Soil Science Section 3

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Loam

a mixture of sand, silt, and clay particle that exhibit the properties of those separates in about equal proportions

Soil Aggregates

many soil particles held in a single mass or cluster such as a clod, crumb, block or prism

Effected by:
-flocculation: the mutual attracting among clay and organic molecules

-shrink and swell

Structure Types

granular- porous
crumb- very porous
platey- caused by compaction
blocky
columnar- round tops
prismatic- flat, angular tops

Bulk Density (Db)

oven dry soil mass (g)/
total soil volume (cm3)

*Root penetration decreases with increasing Db and soil strength

Textural Class Determination

*EXAMPLE
Textural Triangle: 10-60-30
10% sand
60% silt
30% clay

Db of Soils

sandy loam= 0.84 g/cm3
silt loam= 0.78 g/cm3
clay= 1.2 g/cm3
sandy loam= 1.54 g/cm3

Particle Density (Dp)

mass per unit volume of soil particles
Dp= oven dry soil mass (g)/
volume of solids (cm3)
avg.= 2.65 g/cm3

Porosity (%)

100% - (Db/Dp x 100)

Macropores

*larger than 0.08 mm
sandy soils -> water flow fast

Micropores

*smaller than 0.08mm
clayey soils -> water flow fast

Water Flow in Soils

Texture:
-macropores and micropores
Structure:
-VERY IMPORTANT FOR CLAYEY SOILS
-granular structure -> water flow fast
-prismatic structure -> water flow slow
Compaction:
-increase compaction -> decrease water flow
Depth to Water Table
-causes landslides because water will build up
Slope
-steeper slope= less water moving into and
through soil profile

Soil Temperature

aspect: the angel at which the sun's rays strike the soil influences soil temperature
Rain
Soil Cover: bare soils warm up more quickly

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