Organic Agriculture:
Microbial Activity and Soil
Health
Warren Roberts
Jim Shrefler
Merritt Taylor
Lane Agricultural Center
OSU
We All Want Food that is
Plentiful
Nutritious
Safe
Why Have Organic Food?
Public Concern about Food Safety
– Perception that Organically Grown Foods
are Safer & More Nutritious
It’s a Matter of Life and ?
Microbial Activity and Soil Health
Define Microbial
– Micro-organisms
Define Activity
– Growth, Reproduction, Function
Define Soil Health
– Ability of a Soil to Function
Chemistry, Physics, Biology
Define Biology
– Study of Life and Life Processes
Purpose of Soil Health
Promote Plant and Animal Systems
Promote Clean Water
Prevent Soil Erosion
Promote Human Health
Promote Life !
Soil Microorganisms
Larger Animals
Bacteria (Often Single Cell)
Fungi (Often Long Filaments or Hyphae)
Actinomycetes (Properties of Both)
Microorganisms
Affected by
– Moisture
– Temperature
– Aeration
– Food Supply (Organic Matter)
– Acidity
Location in Soil
Mostly in top inch
Almost all in top 6 inches
Rhizosphere
– Adjacent to plant roots
– High microbial activity
– Contains root exudates
Soil Animals
Earthworms
Mites
Nematodes
Protozoa
Beetles
Termites
Bacteria
Mostly Single Cell
Millions per Gram
Millions of Billions per Acre
Roles of Bacteria
Nitrogen Fixation
Mineralization
Organic Matter Decomposition
Soil Stabilization
Aeration
Tilth
Nitrogen Fixation
Bacteria (Rhizobium and others)
Symbiotic
– Bacteria gets carbon from plants
– Bacteria supplies Nitrogen to plants
– Usually with Legumes
Mineralization
Conversion from Organic Substance to
Molecular Level Minerals
Decay
Physical and Chemical
Organic Matter
Decomposition
Physical changes
– Organisms eat, crunch, rip, tear
– Earthworms, mites, ants, etc
Chemical changes
– Digestion with enzymes
What Controls Rate of Decay
Temperature
Moisture
Food Supply
Oxygen
C:N Ratio
C:N Ratio
Microbes Need Carbon
Microbes Need Nitrogen
Nitrogen is Often the Limiting Factor
Stinky
Slow
C:N Ratio
Sawdust
Newspaper
Corn Stalks
Leaves
IDEAL RATIO
Vegetable Scraps
Grass Clippings
Clover
Manure
Alfalfa
300:1
175:1
75:1
60:1
30:1
25:1
20:1
20:1
15:1
12:1
Soil Stabilization
Soil Aggregation
Clumps of Particles
– Organic Matter
– Bacterial Residues
– Fungal Hyphae
Aeration & Tilth
High Organic Matter
Low Compaction
High Aggregation
Raised Bed Gardening – Noble
Foundation
Fungi
Hundreds of Thousands per Gram
Perform Functions Similar to Bacteria
– Decomposition
Important in Plant Nutrition
– Mycorrhizae (fungus root)
Mycorrhizae
Mutualism or Synergism
Benefits Plant and Fungus
– Ectomycorrhizal
Hyphae do not penetrate root cells
– Endomycorrhizal
Hyphae do enter root cells
Arbuscular
Very Common
– 90+ % of plant families
Ectomycorrhizae
Ecto- (outer)
Hyphae form sheath
around root tip
Promotes nutrient
absorption
Promotes nutrient
translocation
Endomycorrhizae
Endo – (inner)
Hyphae Penetrates Cell Wall
Promote Nutrient Uptake and Exchange
Increase Surface Contact Area
To Your Good Health (Soil)
Keep pH near neutral
Avoid Compaction
Maintain Good Moisture
Promote Drainage
Good Temperature
Organic Matter
A Noble Soil
ProBiotics
Cultures of Beneficial
Microorganisms
– Compost Teas
– Inoculants
Organism Food
– Sugar
– Molasses
– Nitrogen
Where We Are
50 + years of Chemical
Research
What If ?
– 50 + Years of Biological
Research ?