There is more life below the soil surface than there is above. This includes the burrowing animals such as moles and earthworms. Many soil creatures are not much bigger than the head of a pin. They include mites, springtails, nematodes, virus, algae, bacteria, yeast, actinomyetes, and protozoa. There are about 50 billion microbes in 1 tablespoon of soil. A typical soil may contain the following estimated number of organisms in each gram of soil:

Bacteria 3,000,000 to 500,000,000
Actinnomycetes 1,000,000 to 20,000,000
Fungi 5,000 to 1,000,000
Yeast 1,000 to 1,000,000
Protozoa 1,000 to 500,000
Algae 1,000 to 500,000
Nematodes 10 to 5,000
1 gram of soil is the approximate weight of a standard paper clip.

As soil life forms move through the soil they create channels that improve aeration and drainage. Nematodes and protozoa swim in the film of water around soil particles and feed on bacteria. Mites eat fungi; fungi decompose soil organic matter. The microorganisms' primary role is to break down organic matter to obtain energy. They help release essential nutrients and carbon dioxide, perform key roles in nitrogen fixation, the nitrogen and phosphorus cycles, denitrification, immobilization and mineralization. Microbes must have a constant supply of organic matter or their numbers will decline. Conditions that favor soil life also promotes plant growth.

When the soil is tilled and left bare, soil life can be injured by high temperatures. To promote soil organisms; incorporate organic matter, till as little as possible, minimize soil compaction, maintain favorable soil pH and fertility, and use an organic mulch on the soil surface.


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© Erv Evans, Consumer Horticulturalist
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