Ren R 210 Module 3

Physical Properties of SOM

* water holding capacity (can hold up to 10x it’s weight)
* soil structure and aggregation (↑ SOM, ↓ bulk density, ↑ porosity)

Chemical Properties of SOM

* absorptive capacity = CEC (↑ SOM, ↑ CEC for pH dependant charges)
* buffering capacity (↑ SOM, ↑ resistance to pH changes)

Biological Properties of SOM

* ↑ SOM, ↑ fertility of soil
* acts as slow release fertilizer (source nutrients: N, P, K, S for plants and biota)
* supports large and varied microbial population (↑ SOM, ↑ biological biomass)

Chemical Forms of Carbon

Inorganic C (CO2, CO, CH4)

Organic C (SOM, SOC)

Labile

(refers to soil C quality) easy and fast decomposition → low C/N ratio → excess N

Recalcitrant

(refers to Soil C quality) hard and slow decomposition → high C/N → limited N availability

Human Alterations to Carbon Cycle

CO2 Emissions

* combustion of fossil fuels
* deforestation

CH4 Emissions

* rice paddies
* cows

(CH4 emissions are several orders of magnitude lower than soil stocks, and therefore can be offset by SOM accumulation)

Carbon Use Efficiency (CUE)

33%

for every 1 C assimilated, 2 C are respired

C/N Ratio of Forests vs. Agricultural Soils

forest → between 20-30

agriculture soils → < 20

SOM Composition

Living Biomass (0.5-3%)

* roots
* microbes
* animals

Residues/Detritus → LF (5-40%)

* dead roots
* feces
* litter

**Humus (H, black greasy material) divided into 2 groups**

Non-Humic Substances (5-10%)

* biopolymers
* low MW
* known chemically

Humic Substances (40-90%)

* biopolymers
* *high MW*
* \*\*unknown chemically\*\*

Decomposition Definition

* chemical reaction occurring during decay of plant/animal remains
* altered chemical composition → produce energy

Mineralization Definition

* release of soluble or gaseous inorganic constitutes during decomposition
* SOC → CO2
* SON → NH4^-

Humification Definition

* decomposition results in black greasy OM
* old theory - condensation reaction: low MW biopolymer → high MW biopolymer
* new theory - stabilization of SOC by three mechanisms…
* chemical
* aggregate
* mineral associated OM

Non-Humic Substances

**Cellulose** (\~30% of plant material, cell walls) → linear polymer of glucose units (polysaccharides, carbs)

**Hemi-Cellulose** (\~20% of plant material) → branched polymer of diff sugars (glucose, fructose: polysaccharide)

**Lignin** (\~20% of plant material, woody material) → branched, aromatic polymer (volatile)

**Lipids** (\~20% of plant material, cellular material) → fats and waxes

**Protein** (\~5% of plant material) → amino acids (N is present), biochemical machine, photosynthesis

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Protein → Hemi-Cellulose → Cellulose → Lignin → Fats

Easy to decompose → Hard to decompose

New Humic Fractions

INSOLUBLE ORGANIC

* Humin (highly condensed, complexed with clays)

SOLUBLE ORGANIC

* Humic acids (dark brown to black, high MW)
* Fulvic acids (yellow to red, lower MW)

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*Microbes use enzymes to cleave off functional groups. No such thing as Humin, HA, and FA in nature*

SOM Stabilization

* contemporary theory
* based on decreasing molecular size
* stabilization in aggregates and mineral surfaces

SOM Theoretical Pools

Chemical protection → structural C and charcoal C

Physical protection → aggregation

Organo-mineral associations → MAOM

Autotrophs

Use CO2 as carbon source

Heterotrophs

Use organic C as carbon source

Photo-

Use sun as energy source

Chemo-

Use organic C as energy source

Litho-

Uses energy from soil redox reaction

Chemoheterotroph example

People

Photoautotroph example

Plants

Chemoheterotroph example

Fungi

Nitrogen Fixation

chemical/biological conversion of N2 to R-NH2

chemical → lighting, humans

biological → symbiotic (bacteria and plant sharing C + N), mutualistic, free-living bacteria in soil

Bacteria Genera and Associated Plant Family

Rhizobium → Pea Family

Frankia → Alder Family

Nitrogenase

Enzyme that catalyzes N fixation

N Cycle

REDOX Reactions

Ao + Dr → Ar + Do

A → e- acceptor

D → e- donor

o → oxidized (lose e-, becomes less negative)

r → reduced (gain e-, becomes more negative)

Human Alteration of N Cycle

Human N fixation

* fertilizers
* leguminous crops
* combustion of fossil fuels
* land clearing
* burning of forests
* draining of wetlands

Chemical N fixation

Haber Bosch process → need lots of natural gas to break triple bond in N2

Eutrophication

Increase in nutrients (N+P) in surface waters

* causes algae growth → kills fish
* ↑ turbidity, ↓ light
* ↓ water quality

Phosphorus Cycle

* very different form N
* no REDOX potiential
* all from lithosphere
* no organic form
* overtime all P precipitates out of the solution into insoluble forms → availability ↓ over time

Potassium Cycle

* no REDOX
* from lithosphere
* macronutrients: N, P, K, S, Ca, Mg

Sulfur Cycle

* like N, have REDOX potential
* unlike N, from lithosphere
* organic forms of S → C-S, C-O-S
* e- acceptor in anaerobic environments

Micronutrients

Fe, Cu, Ni, Mo, B, Zn

Trace metals → require chelates (elements that make these metals more soluble)

Plant Nutrients

evolving, new concept includes functional nutrients

Law of the Minimum

Agricultural idea → appropriate for agroecosystems

crop growth is limited by one factor

Concept of Fertility in Agriculture

* monoculture, known plant requirements
* possible to measure limitations
* NPKS, maximize yield

Concept of Fertility in Wildlands

* multiple species, funstional types
* not possible to know of define limitations
* microbial function, bioavailable nutrient profile, SOM quality all contribute to ecosystem function

Soil Food Web

Meagfauna

* mostly rodents
* bioturbation → soil mixing/predation

Macrofauna

* ants, millipedes, termites, earthworms, beetles, etc.
* bioturbation
* predatory, but smaller size
* OM shedders (↓ particle size)

Mesofauna

* mites and other small insects (0.1-1.0 mm)
* shedders
* OM consumers
* predators
* invertebrates

Mite Diversity

* very high in grasslands and forests
* diversity indicates ecosystem function

Microfauna

* Nematodes
* Protozoa → largest to smallest: ciliates (hair), amoebae (flowing cytoplasm), flagellates (whip-like appendages)

Microflora

* fungi
* bacteria
* archaea

Types of Mycorrihiza

* echo → outside cell, gymnosperms
* erricoid → species specific
* arbuscular → inside cell, angiosperms
* orchid → species specific

Soil-Plant Relations Lab

Phase 1 - Soil Quality Monitoring

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Phase 2 - DASH/DIRTS Health App

Phase 3 - Regenerative Agriculture