I thought I'd better write a quick blurb about the soil food web for those who aren't familiar with the term.
When people talk about soil food webs, they're referring to the (mostly tiny) inhabitants of the soil, and more specifically, the complex relationships between them (hence the word "web").
Here, I'm writing about the tiny soil organisms - the microorganisms. It turns out they have some very important jobs. They basically make the soil and maintain it. They transform the minerals and organic matter in the soil into something that can support an abundance of life. They rearrange soil particles to create good soil structure.
Some of them pull nitrogen out of the air and change it into a form that they, and plants, can use. Some bring nutrients directly to plants in exchange for food from those same plants. They also work to protect plants from plant-feeding predators, both in the soil and above ground.
Mycorrhizal fungi inside a plant root. Source.
What Do They Need?
Some microbes breathe air, just like us. They’re called aerobic microbes. Other microbes die in the presence of gaseous oxygen, so they live in places where there is none, such as deeper in the soil. They’re called anaerobic microbes, or anaerobes. Others switch between oxygen and other methods.
Microbes need water, some more than others. Some microbes need light. In fact, some of them photosynthesize like plants. They all function best in their own specific temperature range. So, just like our plants, they need air, water, certain temperatures and sometimes even light. Let's look at the 3 groups, or "kingdoms":
Bacteria
Bacteria are the tiniest members of the soil food web. They are single-celled organisms - they each have just one cell. There are hundreds of millions of them in a gram of healthy compost, even a billion. Bacteria occupy the majority of the leaf and root surfaces of a plant. They break down simple substances and toxins and aggregate the basic building blocks of the soil.
Fungi
Fungi are another vital life form in the soil food web. They may be single-celled (such as the yeast that makes your bread, yogurt, wine and beer), or they may have billions of cells (like in a mushroom). A mushroom is the fruit of certain types of fungi, but the majority of those fungi’s biomass is actually underground, winding through the soil kind of like a microscopic root.
They eat complex organic materials that most other living things can’t easily digest (such as lignin), and they harvest minerals from rocks that are virtually inaccessible to other organisms until released by the fungi (such as phosphorus). Like bacteria, fungi get food in the form of carbohydrates from the plants in exchange for their services.
Protozoa
Protists are the outcasts in the soil food web, whose main distinguishing feature seems to be what they aren’t - they’re neither bacteria nor fungi nor animals nor plants. A protozoan can eat 10,000 bacteria in a day. During this process, nitrogen is converted to ammonium, upon which many of your plants will happily dine.
We say that bacteria and fungi immobilize nutrients by storing them in their bodies, and then protists (along with other microbes, plants and animals) mineralize these nutrients - meaning they make them available again.
Why Does This Matter?
If we use toxic chemical fertilizers or pesticides, or withhold water from the landscape (that includes drip irrigation), or do a lot of deep rototilling or other soil disturbance, many of these soil workers probably won’t be around for very long.
And we desperately want them around, or our garden becomes a desert (literally).
Of course, many plants and animals are part of this food web, too, and I'll write about them next week. Here, I just want to make sure we're all on the same page with the knowledge that it's very important to take care of our soil food webs. For now, I'm interested in learning what you're doing to cultivate a healthy soil food web.
I give plenty of tips on how to do just that in the academy, but I really want to hear about what you're doing. Let me know below.
