Changes to the order of RSGs in the key and how decision are/have been made

[StephanMantelISRIC]

Dear Peter,
Thanks for the response. I trust you have read the historical reviews on the use of criteria for classification from 1974 to 2022 (on the KU Leuven WRB website). In the 6 editions of related soil classification systems (FAO and WRB), the differences in criteria and limits used for diagnostic horizons and definitions of RSGs accepted by “consensus” by these different groups of high-level soil experts is extremely high. “Consensus” seems therefore to be a very flexible and changing matter depending on who is there or not there to make a decision.
On Retisols: the discussion in the WRB working group in Rome in 2014 focused on the renaming of Albeluvisols as Retisols and the definition of the retic properties that expanded the concept of the Albeluvisols and was approved indeed with a large consensus. This is also what is mentioned in the Manual on the changes introduced by WRB2014.
However, the Retisol discussion did not go into the fact that Planosols and Stagnosols were now allowed to have albeluvic glossae (making many former Albeluvisols Retic Stagnosols) . The larger picture therefore is that Retisols now cover a smaller area than the Albeluvisols did, although the Manual says the opposite.
Note that the Munich WRB meeting that came before the Rome one, explicitly stated that Stagnosols should not have albeluvic glossae.
As there are no minutes of both meetings to my knowledge, it is difficult to prove if a large consensus existed or not on the specific decisions considering the whole picture.
Solutions: misunderstanding could be avoided by better documenting changes (and their justification) and by making decisions affecting RSGs subject to consulting a truly international external group of knowledgeable experts and/or major users (for instance national soil correlators)
Best regards
Freddy

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From: Peter Schad <peter.schad@tum.de>
Sent: Friday, November 21, 2025 5:14 PM
To: Freddy Nachtergaele <freddy_nachtergaele@hotmail.it>; Ólafur Gestur Arnalds - LBHI <oa@lbhi.is>; Seppe Deckers <seppe.deckers@kuleuven.be>
Cc: Cezary Kabała <cezary.kabala@upwr.edu.pl>; Mantel, Stephan <stephan.mantel@wur.nl>
Subject: Re: Old letter (decision) from Otto Spaargaren (and Deckers and Nactergaele) on Andosols/Gleysols

Dear Freddy,

I don't remember how broad was the consensus for giving Gleysols priority over Andosols in 2013. But I do remember about the two other decisions, which you brought up: The consensus was very broad!

Kind regards
Peter

[StephanMantelISRIC]

Dear Freddy,

I can only contribute with my personal memory. And I remember a broad consensus in the WRB Board. But the two decisions were different. The Fluvisols was just one decision. The Retisols was an evolutionary process with suggestions, decisions, new suggestions, re-decisons etc. (meetings in Freising, Ulm, Rome and Hannover).

Albeluvic tonguing and retic properties required and require a marked textural difference between the lighter-coloured and the intensively-coloured parts. This has often been overlooked. People saw the different colours and concluded Albeluvisol and Retisol without checking if the texture is different. Many of the soils called Albeluvisol or Retisol in fact always have been Stagnic Alisols, Stagnic Luvisols or Stagnosols, because the lighter-coloured and the intensively-coloured parts have the same texture. They are not Retisols, and this is not because of the position in the key, but because they fail criterion 4 of the retic properties (criterion 4 of the albeluvic tongues).

About the historical review: You draw a conclusion about the decision-makers: The did not act carefully, when making big changes, especially in 1998 and in 2014, but also in 1974, when the Podzoluvisols abruptly ended at the Polish-Soviet border. But one can also draw a conclusion about the soils: The design of this RSG has been obviously very arbitrary, and it would therefore be better to abolish it. Indeed, when preparing the 3rd edition of WRB, there was a strong motion to abolish Albeluvisols completely.

Please, find attached two beautiful Retisols. Names according to the third edition of WRB. No stagnic properties, no albeluvic tonguing, just retic properties. They cover large areas in eastern Europe.

