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 EarthwormsMitesNematodesProtozoaBeetlesTermites

Bacteria Mostly Single Cell Millions per Gram Millions of Billions per Acre

Roles of Bacteria Nitrogen Fixation Mineralization Organic Matter Decomposition Soil Stabilization AerationTilth

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 TemperatureMoisture Food Supply Oxygen C:N Ratio

Microbes Need Carbon Microbes Need Nitrogen Nitrogen is Often the Limiting Factor

C:N Ratio Sawdust300:1 Newspaper175:1 Corn Stalks 75:1 Leaves60:1 IDEAL RATIO 30:1 Vegetable Scraps 25:1 Grass Clippings 20:1 Clover20:1 Manure15:1 Alfalfa12:1 Slow Stinky

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 ?