SSC 100 - Soil Formation and Classification

What is a soil profile?

Vertical arrangement of soil horizons

What is a soil pedon?

Smallest unit of soil that can be studied that contains all soil properties

What is a soil horizon?

Layers formed over time with soil development and as a product of soil forming factors and processes

What are the 6 master horizons?

Most common horizons present in developed soils:

O - Organic materials

A - Topsoil

E - Loss of material; eluviated zone

B - Subsoil; accumulation zone

C - Weathered rock

R - Solid rock

What are the differences between an O and A horizon?

O = organic horizon vs. A = mineral horizon with decomposed OM

What processes form E horizons?

Losses (eluviation of clays)

What processes form B horizons? 

Additions and translocations (illuviation of nutrients)

How are E and B horizons different?

E = mineral horizon leached (eluviated) of clays, OM, Fe, Al, and other mobile constituents

B = mineral horizon of alteration or accumulation of materials from overlaying horizons

What is the main difference between a C and R horizon?

Both dominated by parent material, but C is the layer of parent material (not bedrock), little affected by soil formation vs. R is hard bedrock

What is a W horizon?

Water (frozen or liquid)

What is a V horizon?

dominated by vesicular pores

What is a M horizon?

human-made layer (i.e. asphalt)

What is a L horizon?

biologically produced material deposited in water

horizon subordinate distinctions: p

plowed

horizon subordinate distinctions: w

weak or change in soil structure

horizon subordinate distinctions: g

gleying - prolonged soil-water saturation —> Fe reduction and gray color

horizon subordinate distinctions: k

accumulation of CaCO3

horizon subordinate distinctions: s

illuvial accumulation of Fe and Al oxides with OM

horizon subordinate distinctions: f

frozen

horizon subordinate distinctions: l

slightly decomposed OM

horizon subordinate distinctions: e

intermediately decomposed OM

horizon subordinate distinctions: a

highly decomposed OM

horizon subordinate distinctions: m

cemented

horizon subordinate distinctions: ss

slickenslides

horizon subordinate distinctions: h

humus - accumulation of OM

What are the factors of soil formation? Write an equation that shows the relationship between soil properties and the soil forming factors.

S = f (cl, o, r, p, t)

Climate (i.e. when temp and precip increase, weathering increases)

Organisms (i.e. soil engineers– earthworms– mix the soil)

Topography (i.e. steep slope = low infiltration into soil vs. flat slope = high infiltration)

Parent material (i.e. felsic or mafic = different particle size, mineralogy, and weathering rates)

Time (i.e. all factors are relative to time–soil in hot/wet climate or on bottom of slope = more weathering over longer periods of time)

What is the main factor that drives the formation of an andisol?

Volcanic ejecta and ash

What is the main factor that drives the formation of gelisols?

Permafrost

What are some morphological features of vertisols?

Self-churning soils by shrink-swell processes 

How are Mollisols formed? What are some of the main characteristics of Mollisols?

Thick surface accumulation of soil organic matter; grassland soils transition to arid climate

General properties of Entisols

soils with little or no profile development

General properties of Inceptisols

soils with subtle profile development

General properties of Ultisols

highly weathered soils with subsurface accumulation of clay and low base saturation

General properties of Alfisols

soils with subsurface accumulation of clays

General properties of Spodsols

common in boreal forests

General properties of Oxisols

completely weathered soils

Residuum

Bedrock

Eolian

Transported by wind

Alluvium

deposited by streams and rivers

Till

transported by glaciers

Colluvium

Transported by gravity

Lacustrine

Lake deposits - tend to have beds oriented parallel to surface

Contrast the properties of basalt and granite and explain why these rocks are different

Basalt - Mafic (heavy elements), dominated by small-grains, extrusive, easily weathered, nutrient rich minerals (fertile)

Granite - Felsic (light elements), course-textured, intrusive, low fertility

What is aspect in the context of topography?

direction a slope is facing, like north or south. It’s relevant to soil because it has an effect on temperature/moisture (south-facing slopes get more sunlight, making them warmer and drier) and impacts the vegetation that grows, all of which affect soil

What are the five hill slope components?  How does water and sediment movement vary among the five components?

From top to bottom: summit, shoulder, backslope, footslope, toeslope. As you move from the summit to the footslope, infiltration decreases and erosion increases. Runoff and eroded material accumulates at the toeslope.

main attributes and outcomes of the soil forming processes: melanization

Accumulation of organic matter in the upper soil horizons

Formation of dark A horizons (from humus enrichment)

main attributes and outcomes of the soil forming processes: calcification

Accumulation of calcium carbonate in the soil in dry climates

Alkaline soil, formation of Bk horizons (k = calcium carbonate)

main attributes and outcomes of the soil forming processes: podzolization

Fe, Al, and humus leaching caused by organic acids

Bleached E (elluviation) horizon, high acidic soil (pH 4-5), reddish-brown Bh/Bs horizons from Fe/Al/humus accumulation

main attributes and outcomes of the soil forming processes: lessivage

Downward movement of clay particles

Bt horizons with clay films (argillians) on ped faces, E horizon lacking clay

main attributes and outcomes of the soil forming processes: laterization

Intense leaching leaving behind high concentrations of Fe/Al oxides

Poor soil fertility, clay-poor and Fe/Al-rich, reddish in color, very hard

main attributes and outcomes of the soil forming processes: gleization

Prolonged saturation leads to reduction of Fe

Gray/blue/greenish color, indicator of waterlogged conditions

Bt

the illuviation of clay in the B horizon 

Bk

accumulation of carbonate (k = ‘karbonate’)

Bs

illuvial accumulation of Fe/Al oxides (s = sesquioxide)

Bh

organic matter (humus) accumulation (h = humus)

Bqm

cemented silica formation (q = ‘siliqa’, m = ceMented)

Bo

residual accumulation of sesquioxides

Bw

reddening of soil 

Bss

slickensides present (ss = slickensides)

Bg

gleyed

Name the six categorical levels of Soil Taxonomy.  Which level provides the most general information about soils?  Which level provides the most specific information about soils?

Order → Suborder → Great Group → Subgroup → Family → Series

(most general)                                →                               (most specific)

What is the California state soil?

San Joaquin

What is the California state rock?

Serpentinite