Soil Organic Carbon Sequestration: Importance and State of Science

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Soil Organic Carbon Sequestration:Importance and State of Science

Dr. Rattan LalCarbon Management and Sequestration CenterThe Ohio State UniversityColumbus, Ohio

#Carbon Management and Sequestration CenterConstituents of Soil Carbon Pool

Soil Carbon Pool

Organic

Inorganic

PedogenicLithogenicCarbonatesBicarbonates

Live- Fauna - MBCUndecomposed(Detritus)Decomposed

ProtectedUnprotected

DOC

POC

MOC

#Carbon Management and Sequestration Center

Sediment

0.55 Pg/yr

The Short-Term Global Carbon Cycle (2005-2014 Data)

Soil Respiration

60 Pg/yr

Biomass- C Input

60 Pg/yr

Plant Respiration

60 Pg/yr

GPP

123 Pg/yr

Anthropogenic Activities

9.9 Pg/yr

Soil Erosion

1.1 Pg/yr

Emissions

90 Pg/yr

Uptake

92.6 Pg/yr

ATMOSPHERE800 Pg+4.4 Pg/yr

OCEAN

The ultimate graveyard+2.6 Pg/yr

SOIL

6000 Pg to 3-m depth(Organic & Inorganic)+3.00.8 Pg/yr(Land)

Anthropocene

VEGETATION

620 Pg Live: 560 PgDetritus: 60 PgEFF= 9.00.5ELUC=0.90.5 Le Quere et al. (2015); Lal (2004); Batjes (1996); Tarnocai et al. (2009); Jungkunst et al. (2012)

MRT = Pool Flux

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Aggregation (Physical Protection) enhances the MRTShaking and erosion lead to release of C and its oxidation by microbial processes

Clay particles Domains Micro-aggregates Aggregates Peds

Clay particles Domains Micro-aggregates Aggregates Peds

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Soil Erosion and the Global Carbon BudgetTransport and fate of soil organic carbon by erosional processes is an integral component of the global C budget, but ignored.

Soil erosion affects C budget directly and indirectly

Direct EffectSoil transportTopsoil truncation

Indirect EffectsPlant growth/biomass productionSoil water and temperatureSoil aggregationSoil aeration and CO2, CH4, N2OSOC redistribution

The Global Carbon Project must consider erosion-induced transport in its annual assessment.

#Carbon Management and Sequestration Center

CO2, N2O

CO2, CH4, N2O

Gaseous Emissions

ErosionRedistributionDeposition & Burialof C-rich Soil Water TableRunoff

Stream

Top Soil

Transport, redistribution and deposition of soil organic carbon on an eroded landscape (Lal, 2016)Delivery ratio is about 10%. It decreases with increase in distance from the source.

#Carbon Management and Sequestration CenterCumulative CO2 Emissions and Sinks Between 1750-2015Le Qur et al. (2016)Source/Sink1750-2015 (PgC)

Source/Sink1750-2015 (PgC)SourcesFossil fuel and industry41020Land use change19065Total emissions60070SinksAtmosphere2605Ocean17520Residual terrestrial16570

SourcesFossil fuel and industry41020

Land use change19065

Total emissions60070

SinksAtmosphere2605

Ocean17520

Residual terrestrial16570

With sources and sinks of landuse being uncertain, the global carbon budget remains a work-in-progress.

#Carbon Management and Sequestration CenterSoil Organic Carbon SequestrationIt is the process of transferring CO2 from the atmosphere into the soil of a land unit plants, plant residues and other organic solids which are stored or retained in the unit as a part of the soil organic matter with a long mean residence time.

Thus , deposition/burial of C by erosion , land application of C-enriched amendments( e.g., bio-char , compost , manure ,mulch etc.) and the burial of biomass in deep mines or ocean floor brought in from outside the land units are not sequestration.

Olson, Al-Kaisi, Lal, Lower (2014)

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Disease-Suppressive soil High Soil Biodiversity

Mulch

Cover crop

Managing Soil Health and SOM

Mycorrhizae

Integrated Nutrient Management

Rhizobium

Molecular-based signals

Resilient EcosystemsComplex RotationsPhyto-engineeringIntegrated livestock-tree systems

N, P, K, Zn, H2O

No-till

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Plant Functional Traits and SOC SequestrationYearState of the Terrestrial Biosphere (%)WildSemi-natural stateComplete change8000 BC100001700504552000252055

The rate of C assimilation,

C storage in belowground biomass (root architecture),

Plant respiration rate,

Recalcitrant aliphatic bio(macro) molecules

Phytolith occluded carbon (PhytoC) especially in cereals, and differences among genotype

#Carbon Management and Sequestration CenterThe Priming EffectsIt refers to the enhanced or retarded soil organic matter composition due to amendment of fresh biomass-C or mineral N. Large amounts of C, N, and other nutrients can be released or immobilized over a short-time by microbial activities.

