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OM humus1º minerals clays
OM, clay, ions Transformations:
runoff
leaching
Rain, OM
capillary rise
Four processes:
• Additions
• Losses
• Translocations
• Transformations
Effect of Climate on Soil Formation
limestone dry climate
40cm
A
R
limestone wet climate
60cm
A
Bw
Cr
note depths of these profiles
Effect of Vegetation on SOM
Grass/Agric Land
Deciduous Forest
Coniferous Forest
Nutrient content of OM residue
OM decomposition
O horizon present
High High Low
Rapid Rapid Slow
No Seasonal Yes
SOM = soil organic matter
Blocky structure
Unweathered loess
Organic matter
CaCO3
Time
Grassland
Time
Temperate Deciduous Forest
Organic layer
Leached zone
Unweathered bedrock
Weathered PM Clays, oxides
Effect of Vegetation on Development
Soil Samples!
Time
Temperate Deciduous Forest
Organic layer
Leached zone
Unweathered bedrock
Weathered PM Clays, oxides
Effect of Vegetation on Development
Ultisol Sample!
Blocky structure
Unweathered loess
Organic matter
CaCO3
Time
Grassland
Effect of Vegetation on Development
Meadow Soil Sample!
Trinity Alps Wilderness AreaNorthern California
Topography as an Influence on Soil Formation
• Relief
• Aspect
• Elevation
(steep vs. flat)
(N,S,E,W)
(link to climate, organisms)
Effect of Topography on Soils
Position Summit Shoulder Backslope Footslope Toeslope
% OC in
A horizon
Thickness of A
(cm)
Texture of A
4.01.5
lowest3.0 4.5
5.5
highest
156
lowest10 18
25
highest
si l l si lsi c lMost clay
si c lMost clay
E. Colorado; grassland; limestone
pH 7.0 7.2
Effect of time on soil development
Very mature
MatureYoungParent material
1m >1m 15mC C
A
C
A
Bw
C
A
E
Bt
Modern floodplain
Higher terraces
10cm
80cm
Time
A
C
A
Bt1
C
Bt2
• both formed in alluvium from mixed sources • similar topography
Effect of Time on Soils
Soil age, development
Immature (young)
Mature (old)
Mineral status
Fertility
Amount of clay
Primary: quartz,
feldspar, etc.
Secondary: smectites, illite, etc.
low
low high
high
Factors That Retard Soil Development
• Low rainfall and RH• Cold temperatures• High water table• Parent materials that are mostly quartz• Very high clay content• Presence of substances toxic to plants• Very steep slopes erosion• Disturbance frequency – e.g. fire
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