sol biology and_som
TRANSCRIPT
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
Organic Matter Decomposition
• 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
Organic Matter Decomposition
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
Organic Matter Decomposition
• 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
Organic Matter Decomposition
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