Nitrous oxide (N2O) significantly contributes to global greenhouse gas emissions, with 10% of anthropogenic emissions attributed to agriculture, primarily from microbial activities. Measurements from intensively managed grasslands show that N2O emissions often negate carbon sequestration efforts, highlighting a net emission scenario despite carbon inputs. The document discusses strategies for minimizing greenhouse gas emissions while enhancing carbon sequestration in agricultural systems.

1. 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

2. • 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

3. Global Sources of N2O
Nitrous oxide (IPCC, 2006)

4. 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

5. Agriculture is responsible for 10% of UK GHG emissions
5.4% N2O, 4% CH4, 0.7% CO2
0
200
400
600
MTCO2eqin2012
Agriculture All sources
UK Agricultural
sources
0.9% CO2
44% CH4
81% N2O
of annual
budgets
CO2
CH4
N2O
+ Waste

6. 0
5
10
15
20
25
30
NAEI2009 'Agricultural sources'
GgN2O
Agricultural
emissions
Gg
N2O
Direct 51.4
Indirect 29
manure 6.4

7. 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

8. 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

9. Rainfall and fertiliser induced N2O
emissions
-500
0
500
1000
1500
2000
17.1.07
20.03.07
18.04.07
21.5.07
10.7.07
30.7.07
24.9.07
27.11.07
18.3.08
6.4.08
18.4.08
16.5.08
19.6.08
04.07.08
01.08.08
29.08.08
23.9.08
19.2.09
6.4.09
15.5.09
23.6.09
27.7.09
21.8.09
21.10.09
9.3.10
12.4.10
21.5.10
28.6.10
soilN2O-Nfluxes
(mgm-2h-1)
N2O fluxes at Easter Bush grassland 2007 - 2010
N2O loss as % of N fertiliser input
2007 6.5
2008 3.3
2009 1.4
2010 1.4
red arrows: N fertiliser application
Skiba et al, 2013, Biogeosciences, 10, 1231–1241

10. Comparing NEE from intensively and
extensively managed sheep grazed land
-15
-10
-5
0
5
10
0 365 730 1095 1460
mmoleCO2m-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

11. 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

12. Greenhouse gas budget for the intensively
managed grassland (Easter Bush) 2002 - 2010
-2500
-2000
-1500
-1000
-500
0
500
1000
2002
2003
2004
2005
2006
2007
2008
2009
2010
gCO2equivalentm-2y-1
CO2 N2O CH4
Average
On average 60% of NEE sequestration is counteracted by N2O & CH4 emissions

13. 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
average
Carboninput(-)andlosses(+)[gCm2y-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

14. 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

15. 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

16. 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

17. 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?

18. DEFRA GHG Platform Project
NitroEurope
CarboEurope
GREENGRASS