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Overview of the Underpinnings and Building Blocks of Soil Taxonomy

Soil Forming Processes. Overview of the Underpinnings and Building Blocks of Soil Taxonomy. Why is this topic important?. Associating soil morphology with pedogenic process will make you a better pedologist

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Overview of the Underpinnings and Building Blocks of Soil Taxonomy

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  1. Soil Forming Processes Overview of the Underpinnings and Building Blocks of Soil Taxonomy

  2. Why is this topic important? • Associating soil morphology with pedogenic process will make you a better pedologist • An appreciation of these scientific underpinnings is required in order to understand rationale for the concepts in Soil Taxonomy

  3. Objectives • List Simonson’s 4 general processes of soil formation • Understand purpose of the diagnostic horizons in Soil Taxonomy • Know the difference between “diagnostic horizons” and “horizon designations (e.g., A-Bt-Bk-C)”

  4. Generalized Theory ofSoil Genesis (Simonson, 1959) Processes Parent Material (Phys, Chem., Biological) “biogeochemical” Today Time ‘0’

  5. Physical, chemical and biological reactions and interactions are categorized as soil-forming processes Additions Removals Transfers Transformations

  6. (Bockheim and Gennadiyev, 2000)

  7. Objectives • List Simonson’s 4 general processes of soil formation • Understand purpose of the diagnostic horizons in Soil Taxonomy • Know the difference between “diagnostic horizons” and “horizon designations”

  8. (Guy Smith, 1963) • Where Jenny’s soil forming factors (clorpt) are the same: • genetic expression is similar [result of soil forming processes] • the soils are the same due to pedogenesis • Similar soils respond equally to the same management.

  9. (Guy Smith, 1963) If soils w/ similar genetic expression respond the same, our goal is to: • Have a taxonomy that groups soils with similar genesis But you can’t observe soil genesis, so what’s the next best thing? Measure the morphological expression of soil genesis Guy Smith - Genesis does not appear in the definitions of the taxa but lies behind them.

  10. Ochric epipedon Albic horizon Spodic horizon Spodosol Diagnostic Horizons Processes Morphology - Addition of organic matter - Removal of base cations by leaching - Transformations to form amorphous alumino-organic complexes - Transfer of alumino-organic constituents and iron from surface to the subsurface

  11. Diagnostic Horizons • Taxonomic standards that reflect our understanding of soil genesis • Definitions are quantitative; objective. • Focus is on properties, not theories of genesis • Any competent soil scientist can classify • Based on measurable & tactile soil properties that are present today. • Not presumed for native state • Identified partly by • their own morphology and • how their properties compare to those in the overlying and underlying horizons • Not all mutually exclusive.

  12. Mollic epipedon Argillic horizon Not all mutually exclusive

  13. Objectives • List Simonson’s 4 general processes of soil formation • Understand purpose of the diagnostic horizons in Soil Taxonomy • Know the difference between “diagnostic horizons” and “horizon designations”

  14. Terminology • Horizon designations • Opportunity for the describer to express their opinion of soil genesis (A, Ap, Bt, Btk, Bk, Bkqm, C, etc.) based on what they see or infer • Horizon designations are subjective, based on the describer’s experience/understanding of soil-forming factors and processes

  15. Spodosol Diagnostic Horizons Processes Morphology - Addition of organic matter A Ochric epipedon E - Removal of base cations by leaching Albic horizon Bhs Spodic horizon - Transformations to form amorphous Alumino-organic complexes Bs C - Transfer of alumino-organic constituents and iron from albic to spodic

  16. Terminology • Horizon designations • Therefore, DO NOT ASSUME horizon designation implies a diagnostic horizon • Some examples: • Oa ≠ histic epipedon • Bk ≠ calcic horizon • Bt ≠ argillic horizon • Bw ≠ cambic horizon • Bx ≠ fragipan

  17. Diagnostic Horizons Definitions are measurable/observable Only 1 correct answer Horizon Designations Definitions less objective Reflects describers theory of genesis Diagnostic Horizons and Horizon Designations

  18. Summary • Horizons are morphological expressions of soil-forming processes • Diagnostic horizons are objectively defined taxonomic entities with strict criteria • Horizon designations are subjectively assigned and reflects the describer’s theory of soil genesis

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