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Unit 2: Applying Ecological Principles

Soil organic matter is the foundation for healthy and productive soils, although it is generally present in relatively small amounts. Agricultural soils may have anywhere from 1% to 6% organic matter depending on location, soil type, and management. Soil organic matter consists of three general categories of materials:

• living organisms

• fresh and partially decomposed residues

• well-decomposed residues (humus)

How can organic matter, which only makes up a small percentage of most soils, be so important?

The reason is that organic matter positively influences, or modifies the effect of, essentially all soil properties. This idea is evident in the activity you completed on the previous page: in the table, soil organic matter is identified as a major indicator of soil quality with its own slot in the table, and yet its effects are closely linked to each of the other 3 indicators listed (physical, biological, and chemical). It could have been placed in any space in the left hand column and you would be correct!

On many farms and ranches, especially those with a focus on sustainability, maintaining soil health and quality is centered largely on management of soil organic matter. For a more in-depth discussion of the scientific basis for organic matter’s effects on soil quality, take a look at the SARE publication Building Soils For Better Crops. Other resources include:

    - Organic Matter Management (University of Minnesota Extension)
    - Advanced Soil Organic Matter Management (Michigan State University Extension)