The Soil Food Web

“It’s not the soil itself – it’s the soil life that is the most important element.” Geoff Lawton

A World of Microorganisms: The Soil Food Web

Microorganisms in the soil food web make up a living, thriving community. This community includes a wide range of microorganisms, seen and unseen, that grow, eat, reproduce, live and die. It is a busy little world bustling right beneath our feet.

A Busy Community

Because you don’t notice them, you may think they are unimportant. However, this little community makes it possible for us to have clean air and water as well as healthy plants. Within this community live tiny creatures with big jobs to do.

Tiny one-celled creatures such as bacteria, algae, fungi, and protozoa that are too small to see, arthropods, and larger creatures such as earthworms and insects help to break down waste and organic matter from plants and animals. They break down nitrogen and other materials that could become pollutants in our water. They fix nitrogen from the atmosphere so plants can utilize it. The also protect plants from pests that damage crops. In a nutshell, they make the environment as a whole a healthier place for everyone without us even noticing it! And this is just a small sample of what these organisms do.


There are thousands of kinds of bacteria in a spoonful of soil and those bacteria have many jobs. Depending on the type, bacteria may help add organic material to the soil, inhibit organisms that cause disease and protect plant roots from disease which enhances plant growth.

One of the most important jobs of bacteria is the fixing of nitrogen in the soil. Nitrogen is an essential nutrient for plants but it isn’t found in high enough concentrations in the soil. The air, on the other hand, is about 80 percent nitrogen, but that does little to help the plants.

Nitrogen-fixing bacteria take the nitrogen from the air and concentrate it into the roots of certain plants in growths called nodules. There it is converted into a form of nitrogen that the plants can use. If you were to cut open one of these nodules, it would look red inside. That is because of an oxygen scavenging molecule called leghaemoglobin that is only found in these nodules. It serves a similar function that hemoglobin does in our blood, scavenging oxygen to protect the nitrogen-fixing enzyme nitrogenase, which in activated by oxygen.

When the plant and roots decompose, the nitrogen is left in the soil for future plants. Thus the soil is enriched by the bacteria for future generations of plants.


Fungi don’t sound very appealing, but they play an important role in the soil food web. Fungi excrete humus by consuming organic matter. This is why the forest floor is so dark and rich. Leaves and fallen branches are broken down naturally by a fine web of fungi that effectively cleans up what has fallen and turns it into beautiful soil teeming with nutrients.

Fungi are important in soil’s ability to absorb and retain water thanks to fine threads called hyphe that bind soil particles together. Hyphe also release enzymes that break down nutrient molecules, allowing them to be reabsorbed.


Protozoa are similar to bacteria in that they add nitrogen into the soil in a form that plants can use. They also have the job of eating bad bacteria that can cause disease. Being single-celled organisms, they are certainly not at the top of the food chain, however. Protozoa are also food for nematodes, and when they are excreted they become part of the nitrogen and other nutrients in the soil that plants need.


Some types of nematodes can cause problems in the soil, but the good news is that beneficial nematodes think of the bad ones as food. Beneficial nematodes also feed on protozoa, bacteria and other microorganisms. Their waste provides nutrients vital for healthy root growth in plants.



Arthropods are the creepy-crawlies of the soil food web. They can consist of creatures as small as mites to sow bugs, centipedes, spiders, ants, and more. Often these are the critters you think you want to get rid of in your garden, but the fact is, if you see lots of them, you have a robust, healthy garden. Bugs are good!

Arthropods play many different roles in your soil. There are shredders, predators, herbivores and fungal feeders, and all are important for a balanced food web. They keep each other in check and help break down debris, making it easier for other microorganisms to continue the process of breaking down organic materials. They also excrete nutrients in forms that are more easily used by plants.

Soil is bursting with life! You may never look at it the same way again.