I strongly oppose the creation of a master ""V"" horizon based simply on the presence of vesicular pores. I would reluctantly support a horizon suffix instead as a compromise.
Before my retirement June 1, 2012 I served for years on the West Region NCSS Standards committee and provided many, many comments on this topic. I spoke at length with Drs. Buck and Graham about this topic, and my experice with soils with vesicular pores.
During my nearly 35 year career I mapped and correlated over a million acres of soils in MLRAs 35, 36, and 42 in Colorado, New Mexico, and Utah. I also described and sampled soils in the Peruvian Desert in 2008 where I observed soils/horizons very similar to those hyper desert soils of southern California.
Many of the Natrargids I mapped and correlated in New Mexico often had thin (.25 to 1 inch) E horizons with platy structure and fine and medium vesicular pores. These E horizons were occasionally covered by desert pavement but not always. These E horizons overlaid Btn horizons that had very restricted water movement due to the high SARs. The E horizon itself did not have restricted water movement. These horizons were fragile and could be easily eroded upon physical disturbance and/or high precipitation events. In New Mexico these soils occurred in both the thermic and mesic soil temperature regimes. I also observed some occurring in a frigid regime in the deserts of southwestern Wyoming.
Another situation where I often observed E horizons with vesicular pores were in soils in the Big Sage-Pinyon-Juniper ecozone of the Colorado Plateau in Western Colorado and New Mexico, and eastern Utah. The soils in this zone typically have a mesic soil temperature regime and an Ustic bordering on Aridic (Aridic Ustic) soil moisture regime. A dominant subgroup was Aridic Haplustalfs. E horizons with platy structure and fine and medium vesicular pores were commonly found and described. The dominant parent material of these soils was slope alluvium derived from eolian deposits. These E horizons often overlaid a cambic or argillic horizon. Their thickness ranged from about 0.5 to 1 inch. These horizons typically had no to very few rock fragments. These horizons did not have restricted water infiltration or movement. These E horizons tended to be found more in the bare areas that occurred in the interspaces between trees/shrubs. Where there was good ground cover, with OM being added to the surface, these horizons were darker and were described as ""A"" horizons with vesicular pores. The platy structure and vesicular pores are created by the intense heating and wetting cycles that occur on these soils.
In the Colorado Plateau situation, when we were selecting type locations for soil series, we often tried to find locations that were in the best possible rangeland condition possible. Because these locations had better ground cover, with more OM input, these soil series type locations were mostly described with ""A"" horizons. That is the reason why few of the soil series in this area are typified with E surface horizons. However, for those that mapped these areas it was common knowledge that an E horizon with vesicular pores was part of the natural variation within a soil series concept. Whether it was an ""A"" or an ""E"" we saw no significant difference in infiltration or permeability. Pore type was insignificant compared to OM content.
I have also observed some Mollisols in eastern Colorado that have ""A"" horizons that have vesicular pores. Granted, most have granular or subangular blocky structure, but some have vesicular pores.
While working in the Peruvian Desert, whose average annual precipitation was 0.2 inches of rainfall, I observed soils with E horizons similar to those soils in the desert regions of California. The soils I described in Peru formed in loamy-skeletal colluvium on mountain sideslopes, debris flows, and debris fans. These E horizons were much thicker, up to 12 inches thick, and were dominated by coarse and very coarse vesicular pores. Their structure was weak coarse and very coarse subangular blocky. Rock fragment content was greater than 35% with loamy coarse sand and loamy sand fine earth textures. These E horizons were sometimes at the surface, but could also be found underlying very recent ""C"" material layers. They often overlaid weak cambic or argillic horizons. The area was devoid of vegetation. Since it never rained while I was there, I do not know if these Peruvian soils with E horizons with vesicular pores are water restrictive.
I would like to believe that most of us would agree that soils with horizons with vesicular pores can, and do, occur in many different climates, parent materials, land forms, and vegetation types. It may be that in some situations, horizons with vesicular pores be of significant thickness, and have a significant quantity and size of vesicular pores, that they do have an overarching influence on water movement through the soil.
However, there are many more situations where vesicular pores may be present, but are an insignificant property and do not restrict water movement. To insist that a master ""V"" horizon designation be assigned to all horizons where vesicular pores are present is not good science, and sets a dangerous precedent to the future of Soil Taxonomy.
