Carbon Budget of Mature No-till Corn/Soybean Ecosystem in the

North Central Region of the United States

Carl J. Bernacchi

Steven E. HollingerIllinois State Water Survey, Champaign, IL

Tilden P. MeyersNOAA Atmospheric Turbulence Diffusion Division, Oak Ridge,

Tennessee

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Why Corn and Soybean?

Agricultural Land and C-sequestration

• Soils of native prairie were high in Soil Organic Carbon (SOC)

• Only ~40% of SOC still remains

• Can we increase SOC in the soils of Midwestern agriculture?

Donigian, et al. (1994), U.S.EPA, Athens, GA

Lal, R., 2004, Science, 304, 1623-1627

Rising Atmospheric CO2

• Controlling atmospheric CO2 is the focus of domestic and international efforts– Improvements in energy

• More efficient technology

• Improved fuels

– Kyoto protocol• Sequester C

• Sell C-credits

Focus on No-till

• No-till farming has many benefits– Lower costs– Minimize erosion– Better soil moisture– More pest predators, earth worms– Higher SOC (?)

Measuring SOC

• Soil measurements and models are traditionally used, but:– Soil measurements are prone to uncertainties

over time and space– Models require validation

• Augment the wealth of soil measurements / models with a different technique

Using Eddy Covariance to Estimate C Sequestration

• Eddy Covariance is a method in which fluxes of CO2, water, and energy can be measured directly

• Measurements represent a large area

• Measurements are made continuously throughout the year

CO2 fluxes to measure NEE

• Net Ecosystem Exchange = net total amount of C transferred between the atmosphere and an ecosystem over a given period of time

• Pn = Net photosynthesis

• Ra = Autotrophic Respiration

• Rh = Heterotrophic Respiration

n a hNEE P R R

Bondville Ameriflux Tower

Experimental Method

• 6 years of continuous eddy covariance measurements

• Corn/soybean rotation agro-ecosystem– 3 years of corn data– 3 years of soybean data– 3 complete rotation cycles

• Data collected and back-filled (modeled) as needed

Carbon Sequestration Potential

• If the amount of CO2 ENTERING the ecosystem is greater than the amount of CO2 LEAVING the system, then carbon is being sequestered

NEE over Six Years

1997 1998 1999 2000 2001 2002 2003Y ear

-30.0

-20.0

-10.0

0.0

10.0

NE

E (

mo

l C m

-2 d

-1)

C orn Soybean C orn Soybean C orn Soybean

Local C Fluxes

1997 1998 1999 2000 2001 2002 2003Y ear

-20.0

-15.0

-10.0

-5 .0

0.0

5.0

Cu

mm

ula

tive

NE

E (

me

tric

ton

s/h

a)

Large C-Sink, however…

• A large amount of C is removed from the field (yield)

• 100% of grain C is consumed annually

• Does yield explain all of this sink?

How much C is removed from the no-tilled field?

1997 1998 1999 2000 2001 2002 2003Y ear

-20.0

-15.0

-10.0

-5 .0

0.0

5.0

Cu

mm

ula

tive

NE

E (

me

tric

ton

s/h

a)

Regional C sink assessment• An Intensive Campaign (NACP) has been

proposed to do the most comprehensive C budget ever for a certain region of the U.S.

• Midwest defined as an ideal location– Relatively few urban areas– Single ecosystem type dominates

• A Regional Intensive Campaign requires as much information as possible for each ecosystem type

Regional C Budget

• Here in the Midwest, a large amount of C is fixed into grain

• The grain is removed from the field

• 100% of grain harvest is utilized

• Only ~20% of the total grain consumption occurs in the Midwest

Assessing the Regional C Budget

• Have– Three years of NEE

data for corn, soybean

– Precise yield data for these years on the exact field

– Yield data for each state in the U.S.

– Grain consumption statistics

• Need– NEE data for all states

• Assumptions– Our field is

representative of all fields

Ecosystem Harvest Index (EHI)

• Grain carbon (Cgr) was measured via combine yield monitors

• Growing season NEE (NEEg) was measured using eddy covariance

• EHI was then used as a proxy for NEE over the whole Midwest

gr

g

CEHI

NEE

grg

CNEE

EHI

Midwestern Carbon Fluxes (MMT)

C Fluxes (MMT) Maize Soybean Total

Growing season -154.7 -59.3 -214

Fallow season 49.5 65.0 114.5

Midwest Consumption 13.9 4.3 18.2

Net Midwest -91.3 10.0 -81.3

Regional C sink assessment

1997 1998 1999 2000 2001 2002 2003Y ear

-20.0

-15.0

-10.0

-5 .0

0.0

5.0

Cu

mm

ula

tive

NE

E (

me

tric

ton

s/h

a)

Conclusions

• Locally, Midwestern corn/soybean ecosystem represents a large C-sink to the atmosphere

• Globally, most of the C-sink is found in grain– Accounting for all Grain C, ecosystem is still a

sink (C sequestration potential exists)

Conclusions (cont’)

• Regionally, a huge C sink exists– Most C stored in grain is consumed out of the

region

– Over 81 MMT of C is fixed in this region

Acknowledgements• Office of Science (BER), U.S. Department

of Energy, Grant No DE-FG02-03ER63685

• National Oceanic and Atmospheric Association (NOAA)

• John Reifsteck

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