Hyperarid Soils and the Soil Taxonomy.

The Soil Taxonomy has continued to undergo evolution since its initial publication in 1975. Much of the criteria currently used to classify Aridsols are derived from the deserts of western North America that span a broad range of altitudes, latitudes, temperatures, and moisture. In the past decade, research in hyperarid environments has revealed soil features that are regionally prevalent and distinctive, but not well captured in the current Soil Taxonomy (Amit and Yaalon, 1996; Ewing et al., 2006; Quade et al., 2007; Bockheim and McLeod, 2008). These soils bear features that can differ considerably from those in more humid desert environments. In particular, they often contain horizons cemented with halite (NaCl) or heavily enriched with nitratine (NaNO₃). Unlike soils commonly found in more humid regions, they may also lack most vascular plants, pedogenic carbonates, and biotic mixing processes

Here we propose that these omissions hinder the ability of scientists and researchers to clearly communicate relevant genetic, ecological, and economic information about these soils. We characterize soil from the Atacama Desert to illustrate how pedogenesis in extreme hyperarid environments differs from that in more humid environments, and we review the current literature regarding soils in other hyperarid locations with indurated soluble salt horizons. Based on the global occurrence of indurated salic horizons and nitric horizons in hyperarid soils, we propose that the Soil Taxonomy be amended to include a petrosalic diagnostic subsurface horizon, a nitric diagnostic subsurface horizon, and Petrosalids great group within the Aridisols order. Additionally, we suggest the establishment of a Hyperaridic Soil Moisture Regime (SMR). These changes to the Soil Taxonomy would create a more encompassing classification system.