1. Using DayCent for estimating
greenhouse gas emissions
Tamara Hochstrasser
University College Dublin
with help from:
Steve del Grosso, Colorado State
University, Catherine Watson, AFBI,
Christoph Mueller, Florence Renou-
Wilson

2. Outline
 UCD-soils group
 DayCent: some simulations of Irish
grasslands
 Using DayCent for the whole of Ireland

3. UCD-soils group (Christoph Müller)
 Forests: Thomas Cummins
 Grasslands: Tamara Hochstrasser
 Peatlands: Florence Renou-Wilson,
David Wilson
 Ibrahim Khalil
Main aim: to develop a mechanistic
understanding of organic matter
dynamics and greenhouse gas emissions
from Irish soils

4. Techniques
 Field gas measurements using closed
chambers
 Stable isotope tracing techniques
 Modelling: statistical techniques, small
process-specific mechanistic models, for
grasslands: ecosystem model (DayCent)

5. Grassland DayCent modelling
 Aim: to provide greenhouse gas balance
for agricultural grasslands under different
management regimes in Ireland
 Two step approach:
1) Parameterisation of DayCent based on
long-term (1989-99) dataset from
experiment in Northern Ireland (Watson et
al. 2007)
2) (planned) Extrapolation to different soil
types and management regimes under a
range of climates

6. Parameterisation for Irish grasslands
Daily weather data
Fertilizer
Longitude and latitude
Grazing / cutting
Grass/
Crop
Management Growth rate
Atmosphere
C:N ratio
Lignin content
Root:shoot ratio
(Whitehead, 1995)
Soil texture
Field capacity
Bulk density
Soil
pH
Flux of carbon/
nitrogen
Control

7. Net Ecosystem Exchange
NEE component Units High N loam High N clay Low N loam Low N clay
Harvested C gC/m2 293 (37) 331 (24) 212 (19) 232 (10)
N2O g N2O/m2 0.45 (0.04) 0.77 (0.11) 0.18 (0.02) 0.27 (0.04)
N2O eq g CO2/m2 133.5 (10.5) 230.6 (32.5) 52.7 (4.6) 81.9 (13.0)
CH4 g CH4/m2 -0.21 (0.02) -0.12 (0.01) -0.21 (0.02) -0.12 (0.01)
CH4eq g CO2/m2 -5.2 (0.4) -3.0 (0.2) -5.2 (0.4) -3.1 (0.2)
CO2 g CO2/m2 380.9 (31.6) 444.9 (29.6) 329.2 (22.9) 373.1 (20.1)
NEE tC/ha -1.5 -1.5 -1.1 -1.1
Hochstrasser et al. unpublished manuscript

8. Yield
16 16
14 14
12 12
Yield (t/ha)
Biomass Biomass
10 10
measured measured
8 8
6 6
4 4 Simulated Simulated
biomass biomass
2 2
0 0
88 89 90 91 92 93 94 95 96 97 98 99 88 89 90 91 92 93 94 95 96 97 98 99
Time (Years) Time (Years)
100 kg N/ha/yr 500 kg N/ha/yr

9. Volumetric soil water content
1992
0.7
0.6
0.5
0.4
Simulated
VSWC
Actual
0.3
0.2
0.1
0
0 50 100 150 200 250 300 350 400
Time (days)
Data from Hillsborough, NI

10. Soil Carbon
8000
7000
somtc
6000
Total C (with roots)
5000
g/m2
rootC
4000
measured C
3000
2000
1000
0
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
year
100 kg N/ha/yr

11. Peatland
Raised bog: Allen series, Co. Offaly. Picture by: Bob Hammond

12. What about peatlands?
1) Soil moisture is usually evenly distributed
which is not the case in peat soils
2) Soil temperature vary differently to
mineral soils, especially in the winter time
3) Gas-diffusion processes are different in
the peat matrix
4) Processes of anaerobic biogeochemistry
are also different to mineral soils
5) Low pH
Slide by: Florence Renou-Wilson

13. Preliminary conclusions
 DayCent is capturing the main processes
in grasslands on mineral soils, but not
peatlands
 Further improvement of model
parameterisation may allow for a more
realistic simulation of soils high in organic
matter
 Long-term data are essential to develop
an understanding of complex system
dynamics

14. Extrapolation to Ireland?
 Will need:
- climate (daily weather for 30+ years)
- soil information
- ‘typical’ management
 All existing combinations will have to be
run separately and then a weighted (by
area) average of the output values
calculated
 Expensive, but has potential to show
where large difference can be made

15. Conclusions
 An ecosystem model such as DayCent can be
used to interpret data and enhance our
understanding of soil organic matter
dynamics
 If application for the whole of Ireland is
envisaged, it is very important to change and
develop the model so it is able to simulate
organic soils
 In the longer term, if DayCent is used for
greenhouse gas inventories, it is important to
have the capacity to adapt the model as new
insights are gained