Sequestration Rates, Duration, Capacity, and Saturation: Determining Factors for Current and Future Soil Carbon Stocks

A Joint CASMGS-CSITE Session onSoil Carbon Sequestration:

Science, Technology, and Economics

Third Annual Conference on Carbon Capture & SequestrationArlington, Virginia

May 3-6, 2004

Tris WestEnvironmental Sciences DivisionOak Ridge National Laboratory

Johan SixUniversity of California-Davis &

Colorado State University

I. Introduction to terms• Soil carbon capacity is the amount of carbon held by the

soil in a steady state under a specific management scenario.

• ∆ Soil C capacity =Mean sequestration rate x Sequestration duration

• Duration is:(a) the time period in which rates of soil carbon

accumulation or loss occur until a new steady state is reached (i.e., duration of active sequestration); and

(b) the time period in which soil carbon remains sequestered (i.e., duration of previously sequestered carbon).

• Soil carbon capacity may be (i) increasing or decreasing, (ii) remaining at steady state, or (iii) may have reached saturation.

• Soil carbon reaches a new steady state some time following the adoption of a new practice; it does notnecessarily reach saturation following adoption of a new practice.

• Soil carbon saturation occurs when soil can no longer accumulate carbon.

I. Introduction to terms

Time

Soil Ccontent

Soil C steady state vs. C inputs vs. time

Inputs > respiration

Inputs ≈ respiration

New steady state

Saturation

Increased inputs result in additional soil C

Increased inputs do NOT result in additional soil C

Revised from Johan Six, CASGMS Forum presentation (2004)

Rates, duration, capacity, and saturation of stored carbon depend on carbon cycle dynamics and carbon sequestration strategies.

SoilCarbon

inputs

outputs

• Fertilize• Irrigate• Weed control• Increase rotation

complexity• Manure application

Increase organicmatter inputs

• Decrease tillage• Increase aggregate

formation (earthworm introduction)

• Increase surface residue / cover crop

Decrease decomposition

and erosion

Temperature; Precipitation;Soil physical and chemical

properties

II. Sequestration rates – brief overview

13 ± 3%

15 ± 3%

10%

CT NT

7 ± 2%U.S.Ogle et al. (2003)

6 ± 2%GlobalWest & Post (2002)

10%Global (temperate)IPCC (1997)

Enhanced residue productionCoverage

Comparison of soil C sequestration rates between IPCC guidelines and two other analyses

IPCC. 1997. Greenhouse Gas Inventory Reference Manual, v. 3.West and Post. 2002. Soil Science Society of America Journal 66:1930-1946.Ogle et al. 2003. Global Change Biology 9:1521-1542.

III. Duration of active soil carbon sequestration

0

50

100

150

200

0 25 50 75 100 125 150Experiment duration (years)

Ann

ual c

hang

e in

SO

C(g

m-2

yr-1

)

Reforestation

05

101520253035

0 25 50 75 100 125 150Experiment duration (years)

Ann

ual c

hang

e in

SO

C (%

) Grassland management

012345678

0 25 50 75 100 125 150Experiment duration (years)

Cropland management

Ann

ual c

hang

e in

SO

C (%

)

Data from West and Post (2002) Data from Conant et al. (2001)

Data from Post and Kwon (2000)

Determining factors represented in Carbon Management Response (CMR) curves

West et al. 2003. Environmental Management (in press).

Ave

rage

cum

mul

ativ

eC

flu

x fro

m s

oil f

ollo

win

g a

chan

ge fr

om C

T to

NT

(%)

-20

-16

-12

-8

-4

0

0 5 10 15 20 25 30Time (years)

Mean95% C.I.

Ave

rage

ann

ual C

flux

from

so

il fo

llow

ing

a ch

ange

fro

m C

T to

NT

(% y

r-1)

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

Capacity (sum of initial C stock and the cumulative % change in initial C stock)

Accumulation rate as a function of time

Duration of active carbon accumulation

III. Duration of active soil carbon sequestration

-14-12-10

-8-6-4-20

0 10 20 30 40 50 60 70Years

Ave

rage

cum

ulat

ive

C

accu

mul

atio

n w

ith ro

tatio

n en

hanc

emen

t (%

)

Cropland management

Estimates of cropland improvement derived from West and Post (2002).

Duration of sequestration rates may be longer for changes in inputs (increased residue production) than for changes in outputs (decreased respiration/decomposition).

-16-14-12-10

-8-6-4-20

0 10 20 30 40 50 60 70Years

Mean95% C.I.

