“Don't play in the dirt” is probably a phrase you've heard before and one you might never have questioned. After all dirt is, well, dirty. But, it’s actually an incorrect statement. It should be “don't play in the soil.” So what? Well, there is actually a pretty large difference between dirt and soil: dirt is actually dead soil. That implies something that might sound crazy: soil is alive.
Yes, you read that right, soil is a living thing. That statement might be hard to wrap your head around, so let's start with the basics: what is soil and how is it made? Soil is composed of minerals, organic matter, liquids and gases, and can be classified into layers and types. The varying types are categorized based on the ratio of sand to silt to clay. Soil forms through a process in which bedrock fractures exposing it to water, oxygen, and CO2 which cause the bedrock to weather (or change texture and appearance). This creates an environment in which plants such as lichens are able to grow, and these plants further the weathering of the rock. All this weathered material and the organic material from the plants collects and becomes what we would call “soil.” This new soil will continue to develop as more plants grow and put nutrients into it and as the bedrock continues to weather. Overtime, this soil will develop different layers based on nutrients and material makeup as well as amount of weathering the soil is exposed to. The top layer is exposed to the most weathering via natural elements (rain, wind, etc.) and the layers below are exposed to less and less the deeper you go. These layers are classified into what scientists call “soil horizons” and the top most layer is called O, below that is A, then E, then B, and finally layer C. The O horizon is at the surface, and is composed of at least 20% organic matter such as slowly decomposing plants or leaves fallen from trees. When you go outside and you see sticks, leaves, and bits of plants on the ground, that is the O layer. Below is the A horizon, which is often classified as topsoil in agricultural operations such as our chocho farms. It also has a high organic matter content, and is prone to erosion, flooding and landslides as water may accumulate in this layer. Layer A often has a lot of biological activity, and may be home to insects, worms, and burrowing animals. (cite 1 and 2).
Below the A horizon is the E horizon, which is often lightly colored soil and often receives the nutrients that are washed down through the O and A horizon via rain. Even deeper is the B horizon, which has a higher clay content and may have more minerals as they accumulate from the upper layers. This layer is lighter brown in color and because of the clay and iron minerals, often holds more water than the topsoil A. Finally there is the C horizon, which is right above the bedrock. This layer experiences the least amount of weathering as it is the deepest, and may even contain some pieces of the original bedrock. Below this is the R layer, which is the bedrock and may be rocks such as limestone, granite, or quartzite (cite 1 and 2).
Within these layers you can find lots of living organisms, called soil organisms. In fact, there are more species of organisms in the soil than there are above it (cite). While it might be hard to believe, a handful of soil is home to millions of living organisms that work to keep the soil healthy (cite). Earthworms, for example, help move soil from one layer to another, helping nutrients cycle. Other living things such as bacteria, fungi, nematodes (types of roundworms), and soil arthropods (such as beetles and ants), help to break down, or decompose, organic matter like dead leaves. They may eat the organic matter and produce waste that goes back into the soil providing nutrients for plant roots. When soil is dark in color, it means that it is rich in these waste byproducts and therefore rich in nutrients. The waste also gives soil structure by helping soil particles (sand, silt, and clay) stick together. (cite).
Other organisms help with water filtration by eating and removing certain algae producing nutrients from water as it percolates through soil (cite). And still others help to capture nutrients such as nitrogen from the atmosphere and this process can also be done in partnership with legumes. Chocho, one such legume, allows soil bacteria to live in its roots and as the chocho plant undergoes photosynthesis, the microorganisms use the sugars produced as energy to fix nitrogen. (cite)
Not all soils are the same or contain the same soil organisms. Different plants, like legumes, can improve the soil nutrient content, and others, such as cotton, can deplete it. Certain kinds of soils might be prone to certain weeds, which then might be treated with herbicides which further damage the soil (cite). Luckily, many weeds can be treated through manipulations of soil nutrients, and may even be symptoms of unhealthy soil. For example, clovers are often found in compact soils with low pH, low fertility and either excessive water or drought conditions. Instead of spraying clovers with toxic chemicals, you might try to up the pH of the soil, aerate the soil to reduce the compactness, and to ensure that the soil is neither excessively wet or dry. Additionally, since clovers grow in soils with low fertility, it might be a sign that your soil needs more nutrients.(cite) This would be a natural way to get rid of the clovers and to help improve your soil’s health.
So, soil is alive with millions of kinds of soil organisms that help provide nutrients and services to plants, and therefore to us, humans. While it might be hard to imagine that soil is alive since you can't see it breathing and moving, it is full of tiny microorganisms that are. Without soil organisms and weathered bedrock, we would not have any food, oxygen, or even be alive ourselves. Soil is an important building block of life, so next time try saying “don't play in the soil,” and let it be because you know that it is important to keep those microorganisms alive and functioning rather than because you don't want to wash dirt out of a t-shirt.