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Physical Properties of Soils
GES175, Science of Soils Physical Properties of Soils
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Particle Size * Physical properties are influenced by particle size
Size Classification (USDA): Soil < 2 mm Sand, mm Silt, mm Clay, <0.002 mm
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Textural Triangle Percent Clay Percent Silt Percent Sand Clay Silt 40
55 Silty Clay Sandy Clay 60 35 Silty Clay Loam Clay Loam Sandy Clay Loam 75 20 Loam Silt Loam 10 Sandy Loam 90 Loamy Sand Silt Sand 70 50 20 Percent Sand
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Clayey Soil (fine textured) Clay 40 55 Silty Sandy 60 Silty Clay Loam
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Loamy/Silty Soils (medium textured) Silt Sandy Clay Loam Silt Loam
Silty Clay 60 75 90 35 20 70 50
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Sandy Soils (coarse textured) Sand Loamy Sandy Loam 20 10 70 50
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(description in laboratory)
Soil Structure granular Cause and Effect (description in laboratory) prismatic
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Creating Structure Flocculation + (chemical)
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Surface Area vs - large grain - aggregate of small particles
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Creating Structure - organic and inorganic ‘glues’ Aggregation
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(what breaks the ‘glue’)
Stress Forces (what breaks the ‘glue’) Vertical Lateral
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Soil Structure: Surface Horizons Spheriodal Granular
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Massive Poor Management Granular
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Compaction of Surface Horizons
- Platy Structure -
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Impact on soil compaction?
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Structure: ---- Prizmatic ---- Subsurface
Increased length in vertical direction - lateral stress > vertical stress
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(subsurface horizons)
Blocky Structure: (subsurface horizons) Increased (relative) age equates stress fractures
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Bulk Densities Organic soil Db » 0.8 Mg/m3
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Bulk Densities Organic soil Compacted Subsoil è Db » 0.8 Mg/m3
versus Compacted Subsoil è Db » 1.7 Mg/m3
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Macroporosity Well Sorted Sand Clay Aggregates
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Micropores + Flocculation Aggregation Internal Porosity
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Timber Harvest Volcanic Ash Soil
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