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