SOILS AND LANDSCAPES IN OUR ENVIRONMENT …...SOILS AND LANDSCAPES IN OUR ENVIRONMENT SOIL ORGANIC MATTER II SOIL ORGANIC MATTER 2 SOIL 3600 Organic Matter II Lecture 11 SOIL ORGANIC

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SOILS AND LANDSCAPES IN OUR ENVIRONMENTSOIL ORGANIC MATTER II

SOIL ORGANIC MATTER

2

SOIL 3600 Organic Matter II Lecture 11

SOIL ORGANIC MATTER SUBSTANCES

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Soil Organic Matter

Labile Carbon Protected or Stabilized Carbon

Living Biomass

Free, recognizable

dead tissue Detritus

Partially degraded tissue

Free Particulate OM

Dissolved or

Free Degradation Products

Protected

Particulate OMHumus

Charcoal

SOIL ORGANIC MATTER• Labile- “liable to change”, organic C materials that are rapidly

oxidized by soil organisms in hours to few years, also called “active carbon”

• Unprotected- organic C materials accessible to soil organisms for oxidation

• Detritus- particulate organic C materials >2mm of bodies or fragments of dead organisms and fecal materials colonized by living organisms, can be collected on a mesh screen

• Free Particulate OM- particulate organic C materials <2mm from degradation of dead organisms and fecal materials, can be collected by flotation in a solution

• Dissolved OM- biomolecules in soil solution from oxidation of dead organisms and fecal material, includes proteins, amino acids, aromatic rings, chained organic C etc., can be collected by extracting soil with water

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SOIL ORGANIC MATTER• Protected- organic C materials not accessible to soil organisms and

thus not subject to rapid oxidation, includes materials in nanopores of microaggregates and deep buried carbon

• Stabilized- degradation products of dead organisms and fecal material that by their chemical nature or complexation with clays, metals and other stabilized C are not readily oxidizable by soil organisms

• Passive- name given to either protected and stabilized organic C

• Humus- degradation products of dead organisms and fecal material that is amorphous in structure and not readily oxidizable because of stabilization processes

• Charcoal- aromatic C molecules produced from burning of plant materials in low oxygen conditions, also referred to as Black Soil C, is chemically very stabile

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GOOD EXAM QUESTION

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What are the organic C groups in

Labile, and Protected/Stabilized

fractions?

HUMUS• Highly decomposed biomolecules produced by microbes

• Very large polymers with amorphous structure

• Contains many aromatic rings in structure

• Many functional chemical groups

• Aromatic rings impact black colour

• Forms complexes with clay and other humus molecules to stabilize it

• High surface area and CEC (150-500 cmol+/kg humus)

• Very low bulk density

• Very high water-holding capacity

• Stimulates root growth and activity

• And so much more……….

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GOOD EXAM QUESTIONS

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What is humus?

What is the benefit of humus?

CLAY STABILIZES SOIL HUMUS

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HUMUS-CLAY COMPLEX

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STABILIZATION OF HUMUS ON CLAY BY THE DIFFUSE

DOUBLE LAYER

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Double layer or Electrical Double

Layer appears on surface of solids

in contact with a fluid

A surface charge (first layer) forms

on the solid from cations attracted

to negative sites of clay or humus

A second charge layer forms of

anions attracted to the surface

charge layer

Degrading enzymes in soil solution

loose their shape as they

encounter the double layer and

thus cannot degrade humus

GOOD EXAM QUESTION

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Why is it easier to build soil organic

C in a clay than sand soil?

CHARCOAL

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STRUCTURE OF CHARCOAL

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WHERE DOES THE C GO DURING DECOMPOSITION?

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A BALANCING ACT

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EXAMPLE PROFILE DISTRIBUTION OF SOIL ORGANIC C

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Native Grassland

Chernozem

Ploughed

Chernozem

Podsol

Luvisol

Solenetz

LABILE C MOST AFFECTED BY MANAGEMENT

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GLOBAL SOIL ORGANIC C

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MANAGEMENT PRACTICES

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CARBON STORAGE WITH IMPROVING SOIL

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GOOD EXAM QUESTION

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How and why can soil organic

matter be increased in soil by

changing management

practices?

SOIL CARBON 4 PER MILLE

• Initiative introduced by the French government at COP21 in Paris

• Goal to increase global soil organic matter in soil by 0.4% per year over the next 20 years as compensation for global emissions of greenhouse gases

• Potential to increase SOM is mostly on agricultural soils by changes practices or conversion to permanent plant cover

• 4 per mille/yr increase on agricultural soils worldwide is 2-3 Gt C/yr sequestered

• That compensates for 20-35% of greenhouse gas emissions

• Disruptive technology required to increase SOM to reach the goal

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COMPOSTING STAGES

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ON HUMUS FORMATION• Up to a few years ago it was thought humus was created

largely from aromatic rings in lignin and phenols

• Evidence for means of creation of humus

• Root turnover more important to humus formation than above ground residues

• Adding sugars to soil creates humus

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MAKING HUMUS WITH SUGAR

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Kaolinite Sand Mixture receiving glucose every week

Before start

of sugar

addition

End of

experiment

what looks

like soil

Kallenbach et al. 2016 Nature Communications

MAKING HUMUS IN THE LAB

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• Three types of organic material added to Kaolinite/Sand and Montmorrilinite/Sand mixtures

• Glucose, syringol (phenol), dissolved free degradation products of soil (DOC)

• Types of compounds present after 18 months compared to an agricultural soil

Kallenbach et al. 2016

ON HUMUS FORMATION• Up to a few years ago it was thought humus was created

largely from aromatic rings in lignin and phenols

• Evidence for means of creation of humus

• Root turnover more important to humus formation than above ground residues

• Adding sugars to soil creates humus

• Now believed humus is formed from aromatics rings of lignin and phenols and also from degradation products produced by microbes

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BEFORE WE LEAVE CARBON

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, soils are

, soils are

Dirt, they are

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RECOMMENDED READING

• N&PofS (15th Edition)

• Chapter 12 pages 543-580

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Documents

SOILS AND LANDSCAPES IN OUR ENVIRONMENT …...SOILS AND LANDSCAPES IN OUR ENVIRONMENT SOIL ORGANIC MATTER II SOIL ORGANIC MATTER 2 SOIL 3600 Organic Matter II Lecture 11 SOIL ORGANIC