1. EPA Dublin, 24th November 2010
Greenhouse gas accounting in
agriculture:
Modelling nitrogen emissions
Tom Misselbrook
Laura Cardenas

2. Nitrogen cycling in agricultural systems

3. Modelling approaches
Empirical IPCC Tier 1 default
Country-specific
- based on measurement
Spatial/temporal
Process-based EF scale
e.g. responding to soil
type, climate
Detailed mechanistic models
Mechanistic

4. Components to be modelled
1. Livestock
a. Nitrogen excretion
b. Manure management
2. Soils
a. Fertilizer
b. Manure
c. Grazing returns
d. Crop residues (incl. legumes)
e. Indirect emissions (deposition, leaching)

5. Livestock – N excretion
Sietske de Vries©1997

6. Livestock – N excretion
e.g. UK Dairy cow
 IPCC Tier 1 default: Western Europe, 600 kg cow = 105 kg N per year
 Country-specific estimate: empirical relationship with milk yield
8 000 120
milk yield
N excretion
N excretion (kg/year)
7 000 110
Milk yield (l/year)
6 000 100
5 000 90
4 000 80
1990 1995 2000 2005 2010

7. Dietary models
Nitrogen balance
N in products
- milk, meat eggs etc.
Animal
N intake
- Retained N
Excreted N
Faeces Urine
• Model different production systems – scales of intensity, breeds
• Model dietary manipulations – crude protein, energy, additives
• ?Characterisation of feed intake for forage-based diets

8. Livestock – Manure management

9. Livestock – Manure management
IPCC Tier 1 default EF
System EF
(kg N2O-N per kg N excreted)
Daily spread 0
Solid storage 0.005
Liquid/slurry 0 / 0.005 (crusted)
Deep bedding 0.01 / 0.07 (mixed)
Poultry manure 0.001
…
IPCC 2006 Guidelines

10. Livestock – Manure management
Ammonia and NOx emissions - FracGasMS
System FracGasMS
(% of N excretion)
Pig – slurry 48 (15-60)
Pig – solid storage 45 (10-65)
Dairy – slurry 40 (15-45)
Dairy – solid storage 30 (10-40)
Dairy – daily spread 7 (5-60)
Poultry – with litter 40 (10-60)
…
IPCC 1996/2000 Guidelines – FracGasMS = 20%
IPCC 2006 Guidelines

11. Manure management – N flow mass-balance approach
Diet manipulation
EXCRETION
NH3 Air scrubbers
N2O
NO
HOUSE PASTURE
N2
Store cover FERTILISER
STORE
SOIL/CROP

12. Description of production systems
 Detailed ‘partial’ emission factors
Straw-bedded
Dairy cows Arable land
Lagoon
Slurry
Grassland
Tank
Beef cows
Replacements
 Evidence-based
 Potential to derive from process-based models

13. Manure management – Comparison of methodologies
System FracGasMS UK model
(% of N excretion)
Pig – slurry 48 (15-60) 46
Pig – solid storage 45 (10-65) 29
Dairy – slurry 40 (15-45) 26
Dairy – solid storage 30 (10-40) 21
Dairy – daily spread 7 (5-60) 8
Poultry – with litter 40 (10-60) 51
…
Important for derivation of indirect N2O emissions from N deposition

14. Soils

15. IPCC Tier 1 approach
Default IPCC EF applied to country-specific (DA, UK) activity data:
Direct emissions
Fertiliser N EF1 x Nfert
Manure N EF1 x Nman
Crop residues EF1 x NcropDM x %residue
Histosols EF2 x Area of histosols
Grazing returns EF3 x Ngraz
Indirect emissions
Deposition EF4 x Ndep
Leaching/run-off EF5 x Nleach
Default IPCC parameters
Default IPCC EF
IPCC 2006 Guidelines

16. Country-specific empirical approaches
Important processes:
 Nitrification
 Denitrification
Important drivers:
Soil water-filled pore space
- texture
- climate
Substrate
- C and N availability
Timing
- in relation to soil conditions and crop requirements
National scaling based on empirical relationships
e.g. Lilly et al., 2009 (Global Change Biology)

17. Country-specific EF for N2O from soils
Direct emissions
Fertiliser N EF1 x Nfert
Manure N EF1 x Nman
Crop residues EF1 x NcropDM x %residue
Histosols EF2 x Area of histosols
Grazing returns EF3 x Ngraz
Indirect emissions
Deposition EF4 x Ndep
Leaching/run-off EF5 x Nleach
Derive CS-EF based on soil/climatic zone, land use, form of N (fertiliser, slurry, FYM,
urine, dung)

