Sol biology and_som

Soil is an EcosystemSoil is an Ecosystem

Slides from: Richard Stehouwer Marcus Buchanan Elaine Ingham Department of Crop & Soil Sciences Extension Viticulturist Soil Food Web Inc. Penn State University Oregon State University

SOM Improves Soil Chemical Properties

– Increases Cation Exchange Capacity so the soil is better able to store and supply plant nutrients

– Increases pH buffering so the soil resists changes in pH

– Reduces Aluminum, Iron, and Manganese toxicity in acidic soil

Why should you care about soil organic

matter (SOM)?

• SOM Improves Soil Biological Properties– Greater abundance, diversity and activity of soil

microbes– Increased nutrient cycling– Increased root elongation and abundance– Increased access to water and nutrients

Why should you care about soil organic matter (SOM)?

What is Soil Organic Matter?

• All material in soil that contains (reduced/organic) carbon

• SOM is derived from– Plant residue (both litter and

roots)– Animal remains and excreta– Living soil microbes (microbial

biomass)

• With time microbes transform fresh organic material into stable soil organic matter

Crop residue

Bacteria

Fungi Actinomycetes

SOM

Components of Soil Organic Matter

Decomposing OM33% - 50%

Stabilized OM

(humus) 33% - 50%

Particleresidues <10%

Living organisms

<5%

Organic Matter Decomposition

• Earthworms– Mix fresh organic materials into

the soil– Brings organic matter into

contact with soil microorganisms

Corn leaf pulled into nightcrawler burrow

Millepede

Ants

• Soil insects and other arthropods

– Shred fresh organic material into much smaller particles

– Allows soil microbes to access all parts of the organic residue


• Bacteria– Population increases rapidly

when organic matter is added to soil

– Quickly degrade simple compounds - sugars, proteins, amino acids

– Have a harder time degrading cellulose, lignin, starch

– Cannot get at easily degradable molecules that are protected

Bacteria on fungal strands

Spiral bacteria

Rod bacteria

• Fungi

– Grow more slowly and efficiently than bacteria when organic matter is added to soil

– Able to degrade more complex organic molecules such as hemicellulose, starch, and cellulose.

– Give other soil microorganisms access to simpler molecules that were protected by cellulose or other complex compounds.

Soil fungus

Fungus on poplar leaf


Fungi and Soil Structure• Fungal hyphae (threads) help hold soil granules together• Fungal exudates (goo) help cement soil particles together

Fungi absent -Soil structure is not maintained when immersed in water

Active Fungi Present –Soil structure is maintained when immersed in water

• Actinomycetes

– The cleanup crew– Become dominant in the final

stages of decomposition– Attack the highly complex

and decay resistant compounds

• Cellulose• Chitin (insect shells)• Lignin• Waxes


• Protists and nematodes, the predators– Feed on the primary

decomposers (bacteria, fungi, actinomycetes)

– Release nutrients (nitrogen) contained in the bodies of the primary decomposers

Amoeba

Bacteria-feeding nematode

Predatory nematodeRotifer


MycorrhizaeMycorrhizae

The fungi use carbon (energy) from the plant to grow. In return, the fungi's hairlike filaments, called hyphae, extend the reach of plant roots. Hyphae function as pipes to funnel more water and nutrients, particularly phosphorus, to the plant.

Ecto - cover the root surface

Endo - penetrate root

Organic Matter DecompositionCarbon and Nitrogen Cycling

During each cycle of degradation about 2/3 of the organic carbon is used for energy and released as carbon dioxide (CO2)

Bacteria, FungiSoil organic matter Nematodes, protists, humus

CO2

CO2

Plant litter

During each cycle of degradation about 1/3 of the organic carbon is used to build microbial cells or becomes part of the soil organic matter

• Soil texture, pH, temperature, and moisture

• The ‘quality’ of organic matter additions C:N ratio and lignin content (L:N ratio)

• Quantity of organic matter

• Placement of materials (surface vs. incorporated)

• Tillage

Organic Matter ConceptsOrganic Matter Concepts

Critical factors that control the rate of decay, nutrient release, and conservation of OM in soil

Organic Matter QualityOrganic Matter QualityEffects soil structure, N,P,S release, microbial populations, nutrient and water holding capacity

Soil Organic Matter QualitySoil Organic Matter Quality

All organic matter in soil is not equalScientists describe 3 pools of soil organic matter

Passive SOM500 – 5000 yrsC/N ratio 7 – 10

Active SOM1 – 2 yrs

C/N ratio 15 – 30

Slow SOM15 – 100 yrs

C/N ratio 10 – 25

• Recently deposited organic material• Rapid decomposition• 10 – 20% of SOM

• Intermediate age organic material• Slow decomposition• 10 – 20% of SOM

• Very stable organic material

• Extremely slow decomposition

• 60 – 80% of SOM

CO 2

Organic additions(manure, compost, crop residues)

Below ground(roots and poop)

Rapid Decay(Sugars, proteins)

Resistant SOM

Organic Residues(leaf, shoots)

Decomposition (microbes)

Soil

Slow Decay(Cellulose, lignin)

Slow SOM

Active SOM

MicrobesPlants

Decomposition (microbes)

Humus

Microbial

Nutrients (N,P,S)

Particulate Click in repetition to view the decay sequence

Technology

Sol biology and_som