The three taxa here represent intergrades/extragrades to other soil moisture regime (SMR) concepts. These soils have a soil moisture regime as well as a soil moisture subclass that is not "typic". Some soils have a moisture regime that is transitional to another regime (intergrades) or one that grades away from the regime they are assigned to (extragrades). See Soil Survey Tech. Note 9 Pby agbr0wn - Soil Taxonomy Forum
I think something that is missing from this discussion is the concept of “soil moisture subclasses.” A taxonomic moisture subclass that is not “typic” reflects a taxonomic intergrade or extragrade. Within the aridic areas of western part of the US we have significant areas of Xeric Aridic and Ustic Aridic soil moisture regimes where Mollisols are found. Ustolls allow either an ustic moiby agbr0wn - Soil Taxonomy Forum
I've been working on a validation script that evaluates "dark surface" epipedon (mollic, umbric) presence/absence and thickness for NASIS pedon records. For non-lab data, this assumes color is a reasonable surrogate for organic carbon and does not take into account base saturation for diff'n of mollic vs umbric. This has made me question when exactly the ochric epipedon hasby agbr0wn - Soil Taxonomy Forum
Thanks for your response! That is how I have always interpreted it. And how it seems to have been interpreted in a lot of the older data from the survey I'm working on. And how almost everyone else I have asked what they thought interprets it. BUT I've been challenging my assumptions about ST lately... and really digging into the wording (or lack thereof)... and found some prettyby agbr0wn - Soil Taxonomy Forum
To my knowledge is not specified where evidence of illuviation/high extensibility must be observed in order to meet the requirements for an argillic. Is it correct to say that the upper boundary of the argillic corresponds to the depth at which the necessary clay increase from eluvial->illuvial occurs regardless of the described morphology of the horizon (i.e. whether first subhorizon has tby agbr0wn - Soil Taxonomy Forum
Ken, Thanks for clarifying! I completely agree that it is within the purview and responsibility of the describer to make sure they tell the story appropriately. And as is obviously the case for the contacts / restrictive features, boundary distinctness/topography and the likely variability across the landscape certainly need to be taken into account when grouping soils for interpretations.by agbr0wn - Soil Taxonomy Forum
From the preface right before the "Key to Soil Orders" is the closest thing to a definition of "within" that I can find. It seems somewhat circular to me. "If diagnostic horizons or characteristics are criteria that must be 'within' a specified depth measured from the soil surface, then the upper boundary of the first subhorizon meeting the requirements forby agbr0wn - Soil Taxonomy Forum
Great! Well, that is very helpful to know what the official precedent on this is. Thank you.by agbr0wn - Soil Taxonomy Forum
I agree that this is probably the most sensible intended meaning. But I wonder whether "within" actually means that. Consider another, perhaps more common, case where we use within... Aquic Humixerepts "in one or more horizons within 75 cm of the soil surface" - in this case, because a horizon is specified we imply that some thickness of the feature of interest occurs aboveby agbr0wn - Soil Taxonomy Forum
Over the years I've encountered pedons described with diagnostic features / properties occurring "on the line" between different taxonomic groups. The word "within" is used throughout ST. Most often in the context of some material of some thickness/diagnostic feature occurring within a certain depth. Many of these usages are unambiguous due to other requirements for parby agbr0wn - Soil Taxonomy Forum