increased crop residue returns.
Long-term min-till probably sequesters C and delivers other benefits for soil.
Conversion of arable land to forest or grass is genuine sequestration, but limited opportunities for this.
Festulolium loliaceum cv Prior reduced event runoff by 51% compared to the UK National Listed perennial ryegrass cultivar L. perenne cv AberStar and by 43% compared to a meadow fescue cultivar Festuca pratensis Huds. cv. Bf993.
Festulolium loliaceum cv Prior reduced event runoff by 51% compared to the UK National Listed perennial ryegrass cultivar L. perenne cv AberStar and by 43% compared to a meadow fescue cultivar Festuca pratensis Huds. cv. Bf993.
C sequestration summary: Maximum CO2-C ‘savings’ in ‘Year 1’
-1000
-500
0
500
1000
1500
2000N2O change
SOC change
kg/h
a/yr
CO
2-C
N2O + CH4 change
For CO2 mitigation
Perennial bioenergy crops (willow, miscanthus) for:
– electricity generation
– liquid transport fuels
– C sequestration in soil organic matter
Grain crops (oilseed rape, maize, cereals):
– Little or no saving of CO2
– Energy needed for growing and processing
– N2O and CO2 from making and applying N fertilizer
X
Global N cycle (99% of N is N2)
■ Natural fixation by legumes and lightning
~ 120 Tg yr-1
■ Anthropogenic fixation by the Häber-Bosch
process, increased use of legumes, biomass
burning, fossil fuel use and cultivation
~ 160 Tg yr-1 (estimated 190 Tg yr-1 by 2050)
■ Return via denitrification
1 Tg = 1015 kg = 1012 tonnes
NO3- NO2
- NO N2O N2
nitrate reductase nitrite reductase nitric oxide reductase nitrous oxide reductase
narG nirK (Cu); nirS (cyt cd1 heme) norB, norC nosZ
NO3 NO2
NO N2O N2
nitrate nitrite nitric oxide nitrous oxide nitrogen
Denitrification
Species Lifetime Time horizon
20 years 100 years 500 years
CO2 Variable 1 1 1
CH4 12+/-3 56 21 6.5
N2O 120 280 310 170
Global Warming Potentials
2013
Biochar
Sources and attributes
Organic material burned slowly under limited oxygen
Bi-product of bioenergy (pyrolysis of biofuel crops, straw, or wastes)
In natural ecosystems from fire
Highly stable, porous, active surfaces
Nitrous oxide emissions along a 7.5 km transect
7.5 km
Deconstructed variation in nitrous oxide emissions at different scales along a 7.5 km transect
7.5 km
1 km 350m 100m 50m
Soil nitrate pH Soil carbon and nitrate
Emission Factors
• Fertiliser, Manure and Grazing Returns
• Direct and Indirect (Ammonia and Nitrate)
Gap filling
• Soil and Climate Factors
• Computer Modelling
• Mitigation - Fertiliser Timing,
Nitrification Inhibitors
Method Development / Verification
• Plot and Field Scale Flux Measurements
• Country Scale Verification (Mace Head)
• Uncertainty Assessments Experimental Platforms ( )
and Soil Typology
AC0116: Nitrous Oxide Emissions (InveN2Ory)
LUC that could sequester C
1. Ley-arable farming – i.e. intermittent pasture
2. Add crop residues
3. Add manures or other organic “wastes”
4. Min-Till / No-Till
5. Grow plants with larger roots (breeding)
6. Grow larger crops by using fertilizers (small
effect)
7. Biochar
Biological Nitrification Inhibition by Plant Natural Products
Brachialactone Dicyandiamide
0
10
20
30
40
50
60
70
80
90
100
0 7 14 21
Nitrate level
Days
Soil 16 - nitrate levels
Water
DCD
B. decumbens root extract
B. humidicola root extract
B. mulato root extract
0
10
20
30
40
50
60
0 7 14 21
Nitrate level
Days
Soil 5 - nitrate levels
Water DCD
B. decumbens root extract B. humidicola root extract
B. mulato root extract B. decumbens exudate
B. humidicola exudate
exudates
extracts
0
10
20
30
40
50
60
70
80
90
1 2 3 4
Ammonium level
Days
Soil 16 - Ammonium levels
Water DCD
B. decumbens root extract B. humidicola root extract
B. mulato root extract
0
10
20
30
40
50
60
70
80
0 7 14 21
Ammonium level
Days
Soil 5 - Ammonium loss
Water DCD
B. decumbens root extract B. humidicola root extract
B. mulato root extract B. decumbens exudate
B. humidicola exudate
extracts
exudates
Using land for bioenergy crops
Willow
Miscanthus giganteus
Greenhouse gas emissions from UK agriculture
c. 9% of total GHG emissions:
9% of UK CO2 emissions
55% of UK N2O emissions
36% of UK CH4 emissions
From cultivated land:
CH4 = small uptake N2O = 31% UK emissions CO2 = considerable potential for C sequestration
2013 UK Greenhouse Gas
Emissions, Provisional
Figures.
