Download Soil Horizons

Soil Composition
Soil is where all 4 spheres meet and interact: geosphere,
biosphere, hydrosphere, atmosphere
Soil Types
Bad for Plants
Sandy: lots of pore space; water
drains too quickly; soil cannot
retain water
Clay-rich: Drain slowly (platy clays
can get compact; hard for roots to
penetrate; Too wet for plants; not
enough aeration
Good for Plants
Loamy: enough pore space for water retention/drainage/ aeration
Sandy Soils: NJ Pine Barrens
Nutrient Poor Soils (drain
quickly)
Plants that can be successful in
nutrient poor soils: pines, shrubs,
carnivorous plants (pitcher
plants)
Clay-Rich Soils
Factors Important to Soil Formation
Factors in Soil Formation
• Parent material: Source of
mineral matter
• Residual soil: forms on parent
material; takes longer
• Transported soil: forms NOT on
“unconsolidated deposits” (moved
from parent material)
Parent Material & Soil Formation
1. Rate of weathering can depend on rock type/minerals present
2. Minerals in parent rock affect soil “fertility”
Factors in Soil Formation: Climate
•Climate = Greatest effect on soil formation
•Climate drives weathering! Weathering creates soil and
removes nutrients from soil (by dissolving ions)
Factors in Soil Formation: Time
Young Soil: Parent material influences soil the most
Old Soil: More time for weathering; Climate & other factors influence most
Factors in Soil Formation:
Organisms
• Vegetation = main source of organic matter
• Microorganisms (bacteria & fungi): decompose
organisms & return nutrients to soil (increase
fertility)
• Earthworms and insects: burrow & aerate soil
• Nitrogen-fixing bacteria: help plants get nitrogen for
amino acids
Nitrogen-fixing bacteria & Soil
• N.fixing bacteria:
convert N2 gas to
ammonium (then
changed to nitrates that
plants can absorb & use)
• Live on roots of legumes
(beans, peanuts, clover)
• Add nitrates to soil
(increase fertility)
• Denitrifying bacteria:
Nitrates in soil --> N2 gas
Proteins/amino acids require Nitrogen. Plants can only
get nitrogen in the form on nitrates in soil.
Factors in Soil Formation: Slope (Relief)
• Steep slopes: Lots of soil erosion (water moves faster); little
soil; can’t hold moisture
• Flat: little erosion; poor drainage
Soil Horizons (Profile)
A: Top soil; Abundant organic
matter (plants, decaying matter,
decomposing organisms, & insects)
B: Sub-soil; Enriched in clay
(weathering product); plant roots
cannot penetrate thru. bottom of
“hardpan” = compact clay
C: Partially weathered parent
material: no plants
http://passel.unl.edu/animation/soilhorizons.swf
http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1130447025&topicorder=4
Soil Types
Pedalfer: Temperate climate (seasons); Eastern U.S.; Forested
areas; B horizon has iron oxide and Al-rich clays (chemical
weathering)
Pedocal: Drier climates; grasslands/prarie; Western U.S.;
abundant calcium carbonate minerals (little chemical
weathering, too dry)
• Hot, wet tropical
areas;
• intense chemical
weathering (lots of
water & warm
temps);
• Iron oxide (red soil)
and Al-rich clay.
Soil Types
Laterites: Poor soils for farming
Left: Nutrient poor soil of
Amazon
Right: Amazon soil enriched by
indigenous practice of adding
manure, bones, etc.
Tropical forests: Bacteria decompose abundant plant matter
quickly and return nutrients to soil; BUT …
• Growing plants absorb nutrients from organic matter in soil
right away;
• Result: nutrients from organic matter are in trees, not soil
Laterites: Poor soils for farming
• Deforestation = clearing forests for lumber, farming, or
housing
• Logging leaves soil exposed; soil erodes
• Forests replaced by farms. Crops do well for a couple of
years; then soil is DEPLETED of nutrients  crops fail  Soil
erodes (water & wind) w/out plants to anchor it down
Eroded top soil from deforested
areas enter Amazon turning it
muddy
Satellite images of the same forested area in
Brazil (Brown = trees removed)
Left: 1975
Right: 2012
Soil Erosion: Human Activities
• Soil Erosion increases when vegetation is removed
– Farming
– Logging
– Housing & Development
Causes : Water & Wind
• Water: Flooding, Heavy rains,
Streams/rivers
• Wind: in dry areas; especially following
drought
– Dust Bowl of 1930s; Prairie states;
Combination of drought and removal or
natural prairie grasses to grow crops
Austrialia
Soil Conservation
• Terracing down slopes
(prevent water erosion_
• Contour plowing to prevent
gullies (water erosion)
• Crop rotation to replenish
soil of nutrients
• Dust Bowl
• http://www.youtube.com/watch?v=8yMarRsd
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