Soils Exam 2

morphological characteristics of soil

consistence, texture, color, effervescence, structure

consistence

resistance to deformation

texture

percentage (by weight) of sand, silt, and clay

loam

equal amounts of sand, silt, and clay

which characteristics are geogenic in nature?

texture, consistence

which characteristics are pedogenic?

color, effervescence, structure

characteristics of iron concentrations (water implications)

oxidized iron, usually in areas of lower water table and lower rainfall

characteristics of iron depletions (water implications)

reduced iron, gleying color, usually in areas of higher water table and higher rainfall

which soils have higher organic matter? (water content)

wetter soils because not broken down anaerobically

what factors impact structure?

freeze-thaw, chemical bonds, organic matter

O horizon

dominated by organic matter

A horizon

mineral horizon with organic matter accumulation

E horizon

loss of weatherable minerals (eluviation), grey, amorphous and platy, often found in forests

B horizon

illuvial accumulations of clay, iron, aluminum, humus etc

C horizon

parent material - weathered bedrock

R horizon

bedrock

Oa

highly decomposed

Oi

slightly decomposed (or not decomposed)

Ap

plow layer (has been turned/disturbed)

Ab

buried (common in Iowa due to prairie soils)

Bt

accumulation of clay (identified by clay films)

Bk

accumulation of secondary carbonates

Bg

iron depletions - gleying

Bss

slickensides (look waxy b/c of clays moving against each other)

Bw

Cambic/weak, must be above other types of B horizons

Cr

weathered bedrock

soil profile

vertical sequence of soil horizons

soil pedon

soil with lateral dimensions

polypedons

groups of pedons

minerology

study of soil’s inorganic materials

primary minerals source

come from magma

secondary minerals

due to chemical/physical weathering

most common cations

Si⁴⁺, Al³⁺, Fe³⁺

oxides

minerals composed of Si, Al, Fe and oxygen

groups of oxides

aluminum (gibbsite and bauxite, Al(OH)₆, iron (FeOOH - goethite), manganese (FeMn concentration), chlorides (Na and Cl), carbonates (CaCO₃)

silicates

minerals formed of silica tetrahedra - primary (quartz, feldspars, micas), phyllosilicates/layer silicates

phyllosilicates

1:1 layer silicates (1 octohedral, 1 tetrahedral sheet, smectites), 2:1 silicates (1 octohedral, 2 tetrahedral sheets, mica group, vermiculite)

cation exchange capacity

soil’s total capacity to hold exchangeable cations, high = fertile soils and high water holding capacity, measured by displacement of base cations

base saturation

ratio of charges due to exchangeable base cations to total CEC, percentage of possible cations sites that are filled

umbric

organic-rich soil with BS < 50%

adsorbed water

held by adhesive forces between water molecules and particle surface

absorbed water

held by cohesive forces between molecules in small pores

capillary water

adsorbed + absorbed water held in soil

free water

gravitational water

gravimetric water content of soil equation

Wg = (mass moist of soil) - (oven dry mass of soil) / (mass of oven dry soil)

bulk density equation

Pd = (mass oven dry) / soil volume (g/cm³)

soil water potential

combination of potential energies that govern water movement in soil

Matric potential

attraction between soil particles and water to remove water

Gravitational potential

water movement due to gravity

field capacity

water content when gravitational water movement stops (-0.3 bars)

permanent wilting point

plants cannot extract beyond this point

hygroscopic water

water held tighter than 15 bars (adsorbed only, takes heat to extract)

infiltration

when water enters the soil

percolation

water movement through soil

drainage

movement out of soil

ponding

water perching on top of soil

soil skeleton

fine sand or larger

soil plasma

clay, organic matter, silt that can be transported by water

leaching

material is removed completely from the profile by eluviation

clay bulge

increase of 1.2x clay between horizon - Argillic

histosols

organic material, usually in ponded, wet, and cold environments

melanization

development of dark organic matter coatings on peds and minerals that results in dark color

weathering sequence

Entisols → Inceptisols → Mollisols → Alfisols → Ultisols → Oxisols

mollisols

high organic matter and melanizaiton, if there is greater than or equal to 30 cm of 10YR 3/3 or darker always a mollisol, BS > 50%, mineral content

alfisols

forest soils with lower organic matter than mollisols, must have Argillans (clay films and increase of 20%), E horizon

ultisols

mainly 1:1 clays, forested soil with low BS

gelisols

permafrost

andisols

volcanic

spodosols

high iron and alumninum accumulations

aridosols

desert soils

vertisols

high shrink-swell soils

what characteristics differ in different soil textures?

pore space, water flow potential, CEC, water holding capacity

polygenetic soils

multiple time zeros and potentially multiple parent materials

regolith

unconsolidated material

residuum

residual regolith

saprolite

bedrock that has been weathered in place

organic

organic material on the O horizon, formed in wetlands

paleosols

old soils, no A horizon

relict paleosols

ancient soils that were never buried, but forming factors have changed

buried paleosols

buried under younger soils

exhumed

once buried and now re-exposed

transported parent materials

alluvium, loess, drift, outwash, colluvium

alluvium

material deposited by running water; in deltas, floodplains, alluvial fans; horizontally and vertically stratified

lacustrine sediments

deposits in lakes; varves (layers caused by turbidity); vertical stratification

loess

material deposited by wind; must be silt or clay sized particles

Eolian sand

sand sized particles deposited by wind, moved by saltation

deflation

moving finer sediments by wind

drift (glacial)

material transported by glacial ice or meltwater

glacial till

material deposited directly from a glacier, unstratified and unsorted

basal till (type of glacial till)

deposited below the ice, unoxidized and very dense

superglacial till (type of glacial till)

material within or in front of glacier, less dense and with sand lenses

glacial meltwater

water created by melted glaciers, high energy so smaller particles wash out, outwash = sand and gravel in pockets, weak organization

colluvium

material transported by gravity, through landslides, slumps, flows, pedialluvium and post-settlement alluvium

solifluction

movement due to freeze-thaw action

Functional Factorial Model of soil formation

S (soil) = function of (factor 1 x factor 2 x factor 3…)

S = f (climate, organisms, relief, parent material, time)

climate

temperature, precipitation, wind, water availability

episaturation

2+ saturated layers underlaid by 2+ unsaturated layers; indicates a perched water table

endosaturation

all horizons between the upper boundary and 2m down are saturated

organisms

roots, bugs, worms, fungi, bacteria, people, animals

krotovina

filling in old holes dug by animals