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Soil Morphology

Willie Harris apatite@ufl.edu. Soil Morphology. Acknowledgments: Wade Hurt Mike Vepraskas FAESS Soil Scientists. Website to download files of talks: wgharris.ifas.ufl.edu.hsw.htm. Properties used in describing soil layers. a. Color: A key property in hydric soil interpretation.

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Soil Morphology

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  1. Willie Harris apatite@ufl.edu Soil Morphology Acknowledgments: Wade Hurt Mike Vepraskas FAESS Soil Scientists Website to download files of talks: wgharris.ifas.ufl.edu.hsw.htm

  2. Properties used in describing soil layers a.Color: A key property in hydric soil interpretation • Most evident • Influenced by OM and redox-sensitive metals • Wetness affects OM and redox-sensitive metals

  3. Color is described using the Munsell Color Book Here, the book is opened to the 10R Page …

  4. Hue: Related to Wavelength Value: Related to reflectance Chroma: Degree of spectral purity

  5. Here, the book is opened to the 10YR Page … Notation works Like this: yellowish brown (10YR 5/6) value hue chroma

  6. Hue Red 0 2.5R 5R 7.5R 10R Yellow-Red 0 2.5YR 5YR 7.5YR 10YR Yellow Hues highlighted in yellow are the common soil hues. 0 2.5Y 5Y 7.5Y 10Y

  7. Value • 10/0 - Pure White • 5/0 - “Gray” • 0/0 - Pure Black The Lightness or Darkness of Spectral Color

  8. Chroma “Neutral” Color “Pure” Color /0 /2 /4 /6 /8 Increasing strength of color Increasing grayness

  9. Reading Soil Colors • Optimum conditions • Natural light • Clear, sunny day • Midday • Light at right angles • Soil moist

  10. Contrast of Colors • Contrast refers to the degree of visual distinction between associated colors. • Faint-- evident only on close examination • Distinct-- readily seen • Prominent-- contrast strongly • Hydric soil indicators specify distinct or prominent.

  11. Abundance and Size of Color Contrasting Areas • Few -- less than 2% • Common -- 2 to 20% • Many -- more than 20% • Fine -- < 5 mm • Medium -- 5 to 15 mm • Coarse -- > 15 mm • Abundance more important for Hydric Soils

  12. b. Texture - proportions of sand, silt, and clay • The mineral component is usually described by it’s texture. Soil texture refers to the relative amounts of the variously sized soil separates. Where: • Gravel and larger fragments are >2 mm in diameter. • Sand is 2 -0.05 mm in diameter. • Silt is 0.05 to 0.002 mm in diameter. • Clay is < 0.002 mm in diameter.

  13. Relative Sizes of Soil Particles Sand (0.05-2.00 mm) Silt (0.002-0.05 mm) Clay (<0.002 mm)

  14. USDA Textural Classes - Defined by “textural triangle”

  15. c.Structure: Way soil particles aggregate into larger units with planes of weakness between them. Individual aggregates called peds. Common surface structure is granular: small spheroids Examples of common subsurface structure: Prismatic or Columnar Blocky Platy

  16. Soil horizons are layers formed via soil processes Soil Horizon Designations Master Horizons O – High organic matter content; “organic soil material”! A – Enriched in organic matter content; but not “organic soil material”! – At surface or below O – May be an “A” if disturbed (e.g., plowing) E – Loss of fine-textured components; “eluviation” – Characterized by clean sand, light color (high value, low chroma) B – Accumulation of components translocated from above – In-situ accumulation of metal oxides – Other in-situ gains and losses C – Little or no alteration; rock structure often evident R – Rock

  17. Transition Horizons

  18. Subordinate Distinctions within master horizons • Convey information about soil genesis and disturbance • Designated by lower case. EX: Bt, Bw, Ap • Important ones for Florida: • Ap - plowed or disturbed surface • Bt - illuvial accumulation of clay • Btg - illuvial clay + iron reduction or depletion • Bh - illuvial accumulation of aluminum and carbon • Oi - fibric organic soil material • Oe - hemic organic soil material • Oa - sapric organic soil material

  19. Horizon Boundaries

  20. Bringin’ it all back home A - 10YR 3/1; sand; cw boundary E1 - 10 YR 5/2; sand; gw boundary E2 - 10 YR 7/1; sand; as boundary Bh - 5 YR 2/1; sand; gw boundary Btg1 - 10 YR 5/2; sandy clay loam; gw boundary; blocky structure Btg2 - 10 YR 6/2; sandy clay loam; blocky structure

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