exam 1 (lectures 1-6) review

soil morphology

description of the features of a soil profile

soil profile

a vertical section of soil that exposes the layers of soil

soil horizon

a layer of soil that has similar properties

what factors help determine horizons

color, texture, structure, density, redoximorphic features, chemical properties

additions

materials added to the soil

how are materials added from above and below?

above: decomposition, rain, wind, illuviation. below: water tables.

redistribution

movement of physical properties through horizons

eluviation

removal of materials by leaching

illuviation

material accumulation from leaching

losses

loss of material in soil

transformations

chemical weathering of sand and formation of clay minerals into different compounds

topsoil

contains the most roots, nutrient uptake, microbial activity.

A-horizon

mineral layer enriched in organic matter

subsoil

decreased organic matter with more structure

B-horizon

layer with highly clay content from illuviation or weathering

E-horizon

eluvial layer, formed from high rainfall, leaching, and in well-developed forest areas.

C-horizon

layer relatively unaffected by weathering and illuviation.

R-horizon

rock parent material

transition horizons

used for classification when change is gradual

Oi

slightly decomposed organic matter

Oe

intermediately decomposed organic matter

Oa

highly decomposed organic matter

Ap

A-horizon affected by plowing

Bg

B-horizon with strong gleying

gleying

light colored soil caused by water saturation leading to reduced minerals

Bh

B-horizon with illuvial accumulation of organic matter

Bk

B-horizon with accumulation of carbonates

Bs

B-horizon with illuvial organic matter and iron, aluminum oxides

Bt

B-horizon with accumulation of clays

Bhs

B-horizon with accumulation of organic matter and accumulation of iron and aluminum oxides

what does the capital letter (Bt2) in a soil horizon designation mean?

master horizon

what does the lowercase letter (Bt2) in a soil horizon designation mean?

subordinate designation

what does the number (Bt2) in a soil horizon designation mean?

division of horizons with similar features

what is the (typical) order of soil horizons?

O, A, E, B, C, R

what conditions will an E horizon form?

high rainfall, leaching, and well-developed forest vegetation (especially coniferous forests)

what does soil color inform?

drainage, organic matter, weathering, minerals

what does soil drainage indicate?

whether or not oxygen is present

what are the three properties of color in the munsell system?

hue, value, chroma

what is hue?

the basic color (10YR)

what is value?

the lightness or darkness of the soil

what does a low value mean?

dark/black

what does a high value mean?

light/white

what value does organic matter tend to be?

low value

what value do salts and carbonates tend to be?

high value

what is chroma?

color intensity/saturation

what is a low chroma?

weak color intensity

what is a high chroma?

strong color intensity

what can chroma indicate?

the weathering of a soil

if a soil has a low value and low chroma, what is it most likely composed of?

organic matter

features of Fe²⁺

blue/green color, aqueous, mobile

features of Fe³⁺

red/yellow color, solid, immobile

what is the relationship between Fe²⁺ and Fe³⁺?

when Fe²⁺ oxidizes it turns into Fe³⁺

features of a red soil

Fe³⁺ presence, oxygen present, well drained

features of a red/yellow soil

Fe³⁺ presence, oxygen present, well drained

features of a blue/green soil

Fe²⁺ presence, no oxygen, poorly drained

true or false: texture is the most important soil characteristic

true

what size particles are considered soil?

less than or equal to 2mm

size of sand

0.05-2mm

size of silt

0.002-0.05mm

clay

<0.002 mm

true or false: organic matter and rocks are considered in soil texture

false

what soil material is ideal for nutrients?

clay

why does clay hold nutrients and water well?

it has a larger surface area

what does a higher surface area increase?

water retention, binding of pesticides, metals, & nutrients, habitats for microorganisms, weathering

texture test for clay

smooth and forming ribbons

texture test for sand

crumbling

texture test for silt

smooth and dull

water-holding capacity of sand

low

water-holding capacity of silt

medium to high

water-holding capacity of clay

high

aeration of sand

good

aeration of silt

medium

aeration of clay

poor

shrink-well potential of sand

very low

shrink-well potential of silt

low

shrink-well potential of clay

moderate to very high

pollutant leaching potential of sand

high

pollutant leaching potential of silt

medium

pollutant leaching potential of clay

low (unless cracked)

what does the soil texture triangle show?

the sand-silt-clay composition of the 12 major textural classes

what is the ideal soil texture for gardening?

loam

why is loam ideal for agriculture?

it holds nutrients well and is easy to handle

soil structure

how different sizes of soil particles form together

surface structures

granular and crumb

properties of granular and crumb particles

small, held together by organic matter, porous

platelike structures

flat and platelike, formed by compression

blocklike structures

angular blocky and subangular blocky

angular blocky

sharp, caused by clay content

subangular blocky

round

primslike structures

prismatic and columnar

prismatic

angular, caused by clay

columnar

rounded top, caused by arid climates and high salt content

binding agents

clay, organic matter, roots, microbial secretions, calcium

what causes destructions of structures

sodium, tillage, loss of organic matter

single grain

unsolidated soil without aggregation or structure development

massive

no visible soil structure, a continuous, unconsolidated mass

parent material

material from which soils are from

where do mineral components of soil come from?

weathering

weathering

physical disintegration and chemical decomposition of rocks

where do the organic components of soil come from?

the decomposition of plant, microbial, and other living biomass