Dirt & Soil, part 1
Dirt & Soil, part 1
What makes the stuff that feeds our plants?
If we think about our conversation about global warming and complex systems, one thing that becomes really apparent is that we need to focus on creating anti-entropic systems, which puts things back into the environment. In this case, more specifically, into the soil. For context, over the last 40 years, we have abandoned about 1/3 of arable land because it has become incapable of hosting plants.1 The UN Global State of Soil Assessment estimates that humanity loses .3% of or global food production capacity each year to soil erosion.2 It’s not a big number, but we’re on track to destroy all of our arable soil once you factor in the growth of human population within the next 75 years. Our traditional farming processes not only destroy the soils quickly, but we are actually making the soil disappear up to half an inch a decade-- and in some extreme examples, soils have been decimated far worse.3 That’s a problem, right? So, we have to do the opposite of that, and rebuild our soils. In order to do that, we need to understand what that means. The first thing we need to understand is what’s in our soil, and what’s in our air, because these are both interconnected.
Primary Mineral Content in Soils
Let’s start with the obvious stuff-- when we go out and buy fertilizer to feed out tomato plants, what is it doing to help our soil? NPK-- those numbers on the front of the bags of fertilizer, if you didn’t know, stand for nitrogen, phosphorus, and potassium. The big one everyone knows is nitrogen, which, conveniently, is about 78% of our atmosphere. And if you’re not green to gardening ,*Zing*, then you know that there are some plants that actually provide nitrogen for you, free of charge. Well, not actually. The plant can’t, but certain plants are able to host certain rhizobial bacteria which can convert the insoluble nitrogen in the air into a soluble form for the plants. The plants provide carbon for the bacteria, which all plants produce in photosynthesis. Carbon is the foundation of how all soil works.
Nitrogen is a crucial element for plants to be able to photosynthesize. Without it, plants will grow slowly, and usually will yellow. Too much nitrogen and you’ll see the plant usually grow thick and bushy, with dark leaves, which will sometimes get thick and leathery. When there’s too much nitrogen, you’ll usually get a poor fruit volume from the plant your growing, which is more common in planter gardening, because in nature, the excess nitrogen will wash away.
Phosphorus, in contrast, is a crucial element for root and fruit development. When there’s not enough phosphorus, you’ll see some purpling in the veins. However, when there’s too much phosphorus, the plant will struggle pulling other nutrients from the soil, causing yellowing leaves and stunted growth. The problem with phosphorus additions to soil is that it will not wash away, and can build up in the soil for years. Further, it can limit the fungi of the soil’s ability to interact with the plant, forcing the plant to struggle even further. It’s definitely the one that you’re better off not adding it if you aren’t positive you need it.
Potassium, the third ‘major’ element is important for cellular functions, pest resistance, and temperature resistance, as well as maintaining the water flow within the plant. Plants tend to try to take up as much potassium as they can store in the spring to have a reserve to handle the ebbs and flows of the summer season’s weather. When potassium levels are low within a plant, many of the green new-growth branches will begin to hollow out as the water pressure is left unchecked, and the leaf tips will turn yellow and sometimes appear burnt. Which, if you think about it, makes sense, since if there’s no water regulation, the water cannot make its way to the very ends of the plant. What’s interesting is that the plant is aware of this deficiency, and sacrifices the lower level leaves first and pushes the resources available to the new growth, which is where the bulk of photosynthesis is happening. Too much potassium blocks the flow of other nutrients, like calcium, magnesium, and nitrogen.
I don’t want to dig too deep into these nutrients, because our end goal isn’t to be feeding our soil in any traditional way, but I wanted to at least cover these three main nutrients, since these are the big 3 fertilizer inputs that we commonly see, and the average backyard gardener is familiar with. These are also the three most common nutrients that are deficient in soils. Not long ago, this was the depth of our understanding of plant science, and that’s part of why we saw the industrial petro-fertilizer complex develop as the soils degraded. But then something weird happened—we had pest issues like never before. Some of it, sure, was due to monocrops lacking diversity around them, but another major factor was the lack of good microbes within the soil. The mutualistic relationship between the plant and the microbes in the soil-- the bacteria, fungi, nemotodes, and micro-anthropods was destroyed and the plant couldn’t defend itself.
Soil Biology
So what makes a healthy soil? Let’s narrow that question down a little further, and that is what makes a healthy biological community in the soil, specifically in regards to conventional soils geared around mainstream crops? Covered soil surface, diversity, decaying organic matter, good soil drainage, and minimal or no soil disturbance. Context matters, though. Healthy biological communities in dunes ecosystems look and require very different things than an oak-hickory forest.
