Proposed changes to soil classification

Bienvenue / Welcome Forums Soil Pedology Discussion Forum Proposed changes to soil classification

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    • #4488

      Hello all,

      Below are a few suggestions to changes to existing soil orders and subgroups, or places where the existing classification tends to fall apart in the field:

      Black Chernozems vs. Dark Gray Chernozems

      These great groups are very similar, which is understandable given that they are ‘next’ to each other on the ‘soil continuum’.

      Orthic Dark Gray Chernozem (O.DGC)

      Common horizon sequence: Ahe, Ae, Bm or Btj or Bt, Cca or Ck

      Orthic Dark Gray Chernozems are identified by the following properties:

      -They have a Chernozemic A horizon with a color value darker than 3.5 moist and 3.5-4.5 dry for virgin soils (3.5-5 dry for Ap).
      -They have a B horizon (Bm, Btj, Bt) at least 5 cm thick that does not contain alkaline earth carbonates.
      -They lack an Ae horizon more than 5 cm thick.
      -They lack a Bnjtj horizon or a similar horizon characteristic of intergrades to the Solonetzic order.
      -They lack evidence of gleying as indicated by faint to distinct mottling within 50 cm of the mineral surface.

      Orthic Black Chernozem (O.BLC)
      Common horizon sequence: Ah, Bm Cca or Ck

      Orthic Black Chernozems are identified by the following properties:

      -They have a Chernozemic A horizon with a color value darker than 3.5 moist and dry.
      -They have a B horizon (Bm, Btj, Bt) at least 5 cm thick that does not contain alkaline earth carbonates.
      -They lack an eluvial horizon (Ahe, Ae, Aej) at least 2 cm thick.
      -They lack a Bnjtj or similar horizon characteristic of intergrades to the Solonetzic order.
      -They lack evidence of gleying as indicated by faint to distinct mottling within 50 cm of the mineral surface.

      Eluviated Black Chernozem (E.BLC)
      Common horizon sequence: Ah, Ae, Btj, or Bt, Cca or Ck

      These soils have the general properties of the Chernozemic order and the Black Chernozem great group. They differ from Orthic Black Chernozems by having an eluvial horizon or horizons at least 2 cm thick (Ahe, Ae, Aej) usually underlain by a weakly to moderately developed illuvial Btj or Bt horizon.

      As you can see, there is quite a bit of overlap

      The soil groups share the following common points:
      – A colours of 3.5 moist
      -They can have an eluvial horizon <5 cm thick (Orthic Black have <2 cm, Eluviated Black and Dark Gray <5 cm)
      -They can both have Ae and Bt horizons, and still be considered “Orthic”

      While the 5 cm cut-off makes sense in distinguishing between Chernozems and Luvisols, a 3 cm difference between Dark Gray and Black Chernozems is confusing, particularly given how little colour difference there can be between the A horizons of the two groups. While one could argue that an O.DGC can have a thick Ahe horizon, while an O.BLC cannot, the prevalence of tillage makes things even less clear. Natural Chernozems are becoming increasingly rare, and with such minimal differences in colour requirements for A horizons, it’s beginning to make less sense to keep the great groups separate. While there may be (slight) pedological differences between the two groups, there is little functional difference in how they are managed or salvaged. I suggest it may be better for the sake of clarity to merge the Dark Gray Chernozems into the Black chernozem great group.

      Cumlic Soils

      Gleyed Cumulic Humic Regosol (GLCU.HR)
      Common horizon sequence: Ah, Cgj, Ahb, Cgj

      These soils have the properties specified for the Regosolic order and the Humic Regosol great group. They differ from Cumulic Humic Regosols by having faint to distinct mottles that indicate gleying within 50 cm of the mineral surface.

      Another place where the orange book falls apart is with Gleyed Cumulic Humic Regosols, or rather, the absence of a Cumulic subgroup in the Gleysol order that captures a very similar profile as that outlined above, but with prominent mottles in the upper 50 cm of the solum (e.g., Ah, Cg, Ahb, Cg). Organic cumulic profiles are accurately captured with cumuluic subgroups (e.g., CU.H), yet no Cumulic Humic Gleysol exists (nor Cumulic Orthic Gleysol). All three examples(GLCU.HR, CU.H, proposed CU.HG) follow the same formation trajectory, and occur in similar locations (e.g., along rivers, etc.), where flooding has deposited material upon existing soil profiles and buried them. Yet the presence of prominent mottles causes gelysolic soils formed this way to be shoe-horned into existing classification with a string of series modifiers.

