Carbon Sequestration: Magnitude, Measurement, and Potential to Mitigate Climate ChangeKen Cassman, Director, Nebraska Center for Energy Sciences ResearchShashi Verma, School of Natural Resources

The Greenhouse Effect

Solar radiation may be reflected (2/3) or absorbed (1/3)

Absorbed radiation heats the earth

Infrared radiation is emitted from the earths surface

Greenhouse Gases:Water vaporCarbon dioxideMethaneNitrous oxideOzoneChlorofluorocarbonsFluoronated hydrocarbons

Source: EPA, 2000

Slide courtesy of T.S. Murrell, PPI

http://www.epa.gov/methanetomarkets/docs/methanemarkets-factsheet.pdf

0 200 400 600 800Potential Annual Carbon Sequestration (Tg) in USA Crop, Forest, and range lands. Adapted from Metting FB, Smith JL, Amthor JS. 1998.

UNL Carbon Sequestration Program: GoalsQuantify the annual amounts of carbon (C) sequestered in major rainfed and irrigated agroecosystems in the north-central USA.Improve our basic understanding of the biophysical processes that govern C exchange in these ecosystems.

University of Nebraska Ecological Intensification ProjectWhat is the potential for maximizing yield, carbon sequestration, greenhouse gas mitigation, and nutrient use efficiency concomitantly with progressive management that achieves high yields and high input efficiencies?N fertigation and precise N and water management, Bt hybrids, Round-up Ready soybeans, higher plant densities, no tillage

Annually Integrated NEE(g C m-2 y-1)

Maize, NE300 to 500 (Verma et al., 2005)Harvard Forest, MA200 (Barford et al., 2003)Howland Forest, ME174 (Hollinger et al., 2004)Univ. of Michigan Biological St80 to 170 (Schmid et al., 2003)Wind River, WA-50 to 200 (Pers. Comm.)Douglas Fir, B.C.270 to 420 (Morgenstern et al., 2004)Tallgrass Prairie, OK50 to 275 (Suyker et al., 2003)Northern Temperate Grassland, Alberta-18 to 20 (Flanagan et al., 2002)Mediterranean, Annual Grassland, CA-30 to 130 (Xu and Baldocchi, 2003)Soybean, NE-10 to -75 (Verma et al., 2005)

Co-Principal Investigators

Shashi B. Verma. . . . . . . . . . . . . . School of Natural Resources Kenneth G. Cassman. . . . . . . . . . .Agronomy and Horticulture

Co-Investigators

Timothy J. Arkebauer. . . . . . . . . . .Agronomy and HorticultureAchim Dobermann. . . . . . . . . . . . .Agronomy and Horticulture Anatoly A. Gitelson . . . . . . . . . . .School of Natural ResourcesKenneth G. Hubbard . . . . . . . . . . School of Natural ResourcesJohannes M. Knops. . . . . . . . . . .School or Biological SciencesGary D. Lynne. . . . . . . . . . . . . . . Agricultural EconomicsMadhavan Soundararajan. . . . . . .BiochemistryAndrew E. Suyker . . . . . . . . . . . . . School of Natural ResourcesElizabeth A. Walter-Shea . . . . . . . School of Natural ResourcesDaniel T. Walters . . . . . . . . . . . . . Agronomy and HorticultureHaishun Yang. . . . . . . . . . . . . . . .Agronomy and HorticultureCarbon Sequestration Program

Carbon Sequestration Program Field SitesSite 1 Irrigatedcontinuous maizeSite 2 Irrigatedmaize soybeanSite 3 Rainfedmaize soybeanIrrigated C-C Irrigated C-SDryland C-S

Research ComponentsTower eddy covariance fluxes of CO2, water vapor and energy: Verma, SuykerMonitoring and mapping soil C stocks: Dobermann, WaltersLitter decomposition: KnopsAbove biomass and leaf area index: ArkebauerLeaf gas exchange: ArkebauerSoil surface fluxes of CO2, N2O and CH4: ArkebauerBelowground processes: WaltersMonitoring soil water: Hubbard, SchimelfenigEcosystem modeling: Yang, CassmanRemote sensing: Gitelson, Walter-SheaLife-cycle GHG emissions analysis for both the cropping system and when crops are used for biofuel production: Walters, Cassman, Liska