Kind regards
Peter

[StephanMantelISRIC]

Dear Peter,
Thanks for your prompt reply, the pictures and the clarification of the process in the case of the Retisols.
I am not sure why you state that the textural difference between the glossae and the argic horizon is often not fulfilled.
If there is a clear albic horizon over an argic with glossae, one would safely presume that the texture in the glossae would be the same as in the albic. The problem occurs when the albic horizon has been ploughed and one is only left with claric material in the argic. I doubt that routine sampling would involve separating the glossae from the argic for textural determination. The difference in field texture and the colour would suffice in that case.
Three decisions made since 2014 have made the classification of Retisols indeed problematic: (1) the raised clay increase required to have an argic horizon (2) allowing albeluvic glossae in Stagnosols (3) the weakened requirements to qualify for a Stagnosol.
Also note that the attention paid to the glossae during surveys was different from country-to-country eg I understand Poland did not record them, which partly explains the artificial border or the Podzoluvisols in the soil map of the world.
Of course I do not question the existence of non-stagnic Retisols (thanks again for the photographs, but it would be nice if you could share the associated standard description and analysis), but a high proportion of Albeluvisols were stagnic…
As for getting rid of the Retisols that would be fine, provided the Stagnosols are downgraded as well. After all we do not want to have 31 RSGs.
Best regards
Freddy

[cyrus621]

For reference, the Soil Taxononmy glossic horizon is somewhat more broadly defined than the WRB retic properties:

Glossic Horizon
The glossic (Gr. glossa, tongue) horizon (fig. 3-15) develops
as a result of the degradation (note 42) of an argillic, kandic,
or natric horizon from which clay and free iron oxides are
removed. It consists of two major parts: (1) an argillic, kandic,
fragipan, or natric horizon, and (2) albic materials.
Required Characteristics
The glossic horizon is 5 cm or more thick and consists of:

1. An eluvial part (albic materials, defined below), which
   constitutes 15 to 85 percent (by volume) of the glossic horizon;
   and
2. An illuvial part, i.e., remnants (pieces) of an argillic,
   kandic, or natric horizon (defined below).

Notice the 15-85% here and 10-90% in WRB. Also here no texture requirements. The ST albic materials have colour requirements by themselves, but unlike WRB there is no definition of colour differences with the remnant argillic etc.

[cyrus621]

There is some discussion of this off-forum, which could be put here for reference. But I can add an interesting perspective on how key order might be decided. A recent paper about the soil classification used in the ongoing 3rd (Chinese) National Survey is here: 龙怀玉卢昌艾, & LONG HuaiYu, L. C. (2024). 《第三次全国土壤普查暂行土壤分类系统》土类检索系统构建 A Retrieval System for Great Soil Groups from China’s Provisional Soil Classification System for the 3rd National Soil Census. 中国农业科学, 57(21), 4264–4275. https://doi.org/10.3864/j.issn.0578-1752.2024.21.008

This survey uses an updated version of the older Genetic Soil Classification of China (GSSC) inherited/adapted from Soviet ideas. Despite there being a modern Chinese Soil Taxonomy (CST), the older system is used in the 3rd survey, I think because it updates a 2nd survey which used that older system, before CST was developed.

Interestingly and amazingly, the GSSC never had a priority key -- at least as far as I can determined. Each group was defined as a central concept. This of course lead to “one soil having multiple names” and “different soils sharing the same name” as the (English) abstract states. So these authors decided to make a priority key of the 62 "great groups" (3rd level) to be used for mapping in the 3rd survey.

Now to the interesting point -- how to establish a priority key? "Four principles for retrieval order were set up, which included

1. prioritizing the importance of agriculture
2. prioritizing ease over difficulty in identification
3. narrowing down meaning,
4. clustering similar types, and
5. reflecting the spatial evolution and development patterns of soil." (numbers added by me).

I am not advocating this for WRB, but presenting as an interesting way to make a key that is useful for its purpose, here updating a soil survey whose main purpose is for agriculture, making it as easy as possible for the field scientists (a huge group and not all with full training) to identify a soil, and resolving naming conflicts. You can see the order in the English abstract, it's quite interesting. And now with translation, you can read each group's definition. Each except the first starts with "其他土壤 other soils" as in WRB, ST etc.

And finally, the first group to key out is "Artificial Soils" (Technosols)! I guess because (1) not used for ag. -- point 1. above, (2) easy to identify (point 2. above)