Soil. To many people it seems like a lifeless substance where there isn’t much to learn about it. However, anyone that’s ever tried to grow a plant in any way quickly figured out how much they had to learn about soil.
How can you find the soil type for your area? Most areas have local extensions that analyze soil samples for a reasonable cost. The USDA also maintains a soil map, which details the various soil types present throughout the United States. Different applications allow users to find the scientific properties associated with a soil type.
Keep reading and you’ll find out everything you need to know in order to test your soil and put it in the proper context.
Two Different Approaches
This post will have a lot going on, but it might be most helpful to think of it as two separate methods that are trying to answer the same question:
- What can I learn about my soil from the testing of samples taken of my soil?
- What can I learn about the expected properties and potential of my soil based on an existing soil map built by the USDA?
There’s no right answer as to which method is appropriate for your situation, as both can provide unique insights into our soils.
Manually Testing the Actual Soil on Your Land
Without a doubt, this is likely the approach that most people have in mind when first becoming interested in the soils in their area. The idea is that you go out to your land and collect a few samples of your soil. Then either you perform some simple DIY tests, or you send off the samples for analysis at a nearby soil laboratory.
While most of this post will not be focused on this soil testing approach, that doesn’t mean that I don’t find it to be incredibly valuable. I think anyone interested in understanding their local soil should without a doubt perform some sort of soil testing, whether DIY or professional. Whether you’re interested in growing a few flowers in the front yard or you’re starting your own homestead, a soil test will give you valuable feedback. Even if the results of your soil test simply confirms the freely-available information you find in the next approach, that confirmation is still valuable feedback.
Finding Soil Data for Your Location From the USDA
On the other hand, there’s a different approach that we can take in order to quickly gain understanding of our local soil environment with a 10,000 foot view. This doesn’t involve us actually sampling any of our soil, it merely relies on the work that the United States Department of Agriculture already did.
Let me explain what I mean: the USDA underwent a massive effort to produce a soil map for the entire continental United States. This soil map has data on the many physical attributes of soil that we’re interested in, but it also provides helpful ratings and information on how each type of soil is suited for different real-life activities.
Here’s an example of what I’m talking about: there are ratings that indicate how suitable a specific soil series (more on what that means later) is for the production of wine grapes. From construction applications to native vegetation information, there’s quite a lot of valuable information in these reports.
Things to Think About: Context, Desired Outcomes, and Purpose
What ends up being right for you really depends on the context of your situation and the desired outcomes that you’re seeking. I think almost everyone should perform some type of manual testing of soil samples from their land, while not everyone is in a position to gain a lot of value from the USDA approach.
There is one caveat in all of this: if you’re aiming to understand the soils of lands that you don’t technically own (i.e. public land, prospective lands, just for fun research, etc.), then you obviously should only employ the USDA approach.
What I will say is that the USDA approach is generally better if you’re discussing soils from landscapes that haven’t been so greatly disturbed. The data from the USDA indicates what your soil should be based on your location; so if you live in the suburbs and your native soils were trucked away and replaced with less valuable sub-soils, you might be out of luck. I view the USDA information as more valuable for those looking to analyze rural areas, specifically areas that are left a bit more natural such as National Forests and state parks.
Manually Testing Your Actual Soil
The conversation around soil testing can be a little confusing at times, especially if you’re unfamiliar with the different terms floating around.
It’s important to take a little time to understand the basic concepts about soil types before we start digging around in the cupboards for mason jars and dish soap.
Basic Concepts to Keep in Mind Before We Begin
You may have seen heard some of the terms thrown around before:
- Clay loam
- Loamy sand
- Silt loam
- Silty clay
And so on. These are terms used to describe a specific soil texture, which can be calculated on this page provided by the USDA. At the bottom of the screen you’ll notice a chart that looks like the following:
What we’re looking at is a graph with three different axes. Overlayed on this chart are the different soil texture groups. For example, you can see that the top section of the graph is almost entirely the ‘clay’ texture. Each of these textures is covering how much of your soil sample is made from these three particle types:
These are in order of the largest to smallest particle sizes, with clay particles being the smallest.
DIY Soil Tests: a Few Different Approaches
Okay, now you’re free to start digging around for mason jars. Despite the fact that these tests are rather simple, there are still some very valuable insights we can obtain from the results.
