soil organic carbon sequestration: importance and state of science

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Carbon Management and Sequestration Center

Soil Organic Carbon Sequestration:Importance and State of Science

Dr. Rattan LalCarbon Management and Sequestration Center

The Ohio State UniversityColumbus, Ohio

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CONSTITUENTS OF SOIL CARBON POOLSoil Carbon Pool

Organic Inorganic

Pedogenic Lithogenic

Carbonates Bicarbonates

Live- Fauna - MBC

Undecomposed(Detritus) Decomposed

Protected Unprotected

DOC POC MOC

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Sedim

ent

0.55 P

g/yr

THE SHORT-TERM GLOBAL CARBON CYCLE (2005-2014 DATA)

Soil Respiration

60 Pg/yr

Biomass- C Input60 Pg/yr

Plant Resp

iratio

n

60 Pg/yr

GPP

123 Pg/yr

Anthropogenic Activities9.9 Pg/yr

Soil Erosion

1.1 Pg/yr

Emissions90 Pg/yr

Uptake92.6 Pg/yr

ATMOSPHERE800 Pg

+4.4 Pg/yr

OCEANThe ultimate

graveyard+2.6 Pg/yr

SOIL6000 Pg to 3-m depth(Organic & Inorganic)+3.0±0.8 Pg/yr(Land)

VEGETATION620 Pg

Live: 560 PgDetritus: 60 Pg

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 MRT

Shaking 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 BUDGET

• Transport 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 Effect• Soil transport

• Topsoil truncation

Indirect Effects• Plant growth/biomass production

• Soil water and temperature

• Soil aggregation

• Soil aeration and CO2, CH4, N2O

• SOC redistribution

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

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CO

2, N

2O

CO

2, C

H4,

N2O

Gas

eous

Em

issi

ons

Water Table

Runoff

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.

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CUMULATIVE CO2 EMISSIONS AND SINKS BETWEEN 1750-2015

Le Quéré et al. (2016)

Source/Sink 1750-2015 (PgC)Sources Fossil fuel and industry 410±20

Land use change 190±65

Total emissions 600±70

Sinks Atmosphere 260±5

Ocean 175±20

Residual terrestrial 165±70

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

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SOIL ORGANIC CARBON SEQUESTRATION

It 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

MycorrhizaeIntegrated Nutrient

Management

Rhizobium

Molecular-based signals

Resilient

EcosystemsComplex

Rotations

Phyto-

engineering

Integrated livestock-tree systems

N, P, K, Zn, H2O

No-till

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PLANT FUNCTIONAL TRAITS AND SOC SEQUESTRATION

• 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

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THE PRIMING EFFECTS

It 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

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SOIL FUNCTIONAL ATTRIBUTES FOR SOC SEQUESTRATION

• Clay + fine silt content

• Clay minerals

• Soil depth

• Water retention and internal drainage

• Nutrient reserves (N,P,S micronutrients)

• Slope aspect

• Slope shape

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MECHANISMS OF LONGER MRT OF ROOT VS. SHOOT-DERIVED SOC

• Chemical recalcitrance (cutin, suberins)

• Deep placement

• Interaction with mycorrhizae and root hairs

• Interaction with polyvalent cations

• Physico-chemical protection

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TOWARDS INCREASING CARBON STORAGE IN SOIL

1. Increasing the input of biomass-C and of Ca2+ and Mg2+

2. Decreasing losses by decomposition, erosion, leaching.

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

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

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

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Elemental Ratio Cereal Residues HumusC:N 100 12C:P 200 50C:S 500 70

Crop Residues HumusBiochemical Transformations

+ (N, P, S etc.)

NUTRIENTS REQUIRED TO CONVERT BIOMASS INTO HUMUS

There are hidden costs associated with the process of humification.

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Carbon Management and Sequestration Center Sustainable use of soil &

water resources

H2O

S• C sequestration

• Biodiversity

Ecos

yste

m

Serv

ices

• Water quality • NPP

Note: The stuff that appears beyond the frame won’t appear in the slide itself.

PN

C

AND THE ECOSYSTEM SERVICES GENERATED

COUPLED CYCLING OF H2O, C, N, P

Lal (2010)

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CONSEQUENCES OF THE COUPLED BIOGEOCHEMICAL CYCLING

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

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MECHANISMS OF STABILIZATION OF SOC

Mechanism Process ReferencePhysical • Access to microbial processes Dungait et al. (2012)

• Stable microaggregates Vitro et al. (2008, 2010)

• Deep placement in sub-soil Lorenz and Lal (2005)

Chemical • Absorption on clay particles Theng et al. (2012, 2014)

• Formation of organo-mineral complexes Plaza et al. (2013), Chenu and Plante (2006), Rumpel and Kögel-Knaber (2011)

Biochemical • Supra-molecular structure Piccolo (2001)

• Formation and selective preservation of molecules

Schnitzer and Monreal (2011)

• Recalcitrant substances Lorenz et al. (2007)

• Clay hutches Lündsdorf et al. (2000)

Ecological • Ecosystem property Schmidt et al. (2011)

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TEMPERATURE DEPENDENCE OF SOM DECOMPOSITION AND FEEDBACK TO CLIMATE CHANGE

(Kinetic Theory, Arrhenius, 1889)

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

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

3. 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).

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THE DEBATE ABOUT TEMPERATURE-SENSITIVITY OF SOM

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 (Lützow et al., 2009), and on the fact that the persistence of SOM is an ecosystem property (Schmidt, 2011).

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SOM AS AN ECOSYSTEM PROPERTY

• 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).

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THE CASE OF PERMAFROST

• 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.

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SOIL CARBON STOCKS

• SOC stock: prehistoric, 1750, 1800, 1900, 1950, 2000

• Gaseous emissions• SIC stocks (3-m)• SOC stock vs. yield

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OTHER RESEARCHABLE PRIORITIES

• 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).

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CARBON PIE

320 Gt

Total 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 Change

ADAM

2 – Food & Nutritional Security

4 - So

il

Resto

ration

& Re

mediat

ion

5 – Water Quality &

Renewability

3 – Climate Change

ADAMSOIL AS A COMPONENT OF THE NEXUS

soil organic carbon sequestration: importance and state of science

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