|With a quick glance, you’d overlook it all. The measure of soil health is soil life, and to see that, you’ll need a microscope. These organisms are so small that a single teaspoon of healthy soil can hold MORE THAN 4 BILLION microbes. And that is just the beginning of the vast diversity of soil microorganisms- we’re talking about earthworms, beetles, mites, and a long list of organisms that are microscopic: bacteria, fungi, nematodes, and others. Did you ever think the health of a big leaf maple tree depended on these teeny organisms?
Each of these organisms is a specialist and therefore plays a critical role in the soil food web, eating, digesting, and pooping their way through the soil. Some of the combined effects of these communities are:
- nutrient cycling
- nutrient retention
- soil structure
- water infiltration and water holding capacity
- disease suppression
- degradation of pollutants
- improved soil structure
While there is an incredible diversity in the variety and niches of these soil organisms, here’s a short list that explains what happens below the surface of the soil, that we depend on everyday.
Bacteria are among the smallest of the soil organisms, and can be found in quantities of up to 100,000,000,000 per gram of soil! Bacteria help convert atmospheric nitrogen into a solid form, can break down woody material, and are necessary for making stable phosphorous into a form accessible by plants.
Fungi can form threads 1/60th the diameter of a root hair. They are commonly known for decomposing wood (mushrooms), but they have many other functions. Fungi can grow into plant roots, and form a symbiotic relationship with the plants, helping transfer more water and food to the host plant. In this give-and-take process, they secrete a sticky substance that helps soil bond together into larger clumps, called aggregates. This clumping effect of soil creates necessary passages for air, water and larger organisms to move through. Also important is that fungi are active even at low soil pH, when not all microorganisms are, something we often struggle with here in the PNW.
Nematodes are sometimes known for their predatory nature towards plants, but most nematodes are actually beneficial. They’re important for consuming and cycling bacteria and digesting Nitrogen into a plant available form. Being of an intermediate size, they feed on bacteria and fungi, and are food to other soil insects.
What earthworms eat, they leave behind in a form that is easy to use by plants, along with the bacteria and digestive enzymes. As the larger organisms in soil, they are much more mobile and integrate their food (plant debris) into deeper layers of the soil, providing a natural form of what we think of as tillage.
All of these microorganisms are most abundant near the root zones of plants, another reason we encourage watering practices that expand and deepen the root zones of plants.
Soil Food Web Illustration