Soil Basics

*This is a quick overview of soil basics. There are links to other, more in depth sites and we will add more detailed FRESH links here from time to time.

What is soil exactly? Few people really take the time to think about what makes up the ground that they walk on. We’re going to go a little deeper (pun intended) into what soil really consists of. Here’s the basics of what’s in the dirt:

  • Organic matter – The living organisms, both large and small, plant and animal. The dead and decomposing residues of former organisms. And the stable, well-decomposed residues. All three of these have specific benefits to the health of the soil. The living organisms serve to make nutrients available to plants and bind the mineral solids together or break them down. These include large and small animals that burrow in the soil, worms and insects that feed off of plants, other organic matter and smaller organisms, protozoa that feed on even smaller microorganisms like fungi and bacteria. This category includes the plant roots as well. The decomposing plant and animal matter serves as food for the living organisms. The long dead, stable residues are smaller and have the ability to harbor nutrients, moisture and microorganisms.
  • Mineral solids – The three main categories are sand, silt, and clay. They all have different qualities related to the other components of the soil. For example, sand has numerous air pockets and is great for drainage but too much sand and the organic matter has no place to latch onto so it is leached out along with the nutrients it provides. Each one is a different makeup of mineral combinations like silicone, potassium, calcium and so on. The amounts of these three kinds of solids in a soil is the soil texture. The way these combine and form aggregates or clumps of soil is the soil structure.
  • Water – Depending on the structure and texture of the soil, water can be helpful or harmful. Tight, compacted soils repel water and cause erosion. Soil that is healthy and well aggregated allows water to infiltrate and has numerous storage areas for water to remain and be available to plants.
  • Air – Believe it or not, most soils are largely made of air. Organic matter makes up 1-6% of the soil, the rest is about half mineral solids and half air. These pockets of air between the soil particles are a very important part of water storage and infiltration but they are also the home of the decaying organic matter and microorganisms, a place for roots to grow through and a source of oxygen for the living parts of the soil. When these pores are compressed, it effects the health of the soil by limiting all of these aspects that are beneficial. This is called compaction.

These four soil elements work together and are dependent upon one another. Their presence or absence, in their relative amounts, serve to create the health of the soil and a productive soil is a perfect combination of these.

Partly adapted from Building Soils for Better Crops . <—–click to download this entire text in PDF from our education partner the Sustainable Agriculture Research and Education program.

We hope you can join us as we dive into each of these in more detail. Check back regularly for more on soil and other topics on our Teaching Series page.

Want to learn more on your own? Go to our Resources page or click on these great links below for more information: