Another important change was that ICOMOD introduced "Spodic Materials" as a diagnostic property. See pg 22/23 of the latest Keys. To be a spodic horizon, the layer must have spodic materials. Item 1 of the required characteristics for spodic materials includes both pH and carbon. Item 2b3 addresses iron and aluminum. The spodic horizon, by definition, must contain spodic materials, so the properties you ask about are still there. An important goal for ICOMOD however was to try to put more emphasis on field morphology and less on chemistry. Of course this is not entirely possible to achieve. If you read the spodic materials criteria carefully you'll see that item 1, required in all instances, is chemical in nature (pH and OC). Item 2a is strictly morphological and allows some layers to be identified as spodic materials with pH, OC, and morphology alone. Item 2b 1&2 can also be considered as morphological criteria. Items 2b3 and 2b4 cover the remaining instances and involves chemistry in the form of Fe and Al or ODOE in and above the layer with spodic materials. You might consider these as a "last resort" when morphology alone (plus OC And pH) is not enough.
A common "complaint" about soil taxonomy is the reliance on laboratory data. The introduction of the concept of spodic materials is a good example of how this ICOM responded to those concerns by constructing a definition that only requires extensive laboratory data for the more difficult situations. Since the adoption of these changes it became significantly easier for soil scientists in the field identify a spodic horizon with pretty high confidence without having to relay on laboratory results.
