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.