The Soil Food Web: Life Beneath Our Feet

Author(s): 
Jefferson Edward
Soil Food Web
The Soil Food Web

Walking through a healthy forest is a sensual experience for me. I use my body to see, smell, hear, touch and even taste to fully experience flora and fauna of the bioregion I'm visiting. It all seems so balanced, and it is always hard not to think there was a sort of "guiding hand" behind it all. At the very least it has never felt like space where all of the different species compete for a limited amount of resources with survival going to the strongest, as the school tale goes.

In what appears to be a weird twist of the Hermetic axiom, “As Above, So Below,” just under the surface of the dirt beneath our feet, is a plethora of life consisting of bacteria, algae, fungi, and protozoa, nematodes, micro-arthropods, and earthworms; working together to provide a variety of services for the forest and make up what soil scientists are now calling the Soil Food Web. As these organisms eat, reproduce and wriggle through the soil they support plant health through:

• Decomposition of organic matter

• Nutrient cycling (for example, some bacteria absorb (called fixing) Nitrogen from the atmosphere and then release it, through a complex myriad of symbiotic relationships, to the roots of the plants).

• Enhance soil structure and porosity, in turn increasing soil tilth and allowing the infiltration of water, which decreases runoff of water, nutrients, and pollutants.

• Control organisms pathological to plant

When considering the soil food web, it helps to see soil as a vast community of organisms and how each of them eat, excrete and, in turn, are dinner for something else. Through the exudation of a wide variety of compounds, roots regulate the soil microbial community in their immediate vicinity encouraging the development of beneficial symbioses.

As earthworms move through the soil, they leave a trail of excrement, (called castings), filled with bacteria, fungi and raw materials that have been pulverized by the gut of the worm. Plant roots looking for the path of least resistance, occupy the hole provided by the red wigglers. Surrounded by colonies of macrobiotic life, the roots release compounds secreted by plant roots, broadly referred to as root exudates.

Bacteria and fungi feed on root exudes full of simple sugars and plant residues left in the soil and in the process break them down and capture the nutrients (e.g. nitrogen, calcium, iron, potassium, phosphorus, etc.) in their bodies; their bodies are glued and bound to soil particles, preventing them from being lost through leaching. The nutrients bound in the bacteria and fungi are not available to plants until protozoa, nematodes, small microarthropods, and earthworms consume the bacteria and fungi. 

It’s a basic principle of ecological stoichiometry that organisms assimilate carbon and nitrogen from their diet in roughly the same proportions as their tissues contain these elements. Any excess nitrogen is excreted back into the environment. All higher organisms including most of the soil organisms have a Carbon/Nitrogen ratio of 30:1; however organisms at the bottom of the soil food web—bacteria and fungi—have proportionally more nitrogen. Bacteria have a C:N ratio of 5:1—they’re 20% protein and have more nitrogen than any other organisms. When a higher organism eats a bacterium, the excess nitrogen is released back into the environment in plant-available form, in essence, they represent billions of microscopic bags of fertilizer around your vegetable roots.

It is the soil food web that keeps everything in balance. Nutrients are released as needed to feed the plants, and when the plants are finished for the year they drop their leaves and feed the soil food web. Nothing is wasted, nothing lost. When you combine this with experiments that show the forest species "talk" to one and other through the mycelial network if you will pardon the pun, but we have only begun to scratch the surface. Stay tuned to further posts about the soil food web, its inhabitants and how you can use this knowledge to allow nature to go to work for you.

Walking through a healthy forest is a sensual experience for me.  I use my body to see, smell, hear, touch and even taste to fully experience flora and fauna of the bioregion I'm visiting.  It all seems so balanced, and it is always hard not to think there was a sort of "guiding hand" behind it all.  At the very least it has never felt like space where all of the different species compete for a limited amount of resources with survival going to the strongest, as the school tale goes.

In what appears to be a weird twist of the Hermetic axiom, “As Above, So Below,” just under the surface of the dirt beneath our feet, is a plethora of life consisting of bacteria, algae, fungi, and protozoa, nematodes, micro-arthropods, and earthworms; working together to provide a variety of services for the forest and make up what soil scientists are now calling the Soil Food Web. As these organisms eat, reproduce and wriggle through the soil they support plant health through:

•    Decomposition of organic matter

•    Nutrient cycling (for example, some bacteria absorb (called fixing) Nitrogen from the atmosphere and then release it, through a complex myriad of symbiotic relationships, to the roots of the plants).

•    Enhance soil structure and porosity, in turn increasing soil tilth and allowing the infiltration of water, which decreases runoff of water, nutrients, and pollutants.

•    Control organisms pathological to plant

When considering the soil food web, it helps to see soil as a vast community of organisms and how each of them eat, excrete and, in turn, are dinner for something else. Through the exudation of a wide variety of compounds, roots regulate the soil microbial community in their immediate vicinity encouraging the development of beneficial symbioses.

As earthworms move through the soil, they leave a trail of excrement, (called castings), filled with bacteria, fungi and raw materials that have been pulverized by the gut of the worm.  Plant roots looking for the path of least resistance, occupy the hole provided by the red wigglers. Surrounded by colonies of macrobiotic life, the roots release compounds secreted by plant roots, broadly referred to as root exudates.

Bacteria and fungi feed on root exudes full of simple sugars and plant residues left in the soil and in the process break them down and capture the nutrients (e.g. nitrogen, calcium, iron, potassium, phosphorus, etc.) in their bodies;  their bodies are glued and bound to soil particles, preventing them from being lost through leaching.  The nutrients bound in the bacteria and fungi are not available to plants until protozoa, nematodes, small microarthropods, and earthworms consume the bacteria and fungi. 

It’s a basic principle of ecological stoichiometry that organisms assimilate carbon and nitrogen from their diet in roughly the same proportions as their tissues contain these elements. Any excess nitrogen is excreted back into the environment.  All higher organisms including most of the soil organisms have a Carbon/Nitrogen ratio of 30:1; however organisms at the bottom of the soil food web—bacteria and fungi—have proportionally more nitrogen. Bacteria have a C:N ratio of 5:1—they’re 20% protein and have more nitrogen than any other organisms. When a higher organism eats a bacterium, the excess nitrogen is released back into the environment in plant-available form, in essence, they represent billions of microscopic bags of fertilizer around your vegetable roots.

It is the soil food web that keeps everything in balance.  Nutrients are released as needed to feed the plants, and when the plants are finished for the year they drop their leaves and feed the soil food web.  Nothing is wasted, nothing lost.  When you combine this with experiments that show the forest species "talk" to one and other through the mycelial network if you will pardon the pun, but we have only begun to scratch the surface.  Stay tuned to further posts about the soil food web, its inhabitants and how you can use this knowledge to allow nature to go to work for you.

About the Author:

Jefferson Edward is a student of all living systems, budding herbalist and simple living coach.

Edition: 
June 1, 2017