Landscape-level(Eddy Covariance)Measurement of CO2 and Other FluxesMeasuring Componentsof Solar RadiationClose-up ofEddy CovarianceFlux SensorsTower Flux StudiesVerma, Suyker, & the team

Seasonal and Interannual Variability:Net Ecosystem CO2 Exchange (NEE) Mead, Nebraska

Extrapolation to Regional ScalesTower CO2 Flux vs Remotely Sensed Data Maize-Soybean, Mead, NebraskaChlorophyll Index, CIgreen = [(RNIR/Rgreen)-1], where Rgreen and RNIR are reflectances in TM Landsat bands 2 (520-600 nm) and 4 (760-900 nm), respectively. (Gitelson et al., 2005)

GPP distribution retrieved from Landsat ETM+ imagery1- Irrigated Continuous maize2- Irrigated Maize-Soybean Rotation3- Dryland Maize-Soybean Rotation123

Leaf/plot levelLandscape levelRegionalScaling ProcessRemote Sensing Studies: Gitelson et al.; Walter-Shea et al.

Biomass and Leaf Area IndexArkebauer et al.

Leaf Gas ExchangeArkebauer et al.

Soil Surface FluxesArkebauer et al.

Below Ground ProcessesWalters et al.

Monitoring Soil WaterHubbard, Schimelfenig & the team

Litter DecompositionKnops et al.

Mapping Soil Carbon StocksDobermann et al.

Site 1: Irrigated Continuous MaizeFuzzy soil classes, intensive measurement zones for scaling to the whole field

Initial soil C profiles at CSP site 3, 2001Rainfed site: soil cores representative of the six soil types within the 150 acre production field.

Average annual change in soil carbon stocks in a four-year period that included two complete rotation cycles for the corn-soybean rotation treatments: based on eddy tower CO2 flux measurements or direct measurement of changes in soil carbon content.BOTTOM LINE: no detectable C sequestration!Negative value indicates net loss of soil C.

4-year average (2001-2004)NBP: eddy co-variance towersSOC:direct measure Irrigated continuous maize-53 to -33-80 Irrigated maize-soybean-106 to -89-56 Rainfed maizesoybean-22-36

Modified Century Soil Carbon Model: overpredicts C sequestration potential of our CSP sites; we find no net sequestration, i.e. C neutral

http://www.nrel.colostate.edu/projects/century5

Net PrimaryProductivity

Harvest Removal C

Hybrid-MaizeModel

AGLive C

BGLive C

Pioneeer HiBred Intl Presentation--Omaha

What are reasons for over-predition of soil C sequestration?Ecosystem C models calibrated to long-term field experiments that:Only evaluated soil C changes in upper foot of soil; ignored full active root zone profileDid not account for the decrease in soil bulk density that occurs when soil organic matter content increasesWhile soil C turnover model components were mechanistic, crop productivity components were empirical and not robustPoints to critical role of detailed measurements to validate ecosystem models, especially those used to inform lawmakers and guide policy

Greenhouse Gas Mitigation and Net Energy Yield of USA Maize-EthanolWhile there are many life-cycle analysis (LCA) studies of maize-ethanol systemsIncludes crop production, ethanol conversion, co-product processing and utilizationResults vary depending on selection of system boundaries, energy content of crop inputs, crop yields and input levels, energy use in ethanol plant

Backward-looking vs forward-looking LIFE-CYCLE ANALYSES Previous studies use aggregate data from the recent pastBut efficiencies of maize production and ethanol conversion are continually improvingMore relevant question: what is the energy efficiency and greenhouse gas mitigation potential of current and future maize-ethanol systems?

Biofuel Energy Systems Simulator (BESS) Recently released life-cycle assessment software available at: www.bess.unl.eduUses updated input values for maize yields and production practices, energy requirements for ethanol fermentation-distillation, and co-product processing and utilizationEstimates much higher net energy efficiency and greenhouse gas mitigation potential than previous estimates

BESS LCA Analysis: GHG Emissions Reduction (%, Mt CO2eq*) -----Corn Production System-----Based on a 378 ML/yr maize-ethanol plant: from www.bess.unl.edu

Type of ethanol plantUSA averageNE averageIowa averageAdvanced High-Yield IrrigatedCoal, dry DG26%, 197,81736%, 270,66846%, 342,35939%, 294,171natural gas, dry DG51%, 381,21361%, 454,06470%, 525,75663%, 477,567natural gas, wet DG60%, 447,46269%, 520,31379%, 592,00473%, 543,816closed-loop facility67%, 504,26977%, 577,12087%, 648,81280%, 600,623

