14.5 From Prairie Black To Red Dirt: A Tour Of Soil Orders

We break down soil orders like a field guide, linking what you see in a soil profile to how soils behave and how to manage them. From prairie-black mollisols to red-dirt ultisols, we share traits, regions, and practical tips growers can use today.

• soil taxonomy as a practical framework
• mollisols and their dark, organic-rich surface
• vertisols with shrink–swell clays and timing risks
• spodosols in conifer forests with leached E horizons
• alfisols, clay accumulation, and hardpan concerns
• histosols in peat bogs with high organic matter
• ultisols in the South, iron oxides, and low-activity clays
• regional patterns across the Upper Midwest to the Southeast
• field tips for digging, observing, and managing horizons

Tune in next time for a Tiny Byte of knowledge from GK Technology, where we have a map and an app for that!

https://gktechinc.com/

https://gktechinc.com/

Chapters

• 0:00 Framing Soil Taxonomy
• 1:02 Soil Orders Overview
• 2:42 Mollisols: Prairie Black Gold
• 3:39 Vertisols: Shrink–Swell Clays
• 4:26 Spodosols And Alfisols In Forests
• 7:26 Hardpans And Alfisol Features
• 7:26 Histosols: Peat And Organic Soils
• 8:18 Ultisols And Red Dirt Clays
• 9:52 Big Takeaways And Field Curiosity

Transcript

Jodi: 0:00

And now it's time for a Tiny Byte of knowledge.

Sarah: 0:13

Hey Jodi do you remember? Oh, sometime last year we did a tiny bite episode on what a soil series is. Remember how when you read what a soil series is, you can read all about the characteristics of that soil and everything that's in that. I think it's important for us to realize that there is a definite classification system. And one of the things within that system has to do with the broad base brush stroke of how we group together different soils and what their characteristics are that make them act similarly to each other.

Jodi: 0:49

Are you saying that there is a way of breaking down soils at a larger, more general way than just soil series?

Sarah: 1:00

Absolutely. There's a whole taxonomy system that we've got in the United States of America to help us think about the ways that soil are similar to each other and different from each other and different ways that we classify them. So just like we think about grouping together animals and animal taxonomy, we also can think about soils in that manner as well. So let me let me help you put this frame of reference together. So when you think about animals, you might think about animals being mammals or reptiles or amphibians or birds. They're all animals, but they're very different from each other. And I think we all know, especially in agriculture, that soil is all soil, but it can be very different. You know, we've got soil out there that's extremely sandy, we've got soil out there that's extremely clay, we've got soil that's in the desert, we've got soil that's in the Arctic. And we actually have a way of classifying those from a broad standpoint into what we call soil orders. Well, let's go through and name them all and let's see if we get them. Here we go. Ready? Entisols and septosols, vertisols, mollusols, olifosols, aridosols, spotosols, altosols, oxisols, histosols, andosols, and gelosols. Woo! That's a lot. That's a lot of cells. They all have different meanings behind them. And we can all we can think about like what these things are most common. So, for example, a mollusol. Jodi, what's a mollusol?

Jodi: 2:45

Mollusol is your basic prairie soil. It is a soil that when the way that you think about them is that they have a really dark soil or like a really dark color at the top. That is an artifact of having grown up under grass-like vegetation for a very long period of time. That black is organic matter. And typically they are grown in climates that are, you know, kind of more moderate. They're not arid, they're not really humid, but they're kind of in the areas between forested areas and arid desert areas. So, like for us in the United States, the Great Plain region, and also the Midwest region where there were grasslands. Those would be areas that have these soils that are mollusols.

Sarah: 3:27

And in North Dakota and Western Minnesota, we've got a lot of mollusols. So make up about 7% of the world's ice-free land. So if it's all right, I'm gonna talk about my favorite soil order, which is vertasols. Vertisols have high con have high clay content of highly reactive clays, which means there's a lot of shrink and swell to them. Um they crack open. So think about like when you get a drought and you lose your wrench down the crack in the soil. That's that's that type of soil. Okay. It's a vertisol. So in North Dakota, um, Minnesota, up here, we've got a lot of Fargo Hegney clays, but there's a lot of other places in the world that have them too. Only about 2% of the world's ice-free land surface is vertasols.

