Soil
http://www.youtube.com/
watch?v=qajjl3esi5E
(intro sent out via kmail)
What is topsoil made of?
Topsoil
 Soil
is the topmost portion of the
earth's crust; it supports life.
 Soil
is composed of minerals and
organic material.

Composition is based on "parent"
material (in the lower crust).
How Soil Forms
 Residual
Soil: parent material is bedrock
beneath the soil
 EX:
 Transported Soils: soil is made from
deposits left by wind, rivers and glaciers
 EX:
Soil Formation
 How
long can take to make
topsoil? (see next page)
 SOIL
FORMATION
 It can take 1,000 yrs to form topsoil.
 A soil forms as parent material is
weathered away.
 Organic material (dead plants and
animals) are mixed with weathered rock)
Soil composition
 Every
soil is a mixture of
clay, silt, and sand
 Clay: Very fine/small
particle, tiny space
between particles,
dense
 Silt: Too light, blown
away (found in
floodplains)
 Sand: course, big spaces
between particles
Soil composition Cont’d
 Perfect
soil for plants is Loam
 LOAM: mixture of sand (40%), silt (40%),
and little clay (20%)
Soil Horizons (fill in)
A
Horizon:
B
Horizon:
C
Horizon:
Stalinization of soils
 Build
up of salts in soil—toxic for
plants (can’t take up water)
 Associated with excessive
irrigation of water
 Problem associated with poorly
drained soils (CA, Colorado
River Basin)
 Treatment: flush soils with lots of
water
 Extreme cases: salt crust too
thick to be flushed
Check In



1. Which zone
contains weathered
parent rock?
2. Which zone
contains inorganic
materials that have
been washed from A
horizon?
3. Which zone
contains
microorganisms that
breakdown material
into nutrients?
Soil Types
 11
major categories
 What affects soils composition? (read)
Soil Composition
 Parent
material
 Plants and animals
 Topography---flow of water
 Climate


Heavy rains wash away nutrients
Rainfall/high temp result in high clay
Soil is an ecosystem
BRAINSTORM: What would
happen if we lost soil? How DO
we loss soil?
Soil loss
 Erosion:
soil lost by water or wind
 Chemical contamination
 Salinization
 Compacting by cattle hooves/machinery
 40%
of cropland is degraded
Stalinization of soils
 Build
up of salts in soil—toxic for
plants (can’t take up water)
 Associated with excessive
water application/irriga6tion of
water
 Problem associated with poorly
drained soils (CA, Colorado
River Basin)
 Treatment: flush soils with lots of
water
 Extreme cases: salt crust too
thick to be flushed
Soil Horizons

A Horizon: (topsoil)humus,
inorganic particles,
microorganisms decompose
organic compounds into nutrients

B Horizon: (subsoil) inorganics
(iron, clay, calcium) that have
been washed down into the Bhorizon

C Horizon: slightly weathered
parent material—rock fragments

Bedrock
Extension: Soil Scientists
 Some




things to think about:
What do scientists do?
What type of schooling do they have?
Do we need soil scientists?
http://www.youtube.com/watch?v=53pNG
EO08ck&feature=related
Why is soil an
important resource?
Soil as a Resource
 Countless
living organisms and numerous
species live in soil
 Chemical processes by these organisms
enable food to grow.
 Soil provides the fertility for food to grow.
 Soil is a very important part of an
ecosystem
Questions?