Interactions between different qualities of biomass,

Interaction between living and dead organic matter,

Mechanisms and the magnitude of effects depend on a

Effects of macro-organisms on micro-flora

Impact of INM

#Carbon Management and Sequestration CenterSoil Functional Attributes for SOC SequestrationYearState of the Terrestrial Biosphere (%)WildSemi-natural stateComplete change8000 BC100001700504552000252055

Clay + fine silt contentClay mineralsSoil depthWater retention and internal drainageNutrient reserves (N,P,S micronutrients)Slope aspectSlope shape

#Carbon Management and Sequestration CenterMechanisms of Longer MRT of Root vs. Shoot-Derived SOCYearState of the Terrestrial Biosphere (%)WildSemi-natural stateComplete change8000 BC100001700504552000252055

Chemical recalcitrance (cutin, suberins)Deep placementInteraction with mycorrhizae and root hairsInteraction with polyvalent cationsPhysico-chemical protection

#Carbon Management and Sequestration CenterTowards Increasing Carbon Storage in SoilIncreasing the input of biomass-C and of Ca2+ and Mg2+

Decreasing losses by decomposition, erosion, leaching.

Enhancing stabilization of SOC by physical, chemical, biological and ecological protection measures.

Enhancing the deep transport of C into the sub-soil.

Improving linkages between processes governing SOC and SIC interactions of mutual enhancement.

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Elemental RatioCereal ResiduesHumus

Elemental RatioCereal ResiduesHumusC:N10012C:P20050C:S50070

C:N10012

C:P20050

C:S50070

Crop Residues

Humus

Biochemical Transformations+ (N, P, S etc.)Nutrients Required to Convert Biomass into HumusThere are hidden costs associated with the process of humification.

#Carbon Management and Sequestration Center

Sustainable use of soil & water resources

H2OS C sequestration BiodiversityEcosystem Services Water quality NPPNote: The stuff that appears beyond the frame wont appear in the slide itself.PNCand the Ecosystem Services GeneratedCoupled Cycling Of H2O, C, N, P

Lal (2010)

#Carbon Management and Sequestration CenterConsequences of the Coupled Biogeochemical CyclingYearState of the Terrestrial Biosphere (%)WildSemi-natural stateComplete change8000 BC100001700504552000252055

Because of the coupled cycles of C, N, H2O, P, S, etc., management-induced changes in one can affect cycling of others often with adverse environmental impacts or trade-offs:

Gaseous emission of CH4, N2O

Leaching of NO3, N2 or NH3

Changes in soil inorganic C and N

#Carbon Management and Sequestration CenterMechanisms of Stabilization of SOCYearState of the Terrestrial Biosphere (%)WildSemi-natural stateComplete change8000 BC100001700504552000252055

MechanismProcessReference

MechanismProcessReferencePhysicalProtection against microbial processesDungait et al. (2012)Stable microaggregatesVitro et al. (2008, 2010)Deep placement in sub-soilLorenz and Lal (2005)ChemicalAbsorption on clay particlesGreenlandFormation of organo-mineral complexesPlaza et al. (2013), Chenu and Plante (2006), Rumpel and Kgel-Knaber (2011)BiochemicalSupra-molecular structurePiccolo (2001)Formation and selective preservation of moleculesSchnitzer and Monreal (2011)Recalcitrant substancesLorenz et al. (2007)Clay hutchesLndsdorf et al. (2000)EcologicalEcosystem characteristics Schmidt et al. (2011)

PhysicalAccess to microbial processesDungait et al. (2012)Stable microaggregatesVitro et al. (2008, 2010)Deep placement in sub-soilLorenz and Lal (2005)

ChemicalAbsorption on clay particlesTheng et al. (2012, 2014)Formation of organo-mineral complexesPlaza et al. (2013), Chenu and Plante (2006), Rumpel and Kgel-Knaber (2011)

BiochemicalSupra-molecular structurePiccolo (2001)Formation and selective preservation of moleculesSchnitzer and Monreal (2011)Recalcitrant substancesLorenz et al. (2007)Clay hutchesLndsdorf et al. (2000)

EcologicalEcosystem propertySchmidt et al. (2011)

#Carbon Management and Sequestration CenterTemperature Dependence of SOM Decomposition and Feedback to Climate ChangeYearState of the Terrestrial Biosphere (%)WildSemi-natural stateComplete change8000 BC100001700504552000252055

(Kinetic Theory, Arrhenius, 1889)Decomposition rate increase with increase in temperature when substrate availability and enzyme activity do not constrain the reaction rate (Davidson and Janssens, 2006).

