Presented by Steve Frolking at "OECD workshop Peatlands for climate change mitigation in agriculture", Denmark, 4 - 6 Oct 2022

1. Modeling peat CO2 & N2O emission factors for oil palm plantations
Steve Frolking (UNH), Erin Swails (CIFOR), Jia Deng (UNH), Nisa Novita (CIFOR), Kristell Hergoualc’h (CIFOR)
Peatlands for climate change mitigation in agriculture, Aarhus Denmark, 4-5 Oct 2022
Photo:
Nanang
Sujana;
www.cifor.org/knowledge/photo/38802487905

2. Objective: explore potential for process-based modeling to refine IPCC default CO2
and N2O emission factors (EFs) for oil palm grown on drained peat.
Part 1: DNDC model calibration and evaluation at field site in Central Kalimantan, Indonesia.
Part 2: Use DNDC to simulate CO2 & N2O emissions over 30-year oil palm rotation and compare
to IPCC emission factors .

3. Gas fluxes: monthly 9/12 – 6/15 & 9/15
• N2O not focused on fertilization events –
peat decomposition N2O, not fertilizer enhancements.
• CO2 total soil respiration –
heterotrophic respiration estimated from field-based
partitioning ratios.
concurrent 0-5 cm soil temperate and moisture (WFPS) and water table depth.
Site: smallholder oil palm plantations adjacent to Tanjung Puting National Park, Central Kalimantan, Indonesia.
Data
Indonesia
Malaysia
Pangkalan Bun

4. CT plots
FT plots
Field sites (planted in 2007, 2009, 2011) and sampling layout
CT: close to tree
(fertilizer within 2 m)
FT: far from tree
~
1
0
m

5. Part 1: DNDC model calibration and evaluation
Scenarios (all driven by daily weather data collected ~10 km from field site)
• CT plots: oil palms,
fertilization, fruit harvest,
palm litter (not pruning)
• FT plots: no vegetation/roots/litter
no fertilization
Model calibration:
• oil palm growth data (literature and field site)
• WTD, WFPS, soil temperature: three years of field data
• CO2 and N2O gas flux: one year of field data (9/2012 – 8/2013)
Model evaluation:
• CO2 and N2O gas flux: two years of field data (9/2013 – 6/2015, 9/2015)
CT FT

6. New Parameterizations:
• tropical peat soil hydrology
• oil palm biomass, litterfall,
root mortality
The DNDC Model
Changsheng Li
(1941-2015)

7. DNDC
DNDC
DNDC
DNDC
Henson & Dolmat (2003)
Henson & Dolmat (2003)
+
#
*
OP-2011
OP-2009
OP-2007
Lamade et al. 2006
Henson & Chai 1997
Dresscher et al. 2016
Lamade & Setiyo 2002
x Wakhid & Hirano 2021
OP aboveground biomass OP belowground biomass
OP aboveground litterfall OP root mortality
DNDC oil palm (OP) calibrations:
above- and below-ground biomass
and litter production dynamics
over 30-year crop cycle (black
lines), compared to field data (site
and literature) and other models
(lines).

8. soil climate calibration – model & obs.
DNDC CT (with oil palm)
DNDC FT (no vegetation)
Observed CT
Observed FT
Water table depth:
• FT ~ CT, both observed and model.
• Very deep ‘brief’ excursions (obs.) not simulated.
Soil water-filled pore space:
• CT drier than FT, both observed and model.
• High-frequency variability simulated (no data).
Soil temperature:
• Obs. soil T declines with stand age (shading?).
• not simulated in DNDC; warm bias.

9. gas flux calibration – model & obs.
DNDC CT (with oil palm)
DNDC FT (no vegetation)
Observed CT
Observed FT
Total soil respiration (CO2):
• CT (close to palms) > FT
• CT – FT difference: simulated > obs.
• HR fraction: model~80%, field~70%
N2O fluxes (NOTE: scales vary)
• FT (far from or without palms) > CT
• Negligible CT N2O flux (sim. only?)
• Episodic high N2O fluxes (obs. only)
• Low rates of N2O uptake (obs. only)
OP-2007 OP-2009 OP-2011

10. Total soil respiration Heterotrophic respiration Peat decomposition N2O flux
gas flux evaluation – modeled & observed annual fluxes, years 2 and 3
OP-2011
OP-2009
OP-2007
1:1
1:1 1:1
MSE: mean squared error
SB: squared bias (simulation bias)
SDSD: squared diff. between std. dev. (difference in magnitude of fluctuation between simulation and measurement)
LCS: lack of correlation weight by std.dev. (correlation between simulation and observation)

