Soil Morphology Willie Harris apatite@ufl.edu 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 Most evident Influenced by OM and redox-sensitive metals Wetness affects OM and redox-sensitive metals

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

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

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

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

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

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

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

Contrast of Colors Faint -- evident only on close examination 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.

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

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.

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

USDA Textural Classes - Defined by “textural triangle”

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

Soil Horizon Designations Soil horizons are layers formed via soil processes 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

Transition Horizons

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

Horizon Boundaries

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