Physical Properties of SoilsPhysical Properties of Soils

GES175, Science of SoilsGES175, Science of Soils

Particle Size

* Physical properties are influenced by particle size

Size Classification (USDA):

Soil < 2 mm

Sand, 2 - 0.05 mm

Silt, 0.05 - 0.002 mm

Clay, <0.002 mm

Textural TriangleTextural Triangle

Clay

SiltSandLoamy Sand

Sandy Loam

Sandy Clay Loam

Silt LoamLoam

Clay LoamSilty Clay

Loam

SiltyClay

Percent SiltPerc

ent C

lay

Percent Sand

40

60

75

90

55

35

20

10

SandyClay

70 50 20

Clayey Soil(fine textured)

Clay

Clay LoamSilty Clay

Loam

SiltyClay

40

60

55

SandyClay

Loamy/Silty Soils

(medium textured)

Silt

Sandy Clay Loam

Silt LoamLoam

Silty ClayLoam

60

75

90

35

20

70 50 20

Sandy Soils(coarse textured)

SandLoamy Sand

Sandy Loam

20

10

70 50

Soil Structuregranular

prismaticCause and Effect

(description in laboratory)

+ Flocculation

Creating Structure

(chemical)

Surface Area

- aggregate of small particles

- large grain

vs

Aggregation

Creating Structure

- organic and inorganic ‘glues’

Lateral

Stress Forces(what breaks the ‘glue’)

Ver

tical

Spheriodal

Granular

Soil Structure:Surface Horizons

Poor Management

Granular

Massive

Compaction of Surface Horizons

- Platy Structure - compaction

Impact on soil compaction?

---- Prizmatic ----

Structure:Subsurface

Increased length in vertical direction

- lateral stress > vertical stress

Blocky Structure:(subsurface horizons)

• Increased (relative) age equates stress fractures

Organic soil

Db 0.8 Mg/m3

Bulk Densities

Compacted Subsoil Db 1.7 Mg/m3

Bulk DensitiesOrganic soil

Db 0.8 Mg/m3

versus

Well Sorted Sand

Macroporosity

Clay Aggregates

+ Flocculation

Aggregation

Internal Porosity

Micropores

Volcanic Ash Soil

Timber Harvest