I noticed that there was an error in the depiction of the placic horizon (section 3, page 113 and 114). As noted on pg 113, placic horizons may not be more than 25mm thick when associated with spodic materials. Page 114 then shows a 20cm thick “placic horizon” above a spodic horizon. I realize one could argue what the key words “associated with spodic materials” actually means, but I think if the horizon in question is found directly on top of a spodic horizon then the association is clear. According to the scale in the photo, it looks as if the horizon is actually 20cm thick, and its not just an error in the photo caption (ie, "cm" should be "mm").
I think this photo is actually showing continuous ortstein. Working with these soils in New England and New York, I know that it is often difficult to determine in the field whether or not the cemented horizon actually contains spodic material due to the very dark colors imparted from the organic matter (ie, the spodic colors are “masked”). However, taxonomy allows for dark colored horizons to be called spodic if they are more than 50% cemented, and these horizons are often described as a “Bhsm” when occuring adjacent to more easily identifiable spodic horizons ("Bs" or "Bsm" horizons).
Additionally, I would like to see a description of ortstein included in the next version of this guide, since the photo is already available. Any thoughts on this?
This is another forum topic altogether, but I think this calls into question the utility of having both of these diagnostic horizons, placic and ortstein. If anyone would like to explore that topic further I would be happy to start the discussion.
-Josh Paul
Soil Scientist
Fairbanks, AK
