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