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Parent materials... Unconsolidated materials Sediments of erosion and weathering Can vary in mixture and particle size – rocky, sandy, clayey
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SoilChapter 6
Soil Formation & MorphologyPages 159 – 192
Soil formation . . . Parent materials and topography
determine the amount and types of soil formation
Parent materials . . .Unconsolidated materialsSediments of erosion and
weatheringCan vary in mixture and particle size
– rocky, sandy, clayey
CROPT . . . Acronym for soil forming factors . . .
climaterelieforganismsparent materialstime
Climate and soil formation . . .
And climate is?average patterns and conditions of weather (rain, wind, relative humidity, fog, average high and low temperatures, etc.) at a given location over a period of years
Climate and soil formation . . .
vs. weather?current state of the atmosphere with respect to rain, wind, relative humidity, fog, high and low temperatures, etc.
Climate and soil formation . . .
Formation of soils is faster in regions with higher precipitation and higher temperatures . . .
And is slower in more arid regions
Relief and soil formation . . .
How do you spell relief?T-O-P-O-G-R-A-P-H-Y
And topography is?the difference between the high and low areas in a landscape – the natural landscape that is. . . .
Relief and soil formation . . .
Soils develop more quickly and more deeply on terrain with a shallow slope
Rainfall tends to runoff on steep terrain slowing soil development
Rainfall tends to infiltrate on terrain with less slope
Organisms and soil formation . . .
Plants, animals and their residue found in soilalso referred to as biota
Where they exist in large numbers, burrowing animals turn and incorporate materials speeding soil formation
Organisms and soil formation . . .
Microorganisms aid soil development through the decomposition of organic matter
Areas with abundant vegetation contribute humus to the soil
Parent materials and soil formation . . .
Weathering and chemical erosion of parent materials can form secondary minerals or clays
Source of A and B soil horizons
Parent materials and soil formation . . .
Unconsolidated materialsSediments of erosion and weatheringCan vary in mixture and particle size
– rocky, sandy, clayeyWeathering and chemical erosion of
parent materials can form secondary minerals or clays
Time and soil formation . . .Time as related to climate, relief,
organisms and parent materialsSoils can begin to form quickly –
years to decades – as results of river deposits on floodplains
Time and soil formation . . .Glacial sediments may be several
thousand years oldSoil formation can occur rapidly in
warm, humid, forested regions
BajadasMerging and blending of a series of
alluvial fansFormed as alluvium descends
downhillLarge bajadas can take on the form
of gravely plains
AlluviumEroded soil sediments deposited on
land by streamsLarger particles drop out sooner
AlluviumAs particles move further
downslope, particle sizes decrease leaving larger particles behind
AlluviumpH and salinity often increase
moving downslope Carbonates and bicarbonates (of Ca,
Mg) levels increase
Santa Ana RiverDeposits deep alluvial sands and
gravels in Orange County as a result of being watershed of San Bernardino and Riverside Counties
Weathering . . . Chemical action of air and rainwaterBiological action of animals, plants,
fungi, etc. Carbonic acid (H2CO3) formed from
the combination of air and water
Weathering . . .Rocks and minerals decompose and
disintegrate and change characteristics
Clays are formed by weathered or chemically broken-down soils
Basalts are an example of a clay producing mineral
Erosion . . . Wearing away of land surfaces by
wind, water, ice, and other geologic forces
Physically eroded soils produce sands and silts
Serpentine soils . . . Derived from ultramafic rockLow in silica High in magnesium and ironLow calcium to magnesium ratio
Serpentine soils . . .Low in essential nutrients – nitrogen,
phosphorus and potassiumPlants characteristic to serpentine
soils are called serpentine
Organic matter . . .Rich in humusHolds cationsHolds nutrientsReduces pHIncreases water-holding capacitiesIncreases soil porosityChanges structure
Department of repetitive redundancy department . . .In flatter areas with warmer, wetter
weather, soils form faster
In colder, dryer areas with more slope soils form more slowly
Soil horizons . . .
O-Horizon . . .Organic horizon Surface layer
inc. leaves, moss and other plant materials
Rich in organic matter in various stages of decomposition
O-Horizon . . .The O-Horizon can be further divided
into two layers . . .Oi – where organic mater is still
identifiableOa – where organic matter is
becoming highly decomposed
A- Horizon . . .‘Topsoil’ layer Often darker in color and contain more
organic matter than deeper layersMay contain less clay and sesquioxides
(metal oxides)Most biological activity occurs Closely associated with plant root
growth
A- Horizon . . .May be rich in soil organisms: worms,
nematodes, fungi and bacteriaThe term “biomantle” can only be
used if biological activity does not extend deeper into subsequent horizon layers
‘Eluvial’ layer – layer in which materials leach (migrate) from
E-Horizon . . .Leached by waterOrganic matter and
clays may be removed by leaching
‘Eluviated’ layer (migrated out from)
E-Horizon . . .Often pale containing mostly
silicates Only present in older, well-
developed soilsGenerally occurs between the A- and
B-horizons
B-Horizon . . .‘Subsoil’ layer‘Illuviated’ layer (migrated into)Leached minerals may accumulate –
clay minerals like iron or aluminum
B-Horizon . . .Organic materials
may accumulateMay have more
intense colors or a stronger chroma than the a-horizon
C-Horizon . . .Follows the A- and
B-HorizonsMostly unweathered
materials Contains mostly
parent materials
D-Horizon . . .May be recognized by contrasting
pedologic organization between it and overlying layers
Found below layers referred to as ‘solum’ (O-, A-, E-, and B-horizons)
R-Horizon . . .Partially weathered
bedrock at the base of the soil profile
Degradation of Soils . . .Soils with various accumulations of
different minerals
Soils with accumulated salts
Calcic – accumulated carbonatesGypsic - accumulated gypsumSalic – accumulated soluble salts
Soils with accumulated clays
Argillic – accumulated clayKandic – accumulated low-activity
clayNatric – accumulated clay with
sodium
Soils with accumulated humus
Orstein – cemented soils; high in humus and aluminum
Sombric – acidic; high in humus without aluminum
Spodic – acidic; high in humus and aluminum
Soils with hardpansDuripan – silica cemented soilsFragipan – brittle soilsPetrocalcic – soils cemented by
carbonatesPetrogypsum – soils cemented by
gypsumPlacic – soils cemented by iron
Soils showing losses of materials
Albic – leached and light coloredGlossic – leached, degraded clay
layer
Other conditionsAgric – caused by tillageCambic – showing little developmentOxic – excessively weathered PesticidesOther toxic materials
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