Using the Jar Test to Get a Rough Estimate of Your Soil Composition
The ‘jar test’ is the iconic version of the DIY soil test. The objective with the jar test is to get a rough estimate of the composition of your soil from the three components discussed earlier.
Here’s an excellent video that slowly goes through the process of the test and then walks you through the science behind it:
Getting an Approximate pH Measurement of Your Soil
You may also be curious about the pH of your local soils. While a pH measurement is usually something that’s best left to the soil scientists with labs and decent equipment, you can get a “rough estimate” of your pH with a few precautions.
This video will walk you through how you can test your soil pH at home with some rudimentary equipment:
The Jar Test for Those With Heavy Clay Soils
Those with heavy clay soils are accustomed to a life where everything’s just a little more difficult than it might need to be. If that’s the case for you, you might want to check out this video that shows a jar test in a region with heavy clay:
Sending Samples in for Lab Testing
Even if you do the DIY soil testing discussed above, it’s almost certainly worth your time to seek out a local lab that is capable of testing your soil professionally.
Most counties or university extensions will have information on locations that provide this kind of testing, so your best bet is to search around to find that page. This page may also have valuable resources on other aspects of soil and gardening, so you might want to bookmark it for future use.
Basic Concepts: Using Existing USDA Soil Maps
This method is all about leveraging the decades of work that soil scientists already did for us. It’s normal to feel a sense of mystery when you step into a natural environment, but the reality is that thousands of people have spent decades studying these natural environments.
A great example of this is the soil map and all of its associated data compiled by scientists that work for the USDA. There was so much work that went into this project that the USDA has a page where they list the ‘Million-Acre Mappers,’ which are past or present USDA employees that did exactly that: map more than a million acres of soil in their careers (side note: they also receive a lapel pin for their work).
My point is this: it’s much easier to take advantage of the product of this tremendous effort than it is to try to learn everything about soil science for yourself.
What Concepts You Should Keep in Mind When Starting Out
Before we dive into the specific details for each application, I think it’s most helpful to cover some basics about soil science and the potential of these applications.
This will help establish a solid baseline of knowledge before we start flooding your screen with unfamiliar maps, symbols, and charts. There’s a lot going on with some of these screens, so it helps to define some key terms to prevent you from feeling overwhelmed.
Keep the Science Side of Things Simple
As I would bet that these applications are mostly used by soil scientists, the reality is that there’s a lot of complex data fields present at any one point of time. Our job is to stick with only the data points we’re interested in, to resist getting lost in the weeds.
Of all of the scientific data fields available in the reports, we’ll stick to the most basic options. The most important fields will be on the composition of the soil itself, which will consist of percent levels of the following materials:
- Organic matter
Besides that we’ll also maybe dabble in the ‘pH’ field, as I think that’s one of the more approachable fields for just about anyone interested in this kind of stuff. All of the other scientific fields will be left to the scientists.
Quick Notes on How Soil is Classified by the USDA
Before we dive into the different applications, I think it’s important to provide a little background on how soils are classified according to the USDA.
Let’s start with the basics. The USDA has created a ‘soil map’ for the continental United States that is comprised of pre-defined soil units. The map is just like a map of the states in the US, as it contains borders that identify the specific lands that are each soil unit.
Soil units are named with symbols that tell you exactly what soil unit you’re looking at. There are different naming conventions employed throughout the country, but an example of a soil unit is ‘KbC’.
This brings me to the next point: soil units are comprised of pre-defined soil series. This is perhaps best explained in a screenshot:
Here you can see at the top that this is the composition of the KbC soil unit that I mentioned previously. The blue links that you see throughout the table are all the names of soil series that contribute to the KbC soil unit, as soil units can be comprised of multiple soil series.
This brings me to my last point here: the most valuable information that we have available from the USDA is assigned to the soil series, not the soil unit. This may make it a bit confusing when dealing with soil units that aren’t necessarily dominated by a single soil series. Hopefully this makes sense, but I understand that it can be a bit confusing when you first get started.
Focus on Utilizing Application-Based Features
I’m not going to lie: there’s a lot of different data points available with the USDA soil information set, so it’s tempting to try and learn as much as you can (at least for me it is). Your best bet is to forget everything but the most basic soil properties, and then to focus on the most relevant application-based properties?
