Components of Soil

If you'd like to learn about the components of soil and understand what good dirt is comprised of, welcome to Learn Dirt. You're in the right place!

Textural Components of Soil

Soil texture is the 'feel' of the soil. Texture affects drainage and infiltration rates, water holding capacity, and stability for rooting in.

Each of the main types of particles found in soil are differently-sized. Because of this, their ratios to one another drastically change the properties of the dirt.

Coarse sand –> diameter 2-0.2mm
Fine sand –> diameter 0.2-0.02mm
Silt –> diameter 0.02-0.002mm
Clay –> diameter less than 0.002mm

If you'd like to learn more about the textural components of soil and how their ratios affect your soil, refer to this article: Soil Texture Triangle.

Mineral Components of Soil

Mineral components comprise roughly 45% of the average soil.

The most common mineral in soil is quartz.

Clay and silt are the primary water-holding components. They have tiny particles and water becomes trapped between them via capillary action.

Weathered bedrock and mineral components reveal trace elements required by plants. Carbonic acid released by certain bacteria, fungi, and lichen can help to bread down minerals and release trace elements.

The macronutrients elements required by plants are:

• Nitrogen (N)
• Phosphorous (P)
• Potassium (K)
• Calcium (Ca)
• Magnesium (Mg)
• Sulfur (S)

The micronutrient elements required by plants are:

• Chlorine (Cl)
• Copper (Cu)
• Iron (Fe)
• Boron (B)
• Manganese (Mn)
• Molybdenum (Mo)
• Nickel (Ni)
• Zinc (Zn)

The following micronutrients are not strictly required by plants, but may aid in development and resistance for some species:

• Silicon (Si)
• Vanadium (V)

Biological Components of Soil

They say that there are more living organisms in one teaspoon of healthy soil than there are human beings on the Earth.

Healthy soil is a thriving microcosm of biological activity which facilitates plant growth and health in organic systems.

You can think about soil biology somewhat like gut biology.

We humans rely on healthy, thriving gut microbiomes in order to digest our food. Our microbiomes help us break down food, convert nutrients, and make them bioavailable for our bodies to utilize.

Plants have the same thing, but their microbiome lives on the outside. Think of plant roots like an inside-out intestinal tract - they absorb nutrients which plants need from the outside. The microbiome which plants utilize therefore extends from its roots and rhizosphere outward through the soil.

Plants rely on the soil microbiome to break down nutrients, convert it, and make it bioavailable to plants in a very similar way to our own gut microbiomes.

Plants require these biological components in their soil in order to access nutrients in organic contexts.

Testing Your Soil Composition

To learn about the textural components and identify your soil texture, check out Soil Texture Triangle (Soil Composition).

To test the pH of your soil and find out if you're in the right range, any digital pH tester such as this works great.

Litmus paper or color change kits also work, but can be more difficult for soil than they would be for plain water pH checks. Soil stains, afterall, and can muddle the colors of your test kits. This is why I prefer the accuracy of an inexpensive digital pH tester.

For testing soil moisture levels, a simple moisture meter works great. You can probe around with this and understand how moisture is moving and diffusing through different areas and layers of your soil.

To find out what macro and micronutrients your soil has and in what amounts, I love these soil test kits. They run your dirt @ the lab and give you digital soil composition results.

You can also give your local Cooperative Extension a call for a soil test, which I've found is often less expensive than the commercial test above. They'll send you a kit and you send it in to the lab.

No matter what you use to check your soil composition, it's important to gain as much understanding as you can about your dirt. This gives you valuable insight into what it might need, what's lacking, and how any of your soil-building efforts are paying off.

Good luck!