Bottom line: Energy Efficiency and GHG MitigationCurrent state-of-the-art USA maize ethanol systems Large net energy yield, 30-75% net energy surplus, 25-90% GHG reduction when corn-ethanol replaces gasoline

NPPD Generation CO2 ProjectionsPotential C-credits from 1 billion gallons of NE ethanol production (BESS software estimate: www.bess.unl.edu)

Chart1

109277306544467892962910927730

107067506544467892962910927730

108977606544467892962910927730

110579806544467892962910927730

116239606544467892962910927730

119775306544467892962910927730

119872606544467892962910927730

121384906544467892962910927730

12034426.66666676544467892962910927730

12113806.93200226544467892962910927730

12194256.7524976544467892962910927730

12276187.29027946544467892962910927730

12120313.41932836544467892962910927730

12368758.46999066544467892962910927730

12621817.96473826544467892962910927730

12879525.59370666544467892962910927730

13141913.88111576544467892962910927730

13409014.13746146544467892962910927730

13680856.41143156544467892962910927730

13957469.44157826544467892962910927730

14238880.60778586544467892962910927730

14525115.88256936544467892962910927730

14816199.78224226544467892962910927730

15112155.3179946544467892962910927730

15413003.94691686544467892962910927730

15718765.52302236544467892962910927730

Projections

Est 1990

2000

2005

Metric Tons

NPPD Generation CO2 Projections(excluding LES)

Data

Sources:NPPD CO2 Emission Inventory 06.xls (3/29/07)Hope email to Fehr, 3/27/07

Hope email to Fehr, 3/29/07

conversion factor0.9071847

(w/o LES)metric tonsshort tons

metric tons70%92%

ProjectionsEst 199020002005Total w/o LESTotalSheldonGGSCanadayBPSHallamHebronMcCook

historical19906,544,46765444678,929,62910,927,73000

19916,544,4678,929,62910,927,73000

19926,544,4678,929,62910,927,73000

19936,544,4678,929,62910,927,73000

19946,544,4678,929,62910,927,73000

19956,544,4678,929,62910,927,73000

19966,544,4678,929,62910,927,73000

19979,458,1126,544,4678,929,62910,927,7309,458,11211,758,3111,781,1919,977,120

19989,336,6476,544,4678,929,62910,927,7309,336,64711,586,9301,728,7359,705,220152,975

19998,989,1986,544,4678,929,62910,927,7308,989,19811,161,1261,658,9569,431,80070,370

20008,929,6296,544,4678,929,62910,927,7308,916,67911,082,1821,734,1149,162,390185,678

200110,678,5676,544,4678,929,62910,927,73010,678,56713,216,0971,811,52511,269,170135,402

200210,818,4126,544,4678,929,62910,927,73010,818,41213,415,9501,925,12911,414,41076,411

200310,915,7836,544,4678,929,62910,927,73010,915,78313,499,7441,783,62411,650,82065,300

200410,475,2776,544,4678,929,62910,927,73010,475,27712,997,9001,873,60911,110,00014,291

200510,927,7306,544,4678,929,62910,927,73010,914,69113,556,7272,071,70811,297,84031,207155,972

200610,706,7506,544,4678,929,62910,927,73010,702,59913,261,7921,895,75411,193,37028,558144,110

projected200710,897,7606,544,4678,929,62910,927,730

200811,057,9806,544,4678,929,62910,927,730

200911,623,9606,544,4678,929,62910,927,730

201011,977,5306,544,4678,929,62910,927,730

201111,987,2606,544,4678,929,62910,927,730

201212,138,4906,544,4678,929,62910,927,730

201312,034,4276,544,4678,929,62910,927,730

201412,113,8076,544,4678,929,62910,927,730

201512,194,2576,544,4678,929,62910,927,730

201612,276,1876,544,4678,929,62910,927,730

201712,120,3136,544,4678,929,62910,927,730

201812,368,7586,544,4678,929,62910,927,730

201912,621,8186,544,4678,929,62910,927,730

202012,879,5266,544,4678,929,62910,927,730

202113,141,9146,544,4678,929,62910,927,730

202213,409,0146,544,4678,929,62910,927,730

202313,680,8566,544,4678,929,62910,927,730

202413,957,4696,544,4678,929,62910,927,730

202514,238,8816,544,4678,929,62910,927,730

202614,525,1166,544,4678,929,62910,927,730

202714,816,2006,544,4678,929,62910,927,730

202815,112,1556,544,4678,929,62910,927,730

202915,413,0046,544,4678,929,62910,927,730

203015,718,7666,544,4678,929,62910,927,730

Projections

ED 2007.02 (3/29/07)

