Chapter 6
Soil Formation & Morphology
Pages 159 – 192

Parent materials and topography determine the amount and types of soil formation

Unconsolidated materials
Sediments of erosion and weathering
Can vary in mixture and particle size – rocky, sandy, clayey

Acronym for soil forming factors . . . climate relief organisms parent materials time

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

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. . . .

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 soil also 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 materials
Sediments of erosion and weathering
Can vary in mixture and particle size – rocky, sandy, clayey
Weathering and chemical erosion of parent materials can form secondary minerals or clays

Time as related to climate, relief, organisms and parent materials
Soils can begin to form quickly – years to decades – as results of river deposits on floodplains

Glacial sediments may be several thousand years old
Soil formation can occur rapidly in warm, humid, forested regions

Merging and blending of a series of alluvial fans
Formed as alluvium descends downhill
Large bajadas can take on the form of gravely plains

Eroded soil sediments deposited on land by streams
Larger particles drop out sooner

As particles move further downslope, particle sizes decrease leaving larger particles behind

pH and salinity often increase moving downslope
Carbonates and bicarbonates (of Ca,
Mg) levels increase

Deposits deep alluvial sands and gravels in Orange County as a result of being watershed of San Bernardino and
Riverside Counties

Chemical action of air and rainwater
Biological action of animals, plants, fungi, etc.
Carbonic acid (H
2
CO
3
) formed from the combination of air and water

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

Wearing away of land surfaces by wind, water, ice, and other geologic forces
Physically eroded soils produce sands and silts

Derived from ultramafic rock
Low in silica
High in magnesium and iron
Low calcium to magnesium ratio

Low in essential nutrients – nitrogen, phosphorus and potassium
Plants characteristic to serpentine soils are called serpentine

Rich in humus
Holds cations
Holds nutrients
Reduces pH
Increases water-holding capacities
Increases soil porosity
Changes 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 . . .

Organic horizon
Surface layer inc. leaves, moss and other plant materials
Rich in organic matter in various stages of decomposition

The O-Horizon can be further divided into two layers . . .
Oi – where organic mater is still identifiable
Oa – where organic matter is becoming highly decomposed

‘Topsoil’ layer
Often darker in color and contain more organic matter than deeper layers
May contain less clay and sesquioxides
(metal oxides)
Most biological activity occurs
Closely associated with plant root growth

May be rich in soil organisms: worms, nematodes, fungi and bacteria
The 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

Leached by water
Organic matter and clays may be removed by leaching
‘Eluviated’ layer (migrated out from)

Often pale containing mostly silicates
Only present in older, well-developed soils
Generally occurs between the A- and Bhorizons

‘Subsoil’ layer
‘Illuviated’ layer (migrated into)
Leached minerals may accumulate – clay minerals like iron or aluminum

Organic materials may accumulate
May have more intense colors or a stronger chroma than the a-horizon

Follows the A- and B-
Horizons
Mostly unweathered materials
Contains mostly parent materials

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)

Partially weathered bedrock at the base of the soil profile

Soils with various accumulations of different minerals

Calcic – accumulated carbonates
Gypsic - accumulated gypsum
Salic – accumulated soluble salts

Argillic – accumulated clay
Kandic – accumulated low-activity clay
Natric – 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

Duripan – silica cemented soils
Fragipan – brittle soils
Petrocalcic – soils cemented by carbonates
Petrogypsum – soils cemented by gypsum
Placic – soils cemented by iron

Soils showing losses of materials
Albic – leached and light colored
Glossic – leached, degraded clay layer

Agric – caused by tillage
Cambic – showing little development
Oxic – excessively weathered
Pesticides
Other toxic materials