Willie Harris apatite@ufl.edu Acknowledgments: Wade Hurt Mike Vepraskas FAESS Soil Scientists Overview of Soil Properties 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 Climate Soil Organisms Relief Time 1
Morphological effects of factors river system example 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. Mineral vs Organic Soil Material Organic Soil Material if: %OC 12% + 0.1 x % Clay Keep in mind that this is USDA speak ; Organic Soil Material can be dominated by inorganic components Rationale A little OM goes a long way in controlling soil properties 2
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 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, book is opened to the 10R Page 3
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) hue value chroma Red Hue 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 4
Value The Lightness or Darkness of Spectral Color 10/0 - Pure White 5/0 - Gray 0/0 - Pure Black Chroma Neutral Color Pure Color /0 /2 /4 /6 /8 Increasing strength of color Increasing grayness Optimum conditions Natural light Light at right angles Light at right angles Soil moist Sobriety Reading Soil Colors 5
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. 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 Properties in describing soil layers (cont.) 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. 6
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 Sand & Loamy Sand Textures Sand Sandy Clayey Loamy Silt 7
Properties in describing soil layers (cont.) Structure: Way soil particles aggregate into larger units with planes of weakness between them. Individual aggregates called peds. Common surface structure: granular (small spheroids) Images taken or adapted from USDA Soil Survey Manual Examples of common subsurface structure: Prismatic or Blocky Columnar 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 For zones intergradient between horizons above and below: Use letters for the 2 horizons, putting horizon of dominant influence first. Ex: BA, AE For cases where homogeneous zones of one horizon occur within another: Put matrix (dominant) horizon first & use a / between them. Ex: E/A, B/A 8
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 f. Horizon Boundaries boundaries Distinctness (thickness) Topography ------------ ---------- Abrupt: <2 cm Smooth Clear: 2-5 cm Wavy Gradual: 5-15 cm Irregular Diffuse: >15 cm Broken Bringin it all back home A - E1 - E2 - Bh - 10YR 3/1; sand; cw boundary 10 YR 5/2; sand; gw boundary 10 YR 7/1; sand; as boundary 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 9