Transcript Controlling Greenhouse Gases and Feeding the Globe Through

The Societal Value of Soil
Carbon Sequestration
Rattan Lal
Director, Carbon Management and Sequestration Center
The Ohio State University, Columbus, Ohio
Global Climate Change
∆T over the 20th century…………. +0.6+0.2°C
Rate of ∆T increase since 1950…… +0.17°C/decade
Sea level rise over 20th century….. +0.1-0.2 m
Change in precipitation………….. +0.5-1%/decade
Extreme events……………………. +2-4%
………..IPCC (2001)
Atmospheric Concentration of Trace Gases
Between 1750 and 1999
Gas
Concentration
Rate of increase
Conc./yr
CO2
CH4
N 2O
CFCs
280 - 367 ppm
700 - 1745 ppb
270 - 314 ppb
0 - 268 ppt
1.5 ppm
7.0 ppb
0.8 ppb
-1.4 ppt
IPCC (2001)
Radiative
forcing
(w/m2)
1.46
0.48
0.15
0.34
Global Carbon Budget
Activity
1980-1989
1989-1998
-----------Pg C/y---------A. Source
Fossil fuel emission
Land use change
5.0 + 0.5
1.7 + 0.8
6.3 + 0.6
1.6 + 0.8
B. Sink
Atmosphere
Ocean
Terrestrial/ missing carbon
3.3 + 0.2
1.9 + 0.6
1.9 + 1.3
3.2 + 0.2
1.7 + 0.5
2.3 + 1.3
IPCC (2001)
How Much C is in Soil?
(i) Soil organic C
= 1550 Pg
Soil inorganic C
= 750 Pg
Total
= 2300 Pg
(ii) Atmosphere
= 720 Pg
(iii) Biota
= 560 Pg
(iv) Ocean
= 38,000 Pg
• SOC pool = 40 - 100 Mg/ha
Soil vs. Atmospheric C
1 Pg (billion tonnes) of soil C = 0.47 ppm
of CO2
Mean Residence Time of C in
Different Pools
The average atom of C spends about:
• 5 yrs in the atmosphere,
• 10 yrs in vegetation (including trees),
• 35 yrs in soil, and
• 100 yrs in the sea.
Residence time = pool / flux
The residence time is longer in soils of high
latitude.
ra
Effects of Soil Erosion and Redistribution on
Trace Gases Emissions.
CO2
CO2
CH4 N2O
Depressed
oxidation of CH4
CH4 N2O
C burial
Erosion
Redistribution
Depression
C burial
DOC
Soil erosion and C emission
Land
Area Emission Reference
(Mha) (Pg C/yr)
World cropland
World soils
1500
13,048
0.32
1.1
Jacinthe & Lal (2001)
Lal (1995)
C
sequestratio
n
1500 x 1015
C in world
soil
5.7 x 1015 g/yr C
displaced due to
erosion
1.14 x 1015 g/yr
decomposition
and emission to
the atmosphere
3.99 x 1015 g/yr stored
within the terrestrial
ecosystem
0.57 x 1015 g/yr
transported to
the ocean
Global soil erosion and dynamics of soil organic carbon
(Lal, 1995).
Historic Soil C Loss
World soils…….. 66-90 Pg
U.S. soils……….. 5 Pg
Recoverable C…. 50-75%
Time horizon……25-50 yrs
The magnitude of soil C loss
30-40 Mg/ha
Agricultural soils now contain lower SOC pool
than their potential, and thus have a C sink
capacity.
Anthropogenic emissions (1850-2000)
1. Fossil fuel:
270 + 30 Pg
2. Land use change: 136 + 55 Pg
Soil:
78 + 12
Soils and Global Warming
Can we use soils and vegetation for
scrubbing a dirty atmosphere?
Carbon Sequestration
It is the net removal of CO2 from
the atmosphere into the long-lived
pools of C such as vegetation and
soil by biotic and abiotic
processes.
A New Definition of Agriculture
It is an anthropogenic manipulation of
carbon through: uptake, fixation,
emission and transfer.
C U + CF = C E + CT
How to Increase Soil C
A. Increase
(i) density of C in the soil
(ii) depth of C in the profile
B. Decrease
(i) decomposition of C
(ii) losses due to erosion
Increasing Density of C in Soil
Plow
Residue removed
Bare fallow
Low input
No water control
Fence to fence cropping
No till
Residue return
Cover crops
Judicious input
(precision farming, IPM)
Water conservation and
supplemental irrigation
Forestation/vegetation on
marginal lands/CRP
Disposition of Organic Residues
CO2
60-80%
Organic residues
100 grams
3-8%
3-8%
Biomass
(soil organisms)
10-30%
Nonhumic
compounds
(polyuronides,
acids, etc.)
