Post on 05-Jan-2016
transcript
Soil Properties
Website to download files of talks:wgharris.ifas.ufl.edu.hsw.htm
Willie Harrisapatite@ufl.edu
Acknowledgments:Wade HurtMike VepraskasFAESS Soil Scientists
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
Climate
Parent Material
Organisms
Relief
TimeSoil
•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 ariver once was there.
Difference Between Mineral and Organic Soil MaterialOrganic 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 decompositionHemic = intermediate degree of decompositionSapric = high degree of decomposition
a. Color: A key property in hydric soil interpretation
Properties used in describing soil layers
• 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, thebook is opened to the 10RPage …
Hue:Related toWavelength
Value:Related toreflectance
Chroma: Degree of spectral purity
Here, thebook is opened to the 10YRPage …
Notation worksLike this:
yellowish brown (10YR 5/6)
hue value chroma
HueRed
Yellow-Red
Yellow
0 2.5R 5R 7.5R 10R
0 2.5YR 5YR 7.5YR 10YR
0 2.5Y 5Y 7.5Y 10Y
Hues highlighted in yellow are the common soil hues.
Value
• 10/0 - Pure White
• 5/0 - “Gray”
• 0/0 - Pure Black
The Lightness or Darkness of Spectral Color
“Neutral”Color
“Pure”Color
/0 /2 /4 /6 /8
Increasing strength of color
Increasing grayness
Chroma
Reading Soil Colors
• Optimum conditions– Natural light– Clear, sunny day– Midday– Light at right angles– Soil moist
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
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
Sand Silt
Loamy
Sandy
Clayey
c. Structure: Way soil particles aggregate into larger units with planes of weakness between them. Individual aggregates called peds.
Examples of common subsurface structure:
BlockyPrismatic orColumnar Platy
Common surface structure is granular: small spheroids
Soil Horizon DesignationsSoil 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)
B – Accumulation of components translocated from above – In-situ accumulation of metal oxides – Other in-situ gains and losses
E – Loss of fine-textured components; “eluviation” – Characterized by clean sand, light color (high value, low chroma)
C – Little or no alteration; rock structure often evident
R – Rock
c. Transition Horizons
(1) For zones which exhibit properties which areintergradient between overlying andunderlying master horizons:
* Use letters for the 2 horizons, putting thedominant horizon first. Ex: BA, AE
(2) For cases where homogeneous zones of onehorizon occur in another.
* Put matrix (dominant) horizon 1st and usea "/" between them. Ex: E/A, B/A
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
f. Horizon boundaries
Distinctness (thickness) Topography------------ ----------Abrupt: <2 cm SmoothClear: 2-5 cm WavyGradual: 5-15 cm IrregularDiffuse: >15 cm Broken
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