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Proposed Master V Horizon: Importance in Arid Landscapes

Learn about the significance of V horizons in soil and the proposed terminology change to highlight their ecological importance in arid and semi-arid regions.

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Proposed Master V Horizon: Importance in Arid Landscapes

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  1. A proposed master V horizon for near surface horizons with vesicular porosity Judith Turk University of California, Riverside Carrie-Ann Houdeshell USDA-NRCS, Victorville Robert Graham University of California, Riverside

  2. Vesicular Horizons

  3. Vesicular horizons Vhorizon 0 20 40 Depth (cm) Vhorizon 60 (Rossi, 2009) 80 10 15 20 25 30 35 40 45 Silt (%)

  4. Vesicular Horizon Formation

  5. Formation in Laboratory Miller, 1971

  6. Why we need a master V horizon: • V horizons are critical to hydrologic and ecological function of arid and semi-arid lands • V horizons are abundant and widespread • Currently there is no NCSS-approved terminology for V horizons • V horizons are designated as A horizons in NCSS terminology, but do not fit the main concept of an A horizon

  7. Definition of proposed horizon V horizons: Mineral horizons that have formed at the soil surface, or below a layer of rock fragments (e.g., desert pavement), physical or biological crust, or recently deposited eolian material. They are characterized by the predominance of vesicular pores and have platy, prismatic, or columnar structure.

  8. Hydrologic and ecological function: Vesicular horizons have low infiltration rates Young et al., 2004

  9. Occur primarily in intercanopy spaces Undercanopy: Absent or weak V horizon Intercanopy: Strong V horizon

  10. V horizon formation in intercanopy leads to heterogeneity of hydraulic properties Schafer et al., 2007

  11. Infiltration rates in soils with V horizons are consistently lower than those with non-vesicular A horizons

  12. Runon from intercanopy soils helps to support plant growth in shrub islands

  13. Distribution of V horizons • V horizons occur on every continent • In the United States there are 1460 soil series with vesicular horizons • These soil series include Aridisols, Mollisols, Entisols, Alfisols, Inceptisols, Andisols, and Vertisols • The total mapped area of these soil series is 200,000 km2 (52 million acres)

  14. Current vesicular horizon nomenclature • Terms used in scientific literature • Av horizon • Vesicular layer • Schaumböden (foam soil) • FAO-WRB • Yermic diagnostic horizon (desert pavement and vesicular layer) • USDA-NRCS • Usually designated as A horizons • No terminology specific to the vesicular horizon

  15. Limitations of current NRCS nomenclature: Vesicular horizons as A horizons • Does not fit the main concept of A horizon • Not enriched in humified organic matter • Designated as A horizons because they are at the surface • Does not distinguish between surface horizons that support rapid infiltration and those that impede infiltration (V horizons) in desert landscapes

  16. Summary Currently there is no NCSS terminology to distinguish the vesicular horizon from other types of surface horizons. Adoption of a master V horizon by the NCSS will highlight the presence of a widespread and ecologically important soil feature in arid and semi-arid lands.

  17. Acknowledgments Supporting research funded by: USDA-NRCS Helpful comments on the proposal were provided by: Joe Chiaretti Craig Ditzler Brenda Buck Patrick Drohan Les McFadden

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