soils and landscapes in our environment …...soils and landscapes in our environment soil organic...
TRANSCRIPT
@soilecologyUMan
SOILS AND LANDSCAPES IN OUR ENVIRONMENTSOIL ORGANIC MATTER II
SOIL ORGANIC MATTER
2
SOIL 3600 Organic Matter II Lecture 11
SOIL ORGANIC MATTER SUBSTANCES
3
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 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
4
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 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
5
SOIL 3600 Organic Matter II Lecture 11
GOOD EXAM QUESTION
6
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……….
7
SOIL 3600 Organic Matter II Lecture 11
GOOD EXAM QUESTIONS
8
SOIL 3600 Organic Matter II Lecture 11
What is humus?
What is the benefit of humus?
CLAY STABILIZES SOIL HUMUS
9
SOIL 3600 Organic Matter II Lecture 11
HUMUS-CLAY COMPLEX
10
SOIL 3600 Organic Matter II Lecture 11
STABILIZATION OF HUMUS ON CLAY BY THE DIFFUSE
DOUBLE LAYER
11
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
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
12
SOIL 3600 Organic Matter II Lecture 11
Why is it easier to build soil organic
C in a clay than sand soil?
CHARCOAL
13
SOIL 3600 Organic Matter II Lecture 11
STRUCTURE OF CHARCOAL
14
SOIL 3600 Organic Matter II Lecture 11
WHERE DOES THE C GO DURING DECOMPOSITION?
15
SOIL 3600 Organic Matter II Lecture 11
A BALANCING ACT
16
SOIL 3600 Organic Matter II Lecture 11
EXAMPLE PROFILE DISTRIBUTION OF SOIL ORGANIC C
17
SOIL 3600 Organic Matter II Lecture 11
Native Grassland
Chernozem
Ploughed
Chernozem
Podsol
Luvisol
Solenetz
LABILE C MOST AFFECTED BY MANAGEMENT
18
SOIL 3600 Organic Matter II Lecture 11
GLOBAL SOIL ORGANIC C
19
SOIL 3600 Organic Matter II Lecture 11
MANAGEMENT PRACTICES
20
SOIL 3600 Organic Matter II Lecture 11
MANAGEMENT PRACTICES
21
SOIL 3600 Organic Matter II Lecture 11
MANAGEMENT PRACTICES
22
SOIL 3600 Organic Matter II Lecture 11
CARBON STORAGE WITH IMPROVING SOIL
23
SOIL 3600 Organic Matter II Lecture 11
GOOD EXAM QUESTION
24
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
25
SOIL 3600 Organic Matter II Lecture 11
COMPOSTING STAGES
26
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
27
SOIL 3600 Organic Matter II Lecture 11
MAKING HUMUS WITH SUGAR
28
SOIL 3600 Organic Matter II Lecture 11
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
29
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
30
SOIL 3600 Organic Matter II Lecture 11
BEFORE WE LEAVE CARBON
31
SOIL 3600 Organic Matter II Lecture 11
, soils are
, soils are
Dirt, they are
32
SOIL 3600 Organic Matter II Lecture 11
RECOMMENDED READING
• N&PofS (15th Edition)
• Chapter 12 pages 543-580
33
SOIL 3600 Organic Matter II Lecture 11