What this is, really, is a nutrient cycle system. The soil food web starts with the sun, which is photosynthesized by plants, capturing carbon in their roots and processing the carbon into sugars. The sugars travel through the roots and the plants essentially trade the sugars through diffusion with the biology of the soil, in what’s called the rhizosphere— where the roots, fungi, and bacteria lives.
These proto-cooperative and mutualist relationships sound awfully familiar right— this sounds like the complex systems we’ve been talking about. We need biology to retain and hold nutrients in the soil, and that’s what bacteria and fungi does within the soil. These bacteria and fungi demand organic matter to survive, and that material is provided by the plants, so the relationship is very much a mutualist one. When the plants release their sugars and other compounds—mostly protein and carbohydrates—into the soil, what are called exudates, the plant releases the compounds related to the specific nutrients they need.4 If they need— say, iron— they release a specific compound which helps the beneficial bacteria or fungi necessary to provide that nutrient in soluble form. So the bacteria and fungi take the exudates from the plant and work the soil to make it more aerobic and accessible for the plants roots, so that the roots can continue to feed them.
However, bacteria and fungi will kill the plant if they are left alone, because a system of checks needs to be in place to keep these from feeding too heavily from the plant. There are bacteria and fungi predators, such as protozoa, beneficial nematodes, and micro-arthropods, who are attracted to the root systems of plants, since that is where the bacteria feed, and eat the bacteria, releasing soluble nutrients for the plant to absorb as well.5 Nitrogen is released as ammonia, phosphorus as phosphate, sulfur as sulphate, calcium as chelated calcium, and so on and so on.6 There are 42 necessary nutrients for plants to grow, possibly more, and the bacteria and fungi can provide all of them, but for them to be successful in providing these nutrients there needs to be a full ecosystem to provide the environment for these organisms to be successful in the soil.7
Anaerobic soils, on the opposite end of the spectrum, releases all of those nutrients, the sulphates, phosphates, and so on, back into the air, killing the nutrients that most plants need to survive and thrive. If too many protozoa, nematodes, and micro-arthropods develop, because they are left unchecked, they will wipe out the fungi and bacteria, creating an anaerobic soil.8 So what keeps these guys in check? That’s where your bugs, spiders, and mites come into play, and the transition into our traditional ‘food web’ as we think of it begins to take hold from the world beneath our feet.
In all this discussion about soil, bacteria, and fungi, there seems to be one thing that we have managed not to bring up yet, and it’s one of the first things folks think of when discussing healthy soils: Worms. And worms do play a huge part of soil health, for better or worse. Worms can move about 1 to 50 tons of soil to the surface per acre each year.9 This process not only helps aerate the soil, but helps soil retain moisture during downpours reducing runoff, and they function as nature’s plow, tilling up subsoil and mixing it with new organic resides. Further, earthworms in particular are surface feeders, which works well when you’re dropping lots of organic matter on the surface of your soil to build the organic material of your topsoil. Studies have show that earthworms are more plentiful under no-till practices, that is farms where the soil isn’t tilled over, than under conventional tillage systems, meaning they are more capable of supporting soil health when you leave the soil alone. Further, many diseases that overwinter on leaves of crops can often although not always be controlled by high earthworm populations because the worms eat the leaves and incorporate the residues deep into the soil.10
All of that said, earthworms are an invasive species in many places, and their capacity to quickly break down leaves and the duff layer on the surface disrupts the natural cycles of forest floors, and is destroying many ecosystems. Worms are a valuable resource in the appropriate spaces.
The simple answer is to not add earthworms to your local ecosystem.11
Complex Soils
Let’s talk about what having this complex system provides. Healthy soil creates complex systems which regulate negative insects for your plants, inhibit disease, and provide structure. Healthy aerobic soils—meaning soils with large amounts of oxygen—in what we call a ‘healthy food web’, not only suppress disease, but help soil reduce water use and in fact even increases the capacity the soil has to retain moisture, helps recycle nutrients within itself, and keep nutrients available for plants when needed, eliminating petrochemical fertilizer use.12 We build soil structure with the help of bacteria, which is the primary agent in this process. Bacteria create what’s called micro-agreggates, which are the smallest structure in our soil, and operate as a glue in the soil.
You know, you’ve seen pictures of people with a handful of soil, and it looks like it’s almost chunky, right? It’s so healthy and dark. You don’t know why, but you know it’s glorious. It’s those micro-agreggates that provide that texture, and the fungi collects these micro-agreggates and using glanolin—which is essentially fungus glue— to develop its network and to create passages for oxygen to stay absorbed within the soil itself. The crazy part of this is that organic matter like this is only up to 5% of the entire soil content and biological organisms only comprise 1% of the total soil content.
