Soils
Microenvironments
Aboveground
environment
Microclimate
Edaphic factors –
soil environment
Belowground
environment
Definitions of SOIL
“Typical” soil composition
Geologic definition:
Loose surface of the earth as distinguished from solid
bedrock (support of plant life not required).
Air 25%
Traditional definition:
Material which nourishes and supports growing plants
(i l d rocks,
(includes
k water,
t snow, air).
i)
Mineral Matter
45%
Water 25%
Component definition:
Mixture of mineral matter, organic matter, water, and air.
Combined definition:
Loose material on the Earth’s surface supporting plant
life that is composed of a mixture of mineral and organic
matter, water, and air.
Organic Matter
5%
How would you expect this to be different for a wetland soil ?
Typical soil horizons:
Typical soil horizons:
a result of soil development
a result of soil development
Soil development results from
an interaction of:
O Horizon:
Organic matter: litter & humus
• Weathering of parent material
(climate, type of parent material,
vegetation)
• Input of transported material
and/or loss of on-site material
Litter
• Organic matter input
(vegetation)
• Soil biota actions
Parent
material
Biota
Climate
Humus
Soil
development
Parent material
Parent material
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Typical soil horizons:
Typical soil horizons:
a result of soil development
a result of soil development
A Horizon:
E Horizon:
Nutrient-rich soil layer
A leached layer sometimes present
below the A horizon (Fe, Al removed)
A horizon
Thin A
horizon
in forest
soil
E horizon
B horizon
Thicker A
horizon in
grassland soil
Parent material
Typical soil horizons:
Typical soil horizons:
a result of soil development
a result of soil development
B Horizon:
C Horizon:
Nutrient-poor soil layer
Soil layer dominated by parent material
B horizon
in forest
soil
B horizon
in arid
zone soil
C horizon
in forest
soil
Parent material
Parent material
Selected Soil Edaphic Factors
• Texture
Physical or chemical attribute of
soil that impacts plant function
• Structure
• Organic Matter
• Moisture content & availabilityy
• pH
Selected Soil Edaphic Factors
Soil Texture
Particle size attributes
Texture Particle size range
category (mm diameter)
Clay
< .002
Silt
.002 - .05
Sand
.05 – 2.0
Gravel
> 2.0
• Aeration
• Nutrients
9“available”
9nutrient holding capacity (CEC)
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SOIL TEXTURE CLASSES
Selected Soil Edaphic Factors
Clay soils:
Fine textured
Soil Texture
Particle size composition
Texture
class
Particle size range
(mm diameter)
Clay
< .002
Silt
.002 - .05
Sand
.05 – 2.0
Gravel
> 2.0
Soils have varying proportions of
these particles
Silty soils:
Intermediate textured
The relative proportions of different
particles place
p
a soil into a
sized p
certain SOILTEXTURE CLASS
Sandy soils:
Coarse textured
Loam soils:
Balanced texture
% Sand
USDA Soil Texture Triangle
SOIL TEXTURE CLASSES
Selected Soil Edaphic Factors
Soil Texture
Determining a texture class:
70% silt
Particle size composition
Effects of soil texture
Texture
class
Particle size range
(mm diameter)
• Water holding capacity
15% clay
Clay
< .002
• Aeration
15% sand
Silt
.002 - .05
Sand
.05 – 2.0
• Temperature
T
t
Gravel
> 2.0
• Nutrients
• Erosion
The intersection is
the texture class:
Silt loam
% Sand
USDA Soil Texture Triangle
Selected Soil Edaphic Factors
Soil Structure
Selected Soil Edaphic Factors
Soil Structure
G ra n u la r
Effects of soil structure
G ra n u la r
B lo c k y
(S u b a n g u la r)
B lo c ky
(A n g u la r)
(S u b a n g u la r)
(A n g u la r)
• Water movement
• Root growth
P la ty
• Erosion
E i / slope
l
stability
t bilit
P la ty
P ris m a tic
P ris m a tic
C o lu m n a r
C o lu m n a r
W edge
W edge
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Selected Soil Edaphic Factors
Soil organic matter
Effects of soil OM
Soil pH
Selected Soil Edaphic Factors
Soil bulk density
Effects of soil pH
Soil surface hardness
Effects of soil bulk density
Effects of surface hardness
• Nutrient input
• Soil organism / plant function
• aeration
• Water infiltration
• Moisture retention
• Nutrient cycling & retention
• Water retention and flow
• Seed incorporation / germination
Soil moisture
Soil aeration
Effects of soil H2O
Soil water infiltration
Effects of soil aeration
Effects of soil H2O infiltration
• Organism function
• Soil organism / plant function
• Moisture input to soil
• Aeration
• Nutrient cycling & retention
• Water availability to
organisms
• Nutrient cycling
Other Soil Properties Often Assessed
• Color
Regional Soils
Tremendous Soil Variation across WA
• Horizon development / descriptions
• Variation in parent material
• Soil macrofauna
• Variation in climate
• Soil microorganisms
g
• Variation in plant communities
Greatest variation on east slope of Cascades & Olympics
Regional Soils
Regional Soils
Glacial Outwash
Puget Sound Area
• Glacial deposits
9Glacial till (e.g., “Alderwood” series)
9Glacial outwash (e.g., “Everett” series)
Lacustrine clays
Glacial till
Lacustrine clays
Development under coniferous forests
¾ Acidic conditions, low temperatures = slow development
Puget Sound Area
• Glacial deposits
9Glacial till (e.g., “Alderwood” series)
9Glacial outwash (e.g., “Everett” series)
• Old sedimentary deposits
• Wetland mucks
Springs & slides
¾ Interbedding of (1) clay and (2) sand layers with glacial till
• Alluvial soils
can lead to (1) springs and (2) slope instability
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Soil Measurements Today
For each group:
Field measurements today
Soil horizon descriptions (1 / site)
Later lab analyses on
collected soil
pH
Soil Measurements Thursday
Measurements by EACH group
Use same vegetation stands as we used for the forest vegetation lab
Red alder – sword fern
W. hemlock – sword fern
Soil water infiltration
(4x)
Litter type and depth, humus depth (4 / site) Organic matter content
Soil texture class (4 / site)
Moisture
Surface hardness (4 / site)
Texture
Soil infiltration rate (4 / site)
Bulk density
Litter & humus (4x)
Surface
hardness (10x)
Soil horizon
description
(1 x)
Soil texture class
(4x)
Soil Collection Thursday
• Six soil tins from each site – collected by bulk density corer
9 5 – 15 cm deep (A horizon)
• Four 1-liter bulk samples in paper bags (labeled)
9 5 – 15 cm deep
p
These samples will be used next week to assess
• Soil moisture
• Soil pH
• Soil bulk density
• Soil texture
• Soil OM
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