Soil Food Web » Compost Santo

About the Soil Food Web

Soil contains one of the most diverse habitats on earth. A single teaspoon of soil may contain millions of individual organisms and tens of thousands of species of microbes: bacteria, fungi, protozoa, nematodes, arthropods … on up to earthworms, ants, spiders, and voles.

Soil Food Web Diagram. Click image to enlarge.

The more biodiversity contained within the soil, the healthier and more resilient the plants (and the animals that eat the plants) will be. Unfortunately, modern agricultural practices have abused our soil to the point where it can no longer support or sustain a healthy and diverse array of soil “critters”. Compost can return the nutrients absent in a lifeless soil, and support the organisms which will continue to build the soil for years to come.

Bacteria & Fungi

Bacteria and fungi form the base of the soil food web. They decompose plant and animal matter, absorb nutrients into their bodies, and eventually become food for other predatory organisms.

Image of bacteria and fungi — Bacteria, digital magnification (left), and a strand of beneficial fungi (right). Click image to enlarge.

Ninety percent of all plants on earth depend on a mutualistic relationship with beneficial fungi. Beneficial fungi protect plants from disease and help the plant absorb water and nutrients; in return, plants feed the fungi (and other soil organisms) foods they produce from photosynthesis.

Protozoa

Image of a dividing ciliate and a testate amoebae — Ciliates dividing (left), and a large testate ameba (right). Click image to enlarge.

Next up in the food chain, protozoa are single-celled organisms that tend to feed on bacteria or fungi. Protozoa have huge appetites. It’s estimated that a single protozoan can consume 10,000 bacteria and release 8,000 molecules of plant-available nitrogen per day! (E. Ingham, Life in the Soil Lecture).

Nematodes and Arthropods

Higher level predators consume bacteria, fungi, and protozoa and are an important component of nutrient cycling. Nutrients released by microbes when they excrete wastes, or die, then become available to plants.

Image of microarthropod and nematode — Soil-dwelling microarthropod (left), and a bacterial feeding nematode (right). Click image to enlarge.

Earthworms

Earthworm tunnels direct air and water down through the soil and they leave deposits of nutrients and microorganisms in the form of castings. Their gut and outer slime layers kill pathogenic organisms, so earthworms cleanse the soil as they move through it.

Disease Causing Organisms

If soil becomes unhealthy – usually due to toxic, compacted, or anaerobic conditions – beneficial microbes die off, allowing the disease-causing organisms to outcompete, multiply and damage plants. When organisms like ciliates, root-feeding nematodes, mildews or pathogenic fungi exist in high numbers, they indicate that something is out of balance in the soil food web system. Compost can help restore life in unhealthy soil.