Jodi: 4:26

One other common one, and I think the two other common ones that I think are very important for us to talk about in the Midwest region would be spotosols and alpha sols. These are both forest soils. And spotasols, think about that as being like your northern Minnesota, your boreal forest areas, northern Wisconsin, that kind of thing. What makes these really characteristic are they kind of have these e-horizons or these horizons that are stripped of um organic matter from the second horizon down. And they're typically formed in areas, again, that are grown under spruce and pine trees. They're typically found in areas that have coarser textured deposits. And so the question is like, did they form because of the trees or did the trees grow there because of the soil? It's kind of a chicken and an egg thing. But the point is that spotosols are what we will find in coniferous forest areas, and we'll find those areas that e-horizon, that kind of white layer underneath that top organic matter layer.

Sarah: 5:29

And alpha sols are also have a history of being in the forested area. We actually do farm a number of alpha sols. Today they've been cleared of the trees. Alpha cells kind of result from a weathering process that leach clays and minerals and other constituents out of the surface layer and into the subsoil. Okay. Now, alpha cells make up about 10% of the world's ice-free land surface. Spotosols make up about 4% of the world's ice-free surfaces. So if you go over into Minnesota, for example, in northwest Minnesota, and you start heading east, there's a lot of alpha cells as you move into that neck of the woods. As you move further east, getting up towards uh like uh Duluth and the North Shore and all that, that's where we run into spotasols. And one of my personal dreams is to be in a root pit of a spotasol, because oftentimes they're really high in iron content as well, and maybe a little bit more acidic. So you get those bright red colors kind of going through there, along with that E horizon that Jody was talking about, and they're really colorful to look at. So one of my lifelong dreams is to be in a in a root pit of a spotasol. Wanna go with me? Vacation?

Jodi: 6:50

Absolutely, please. Those alpha cells, like that area where all those clays leach into, like that's what we typically think of. Like when we have like a clay hard pan, like you start talking about places like Missouri that have these hard pans that they're dealing with, and that is typically an artifact of the alpha-sol soil order, where you've got that zone where that clay accumulates, and you have that, it can be in some cases a restrictive layer where it's hard for water to move down. That's kind of a distinguishing characteristic and kind of a feature of the alphasol soil order.

Sarah: 7:25

Absolutely. For one second, I think it's really important for us to talk about histosols because in GK Technology's backyard of the home area, um, we actually have some histosols. You have to get up to northwest Minnesota into the peat bogs. Histosols are known for having a lot of organic matter and no permafrost. Um, because there's another soil order that allows for permafrost. But these are usually saturated, very high in organic matter. So really think about like what that peat is. Histosols make up only about 1% of the world's ice-free land surface. With that, I think it's important to note that there's a bunch of other soil orders that exist. A lot of them are um, oh, there is one that's also really important for agriculture. Ultasols, not around the Midwest, but when you move to the southern United States, there's a lot of ultasols when you get down there. Usually it's a little bit more humid. A lot of times they're dominated by a more one-to-one clay, which is very interesting from a standpoint that our clays that are on vertasols, known for that shrinking and swelling that we consider to be really reactive. One-to-one clays are not that reactive. They have a very low cation exchange capacity and they do not shrink and swell. So compaction can actually get to be a bigger issue uh in that soil. But there is definitely some farming that happens down there on these types of ultasols. Think like your Alabama's Mississippi's kind of that area. There's definitely some ultasols in that neck of the woods. Ultasols make up about 8% of the world's ice-free land surface.

Jodi: 9:13

They also have they also tend to have a lot of iron oxides. And for this is for young Jody who listened to a lot of country music growing up and always wondered about red dirt roads and always thought they were referring to like scoria um in western North Dakota. No, they were not referring to scoria. They were referring to the iron oxides found inside of their clays in their altasolic soil. So breaking Jodi's dreams of relevance in country music as a child, the red dirt roads, that red dirt country that all comes from the fact that they've got a different order of soils down in the south than we do up here. So even though we haven't covered all, or even though we haven't gone in depth in all 12 of the different soil orders, what am what's important to know is that soils vary a lot, just like we talked about and how we classify different animals or different types of life from like bacteria and between reptiles and mammals and birds, those are big differences, just like there are big differences in the different soil orders. And so as you travel in different climates to different um types of parent material where soil is formed, you're gonna find different different soils and you're gonna find different characteristics associated with those two. So be curious, grab a shovel, maybe even a Montana sharpshooter, dig some holes and see what's below your feet.

Sarah: 10:34

It's a lot of fun to check it out.

Jodi: 10:37

Tune in next time for a Tiny Byte of knowledge from GK Technology, where we have a map and an app for that.