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Eidgenössisches Departement für Wirtschaft,
Bildung und Forschung WBF
Agroscope
www.agroscope.ch I gutes Essen, gesunde Umwelt
Process-based model estimation of N2O Emission
factors for urine patches in a Swiss grazing system Kate Kuntu-Blankson (1,2), Lena Barczyk (1,2), Johan Six (2), Christof Ammann (1), and Pierluigi Calanca (1)
1 Climate and Agriculture group-Agroscope, Reckenholzstrasse 191, 8046 Zürich2 ETH Zürich, Institute of Agricultural Sciences (IAS) – Sustainable Agroecosystems, Tannenstrasse 1, 8092 Zürich
2
Background
Understanding the processes driving grassland N2O emissions is of paramount
importance for developing national GHG emissions inventories
Controls on N2O production processes
Climate (precipitation, temperature)
Soil N and properties affecting O2 availability
Management: timing of grazing
Grazing related N2O emissions
Cattle excreta returned during grazing has ~ 80% of N intake by cattle
Spot covered by a urine patch has high N load (500 to 1000 kg N ha-1)
N load usually in excess of pasture needs
Urine patches become hotspots for N2O emissions
Rates and extends of N2O emissions
depend on the complex interactions
between soil conditions, short-term
weather and management
Unlike mineral fertilizer, excreta return
is heterogeneous in nature creating a
spatial variability in the field
3
Background
Quantifying grazing related N2O emissions: IPCC (2006)
Emission factor (EF) guidelines
Tier 1 method used for GHG inventory in Switzerland
Global default value of 1% is assumed for uniform N
inputs whiles 2% is assumed for grazing related N input
Tier 2 uses country-specific EF inferred from scientific
evaluations
Studies using Tier 2 show country-specific EF much lower
than 2%
Tier 3 involves the use of process-based models to
estimate non-constant EF
Objectives:
Use ecosys (model) to simulate N2O emissions from artificially applied urine patches and investigate the pathways
taken by the high N load.
Examine the effects of seasonal variations in the environmental drivers on N2O EF.
Process-based modeling of N2O emissions
Provide opportunity to improve N2O inventories
However, most grassland N2O emissions
modeling studies refer to one-dimensional, multi-
layered runs that assume a uniform return of
nutrient across the field and do not account for
field heterogeneity
Explicit representation of urine patches
is necessary for accurate estimation of
grazing-related N2O EFTier 1 EF does not take into account spatial
variability of N2O controlling factors,
therefore, Tier 2 and 3 approaches preferred
for EF estimation
4
Method
Ecosys: Canadian Ecosystem Model
A comprehensive process-based mathematical model that simulates C, N and P dynamics.
Runs on an hourly time-step to allow accurate tracking of N2O pathways and makes it easier to identify
environmental interactions that cause surge in emissions
It can integrate spatial scales from mm to km and can run as 1-. 2- or 3-D model allowing for spatial explicit
simulations at the landscape level
Model setup and Experiments
Model already tested wrt N2O emissions from mineral/organic
fertilizers for a grassland site in Switzerland (Grant et al., 2016)
A similar setup is used here
Experiments
Urine is simulated as urea with a fast hydrolysis rate
200g of urea diluted with 20 mm of water is applied to an area of
1 m-2 to mimic cattle urine
Model is run in 1-D (exchange processes only in the vertical)
Urine patch emissions measured in the framework of the REFGRASS
field experiment in Tänikon will serve as benchmarks for testing the
model (see pres. …)
Ecosys allows to explicitly model
spatial heterogeneity of urine patches
Ecosystem-atmosphere exchanges and subsurface transfers of heat,
gases, water, C, N, and P simulated in ecosys. Grant (2001)
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Preliminary Results
N in excess of plant
uptake remains in the
system for ~100 days
Total N2O emissions
from the urine patch over
a 100 day period:
~6 g N m-2 or 3 %
The simulation results presented here show N2O
emissions from
A. fertilizer source with 3 g NH4NO3 m-2 and
B. urine patch with 200 g N m-2
both of which were applied on day 123 (3rd May) of
the year
A
B
Total N2O emissions
from mineral fert:
~0.03 g N m-2 or 1 %.
Peak emission driven by
rainfall event
6
Preliminary Conclusions & Outlook
Conclusions
The dynamics of N2O emissions from urine patches differs from emissions due to mineral N
applications
EF for the simulated urine patch is ~ 3%.
This value is higher than the IPCC default but the latter is valid for the whole field scale
Outlook
Devise an upscaling strategy for infer EF for the field scale from the simulations
Perform 3-D simulations to see the effects of lateral diffusion on N2O emissions
Verify simulated urine patches emissions (and other relevant quantities) against experimental data
Conduct sensitivity analyses to determine model response to varying N input rates
7
THANK YOU !
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