Effect of global warming on soil organic carbon
Dina Khadijaand
Dr. P. K. ManiDepartment of Agril. Chemsitry and Soil Science
Bidhan Chandra Krishi Viswavidyalaya West Bengal, India
GLOBAL WARMING• According to IPCC (2001) the average temperature of Earth is
projected to increase by 1.5-5.8°C during the 21st century
• Climate change is related to Green House Gas(GHG) causing Global Warming
Different sectors contributing to GHGs emission (percent)Water
vapourCarbon dioxide Methane Nitrous oxide Ozone HFCs PFCs SF6
36-76% 9-26% 4-9% 5% 3-7% 2.2% 2.2% 2.2%
[HFC= hydro fluro carbon; PFC= poly fluro carbon; SF6= sulfur hexa fluride]
(Source : Kyoto Protocol)
Change in global average temperature 1850-2005 shown as a change(°C)relative to the 1961-1990 long- term
average (from IPCC WGI,2007)
Temperature is projected to increase by 1.5 to 5.8 oC by 2100
FUTURE TEMPERATURE PROJECTION
CARBON DIOXIDE METHANE
NITROUS OXIDE
Green House Gases on the rise
Soil Organic CarbonAll availed amenities by industrialized societies are based on fossil fuel derived energy. Thus, the modern civilization can be appropriately termed “the Carbon Civilization” or the C-Era (Rattan Lal,2007),
The modern civilization is dependent on C-based energy sources. It is literally hooked on carbon, and in need of a big-time rehabilitation.
World soil constitute 3rd largest global C poolPool Amount(Pg )
Ocean 38,100Soil (1 m depth)SOC(soil organic carbon)SIC(soil inorganic carbon)
1550950
Vegetation 610Atmosphere 760Fossil fuels 4130
% of global C pool (Source: Hillel, 2011)
Major C sink. (Source: Lal, 2008)
Soil organic carbon forms part of the natural carbon cycle
Additional human inputs
Active – easily oxidizable and fuels soil food web
Passive – longer residence time and contributes to SOC build up
Carbon pool
Why is carbon important ?
Major building block for life of all organisms in Earth.
Basic input for crop production, important from agricultural point of view.
Some beneficial role of SOC in soil: Physical effect
Chemical effect
Biological effect
C
Carbon is a “keystone”
N PK Ca
Mg S
Zn Mn
Cl Bo
Building of agriculture
H2O N
Carbon is the “Lord of the Rings”
KP Ca Mg
Bo
Cu
S Cl Zn
Mn
Mo Fe Na
C
Nutrient cycling requires carbon!
Soil Organic C Dynamics
Time
Rel
ativ
e C
con
tent
(g C
m-2)
P > D P > DP < D
P = net primary production D = decomposition
(Janzen et al., 1998)
loss
sequestration
Originalaccumulation
Conversion tocultivated agriculture
Adoption ofconservation
practices
prairie agroecosystem
Managing soil organic matter as the key to soil, air, and water quality.
(Source:Lal,2007)
Losses of Carbon from the Soil
A. Oxidation of C (as Carbon-di-oxide)
B. Agricultural practices causing reduction of SOC in
soils
Removal of C from fields
Why is the response of soil carbon to global warming important ?
The size of the pool of SOC is large compared to gross and net
annual fluxes of carbon to and from the terrestrial biosphere.
Small changes in the SOC pool could have dramatic impacts on
the concentration of CO2 in the atmosphere.
Increased release of terrestrial C under warming would lead to a
positive feedback,resulting in increased global warming.
Factors affecting the response of SOC to global warming
1. The balance of carbon inputs to , and outputs from , the soil
2. Increasing decomposition rate under global warming
3. Global and regional trends in changes in NPP and SOC loss
4. Overall impact – transient versus equilibrium effects
1.The balance of inputs to & outputs from the soil
The level of SOC in a particular soil is determined by many
factors including climatic factors (e.g., temperature and moisture
regimes) and edaphic factors (e.g., soil parent material, clay
content, cation exchange capacity; Dawson and Smith, 2007).
The rate of carbon input to the soil is also related to the
productivity of the vegetation growing on that soil , measured by
NPP. NPP varies with climate, land cover, species composition,
and soil type (Falge et al.,2002).
2. Increasing decomposition rate under global warming
Increased temperatures accelerate rates of microbial
decomposition
Increase CO2 emission by soil respiration
Results a positive feedback to global warming.
Assumed temperature dependencies of SOC decomposition
(Parton et al. 1987)
Temperature sensitivity of SOC pools
Some studies suggest that recalcitrant C is not sensitive to
temperature variation (Giardina and Ryan, 2000).
Recalcitrant and labile pools have a similar temperature
sensitivity (Fang et al., 2005).
The temperature dependence of SOC decomposition is the
result of a number of processes that effectively contributes to
the rate of mineralization (Agren and Wetterstedt, 2007).
Schematic diagram of temperature sensitivities derived from various methods and their affecting factors.
(Source : Smith et al.,2007)
Sensitive/vulnerable regions and soils
High latitude regions are thought to be particularly vulnerable
High latitudes are projected to experience some of the greatest
warming (Mitchell et al ., 2004).
This is particularly true of permafrost soils in the taiga and
tundra that hold around 500 Pg C, and could lose this carbon
rapidly under warming ( Zimov et al ., 2006).
MEASURING SOIL RESPONSES TO GLOBAL WARMING
A.Soil respiration measurement in the laboratory
B.Soil respiration measurement in the field
1.Static absorption 2.Dynamic (or steady-state)chambers
3.Enrichment(or non-steady-state)methods
Dynamic (or steady-state) chambers
Sr =∆c (f/A)
Where Sr is the efflux of CO2 from the soil, ∆c is the
difference in CO2 mass fraction in the incoming and
outgoing air streams, f is the gas flow rate through
the chamber, and A is the surface area covered by the
chamber (Nakayama, 1990).
Enrichment (or non-steady-state) methods
The soil efflux(Sr) can be measured by:
Sr=(∆c/∆t)(V/A)
where ∆c is the CO2 concentration increment in the chamber in the time interval ∆t, V is the volume of air within the chamber, and A is the soil surface area covered by the chamber.
Holding carbon in the soil!
Sequestering carbon
Creating negative carbon
emission
Mulching Cover cropping
Soil amendment
s*Biochar*Manure
Creating positive nutrient budget
Biofertilizer
Chemical fertilizer
Strategies of soil carbon sequestration(Lal,2004)
ConclusionCarbon content in soil is about twice as large as that of in the
atmosphere and about three times that in the vegetation.
Global warming causes large amounts of carbon in terrestrial
soils to be lost to atmosphere , making them a greater carbon
source than sink.
Strategies of soil carbon sequestration will help to mitigate
climate change itself.
Soil is meant to be covered.
Manage soil carbon - make the world a better place.
Soil is meant to be covered.
Manage soil carbon - make the world a better place. Thank you for your attention
We need stronger footprints on / for soils!