Physical Properties 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 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

Clayey Soil (fine textured) Clay 40 55 Silty Sandy 60 Silty Clay Loam

Loamy/Silty Soils (medium textured) Silt Sandy Clay Loam Silt Loam Silty Clay 60 75 90 35 20 70 50

Sandy Soils (coarse textured) Sand Loamy Sandy Loam 20 10 70 50

(description in laboratory) Soil Structure granular Cause and Effect (description in laboratory) prismatic

Creating Structure Flocculation + (chemical)

Surface Area vs - large grain - aggregate of small particles

Creating Structure - organic and inorganic ‘glues’ Aggregation

(what breaks the ‘glue’) Stress Forces (what breaks the ‘glue’) Vertical Lateral

Soil Structure: Surface Horizons Spheriodal Granular

Massive Poor Management Granular

Compaction of Surface Horizons - Platy Structure -

Impact on soil compaction?

Structure: ---- Prismatic ---- Subsurface Increased length in vertical direction - lateral stress > vertical stress

(subsurface horizons) Blocky Structure: (subsurface horizons) Increased (relative) age equates stress fractures

Bulk Densities Organic soil Db » 0.8 Mg/m3

Bulk Densities Organic soil Compacted Subsoil è Db » 0.8 Mg/m3 versus Compacted Subsoil è Db » 1.7 Mg/m3

Macroporosity Well Sorted Sand Clay Aggregates

Micropores + Flocculation Aggregation Internal Porosity

Timber Harvest Volcanic Ash Soil