Increase in decomposition rate with the warming temperature is more in colder than that in warmer climates (Del Grosso et al., 2005; Kirschbaum, 1995).

The decomposition reactions with high activation energies (i.e., slow rate) will experience greater temperature sensitivity than those with low activation energy (i.e., fast rate).

#Carbon Management and Sequestration CenterThe Debate about Temperature-Sensitivity of SOMYearState of the Terrestrial Biosphere (%)WildSemi-natural stateComplete change8000 BC100001700504552000252055

Assumption: Increased response in the rate of decomposition of recalcitrant substrate with increase in temperature will result in large loss of SOC stock.

Argument: Such a rate increase may not be important because the decomposition rate of recalcitrant materials, while being kinetically sensitive to temperature, may be so slow that little SOM would decompose regardless of the temperature (Conant et al., 2011).

Debate: Thus feedbacks to atmospheric CO2 concentrations from soil carbon are uncertain (Zhou et al., 2009; Janssen and Vicca, 2010), the decomposition rate (turnover) also depends on the accessibility (Dungait et al., 2012), the physiology of soil microfauna (Ltzow et al., 2009), and on the fact that the persistence of SOM is an ecosystem property (Schmidt, 2011).

#Carbon Management and Sequestration CenterSOM as an Ecosystem PropertyYearState of the Terrestrial Biosphere (%)WildSemi-natural stateComplete change8000 BC100001700504552000252055

Molecular structure alone does not control SOM stability.

Environmental and biological controls predominate (Schmidt et al., 2011).

The MRT of the fire-derived SOM (biochar), widely believed to be recalcitrant, also depends on physical protection and interaction with soil minerals (Brodowski et al., 2006), and the soil fertility trade-offs must also be considered.

Thus, management (soil, plant, animals, water, nutrients, tillage, phytoengineering, cover crops, residues) can play an important role in SOM persistence and in moderating feedback to climate change (Lal, 2004).

#Carbon Management and Sequestration CenterThe Case of PermafrostYearState of the Terrestrial Biosphere (%)WildSemi-natural stateComplete change8000 BC100001700504552000252055

Cryosols contain 1672 PgC (Tarnocai et al., 2009; Jungkunst et al., 2013)

With stabilization due to low temperature, thawing may accentuate mineralization (Nowinski et al., 2010) even of older SOM.

However, formation of pedogenic carbonates (Strigel et al., 2005; Kawahigashi et al., 2006) and enhanced aggregation in active layer (Schmidt et al., 2001) may stabilize SOM.

#Carbon Management and Sequestration CenterSoil Carbon Stocks

SOC stock: prehistoric, 1750, 1800, 1900, 1950, 2000Gaseous emissionsSIC stocks (3-m)SOC stock vs. yield

#Carbon Management and Sequestration CenterOther Researchable PrioritiesYearState of the Terrestrial Biosphere (%)WildSemi-natural stateComplete change8000 BC100001700504552000252055

Initiating long-term field experiments to assess stabilization/destabilization processes and MRT,

Evaluating global C budget with due consideration to the fate of erosional processes, soil/water management,

Mapping SOC stocks to 3-m depth, gaseous fluxes, productivity effects and critical limits.

Assessment of SIC and SOC stocks at landscape level.

Developing new technologies for measurement of stocks (INS, Mid-infrared reflectance spectroscopy-MIRS).

#Carbon Management and Sequestration CenterCarbon Pie320 GtTotal C Pie = (560ppm-400ppm) 2Gt/1 ppm = 320 Gt

How do we divide the pie among nations?

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1- Dynamic Global Map & C stock

3 Climate ChangeADAM

2 Food & Nutritional Security

4 - Soil Restoration & Remediation

5 Water Quality & Renewability3 Climate ChangeADAM

Political Will & GovernanceSoil as a Component of the Nexus

#Carbon Management and Sequestration Center

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