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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 ?