What do I mean by that? I’m talking about all of the fields that are used to indicate how suitable that soil series is for a specific real-world application. Here’s a good example: there’s a data field that is called the ‘Potential Fire Damage Hazard’ rating, and it provides a rating for a specified soil series. The Seelyeville soil series rates ‘low’ in this field, as this series is typically very poorly drained and often swampy.
The value here for us non-scientists is that we’re leveraging all of the hard work already done by the folks at the USDA, and using their assessments to better help us understand our land. We’re fortunate that there are a wide variety of data fields available to us, from agriculture to forestry to engineering and so on.
Three Different Approaches Using the Same Data
This is an important point that might help add some clarity to this somewhat confusing landscape of smartphone apps and online applications. As far as I can tell, each of these applications uses the exact same data set.
The main difference here is that each application is unique around the way that it formats the data. They are also unique in the manners that they allow users to interact with them.
Exactly how each application works and who they might be best for will be covered in the detailed instructions below. I’ve covered them in order of easiest to hardest, which also happens to be in the order of least to most powerful.
The SoilWeb Application for Mobile Phones: Simple and Straightforward
This application was developed by the California Soil Resource Lab at UC-Davis, and it is built to leverage the work by the USDA soil team while employing modern functionality.
Who is Best Suited for This Option
This is likely going to out me as a huge nerd, but I’m going to do it anyways: this is without a doubt one of my favorite applications for my phone. As there are only 13 reviews in the Google Play store at the time of this writing, I consider this app to be massively underappreciated and I’m more than happy to shed some light on it.
I think anyone that’s interested in soil at all should have this app installed on their phone. If you’re still reading this piece and haven’t abandoned me yet, you’re the perfect candidate for the SoilWeb app.
Here’s where this app is available:
I do have to confess that there is a bit of a limited scope with this app, as it is strictly designed to pull up the soil information at your device’s present location. I think most people will find this more than acceptable, as it’s just enough functionality and probably all that most people need when in the field.
Using the SoilWeb Phone Application for the First Time
When you launch the SoilWeb phone application for the first time you should be presented with something like this:
All you should have to do to run the app is to click the ‘Get Soil Data’ button at the top of your screen. You’ll then likely be prompted to allow SoilWeb to access the current location of your smartphone.
Once you grant permission your screen should update and you should see something similar to this:
There are a few things going on here, and we’ll go through each of them in detail in the next section.
Navigating the Results Page for Your Location
Now that you’ve gone through the difficult task of clicking a button or two, let’s actually figure out what the heck’s going on with this screen.
Details About Your Soil Map Unit
As we discussed earlier, the soil map unit is the abbreviation given to the specific type of soil present at your location. Remember, soil map units are derived from soil series. Think of it this way: if a soil map unit was a loaf of bread, then the soil series present would be the flour, water, salt and yeast (or whatever bread needs).
The only part of this screen that is dedicated to this specific soil map unit is the segment highlighted in the below screenshot:
There are two parts that we need to understand here. First, the part labeled the ‘Map unit’ is the description assigned to this particular soil map unit. Second, we’ll need to click the ‘Details’ button to find the rest of the information directly associated with this map unit. Once we click that button, our screen should show something like this:
As you can see at the top of the screen, the ‘Map Unit Symbol’ refers to the symbol that the USDA soil map would use to refer to this specific map unit. There is some additional information as you scroll down, but most of that will be irrelevant to the vast majority of people.
Once you are done with this section, click either the back button (sorry iOS users) or the arrow in the upper right section of your screen to return back to the main results page.
Soil Profiles of the Relevant Soil Series are the Majority of the Screen
Now that we’re back to the main results page, we can start to explore the different soil series present in our soil map unit. The majority of the screen here is reserved for the soil profiles of the soil series that this soil map unit consists of:
It may look like there are only two soil series present on my screen, but you’ll notice that the percentage only adds up to 97%. Maybe that’s close enough for most, but we’re dealing with scientists here: there’s more to this.
To find the remaining soil series that make up this unit you’ll need to swipe to the left. Once you do that you might be presented with any remaining soil series. Not all soil map units will be comprised of more than two soil series, but many at least three.
Finding Information on each Soil Series
As the Plainfield soil series makes up the vast majority of my soil unit, I’m looking find more information about it. All I have to do to bring up this information is to push anywhere on this light blue area:
This will bring up a screen with three tabs: Description, Details and Links. It should look like this:
Much of the information in the ‘Description’ tab is geared towards scientists, but there area few sections that may be useful for us. First, the main description right under the series name is a great summary and is very friendly to non-scientists. The other relevant sections are down near the bottom of the page, so you might have to scroll a good bit to get there.
