Friday, April 15, 2016

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 I know the old food pyramid is a bit out of date, but it is a great place to start.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!

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