|Response to Impact of expanding the A horizon definition|
|Author: Joe Chiaretti Created on: 8/29/2012 MessageID: 1547|
|The A horizon has traditionally been regarded as the surface horizon or the first mineral horizon that exists in mineral soils. The genetic information transmitted with the A horizon label is not now and never has been, strictly the accumulation of humified organic matter. Note the use of the “Ap” horizon designation. A disturbed mineral horizon is designated Ap even though it is clearly a former E, B, or C horizon. This suffix symbol “p” indicates a disturbance of the surface layer by mechanical means, tillage, pasturing, or similar uses. So regardless of what genetic process occurred in a mineral surface horizon or whether it has accumulated any humified organic matter or not, it is designed as an A horizon (i.e., an Ap) if it is plowed or disturbed. It also does not matter if the Ap horizon occurs in a perhumid climate or a desert climate. It has universal applicability to connote surface disturbance. You cannot justify the addition of a master V horizon by implying that vesicular A horizons violate the definition of what an idealized A horizon is supposed to be. The definition for the master A horizon currently has two options. One option recognizes the accumulation of humified organic matter. The other option recognizes disturbance by humans or their livestock. Note item (2) in the current definition: “(2) properties resulting from cultivation, pasturing, or similar kinds of disturbance.” This item allows for the Ap horizon designation in mineral horizons that may have theoretically have no accumulation of humified organic matter whatsoever. You cannot disregard this part of the A horizon definition by focusing only on the first part that suits your viewpoint. This part of the A horizon definition has been imbedded in NCSS standards since before we became pedologists. The Ap horizon designation is used in soil descriptions wherever in the world soils are cultivated, pastured, or disturbed by mechanized equipment.|
The NCSS has no control over commercial dictionary definitions for what an A horizon is. We only have control over the definitions we provide in NCSS soil survey information and our soil survey standards documents. You continue to assert that surface horizons dominated by vesicular pores don’t display the accumulation of humified organic matter. Perhaps it is true locally in the extremely arid regions of the Mojave Desert that you are most influenced by. But it is simply not true as a all-inclusive statement for horizons with vesicular pores everywhere. A horizons dominated by vesicular pores obviously do accumulate humified organic matter in many regions, but to a lesser extent than A horizons lacking vesicular porosity. The amounts are all relative. They certainly don’t accumulate as much organic matter as A horizons of soils occurring in humid regions. Just because vesicular A horizons of desert soils aren’t as high in organic matter as the A horizons of hydric soils in the eastern US for example, does not invalidate the designation as an A horizon. We don’t have, nor do we need, regional master horizon designations that connote different degrees of the same pedogenetic processes.
The proposal to expand the definition of the A horizon does not “redefine” the A horizon as you state. This proposal actually validates the current usage of the A horizon designation for dry soils. It does not “complicate communication with the public” in any manner as you assert (assuming the public even cares one bit about any of this). So please don’t kick up a dust cloud of fake issues with phrases like “legal regulations”, “major undertaking”, and “serious consequences.” The proposal simply recognizes that surficial processes of soil formation can allow the formation of vesicular porosity in A and E horizons. That is all the A horizon proposal does-nothing more, nothing less. The proposal to expand the definition of the A horizon supports and validates the numerous existing horizon designations of A horizons that have a morphology dominated by vesicular pores.
On the other hand, the proposal to add the master V would complicate communication on horizon designations. It seeks to create a new mineral surface horizon designation that attempts to carve out a new space of its own and instead overlaps on the existing definitions of horizons A and E. The proposed V horizon is a combination of different and conflicting genetic processes assembled under the overriding concept of a dominance of vesicular pores. I fail to see how the V horizon improves communication about genetic processes when the dominant genetic process that forms it cannot even be categorized as eluvial, illuvial, or neither.
|Total messages in this thread... 3|
Impact of Expanding the A horizon definition
Response to Impact of expanding the A horizon definition (current)
The A Horizon in Rules and Regulations