SOILS AND LANDSCAPES IN OUR ENVIRONMENT SOIL ORGANIC MATTER II @soilecologyUMan
SOIL 3600 Organic Matter II Lecture 11 SOIL ORGANIC MATTER 2
SOIL 3600 Organic Matter II Lecture 11 SOIL ORGANIC MATTER SUBSTANCES Soil Organic Matter Labile Carbon Protected or Stabilized Carbon Living Biomass Protected Particulate OM Free, recognizable Humus dead tissue Detritus Partially degraded tissue Charcoal Free Particulate OM Dissolved or Free Degradation Products 3
SOIL 3600 Organic Matter II Lecture 11 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 What are the organic C groups in Labile, and Protected/Stabilized fractions? 6
SOIL 3600 Organic Matter II Lecture 11 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 What is humus? What is the benefit of humus? 8
SOIL 3600 Organic Matter II Lecture 11 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 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 11
SOIL 3600 Organic Matter II Lecture 11 GOOD EXAM QUESTION Why is it easier to build soil organic C in a clay than sand soil? 12
SOIL 3600 Organic Matter II Lecture 11 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 Native Grassland Luvisol Chernozem Podsol Solenetz Ploughed Chernozem 17
SOIL 3600 Organic Matter II Lecture 11 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 How and why can soil organic matter be increased in soil by changing management practices? 24
SOIL 3600 Organic Matter II Lecture 11 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 Kaolinite Sand Mixture receiving glucose every week Before start End of of sugar experiment addition what looks like soil Kallenbach et al. 2016 Nature Communications 28
SOIL 3600 Organic Matter II Lecture 11 MAKING HUMUS IN THE LAB • 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 29
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 • 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 (15 th Edition) • Chapter 12 pages 543-580 33
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