the societal value of soil carbon sequestration rattan lal director, carbon management and...
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The Societal Value of Soil Carbon Sequestration
Rattan LalDirector, 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 ConcentrationRate of increase
Conc./yr
Radiativeforcing(w/m2)
CO2
CH4
N2OCFCs
280 - 367 ppm700 - 1745 ppb270 - 314 ppb 0 - 268 ppt
1.5 ppm7.0 ppb0.8 ppb-1.4 ppt
1.460.480.150.34
IPCC (2001)
Global Carbon Budget
Activity 1980-1989 1989-1998
-----------Pg C/y----------
A. Source Fossil fuel emission Land use change
B. Sink Atmosphere Ocean Terrestrial/missing carbon
5.0 + 0.51.7 + 0.8
3.3 + 0.21.9 + 0.61.9 + 1.3
6.3 + 0.61.6 + 0.8
3.2 + 0.21.7 + 0.52.3 + 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
Depressed oxidation of CH4
C burial
Effects of Soil Erosion and Redistribution on Trace Gases Emissions.
CO2 CO2
CH4 N2O
C burialDOC
CH4 N2O
ErosionRedistributionDepression
Soil erosion and C emission
Land Area(Mha)
Emission(Pg C/yr)
Reference
World croplandWorld soils
150013,048
0.321.1
Jacinthe & Lal (2001)Lal (1995)
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
5.7 x 1015 g/yr C displaced due to erosion
1500 x 1015 C in world soil
Csequestration
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.
CU + CF = CE + 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 No till
Residue removed Residue return
Bare fallow Cover crops
Low input Judicious input (precision farming, IPM)
No water control Water conservation and
supplemental irrigation
Fence to fence cropping Forestation/vegetation on
marginal lands/CRP
Disposition of Organic ResiduesCO2
60-80%
3-8% 3-8% 10-30%
Biomass(soil organisms)
Nonhumiccompounds
(polyuronides,acids, etc.)
Complexhumic
compounds
Humus10-35%
Organic residues100 grams
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 SOC (0-30 cm)
Kg/m3
Relative SOC
(5 yr)
Continuous corn
Corn-soybean
Continuous soybean
Corn-soybean-wheat
Alfalfa
Birdsfoot trefoil
White clover
Kentucky blue grass
Tall fescue
Smooth bromegrass
Fallow
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
112Lal (1998)
SOC pool in 0-30 cm depth over a 60-year period at Coshocton, OH (Hao, Lal, Owen, 2002)
Management SOC pool(Mg C/ha)
Rate(Kg C/ha/yr)
Conventional tillageConventional tillage-rotationChisel tillage (C-S)No tillage (C-S)No tillage (C-C)No tillage (C-C)+manure
24.529.732.136.839.665.5
--87
127205252683
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
100-1000Kg C/ha/y
Land Use and Soil C Sequestration in the U.S.
Land use Area Net potential
Mha MMTC/yr
CroplandGrazing landForest landCRPWRPUrbanTotal
156.9285.9236.113.80.620.6713.9
75-20881-9149-1869.7-14.60.5-0.92.2-8.6154-509 (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 Quantity needed (kg)
N
P
S
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 tillageMinimum tillageNo tillage
62-7240-4520-23
Hidden C cost of fertilizers
Fertilizer type Kg C/kg of fertilizer
NitrogenP2O5
K2OLime
0.860.170.12
0.0.36
Hidden C cost of pesticides
Pesticide Kg C/kg of pesticide
HerbicidesFungicidesInsecticides
4.75.24.9
Hidden C cost of irrigation
Method Kg C/ha/yr
PumpGravity
140-1600
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.
0 10 20 30 40 500
40
30
10
20
Time after conversion (yrs)
Cu
mu
lati
ve C
seq
ues
trat
ion
(M
/ha)
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.