We All Want Food that is
Plentiful
Nutritious
Safe
To Your Good Health (Soil)
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Keep pH near neutral
Avoid Compaction
Maintain Good Moisture
Promote Drainage
Good Temperature
• Organic Matter
Purpose of Soil Health
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Promote Plant and Animal Systems
Promote Clean Water
Prevent Soil Erosion
Promote Good food + Human Health
• Promote Life !
Topography begins the story
Parent Material
Materials from
volcanoes,
sediment
transported by
wind, water, or
glaciers are some
examples.
Parent Bedrock affects Soil types
Limestone +
CaCO3
Igneous Rocks +
minerals
Soil Formation takes Time
Soil Begins to Develop on a Columbia River Lava Flow
Gotta’ start
somewhere!
Time
It takes hundreds of
years to form one
inch of soil from
parent material.
Soil Profile : thin soil layers shown
Soil, on average,
consists of 45%
mineral, 25%
water, 25% air
and 5% organic
matter.
How does soil form? = weathering
product of minerals/rocks
• 5 factors influencing soil formation:
Parent materials (volcanic, limestone?)
Climate (temp, rainfall)
Topography (slope, landform)
Vegetation (inputs)
Time
• Soil Profile: understanding soil “layers”
O, A, B, C
Climate
Weathering processes
like the cycles of
freezing and
thawing, along with
wetting and drying
vary with each
region.
Soil Particle
Size
Relativity
This diagram
demonstrates
the difference
in size
between the
various soil
elements.
Soil Particle Size
Soil is composed of many particles of varying sizes.
Soil scientists have classified soil particles into three
major groups: Sand, Silt and Clay.
Sand particles are the largest and tend to hold little
water (good drainage) and allow good aeration.
Clay particles are very small in size and tend to pack
down so that water does not drain well and little or no
air can penetrate. Can result in wetland type soils.
Silt particles are medium sized and have properties in
between those of sand and clay.
Particle Size
+ Soil type =
Soil Name
Soils get their names by what soil
elements are found together and in
what ratios.
A soil that is 55% Clay & 45% Silt
would be a Silty Clay.
If the percentages were reversed, the
soil would be a Clayey Silt.
LOAM SOIL
A loamy soil, is one that combines all
three of these types of particles in
relatively equal amounts.
Loamy soil is ideal for most garden
plants because it holds plenty of
moisture but also drains well so that
sufficient air can reach the roots.
Soil consists of:
•minerals and weathered rock fragments
•organic matter
•Gases
•water
•living organisms
Regolith are minerals and weathered rock
fragments.
Humus is decayed organic matter.
Blue-green
Algae
inhabit
soils and
add
nutrients
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What Controls Rate of
Temperature
Decay
Moisture
Food Supply
Oxygen
C:N Ratio
Fungi
• Hundreds of Thousands per Gram
• Perform Functions Similar to Bacteria
– Decomposition
• Important in Plant Nutrition
– Mycorrhizae (fungus root)
Mycorrhizae
• Mutualism
• Benefits Plant and Fungus
– Ectomycorrhizal
• Hyphae do not penetrate root
cells
– Endomycorrhizal
• Hyphae do enter root cells
• Arbuscular
• Very Common
– 90+ % of plant families
Roles of Bacteria
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Nitrogen Fixation
Mineralization
Organic Matter Decomposition
Soil Stabilization
Aeration
Root Nodules
with N-fixing
symbiotic
bacteria.
Experiments
without/ with
N-fixing
bacteria
Soil Animals
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Earthworms
Mites
Nematodes
Protozoa
Beetles
Termites
Earthworms are decomposers
Ameba
attacks
bacteria
Fungus
attacks
ameba
Bacteria attacks fungus
Beetle grub attacks plant roots
Fungus attacks nematode
Centipedes, Isopods, and Mites are
predators
Biologically
important
Reservoirs:
atmosphere++,
soils & sediments,
surface water,
biomass
Key processes:
nitrogen fixation
(Campbell and Reece, 2005)
•Basic Soil Structure:
•Layers (horizons) that change with time
O = organics, at surface
A = zone of leaching, (+) ions removed,
organic rich (dark)
B = zone of accumulation or ions and
clays and metals (red, rusty, clay rich
C = partially weathered bedrock
Bedrock = Parent Material
What is a soil profile?
A soil profile consists of several soil horizons.
•O horizon = This is the layer of humus on the ground
surface.
•A horizon = Top soil; Rich in organic matter. Typically
has dark color. Also called zone of leaching.
•B horizon = Subsoil; Also called zone of accumulation.
May contain soluble minerals such as calcite in arid
climates (caliche).
•C horizon = Weathered bedrock or saprolite (rotten rock).
•Bedrock lies below the soil profile.
A nutrient
poor
canopy
adds does
little to
neutralize
acidic soils
A nutrient
rich canopy
adds a lot of
alkaline
nutrients to
the soils,
neutralizing
acidic soils
Water infiltration in Soils
A thin surface crust caused by raindrop impact on
a bare soil of poor structure
Crusting and subsurface compaction can
result in serious losses of water and soil
Erosion can create
deep channels
carrying away
topsoils in Africa
Calcification
of Soils – too
much
irrigation
The
white
are
calcium
salts
Fight Against Soil Erosion
Contour Plowing to preserve soils
Soil erosion
•Soil may be eroded due to the action of water (runoff) or
wind.
•(Please note that weathering and erosion are two different
things).
•Soil is transported by streams, and most will eventually be
deposited on a floodplain or at the mouth of the river in a
delta.
•The Dust Bowl of the 1930's was due to wind erosion of
soil following extended drought and over-tilling of the soil.