CFAES Give Today
OSU Extension

College of Food, Agricultural, and Environmental Sciences

January 20, 2015 - 1:15pm --

An entire world exists in the soil of your garden.  There are creatures you can see, such as earthworms and insects, but much of this world is made up of microscopic organisms.  They are tiny, but exist in vast numbers; a pinch of soil can contain millions of organisms.  We are dependent on this unseen world to support the plant, and ultimately animal life on earth.

Let us start with the smallest creatures, the tiny one celled bacteria, some of which are so small they can only be seen with an electron microscope.  Until very recently it was impossible to grow over 90% of these organisms in the laboratory, so studying them was very difficult.  The bacteria in the soil primarily live around plant roots, consuming organic matter in the soil and converting nitrogen and vital minerals into forms the plants can absorb.  Bacteria are important in the release of carbon from dead plant material.  One group of bacteria, the actinomycetes are responsible for the distinctive smell of freshly turned over soil.  Bacteria thrive when soil is tilled because this increases the amount of oxygen and allows them to digest more organic material, but in the long term their growth spurt reduces the soil organic matter and in a very few years the soil becomes much less fertile and requires the addition of nitrogen and other nutrients for good crop yields. 

Another group of much larger one celled organisms are protozoa.  Although they must be in water in order to move around, there is enough water even in desert soil for them to survive.  Protozoa also live primarily near plant roots and most of them live by eating bacteria and in the process releasing nitrogen the plants need to grow and survive. 

Fungi are extremely important to healthy plants and soil.  One large group of fungi, the mycorrhizal fungi, grow either around or within plant roots forming a mass of cells that greatly increases the reach of the plant roots making them more efficient.  Some species grow to the surface and form mushrooms.   Fungi are much better at utilizing the hard to digest portions of dead plants and are very important in the conversion of organic matter to substances plants can utilize.  Fungi, using sugars formed by the plant roots, also create the tiny macro-aggregates of soil which make soil light and crumbly and allow water and air to move through the soil.  When macro-aggregates are reduced compaction results.  Fungi are sensitive to disruptions of the soil community and are reduced in soil that is disturbed by tilling. 

Finally, we get to the organisms that are often big enough to see, the arthropods and earthworms.  Members of both groups shred and eat dead and dying plant material turning it into small digestible particles for the bacteria and fungi to utilize.  They also move through the soil stirring it up and moving nutrients from the surface toward the plant roots.  Since the bacterial colonies around plant roots do not travel, they depend on these creatures to bring nutrients to them.  While moving through the soil, these larger organisms create space for the travel of water through the ground.  Some of them are very important in moving seeds; trilliums for example depend on ants to disperse their seeds.

The makeup of this invisible world changes depending upon the climate and the types of plants that grow in the soil.  Grasslands are different from hard wood forests; northern pine forests have different communities than tropical forests.  Human disturbance of the soil often decreases the health of soil communities and the rise of no-till agriculture is recognition of the importance of a healthy diverse soil community to successful crop yields.    

For more information on home, lawn, indoor, or outdoor garden care and tips, as well as other garden topics, visit and click on the Yard and Garden link, or call the OSU Extension, Butler County, at (513) 887-3722, or in Middletown at (513) 424-5351, ext. #3722.

News Release provided by Kathy Maurer