Again, it’s important to remember that soil health is a relative term; ecosystems have evolved in places where nutrient access is low, so when we’re talking about healthy soils, we are talking about the soils we want to build for a specific purpose— in this case, to grow conventional food. I keep bringing the relativity up because it’s important to understand that what we consider good soil is often a reflection of very specific ecosystems where agriculture has thrive, which is often at river deltas and lower valleys. These ‘healthy’ soils are invaluable to human survival, but really they are simply another form of soil that in many environments would actually be detrimental to the survival of native species.
To build this type of healthy soil, we need to know where we start. This requires doing a soil test or doing some kind of approximation to figure out what condition the soil is, which we can do with a relatively inexpensive microscope as cheap as a hundred to a few hundred dollars. Temperatures of the soil significantly impacts what species of bacteria, fungi, nematodes, and so on are actively living in your soil at any given moment. A tablespoon of soil has 75,000 different species of bacteria—it’s impossible to wrap your head around the amount of diversity within our soil and its microbiology. And we know almost nothing about these species, because we cannot recreate them in a lab. We have documented about 30,000 different types of bacteria, despite knowing about so many more.13
Do you want to know the health of your soil, of your compost, or maybe even of your pond? Sure, you could send off a sample somewhere, and it will be helpful to know, but as you probably already know—your property isn’t homogenous. There are dry areas, wet areas, sunny areas and shaded areas, all that are impacted by the plants and dirt of those spots. Well, you could buy a microscope and figure out what’s in your soil on your own. Sure, you’re not a scientist; neither am I. But, if you’re thinking about a long-term investment in your soil, this is one great place to start. With a microscope, you will be able to tell the health of a soil through the micro-organisms that exist within it.
When you look at a nemotoad, how do you know whether or not it’s beneficial? You can tell by whether it has a horn to puncture fungi roots.
Horns are bad for your fungi. Root-eating nemotodes only exist within anaerobic soils, so you know when you see these giant horned nemotodes, you’ve got problems. If you see other types of nemotodes, such as ciliates, in the soil, you’ve got anaerobic soil.
If you see evidence of a honey/tan material in your sample, you’re seeing what’s called fulvic acid, which is decomposed plant material that’s been broken down and stored by fungi. Any dark brown material you might see is humic acids, which, much like fulvic acid, is decomposed nutrients from plants that are readily available for plants and fungi. This stuff can be stored for hundreds of years. So if you’re seeing this, but still have evidence of bad nemotodes, then you know your soil was healthy, but now isn’t, you now understand the history of your soil sample. And you can do this across your property, an unlimited amount of times, and you can use this process to trial and error different solutions to figure out if you’re helping or hurting your soil, instead of just saying, “well, I guess my tomato plants grew better this year. I don’t know if it was what I did to the soil, or the temperature, or the sun, or any other of the million things that can impact plant growth.”
There’s a bunch of different things to look for under a microscope, and I’m not here to teach you how to use one, because that’s ridiculous. But, for a lot of folks, including myself, who think things like microscopes aren’t for me, I’m not a science guy-- I’m a woods guy. I’m the Joe six-pack of science. That doesn’t mean that something like a biology is not accessible to us, too. You can pick up a microscope that can look at bacteria, at 1000x, for less than $150. One soil sample will probably cost you a few bucks. So for the cost of repeated soil samples, you’re saving money.
But, if you can’t, or simply aren’t that invested in your soil at this point and time, you are absolutely better off doing a traditional soil test than just eyeballing it, especially if you’re a first-time gardener. Most states have extension schools which offer testing for free or a menial amount—the only catch is that they are designed to support small grain farmers, and their focus is on helping them maximize profits, which often means they aren’t going to recommend you plant cover crops for increased nitrogen, for example, but will just tell you what kind of fertilizer you need to use and usually a very high amount to meet those high demands, so chances are you’ll have to do some translation of their recommendations.
If it is your first time doing a soil sample, you’ll want to do different samples in different areas of your garden that you expect to have different results-- near a drainage ditch is likely going to yield different results than the area next to your pool, for example, and try to get results for areas used in different ways-- so if you have an old farm where there was corn grown, and another area where there were cows, test those spots.. If you want the best results possible, you’ll want to try to use a trowel to dig straight down in a spot 4-6 inches—or to the depth of the roots for most grasses and annuals, and filter out the rocks and sticks. Mix up the soil so that the topsoil is mixed with what was down 6 inches, and take a small amount from that to send in—usually your soil sample size will be fairly small, and that’s why you need to be are to mix it well.
In the next section, we’ll be diving further into the foundations of our soil and what exactly bacteria and fungi do to build our soils for specific plants.
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