Tree Fruit Soils and Nutrition



Soil Organic Matter

Beneficial impacts of SOM on soil properties:

  1. Physical - stabilizes soil structure, improves water holding characteristics, lowers bulk density, dark color may alter thermal properties
  2. Chemical - higher CEC, acts as a pH buffer, ties up metals, interacts with xenobiotics
  3. Biological - supplies energy and body-building constituents for soil organisms, increases microbial populations and their activities, source and sink for nutrients, ecosystem resilience, affects soil enzymes

Each year, about 1 to 4% of nutrients in the soil organic matter are released through microbial transformations to become available to plants. Release is highest under warm, moist conditions and slowest in cool dry climates. Microorganisms are the driving force for nutrient release to plants.

The soil food web

(figures on this page from USDA NRCS 2001 Soil Planning Guide)

Soil Microorganisms

Microorganisms constitute < 0.5% (w/w) of the soil mass yet they have a major impact on soil properties and processes. 60-80 % of the total soil metabolism is due to the microflora. In numbers, soil microorganisms beat out all other organisms. One gram of topsoil may contain:

  • as many as one billion bacteria
  • up to 100 million actinomycetes
  • one million fungi
  • 100 nematodes

Importance of Soil Organisms

  • Responsible for cycling of C, N and other nutrients
  • Enhance soil structure
  • Relocate and decompose organic materials
  • Maintain soil quality and health
  • Increase soil aeration and penetrability
  • Involved in disease transmission and control

Plant Roots: the Rhizosphere

The narrow region of soil directly around roots, teeming with bacteria that feed on sloughed-off plant cells and the proteins and sugars released by roots. Protozoa and nematodes graze on bacteria also concentrated near roots.


Next page: The soil fauna (or zoo)


Updated July 15, 2004


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