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Transcript
Earth Systems and Resources
D. Soil and Soil Dynamics:
• Rock cycle
• Formation
• Composition
• Physical and chemical properties
• Main soil types
• Erosion and other soil problems
• Soil conservation
Rock Cycle
Three Types of Rocks
• Igneous – from heat, pressure (magma)
• Sedimentary – formed when sediments (sand,
mud, gravel, shells) are compressed
• Metamorphic – form when sedimentary/igneous
rocks are subjected to high pressure and T
http://www.youtube.com/watch?v=sLKXIVHoh54&
edufilter=vH8ntV7keCE-ZLl5wRMzNg
Rock Cycle
Weathering – breaking down rock into soil
Climate(T + water) + biotics
Creates erosion
Physical
Chemical
Biological
Chemical
Weathering
Biotic Weathering
• Roots
• Lichens
• Animals produce CO2 which diffuses into soil,
reacts with H2O & forms carbonic acid (H2CO3)
Soil Composition
•
•
•
•
Sand – largest type of soil; visible with the eye
Silt - flour; barely visible
Clay – very tiny, fine; electron microscope
Larger than 2mm in diameter = gravel/stones
(no value to plants)
Soil Horizons
• O horizon - uppermost layer; organic material
(plant decay)
• May be thick or thin (desert, tropical rain
forests)
• A horizon – mineral mixed with humus
• O + A = topsoil
Soil Horizons
• B – subsoil – clay; rich in Fe, Al compounds (acid
deposition)
• Lighter colored
• C – rock fragments
• Saturated with groundwater
• Usually no roots
• Borders parent bedrock
Soil Texture
• The percentages (by weight) of different sized
particles of sand, silt and clay
• How soil particles are organized and clumped
together. (sand, silt, clay)
Soil Horizons
•
•
•
•
Mature soils are layered
Infiltration – percolation
Leaching – dissolving minerals
Type of soil determines percolation and
leaching.
Soil Composition
• Porosity – volume and space between particles
• Porosity = permeability
• Sand, silt, clay
http://techalive.mtu.edu/meec/module06/Percolation.html
Mosaic of
closely
packed
pebbles,
boulders
Weak humusmineral mixture
Desert Soil
(hot, dry climate)
Dry, brown to
reddish-brown
with variable
accumulations
of clay, calcium
and carbonate,
and soluble
salts
Alkaline,
dark,
and rich
in humus
Clay,
calcium
compounds
Grassland Soil
semiarid climate)
Forest litter
leaf mold
Acidic,
light-colored
humus – little
topsoil
Humus-mineral
mixture
Iron and
aluminum
mixed with
clay
Light, grayishbrown, silt loam
Dark brown
firm clay
Tropical Rain Forest Soil
(humid, tropical climate)
Deciduous Forest Soil
(humid, mild climate)
Acid litter
and humus
Light-colored
and acidic
Humus and
iron and
aluminum
compounds
Coniferous Forest Soil
(humid, cold climate)
Soil pH
• Determines solubility of
minerals
• Most soils - 4.0 to 8.0
• Pygmy Forest in
California (2.8-3.9)
• Death Valley, California,
(10.5)
Factors Effecting Soil
• Depth - depends on erosion, plant life, etc.
• Color –
• Dark soil, rich, lots of organic matter (leaf
decay)
• Light soil (sand) very little organic matter
• Slope – runoff, erosion
Erosion
•
•
•
•
•
•
After plowing/harvesting
6.4 billion tons of soils per year (U.S.)
Renewable but recycles slowly
Unsustainable
Lowers fertility
Overloads lakes, rivers with sediments
Case Study: Soil Erosion in the U.S.
• 1985 Farm Act - subsidy for taking highly
erodible land out of production and
replanting it with soil-saving plants for 1015 years
Reducing Erosion
• No-till
• Minimum Tillage (reduced tillage)
Reducing Erosion
• Terracing
• Contour Plowing - plowing across the slope
• Windbreaks - also help retain soil moisture,
supply some wood for fuel, and provide habitats
for birds
• Strip cropping – a row crop (corn) is alternated
in strips with another crop that completely covers
the soil:
• Helps prevent the spread of pests and plant
diseases
Cover Cropping (alley cropping) – several
crops are planted together in strips or alleys
between trees and shrubs that can provide
shade (which reduces water loss by
evaporation) and helps to retain and slowly
release soil moisture.
Surface Creep – mountains/sand dunes
Desertification
• About one-third of the world’s land has lost
productivity due to desertification
• Drought
• Human activities that reduce or degrade
topsoil***
Salinization
• Repeated
irrigation causes
salt buildup
Solutions
Soil Salinization
Prevention
Cleanup
Reduce irrigation
Flush soil
(expensive and
wastes water)
Stop growing crops
for 2–5 years
Switch to salttolerant crops
(such as barley,
cotton,
sugarbeet)
Install underground
drainage systems
(expensive)
Fig. 13-15, p. 281
Transpiration
Evaporation
Evaporation
Evaporation
Waterlogging
Less permeable clay layer
Waterlogging:
1. Precipitation and irrigation water
percolate downward.
2. Water table rises.
Soil Conservation
• Fertilizers can help restore soil nutrients,
but runoff of inorganic fertilizers can cause
eutrophication pollution.
• Organic fertilizers: from plant and animal
(fresh, manure, or compost) materials.
• Commercial inorganic fertilizers: Active
ingredients contain nitrogen, phosphorous, and
potassium and other trace nutrients.
Fertilizers
• Organic Fertilizers – animal manure, crop
residues, bone meal, and compost
• Inorganic Fertilizers – man-made from chemical
compounds
• Benefits – exact compositions are known; they
are soluble & thus immediately available to the
plant
• Costs – quickly leach away (pollutes water);
doesn’t increase water holding capacity of the
soil as organic fertilizers do.