Starting in 2014

Native Load per Feb-2007 Forecast (3/29/2007)

Total Gen & Purch = average of 2010-12

Part Sale - LES only except 4 months of MEAN in 2014 & 18 days of Aquila in 2014

NF Sale - Always keep a min of1,200,000MWh/yr in 2014, reducing by 1%/yr

Assume the following CO2 emission rates for add'l gen or purch

10.50mt/MWh

metric tonsGGSSheldonTotal Gen & PurchPart SaleCap SaleNF SaleNative LoadAdd'l Gen & PurchCoal BasedGas Fired CCEmission Free Gen or Purch

20109,509,4571,441,23621,584,2203,121,136795,3781,831,77315,835,9330

20119,393,1911,444,45121,464,0622,604,941481,6391,854,96116,522,5210

20129,404,0871,421,41621,693,4732,334,664380,0411,891,23817,087,5300

201312,034,4279,295,9551,437,24922,000,4322,408,779396,6861,686,82817,508,139040%30%30%

201412,113,8079,435,5781,435,70121,580,5851,430,5622,353,22817,941,122144,32840%30%30%

201512,194,2579,435,5781,435,70121,580,5851,290,1622,201,08318,379,939290,60040%30%30%

201612,276,1879,435,5781,435,70121,580,5851,290,1621,903,15418,826,833439,56540%30%30%

201712,120,3139,435,5781,435,70121,580,5851,290,1621,164,70819,281,872156,15840%30%30%

201812,368,7589,435,5781,435,70121,580,5851,290,1621,153,17619,745,122607,87640%30%30%

201912,621,8189,435,5781,435,70121,580,5851,290,1621,141,75920,216,6481,067,98440%30%30%

202012,879,5269,435,5781,435,70121,580,5851,290,1621,130,45420,696,5121,536,54440%30%30%

202113,141,9149,435,5781,435,70121,580,5851,290,1621,119,26221,184,7742,013,61340%30%30%

202213,409,0149,435,5781,435,70121,580,5851,290,1621,108,18021,681,4932,499,25040%30%30%

202313,680,8569,435,5781,435,70121,580,5851,290,1621,097,20822,186,7232,993,50940%30%30%

202413,957,4699,435,5781,435,70121,580,5851,290,1621,086,34422,700,5203,496,44140%30%30%

202514,238,8819,435,5781,435,70121,580,5851,290,1621,075,58823,222,9324,008,09840%30%30%

202614,525,1169,435,5781,435,70121,580,5851,290,1621,064,93923,754,0094,528,52640%30%30%

202714,816,2009,435,5781,435,70121,580,5851,290,1621,054,39524,293,7975,057,76940%30%30%

202815,112,1559,435,5781,435,70121,580,5851,290,1621,043,95624,842,3375,595,87040%30%30%

202915,413,0049,435,5781,435,70121,580,5851,290,1621,033,61925,399,6716,142,86840%30%30%

203015,718,7669,435,5781,435,70121,580,5851,290,1621,023,38625,965,8356,698,79840%30%30%

40%30%30%

Sheet3

Annually Integrated NEE(g C m-2 y-1)

Maize, NE300 to 500 (Verma et al., 2005)Harvard Forest, MA200 (Barford et al., 2003)Howland Forest, ME174 (Hollinger et al., 2004)Univ. of Michigan Biological St80 to 170 (Schmid et al., 2003)Wind River, WA-50 to 200 (Pers. Comm.)Douglas Fir, B.C.270 to 420 (Morgenstern et al., 2004)Tallgrass Prairie, OK50 to 275 (Suyker et al., 2003)Northern Temperate Grassland, Alberta-18 to 20 (Flanagan et al., 2002)Mediterranean, Annual Grassland, CA-30 to 130 (Xu and Baldocchi, 2003)Soybean, NE-10 to -75 (Verma et al., 2005)

Contribution of other biomes to GHG emissions or mitigation, and impact on water quality?CRP land and parksPrairie grass biofuel systemsNutrient storage and fluxesBiological diversity