Soil Nutrition

I have already talked about soil as a living organism, one that needs to eat. But what do we feed the soil? What does a healthy diet look like for a soil ecosystem? In a natural setting, the organisms don’t really travel around all that much, so the soil gathers what falls to it and runs the most efficient recycling program possible. But in a system managed by people, we choose what to feed it.

Let's start with human nutrition. I know the old food pyramid is a bit out of date, but it is a great place to start. At the bottom of the pyramid is the bulk of the foods to eat, the breads and cereal group. These are the calorie dense foods and are important for the daily energy needs. Just above that are fruits and vegetables. These are the nutrient dense foods and make sure the body has all the nutrients it needs to properly rebuild itself. Next up are the meats and dairy groups. These are primary sources of protein, the material needed by the body to build more tissue and grow. At the top of the pyramid are the sweets. These are the junk foods that should be eaten sparingly. Each of these has a corresponding source in soil nutrition.

First of all, there are the carbohydrates. Carbohydrates give the energy needed to grow. In soil, just as in human nutrition, the more complex the carbohydrates, the better. In human nutrition, the bottom tier are simple carbohydrates like refined flour and sugars. Then there are more complex carbohydrates, like whole wheat. The more complex, the longer it takes for your body to digest them, and the longer the energy spike is spread out. Simple carbohydrates give a lot of available energy quickly, often followed by a crash, while complex carbohydrates give sustained energy for hours. In soil, though, there is an even more complex carbohydrate that is unavailable to humans for energy: wood. The cellulose in wood, which is indigestible to us, is actually just chained together sugar molecules. It takes some special enzymes to break those chains, but for those organisms that can, there is a lot of energy available. Fungus, particularly those that produce mushrooms, are quite good at this. Like the very complex carbohydrates they are, those woods take a very long time to break down, often years, but in the process they provide the soil organisms a sustained source of energy.

Then you have the nutrient dense foods. This one needs to be looked at a little differently. Yes, fruits and vegetables are good for the soil, but more in the form of compost. Compost adds a huge amount of nutrients to the soil. All that broken down plant matter once contained the nutrients the original plant needed to grow and survive. But compost isn't the only source of nutrients. Soil is pretty good at breaking down stone as well, though it does it very slowly. One thing that the most fertile soils in the world have in common is lots of mechanically weathered stone. During the last ice age, the glaciers over Canada ground up stone into a fine powder and deposited them in what is now the American Midwest. The soil there is incredibly fertile mostly because of that stone. Chemically weathered stone has lost most of its nutrients in the weathering process, but mechanically ground stone still has the nutrients intact and the mushroom mycelium in the soil, often the mycorrhizal mushrooms, will mine it out to give to the plants. As for sources, rocks with colors are typically better. Greensand and rock phosphate are great sources. Granite dust would be good as well.

Next up are the protein sources. Plants really are the original source of protein, but there is one caveat. Chlorophyll combines carbon dioxide and water to make sugar and oxygen. Plants have the ability to produce huge amounts of sugar, and have learned to be very versatile with how they use it. They use it as bribes to animals in the form of fruit and nectar. They chain it together to make wood, they use it as a bribe to the mycorrhizal fungus. But there is only so far the one tool can go, and it can't make protein. Protein is made from chained up amino acids and each of those have nitrogen molecules. While we swim in an atmosphere made of nearly 80 percent nitrogen, it isn't accessible in that form. It has to be converted to nitrate to be usable by plants. If they get the nitrate they need, they will make all kinds of protein, and usually grow a lot in the process. So how do we give the plants nitrogen? There are several ways. Compost again is a great source. Animal waste is another great source, with waste products of herbivores, like rabbits and llamas, being preferred. Nitrogen fixing bacteria are also great, often in the form of the relationship they create with certain plants, like beans, peas, and clover.

