The term “soil” is commonly used by all of us. However, we think that the average interpretation and understanding of the word “soil ” are highly variable.
“Soil: the top layer of the earth’s surface, suitable for the growth of plant life.” Well, that doesn’t really help much, no thanks to the dictionary.
So what is soil? It is former rocks, seashells, critters, plants, water and air. In a more classic sense, soil is made up of minerals, air, water and organic materials. The percent of each of the components present in our soil is demonstrated in this pie chart.
The Organics: A Small but Mighty Contribution
There is a soil food web: a large community of plants and organisms, each of which contributes to making our soil healthy. Plants photosynthesize, fix carbon dioxide and release oxygen, that stuff we need to breath with. Plants decompose and add organic matter to the soil.
Decomposers (bacteria and fungi) help to break down the organic material and make it available to plants and animals. Bacterial and fungal feeders(nematodes and tiny arthropods, etc.) control many diseases and pests in the soil. Shredders, such as the earthworm, shred the plant litter. Earthworms enhance the soil structure (with earthworm castings and by aerating the soil) as they produce fecal pellets and burrow in the soil. There are even above ground level predators such as mice, shrews, birds and others, feeding upon some of these subterranean creatures.
So as you may not have imagined, the soil is a living place for many-and a highly complex community at that. In addition, it is an important ecosystem that we humans, gardeners and non-gardeners, need to understand, protect and keep healthy.
The Minerals
The mineral composition of your soil will vary depending upon your location. This portion comes from the rocks and shells deposited long, long ago. There can even be variation on your own little plot of land, sometimes within just a few feet. The native mineral composition may be mixed or covered over by topsoil from another location that was brought in during the building of the house. How can you know if you have different types of soil on your property?
There are several simple tests that you can do at home. One is to collect small scoops of soil from different areas of your yard, if you suspect that you have a variation. Note the color of the soil while wet. Let it dry out and again check color. If the soil color when wet and the color when dry is different in each location, then you may have different soil composition. Will that matter to how your plants grow? Probably not. But if one area in your garden is a problem, perhaps that is a good area to sample and send off to the county soil testing lab.
Do you have sand, silt or clay soil? And how much organic material is in your soil? You can answer that with another simple test. This one is fun to do with your children. Get a clear, straight-sided jar with lid. Fill it about 3/4 full of soil from one location in your yard. Add water to within 1 inch of the top of the jar. Add about 4 teaspoons of Calgon (or a like product). Tighten the lid. Mix by shaking for about a minute, rotating the jar 180 degrees to fully mix. Set the bottle down and follow the time line below:
- After 1 minute, mark the sediment level of what has reached the bottom.
- This is the sand layer, made up of the heaviest mineral particles.
- After 30 minutes, mark the next sediment level. This is the silt layer.
- Wait a day or two to mark the 3rd layer. This is the clay layer, made up of the lightest mineral particles, which can take up to 48 hours to fully settle.
At the end of this test, you’ll see layers of soil in your jar. They may not be equal. You might not see any sand, just all silt and/or clay or vice versa. Another layer that may appear on the very top, if you are lucky, is the organic layer.
You may already have a sense of what your soil type is by the ease or difficulty in digging in the garden. Clay soil, especially un-amended clay soil, is hard to dig in. Sandy soil, of course, is not hard to dig, but the hole that you are digging keeps refilling as the sand pours back with each shovel removal.
The Water
You can purchase water measurement probes to measure the water content of your soil. Or you can simply look at your soil. If you have sandy soil and it rapidly sifts through your fingers, it is probably a bit dry. If you have clay soil and you can see cracks like the San Andreas Fault, it is probably too dry. Conversely, you never want your soil to be super-saturated with water, which would be demonstrated a handful that drips through your fingers.
The Air
The amount of air space in your soil is controlled by everything described above. It is dependent upon the type of mineral composition, the amount of organic material, and the amount of water. Too much water, too few minerals (as in lots of clay particles) with no organic material would not allow any room for air. What is a quick solution for this? Amend your soil.
In the end, one of the best ways to contribute to the continuing health of your soil is to use organic mulch. As the organic mulch material decomposes, it provides a “home” and food source for microorganisms, fungi, bacteria, earthworms, and so on. Encouraging this healthy ecosystem to thrive will build healthy soil in your garden. In return, that healthy soil will grow healthy plants for you.