Final Study Guide - Soil Formation and Classification Flashcards
Soil profile
The vertical arrangement of soil horizons
What is a soil pedon?
Basically a clump of soil that has all soil horizons
Soil horizon
A layer of soil with distinctive properties
What are the 6 master horizons?
O, A, E, B, C, R
What are the differences between O and A?
O is mostly organic material, while A is a mix of organic and mineral material
What processes form the E horizon?
Minerals leaching out
What processes form the B horizon?
Accumulated leaching into the subsoil
How are the E and B horizons different?
E is leached of clays, OM, Al, Fe, and other mobile constituents while B is accumulated of materials from above horizons
What is the main difference between the C and R horizon?
C is weathered rock while R is solid rock
W, M, L, V horizons
W: Water
M: Human-made
L: Biologically produced material deposited in water
V: Dominated by vesicular pores
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)
Soil is the result of climate, organisms, parent material, topography, and time
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?
Residuum - formed from residual materials
Eolium, alluvium, till, colluvium, lacustrine - formed from transported materials
Wind - eolium
Water - alluvium, till, lacustrine
Gravity - colluvium
Residuum properties of the resulting soil parent material
Residuum: properties depend on hardness, grain size, and composition of rock. Gabbro and basalt are easiest to weather.
Eolium properties of the resulting soil parent material
Eolium: deposited by wind, uniform particle size (sandy), weather slowly (made of quartz), tend to be perpetually young
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?
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
Lacustrine properties of the resulting soil parent material
Lacustrine: layered bands of sediment corresponding to seasons
Colluvium properties of the resulting soil parent material
Colluvium: transported by gravity. Typically poorly sorted, creating soils high in rock fragments. Tend to be perpetually young
Contrast the properties of basalt and granite and explain why these rocks are different
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
How do basalt and granite differ from gabbro, andesite, rhyolite, and diorite?
They differ variably based on grain size and how mafic/felsic they are
What is aspect in the context of topography?
Aspect is the direction of slope faces
What are the five hill slope components? How does water and sediment movement vary among the five components?
Summit, shoulder, backslope, footslope, toeslope
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
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
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
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
How does climate influence soil processes? How are precipitation, temperature, and evapotranspiration relationships depicted in a water budget graph?
It can slow down or speed up soil processes
What is meant by the statement: “Soils are clay factories.”?
It means that clay content increases over time
As soils weather in a well-drained, humid environment, what major properties are expected to change on progressively older landscapes?
Clay content (increase), color, soil depth, horizon differentiation
As soils weather in an arid environment, what major properties are expected to change on progressively older landscapes?
Salt and carbonate accumulation (eventually calcic horizon formation)
What is meant by base saturation?
It is the percentage of the cation exchange capacity (CEC) of soil that is occupied by basic cations
In highly weathered soils, explain the effects of Al on soil pH, base saturation, plant cation nutrient supply, and soil phosphate supply
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
How can the effects of Al in soils be overcome?
Raise soil pH
What are the main attributes and outcomes of melanization?
Attributes: incorporation and mixing of OM into the surface horizon, common in areas w/ high root biomass
Outcomes: formation of dark-colored A horizon
What are the main attributes and outcomes of calcification?
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
What are the main attributes and outcomes of podzolization?
Attributes: intense leaching of iron/aluminum oxides and organic acids to the lower horizons
Outcomes: development of E horizon
What are the main attributes and outcomes of lessivage?
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
What are the main attributes and outcomes of laterization?
Attributes: intense weathering of primary minerals in hot, humid tropical environments
Outcomes: nutrient poor, acidic, and low CEC soils
What are the main attributes and outcomes of gleization?
Attributes: occurs in waterlogged soils with anaerobic conditions, reduction of iron occurs (Fe3+ –> Fe2+)
Outcomes: distinct gray/blue horizons with poor aeration
What is meant by Bt, Bk, Bs, Bh, Bqm, Bo, Bw, Bss, Bg?
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
