Soil Organisms—Their Location,
Living Conditions and Functions

Many people think that soil is just dirt, something there to anchor plants. But soil isn't just clay, sand or silt, with some organic matter tossed into the mix.

Each inch of healthy soil is alive with millions of soil organisms doing their thing.

And that "thing" makes nutrients available to the plants we put into the soil. Without those nutrients, the plants won't grow, or their growth will be limited.

Soil organisms are the main force behind the cycle of nutrients going through our local ecosystems.

Soil organisms are divided into six groups, each with its own set of functions.

Each group plays an important role in plant health.

Six Groups of Soil Organisms

There are six groups of organisms in our soils. Each soil will have a different combination of these:

  1. bacteria
  2. fungi
  3. protozoa
  4. earthworms
  5. nematodes
  6. arthropods

Their part in nutrient cycling includes:

  • Decomposition of organic matter
  • Mineralization
  • Nitrogen cycling
  • Storage and release of nutrients
  • Carbon cycling
  • Removing excess nutrients from water before they reach underground or surface water and become pollutants.

Soil Microorganisms

Bacteria, including actinomycetes, fungi, including mycorrhizal fungi, and protozoa make up the soil microorganisms that are essential to healthy, living soil.


The earthworm is a very important part of soil health in many areas of the world. Earthworms improve the soil by eating the organic matter in it. They produce castings that are equivalent to compost, which you can use as an organic fertilizer and soil amendment.

If you have a large family and produce a lot of organic waste every week, you can raise your own worms, reduce your garbage production (keeping it out of the landfill), and improve your gardens with the worm castings.


Nematodes exist in almost all moist soils. In dry spells, they're dormant. They become active when there's moisture in the soil.

There are both beneficial nematode and destructive types. The beneficial ones control termites, grub worms, and other pests that inhabit the soil and damage your plants.

The destructive ones feed on roots and cause root knots. Researchers are investigating them as a biological control of noxious weeds.


Arthropods are all the hard-shelled organisms, such as ants, sow bugs, spiders and centipedes. Arthropod functions vary widely:

  • Stir and churn the soil.
  • Shred organic matter, which assists other soil organisms, especially microorganisms, in decomposing it.
  • Help distribute beneficial microorganisms in the soil.
  • Help regulate the population of other soil organisms.
  • Improve soil structure and change nutrients into forms available to plants through consumption, digestion, and excretion of organic matter.

Avoid Chemical Fertilizers

Before you decide to dump a chemical dose of NPK fertilizer on your lawns or gardens, remember the soil organisms that are protecting, improving, and, indeed, creating the soil that your plants grow in.

Stick to organic fertilizers, and be sure to read the directions for applying those nutrients.