Soil as a Living Organism

Sometimes, looking at something commonplace with new eyes, new perspective, and new insight can be one of the hardest things there is to do. And sometimes there is nothing more important to do. What can be more commonplace than soil? We walk over it every day. Yet to dismiss its importance, its power, is to miss a great deal. Sylvia Bernstein, in her book Aquaponic Gardening, printed a quote from Kobus Jooste from South Africa that attempted to strip down soil into its constituents, ending in the following conclusion: “UBERFACT: Soil is an anchoring medium to plants that may or may not, over time, release some of the stuff plants need to grow.” I nearly stopped reading the book at that line, but powered on for the other wisdom the book has to offer. Still, that sentence comes back to me often. Rarely have people been more wrong.

The first thing to realize when looking at soil with new eyes is that soil is a living thing. True, it is not a single organism, but rather a complex media filled with tens of thousands of different organisms. But the organisms work so well together that they can almost be treated as one organism.  So, when a biologist studies an organism, what are the first couple of things they look for? Two of the most important aspects in understanding an organism are what it eats, and what role it fills in the ecosystem.

First let’s tackle the food source for soil. Yes, soil needs to be fed. Like any other living organism, soil breathes air, drinks water, and consumes a food source. In the absence of any of those, the soil will fail and die. As for what soil eats, it is really simple. It eats whatever organic matter falls to the soil surface. From there, through a series of digestive processes of different organisms, the particles of decaying organic matter get broken down into smaller and smaller pieces, the larger organic molecules digested into smaller ones. Mass is lost as carbon from cellulose and lignin and a host of other molecules are slowly turned into carbon dioxide. But the process is so much more complex. The cellulose and lignin were locked in what used to be the body of a plant, a plant that had metabolic processes and scent and its own DNA. All of those complex molecules that created the things that made the plant alive came with their own chemical signature. As they break down, the carbon is lost to the air, as is some of the nitrogen. However, the phosphorus and potassium and calcium and iron stay behind. They get recombined and further broken down by that wonderful process of decomposition and soil creation. What they finally create is exactly what the plants need to take up and start all over again.

The pile of mostly decomposed plants in the background
was living white clover two months earlier. The heat of
summer killed them and the soil gobbled up the readily
available food source.

 As an engineer, understanding soil isn’t just enough. What does it DO? What can I use it for? In order to tackle that question, I need to answer the other question: what role does soil play in its ecosystem? You probably learned in grade school science class, as I did, that soil provides nutrition and structure for plants. While this is true, it is a tiny portion of what is really going on. Soil plays an incredibly important role in the ecosystem. To work that out, let’s look again at soil’s food source. It needs decaying plant matter to feed on. Where does it get decaying plant matter? Well, it first needs healthy plants to grow, so they can drop leaves and eventually die. What produces more decaying plant matter, a lush growth of plants, or a few spindly plants that are already dying? Anyone with a lush landscape in their yard can tell you the answer to that one. The more plants there are, the more waste they drop.

So now we know that the soil organisms have a vested interest in growing a lush stand of plants. How do they do this? Again, we will answer a question with a new question. What is the biggest problem facing the plants? Plants need sun, water, air, and a good source of all the minerals and micronutrients they need to grow. The first three are outside the control of the soil organisms, but the last is fully within their control. There are two primary sources for the nutrients the plants need: decaying plant and animal material and the minerals in the soil around them. The soil needs to be effective at releasing those nutrients from both sources and getting them to the plants.

That brings up the next problem. How does the soil retain the nutrients long enough for the plants to get them? Have you ever performed a soil test? You put soil in a jar with water and shake it really well, then test the water for nitrogen, phosphorus, and potassium. Why is that? Well, the shaking is because the soil is working really hard to hold onto those nutrients. You test the water and not the soil because those nutrients are soluble in water. The soil has to find a way to lock those nutrients in, and where they fail, filter them back out of the water before they are lost to the water cycle.

It turns out that soil is remarkably good at doing just that. The bacteria produce polysaccharide glues that hold soil particles together. Fungal strands also serve to bind soil particles together. Fungal networks are shaped like a tight net, and have proven to be very good at filtering water.

There is another function of soil that is often overlooked. There is an old gardening addage: If you want to raise the pH of your soil, add compost. If you want to lower the pH of your soil, add compost. Plants are only able to absorb nutrients within a certain pH range. The problem is, different compounds work best at different ranges. Since the organisms in the soil have a vested interest in getting those nutrients into the plants, they also want to make sure the plants can absorb the nutrients. So they also take on the task of balancing the soil chemistry.

Naturally, all this is a gross oversimplification, but it has to be. There have been volumes written on tiny portions of this process. There are whole fields of science that study nothing but soil chemistry and biology. But when you think of the problems you have, think of what soil needs to do and how a healthy, living soil can help you and your plants. Then go out and feed your soil.