The last group is the sugar group, that which gives a quick burst of energy followed by a crash. In people, this should be used sparingly, or, better yet, not at all. In plants, synthetic fertilizers fall nicely into this group. Synthetic fertilizers give a large burst of readily accessible nutrients. In the short run, they are immediately usable by the plants, resulting in a quick burst of growth. In the long run, they aren't really healthy for the plant, but also stimulate soil bacteria and help deplete the natural reserves of humus in the soil. So extended use of synthetic fertilizers is bad for the soil and the plants and is not advised. Instead, give your soil a lovely diet of healthy organic matter and lots of it!

The Most Important Concept

Let’s say you discovered a concept. This isn’t even a new concept, just one new to you. And let’s say it caught your eye, changed your worldview, and occupied your thoughts for some time. And let’s say that through that thinking process you discovered that this is the most important concept that there is, that without this, life on Earth would cease to exist. Then you look around and see that despite this concept being fairly well understood in the scientific community, almost no one else understands it. And not understanding it is driving people’s actions in a way that is causing a huge amount of long term harm. What would you do? Would you harp on it quite a bit? Me too.

So what is this concept? Quite simply: Soil is a living organism.

Okay…that doesn’t seem so ground breaking. But let’s take a moment to examine this, maybe look at it from a slightly different angle that might clarify things. You are a living organism. You are composed of a tight association of smaller organisms that all have the same DNA. Each organism has a job, a purpose, to help the whole system function optimally.

Soil is composed of a tight association of smaller organisms that all have different DNA. Each organism has a job, a purpose, to help the whole system function optimally.

Let’s take the biological approach. To understand an organism, you need to understand its food source, how it acquires its food, and the role it occupies in the ecosystem it occupies. Let’s deal with those one at a time.

What is soil’s food source? Well, nothing, you might say. The different organisms eat each other. Well, yeah, sort of. But what happens to an animal when you stop giving it food. It begins consuming its own body, losing weight in the process. As it loses weight, it loses functionality, until the whole system is no longer able to function and it perishes. Our soils worldwide are doing exactly this. Soil feeds on decaying organic matter. Wood, roots, leaves, and sticks form the bulk of soil’s diet, but dead insects, rotting mushrooms, and feces provide sustenance as well.

How does soil acquire its food? In a natural ecosystem, it falls to the ground from the vegetation growing above. It doesn’t matter whether it is a forest or a grassland or something in between. Everything dies eventually and gravity delivers it to the soil to be consumed.

That little pile of mostly decomposed vegetation at the top
was living clover just one month before this picture was taken

What role does soil play in its ecosystem? Disease causing organisms aside, the organisms that evolve in an ecosystem evolve to play a role in the healthy version of that ecosystem. Soil needs decaying organic matter to survive, right? So why doesn’t it just kill all the plants and feast? That’s a lot of food in the short term and no food in the long term. So it could just keep the plants sickly and they would drop small numbers of leaves frequently and die early. That is a better long term solution, but it is a recipe for a permanent diet of not quite enough. No, anyone who has tried to maintain a landscape in their yard knows that the more plants you have and the more lush and healthy they are, the more debris they drop to the soil surface. So soil has a vested interest in keeping the plants lush and healthy and growing as fast as possible. How do they do this? They break down the nutrients in the decaying organic matter and feed them back to the plants so they have what they need to grow more.

Just how poorly is this concept understood? In 1975, Masanobu Fukoka wrote The One Straw Revolution. The book chronicles his decades long quest to get academia to understand the concept that the organic matter needs to be returned to the soil. We still aren’t there. In fact, I recently found this great video from a soil scientist at the Soil Conservation Service trying to convince farmers that soil is alive and needs to be treated as such. We are just not getting it.

 

And as we starve our soils, they become emaciated and unable to do their job, so we dump fertilizers on them, hoping that the chemicals will make up the difference. But it can’t really. Living soil does so much more than just hand out nutrients. It stores massive amounts of carbon in its body (finished humus, the final form of organic matter in soil is over 50% carbon), it serves as a sponge to soak up rainwater and reduce runoff and erosion. It works with the plants to increase resiliency and reduce the impact of diseases. As we let our soils waste away and die, our fields lose productivity, and right at a crucial time when we are trying to figure out how to feed a lot more mouths.

So remember, take care of your soil and feed it with lots and lots of decaying organic matter. Our lives all depend on it.