Transcript Soil and Erosion

Soils
Soils
• Products of weathering
Soil Characteristics
• Regolith
– Loose material covering solid rock
• Dust, sediment, broken rock
– Soil is the only part that supports the growth of
plants
Soil Characteristics
• Composition
• Texture
• Structure
Soil Composition
• Mineral matter
– Broken rocks
• Organic matter (humus)
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Remains of dead organisms
Source of nutrients
Increases ability to retain water
Percentage varies
• Bogs are almost all humus, deserts have very little
Soil Composition
• Water
– Provides moisture for chemical reactions
– Provides nutrients in a form that plants can use
• Air
– Source of CO2
Soil Texture
• The proportions of particle sizes
• Influences ability to support plant life
• Based on % of clay, sand and silt
Soils
SAND:
• Drains quickly; dries out
Soils
LOAMY SAND:
• falls apart when handled.
Soils
LOAM:
• feels spongy
• Drains well without drying out
• Contains more nutrients
Soils
SANDY LOAM:
Soils
SANDY CLAY:
Soils
SILT LOAM:
Soils
CLAY:
• Drains slowly
• Hard for plant roots to grow
Soils
SILTY CLAY:
Soils
SILTY CLAY LOAM:
Soils
CLAY LOAM:
Good Quality Soils
• Typically consist of 50 % organic and mineral
matter
• Other 50 % consists of pore spaces
– Air and water circulation
Soil Structure
• Soil particles form clumps that give soils a particular
structure
– Determines:
• How easily it will erode
• How easily it can be cultivated
• Water infiltration
Soil Formation
Parent Material
• Source of the mineral matter
• Bedrock
– Residual soil
• Unconsolidated material
– Transported soil
Parent Material
• Affects:
– Rate of weathering and soil formation
• Unconsolidated material forms soils more quickly than
residual
– Plant fertility
• Determines types of plants that can grow
Soil Formation
• Climate:
– Temperature, humidity, precipitation
– Most important factor
• Time:
– Older soils are thicker
Soil Formation
• Organisms
– When living things die, decomposers break them
down
• They become part of the soil
• Add nutrients to soils
• Plant acids speed up weathering
– Burrowing
• leaves holes for air and water circulation
Soil Formation
• Topography/Slope
– Steeper slopes have more erosion, less water
Soil Profiles
• Soil forms top down
• At different depths, soil varies in:
– Composition, texture, structure and color
Soil Profiles
• Mature soils tend to have 3 distinct horizons
Soil Horizons
• O
– Humus, typically considered part of A
• A
– Topsoil, mostly organic matter
• B
– Subsoil, lower limit of roots and burrowing,
– Hardpan – clay that forms a compact layer
• C
– Partially weathered parent material
Pedalfer
• Forms in temperate areas with more than 63 cm of
rain each year
– Much of the eastern US
– B horizon
• Large amts. of iron oxides (reddish brown)
Pedocal
• Forms in drier western US
– Less clay (b/c weathering is slower)
– Contain calcium carbonate – light brown
Laterite
• Hot, humid, tropical areas
• Lots of water
– Distinctive orange-red
• Almost no organic material (quickly used)