Ave

rage

cum

ulat

ive

C

accu

mul

atio

n fo

llow

ing

a ch

ange

from

CT

to N

T (%

)

III. Duration of active soil carbon sequestrationDuration and climate regime

01020304050607080

WarmTemperate

Moist

WarmTemperate

Dry

ColdTemperate

Moist

ColdTemperate

Dry

TropicalDry

Tropicalmoist/wet

All climates

Climate regime

Act

ive

sequ

estr

atio

n du

ratio

n (y

ears

) Cropland management Grassland management

III. Duration of active soil carbon sequestrationDuration and climate regime

020406080

100120140160

WarmTemperate

Moist

WarmTemperate

Dry

ColdTemperate

Moist

ColdTemperate

Dry

TropicalDry

Tropicalmoist/wet

All climates

Climate regime

Act

ive

sequ

estr

atio

n du

ratio

n (y

ears

)

Cropland management Grassland managementForest conversion

Hypothetical scenario consists of (a) deforestation and cultivation of soil using conventional tillage, (b) changing from conventional tillage to no-till, (c) use of conventional tillage for one year, (d) returning to the use of no-till, and (e) abandoning the land and allowing forest conditions to re-establish. From West et al. (2003).

IV. Duration of previously sequestered carbonTerrestrial carbon is expected to remain sequestered until thereis a subsequent change in management.

05

101520253035

0 20 40 60 80 100Time (years)

Deforestation/CTChange to no tillageReforestation

a

b

c

d

e

Cum

ulat

ive

net C

flux

to

the

atm

osph

ere

for a

hy

poth

etic

al s

cena

rio

(% o

f ini

tial s

oil C

)

IV. Duration of previously sequestered soil carbonDuration and capacity of soil carbon also depend on changes in climate and annual variation in weather (i.e., mean annual temperature, precipitation, and percent radiation). Shown below are possible effects of a climate anomaly on soil carbon in the early 1990’s.

Sas05

0500

100015002000250030003500

1984 1986 1988 1990 1992 1994 1996Time (years)

soil c

arbo

n(g

m-2

per

15c

m d

epth

)CT cont w heatNT cont w heat

Sas04

17501800185019001950200020502100

1984 1986 1988 1990 1992 1994 1996

Time (years)

Soil c

arbo

n(g

m-2

per

15c

m d

epth

)

CT cont. w heatNT cont. w heat

Alb02b

4000

4500

5000

5500

6000

6500

7000

1950 1960 1970 1980 1990 2000Time (years)

Soi

l car

bon

(g m

-2 p

er 3

0cm

dep

th)

wheat-fallow 0

w-w-fallow fallow with manure

Edi01 barley

0

3000

6000

9000

12000

15000

18000

1970 1975 1980 1985 1990 1995Time (years)

soil c

arbo

n(g

m-2

per

30c

m d

epth

)

CTNT

IL01 corn-soy

2000

3000

4000

5000

6000

1988 1990 1992 1994 1996 1998Time (years)

Soi

l car

bon

(g m

-2 p

er 3

0cm

de

pth)

CTNT

Paustian et al.(1997)

Increase in inputs ~ increase in soil C

V. Soil carbon saturation

Evidence of C saturation in high C soils

V. Soil carbon saturation

Campbell et al. (1991)

Soil carbon may be increased over that in native soils.

Continuous corn under conventional (CT) and no-tillage (NT) management. Results averaged across fertilization treatment rates of 0, 84, 168, and 336 kg N ha-1. From Ismail et al. (1994).

Bluegrass sod CT NT-------Mg C ha-1 (0-30 cm)-------

1970 53.4 53.4 53.41975 53.4 43.3 48.71980 53.4 42.9 48.81989 54.9 55.7 59.9

V. Soil carbon saturation

VI. Duration and saturation in soil C models: Rothamsted Carbon Model

0

50

100

150

200

250

300

0 25 50 75 100 125 150 175 200Years

Tota

l C

(Mg/

ha p

er 2

3cm

dep

th)

140 t/ha manure, 23% clay, wheat/fallow, high DPM/RPM ratio

0102030405060708090

0 25 50 75 100 125 150 175 200Years

Tota

l C(M

g/ha

per

23c

m d

epth

)

No fertilizer or manure, 23% clay, wheat/fallow, high DPM/RPM ratio

0102030405060708090

0 25 50 75 100 125 150 175 200Years

Tota

l C(M

g/ha

per

23c

m d

epth

) No fertilizer or manure, 46% clay, continuous wheat, low DPM/RPM ratio

Decrease in decomp.~20 g m-2 yr-1 for 20yr

0

20

40

60

80

100

0 25 50 75 100 125 150 175 200Years

Tota

l C(M

g/ha

per

23c

m d

epth

)

35 t/ha manure, 23% clay, wheat/fallow, high DPM/RPM ratio

Increase in inputs:~25 g m-2 yr-1 for 200 yr

VII. Summary

• Sequestration potential depends on both the rate of sequestration and the duration of sequestration rates.

• The new carbon capacity represents a new steady state of soil carbon, and not necessarily soil carbon saturation.

• The “ultimate” carbon capacity, based on estimates of soil carbon saturation, may be significantly larger than traditional estimates of sequestration potential and larger than the “natural” capacity.

• Current soil carbon sequestration potentials may be underestimated without fully considering issues of “duration” and “saturation”.

Acknowledgments

Consortium for Research on EnhancingCarbon Sequestration in Terrestrial Ecosystems

OAK RIDGE NATIONAL LABORATORYU.S. DEPARTMENT OF ENERGY