Tree Fruit Soils and Nutrition



The Soil Flora (or Garden)

  • Macroflora: Vascular plants, Mosses, etc.
  • Microflora: Bacteria, Actinomycetes, Fungi, Algae

Influences on Microbial Activity

  • Temperature (70°-100°F most active microbes)
  • Moisture (Field capacity is optimal)
  • Aeration (want a nice mix of pores filled with water and air)
  • pH (optimal pH is 6-7)
  • Soil organic matter

Soil Microorganisms: Bacteria

  1. Most numerous in soil
  2. Most diverse metabolism
  3. Can be aerobic or anaerobic
  4. Optimal growth at pH 6-8
  5. Examples: Nitrosomonas and Nitrobacter in nitrification processes, N2 fixers, fire blight is caused by a bacterium

Soil Microorganisms: Actinomycetes

  1. Transitional group between bacteria and fungi
  2. Active in degrading more resistant organic compounds
  3. Optimal growth at alkaline pH
  4. 2 important products:
    – produce antibodies (streptomycin is produced by an actino)
    – produce geosmin
  5. Negative impact - potato scab (Streptomyces scabies)

Soil Microorganisms: Fungi

  1. Dominate the soil biomass
  2. Obligate aerobes
  3. Can survive desiccation
  4. Dominate in acid soils
  5. Negative impacts:
    – Apple replant disease (Rhizoctonia, Pythium, Fusarium, and Phytophtora)
    – Powdery mildew is caused by a fungus
  6. Beneficials:– Penicillium

Nematode-trapping Fungus


Plant root / Soil / Microbial Interactions

  • Symbiotic associations such as that found with Rhizobia (N2 fixing bacteria, ex. legumes)
  • Fungi-mycorrhizal associations: important for water and P uptake; also improves soil structure
  • Earthworm channels: improve permeability and aeration
  • Agrobacterium (bacteria) cause gall formation in plants
  • Fungi causing soil-borne plant rot diseases
  • Rhizoctonia and Pythium (involved with replant disease)

Next page: Nutrient cycling and composting


Updated July 15, 2004


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Tree Fruit Research & Extension Center, Washington State University,1100 N Western Ave., Wenatchee, WA, 98801 USA