Arable soils
Arable land covers about 14M km2 (FAO)
% by country
Global carbon stocks (Gt = billions of tonnes)
© Queensland Government
48
Spatial variation of N2O emissions in the landscape
1 km
0
200
400
1 64 127 190 253
Position along the transect
Flux N
2O-N
µg kg
-1d-1
5.00
6.00
7.00
8.00
9.00
pH
Spatial and temporal variation
0
100
200
300
400
500
600
700
0:00
0:00
0:00
0:00
0:00
0:00
0:00
0:00
g N
2O
-N h
a-1
d-1
6
8
10
12
14
16
so
il t
em
p.
(3c
m)
chamber 1 chamber 2 chamber 3 soil temp.
AC0116: results for 2011-12 season
0
500
1000
1500
2000
2500
3000
3500
4000
4500
Co
ntr
ol
AN
1A
N 2
AN
3A
N 4
AN
5A
N s
plit
Ure
aA
N +
DC
DU
rea
+ D
CD
Co
ntr
ol
AN
1A
N 2
AN
3A
N 4
AN
5A
N s
plit
Ure
aA
N +
DC
DU
rea
+ D
CD
Co
ntr
ol
AN
1A
N 2
AN
3A
N 4
AN
5A
N s
plit
Ure
aA
N +
DC
D
An
nu
al c
um
ula
tive
flu
x (g
N2O
-N h
a-1) Rosemaund Woburn Gilchriston
Bell et al. submitted to
0
0.2
0.4
0.6
0.8
1
1.2
Rosemaund Woburn Gilchriston
Emis
sio
n F
acto
r (%
)
Bell et al. submitted to
AC0116: results for 2011-12 season
0
0.2
0.4
0.6
0.8
1
g N
kg-
1 D
M
G N / kg DM
Bell et al. submitted to
AC0116: results for 2011-12 season
0
0.1
0.2
0.3
0.4
0.5
0.6
Rosemaund Woburn Gilchriston
g N / kg DM g N / kg DM
Largest emissions at the wetter Scottish site (822 mm rainfall cf 418 mm and 472 mm at the English sites).
N fertiliser treatment differences apparent but not consistent between sites and in most cases insignificant.
No effect of DCD, split fertiliser applications or fertiliser type on N2O emissions or crop production at any of the sites.
Emissions at English sites low on all treatments reflecting very dry conditions after the fertiliser was applied; EFs of < 0.5 %. EFs higher at the Scottish site but IPCC default value of 1% only exceeded for the 120 kg N ha-1, 120 kg N ha-1 split and 200 kg N ha-1 treatments.
AC0116: results for 2011-12 season
Rees et al. (2013) Biogeosciences 10, 2671-2682.
Nitroeurope data (8 arable sites)
The effect of different tillage systems on soil physical properties
15
30
45
60
75
16/9/03 17/12/03 18/3/04 18/6/04 18/9/04
Date 2003-2004
% W
FP
S
Min Till
Plough
Min
Till
Plough
Soil
Bulk
Density
g cm-3
1.13
1.04
Porosity
%
51 55
Bulk density and porosity, November
2003
Water Filled Pore Space
Nitrous oxide emission from winter wheat fields under plough or Min-Till
0
40
80
120
160
Date 2003-04
Em
iss
ion
g N
20
-N
ha
-1 d
ay
-1
Min Till
Plough
16 Sept 17 Dec 18 Mar 18 June 18 Sept
GWP of 33 Paired conventional- and Zero-Tilled fields
Mangalassery et al. (2014) Scientific Reports 4: 4586 | DOI: 10.1038/srep04586
(5-10 years)
Arable Grassland or Forest
Genuine C sequestration. But must be certain that removal of land from
crop production at one location on the planet does not cause land clearance (deforestation, ploughing grassland, wetland drainage) elsewhere.
