Fabio,
I don't have an answer for you, but I did some reading and found a little information on the subject.
There is a Guy Smith publication (1986) called, "The Rationale for Concepts in Soil Taxonomy" that discusses lab vs. field identification of Spodosols. He mentions New York, where they set up chemical requirements to differentiate Spodosols and Inceptisols. They received additional data on much older Spodosols, many of which failed to meet the chemical requirements established in New York. So they included crack coatings as field criteria. He states, "the chemical requirements are for the intergrades with the Dystrochrepts, and only for that." He also mentions that the most developed of the Spodosols often failed to meet the chemical criteria, that people were unhappy with the spodic definition, and that there were proposed changes to the chemical criteria.
My take on this is that the original chemical requirements, based on rations of pyrophosphate extractable, iron and aluminum were only sufficient where they were developed, so new chemical and physical criteria were established. We currently use ammonium oxalate extractions and ODOE values.
I wonder if the Canadians still use pyrophosphate ratios. Below is the citation for the publication I mentioned.
- Andysol
1986. The Guy Smith Interviews: Rationale for Concepts in Soil Taxonomy (SMSS technical monograph no. 11) USDA Soil Conservation Service. T.R. Forbes (Editor)
Edited 2 time(s). Last edit at 03/29/2017 03:39PM by Ken Scheffe.
