What is a Soil Series?

The soil series: a slightly mysterious thing that takes on the Herculean task of trying to assign a classification to the soil beneath your feet.

What is a soil series? A soil series is a type of classification for soils that is typically named after a local area heavily featuring that kind of soil. This effort was lead by the National Cooperative Soil Survey of the USDA. Soils are grouped together based on their appearance, chemistry, and physical properties.

Now that we have the quick and easy definition out of the way, let’s dive into the rest of this post.

History of the Soil Series: a Brief Overview

In the sections below we’ll briefly cover the history of soil series and how they came to be, and then also provide a little clarity on terminology of the soil science world.

Introduced by the USDA

As you might have gathered in the discussion above, the soil series is a concept specific to the United States. This is because it is the result of a great effort to provide a classification for the soils of the entire continental United States.

As you probably can imagine, this project was a tremendous undertaking, as soil scientists of the USDA were responsible for manually cataloging the properties of local soils. Given the massive size of the United States and the wide variety of soils present, it’s easy to see how this project needed a small-army of soil scientists ready at the helm. In fact, the USDA maintains a list of Million-Acre Mappers, those being scientists that mapped out more than a million acres of land in their careers.

This effort was launched around the beginning of the 20th century, and in 1903 the National Cooperative Soil Survey from the USDA established the idea of the soil series.

Derived From a Variety of Factors

This isn’t always the case, but soil series are almost always given a name that refers to a location where that specific soil series is most prominent. What do I mean by this? If you take the Antigo soil series, you’ll notice that the extent map shows that it is consistently present in the vicinity of Antigo, WI, as seen below:

Going beyond the name of the soil series, a variety of factors are taken into account when deciding how to group soils together in an orderly and logical manner. You might not think about it right away, but all of the following factors and more will play a role in determining a soil series:

  • Soil pH
  • Percentage of different components (i.e. sand, clay)
  • Soil color
  • Depth of different layers
  • Soil structure
  • Drainage capabilities

And so on. Clearly there’s a lot going on here, but the hard-working folks at the USDA have been working on this system for more than a hundred years.

Terms to Keep Straight: Soil Series, Mapping Units, and Soil Description

One of the most confusing aspects of the world of soil series can sometimes be the similar terms being thrown around. This is especially true for non-scientific users that are perhaps looking for quick answers to their end-use focused questions, and might not be so interested in the granular specifics. So in order to keep the confusion to a minimum, let’s define a few terms you might frequently see.

First and foremost, the soil series term refers to a pre-defined type of soil that is found throughout parts of the continental United States. Each soil series has a long list of data fields associated with it.

You may have also have heard the term soil map units. While map units are related to soil series, they are not the same. The relationship here is that soil map units are comprised of individual soil series at specified percentages. An example of this is the ‘PgB’ soil map unit, which is primarily comprised of the following two soil series:

  • Padus (65%)
  • Wabeno (33%)

How to Find the Soil Series for Your Local Area

Now that we have a good understanding of exactly what a soil series is, let’s see how this information can be useful for the average person.

While it is true that the USDA does provide applications that allow for access to this information, they unfortunately aren’t terribly user-friendly as of this time of writing. A better approach is to leverage the work of the soil scientists from the University of California-Davis, which have built modern applications with the USDA data.

If you’re in the browser, a great option is the SoilWeb mapping application, which allows you to zoom into your local area and then explore which soil series are present.

Referencing the example from the previous section, the PgB soil map unit has the following soil series present:

If you then click on the blue links in the Map Unit Composition part of the menu, you’ll then be taken to a screen that looks like this:

This menu provides a jumping-off point for all sorts of information, but it’s important to note that you are now on the soil series section, not the soil map unit.

There’s also a mobile app for both Android and iOS that was developed by the UC-Davis team, and that is best used to pull up information on the soil at your current GPS position.

If you are interested in learning more about finding information on soil series, you can check out this post that goes into great detail on the various applications available.

Final Thoughts

Hopefully you enjoyed reading this piece and came away having learned a little bit about the humble soil series.

If you are interested in learning more about similar topics, feel free to check out any of the following articles:

By Drew Meulemans

I've long admired forests and devote much energy to learning about them and exploring. I enjoy sharing what I learn and wish to inspire others to do the same.