Final Study Guide - Soil Formation and Classification

Question 1

Soil profile

Answer 1

The vertical arrangement of soil horizons

Question 2

What is a soil pedon?

Answer 2

Basically a clump of soil that has all soil horizons

Question 3

Soil horizon

Answer 3

A layer of soil with distinctive properties

Question 4

What are the 6 master horizons?

Answer 4

O, A, E, B, C, R

Question 5

What are the differences between O and A?

Answer 5

O is mostly organic material, while A is a mix of organic and mineral material

Question 6

What processes form the E horizon?

Answer 6

Minerals leaching out

Question 7

What processes form the B horizon?

Answer 7

Accumulated leaching into the subsoil

Question 8

How are the E and B horizons different?

Answer 8

E is leached of clays, OM, Al, Fe, and other mobile constituents while B is accumulated of materials from above horizons

Question 9

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

Answer 9

C is weathered rock while R is solid rock

Question 10

W, M, L, V horizons

Answer 10

W: Water
M: Human-made
L: Biologically produced material deposited in water
V: Dominated by vesicular pores

Question 11

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

Answer 11

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

Soil is the result of climate, organisms, parent material, topography, and time

Question 12

Differentiate among residuum, eolium, alluvium, till, lacustrine, and colluvium materials with respect to processes

Which were formed from residual or transported materials?
Which were formed by wind, water, or gravity?

Answer 12

Residuum - formed from residual materials
Eolium, alluvium, till, colluvium, lacustrine - formed from transported materials

Wind - eolium
Water - alluvium, till, lacustrine
Gravity - colluvium

Question 13

Residuum properties of the resulting soil parent material

Answer 13

Residuum: properties depend on hardness, grain size, and composition of rock. Gabbro and basalt are easiest to weather.

Question 14

Eolium properties of the resulting soil parent material

Answer 14

Eolium: deposited by wind, uniform particle size (sandy), weather slowly (made of quartz), tend to be perpetually young

Question 15

Alluvium properties of the resulting soil parent material

How do properties differ based on size of floods?
How do the floods affect weathering? Horizon orders?

Answer 15

Alluvium: deposited by streams and rivers. With layering, the fineness of material depends on how big the floods were.

Big floods: there’d be big particles at the bottom followed by smaller particles higher up (“fining upwards”). Small floods: small bands of fine and loamy soil

Tend to be perpetually young

Also can get strange horizon orders - a C layer can be deposited on top of an A

Question 16

Lacustrine properties of the resulting soil parent material

Answer 16

Lacustrine: layered bands of sediment corresponding to seasons

Question 17

Colluvium properties of the resulting soil parent material

Answer 17

Colluvium: transported by gravity. Typically poorly sorted, creating soils high in rock fragments. Tend to be perpetually young

Question 18

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

Answer 18

Basalt is mafic and fine-grained
Granite is felsic and large-grained

Increased grain size = more susceptible to physical weathering
More felsic = more silica content
More mafic = more Fe & Mg content + susceptibility to chemical weathering

Question 19

How do basalt and granite differ from gabbro, andesite, rhyolite, and diorite?

Answer 19

They differ variably based on grain size and how mafic/felsic they are

Question 20

What is aspect in the context of topography?

Answer 20

Aspect is the direction of slope faces

Question 21

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

Answer 21

Summit, shoulder, backslope, footslope, toeslope

Question 22

Forest and prairie vegetation have profound effects on the cycling of organic matter and its distribution in the soil. Discuss these effects in the context of root:shoot ratio for the two vegetation types

Answer 22

Grassland has a higher root:shoot ratio whereas forest has a lower root:shoot ratio

What this means is that grassland has roots that go deep into soil whereas forest just deposits OM on top of soil, so the former has OM distributed deeply into soil whereas the latter only has it on the top

Question 23

On average soils of high latitudes store more organic carbon than do soils in the tropics. Explain why this is the case, taking into consideration biomass production in the two environments

Answer 23

Soils in high latitudes produce less organic matter, but it decomposes slower so it builds up. Tropic soils produce more organic matter but it decomposes much more quickly

Question 24

How does climate influence soil processes? How are precipitation, temperature, and evapotranspiration relationships depicted in a water budget graph?

Answer 24

It can slow down or speed up soil processes

Question 25

What is meant by the statement: “Soils are clay factories.”?

Answer 25

It means that clay content increases over time

Question 26

As soils weather in a well-drained, humid environment, what major properties are expected to change on progressively older landscapes?

Answer 26

Clay content (increase), color, soil depth, horizon differentiation

Question 27

As soils weather in an arid environment, what major properties are expected to change on progressively older landscapes?

Answer 27

Salt and carbonate accumulation (eventually calcic horizon formation)

Question 28

What is meant by base saturation?

Answer 28

It is the percentage of the cation exchange capacity (CEC) of soil that is occupied by basic cations

Question 29

In highly weathered soils, explain the effects of Al on soil pH, base saturation, plant cation nutrient supply, and soil phosphate supply

Answer 29

Lowers soil pH (if it’s below 5.5)

Decreases base saturation (occupies exchange sites on cation exchange complex)

Interferes w/ cation nutrient supply

Decreases soil phosphate availability

Question 30

How can the effects of Al in soils be overcome?

Answer 30

Raise soil pH

Question 31

What are the main attributes and outcomes of melanization?

Answer 31

Attributes: incorporation and mixing of OM into the surface horizon, common in areas w/ high root biomass

Outcomes: formation of dark-colored A horizon

Question 32

What are the main attributes and outcomes of calcification?

Answer 32

Attributes: accumulation of CaCO3 in the B horizon or just below the surface, occurs in arid/semi-arid climates

Outcomes: formation of white or powdery layers in subsoil

Question 33

What are the main attributes and outcomes of podzolization?

Answer 33

Attributes: intense leaching of iron/aluminum oxides and organic acids to the lower horizons

Outcomes: development of E horizon

Question 34

What are the main attributes and outcomes of lessivage?

Answer 34

Attributes: movement of fine clay particles from A/E horizon to B horizon via percolating water, happens in well-draining soils

Outcomes: formation of Bt horizon

Question 35

What are the main attributes and outcomes of laterization?

Answer 35

Attributes: intense weathering of primary minerals in hot, humid tropical environments

Outcomes: nutrient poor, acidic, and low CEC soils

Question 36

What are the main attributes and outcomes of gleization?

Answer 36

Attributes: occurs in waterlogged soils with anaerobic conditions, reduction of iron occurs (Fe3+ –> Fe2+)

Outcomes: distinct gray/blue horizons with poor aeration

Question 37

What is meant by Bt, Bk, Bs, Bh, Bqm, Bo, Bw, Bss, Bg?

Answer 37

Bt: accumulation of clay
Bk: accumulation of carbonates
Bs: accumulation of Fe and Al oxides
Bh: accumulation of OM (humus)
Bqm: cementation by silica
Bo: residual accumulation of Fe and Al oxides
Bw: weak development or alteration
Bss: slickensides
Bg: gleying or reduction under waterlogged conditions