18. N2O emission (g N2O-N ha-1 d-1)
-20
0
20
40
60
80
100
120
140
16-Feb 160
Control
9-Mar
13-Mar
14-Mar
12th March
15-Mar
27-Mar
3-Apr
4-Apr
70 kg N ha-1
2nd April
5-Apr
19-Apr
3-May
4-May
30th April
8-May
10-May
11-May
140 kg N ha-1
16-May
29-May
15-Jun
20-Jun
4-Jul
Date
20-Jul
1-Aug
210 kg N ha-1
15-Aug
16-Aug
20-Aug
31-Aug
14-Sep
24-Sep
10-Oct
280 kg N ha-1
18-Oct
2-Nov
15-Nov
30-Nov
20-Dec
Fertiliser applications to arable land
10-Jan
16-Jan
350 kg N ha-1
1-Feb
22-Feb
4-Mar
0
10
20
30
40
50
60
70
80
90
WFPS (%)
WFPS (%)
Defra project AC0101

19. Fertiliser applications to grassland
40000
35000
30000
Flux, g N ha-1 yr-1
y = -19460+19450*1.00301 x
25000
20000
15000 y =-2780+4720*1.005 x
10000
5000
y = 70+474*1.00812 x
0
0 100 200 300 400
Fertiliser applied, kg N ha-1 yr-1
Cae Banadl Rowden High Mowthorpe
Defra project AC0101

20. Indirect emissions - Deposition
Fertilisers
IPCC (2006) default:
N2O = Nfert x FracGASF x EF4
Default FracGASF = 0.10
Empirical modelling approach:
EFNH3 = f (type, soil_pH, land_use, application_rate, rainfall, temperature)
Misselbrook et al., 2004 (SUM)
Modelled mean UK EF (as % N applied)
Fertiliser type EF tillage EF grassland
AN 1.7 1.8
Urea 8.9 9.7
UAN 4.6 5.0
AS/DAP 2.7 3.0

21. Indirect emissions - Deposition
Manures
IPCC (2006) default:
N2O = Nfert x FracGASM x EF4
Default FracGASM = 0.20
Empirical modelling approach:
EFNH3 = f (manure_type, soil_moisture, land_use, slurry_DM, application
technique, wind_speed, rainfall, incorporation_timing, incorporation_technique)
MANNER_PSM – Defra KT0105
Modelled mean UK EF (as % N applied)
Manure type Slurry FYM
Cattle 14.4 7.3
Pig 12.1 9.3
Poultry 21.5

22. Indirect emissions – Leaching
IPCC (2006) default:
N2O = N x FracLEACH x EF5
Default FracLEACH = 0.30
Nitcat model
Lord, 1992 (Aspects Applied Biol)
•Soil
•Cropping
•Management (fertiliser and manure N, timings)
•Environment (rainfall, temperature)
Defra project AC0101

23. Mechanistic models - DNDC
Ecological Climate Soil Vegetation Anthropogenic activity
drivers
Plant growth
Soil climate Decomposition
Soil environmental
variables Temp. Moisture pH Eh Substrate
Denitrification Nitrification Fermentation
NO, N2O, N2 N2O, NO, NH3 CH4
Li et al., 1992 (J Geophys Res)

24. UK_DNDC
Developed to run at county-scale
Grazing and manure applications included
UK-specific data bases created
Brown et al., 2002 (Atmos Env)

25. UK_DNDC - validation
N2O fluxes; Rowden 2006 Plot 3
500
450
400
350
300
g N/ha/day
250
200
150
100
50
0
-50 1 31 61 91 121 151 181 211 241 271 301 331 361
UKdndc Observed
J day
Defra project AC0101

26. UK_DNDC - validation
Defra project AC0101

27. Comparison of emission factors
IPCC (2006) 0.01
Measurement (Defra AC0101)
Ammonium nitrate to:
Arable 0.007 – 0.022
Grass 0.005 – 0.039
Modelled UK_DNDC (Defra AC0101)
Fertiliser 0.011 (0.001 – 0.029)
Manure 0.004 (0.000 – 0.015)
Defra project AC0101

28. Summary
Nitrogen models exist at a range of scales and complexities
Modelling approach will depend on importance of the source and
the need to reflect potential changes in management practices
Three main components to be modelled: N excretion, manure
management, soils
Importance of modelling N-flow – impacts on other pathways and
losses
A combination of approaches (complexities), tailored to different
sources and reporting requirements, may be best
Available activity data may limit the temporal and spatial
resolution achievable

29. Defra GHG Research Platform
Data management and modelling: project AC0114 – bringing existing data
together to create a new inventory model and a set of revised emission factors
with an assessment of uncertainty.
Methane (CH4) emissions: project AC0115 – discrimination between CH4
emissions from different livestock species and breeds/genotypes under different
farming systems and representative farm business structures.
Nitrous Oxide (N2O) emissions: project AC0116 – understanding N2O emissions as
a function of nitrogen inputs through time, influence of climate, crop, soil types
and conditions, and land management under different farming systems and
representative farm business structures.
Inventory delivery: project AC0112 – annual reporting and mapping of inventories
of ammonia and GHG from UK agriculture

30. Any questions?