Most people would be interested in these two sections:
- Drainage and Permeability
- Use and Vegetation
Here’s an example of what the content in these sections may look like:
Hopefully you can now understand at least part of the reason why we can get so much value out of this application.
The ‘Details’ tab contains many different fields but it is formatted exactly the same in the browser version of SoilWeb. As such, we’ll cover this later in the piece to avoid repetition.
SoilWeb in the Browser: Best of Both Worlds
As this browser application was developed by the same team that built the smartphone app that we just discussed, it’s very easy to leverage what we just learned and apply it here.
Here’s what the team at UC-Davis did with the SoilWeb browser application: they took the USDA’s Web Soil Survey browser app (which will be discussed after this) and applied a much smoother interface while enabling modern the modern functionalities we’ve come to expect from any mapping application.
Who is Best Suited for This Option
As you might expect, this makes the SoilWeb browser application an incredibly functional option that makes the most sense for the vast majority of users. The similarities between the two applications means there’s a low barrier of entry for those already acquainted with the smartphone app
There are additional reporting capabilities that the USDA Web Soil Survey application has over the SoilWeb application, but most people won’t be interested in exploring those capabilities. This makes the SoilWeb application a great choice for anyone that wants to quickly access loads of information about their local soils without having to put up with a slightly frustrating navigational setup.
Introduction to the USDA Soil Map
You may not have familiarity with the soil map put together by the USDA, so this is likely the first time you’ve seen something like this:
Don’t worry, it’s not as crazy as it looks. The concept is pretty simple: the USDA took the entire continental United States and then divided the land into different soil map units. These map units are denoted on the screen with the symbols you may have noticed in the above screenshot (e.g. SfD, WaA, W, IsA, etc.).
Much like the world is divided into countries in a way that doesn’t always result in the cleanest or most sensible borders, the soil map has many different map units that interact in many different ways. Let’s zoom in on this map to get a good example of that. Here’s an area that has a couple of interesting things going on:
You’ll notice that I’ve highlighted two different map units: WaA and SfD. As you may have noticed, the ‘WaA’ unit that I highlighted is entirely surrounded by the ‘SfD’ unit, which covers a large portion of the area in the screenshot.
It’s worth noting that these unit shapes and borders are approximations, as it would be difficult for the USDA to fully covers the complexities and variations that can occur even on a few acres of land. With that being said, this still is very useful for our purposes.
How Information is Organized in the SoilWeb Browser Application
One quick tip before we start looking into specific soil profiles: if you’re in SoilWeb and you’re confused about any of the terminology used, check out their help page. You can find this by clicking the ‘Menu’ button in the upper left corner and then clicking the ‘Help’ button.
The help section is mostly just a collection of frequently used terms, where if you click on the link you’ll be presented with their definition. It’s definitely not necessary to read these, but it’s useful for those who want to learn more.
Soil Map Unit Specific Information
When you click anywhere on the map the screen should update to display all relevant information on the soil map unit clicked. This is about what you can expect to see when you click on a unit:
The first thing you should notice is that the symbol in the parentheses at the top of the screen matches the symbol on the map where the ‘red x’ is located (AoB). The description to the left of that is the name for that particular soil unit.
You can see at the bottom of the screenshot that there’s more information below, but most of this information won’t be useful for our purposes.
Compositional Information on a Soil Series
In the most recent screenshot there is a ‘Map Unit Composition’ section. This shows what soil series are included in this map unit. You can see that 80% of the AoB map unit is comprised of the ‘Antigo’ soil series. This is handy for us, as the rest of the information that we’re interested in is tied to the soil series, not the soil map unit.
To pull up the information on the soil series, click the blue link of the series name. This should bring up a screen that looks like this:
The stacked bar chart that you see on the right looks interesting, but we’ll ignore it for our purposes. What we’re most interested in is the following menu items on the left side:
- Org. Matter
If you click on the ‘Sand’ button you should be presented with a graph that looks similar to the following:
I’ll be the first to admit that this is a bit of a funky looking graph, as I’m not accustomed to the data flowing in this direction. With that being said, it’s a pretty simple graph once you understand their intentions.
