The role of nitrous oxide in the agricultural greenhouse gas budget

Ute Skiba Centre for Ecology and Hydrology

Bush Estate, near Edinburgh ums@ceh.ac.uk

• Long lived greenhouse gas >100 years • Responsible for 10% of the total global anthropogenic radiative forcing •Largest source of stratospheric NOx (ozone hole) • ~77% is produced by microorganisms

•nitrification/denitrification

Nitrous Oxide: The Facts

Global Sources of N2O

Nitrous oxide (IPCC, 2006)

The atmospheric increase of N2O is largely attributed to agricultural activity and CH4 to fossil fuel use and animal rearing

Atmospheric increase of N2Oand CH4

Agriculture is responsible for 10% of UK GHG emissions 5.4% N2O, 4% CH4, 0.7% CO2

0

200

400

600

MT

CO

2e

q in

20

12

Agriculture All sources

UK Agricultural sources 0.9% CO2

44% CH4

81% N2O of annual budgets

CO2

CH4

N2O

+ Waste

0

5

10

15

20

25

30

NAEI 2009 'Agricultural sources'G

g N

2O

Agricultural emissions

Gg N2O

Direct 51.4

Indirect 29

manure 6.4

Intensively managed grasslands are important sources of N2O

• Dominant in western high rainfall areas

• Large and frequent input of N fertiliser

• Soil compaction by livestock

Easter Bush

The role of N2O in the GHG budget at Easter Bush

•Eddy covariance flux measurements • CO2 since 2002 • CH4 short campaigns • N2O several ~ 1 year campaigns

•Manual static chamber measurements since 2002 • weekly/fortnightly 2006 – 2010

•Chamber/eddy covariance inter-comparison campaigns •Livestock CH4 /eddy covariance •Carbon stocks – ploughing effects •Carbon and nitrogen budgets

Rainfall and fertiliser induced N2O emissions

-500

0

500

1000

1500

2000

17

.1.0

7

20

.03

.07

18

.04

.07

21

.5.0

7

10

.7.0

7

30

.7.0

7

24

.9.0

7

27

.11

.07

18

.3.0

8

6.4

.08

18

.4.0

8

16

.5.0

8

19

.6.0

8

04

.07

.08

01

.08

.08

29

.08

.08

23

.9.0

8

19

.2.0

9

6.4

.09

15

.5.0

9

23

.6.0

9

27

.7.0

9

21

.8.0

9

21

.10

.09

9.3

.10

12

.4.1

0

21

.5.1

0

28

.6.1

0

so

il N

2O

-N fl

ux

es

(mg

m-2

h-1

)

N2O fluxes at Easter Bush grassland 2007 - 2010N2O loss as % of N fertiliser input

2007 6.52008 3.32009 1.42010 1.4

red arrows: N fertiliser application

-500

0

500

1000

1500

2000

17.1

.07

20.0

3.0

7

18.0

4.0

7

21.5

.07

10.7

.07

30.7

.07

24.9

.07

27.1

1.0

7

18.3

.08

6.4

.08

18.4

.08

16.5

.08

19.6

.08

04.0

7.0

8

01.0

8.0

8

29.0

8.0

8

23.9

.08

19.2

.09

6.4

.09

15.5

.09

23.6

.09

27.7

.09

21.8

.09

21.1

0.0

9

9.3

.10

12.4

.10

21.5

.10

28.6

.10

so

il N

2O

-N fl

uxes

(mg

m-2

h-1

)

N2O fluxes at Easter Bush grassland 2007 - 2010N2O loss as % of N fertiliser input

2007 6.52008 3.32009 1.42010 1.4

red arrows: N fertiliser application

Skiba et al, 2013, Biogeosciences, 10, 1231–1241

Comparing NEE from intensively and

extensively managed sheep grazed land

-15

-10

-5

0

5

10

0 365 730 1095 1460

mm

ole

CO

2 m

-2s

-1

Day number (1.1.2007 - 31.12.2010)

Easter Bush grassland

2007 2008 2009 2010

Auchencorth Moss

Skiba et al, 2013, Biogeosciences, 10, 1231–1241

Measuring ruminant CH4 fluxes by eddy covariance showed agreement with IPCC emission factor

Methane flux measured by EC in 2010 using Li-7700 open-path CH4 sensor

Dengel et al, 2011 Global Change Biology doi: 10.1111/j.1365-2486.2011.02466.x

Greenhouse gas budget for the intensively managed grassland (Easter Bush) 2002 - 2010

-2500

-2000

-1500

-1000

-500

0

500

1000

2002

2003

2004

2005

20

06

2007

2008

2009

2010

g C

O2

equ

ival

ent m

-2y-1

CO2 N2O CH4

Ave

rage

On average 60% of NEE sequestration is counteracted by N2O & CH4 emissions

Carbon budget for the intensively managed grassland (Easter Bush) 2002 - 2010

-700

-600

-500

-400

-300

-200

-100

0

100

200

300

400

2002

2003

2004

2005

2006

2007

2008

2009

2010

aver

age

Car

bo

n in

pu

t (-

) an

d lo

sses

(+)

[g C

m2

y-1

CH4 (enteric ferm.)

CH4 (excretion)

CH4 (soil)

CH4 (organic fert.)

Leaching*

Wool

Meat

Harvest

Organic fert.

CO2 (NEE)

Net sequestration of -180.7 (91.5) g C m-2y-1

Two ways to study carbon cycling

• Eddy covariance measurements of net ecosystem exchange of CO2 and C losses

• Soil carbon stock measurements

2004 & 2011

100* 60 cm cores

Marion Schrumpf (MPG, Jena, DE) CarboEurope

The intensively managed grazed grassland in SE Scotland on clay loam soil is NOT a significant carbon sink

Net C sequestration (- export of cut grass, meat,

wool, C leaching, CH4) -180.7 (91.5) g C m-2y-1

Carbon stock change 9.0 ± 215 g C m-2y-1

Intensively managed grazed grasslands are a net source of nitrous oxide from soil

methane from ruminants But it is unlikely that these emissions are off-set by carbon

sequestration Ploughing does lead to large CO2 losses

Can grasslands be carbon neutral?

Jean-Francois Soussana, Gilles Lemairec:

Coupling carbon and nitrogen cycles for environmentally sustainable intensification of grasslands and crop-livestock systems

Agriculture, Ecosystems and Environment 190 (2014) 9–17

Extensive grazing can increase soil N cycling and C sequestration. What is the tipping point to a N2O/CH4 emitting system? How can management be used to minimise N2O/CH4 emissions and increase C sequestration?

DEFRA GHG Platform Project

NitroEurope

CarboEurope

GREENGRASS