Soils exam 1

What is soil to a pedologist?

Earth material that has been so modified (physically, chemically, and biologically) that it can support rooted plants

What is soil to an engineer?

a layer of incoherent material that can be excavated by conventional means without drilling or blasting

what is dirt?

undesirable debris which may contain soil

Edmund Ruffin

helped restore the fertility of farm soil

Vasily V. Dokuchaev

“Father of modern soil science”

discovered soil can be tied to climate

worked for russian tzar

C.F. Marbut

borrowed dokuchaev’s ideas for the united states

Guy Smith

combined existing ideas and modern issues

created our modern version of the soil classification

Hans Jenny

first to quantify the characteristics of soil

Karl Terzaghi

“father of soil mechanics”

sorted soil

Peter Birkeland

brought soil and geology together

Robert Ruche

used soil to understand glacial episodes and pieced together the advances

W. Cullen Sherwood

founder of many of our JMU geology courses including soils

Soil profile

a two dimensional body, commonly studied in artificial cuts

Soil pedon

a three dimensional body, with the same thickness as a profile, but with a surface area that ranges from 1-100 square meter

Major components of soil and their peercentages

Mineral matter - 45%

Organic matter - 5%

Water - 25%

Air 25%

O horizon

dominated by organic material

A horizon

mix of organic and mineral fraction. 

“zone of leaching” - elluviation

E horizon

very white

concentration of sand and silt particles of resistant minerals

rare

B horizon

zone of accumulation dominated by obliteration of original rock

C horizon

partially altered parent material grading down into unaltered parent material

R Horizon

hard bedrock underlying a soil “resiuum”

what is solumn?

consists of the surface and subsoil layers that have undergone the same soil forming conditions. 

what is an epipedon?

the uppermost layer of soil that serves as the diagnostic horizon

Ap, Bw, Bt, Bk, Bx (what are these subhorizons)

Ap - tillage

Bw - young

Bt - more mature, translocated

Bk - calcite

Bx - poor drainage

ways to determine texture of soil

ability to form a ball and ribbon

seives

stokes law

what is the munsell color chart

a system where the color of soil can be described using hue, value, and chroma

what is hue

the actual color of the soil relative to primary color

what is value

the lightness or darkness of color

what is chroma

the strength of color, the amount of pigment in the sample.

what do mottles or redox features tell us?

that there has been a presence of long term standing water

soil colloids

particles with charge (clays) will cluster together

what is the significance in soil structure?

critical in soil drainage

related to genesis and rock type

acretion, root penetration, nutrient retention, tilth affect structure

types of structure

Spheroidal

plate like

block like

prism like

spheroidal structure -

loose/granular

plate like structure - 

soil drainage problems (good for wetlands)

block like structure -

well drained, well developed in virginia

prism like structure -

related to attractive soils and or expansive clays

importance of organic matter/humus

helps hold water for longer and increases tilth

increases cation exchange capacity

releases high amounts of CO2

bulk density

a measure of the weight of soil per unit volume

What is parent material

what dominates textures of upper soils

residual soils

this is what is left behind from weather of parent material

saprolite 

appearance of rock but properties of soil - rotten rock

Soils from alluvium

from running water

floodplains and terraces

soils from colluvium

from gravity

base of steep slopes

debris/alluvial fans

from aeolian processes

wind blown sediment

loess - winds coming off of glaciers

from glacial process

ice

glacial till

Microclimate

Exposure, heat conductivity, vegetation

Macroclimate

things like deserts and tundras

Soil moisture regimes

Xeric

aridic/torric

ustic

udic

perudic

aquic

xeric

soils of temperate areas

moist winters and dry summers

aridic/torric

dry more than half the time

ustic

dry for 90 consecutive days and sometimes moist

temp is above 5 degrees Celsius for half the days

udic

soils not dry more than 90 consecutive days

perudic

precipitation exceeds evapotranspiration every month of the year

aquic

sufficiently saturated

usually have low chroma

Soil temperature regimes from hot to cold

Hyperthermic - really hot >22C

thermic - 15-22C

mesic - 8-15C

frigid - 0-8C

cryic - 0-8C

pergelic - really cold <0C

History of soil classification system

-V.V. Dokuchaev proposed a zonal classification

-focus on descriptions rather than genesis

-1950s - evident old system was inadequate

-usda soils survey staff began working on comprehensive soil classification system

-6 revisions by 1965

-7th approximation by 1971

soil orders (12)

entisol

inceptisol

alfisol

ultisol

oxisol

mollisol

aridisol

vertisol

spodosol

histosol

andesol

gelisol

entisol

soils on floodplains, dunes

little to no horizon development

inherently fertile

usually no B horizon present due to frequent disturbances

inceptisol

weak horizon development

thin B horizon

common on steep slopes

ultisol

leached soils of warm, humid climates

B horizon enriched with clays and oxies

typically forested if left undisturbed

sometimes has E horizon from leaching

alfisols

Al and Fe concentrations

medium to high in natural fertility

strong Bt horizon

high base saturation

usually moist, but dry in late summer

oxisol

highly weathered

infertile

dominated by oxide

tropical

high concentrations of Fe and Al oxides

Mollisol

thick, dark A horizon typically under grasslands or savanna

arid to humid climate

lacks moisture at certain times of the year

Aridisol

Dry climates with some development in the B horizon

low organics but high fertility

never moist for more than 3 months per year

in cold and hot deserts

saline/alkaline

vertisol

semi-arid grasslands and savannas

develop deep cracks in dry seasons

humid regions or soils containing high concentrations of montmorillonite

lack of horizonation

spodosol

translocation of compounds Fe, Humus, and Al are dominant

in sandy terrains

most extensive in sub arctic 

ash grey A horizon

low temperatures but also found in Florida

low fertility

histosol

dominated by decomposing organic matter

saturated with water

gelisol

soils with permafrost

no B horizon, A horizon rests on top of permafrost

low nutrients, highly leached

severe restriction on construction

andisols

parent material with a large component of volcanic ash

split out of inceptisols due to weak horizon development

common in pacific northwest

very high in phosphorous