Soil Composition

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Soil Composition
Soil is where all 4 spheres meet and interact
geosphere, biosphere, hydrosphere, atmosphere
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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
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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)
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Clay-Rich Soils
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Factors Important to Soil Formation
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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
• Rate of weathering can depend on rock
  type/minerals present
• Minerals in parent rock affect soil fertility

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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)

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Factors in Soil Formation Time
Young Soil Parent material influences soil the
most Old Soil More time for weathering
Climate other factors influence most
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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

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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 --gt N2
  gas

Proteins/amino acids require Nitrogen. Plants can
only get nitrogen in the form on nitrates in
soil.
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Factors in Soil Formation Slope (Relief)

• Steep slopes Lots of soil erosion (water moves
  faster) little soil cant hold moisture
• Flat little erosion poor drainage

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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?
idinformationmodule1130447025topicorder4
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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)
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Soil Types

• Hot, wet tropical areas
• intense chemical weathering (lots of water warm
  temps)
• Iron oxide (red soil) and Al-rich clay.

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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

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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

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• 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
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Soil Erosion Human Activities

• Soil Erosion increases when vegetation is removed
• Farming
• Logging
• Housing Development

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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

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Austrialia
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Soil Conservation

• Terracing down slopes (prevent water erosion_
• Contour plowing to prevent gullies (water
  erosion)
• Crop rotation to replenish soil of nutrients

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• Dust Bowl
• http//www.youtube.com/watch?v8yMarRsdkzE