soils. products of weathering soil characteristics regolith – loose material covering solid rock...
TRANSCRIPT
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)– 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)