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3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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Soil Organic Matter (Chapter 12) Notes

Soil Organic Matter (Chapter 12) Notes

Did you know .... Did you know that by composting you can create your own soil organic matter? Chapter 12 highlights soil organic matter and role in the global carbon cycle, creation of soil organic matter via decomposition, factors influencing soil organic matter production, and finally soil's role in the greenhouse gas effect.

Lecture content notes are accompanied by videos listed below the notes in each submodule (e.g. Soil Organic Matter (Chapter 12) Videos A though F). Print or download lecture notes then view videos in succession alongside lecture content and add additional notes from each video. The start of each video is noted in parenthesis (e.g. Content for Video A) within each lecture note set and contains lecture content through the note for the next video (e.g. Content for Video B).

Figures and tables unless specifically referenced are from the course text, Nature and Property of Soils, 14th Edition, Brady and Weil.

Content Video A

Soil Organic Matter (SOM)

AGRI1050R50: Introduction to Soil Science (2020S) LH

3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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http://photogallery.nrcs.usda.gov/res/sites/photogallery/

Global Carbon Cycle

World Soil Carbon

Composition of Plants

3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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Rates of Decomposition Sugars, Starches, Simple Proteins (Rapid Decomposition)

Crude Protein

Hemicellulose

Cellulose

Fats and Waxes

Lignins and Phenollics (Very Slow Decomposition)

Content Video B

Decomposition Breakdown of larger particles into smaller ones

Microbial Community – Work Force

Oxidation via Enzymes: Energy, CO2 gas, and H20

Enzymes – Catalyst – Easier/Faster

TONS of microbial enzymes

Important too for soil structure

Disassembly Plant – Aerobic and Anaerobic

Aerobic: CO2, NH4+, NO3-, HPO4-, SO4-, H2O

Microbial Biomass

Recalcitrant materials –Humus –SOM

Content Video C

Rates of Decomposition Physical

Smaller particles – Faster Degradation

Closer material is to microbes – Faster Degradation

Nutritional

Need balance

3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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C:N Ratio – Ratio of Carbon to Nitrogen

C:N Ratio < 20 – Rapid Degradation, Mineralization

C:N Ration > 30 – Slow Degradation, Scavenge Nitrogen

Make additional N: Plant Available

C:N Ratios and Litter Quality Typical C:N Ratios

Litter Quality

Lignin Content

Low C:N: Low Lignin - High Quality, Faster nutrient availability, Less accumulation of SOM

High C:N: High Lignin – Lower quality, Slower release of nutrients, Accumulation of SOM

Manage residues and anticipate nutrient availabilities

Cover Crop Residue Decomposition

3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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Content Video D

Generating SOM SOM – Broad term

Living Biomass: Bugs and Animals

Plant Litter: Dead roots, identifiable residue

Humus: Soil colloid, High MW, unidentifiable reside

Soil Organic Carbon - % of Carbon in SOM

3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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Classifying SOM

Humus Humic Substances

Polymerization of lignin and degradation products

COMPLEX Ring Structures and Ill-defined

High MW

Recalcitrant – Resist microbial attack

Dark in Color

60-80% of SOM

Nonhumic Substances

20-30% of SOM

Less recalcitrant, Less Complex

Biomolecules – Microbial Byproducts

Polysaccharides

Impact soil structure – aggregate stability and nutrient availability

3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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Humus Influence Colloid

High Surface Area

High Water Holding Capacity

HIGH CEC: 150 to 500 cmolc/kg

Bank for nutrients

Promotes soil structure: air/gas exchange, infiltration rates, ETC.

Stable

Portions of SOM are very stable – Centuries old

Clay-Humus combination – further protection and stabilization

Continual, Slow Degradation: Must protect have and continually add residue to build new to replace loss

SOM Pools – Monitor and Predict

3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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Content Video E

Factors Influencing SOM Soil Orders

Alfisols – Lowest

Histosols – Highest

Texture

Clays > Sands

Complexation > Fine vs Coarse

Drainage Rates > Fine vs Coarse

Plant Cover

Plants > Bare

Grasslands > Forrest

Climate

Wet, Cold > Hot, Dry

Histosols: Waterlogged

Management – DO NOT DISTURB!

Distribution of SOM

3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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Managing Agronomic Soils – Building SOM Conservation and No-Till

Tillage: SOM broken down by microbial community

Crop Rotation

Crop Rotation > Monoculture

Maintain Soil pH and Nutrients

Nutrient availability for plants

Good for microbial population

Maximize CEC and Complexation for SOM

Plant Residues - Keep soil covered!

Crop Residues

Green Manures

Animal Manures

Morrow and Rothamstead Plots

Farmer's Challenge Aren’t bugs the bad guy here – Break down SOM?

Microbial community drive ALL nutrient cycling

SOM: CEC, WHC, Nutrient Availability, Structure

BALANCE

Content Video F

3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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Content Video F

Composting Create own humus!

Produce soil amendment from decomposition of organic materials

Management of compost pile – Box 12.4

Composting – animal manure - minimize pathogens

Soils and Greenhouse Effect Soils natural source GHG: CO2,CH4, NOx Loss of SOM – Net Loss CO2 Manage Soils SINK most gases:

Stop draining Histosols Manage wet soils Manage for increased SOM

Carbon Credit Industry

Review What part does soil play in the global carbon cycle? Where is most of the carbon in soils located? What is the primary source for the production of SOM? Are soil nutrients a large portion of the total plant material? Do all plant materials decay at the same rate? What is decomposition? What group drives decomposition? What is an enzyme? Which is more efficient aerobic or anaerobic degradation? Why is the nutrient content of plant material so important in is degradation status? What is a C:N ratio – why is it important – what C:N ratio would cause mineralization and not immobilization? What is litter quality? What qualities of litter promote SOM? Can you describe Figure 12.6? Name the major components of SOM? Of 100 grams of carbon the majority is lost to what? What are some characteristics of humus? Why is SOM so closely tied to soil fertility? Understand the pools of SOM – active vs passive What soil orders might have the highest and lowest SOM? Generally would clay soils or sandy soils tend to have greater amounts of OM and WHY? What climactic conditions are most conductive to maximum SOM? D d t d Fi 12 21?

3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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Do you understand Figure 12 21?

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