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Thursday, February 17, 2022

What is the Nature of Soil?

One of the most fundamental ways of looking at soil is to determine what the main ingredients are. Some soil contains rocks and gravels and it has been determined that anything bigger than 2mm is just a contaminant in soil. Rocks, stones and gravel are considered by soil scientists to be too large to be considered. So, first we have to screen soils through a 2mm mesh to see what portion of the ground beneath our feet is really soil and how much is just a contaminant. I have tried growing a garden on gravelly ground and the plant that did best there is purslane. Sadly, at the time, I didn't know it as a nutrient dense food crop, but I did know that it composted easily and turned it into compost for years, until I could build enough soil to grow other plants for food. Like most living things in soil, which I will discuss later, I have the tenacity to not give up, not give in to pressure, but to hold out long enough for conditions to improve. I put forth as the primary nature of soil to contain and express the deepest level of tenacity our human brains can fathom. Let's not get ahead of ourselves... The most important information to get about soil is what on earth is making up the mass? Luckily, the simplest and most profound question can be answered with a simple and profound test. Take a handful or two of soil, put it in a clear container that is taller than it is wide, fill the container with water, put a lid on it and shake. let it sit overnight or up to several days or weeks until the water has cleared and you will see three separate and distinct layers in the vessel. At the bottom will be sand. These are the largest soil particles, so they fall out of suspension first. The middle section will be silt which ranges from as small as two thousandths of a centimteter all the way up to five hundreths of a cm. Finally the topmost layer will be clay, particles smaller than two thousandths of a cm. I recently heard an interesting way to think about these relative sizes. tiny numbers really don't tell the story, especially when you get down to sizes we can't even see. Think of it this way, if the smallest particles were the size of BBs or marbles, the middle sized particles would be the size of basketballs or beach balls and the large particles would be the size of a chair. Typically, these three ingredients make up over 95% of the soil.
Of course with any hard and fast rule, there are major exceptions. Organic material in the soil, which is often seen as bubbles on the surface of the water used in the previous test, can become a large percentage of the soil, but then it is either called peat or muck. Peat being derived from mosses and growing organic sources and muck being from lake sediments, or detritus (like the waste bin of nature)Across most of the developed world, many soils have been tilled so agressively that no organic material is left in them, less than one percent organic material is frequently seen but it is an extremely dangerous condition for soil. At that point it is more accurately called dirt. It will easily erode with either wind or rain, without a thick mulch layer or some growth and living roots to hold the material together and protect it from rain and sun. Each component of soil is good for some things and terrible for others, so having a good mix is best. If you have a single material dominant it raises management issues but any soil can be worked with. My own personal preference is clay, but the management of that type of soil is just as quirky as would be a predominantly silt or sand soil.The difference is that I have learned to respect the limitations of my clay soil. Sand drains like crazy, which is normally very good, but it presents a problem in that it drains so easily that it is hard to keep soil misture even enough to get plants to grow well.sand also very seriously flirts with contaminating surface and ground water because any nutrients applied to the soil can be washed away because the matrial drains so freely. It can also be a challenge because many organisms will find it difficult to stick around when the soil routinely goest through extreme wet and dry cycles. This also can mean huge variations in surface temperature as well, especially if mulch cover in not maintained.
Silt provides much more surface area which can be available for the soil microbiome to flourish upon and although it drains more slowly and provides more opportunity for life to thive than sand can, it can also be threatened by tilling or not enough nutrients. Most people hate clay because mor ethan likely they inherited poorly managed clay, as I did. It had been seriously compacted through consistently poor management and in large areas it was just lifeless. Although clay can provide the most habitat for soil microbes of all the soils, any land manager who has to deal woith them needs to understand their limitations as well. Most often the limiting factors are the ability to get air and water down into the soil. If water can't even penetrate the soil, it can only run off and it will take some clay particles and nutrients with it as well. The best thing in all three cases mentioned above is to add either compost (or other organic material) for organic carbon or mineral carbon with microbes in the form of biochar. I make the distinction betewwn the two because material that was once living releases most of its carbon over the course of about four years, ninety percent leaves the soil. Mineral carbon is not a food source for any soil organism, nor will it break down if eaten and excreted by soil dwelling creatures. It remains unchanged for hundreds of centuries, continuing to provide habitat for soil organisms. This small but vital part of soil, organic and inorganic carbon are what allows soil to be healthy, well-drained and able to withstand drought. The living and dead roots, provide some large structures that increase porosity, but it is the living organisms and th edead organic meterial they eat, as well as what they excrete that make soil vital and healthy. In soil the tiny percentage of living organic material does most of the work feeding the plant roots and providing smaller structures that allow air and wate rto be available enough under the soil surface to create a rich habitable zone within which millions of other life ofrms co-exist. The most true nature of soil is to be the ultimate team player, providing opportunity and the synergy that comes from diversity and abiding by terms of the give back or give away. When soil is treated badly enough, it often just goes away.

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