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NRES 201 Lec. 3 Soil color, texture and structure

Texture, Structure, Color and Consistence of Soils

Texture Structure Color Consistence

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NRES 201 Lec. 3 Soil color, texture and structure

Soil Texture

· Coarse Fragments > 2mm

­ Gravel < cobbles < stones < boulders

· · · ·

Sand 2- 0.05mm (2000-50 µm) Silt 0.05 to 0.002 mm ( 50-2 µm) Clay < 0.002 mm (<2 µm) Texture Class = relative % of soil separates by weight

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NRES 201 Lec. 3 Soil color, texture and structure

USDA TEXTURAL CLASSES

90

10 20

80

70 CLAY

30

ILT TS EN RC PE

PE RC EN TC LA Y

60

40

50 SANDY CLAY CLAY LOAM

SILTY CLAY

60 70 80

40

30

SANDY CLAY LOAM

SILTY CLAY LOAM

20 LOAM 10 SAND LOAMY SAND

80 70

30

SANDY LOAM

SILT

RGD 5/90

PERCENT SAND

90

SILT LOAM

50

10

90

60

50

40

20

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NRES 201 Lec. 3 Soil color, texture and structure

SOIL STRUCTURE

Soil structure refers to how the individual sand, silt, and clay particles are arranged into stable aggregates. - can be affected by management Structural units are know as aggregates or peds.

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NRES 201 Lec. 3 Soil color, texture and structure

SOIL STRUCTURE

Soil structure results when soil particles are pushed together by: - freezing-thawing

important in temperate climates

- wetting-drying

important in humid climates - tillage operations mixing organic material into soil

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NRES 201 Lec. 3 Soil color, texture and structure

SOIL STRUCTURE

Stability of peds depends on cementing agents that bind the sand, silt, and clay particles together: soil organic matter (humus) chemical bonds, sticky polysaccharides secondary carbonate and iron oxides chemical bonds water films - tension clay - flocculation, cationic bridges

CLASSIFICATION OF SOIL STRUCTURE 1) Structureless Massive or single grained 2) Structured Granular, platy, subangular blocky, angular blocky, prismatic, and columnar Structure provides qualitative information about the physical condition of the soil.

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NRES 201 Lec. 3 Soil color, texture and structure

SOIL STRUCTURE

Soil structure creates a framework of aggregates and establishes the pore space in the soil. Ideal soil; good balance of micro- and macropores

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NRES 201 Lec. 3 Soil color, texture and structure

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NRES 201 Lec. 3 Soil color, texture and structure

SOIL STRUCTURE

Clods vs Peds - clods are produced by improper tillage wet soils, heavy equipment

- peds are produced by natural soil forming processes

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NRES 201 Lec. 3 Soil color, texture and structure

SOIL STRUCTURE

Micropores retain water against the pull of gravity. They contain the soil solution. Macropores drain free of water. They contain the soil atmosphere. For a soil to be well-aerated there must be a continuous arrangement of macropores from the surface to subsoil (i.e. worm holes, cracks, abandoned root channels)

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NRES 201 Lec. 3 Soil color, texture and structure

Soil Color

· · · · · Dark = organic matter Red = iron Brown = well drained Grey (gley) = poorly drained Mottled, redoximorphic concentrations, depletions = restricted aeration, poor drainage

Soil Color (cont'd)

· Interpreting Colors

­ Diagnostic (Mollic epipedon) ­ Productivity (black/yellow) ­ Greys/blues anoxic/water

· Causes of Color

­ Organic matter ­ Water content ­ Fe and Mn

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NRES 201 Lec. 3 Soil color, texture and structure

Hue Red in front of Book, Brown in Middle, Yellow in the Back Value

Munsell Soil Color Charts

Chroma

10YR 4/4

Dark Yellowish Brown

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NRES 201 Lec. 3 Soil color, texture and structure

Soil Consistence

· Response of soil to applied force at various moisture content · Moist = loose, friable, firm, very firm, brittle · Wet = plastic/non plastic, sticky

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NRES 201 Lec. 3 Soil color, texture and structure

Good Topsoil From Dredged Illinois River Sediment

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Microsoft PowerPoint - Lec 3 Soil color, texture, structure Fa 08.ppt

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