Considerations for GHG quantification and
assessment of mitigation practices on saltaffected soils
Keith Paustian
Dept. of Soil and Crop Science
Colorado State University
Colombo, Sri Lanka 2014
What do you need for effective inventory and assessment?
1.
2.
What are the GHG sources and sinks that matter?
Understanding of the processes involved
a.
b.
3.
Generalize your understanding in the form of a model
a.
b.
4.
What are the controlling factors, how do they interact,
what are the main sources of variability?
Both theoretical and empirical (i.e., field studies) knowledge
Empirical or process-based, existing or new
Validate your model for the circumstances of interest
Apply the model for the area/circumstances of
interest
a.
Need the data on the controlling factors (i.e., climate, soil
condition, management practices
GHG Sources and Sinks




Soil C stock change (integrated net CO2 flux)
Biomass C stock change ( “ “ “ )
Nitrous oxide emissions
Methane emissions (net to the atmosphere)
Methane production
 Methane oxidation

Soil C flux processes
CO2
Photosynthesis
& respiration
CO2
Manure
Harvest
CO2
Litterfall
Decomposition
& respiration
Soil deposition
Soil erosion
Humification
DOC & DIC
Controls on soil C stocks

C inputs from plant residues and organic amendments

f (NPP, dry matter partitioning)




f (species, light, temperature, water, nutrients, pest/diseases, salinity,
etc.
f (how much is left on the field)
f (how much is brought in from the outside – e.g., compost,
biochar)
C losses through decomposition

f (microbial activity)


f (litter quality, temperature, moisture, nutrients, salinity, etc)
f (physio-chemical stabilization processes in soils)

f (soil texture, mineralogy, soil structure, disturbance
(tillage)
Measuring net CO2 emissions/removals from soils
Micromet approaches
– Eddy Covariance
Soil C stock change method
• Repeated measures over time
• Chronosequences (‘space for time
substitution’)
Mitigation practices for soil C
sequestration
Depleting Soil Organic Matter
Erosion
Intensive tillage
CO2
Residue removal
Soil organic
matter
Low Productivity
Rebuilding Soil Organic Matter
Conservation tillage
Conservation buffers
CO2
Cover crops
Soil organic
matter
Set-aside
Improved rotations
Soil C – managing the ‘Input’ side (I)
and the ‘Output’ side (R)










High residue yielding crops (I)
Growing perennial grasses and legumes (I, R)
No-tillage and other conservation tillage (R)
Cover crops (I, R)
Manure additions (I)
Reduced frequency of bare fallow (I, R)
Other practices that increase C added to soils (e.g.,
irrigation, improved fertility) (I)
Rewetting (flooding) of organic (i.e., peat) soils (R)
Tree planting on annual cropland (I, R)
Restoration of highly degraded soils (I)
Microbial-mediated transformations of inorganic N
Anaerobic process
Aerobic process
Key Points
• Chamber design and materials
• Deployment time, #gas samples
• Time of day
• Sampling frequency, # of chambers
• Minimum detectable flux
• Temporal integration of fluxes
• ….and more
Flow diagram for DAYCENT.
‘Leaky pipe’ model
N2O, NOx
NO3-
Org. N
NH4+
Davidson & Firestone
IPCC default model (2006)
Direct N2O emissions = 1.0% * N added to soil
N added to soil from:
•N fertilizer
•N fixation (legumes)
•Manure/sludge
•Crop residues
Empirical model based on strip-trials at 6 Michigan farms over 3
years
Millar et al. 2010
N2O Mitigation principles
 Maximize
plant use of added N!
Improved timing and
application rates
Reducing N2O
Improved placement
N2O
+
Water and fertilizer mgmt
NH4
SOM
N
NO3
Plant
N
Nitrification inhibitors/
slow release fertilizer
N2O Mitigation principles
 Maximize
plant use of added N!
 IPNI’s four ‘rights’
 Right
amount
 Right timing
 Right placement
 Right product
Robertson and Vitousek 2009
CAST 2004
Soil CH4 flux processes
CAST 2004
Mitigating rice CH4 emissions

Water management


Provide intermittent drainage
Organic matter additions
Incorporate fresh residues well in advance of
flooding
 Compost residues before applying



Use cultivars with reduced CH4 transport
Nutrient mgmt – e.g. sulfate containing fertilizer,
calcium carbide additions