You’ll notice that the y-axis represents the depth (in centimeters) for this soil series. On the x-axis you have the percent of this soil series that is comprised of sand.
This makes the most sense when you think of the trend line on the graph. For example, at 50 cm of depth we can see that approximately 20% of this soil series is comprised of sand. Switching over to the ‘Clay’ graph, we can see in the below screenshot that this same depth is also approximately 20% clay.
I hope that this makes sense and that you can see how this would be useful when trying to learn more about our soils.
It’s worth noting that the pH is also displayed with a similar graph, it just happens that the pH is represented on the x-axis.
Suitability Ratings for a Soil Series
Now that we’ve learned about the characteristics of our soil, it’s time to learn about how this soil is suited for different real-life applications.
There are two locations in the menu where we’ll find information relevant to our purposes. First, you’ll find a ‘Forest Productivity’ menu item. This doesn’t always contain information, but if it does you may be presented with something like this:
This might be a little confusing to some, but it’s pretty straightforward once you figure out the formatting. We’ll explain what these things mean in detail with an example, so let’s turn our attention to the first entry: sugar maple.
The ‘Site Index Curve Number’ for the sugar maple is 66. This means that sugar maple trees in this type of soil are expected to reach approximately 66 feet in height after a specific number of years.
The other piece of information is the ‘Productivity’ column, which merely refers to the volume of wood (measured in cubic feet) that an acre of this tree would produce in a year. In this case, a stand of mature sugar maples that is one acre in size would be expected to produce 43 cubic feet of wood in a year.
You might also find relevant information in the ‘Soil Suitability Ratings’ section of the menu, which looks like this when you open it:
Clicking on the ‘Forestry’ button, we should see something similar to this:
This clearly demonstrates the main purpose of this section, which is to provide quick ratings for a soil series that cover a wide range of potential uses and applications. You can click around the other buttons in this section to see what other information is available for that soil series.
Additional Information on a Soil Series
There’s one more thing to keep in mind when you’re digging around for information on your soil series, the links in the top bar of the menu:
The first thing you need to know is that the ‘Soil Data Explorer’ link (SDE) and the ‘Description’ link bring up the same information, so you can disregard the latter. The reason we’re interested in the SDE is that it neatly compiles a lot of different information sources and functionalities.
This was discussed previously in the phone application part, but there are two main parts that are valuable in the SDE:
- The initial description under the soil series name
- The ‘Use and Vegetation’ section
There may be additional sections that could be useful for you, but it depends on your soil series.
The last thing to keep in mind is that the ‘Series Extent Explorer’ link brings up a valuable map that indicates where this soil series is present:
I don’t know if there’s necessarily a practical use for this map, but it does seem cool to me. This map can also be found while in the SDE, and all you need to do is click on the ‘Extent’ tab at the very end.
USDA’s Web Soil Survey Application: Most Powerful Option
Last but certainly not least, here we finally get to the soil mapping application provided by the USDA, which is called the Web Soil Survey (the government really does have the most creative names for applications…).
Who is Best Suited for This Option
I don’t anticipate that the majority of people that find this piece will be interested in this application. I think that’s totally fine and I wouldn’t recommend someone start playing around with this application unless they really enjoyed working with SoilWeb’s browser application.
While the SoilWeb application has a ton of information, the simple reality is that the USDA’s Web Soil Survey application has many additional fields that can be really valuable. The application includes everything from reports on the expected native vegetation to the most commonly found trees on that soil series.
This application is a great opportunity to people interested in foraging or people that would like to better understand the natural landscapes around them. Another benefit is that the reports in this application output the results for every soil series present in an area you specify, so you’re not just limited to viewing the data of a single soil series at a time.
The main downside is the fact that the user interface (think more MapQuest and less Google maps) and functionality are a little dated, but that’s more than OK in my book given the value it provides.
Check Out This Post if You’re Interested in Learning More
If any of this sounds interesting to you, you’re more than welcome to check out the following post:
In this post I provide step-by-step instructions on how to use this application, as well as demonstrating what reports I found most valuable for my purposes.
Whew, we’ve reached the end of the post. I hope this was valuable for you and that you didn’t find it too overwhelming. There are a lot of really amazing things that you can learn about your soil with the right methods and tools, and hopefully you enjoyed this post.
If you’re interested in other posts that go into great detail about how we can make the most out of time in nature, feel free to check out any of the following: