What Are Soil Microorganisms?

soil microorganisms
One of the most important part of gardening.

Soil is alive!

MICROORGANISMS We find that more life is living below the surface than above in most environments. Soil are put into six groups: earthworms, nematodes, arthropods, bacteria, fungi, and protozoa with each having their own function. They do play an important role in plant health and water. The cycle of nutrients going thru our environment are mainly driven by these microorganisms. They maintain:

1. Decomposition

2. Mineralization

3. Nitrogen cycling

4. Storage and release of nutrients

5. Carbon cycling

6. Take the pollutants out of the water before it reaches underground or surface water.

The Location, Living Conditions, And Functions Of Microorganisms


Effective microorganism, they are responsible for distinctive scent of freshly exposed, moist soil. Prefer neutral to alkaline soils; high oxygen requirement; prevalent in dry regions. They release carbon, nitrogen, and ammonia during decomposition of organic matter. They help form humus. Associate with non-leguminous plants like bitterbrush to fix nitrogen and make it available to other plants in the area. Some nitrogen may be unusable without the bacteria converting it to a form that can be used.


Microorganisms found all over the world and even found down in the earth as far as 1 mile. It thrives under most conditions but found near plant roots, an important food source. Feeds on organic matter; encourage organic and inorganic chemical reactions that affect plant growth; and fix nitrogen from air in soil.

Earthworms are the reason for a huge industry today. People are raising & selling earthworms all over the world, especially wholesale earthworms. The work of the earthworms in the soil is what earthworms eat. Producing castings that are equivalent to compost as an organic fertilizer and soil supplement.


Basically 2 types of fungi- mycorrhizal and normal. Fungi thrive in well-drained, neutral to acidic, aerated soils. Normal fungi help decompose the organic matter in litter and soil but play less of an overall role. Mycorrhizal fungi help develop healthy root systems by growing on plant roots. The fungus is actually a network of filaments that grow in and around the plant root cells, forming a mass that extends considerably beyond the plant�s root system. This essentially extends the plant�s reach to water and nutrients, allowing it to utilize more of the soil�s resources.


MIcroorganisms exist in almost all moist soils. There are both beneficial and destructive microorganisms types. The beneficial control termites, grubworms, and other soil inhabiting pests. The destructive ones feed on roots and cause root knots. In dry spells they are dormant and with moisture in the soil they are active. They are being looked at for their biological control of noxious weeds.


These microorganisms are present in almost all soils. They feed on bacteria and other protozoa. Classified into 3 types based on their mobility: Amoebae, Flagellates, and Ciliates. There are both good and bad protozoa, just like everything else I guess. Good protozoa feed on bacteria and release nitrogen and other nutrients to the soil. Since they live in and around roots the plants benefit from this supply of food.


Bugs-like insects(ants), crustaceans(sowbugs), arachids(spiders), and myriapods(centipedes). Their functions vary widely:

  • Stir and churn the soil
  • Shred organic matter so to assist other microorganisms in the decomposition.
  • Help distribute beneficial microorganism in the soil.
  • Through consumption, digestion, and excretion of organic matter, arthropods help improve soil structure and change nutrients into forms available to plants.
  • Help regulate the population of other microorganisms.


Common organisms found in 1 gram(1/5th teaspoon) of soil:

  • bacteria- 3,000,000 to 500,000,000
  • actinomycetes-1,000,000 to 20,000,000
  • fungi- 5,000 to 1,000,000
  • protozoa- 1,000 to 500,000
  • nematodes-10 to 5,000

“Every time you take a step in a mature Oregon forest, your foot is being supported on the backs of 16,000 invertebrates held up by an average total of 120,000 legs.” -Dr. Andrew Moldenke, Oregon State University.

Soil Microorganisms Facts

  • A cup of soil can have the equivalent population of bacteria to people on earth.
  • The bacteria in one acre of soil can weigh as much as a cow or even two.
  • Bacteria and actinomycetes make up half of soil biomass, they are small and numerous.
  • On a farm, soil may have yards of fungi available, but in a forest there may be miles of fungi.
  • Practices of no-till farming and crop rotations are rebuilding the stock of soil organic matter.
  • On a 2 acre plot of land of wheat, it can have more than 30,000 miles of roots which is greater than the circumference of the Earth.
  • Within an hour the air in the upper 8 inches of well drained soil is completely renewed.
  • If you dug up a spade full of rich garden soil it would have more species of organisms than can be found in the entire Amazon rain forest above ground.

“We know more about the movement of celestial bodies than about the soil underfoot.” -Leonardo Da Vinci, circa 1500s.

Can you guess what will happen to these essential microorganisms if we keep adding chemicals?

Leave a Comment