Complex
humic
compounds
Humus
10-35%
Mulch Rate and SOC Content in Ohio
No till:
SOC (Mg ha-1) = 15.2 + 0.321 M
R = 0.68
Plow till:
SOC (Mg ha-1) = 11.9 + 0.266 M
R = 0.72
Cover Crop and SOC Pool in a
Miamian Soil in Ohio
Treatment
Continuous corn
Corn-soybean
Continuous soybean
Corn-soybean-wheat
Alfalfa
Birdsfoot trefoil
White clover
Kentucky blue grass
Tall fescue
Smooth bromegrass
Fallow
Lal (1998)
SOC (0-30 cm)
Kg/m3
Relative SOC
(5 yr)
2.30
2.34
2.37
2.36
2.33
2.45
2.36
2.28
2.72
2.75
2.58
100
102
103
103
101
107
103
103
118
120
112
SOC pool in 0-30 cm depth over a 60-year period at
Coshocton, OH (Hao, Lal, Owen, 2002)
Management
Conventional tillage
Conventional tillage-rotation
Chisel tillage (C-S)
No tillage (C-S)
No tillage (C-C)
No tillage (C-C)+manure
SOC pool
Rate
(Mg C/ha) (Kg C/ha/yr)
24.5
29.7
32.1
36.8
39.6
65.5
-87
127
205
252
683
Biofuel vs. Fossil Fuel
1 gallon of biofuel = 0.5 gallon of
oil/diesel saving
Global Cooling Potential
GCP = (GWP)-1
• Conservation tillage
• Cover crops
• Nutrient management
• Soil restoration
• CRP/WRP
• Land use and afforestation
100-1000
Kg C/ha/y
Land Use and Soil C Sequestration in the U.S.
Land use
Area
Net potential
Cropland
Grazing land
Forest land
CRP
WRP
Urban
Total
Mha
156.9
285.9
236.1
13.8
0.6
20.6
713.9
MMTC/yr
75-208
81-91
49-186
9.7-14.6
0.5-0.9
2.2-8.6
154-509 (332)
U.S. Emissions and Soil C Sequestration
• Total U.S. gas emissions……………….1500 MMTC/yr
• Emission from agricultural activities…133 MMTC/yr
• Net soil C sequestration potential……..332 MMTC/yr
Agricultural Soils and
Mitigation of GHE
1 bbl of diesel = 220 L
1 L of diesel = 0.73 Kg C
 1 ton of C = 1370 L of diesel = 6.2 bbl of diesel
C sequestration potential of ag soils = 2 billion
barrels/yr
Potential of Global Soil C Sequestration
1-2 Pg C/yr or
24% of the total emissions by fossil fuel
combustion.
Is Soil C Sequestration A Free Lunch?
• Not really!
• Additional N, P, S etc. are needed for
humification of residue C.
• There are hidden C costs of RMPs.
Building Blocks of Humus
• C is only one of several constituents of
humus.
• Other constituents are H, O, N, P, S and
micronutrients.
Nutrients Needed for Humification
• How much N, P and S are needed to
convert residue into humus?
• How to adjust fertilizer use for desired
productivity and converting residue into
humus?
Elemental Composition of Humus and
Crop Residues
Ratio
Humus
Crop Residue
C:N
C:P
C:S
10-15
40-60
60-80
70-100
200-400
400-800
Additional Nutrients Required to Convert
10,000kg of Carbon into Humus
Nutrient
N
P
S
Quantity needed
(kg)
833
200
143
Energy-based Input and C
Sequestration
1. What is the carbon budget in relation to:
(i) Fertilizer use
(ii) Manure application
(iii) Tillage practices
(iv) Irrigation
(v) Liming of acid soils
2. C sequestration occurs only if output > input.
Hidden C costs of tillage
methods
Method
Kg C/ha/yr
Conventional tillage
Minimum tillage
No tillage
62-72
40-45
20-23
Hidden C cost of fertilizers
Fertilizer type
Nitrogen
P2O5
K2O
Lime
Kg C/kg of fertilizer
0.86
0.17
0.12
0.0.36
Hidden C cost of pesticides
Pesticide
Herbicides
Fungicides
Insecticides
Kg C/kg of pesticide
4.7
5.2
4.9
Hidden C cost of irrigation
Method
Kg C/ha/yr
Pump
Gravity
140-160
0
Farming Carbon
1. Commodification of C (price)
2. Incentives
Societal Value of Carbon
Nutrients and H2O contained in 1 kg of
humus = $0.2
Rational price = $200/ton
Undervaluing a Commodity
Undervaluing carbon has and will
perpetuate its misuse.
Cumulative C sequestration (M/ha)
40
30
20
10
0
0
10
20
30
40
Time after conversion (yrs)
50
Economics of C Sequestration
1. Assessing economics of C by itself is not
adequate.
2. Evaluate the entire package of benefits:
(i) To the farmer
(ii) To the society
Can soil C sequestration mitigate
the greenhouse effect?
Dependency on Carbon
Modern civilization is hooked on carbon. It
needs rehabilitation, in a big way.
Role of soil and biomass C in global C management.
Source: The Global Energy Technology Strategy, Battelle, Washington, D.C., 1998
Soil C Sequestration
• It is a:Development challenge in the tropics
and sub-tropics.
• Policy reform and implementation challenge
in developed countries.
A Bridge to the Future
• C sequestration in soil and vegetation is a
bridge to the future.
• It buys us time while alternatives to fossil
fuel take effect.
• It is a good thing to do, regardless of what
happens to the climate.
It is truly a win-win strategy.