SOILS AND LANDSCAPES IN OUR ENVIRONMENT SOIL ORGANIC MATTER II - - PowerPoint PPT Presentation

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SOILS AND LANDSCAPES IN OUR ENVIRONMENT SOIL ORGANIC MATTER II

SOIL ORGANIC MATTER

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SOIL 3600 Organic Matter II Lecture 11

SOIL ORGANIC MATTER SUBSTANCES

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SOIL 3600 Organic Matter II Lecture 11

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 OM Humus Charcoal

SOIL ORGANIC MATTER

• Labile- “liable to change”, organic C materials that are rapidly
• xidized by soil organisms in hours to few years, also called

“active carbon”

• Unprotected- organic C materials accessible to soil
• rganisms 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 3600 Organic Matter II Lecture 11

SOIL ORGANIC MATTER

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

thus not subject to rapid oxidation, includes materials in nanopores

• f 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

• rganisms
• 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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SOIL 3600 Organic Matter II Lecture 11

GOOD EXAM QUESTION

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SOIL 3600 Organic Matter II Lecture 11

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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SOIL 3600 Organic Matter II Lecture 11

GOOD EXAM QUESTIONS

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SOIL 3600 Organic Matter II Lecture 11

What is humus? What is the benefit of humus?

CLAY STABILIZES SOIL HUMUS

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SOIL 3600 Organic Matter II Lecture 11

HUMUS-CLAY COMPLEX

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SOIL 3600 Organic Matter II Lecture 11

STABILIZATION OF HUMUS ON CLAY BY THE DIFFUSE DOUBLE LAYER

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SOIL 3600 Organic Matter II Lecture 11

Double layer or Electrical Double Layer appears on surface of solids in contact with a fluid A surface charge (first layer) forms

• n 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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SOIL 3600 Organic Matter II Lecture 11

Why is it easier to build soil organic C in a clay than sand soil?

CHARCOAL

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SOIL 3600 Organic Matter II Lecture 11

STRUCTURE OF CHARCOAL

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SOIL 3600 Organic Matter II Lecture 11

WHERE DOES THE C GO DURING DECOMPOSITION?

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SOIL 3600 Organic Matter II Lecture 11

A BALANCING ACT

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SOIL 3600 Organic Matter II Lecture 11

EXAMPLE PROFILE DISTRIBUTION OF SOIL ORGANIC C

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SOIL 3600 Organic Matter II Lecture 11

Native Grassland Chernozem Ploughed Chernozem Podsol Luvisol Solenetz

LABILE C MOST AFFECTED BY MANAGEMENT

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SOIL 3600 Organic Matter II Lecture 11

GLOBAL SOIL ORGANIC C

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SOIL 3600 Organic Matter II Lecture 11

MANAGEMENT PRACTICES

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SOIL 3600 Organic Matter II Lecture 11

MANAGEMENT PRACTICES

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SOIL 3600 Organic Matter II Lecture 11

MANAGEMENT PRACTICES

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SOIL 3600 Organic Matter II Lecture 11

CARBON STORAGE WITH IMPROVING SOIL

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SOIL 3600 Organic Matter II Lecture 11

GOOD EXAM QUESTION

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SOIL 3600 Organic Matter II Lecture 11

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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SOIL 3600 Organic Matter II Lecture 11

COMPOSTING STAGES

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SOIL 3600 Organic Matter II Lecture 11

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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SOIL 3600 Organic Matter II Lecture 11

MAKING HUMUS WITH SUGAR

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SOIL 3600 Organic Matter II Lecture 11

Kaolinite Sand Mixture receiving glucose every week Before start

• f sugar

addition End of experiment what looks like soil Kallenbach et al. 2016 Nature Communications

MAKING HUMUS IN THE LAB

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SOIL 3600 Organic Matter II Lecture 11

• 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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SOIL 3600 Organic Matter II Lecture 11

BEFORE WE LEAVE CARBON

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SOIL 3600 Organic Matter II Lecture 11

, soils are , soils are Dirt, they are

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SOIL 3600 Organic Matter II Lecture 11

RECOMMENDED READING

• N&PofS (15th Edition)
• Chapter 12 pages 543-580

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SOIL 3600 Organic Matter II Lecture 11