Soil Properties 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

Meaning of “Soil” Means different things to different people. USDA definition … if it helps you to sleep. Willie’s take on the USDA concept of soil: Soil is material on landscapes that either: Has horizons formed from processes that occurred since deposition or exposure, or Has the in-place ability to support rooted plants.

Factors of Soil Formation Parent Material Time Soil Climate Relief Organisms

Floodplain Young Minimal development Low terrace “Middle aged” Moderate development High Terrace Old Maximal development

Soils as a Cosmic Experience - Evidence on a high hill that a river once was there.

Difference Between Mineral and Organic Soil Material Organic if: %OC ≥12% + 0.1 x % Clay

Degree of Organic Matter Decomposition ≥ 2/5 fibers (volume) after rubbing = Fibric < 1/6 fibers (volume) after rubbing = Sapric Intermediate = Hemic Fibric = low degree of decomposition Hemic = intermediate degree of decomposition Sapric = high degree of decomposition

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”

“Basic” Soil Texture Triangle Clay Clayey Loamy Sandy Sand Silt

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