11. Part 2: DNDC simulation of CO2 and N2O plantation emission factors
Scenarios (30 years – driven by daily weather data collected ~10 km from field site)
• daily weather: observed 2007-2020, then random years until 2040.
• CT: oil palms planted and managed, fertilization (75 kg N/ha/y in years 1-3, then 125 kg N).
• FT: no vegetation/roots/litter inputs; no fertilization.
• plantation: area-weighted average of CT to FT areas: 25:75 (OP2011), 27:73 (OP-2009), 37:63 (OP-2007).
Peat onsite CO2 emission factor
• peat heterotrophic respiration minus inputs from aboveground litter and root turnover.
• FT scenario het. respiration minus litter inputs from CT scenario.
• plantation: area-weighted average of CT to FT areas (as above).
N2O emission factors
• peat decomposition N2O: CT scenario without fertilization.
• fertilizer-induced N2O: fertilized CT scenario minus CT scenario without fertilization,
compared to IPCC EF for synthetic fertilizer inputs in wet climates (1.6% of inputs).

12. onsite CO2 flux: IPCC Emission Factor (EF) compared to DNDC simulations
• Rapid decline in simulated peat onsite CO2 EF.
• First decade: DNDC consistent with IPCC CO2 EF.
• Most field data from first decade post-conversion,
median site age 7 years.
• After first decade, DNDC CO2 EF < IPCC CO2 EF;
heterotrophic resp. & litter inputs .
IPCC onsite CO2 EF
DNDC annual CO2 EF
DNDC first decade CO2 EF
DNDC second decade CO2 EF
DNDC third decade CO2 EF
✽ Swails et al. (2021)

13. N2O flux from decomposition:
IPCC Emission Factor (EF) compared to DNDC simulations
IPCC decomp N2O EF
DNDC annual decomp N2O EF
DNDC first decade N2O EF
DNDC second decade N2O EF
DNDC third decade N2O EF
OP-2011, 3 years
OP-2009, 3 years
OP-2007, 3 years
• DNDC N2O EF > IPCC N2O EF.
• Rise in simulated N2O EF after first decade.
• IPCC EF based on single value (no uncertainty).
• site field data implies substantial variability.
• simulation: N2O all from nitrification.
• simulation: no N2O uptake .

14. N2O flux from fertilization:
IPCC Emission Factor (EF) compared to DNDC simulations
IPCC decomp N2O EF
DNDC annual decomp N2O EF
DNDC first decade N2O EF
DNDC second decade N2O EF
DNDC third decade N2O EF
• scenario: fertilizer rate increased after 3 years.
• simulated rise in fertilizer N2O flux rises slowly.
• simulated fertilizer N2O flux < IPCC N2O EFfert.
• simulated fertilizer-induced N2O from both
nitrification & denitrification.

15. Conclusions
• Current IPCC Emission Factors for oil palm on organic soil may
1. over-estimate peat onsite CO2 emissions.
2. under-estimate peat decomposition N2O emissions.
3. be improved by considering temporal variation/trends in emissions of both CO2 and N2O.
• There is need for field data from older plantations.
• Peat decomposition N2O flux greater than fertilizer-induced N2O flux.
(a simulation result, consistent with field data from other sites)
• N2O Emission Factors are very uncertain.

17. Extra slides

18. Fig. 8. Mean annual modeled peat onsite CO2 emissions (EFmodeled CO2 onsite) as a function (dashed grey line) of modeled soil C:N ratio (a) and soil NH4
+ content in the topsoil layer (0–10 cm) (b). Each data point represents the average of the three plots in each year of the 30-year simulation and the vertical and horizontal bar are its asso
standard error (n = 30).
Simulated onsite CO2 flux: correlating variables

19. Fig. 9. Mean annual modeled N2O emissions from peat decomposition (EFmodeled N2O decomp) as a function (dashed grey line) of annual precipitation (a) and modeled mean
annual water table level (b) and soil NH4+ content in the topsoil layer (0–10 cm) (c). Each data point represents the average of the three plots in each year of the 30-year
simulation and the vertical and horizontal bar are its associated standard error (n = 30). Water table levels below the soil surface are indicated by negative values.
Simulated peat decomposition N2O flux: correlating variables

20. Fig. 10. Mean annual modeled fertilizer-induced N2O emissions expressed as a percentage of N inputs (EFmodeled N2O fert) as a function (dashed grey line) of modeled soil C:N
ratio (a) and total mineral N content (NO3− + NH4+) in the topsoil layer (0–10 cm) (b). Each data point represents the average of the three plots in each year of the 30-year
simulation and the vertical and horizontal bar are its associated standard error (n= 30).
Simulated fertilizer-induced N2O flux: correlating variables