      While mottling is a very important process in soil classification, there is little standardization between orders as to when the gleyed subgroup kicks in or not. For example:
      -Brunisols (fine or coarse textured) receive gleyed subgroup classification when they have faint or distinct in the upper 50 cm of the solum, or prominent in the bottom 50 cm of the solum
      -Chernozems are gleyed only when there are faint or distinct mottles in the upper 50 cm of the solum
      -Luvisols are gleyed when they have distinct mottles in the upper 50 cm of the solum (faint don’t count), or prominent in the bottom 50 cm of the profile.

      While one could argue that soil texture plays a role, fine textured Brunisols exist, as do fine textured Chernozems (and of course Luvisols). Conversely, all three orders exist with medium texture or moderately coarse textured profiles. Since mottles are important in classification, it would make sense to standardize when and where they are important. To me, the Luvisolic order seems the most intuitive. Faint mottles can be caused by a variety of things such as slight textural changes between A and B horizons. A change from LS to SL texture is enough to slow water movement to cause faint mottling, while distinct and prominent mottling indicate longer-term saturation of horizons. The current system seems unorganized with mottling, and somewhat over-sensitive to it.

      I fully realize I may be kicking the hornet’s nest, but I have extensive experience with soil survey and classification, and these are areas where at the very least a discussion needs to occur (regardless of the outcome). Please feel free to let me know your thoughts an opinions.

      Kind regards,


    • #4489

      Jorden, thank you for the comments and suggestions. Before going into detail, I can tell you that each and every one of the discussion points you have provided have surfaced in many discussions after long days of soil survey. You are not alone in these suggestions. I will try to tackle them in the order provided. And by no means will I promise to give you a satisfactory answer. This forum is really to start the discussions and see where the community lands on the ideas. These are all certainly valid proposals for updating the CSSC.

      I certainly agree with your concerns about the taxonomic distance between the O.BLC, E.BLC and and O.DGC subgroups. We might have to do some more digging here to see how the differentiation were made, and why. It seems to me illogical that O.BLC (and O.BC and O.DBC for that matter) can have a Btj or a Bt horizon with an Ae less than 2cm. I wonder, was this in error? A copy-paste issue? I would think that the Orthic subgroups would not allow for Bt as a horizon. Would be worth a review of the 2011 Special Issue of the CJSS focused on the taxonomic system to see if there might be some more details.

      Cumulic Gleysols:
      I agree with you and have seen this in the field as well. A lot in northern Alberta to be honest. And this would be an easy integration that could be proposed for the CSSCv4. What would be good to see are some example profiles cumulic gleysols from your work, and even some information about estimated acreage from some recent work to highlight the need to this update.

      I can tell you this has been an issue I have dealt with many times over when training students. I have built tables to show this on many occasions. I think part of this has to do with the Soil Key in the CSSC, and part of it has to do with the “status” of the soil orders. If you take the Podzolic Order, gleyed subgroups require distinct to prominent mottles within the top 1m of the soil profile. Notice that the Podzolic Order “keys out” ahead of the Gleysolic Order on pages 33-34 of the orange book, which means the occurrence of prominent mottles is ignored, and makes sense because Podzolic soils in most cases are in very humid climates, and more prone to mottles. With regards to the other soils, I need to do more reading, but have a couple of hunches. For the Luvisols, they are like the “end” members of the soils with clay movement – or the much more developed Brunisols. So the “higher” level soil may require more in terms of mottling to get it to the Gleyed subgroup. In addition, there may have been consideration for perched water tables in Luvisolic soils. The Bt tends to perch water in the profile and slow percolation downwards, and this can lead to mottling in the upper portion of the profile that is an artifact of the perched water table and not an indication of a ground water table, as you indicated in your post. I think the key here might be the source of the water table – perched or the actual groundwater table. As for the Chernozems, a deeper look at the lack of an indication of prominent mottles would be interesting. this seems to be a missing piece, and is worth looking into.

      So I cannot provide you with a quick solution, but I think some of these points are certainly ones that have long been discussed by soil survey crews around the (restaurant) dinner table. I think some more research into some of these issues and a read of the 2011 publication might help sort some of this out – that does not mean these changes should not be considered and discussed, just more context. Maybe a short discussion paper with some references? Are you up for it??

      • #4490


        I’m always up for a challenge, and a rabbit-hole to go down. I’ll do some digging, and see what I can find, and if there is a logical flow for these calls between CSSC, the 82 manual (if needed), and the 2011 special issue.

      • #4491

        For the cumulic Gleysols, I would like to think that in theory, those are most likely to be limited to the Rego subgroups?

        Cumulic Rego Gleysol
        Cumulic Rego Humic Gleysol

        One would think it odd, in s cumulic environment, to have time for development of a Bg??

      • #4492

        Yes, precisely. I’m not so fussed about a buried O.HG or O.G, as I am about a R.HG or R.G. that’s got prominent mottling. These are much more common than a fully developed gleysol, that’s been buried (I don’t think I’ve ever seen anything like that).

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