soil: supporting all life - western coventry...
TRANSCRIPT
• Food and water resources
• Disposing of waste
• Support for human
structures
• Growing timber and fibers
• Interact with forestry, wildlife,
and water resources
Bridgehampton Series, www.nesoil.com
Why Soils?
Characteristics of Soil
5.2 Soil
� Soil is part of the regolith that supports
the growth of plants.
• Regolith is the layer of rock and mineral
fragments that covers most of Earth’s land
surface.
5.2 Definition of Soil
• Depends on field or intended use
• Consists of minerals, organics, water, air
• Supports plants or shows evidence of pedogenesis
• Consists of naturally formed bodies
• Limited by rock/ice and deep water horizontally
• Upper limit air/shallow water• Lower limit where biological
activity stops/rock
Pedogenesis is the
science and study of the
processes that lead to the
formation of soil (soil
evolution)
Characteristics of Soil
5.2 Soil
� Soil Composition
• Soil has four major components:
1. Mineral matter: or broken-down rock
2. Humus: which is the decayed remains of organisms
3. Water
4. Air.
Characteristics of Soil
5.2 Soil
� Soil Texture
• Loam (a mixture of all three sizes) is best suited
for plant life.
• Texture refers to the proportions of different
particle sizes.
- Sand (large size)
- Silt
- Clay (small size)
Characteristics of Soil
5.2 Soil
� Soil Structure
• Soil particles clump together to give a soil its
structure.
Characteristics of Soil
5.2 Soil
� Soil Texture
• Soil particles clump together to give a soil its
structure.
• Sand- will not hold a ball in hand• Loamy sand- will hold a ball in hand, won’t ribbon• Sandy loam- ribbons, gritty texture• Silt loam- ribbons well, smooth texture, silt is floury when dry• Fine sandy loam- ribbons, easily mistaken for silt loam, but
less soapy/slippery in hand• Gravel- >2 mm, “pebbles”
• Note that sand particles can be seen with the naked eye, silt cannot
Soil Formation – Five Factors
5.2 Soil Forming Processes - 5
� The most important factors in soil
formation are parent material, time,
climate, organisms, and slope.
1. Parent material
• Transported soil—parent material has been
carried from elsewhere and deposited
• Residual soil—parent material is the bedrock
5.2 Soil Forming Processes
• Till: Mixed unsorted (unstratified) particle sizes laid down below ice
• Outwash: stratified sands and gravels carried by glacial water, flat areas
• Loess: wind-blown silt-sized materials deposited over till and outwash
• Peat and Muck: organic, poorly drained soils
Receding glacier in Iceland, NASA
Soil Formation
5.2 Soil
• RI soils are young/weakly
developed
• Wisconsonian glacier
retreated in RI ~15,000
years ago
• Mature soils have
maximum horizonation and
are stable/ in equilibrium
with environment
2. Time
• The longer a soil has been forming, the thicker it becomes.
• Important in all geologic processes
Soil Formation
5.2 Soil
Climate
• Precipitation, temperature, humidity, seasonal variability
• Direct effects: temperature and precipitation weathering
• Indirect effects: vegetation
3. Climate
• Greatest effect on soil
formation
Soil Formation
5.2 Soil
• Vegetation most important, depends on climate, parent material, topography, drainage, etc.
• Microorganisms-decompose OM to provide nutrients, aggregation, water holding capacity
4. Organisms
• Furnish organic matter to
soil
• Organisms influence
the soil's physical and
chemical properties.
Soil Formation
5.2 Soil
5. Slope• Orientation, or direction the slope is facing,
influences soil formation.
- Soil temperature
- Moisture
The Soil Profile
5.2 Soil
� Soil varies in composition, texture, structure,
and color at different depths. Soil horizonsare zones or layers of soil. A soil profile is a vertical section through all the soil horizons.
• The A horizon is commonly know as topsoil.
• The B horizon is subsoil and contains clay
particles washed out from the A horizon.
• The C horizon is between B horizon and
unaltered parent material.
Soil Profile
• Vertical cross-section
of soil layers
(horizons)
• Horizons differ in
color, texture,
structure, etc
• Common sequence in
RI:
– O, A (E), B, C
Birchwood Series, www.nesoil.com
Soil Horizons
• O: formed from organic matter (plants and animals), commonly seen in forested areas but often absent in developed/cultivated areas
Oa- highly decomposed
Oi- undecomposed/fibric
• A: “topsoil,” mineral with lots of organics (making color darker), biologically active (roots, fungi, bacteria, mammals, bugs, worms, etc), most affected by acid rain
Ap horizon- plow/disturbed layer, mixed O, A, E, B horizons. Thicker than A horizon (>2 inches)
Soil Horizons
• E: Eluvial horizon, zone of leaching, light in color, rare in RI due to cultivation
• B: “Subsoil,” yellowish or reddish brown in well drained soils, accumulation zone (illuviation)
• C: Under the solum (A and B), less biological activity, weathering, structure, but still more weathered than bedrock
• R: Bedrock- RI soils are not formed in weathered bedrock as in many other areas (we will get to glaciation later)
5.2 Soil Reaction
• pH: 0-14, 7 neutral
• In RI soils acidic due to:
– Granite parent material
– Leaching of bases
– Plants give off H+
• RI soils “very strongly
acid” pH 4.5-5.0
• pH often increased for
agriculture by liming
(CaCO3)
Soil Types
5.2 Soil
� Three common types of soil are pedalfer,
pedocal, and laterite.
1. Pedalfer
• Best developed under forest vegetation
• Accumulation of iron oxides and aluminum-rich
clays in the B horizon
Soil Types
5.2 Soil
2. Pedocal
• Accumulates calcium carbonate
• Associated with drier grasslands
3. Laterite
• Hot, wet, tropical climates
• Intense chemical weathering
Soil Erosion
5.2 Soil
• Human activities that remove natural vegetation,
such as farming, logging, and construction, have
greatly accelerated erosion.
� Water erodes soil.
� Rates of Erosion
� Sediment Deposition
• Reservoirs fill with sediment.
• Sediments are contaminated by pesticides
and fertilizers.