Experts say that a teaspoon of healthy soil contains, on average, more than a billion beneficial bacteria, hundreds of yards of fungal hyphae, thousands of protozoa, and a handful of nematodes. Each of these microorganisms, invisible to the naked eye, interacts and overlaps, consuming and excreting, and — in doing so — recycles complex organic materials back into nutrients for plants to absorb. The vastness of life in our soil defies easy quantification and contains no small amount of mystery. In fact, even with the entire scientific apparatus of the modern world at our command, we have documented only a tiny percentage of the functions, interactions, and various capacities of the microbes in our soil.
What we do know, though, is that they are under threat. Conventional farming methods, like tillage, monocropping, and the use of chemical fertilizers and pesticides, have begun to strip our topsoil of these small but vital life forms. Today, more than a third of the U.S. corn belt has lost its microbially rich topsoil. Soil advocates predict that 95% of our farmable soils will be similarly degraded within the next 30 years.
That’s what makes the work of people like Lynn Fang so important. Fang, who self-identifies as a community soil scientist, trained in compost ecology at the University of Vermont and resides in Los Angeles, where she contributes her microbial wisdom to community-based nonprofits like LA Compost and Integrative Development Initiative. In addition, she runs her own soil consulting firm and teaches classes at local community colleges. Fang sat down with The Rooted Journal to chat about why the invisible life forms in our soil are so critical to the food we grow — and to our health.
THE ROOTED JOURNAL How would you explain what compost is to a beginner?
LYNN FANG Compost is the process of decomposition, where your food scraps and organic materials are transformed, by microbes, into soil organic matter, or humus. Compost is a nice soil amendment that can activate the biology in your soil, support nutrient cycling, provide disease suppression, and provide all these other benefits to the soil.
TRJ There are so many outwardly invisible processes involved in compost, which can make it all seem quite mysterious. What do you see under your microscope? What are these microbes at work?
LF Yes, all these invisible creatures! The smallest organism that we think of with compost is bacteria, a single-celled organism and primary decomposer that feeds directly on carbohydrates and compounds in organic waste material. Fungi are another primary decomposer. They can also feed on food waste, but they’re specialized a little more in woody materials, like wood chips or plants. Fungi are known to be more efficient at incorporating those compounds into what is known as “soil organic matter.” Bacteria primarily release secondary nutrients, like carbon dioxide.
TRJ The microbes of the compost pile are so abundant and complex. What else do you see in there? The stuff people have maybe never heard of.
LF Those are our secondary decomposers. We have protozoa, like amoebas; flagellates, which have a long tail; and ciliates, which have tiny hairs around their bodies. Flagellates and ciliates can move very quickly, because they have these hairs and tails to propel them. Some of them can swim. The more amorphously structured ones can extend these little pseudo-feet from their bodies in order to move better. These guys feed primarily on bacteria. Bacteria have more nitrogen than they need, though, so the protozoa, for example, don’t utilize it all. Instead, they poop it out in plant-available form, like ammonia or nitrate.
We also have actinobacteria, which are a kind of hybrid between bacteria and fungi. They’re tiny bacterial cells that link up to form a filament. They’re super common in soil and compost — ubiquitous, even. You’ll see them when you open up your pile. They look like white, ashy stuff. They are working on some of the tougher, more woody plant fibers.
TRJ What about bugs? Compost piles are somewhat famous for housing insects.
LF We do also have microarthropods, which are insects. Even though they’re larger than these other microbes, some of them are hard to see with the naked eye, like mites and springtails. These guys are kind of chomping down on some of the organic material in the pile, helping to break apart those materials, so it’s easier for things like bacteria to colonize them and break them down further. They’re kind of our little chipper-and-grinder mechanisms. They also help to aerate on a micro level, moving things around.
TRJ How do all these microbes make their way into a compost pile?
LF We live in a microbial world. They’re all around us. They’re in our bodies and in the air. They already exist on your food scraps. They’re in the wood chips you build your pile with. All the ingredients we use to build the compost pile, they already have existing microbial communities on them.
One thing I love about manure is that it has a more unique, enriched microbial community in it because of the animal it came from. Animals are culturing vessels for specific types of microbial communities. That’s why manure is known as an “activator” in a compost pile, because of the microbes it imparts.
