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