Eutric/Dystric qualifiers (by John Hollis, Allan Lilly and Bob Jones, UK)

[StephanMantelISRIC]

Our concern relates to a few specific minor changes that have introduced additional qualifiers or modified existing ones. Of course we recognise that all classification systems change over time as our understanding of soil processes develops. However some of the newly introduced criteria seem to be ‘minor additions’ that are either inconsistent with respect to other diagnostics or add rather complicated details that are not useful for interpreting the soil type with respect to important soil functions. Our work updating the WRB course for the UK has highlighted the four problems specified below.

1. Whilst the linking of pH values to base saturation and the ratio of exchangeable Al to exchangeable base cations (WRB Annex 2, page 220) is to be welcomed, the introduction of different ways for defining Eutric/Dystric qualifiers (based on exchangeable Al to exchangeable base cations) and Mollic/Umbric horizons (based on base saturation) seems to introduce inconsistency. As far as we can see, it means that Umbric topsoils with a pH between 4.9 and 5.3 would also have a Eutric qualifier. We do not understand why this distinction has been made.

(by John Hollis, Allan Lilly and Bob Jones, UK)

[StephanMantelISRIC]

Comment Cezary Kabala:
We know the problem you highlighted (‘Eutric Umbric’) and we must find solution for it, but it requires more data and global analysis (eg, if we want to replace complicated and expensive base saturation with simple/cheap pH).
This is why the newly introduced concepts must be extensively tested and may be removed or modified in the next edition of WRB. Thus, your findings and suggestions are important and will be considered - but not now. The next edition is not planned earlier as in 2030. I am sure that the ‘overcomplication’ at various levels (criteria, qualifiers, rules) will be one of the most common topics discussed in the future. If the pressure from the societies for simplification will be strong, we will remove some solutions and will be more assertive in case of new demands... But we cannot stop a development at all.

[StephanMantelISRIC]

Response ohn Hollis, Allan Lilly and Bob Jones, UK:
Cezary has explained that our concerns about the counter-intuitive possibility of having a Eutric, Umbric qualifier combination is a recognised problem. We understand that these things happen and look forward to the resulting solution once it has been developed. We would stress that the move to include a general relationship between exchangeable cations -anions and pH is a very useful one that provides a potential field assessment to estimate an important property that can only be precisely defined by a complicated analytical procedure. The problem as we see it is the use of two different criteria to define qualifiers that are both effectively a means of identifying Base Status and would like to know the reason for this.

[StephanMantelISRIC]

Comment Cezary Kabala:
The problem of variable methods used for BS calculation and variable BS criteria for particular diagnostics in WRB are questioned during many meetings and in the letters; thus, we are sure it must be harmonized. We discussed this harmonization last year, but (1) we didn't have enough data to select the "best" solution, and (2) there was a fundamental dispute among members of WRB WG about the replacement of BS with pH. There are at least four solutions: (1) to return to BS saturation calculated based on "true" CEC, as in Soil Taxonomy (and in WRB for mollic/umbric), in all diagnostics throughout the WRB (>>changed in the past because 'true' CEC is problematic and not measured in many countries), or (2) to harmonize BS calculation for all diagnostics throughout the WRB based on base cations and aluminium (as it is now) for Dystric/Eutric (>> large difference with Soil Taxonomy for all diagnostics and RSGs), or (3) to harmonize BS calculation for all diagnostics throughout the WRB based on base cations and exchangeable acidity (in 1M KCl) (>> large difference with Soil Taxonomy for all diagnostics and RSGs), or (4) to replace BS with pH value (measured in distilled water) in all diagnostics throughout WRB, as the simplest analytical method, also applicable in the field (>> poor availability of complete and reliable data for "true" CEC and pH for all RSGs, in particular for Ferralsols where negative delta pH may occur). As I wrote previously, we have to harmonize criteria, but first we must complete data for point (4) and discuss the replacement of BS with pH. If we reject this concept, we will discuss selecting one of solutions (1-3).