You’re supposed to layer your greens to browns, your carbon to nitrogen, in a specific ratio, which really allows the most amount of microbes to be introduced. This is an engineered process, based on the natural process of decomposition. But we’re tweaking the variables. On a forest floor, you have leaf litter and some animal droppings, but it’s a much slower decomposition process. With compost, we engineer it to go faster. We activate more microbes. More of them can consume these materials at the ratio we provide.
TRJ How does something so small, like aerobic bacteria, begin to break down something so big, like a piece of food?
LF We zoom in, onto the food. Food is made with cellular structures. Generally, actinobacteria and fungi can help to break through the kind of tough cell wall layer. Then you have different compounds inside your cellular organelles, like proteins and fatty acids. You have different cytoplasmic nutrients and DNA structures — energetic molecules are in there. Once those are released, the bacteria can access all of those things.
We see this, on the macro level, as decomposition. But really, these bacteria are just accessing those organic materials on a much smaller, molecular level.
TRJ How does compost relate to soil health? What does putting compost into your soil do?
LF Compost is a soil amendment. It is very biologically rich. It does help to activate the biology in your soil, although you need good soil structure in order to keep that biology — so you typically need more than just compost to really build soil back from a degraded place.
But there are nutrients in the compost. Compost is typically pretty high in phosphorus; food scraps contribute a lot of potassium, and you also see an abundance of other nutrients, like calcium and magnesium and all those other micronutrients. You go through this metabolic process with the microbes that release micronutrients, beneficial compounds, antioxidants, disease-suppressive properties, and more. All of these things help the soil build structure, which helps it retain more water, sequester more carbon, and — if the microbial community is very good — it can also help suppress diseases, like root rot. Compost can also help break down pollutants like pesticides. A lot of microbes will break down petroleum and hydrocarbons, and they can help sequester heavy metals. That’s not to say that compost is a complete solution for contaminants, but it does help and provide support.
TRJ How do plants and microbes interact in soil?
LF Plants release sugars through their roots. That is directly feeding bacteria, which then attract protozoa and nematodes. And, in addition to releasing nitrogen, these guys are releasing plant-growth-promoting hormones. In a way, the plant is releasing these sugars to cultivate the microbial community around itself that it needs to survive.
Plants also make connections with mycorrhizae. These fungi connect to the plant root directly, where the plant exchanges sugars for other nutrients. Like, maybe the plant needs more phosphorus. The fungi can bring that nutrient in from somewhere else in the soil, where it’s more abundant, and exchange that nutrient with the plant. It can be other nutrients, too. It could be water, as well.
Different types of plants can cultivate different types of microbial communities in the soil. Trees cultivate more fungal relationships, which helps to create more fungal dominance in the soil overall.
TRJ How does this relate to the challenges we now face with conventional agriculture?
LF You should think of soil structure as the home — the habitat — for microbes. If you had a giant tractor tilling up your neighborhood every week, you’d really struggle to rebuild in between and live your life. You don’t have enough time. So, conventional agriculture generally engages in a lot of disruptive practices for microbes, like tillage, synthetic fertilizers, pesticides, and monocropping.
The soil biology then has to expend more energy rebuilding, rather than building on top of what was already there.
People like tilling because it makes the soil soft, it’s easier to germinate things, and it releases a temporary flush of nutrients. So it seems like a good method. But over time, your soil texture and quality will not be able to maintain itself. The biology is not able to sustain, either. And then you end up with compaction.
The use of fertilizers is also a problem. Generally, they’re used to provide an abundance of nutrients to get plants going. The plants can’t use all those nutrients, though. Excess leeches away, which causes all kinds of downstream pollution. It also bypasses the microbiology you need for healthy soil. If nutrients are abundant, the plants don’t develop mycorrhizal relationships. You end up with less mycorrhizae in the soil overall. Pesticides, of course, are going to kill off your soil biology.
So you have all these forces suppressing the ability of your soil to establish itself, and you have to artificially create it instead — which is a lot of work for us to be doing when we could just be helping the soil biology, and then the microbes are doing all the work to create soil structure and nutrient fertility.