Expect increase in CH4 oxidation and reduction in N2O emission provided N deposition low.
Biochar: proposed effects on soil
Near-permanent increase in soil C
Greater stabilisation of other soil C
Suppression of greenhouse gas emission
Enhanced fertiliser-use efficiency
Improvement in soil physical properties
Enhanced crop performance
Increased soil biodiversity
Lots of research and now support from the IPCC
nitrate reductase nitrite reductase nitric oxide reductase nitrous oxide reductase
narG nirK (Cu); nirS (cyt cd1 heme) norB, norC nosZ
NO3 NO2
NO N2O N2
nitrate nitrite nitric oxide nitrous oxide nitrogen
Can we control denitrifying organisms?
Minimising nitrous oxide emissions
Avoid excess fertiliser and manure applications.
Apply fertilisers and manures at the right time and in the right place – Precision Agriculture.
Manage soils to minimise anaerobic conditions.
Possibly Min-Till or Zero-till but needs to be long-term (>5 years).
Nitrification inhibitors.
Biochar – IPCC WGIII says ‘yes’
2013 UK Greenhouse Gas Emissions,
Provisional Figures and 2012 UK Greenhouse
Gas Emissions. 27 March 2014.
Prof. Keith Smith
The UK Agricultural GHG
Research Programme
GHG emissions from agriculture
Enteric fermentn.
Manure managt. Rice cultivation
Agricultural soils
Burning ag. Resid.
Total emissions as CO2 equivalents
Van Groeningen et al (2010) EJSS, 61, 903-913.
Avoid excess N
Rees et al. (2013) Biogeosciences 10, 2671-2682.
EU arable emissions data
Bell et al. submitted to
AC0116 results for 2011-12 season
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
AN1 AN 2 AN 3 AN 4 AN 5 AN split Urea AN +DCD
Urea +DCD
Emis
sio
n F
acto
r (%
)
GHG emissions from agriculture
CO2 (21%–25% of total CO2 emissions) from fossil fuels used on farms; mainly deforestation and shifting patterns of cultivation
CH4 (55%–60% of total CH4 emissions) from rice paddies, land use change, biomass burning, enteric fermentation, animal wastes
N2O (65%–80% of total N2O emissions) mainly from N fertilizers on cultivated soils and animal wastes
Smith (2012) GCB 18, 35-43. After Macleod et al 2010.
Feasible mitigation potential by 2022 for soil and crop management
2013 UK Greenhouse Gas Emissions, Provisional
Figures and 2012 UK Greenhouse Gas Emissions.
27 March 2014.
2013 UK Greenhouse Gas Emissions, Provisional
Figures and 2012 UK Greenhouse Gas Emissions.
27 March 2014.
Carlton et al. (2012) Eur J Plant Path, 133, 333-351.
2013 UK Greenhouse Gas Emissions, Provisional
Figures and 2012 UK Greenhouse Gas Emissions.
27 March 2014.
Driven by an increase in forested land.
AC0114 – Synthesis, Data Management
and Modelling (Synthesis)
Emission Factors
• Synthesis of existing experimental data and mitigation
• Integration of output from projects AC0115 and AC0116
Inventory Structure
• Collation of database e.g. soil and climate mapping, drainage, forage quality
• Synthesis of agricultural survey and farm systems data
• Enhanced spatial and temporal resolution
Farm Practices
• Characterisation of regional farm practices and technical innovation
• Explicit representation of industry trends and uptake of abatement methods
Uncertainty Analysis
• Measuring and communicating confidence in calculated emissions
InveN2Ory data
Nitrification inhibitors
[Ma et al (2013) Biol. Fert. Soil 49, 627-635.]
Equipment